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PTB Testing Instructions Volume 29 Measuring Instruments for Gas Gas Meters Testing of Gas Volume Meters with Air at Atmospheric Pressure drawn up by Dipl.-Ing. Harald Dietrich Dipl.-Ing. Hans-Jürgen Hotze Dipl.-Ing. Bernhardt Jarosch Dipl.-Ing. Franz-Josef Jünger Dipl.-Ing. Matthias Kämpf Dr.-Ing. Rainer Kramer Dr.-Ing. Bodo Mickan Dr.-Ing. Burger Nath

Dipl.-Ing.-Ök. Heino Polzin Dr.-Ing. Gudrun Wendt Published by Physikalisch-Technische Bundesanstalt (PTB) in cooperation with the supervising verification authorities Physikalisch-Technische Bundesanstalt Braunschweig und Berlin ISSN

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The PTB Testing Instructions are intended to serve as a reference and guideline for the testing of measuring

devices and equipment. The most important part of the Testing Instructions is thus formed by a detailed

description of the testing methods, the standard devices required and other testing means. As far as it appeared

suitable, the design of the device types and special features to be allowed for in practical application are also dealt

with. The PTB Testing Instructions refer not only to measuring instruments acceptable for verification and

certification but also to other measuring instruments and objects which are tested at the PTB. The Testing

Instructions are intended for use both by verification authorities, state-approved test centres and supervision

boards and by the test laboratories of industry and trade. Furthermore, they will be of use when establishing test

centres and measurement rooms as well as for instruction and training purposes.

Editor's office: J.-U.Barz

Dr. J. Simon (responsible)

Physikalisch-Technische Bundesanstalt

Bundesallee 100, D-38116 Braunschweig

PTB Testing Instructions, Volume 29

All rights reserved

© 2003 by Physikalisch-Technische Bundesanstalt, Braunschweig

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Contents Preliminary remarks 1 General 1.1 Scope 1.2 Terms and definitions 1.2.1 Gas volume meter 1.2.2 Flowrate 1.2.3 Meter size 1.2.4 Measurement range 1.2.5 Transitional flowrate 1.2.6 Working range 1.2.7 Flowrate ratio 1.2.8 Measurement error 1.2.9 Weighted mean (measurement) error WME 1.2.10 Cyclic volume and test volume 1.2.11 Test element 1.2.12 Constant of test element 1.2.13 Pulse value 1.2.13.1 Low-frequency pulse outputs 1.2.13.2 High-frequency pulse outputs 1.2.14 Gas state 1.2.15 Metering temperature 1.2.16 Metering pressure 1.2.17 Working gauge pressure 1.2.18 Pressure loss 1.2.19 Test mode 1.3 Symbols 1.4 Mathematical and physical bases and original equations 1.4.1 Physical properties of gases 1.4.2 Gas laws and equation of state 1.4.3 Equation of state for ideal gases 1.4.4 Equation of state for real gases 1.4.5 Reynolds number 1.4.6 Recommended equations for the calculation of the density of humid air 1.4.7 Recommended equations for the calculation of the viscosity of air 1.4.8 Conversion factor 1.4.9 Gas law deviation coefficient 1.4.10 Calculation of measurement errors 2 List of rules and regulations 2.1 Rules binding under verification law 2.2 Rules not binding under verification law 3 Procedure 4 Testing means 4.1 General requirements 4.2 Volume standards 4.3 Auxiliary measuring devices

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4.4 Test rigs 4.4.1 General requirements 4.4.2 Hardware 4.4.3 Software 4.4.4 Series test rigs 4.4.5 Single test rigs 4.4.6 Special features of rotary piston gas meters 5 Ambient conditions (test rooms) 6 Testing 6.1 External inspection 6.2 Preparation for metrological examination 6.2.1 Temperature adjustment 6.2.2 Preparation and installation of meters under test 6.2.3 Preparation of standards 6.2.4 Preparatory run 6.2.5 Tightness test 6.3 Metrological examination 6.3.1 General conditions 6.3.1.1 Mode of operation 6.3.1.2 Evaluation method 6.3.1.3 Minimum test volumes 6.3.1.4 Flowrate adjustment 6.3.1.5 Pulse counting 6.3.1.6 Adjustment 6.3.1.7 Check of pulse value and indicating device 6.3.1.8 Data interfaces 6.3.2 Testing of diaphragm gas meters 6.3.2.1 Test flowrate and test volumes 6.3.2.2 Maximum permissible errors 6.3.2.3 Pressure measurement 6.3.2.4 Testing of diaphragm gas meters with mechanical temperature conversion 6.3.2.5 Sampling inspection to extend the period of validity of verification, with reduced test volume 6.3.3 Testing of rotary piston gas meters 6.3.4 Testing of turbine gas meters 6.3.5 Testing of vortex and swirl gas meters 6.3.6 Testing of ultrasonic gas meters 6.4 Metrological evaluation 6.4.1 Measures prior to testing 6.4.2 Performance of testing 6.4.3 Result of metrological evaluation and test certificate 6.4.4 Particular regulations for limited test volume 6.4.5 Diaphragm gas meters with mechanical temperature conversion 6.5 Testing of volume standards 6.5.1 General 6.5.2 Connection of supplementary and auxiliary devices 6.5.3 Particular requirements for test rooms and testing means 6.5.4 Preparation of test 6.5.5 Scope of testing and test sequence 6.5.6 Measurement errors of volume standards 6.5.7 Identification of volume standards 6.5.8 Marking 6.5.9 Test certificate and period of validity of test 6.5.10 Comparison measurements on test rigs for gas meters with

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Qmax > 40 m³/h 6.6 Acceptance and monitoring of test facilities 6.6.1 Preparation for acceptance 6.6.2 Acceptance 6.6.3 Monitoring 7 Marking, identification and certification 7.1 Marking 7.2 Identification 7.3 Certification 8 Transitional provisions

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ANNEXES Annex 1 Designs of gas meters and their measurement properties Annex 2 Test examples 2.1 Domestic diaphragm gas meters 2.2 Turbine gas meters 2.2.1 Testing with one standard 2.2.2 Testing with two standards used in parallel Annex 3 Measurement uncertainty 3.1 Influence quantities 3.2 Inclusion of influence quantities 3.3 Calculation example 3.3.1 Method A 3.3.2 Method B Annex 4 Recommendations for reducing resonant vibrations Annex 5 Additional and deviating requirements for drum-type gas meters as volume standards (section

6.5) 5.1 Working ranges 5.2 Requirements for design and construction 5.3 Indicating device and test element 5.4 Scope of testing 5.5 Test volume 5.6 Temperature measurement 5.7 Permissible measurement errors 5.8 Adjustment of drum-type gas meters 5.9 Identification of drum-type gas meters 5.10 Correct filling of drum-type gas meter APPENDICES 1 Report format for diaphragm gas meters 2 Report format for turbine gas meters 3 Adjustment wheel table 4 Certificate formats 4.1 Preliminary Inspection Certificate 4.2 Verification Certificate 4.3 Metrological Evaluation Certificate 4.4 Test Certificate

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Preliminary remarks Under verification law, measuring instruments used or held ready for commercial transactions (e.g. for gas supply

against payment) or employed in official transactions (e.g. for fiscal or customs law purposes) are subject to

mandatory verification. The verification comprises testing and marking by the appropriate verification authority

or a state-approved test centre. Testing serves to establish whether the device has been accepted for verification

and whether it fulfils the requirements defined in Appendix 7 to the Verification Ordinance and imposed by the

type approval. The test also encompasses a separate metrological examination of each individual measuring

instrument.

The Testing Instructions below implement the above-mentioned requirements for the area of gas volume meters.

In Germany alone, more than 12 million devices of this type are used for supplying industry and private

households with gas using equipment subject to mandatory verification, the meters being mainly employed for the

quantitative determination of technical gases and gas mixtures, mainly natural gases.

In the following, the gas meter types at present approved for verification are presented and the appropriate test

facilities, testing methods and testing means as well as the associated metrological requirements are described.

Within the scope of these Testing Instructions, only the testing of gas volume meters with air at atmospheric

pressure is described. The particular regulations for testing under high-pressure conditions are dealt with in a

separate volume of the PTB Testing Instructions.

All technical and metrological aspects presented are based on the state of science and technology as at the time

when these Testing Instructions were prepared. But particular efforts have been made to take account of

foreseeable development trends and not to impede or restrict the application of novel measuring and testing

procedures. Other conditions and requirements may be applied providing they have been laid down in agreement

with the PTB and the appropriate authority and ensure at least that the same results are obtained.

Unless otherwise provided in the type approvals, the requirements and conditions formulated in the Testing

Instructions are binding for the verification of gas volume meters used in commercial and/or official transactions.

They are intended not only to serve the verification authorities of the federal states and the state-approved test

centres at the gas meter manufacturers' and gas supply companies' as a guideline for the tests to be carried out but

also to give guidance to the development and test laboratories in industry and research as well as to all other users

of gas meters and also to provide information about suitable test methods.

The Testing Instructions below are a complete revision of the former Volume 4 of the PTB Testing Instructions

which was published in 1982 under the title "Gas Volume Meters." As a matter of principle, obsolete

prescriptions which are no longer up to the present state of technology have not been retained. Where necessary,

they are now superseded by appropriate transitional provisions to safeguard the status predating the new

provisions.

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1 General

1.1 Scope

The PTB Testing Instructions "Gas Meters - Testing of Gas Volume Meters with Air at Atmospheric Pressure"

define the metrological requirements and conditions for the verification of all gas volume meter types at present

approved for low pressure in the Federal Republic of Germany. These are diaphragm and rotary piston gas meters

as positive displacement meters (volumetric gas meters) as well as turbine, vortex and ultrasonic gas meters (non-

volumetric gas meters) up to a maximum flowrate of 40,000 m³/h under working conditions. The Instructions do

not deal with the meter runs of differential pressure gas meters accepted for verification and with the Coriolis-

type meters approved as mass meters.

Furthermore, the standards to be used for the verification of the gas volume meter types referred to, including the

applicable requirements and conditions, are specified. In particular, bell provers and piston devices for use as

direct volume standards as well as drum-type, turbine, rotary vane and rotary piston gas meters for use as standard

meters are dealt with. The use of sonic nozzles for gas meter verification (which has already been dealt with in

separate PTB Testing Instructions) is referred to only.

The Testing Instructions cover only the testing at atmospheric pressure with air, irrespective of the use of the gas

meter in question. The high-pressure testing with natural gas will be dealt with in a separate volume.

The PTB Testing Instructions below completely supersede Volume 4 of the PTB Testing Instructions entitled

"Gas Volume Meters“ in its 1982 edition. Transitional provisions are made in chapter 8.

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1.2 Terms and definitions

1.2.1 Gas volume meter Continuously operating measuring instrument by which the gas quantity passed during the measurement

operation is indirectly or directly measured and indicated in units of volume.

1.2.2 Meter size The meter size is a datum characterizing the size of the gas meter deriving from the maximum permissible

working volume flowrate. It is formed, for example, by the letter G with a number as specified in Appendix 7 to

the Verification Ordinance.

1.2.3 Flowrate The flowrate Q arises from the volume passed per unit of time under measuring conditions.

1.2.4 Measurement range The measurement range describes the flowrate range of the gas meter and is bounded by the minimum flowrate

Qmin and the maximum flowrate Qmax.

1.2.5 Transitional flowrate The transitional flowrate Qt separates the measurement ranges with different maximum permissible errors.

1.2.6 Working range The ratio of Qmin to Qmax (e.g. 1:50) is referred to as working range.

1.2.7 Flowrate ratio The flowrate ratio B is the ratio of the measured flowrate Q to the maximum flowrate of the gas meter Qmax.

maxQQB = (1)

1.2.8 Measurement error For the purposes of these Testing Instructions, the measurement error f is the difference between the indicated

quantity V and the quantity actually passed, related to the quantity actually passed Vist.

The determination of the measurement error is carried out separately for each meter by experiment using a

suitable standard. The measurement error is a function of flowrate. Its curve is referred to as error curve. The

verification of a meter requires that all measurement errors in the approved working range of the meter lie within

the maximum permissible errors.

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%100ist

ist ⋅−

=V

VVf (2)

In the context of these Testing Instructions, all measurement errors are stated in percent.

1.2.9 Weighted mean (measurement) error WME For the adjustment of a gas meter it is expedient to calculate a weighted mean error WME from n individually

determined measurement errors fi at the test flowrates Qi and to use it as a criterion. The calculation is performed

according to equation (3) which is equivalent to the relevant equation from the OIML Recommendation R 32:

maxmaxmax

maxmax

1

1

7,0for 4,1 nd

7,0for

QQQQQ

ka

QQQQ

kwithk

fkWME

ii

i

ii

in

ii

n

iii

≤<−=

≤==

∑

∑

=

=

(3)

If the measurement errors fi (as agreed in these Testing Instructions) are stated in percent, the WME is also

obtained in percent.

1.2.10 Cyclic volume and test volume In the context of these Testing Instructions, the gas volume corresponding to one working cycle of the meter is

referred to as cyclic volume Vz of a gas meter. In the case of positive displacement meters, the cyclic volume is

called test volume.

A working cycle is the sum of the movements by which all moving components of the meter - with the exception

of the indicating device and the indicating device transmission - resume for the first time the position they

occupied at the beginning of the cycle. In the case of turbine gas meters, a working cycle is one complete

revolution of the turbine wheel.

For each meter the ratio between the cyclic volume and one complete revolution of the test element (constant tr) is

determined by its design and adjustment.

The calculation of the cyclic volume of a meter is made individually by multiplication of the volume

corresponding to one complete revolution of the test element by the transmission ratio between measuring device

and indicating device allowing for the built-in set of adjustment wheels (computational test volume or cyclic

volume, respectively). The test volume stated on the meters is the rated value.

1.2.11 Test element

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The test element is the lowest element of the indicating device which is specifically provided for the metrological

examination of the meter. It enables the metrological examination to be carried out with sufficient accuracy. If it

is not formed by the last element of the indicating device, the gas meter must have suitable devices allowing a

removable test element to be connected.

1.2.12 Constant of test element The constant tr is the value of the volume corresponding to one complete revolution of the test element which is

indicated by the indicating device. The constant of a meter is determined by the meter design.

1.2.13 Pulse value The pulse value cIW describes the ratio of the pulses imp generated by the pulse generator per unit of volume V

and can be expressed as

Vn

c impIW = (4)

or its reciprocal value.

1.2.13.1 Low-frequency pulse outputs In the case of meters with low-frequency pulse outputs, the pulse value is structurally coupled with the constant

of the test element. Low-frequency pulse outputs are fitted to the indicating device.

1.2.13.2 High-frequency pulse outputs In the case of meters with high-frequency pulse outputs, the pulse value is structurally coupled with the cyclic or

test volume. High-frequency pulse outputs are fitted to the measuring device. A meter may be provided with

several high-frequency pulse outputs with different pulse values.

1.2.14 Gas state The state of a gas is defined by the values of pressure and temperature on which its actual density depends (e.g.

high pressure and low temperature increase the density).

The properties of a gas during measurement are the state of the gas in the measuring device of the gas meter at

the time of volume measurement. As this state generally cannot be accurately determined due to the differences in

design of the various gas meter types, a state as close as possible to the measurement state (metering temperature

and metering pressure) must be used as starting point for the practical conversion.

In Germany the standard state of a gas is the reference state which (according to DIN 1343: "Reference state,

standard state, standard volume") is characterized by the standard values

• of the pressure pn = 1.013 25 bar and

• of the temperature Tn = 273.15 K (tn = 0 °C).

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According to the DVGW Work Sheet G 685, the billing temperature1 Tb has been fixed for diaphragm gas meters

at Tb = 288.15 K (tb = 15 °C) and serves as an intermediate value for complete conversion to the standard state.

Standard state and billing temperature are conventional quantities which are useful for invoicing purposes but are

only in part related to characteristic values as found in practice. They are not the same in all countries.

1.2.15 Metering temperature For the conversion of the gas volume measured by a gas meter to other thermodynamic gas states, a temperature

is determined which is referred to as metering temperature. The metering temperature is measured in different

points depending on the meter type.

1.2.16 Metering pressure For the conversion of the gas volume measured by a gas meter to other thermodynamic gas states, a pressure is

determined which is referred to as metering pressure. The metering pressure is measured in different points

depending on the meter type. The measuring point for the reference pressure is, as a rule, stated on the individual

meter types and is marked pr ("reference pressure"). In some international documents the designation pm

("measuring pressure") is used.

In these Testing Instructions, metering pressures are stated as absolute pressures.

1.2.17 Working gauge pressure The working gauge pressure pe of a gas meter is the difference between the gas pressure at the meter inlet and the

atmospheric pressure. The working gauge pressure here is always stated as gauge pressure.

1.2.18 Pressure loss The pressure loss Δp of a gas meter is the difference between the static pressures of the gas passing through it, as

measured at the inlet and at the outlet. It is a function of the flowrate and limited for gas volume meters.

1.2.19 Test mode Mode of operation of an electronic gas meter which is activated for testing such meters.

1 In OIML R 31, this temperature is also referred to as base gas temperature.

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1.3 Symbols

A resolution of indication

B flowrate ratio

C Sutherland's constant

cIW pulse value

cIW,mess pulse value determined by measurement

cIW,rech pulse value determined by computation

cf correction factor for the change in the behaviour of humid air compared with an

ideal gas

D piping diameter

eP absolute measurement error of the meter under test

f relative error

fN relative error of standard

fP relative error of meter under test

fr rough measurement error

Δf variation of relative error

h relative air humidity

IG total transmission of gear

J1,J2 adjustment wheel constants

K gas law deviation coefficient

kP pressure correction

kt temperature correction

k coverage factor in determination of measurement uncertainty

Ma molar mass of dry air (28.9635 g/mol [7])

Mv molar mass of water vapour (18.015 g/mol [7])

n number of measuring points,

amount of substance (number of moles),

pulse number

nImp number of pulses of a pulse output

nImp,HF number of pulses of a high-frequency pulse output

nImp,NF number of pulses of a low-frequency pulse output

nImp,tr number of revolutions (pulses) of a test element

nImp,Vz number of pulses of a high-frequency pulse output for a cyclic volume

p pressure

pa air (ambient) pressure

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pabs absolute pressure

pe numerical value of the negative gauge pressure or the gauge pressure in the pipe

prover

pN metering pressure at the standard

pn standard pressure (1.01325 bar)

pP metering pressure at the meter under test

pr metering pressure ("reference pressure")

psv water vapour saturation pressure

Δp pressure loss of a meter

differential pressure between meter under test and standard,

pressure variation with time

Q flowrate

QL leakage rate

QL,zul permissible leakage rate

QL,Ist actual leakage rate

Qmax maximum flowrate of a gas meter

Qmin minimum flowrate of a gas meter

Qt transitional flowrate

ΔQrel variation of the relative flowrate

R specific gas constant

R0 universal (molar) gas constant (8.314 41 J/(mol . K))

Re Reynolds number

T temperature in K

t temperature in °C

t testing time

Ta room (ambient) temperature in K

ta room (ambient) temperature in °C

Tb billing temperature in K

tb billing temperature in °C

tmax upper temperature limit in °C

tmin lower temperature limit in °C

TN absolute temperature at the standard in K

tN temperature at the standard in °C

Tn standard temperature in K

tn standard temperature in °C

TP absolute temperature at the meter under test in K

tP temperature at the meter under test in °C

tr dew-point temperature in °C

tr output constant of test element

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ΔT temperature difference between meter under test and standard

Δtprüf testing time for leakage test

U expanded uncertainty with k = 2

u velocity of flow

V volume

Va volume at atmospheric (ambient) conditions

Ve enclosed volume

Vist volume actually passed

Vist,N volume actually passed through the standard

Vist,D volume actually passed through the nozzle(s)

Vist,P volume actually passed through the meter under test

VG working volume passed through the meter during the pulse value check

VN volume indicated by the standard

VP volume indicated by the meter under test

Vn volume in the standard state

Vz cyclic volume of a gas meter

WME weighted mean error

χv mole fraction of water vapour in humid air

Z compressibility factor

Zn compressibility factor in the standard state

z conversion factor

η dynamic viscosity

ρ density

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1.4 Mathematical and physical bases and original equations

1.4.1 Physical properties of gases

The aggregate state of a gaseous substance is determined by pressure and temperature. In a gas the forces

produced by the thermal motion of the atoms and molecules are greater than the molecular binding forces giving

rise to cohesion in solids and liquids. A gas can therefore occupy a volume of any size and completely fills any

space available to it.

1.4.2 Gas laws and equation of state

The relation between the temperature T, the pressure p and the volume V of a gas quantity is described by the gas

laws; the relations which are most important for gas measurement can be represented by the thermal equation of

state f (T,V,p)=0.

It is here mainly used to convert the volumes measured in different thermodynamic states into one another so that

it is possible to compare them in quantitative terms.

1.4.3 Equation of state for ideal gases

An ideal gas is represented in a thermodynamic model in which the proper volume of the gas molecules and the

interaction of the molecules with one another due to van der Waals' attractive forces are neglected. Air at

atmospheric conditions can approximately be considered to be an ideal gas.

The ideal gas satisfies the simplest gas equation - Clapeyron’s equation. It reads

TRnVp ⋅⋅=⋅ (5)

where n is the number of moles and R the gas constant.

For the conversion of one and the same gas to different thermodynamic states, the relation

.const2

22

1

11 =⋅

=⋅

TVp

TVp

or .const2211 =⋅=⋅ VV ρρ (6)

is obtained for an ideal gas, the indices 1 and 2 characterizing the two states to be converted to each other.

Example:

For the conversion of an air volume Va measured at the atmospheric pressure pa and the ambient temperature Ta to

the standard state (denoted by the index n) the following relation is valid:

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aa

an mbar 25.1013

K 15.273 V

Tp

V ⋅⋅⋅

= (7)

1.4.4 Equation of state for real gases

For the real gas the proper volume of the gas molecules and their interaction with one another are of relevance.

For real gases a number of thermal equations of state are available each of which mostly describes a particular

range or particular properties especially well. The equation of state usually used in gas measurement reads:

TRnZVp ⋅⋅⋅=⋅ (8)

where Z is the compressibility factor of the gas. For an ideal gas this is per definitionem equal to 1.000 for all

states. For air at atmospheric conditions it can be assumed in good approximation to be Z=1.000.

1.4.5 Reynolds number

The Reynolds number Re is a parameter which serves to characterize flow processes affected by friction and

describes the ratio between inertia and viscous forces. One form suitable for flowrate measurement reads:

ηπρ

ηρ

⋅⋅⋅⋅

=⋅⋅

=DQDuRe 4 (9)

where u is the velocity of flow, Q the volume flowrate, ρ the density, η the dynamic viscosity and D the piping

diameter.

An identical Reynolds number for different flows means that the flows have identical or comparable flow

properties. In practice, this Reynolds similarity is profited from to transfer metrological and flow properties of

particular kinds of measuring instruments which were determined under selected conditions to other flow

conditions with the same Reynolds number.

1.4.6 Recommended equations for the calculation of the density of humid air

The density ρ of humid air is calculated according to the BIPM Recommendation for the determination of the

density of humid air.

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( )va

vv

0

a 0.37801 0.348353 1 1 χχρ ⋅−⋅⋅

⋅=⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛−⋅−⋅

⋅⋅⋅

=TZ

pMM

TRZMp

(10)

Equations (10) to (18) are scaled quantity equations which require having an eye to the units of the quantities to

be entered. The quantities and their units for use in equations (10) to (18) are given in the table below.

Symbol Unit Description

p mbar absolute pressure

t °C temperature

T K absolute temperature

h % relative humidity

f correction factor for the changed behaviour of humid air

χ sv mole fraction of water vapour in saturated humid air

χ v mole fraction of water vapour in humid air

p s v Pa pressure of water vapour in saturated humid air

Z compressibility factor

ρ kg/m³ density

The compressibility factor Z for humid air is determined at

( ) [( ) ( ) ]

( )( ) 10034.1101.73

15.273

10285.2109297.110589.210757.5

100880.1108969.2101.62419+273.15

1

2v

47-2

2

2v

42v

64

2864-i

χ

χχ

⋅⋅−⋅⋅+

+

⋅⋅⋅−⋅+⋅⋅⋅−⋅+

⋅⋅+⋅⋅−⋅⋅−=

−

−−−−

−−

tp

tt

ttt

pZ

(11)

The mole fraction of water vapour, χv is, as a rule, determined from the ambient conditions in the measurement

room from which the test air is drawn, whereby it is assumed that the humid air in the measurement room or in

the measuring arrangement does not condense and, as a result, that the molar fraction of water vapour does not

vary. The value for χv can be determined either with the dew-point temperature tr or with the relative air humidity

h.

When the dew-point temperature tr is used, the following equations (12) to (14) hold, the respective ambient air

pressure pa being needed as an additional measurement value:

( ) ( ) 2

a

rsvrav 10 , −⋅⋅=

ptp

tpcfχ (12)

with

19

( ) 2r

-7a

-6ra 106.51014.300062.1, tptpc ⋅⋅+⋅⋅+=f (13)

( ) ( ) ( )

( ) ]1r

3

r2-2

r5

rsv

15.273103536311.604926034.34

273.15101.9509874-15.273-102811805.1

exp

−+⋅⋅−+

+⋅⋅+⋅⋅⎢⎣⎡=

t

tttp (14)

If the molar fraction of water vapour χv is determined using the relative air humidity h, not only the ambient

pressure pa but also the ambient temperature ta are needed and equations (15) to (18) hold:

( ) 2asvv 10−⋅⋅= txhχ (15)

with

( ) ( ) ( ) 2

a

asvaaasv 10 , −⋅⋅=

ptp

tpct fχ (16)

( ) 2a

-7a

-6aa 106.51014.300062.1, tptpc ⋅⋅+⋅⋅+=f (17)

( ) ( ) ( )

( ) ]1a

3

a2-2

a5

asv

15.273103536311.604926034.34

273.15101.9509874-15.273-102811805.1

exp

−+⋅⋅−+

+⋅⋅+⋅⋅⎢⎣⎡=

t

tttp (18)

As to the determination of the appropriate measurement values for the χv calculation, it is to be noted that the

dew-point temperature tr or the relative air humidity h shall be measured, if possible, close to the inlet of the

measuring arrangement and that the values used for the ambient pressure pa and the ambient temperature ta are

principally to be measured directly at the hygrometer.

If the determination of the test air humidity is made with the aid of a humidity sensor fitted in the measuring

arrangement in the test air current, the above equations will apply if pa and ta are replaced with the appropriate

pressure and temperature values measured in the place where the humidity sensor is fitted.

1.4.7 Recommended equation for the calculation of the viscosity of air

For the calculation of the viscosity of air, the equations and numerical values given in VDI/VDE Guideline 2040,

sheet 2: "Berechnungsgrundlagen für die Durchflussmessung mit Blenden, Düsen und Venturirohren.

Gleichungen und Gebrauchsformeln“ (Bases of calculation for flowrate measurement using orifices, nozzles and

Venturi tubes - equations and practical formulas) can be used.

The dynamic viscosity η has the unit Pa.s and is dependent on the particular thermodynamic state of the medium.

For gases it increases with rising temperature and is almost independent of pressure in the vicinity of atmospheric

20

pressure. Where in the first approximation it is dependent only on temperature (ideal gases with pressures < 6

bar), η(t) can be calculated with Sutherland's formula

( )

TCTC

TTt

+

+⋅⋅=

1

1n

nnηη (19)

from the viscosity related to the standard state of the gas ηn and the standard temperature Tn using Sutherland's

constant C. For dry air at ta = 20 °C, C = 113 and η20 = 1.820.10-5 Pa.s are valid. Information about the use of

appropriate pressure corrections for pressures above 6 bar as well as about the numerical values of C for other

gases are also given there.

1.4.8 Conversion factor

The conversion factor z is defined as the ratio between volume under normal conditions and under working

conditions.

For an ideal gas the following is valid:

n

n

pTpT

z⋅⋅

= (20)

Considering the compressibility factors under working or standard conditions, the following relation is valid for a

real gas:

ZpTZpT

z⋅⋅⋅⋅

=n

nn (21)

1.4.9 Gas law deviation coefficient

The gas law deviation coefficient of the gas K is defined as the ratio of the compressibility factors under working

or operating conditions:

nZ

ZK = (22)

and in the standard state is 1.000. In tests under low-pressure conditions, i.e. in the case of small deviations of the

conversion factor between meter under test and standard, the gas law deviation coefficient can be assumed to be

equal to 1 and can thus be neglected. In analogy to the compressibility factors it otherwise depends to different

21

degrees on the pressure and temperature of the gas and is to be computationally determined for each gas mixture

pursuant to the Technical Guideline G 9 of the PTB.

1.4.10 Calculation of measurement errors

The measurement error fP of a meter under test is calculated according to:

%1001Pist,

PP ⋅⎟

⎟⎠

⎞⎜⎜⎝

⎛−=

VV

f (23)

with VP - volume indicated by meter under test

Vist,P - volume actually passed through meter under test

The volume actually passed through the meter under test Vist,P is calculated from the volume actually passed

through the standard Vist,N, related to the place of installation of the meter under test. This calculation takes place

in two steps.

For the standard the following relation is valid:

100/1%1001 Nist,

Nist, N

NNN f

VVVVf

+=→⋅⎟

⎟⎠

⎞⎜⎜⎝

⎛−= (24)

with VN - volume indicated by standard

Vist,N - volume actually passed through standard

Application of the equation of state for ideal gases yields:

N

NNist,

P

PPist,

TpV

TpV ⋅

=⋅

(25)

After transformation, V is to be calculated with

NPN

PNN

NP

NNist,Pist, )100/1( Tpf

TpVTp

TpVV

⋅⋅+⋅⋅

=⋅

⋅⋅= P

After insertion into the equation for calculating the measurement error of the meter under test, the following exact

equation is obtained:

%1001)100/1(

PNN

NPNPP ⋅⎟⎟

⎠

⎞⎜⎜⎝

⎛−

⋅⋅⋅⋅+⋅

=TpV

TpfVf (26)

22

If several standards i are operated to determine the relative errors of the meter under test fP, the true volume

passed must be separately calculated for each standard i and the individual results must subsequently be summed

up to a total volume. The complete equation reads:

%1001

1001 iN,

iN,

N,

N,

P

PP

P ⋅

⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢

⎣

⎡

−

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

⋅+

⋅=

∑n

i Tp

fV

Tp

Vf

i

i

(27)

As shown in Volume 25 of the Testing Instructions, the calculation of the volume passed through sonic nozzles is

not the same as for other standards. To ensure that the individual volumes, calculated in different ways, are

comparable in case sonic nozzles are operated in parallel with other standards, they must be related to a reference

state. For the following equation, the standard state of Tn = 273.15 K and pn = 1013.25 mbar has been arbitrarily

selected here as reference state. The volume Vist,D actually passed through the nozzles is calculated according to

the appropriate equations from Volume 25 of the Testing Instructions. The result is:

%1001

mbar25.1013K15.273

1001

mbar25.1013K15.273

Ni

NiNi

P

PP

P ⋅

⎥⎥⎥⎥⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢⎢⎢⎢⎢

⎣

⎡

−

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

⋅⋅

⋅+

+

⋅⋅

⋅=

∑i Ni T

pf

VV

Tp

Vf

Dist,

(28)

The following approximation formula can be used if the changes in state between standard and device under test

are small (temperature differences Δt < 2 K, Δp < 25 mbar), whereby the individual shares in the correction are

split. For the measurement error of the meter under test fP in percent, the following then is approximately valid:

fP = fr + fN + kp + kt (29)

with - represented in percent -:

fr rough measurement error: fr = (VP/VN - 1 )⋅100 %

fN measurement error of the standard from its test certificate, in %

kp pressure correction: kp = 0.1( pP/mbar - pN/mbar) %

kt temperature correction: kt = 0.34(tN/°C - tP/°C) %

23

Under the above-mentioned conditions, the resulting additional uncertainty is < 0.02 %. In case the measurement

error is calculated manually, the approximation formula is to be applied.

24

2 List of rules and regulations 2.1 Rules binding under verification law

Verification Act

Law on metrology and verification (Verification Act) as revised on March 23, 1992 (Fed.Law Gazette I, p. 711),

amended by the law of December 21, 1992 (Fed.Law Gazette I, p. 2134)

Verification Ordinance (EO) – General Prescriptions

Verification Ordinance of August 12, 1988 (Fed.Law Gazette I, p. 1657), last amended by the 3rd Ordinance

amending the EO of August 18, 2000 (Fed.Law Gazette I, p. 1307)

Appendix 7 to Verification Ordinance (EO 7) in its version of August 18, 2000

7-1 Gas volume meters

7-3 Supplementary devices (pulse generators, switching devices)

Ordinance on verification fees (EKVO) in its version of July 11, 2001 (Fed.Law Gazette I, No. 36, p. 1608 foll.)

EEC Directives

71/318 Gas volume meters (09/71)

74/331 1st amendment (07/74)

78/365 2nd amendment (04/78)

82/623 3rd amendment (08/82)

Administrative Regulation "Legal Metrology – General Regulations (GM-AR)" of April 10, 2002 (Fed.Gazette

5/02)

PTB Requirements (PTB-A)

7.1 Gas volume meters (04/88)

Standards

DIN 1319-3 Fundamentals of metrology, part 3: Evaluation of measurements of an individual measurand,

measurement uncertainty (05/96)

DIN 1343 Reference state, standard state, volume at standard conditions

DVGW Work Sheets

G 492/I Facilities for gas quantity measurement ... up to 4 bar ... (06/98)

G 492/II Facilities for gas quantity measurement ... above 4 bar... (12/88)

G 685 Gas billing (04/93), with Supplementary Sheet (4/95)

25

PTB Testing Instructions

Volume 25: Test Rigs with Sonic Nozzles (1998)

Volume 30: Gas Volume Meters - High-pressure Testing (2002)

Technical Guidelines of PTB

G 3: Verification of diaphragm gas meters ≤ G 25 with direct-coupled electronic temperature correctors (12/94)

G 9: Verification of pressure/temperature correctors and differential pressure gas meters with pvt determination

for gas with real pvt behaviour (01/98)

G 13: Installation and operation of turbine gas meters (03/02)

Other

PTB-Mitteilungen 102: Procedures for the sampling inspection of diaphragm gas meters (04/92), with

supplement, in: PTB-Mitteilungen 107 (02/97)

2.2 Rules not binding under verification law

The rules and guidelines below are not binding under verification law at the date of entry into force:

DIN EN 1359 Diaphragm gas meters (05/99)

EN 122 61 Turbine gas meters (05/02)

DIN EN 124 80 Rotary piston gas meters (06/02)

DIN EN ISO 2859 Acceptance of sampling inspection (04/93)

OIML R 31 Diaphragm gas meters (1995)

OIML R 32 Rotary piston gas meters and turbine gas meters (1989)

• Giacomo, P.: Formel für die Bestimmung der Dichte von feuchter Luft (Formula for the determination of the

density of moist air). In: PTB-Mitt. 89 (1979), vol. 4

• VDI/VDE Guideline 2040, sheet 2: Berechnungsgrundlagen für die Durchflussmessung mit Blenden, Düsen

und Venturi-Rohren. Gleichungen und Gebrauchsformeln (Bases of calculation for flowrate measurement

using diaphragms, nozzles and Venturi tubes. Equations and practical formulas) (1987)

• ISO Guide to the Expression of Uncertainty in Measurement (1993)

26

3 Procedure Irrespective of the testing procedure, the standard devices used, the mode of operation and the evaluation method,

the testing of gas meters is carried out according to the following basic schemes for the verification, metrological

evaluation, special examination and other examinations.

For the testing of working standards and test facilities, sections 6.5 and 6.6 are applicable.

Before the testing procedure is selected according to the schemes given, it must be decided whether testing is to

be carried out at atmospheric pressure or at high pressure. At present, verification exclusively at high pressure is

permitted for national purposes only.

Before the tests are started, it is to be checked whether the technical and organizational prerequisites are complied

with.

According to what is applied for, tests can be carried out according to the EEC Directives, to national verification

regulations and to the standards in force. At present, the latter are not valid for verification.

In the following flowcharts, the symbols mean:

start or end of program flow

operation

decision

testing operation

27

report, certificate

alternative

Flussdiagramme Seite 27-29 deutsche Broschüre Flussdiagramme

(Eichung)

Verification

nein no

ja yes

ausschl. mit HD-Gas? exclusively with high-pressure gas?

Start start

EWG-Ersteichung EEC initial verification

organ.+ techn. Voraussetzungen erfüllt? organiz. and techn. conditions fulfilled?

Beschaffenheitsprüfung external inspection

Anforderungen erfüllt? requirements fulfilled?

Messtechn. Prüfung metrol. examination

Anforderungen erfüllt? requirements fulfilled?

Auslieferung ohne HD-Prüfung? delivery without HD test?

Stempelung marking

Bescheinigung beantragt? certificate applied for?

Zertifikat, Bescheinigung certificate

Gebührenerhebung levying of fees

Ende end

Stempelung marking

Vorprüfschein preliminary inspection certificate

28

Gebührenerhebung levying of fees

Durchführung der Eichung mit HD-Gas performance of verification with HD gas

Rückgabe return

ggf. Entwertung obliteration, if necessary

Mitteilung notification

Bemerkungen, Verweise remarks, references

Abschnitt section

Anlage annex

EKVO Ordinance on verification fees (EKVO)

Bearbeitung gemäß… handling acc. to Testing Instructions for HP

testing

(Befundprüfung)

Metrological evaluation

nein no

ja yes

Start start

Antrag auf Befundprüfung application for metrological evaluation

organ.+techn. Voraussetzungen … organ. and techn. conditions fulfilled?

äußere Beschaffenheitsprüfung external inspection

Anforderungen erfüllt? requirements fulfilled?

messtechnische Prüfung metrological examination

Anforderungen erfüllt? requirements fulfilled?

innere Beschaffenheitsprüfung internal inspection

Öffnung, Untersuchung opening, examination

Prüfschein test certificate

Gebührenerhebung levying of fees

Ende end

Fortsetzung möglich? continuation possible?

Entwertung obliteration

besonderer Hinweis im Prüfschein particular reference in test certificate

Bemerkungen, Verweise remarks, references

gemäß… according to

Abschnitt section

Mitteilung notification

gemäß EKVO acc. to EKVO

(Sonderprüfung und sonstige Prüfung)

29

Special examination and other examinations

Mitteilung notification

nein no

ja yes

Start start

organ.+techn. Voraussetzungen… organ. and techn. conditions fulfilled?

Auswahl vergleichbarer… selection of comparable meters acceptable for

verification to define the test program

Beschaffenheitsprüfung external inspection

Anforderungen erfüllt? requirements fulfilled?

Messtechn. Prüfung metrological examination

Anforderungen erfüllt? requirements fulfilled?

Bescheinigung beantragt? certificate applied for?

Bescheinigung, Sonderprüfschein certificate, special examination certificate

Sonderprüfung beantragt? special examination applied for?

Stempelung marking

Gebührenerhebung levying of fees

Ende end

Bemerkungen, Verweise remarks, references

gemäß … acc. to

Abschnitt section

EO Anlage Appendix to EO

Kennzeichnung gemäß… identification acc. to

EA-AV Nr. EA AV No.

4 Testing means

4.1 General requirements

Testing means are subject to the requirements of the Administrative Regulation "Legal Metrology - General

Regulations (GM-AR)" as amended from time to time.

Testing means must have been approved and officially tested by the PTB or by the verification authority.

Measurement errors or corrections stated in the test certificates are to be taken into account and the intervals for

periodic verification are to be complied with.

30

4.2 Volume standards

As standards specifically selected gas meters, test rigs with sonic nozzles, piston-cylinder measuring systems, test

facilities with oval wheel meters and bell provers (gauging apparatus) - all of them tested as standards - are

eligible. Also, combinations of different standards can be approved. Standard gas meters can be used in both

pressure and suction applications. As a rule, bell provers operate only under pressure conditions.

The essential criteria for the selection of the standards depend on the kind, size and components of the meter

under test. These are in detail:

• flowrate range

• test volume necessary

• type of meter under test (minimum influence)

• kind of volume determination at meter under test

Table 1 gives a list of the standards at present used for testing individual meter types.

Table 1: Volume standards at present used

X suitable (X) partially suitable Type of meter under test (measurement principle) Standard Diaphragm Rotary

piston Rotary vane

Turbine Vortex/ swirl

Ultrasonic

Bell prover X (X) (X) (X) (X) (X) Drum-type meter X X X X X X Rotary piston meter X (X) X (X) Low-pulsation rotary piston meter

X X X X X X

Rotary vane meter X X X X X X Turbine meter (X) X X X X Sonic nozzle X X X X X X Piston-cylinder system X Oval wheel meter X

The properties of standards listed below are intended to facilitate selection:

Bell provers (gauging apparatus)

• main range of use for flowrates up to 10 m³/h

• high long-time stability owing to material measure

• stationary arrangement

• limited test volume

• temperature dependent due to overall height (temperature layering)

Drum-type gas meters

• relatively large working range (1:100)

• small overrange capacity

31

• meshing errors to be observed when defining minimum test volumes

• change of place of use poses problems due to oil filling

• subjective influences on sealing liquid level setting

Rotary piston meters / low-pulsation rotary piston meters

• broad spectrum of use owing to sizes

• definition of the working range (up to 1:100) in dependence on mechanical condition

• when provided with four compartment volumes (for standard rotary piston meters, see Annex 1), equipment

with silencers / pulsation dampeners is necessary

Rotary vane gas meters

• main range of use from 10 m³/h to 1000 m³/h

• extension of working range possible with servo drive

Turbine gas meters

• suitable for large and very large flowrates

• relatively small working ranges due to characteristic error curve

• relatively long inlet section for undisturbed aspiration

Piston-cylinder measuring systems

• relatively large working range

• high long-time stability owing to material measure

• limited test volume

• relatively small maximum flowrates

• temperature dependent due to whether arranged as vertical or horizontal cylinder

Sonic nozzles

• good reproducibility

• high long-time stability

• parallel operation for different test flowrates

• immunity to blower pulsations

• high requirements for tightness of system

Metering systems with oval wheel meter (indirect gas volume measurement)

• relatively small maximum flowrates (primarily for diaphragm gas meters up to Qmax < 10 m³/h).

• test volume limited by oil tank

• relatively complicated operation

32

As a rule, standards are stationarily arranged or they are permanently mounted in gas meter test rigs. Due to the

limited flowrate range, standards of different sizes are necessary according to the kind and size of the meters to be

tested, i.e. the test can be carried out by simply switching from a standard to that with the subsequent

measurement range taking into account that the measurement ranges of the standards shall overlap by approx. 10

%. Overlapping is to be required because it enables mutual monitoring of the standards. If the measurement errors

measured when testing a meter in the overlap region of two standards differ by more than 0.3 %, the cause is to be

ascertained and eliminated. In the case of differences up to 0.3 %, the measurement errors may be averaged.

Simultaneous operation of several standards (also of different types) arranged in parallel is admissible if it is

ensured that they do not substantially interact when operated simultaneously. So prior to putting the test rig into

operation, appropriate investigations are to be carried out.

When changing the test sections in which the standards are arranged, it is to be ensured at the same time that the

test sections which are not being used are always safely shut off. The tightness of each of these sections is to be

permanently checked by appropriate measures. Relevant specifications are laid down in the approval of the test

rig.

4.3 Auxiliary measuring devices

By auxiliary measuring devices the sensors, including the indication (also with signal processing), for

atmospheric pressure gauge, gauge or differential pressure, respectively, temperature, time and - in the case of

sonic nozzles - air humidity are understood.

Initial tests are to be performed by the relevant verification authority upon acceptance of the test rigs. It prescribes

periodic retests of the auxiliary measuring devices to be carried out by the test centre as required. It is advisable to

perform a first subsequent test after two years at the latest. This and any necessary adjustments can also be carried

out by the board of the test centre providing suitable measuring means are available. The documentation has to be

made in the test rig manual or electronically.

In detail, auxiliary measuring devices for the measurement of the following measurands are concerned:

Air pressure

If the air pressure enters into the calculation of the measurement error, it shall be measured at least once during a

shift and be taken into account in the evaluation of the measurement results. It is sufficient to determine the air

pressure using an aneroid pressure gauge and to enter it into the computer as a fixed value.

Pressure

All pressures required during the measurements / tests or for the calculations shall preferably be related as

differential pressures to a reference value (e.g. the atmospheric pressure) which is measured as absolute pressure.

33

Measuring devices serving exclusively for pressure loss measurement or tightness testing need not be officially

tested.

The metering pressures of the various meter types are measured in the case of

diaphragm gas meters in the inlet socket / flange

rotary piston / rotary vane gas meters in the inlet socket / flange

turbine gas meters directly upstream of the turbine wheel

vortex gas meters close to the bluff body

ultrasonic gas meters in the inlet socket / flange

other gas meters according to the statements in the approval or by the manufacturer

of the meter under test

In the case of inferential gas meters, pressure tapping should, as a principle, be realized at the pr socket on the test

piece. The same applies to volumetric gas meters. Substitute measuring points in the test rig are to be so designed

that there are no substantial differences from the measurement of the metering pressure. In the area of the pressure

tappings, the pipe sections shall, if possible, not show any changes.

Temperature

For the temperature measurement electronic sensors are to be preferred.

To improve the heat transfer and reduce the reaction times, the thermometers or temperature sensors shall be

mounted directly into the pipe (without protective pocket).

The temperature is to be measured preferably where temperature measuring points are already available for later

use. The temperature is otherwise to be measured up to 2 D downstream ensuring that in this case the velocity of

flow in the temperature measuring point does not exceed 15 m/s.

If the temperature is measured in the inlet and outlet, its mean value may be used as metering temperature.

In series test rigs, the temperature may be assigned to each individual meter on the basis of the measurement in

the inlet and outlet of the meter run.

If further temperature measuring points are used to determine the metering temperature or to monitor the

temperature stability in the test rig, avoidance of inlet disturbances in inferential gas meters is to be ensured by

compliance with diameters for the sensors of ≤ 0.1 D and distances upstream of the meters of ≥ 5 D.

Time

34

There are no specific accuracy requirements for the time measurement as long as it serves only to check whether

the flowrate adjustment is complied with. If the determination of the measurement errors of the meter under test

takes place by comparison of the flowrates at the meter under test and at the standard, it is required that it be

automatically stopped and the minimum requirements of Table 2 be complied with.

The minimum requirements to be met for the auxiliary measurands as regards division and resolution A,

respectively, as well as the measurement uncertainties U (k = 2) are compiled in Table 2.

Table 2: Minimum requirements for the determination of the auxiliary measurands

Measurand Testing of volume standards Testing of gas volume meters Pressure Temperature Time

A < 0.1 mbar U < 0.3 mbar A < 0.05 K U < 0.1 K A < 0.01 s Urel < 1⋅10-4

A < 0.1 mbar U < 0.5 mbar A < 0.1 K U < 0.2 K A < 0.01 s Urel ≤ 2⋅10-4

4.4 Test rigs

4.4.1 General requirements

Test rigs must be designed and realized in such a way that safety of operation is guaranteed at any time within the

permissible measurement uncertainties prescribed for the particular measurement task. For each test rig a test rig

manual is to be kept into which all changes with respect to software and hardware are entered.

4.4.2 Hardware

For the test rig not only the test rig manual but also a documentation must be available from which all auxiliary

measuring devices used and their connecting points and places of installation can be seen.

Tightness checks must be possible without any particular effort. It is to be ensured in particular that the volume

standards are installed in such a way that bypasses and any resulting leakage losses are prevented.

If required by the intended use and/or the design of the test rig, components may be regularly exchanged within

the period for which their metrological examination is valid. Such a replacement is to be separately checked when

the test rig is approved. Relevant conditions with respect to the identification of the components in use and to

assure the correct transfer of calibration parameters into the test rig software are to be laid down. Any

replacement is to be documented in the test rig manual.

35

Table 3: Example of entries into the test rig manual (components in use)

Component Identifica-

tion Place of

installation Test valid

until Date Status Respon-

sible Differential

pressure sensor Serial No. 12345/00

Device against

atmosphere

02-01-02 02-01-01 Initial putting into use

Muster-mann

Differential pressure sensor

Serial No. 12346/00

G 65 against atmosphere

02-01-02 02-01-01 Initial putting into use

Muster-mann

Differential pressure sensor

Serial No. 12347/00

G 250 against atmosphere

02-01-02 02-01-01 Initial putting into use

Muster-mann

Apart from the auxiliary measuring devices, the test rigs must be equipped at least with:

Shut-off devices

They serve to test the internal and external tightness of the test rig.

Flowrate setting valves

For the setting of the test flowrates, shut-off devices such as spherical valves are generally less suitable than flaps,

regulating or other valves.

Flowrate control valves

For flowrate control, the flowrate must be determined in relation to the measured value with an uncertainty

U ≤ 2%. This can be made either using separate flowmeters (in the case of diaphragm gas meter test rigs e.g. with

variable-area meters) or with the aid of the pulses emitted by the meter under test or the standard.

Blower

In order that the heat given off by the blower might not lead to spurious heating of the test air in the test rig, it is

normal to operate under suction conditions, preferably with controlled speed. For testing systems with pressure

operation it is advisable - above all at major flowrates - to carry off the compression heat of the test air by suitable

means, e.g. heat exchangers.

4.4.3 Software

The test rig software is the immaterial program for system control. In conjunction with the hardware it is an

essential component of the overall test rig system. It is the task of the program to organize the system process in

keeping with the specifications, to manage the data, to form new measurement values and to ensure

communication with the user.

High requirements are placed on the correctness of the results obtained. So the need of the user - who monitors

the test process for correctness of the results by plausibility checks - for control, checking and safety devices is to

be determined accordingly.

36

The software employed in the test rig must carry the designation for the version together with the date of creation,

and it must display this information on the screen at least when the program is started. The software shall offer

extensive protection against erroneous operation and unauthorized program changes (see below). Menu-driven

operator prompting without complicated instructions for use is to be aimed at.

The order of the data input from outside shall be in agreement with the actual test sequence. The kind and the

number of measurement values recorded have to satisfy the requirements of verification law (Technical

Guidelines, Testing Instructions).

It must be possible in a straightforward way to correct the entry of erroneous values prior to the evaluation as well

as to interrupt a testing operation and to start it again. After the evaluation it must not be possible to alter

measurement results. Direct comparability of the calculated measurement errors with the maximum permissible

errors applicable must be ensured. The relevant regulations of verification law for official tests are to be complied

with (e.g. the one-sided exploitation of maximum permissible errors is inadmissible).

The calculation of the measurement error of the meters under test must be made according to the equations stated

in these Testing Instructions. It must be possible to submit this calculation including all correction factors and, on

request, the appropriate program listing or a flowchart of the calculations to the verification authority.

To facilitate supervision by the verification authority and control by the user, it must be possible to display or

print out all measurement values used in the calculation of the measurement error. It is advisable to store all data

of the meter under test and all measurement results in a database, e.g. for re-calculation or subsequent statistical

evaluation.

The report on official tests must contain at least the following information (possibly also in a coded form):

• test centre

• test rig

• make, type

• serial number

• size

• year of manufacture

• approval number

• date

• load (theoretical value)

• measurement error, assigned to load

• adjustment

• pulse value

• result of indicating device check

• type of test

37

• test engineer

Authorized access

According to the type of access authorization for the operating staff, different access zones are distinguished. So

the access for the authorized staff to handle the program and modify test-related data as well as data subject to

supervision by the verification office must be protected by providing particular password levels. In detail, the

following provisions are valid:

Operator communication zone

Here the access is organized for the authorized operating staff to operate the facility. All measurement data and

parameters necessary to properly operate the facility must be freely realizable during operation and be available

for checking by the operator (reading function). Modification of the data must not be possible.

Setting zone

Here the parameters are adjusted (set) which have an effect on the sequence and scope of the test but do not

modify parameters of relevance under verification law.

Data in the setting zone are, for example, the reference values for the sequence and scope of the test, the manual

modification of the calculated adjustment and the boundary value setting for the evaluation of the meter (quality

analysis).

Parameterization zone

In this zone access to all parameters which have a direct effect on the measurand searched or are subject to

supervision by the verification office is possible. So, for example, the calibration data of sensors and volume

standards can be modified here.

Access to the setting and parameterization zones must be appropriately protected by a password or the like. This

also applies to swap files.

Duty to inform about software modifications

Modified system software is in any case to be identified by changing the designation of the version. If in the new

software the bases for the error calculation or parts of them have been modified, it is mandatory to inform the

verification authorities. The approval of the appropriate verification authority is to be obtained before the new

software is implemented.

The duty to inform about software modifications does not cover changes relating only to visualization or

communication processes, data management structures or changes of the operating systems.

Identification

38

The test rig software is clearly identified by its name, the version number and the operating system under which it

runs. The organization of the program and of the version designation (update of the version number) is the task of

the manufacturer who also provides the associated program documentation.

By suitable management in the test program (e.g. test rig manual; for an example, see table below), it must be

ensured that the state of revision of the software used for the operation of the rig can be completely displayed.

This access must be possible for each authorized user.

If a system software consists of more than one file or runs in conjunction with network computers, it must be

possible to see the associated swap files or programs.

Table 4: Example of a software list for the test program

Test rig software Cons.No.

Program name

Version System Date of revision

Modification Responsible

1 prfstand.exe V1.9 DOS 2-1-97 initial implementation, control program PC

Mustermann

2 ini.dat - DOS 2-1-97 initial implementation, default data PC

Mustermann

3 sps_p1 V3.4 B&R SPS 2-1-97 initial implementation, control program SPS

Mustermann

4 prfstand.exe V2.0 DOS 1-6-97 pressure monitoring extended, report and data storage modified

Mustermann

39

Data security

If the test documents according to section 61 of the Verification Ordinance are stored on electronic data carriers,

at least those statements are to be stored which must be given in a report on official tests of a meter under test. In

this case, the report need not be printed out.

The organization and documentation of the storage are to be notified to the appropriate supervising verfication

authority before the system is set up.

4.4.4 Series test rigs

For the simultaneous testing of several gas meters as is carried out for diaphragm gas meters and ultrasonic gas

meters up to 40 m³/h in particular, series test rigs are usually employed which principally are set up in the same

way, irrespective of the standard used:

ΔpP1 ΔpP2 ΔpP3 ΔpP4 ΔpP5pPEin

Prüfling 1

tPEin tPAus

Prüfling 2 Prüfling 3 Prüfling 4 Prüfling 5

Figure 1: Schematic sketch of a series test rig

For series test rigs the following criteria are valid:

The temperature need not be determined on each meter under test, however at least at the inlet and outlet of the

series.

For the determination of the metering pressure on the individual meters under test, the results of the individual

pressure loss measurements may be used (e.g. the metering pressure at meter under test No. 3 in the scheme above

is calculated from the inlet pressure at meter under test No. 1 less the pressure losses of meters under test Nos. 1

and 2). As a prerequisite, the cross sections of the pipings between the meters under test must be so large that the

pressure loss in these is negligibly small.

The pressure loss of diaphragm gas meters tested in series must not exceed 12 mbar. As this can also be reached

at the flowrate Qmax, a maximum of six meters may generally be mounted on one test bench. In view of the

potential interaction between the meters under test, the limitation of the pressure loss and the ensuing maximum

permissible number of meters under test which can be tested in series is necessary but may be dispensed with on

condition that:

40

• the conditions at each meter are appropriately accounted for

• in the acceptance according to section 6.6.2, the dispersion of the measurement values for each meter does not

exceed the admissible boundary values.

Frequently the pressure loss of the meters under test is not determined between their inlet and outlet socket but in

substitute measuring points in the mounting devices. Depending on the test rig design, the pressure loss displayed

therefore usually appears to be somewhat increased. For meters of the same type, this difference can be

determined and corrected. Likewise, fixed pressure correction values can be determined for each mounting

arrangement and used for the testing of identical meter types. It is also permitted to measure the total pressure loss

over the test bench and to break it down for the relevant metering pressure to be assigned to the individual meters

under test.

Test rigs for diaphragm gas meters with temperature conversion

For the testing of temperature-converting diaphragm gas meters, test rigs with a temperature chamber are to be

used which are set up as shown below:

ΔpP1 ΔpP2 ΔpP3 ΔpP4 ΔpP5ΔpP5

Δpwt

pPEin

pN

Prüfling 1

Gebläse Normal Wärmetauscher

Klimaschrank

vorgetrocknete Prüfluft

tPEin

tNEin

tPAus

tP5tP5tP3tP1 tP2

tNAus

Prüfling 2 Prüfling 3 Prüfling 4 Prüfling 5

Figure 2: Schematic sketch of a series test rig for temperature-converting diaphragm gas meters

Besides the criteria for series and single test rigs, the following features are valid:

• The test rigs must operate under suction conditions.

• The temperature of the test air supplied to the diaphragm gas meter must have been regulated. This can be

made with the aid of an external heat exchanger or a heat exchanger arranged in the temperature chamber.

• The test air used for testing must not condense in the meters under test. The condensate forming during

temperature regulation upstream of the meters under test is be removed.

41

• The heat exchangers are to be appropriately dimensioned to ensure temperature stability at the meter under

test and at the standard (proof within the scope of test rig acceptance).

• The temperatures in the temperature measuring points in the temperature chamber are to be measured at least

three times per minute. As the meters under test convert the temperature, the temperatures may differ by up to

2 K. Their variation during a test must be smaller than 2 K.

• The pressure loss between the inlet of the pipe prover and the standard (without heat exchanger) shall be

smaller than 12 mbar.

4.4.5 Single test rigs

Large gas meters are usually tested in the arrangement below, the test air being sucked in from the room:

Figure 3: Schematic sketch of a single test rig

Unless otherwise provided in the type approval for the meter under test or in the approval for the test rig, the

following regulations are valid:

Straight pipes upstream of meters under test

• length

diaphragm gas meters none

rotary piston / rotary vane gas meters acc. to 4.4.6

turbine gas meters and other gas meters ≥ 5 D

• other requirements

ΔpPpP

pN2

pN3

pN1

Prüfling Gebläse

Normal 2

Normal 3

Normal 1

tPEin

tN2Ein

tN3Ein

tN1EintPAus

tN2Aus

tN3Aus

tN1Aus

42

nominal diameter identical to that of meter under test

deburred inside edge of flange

gaskets must not protrude into flow section

flow profile disturbances due to installation are to be avoided

Outlet pipes

• length

diaphragm gas meters none

rotary piston / rotary vane gas meters acc. to 4.4.6

turbine gas meters and other gas meters ≥ 3 D

• other requirements

nominal diameter identical to that of meter under test

deburred inside edge of flange

gaskets must not protrude into flow section

flow profile disturbances due to installation are to be avoided

differences in nominal diameter are to compensated by diffusors or confusors

It must be possible for any pipe branches in the test facility to be shut off.

Interactions between meter under test and standard or between standards are to be minimized. This can be

achieved, for example, by large-volume filters and straighteners. A filter additionally serves to protect the

standard from soiling.

4.4.6 Particular features of rotary piston meters

If rotary piston meters are tested, resonance-related discontinuities of error curves (especially in testing using

rotary piston standards and - to a lesser extent - with other standards) can be caused by:

• lack of vibration damping

Due to periodic filling and discharging of the test volume and the increase and decrease in pressure, rotary

piston gas meters always produce vibrations which are hardly reduced by smooth pipings.

• unfavourable piping lengths

Certain piping lengths can lead to intensification of the vibrations. So straight inlet and outlet sections of

three times the nominal meter diameter can be unfavourable.

• unfavourable combination of meter under test / standard

As a rule, if two rotary piston gas meters with essentially the same metrological properties and sizes are

operated in series, interactions result.

• line volume

An unfavourable ratio between test and line volume can lead to pulsations exerting an influence on the

standard or meter under test.

43

For the reduction of resonant vibrations in test rigs, see the recommendations in Annex 4.

44

5 Ambient conditions (test rooms)

The test rooms must be set up, dimensioned and equipped such that the testing of the measuring devices (meters

under test) as well as of the standards and test facilities is possible with the reliability (measurement uncertainty)

required, standards and technical facilities are properly preserved, interim storage of the untested and tested

measuring devices is possible, representative measuring points for the determination of the air pressure, the

ambient temperature and, where applicable, the air humidity can be provided and sufficient ventilation is possible

without the temperature stability being affected.

Test rooms must have a temperature which is stable both in time and in space. This is achieved by air-

conditioning or temperature regulation, respectively, of the test room. Test rooms shall also comply with the

following criteria:

• no direct access from outside or to rooms with a substantially different temperature; if need be, windscreens

or air locks are to be provided

• no windows or only double windows to the north / east or windows with heat and radiation insulation,

• no through rooms,

• arrangement not directly at poorly insulated outer walls or directly under the roof.

Temperature stability can be reached in a rather simple way by drawing in the test air from the test room and

blowing it back again, i.e. the test air is allowed to circulate and thus can adjust to the test room temperature

(when meters are tested which have already been in operation, this is not always possible because of the odour

emanating from the meters).

In the case of great test flowrates, drawing-in of the test air from outside or from neighbouring rooms with

substantially different temperature conditions is sometimes inevitable.

In this case it is necessary beforehand to adjust the temperature of the air sucked in to room temperature.

The following minimum requirements have to be complied with:

Table 5: Minimum requirements for test rooms

Criterion Theoretical value

Mean room temperature close to test rig Variation over 24 h Temperature layering per metre of room height Temperature difference from mean room temperature, in the metering points of standard and meter under test prior to start of measurement with the blower switched off Variation per test run

22 ± 5 °C ≤ 2 K ≤ 0.5 K ≤ 1 K

45

• test method without taking temperature into account • test method taking temperature into account

≤ 0.3 K acc. to test rig approval

Deviating requirements are to be specified in the approval of the test rig.

The requirements stated for the testing of the standards and test rigs in section 6.5.3 can be complied with by

temporary technical and organizational measures.

46

6 Testing

6.1 External inspection

The external inspection encompasses examinations whether

• the measuring device is approved for verification

• the design of the measuring device complies in its details with the type approval

• no damage can be detected from outside

• in the case of measuring devices subjected to preliminary inspection, this inspection is still valid

• in the case of subsequent verification or metrological evaluation, the stamping locations are intact.

For brand-new measuring devices of the same kind, the external inspection can be carried out on samples.

6.2 Preparation for metrological examination

6.2.1 Temperature adjustment

Before the tests are started, the meters under test must be stored for at least five hours in the test room or in a

room with approximately the same temperature. By appropriate heating, the time for temperature regulation can

be reduced. Temperature regulation is terminated when temperature stability during the tests is ensured.

6.2.2 Preparation and installation of meters under test

The meters under test must be prepared according to the manufacturer's specifications so that they are ready for

use.

For diaphragm gas meters with Qmax ≤ 10 m³/h, internal cleaning and preparation of the meters submitted for

subsequent verification can be dispensed with only if the measurement error of the meters when dismounted is 5

% at most at a flowrate of 0.2 Qmax. Meters which do not comply with these error limits when tested are to be

opened and subjected to a basic repair.

Rotary piston gas meters are to be filled with gearing oil unless otherwise provided in the type approvals.

If turbine gas meters are provided with oiling systems, these may not be operated immediately before or during

testing. Otherwise, preparatory operation for at least one hour is to be provided to reduce the effects of oiling on

the measurement results.

47

Mounting into the test facility takes place as specified in the operating instructions of the manufacturers of the

measuring devices. Particular attention is to be paid to the mounting position, and application of too high a

pressure to the meter case is to be avoided. In all other respects, the specifications in the operating instructions

and/or in the approval of the test facility are valid.

For meters which have already been incorporated in the network for a prolonged time, it is advisable to discharge

the test air into the open air so as to avoid unpleasant odours due to odorizers.

6.2.3 Preparation of standards

The standards are to be prepared in dependence on their type. In the case of drum-type gas meters, the

arrangement and the oil level are to be checked and, if necessary, corrected.

To protect the standard from soiling, it is recommended to provide a filter , e.g. a plate filter, between standard

and meter under test. Otherwise the standard should be arranged upstream of the meter under test.

6.2.4 Preparatory run

Preparatory operation of meters under test and standards which have not been used for a prolonged time serves to

dissolve gumming residues in the bearings and to eliminate the clearance between driving and adjustment wheels

as well as the non-uniform pressure distribution in the test rig due to clamping or to the tightness test. Also, in the

case of diaphragm gas meters, any unfavourable valve position which might have been caused by the transport is

corrected. The amount of gas supplied to volumetric gas meters shall be at least 30 times VZ. For temperature

adjustment, the supply of a larger gas volume may be necessary.

6.2.5 Tightness test

Tightness of the test rig is an indispensable prerequisite for the correctness of the measurement results and their

uncertainty. A distinction is made between external and internal tightness. Proof can be furnished for the test

facility as a whole, with the meters under test installed, or for individual sections. The test pressure applied shall

lie in the following range:

10 mbar ≤ test pressure (≤ 3 x working gauge pressure of test facility)

Table 6: Permissible leakage rate in dependence on pressure drop

Type of meter Perm.leakage rate per section

QL,zul

Perm. total leakage rate

∑ QL,zul

Δp in test section max.

mbar

Testing times Δ t prüf

min

Diaphragm gas meter 0.001 Qmin

0.003 Qmin

0.2

3 to 12

Rotary piston gas meter

48

Turbine gas meter Vortex gas meter

0.001 Qmin 1.0 3 to 12

In the tightness test by sections, the sum of all leakage rates for the individual sections must not exceed the

tabular value ∑ QL,zul.

The testing time is calculated by the following equation:

absmin

eprüf 0.001

60p

Vp⋅⋅

⋅Δ⋅=Δ

Qt (30)

Δtprüf numerical value of testing time in min

Ve numerical value of enclosed volume in m³

Qmin numerical value of minimum test flowrate in m³/h

Δp numerical value of pressure variation during time of tightness test in mbar

pabs = pa - pe numerical value of initial pressure as absolute pressure in mbar (suction). In operation under

pressure conditions, the gauge pressure in the pipe prover is to be added to the barometric

pressure.

pa numerical value of barometric pressure in mbar

pe numerical value of negative gauge pressure or gauge pressure in the pipe prover in mbar.

If negative gauge pressure or gauge pressure has been applied to the pipe prover, the latter is to be allowed to

adjust for at least one minute. During the testing time, the temperature in the trapped volume shall not vary by

more than 0.1 K.

A testing time shorter than that given in Table 6 can be sufficient if the enclosed volume has been determined

from geometrical dimensions, the pressure drop is measured with sensors with a resolution of 0.01 mbar and the

boundary values for the leakage rate given in the table are nevertheless complied with. The actual leakage rate

QL,ist is calculated by equation (31):

absprüfist,,L p

VpQ

⋅Δ⋅Δ

=t

e (31)

External tightness of test facility

The tightness of the test rig, including the meter under test, must be checked each time a change has been made

and at regular intervals once weekly. The test is to be documented.

External tightness after installation of meter under test

49

After the devices to be tested have been mounted, the tightness is to be checked before measurement is started. If

equipped appropriately, only that section of the test rig needs to be checked in which the device to be tested is

mounted. (For a calculation example, see Annex 2.1).

Internal tightness of test facility

Once quarterly - preferably on the occasion of the comparison measurement -, an internal tightness test is to be

carried out for the whole system. In order for internal leaks to be detected, it must be possible for partial sections

of the facility to be shut off.

6.3 Metrological examination

6.3.1 General conditions

For the gas meter types not mentioned in the sections below and if the specifications below are deviated from, the

scope of the metrological examination is specified in the type approvals.

6.3.1.1 Mode of operation

The mode of operation depends essentially on the kind and condition of the devices to be tested.

Operation under flying start-stop conditions offers the advantages that the test flowrates can be exactly adjusted

before the beginning of the test run proper and that the measurement times can be kept relatively short. Usually,

high-frequency pulse generators are used on the standards and at least low-frequency pulse generators on the

meters under test. To increase the reliability, it is to be aimed at using multi-channel pulse generators on the

standards.

Operation with standing start-stop conditions is permitted exclusively for volumetric gas meters. It is to be borne

in mind that due to the definition of the test volume the ratio of the total measurement time to the starting and

braking time is not smaller than 20:1.

If drum-type gas meters are used, complete revolutions of the drum shall be used, if possible, in order to avoid the

periodic error of the standard.

6.3.1.2 Evaluation method

The measurement errors can principally be determined by the comparison of the test volumes or the flowrates at

the meter under test and at the standard. For the measurement uncertainty to be complied with, the minimum test

volume or the minimum measurement time, respectively, at the meter under test is to be defined (by conversion to

50

the corresponding test volume) in such a way that the measurement uncertainty does not exceed one fifth of the

respective error limit.

For evaluations with the aid of the test volumes determined, the readings from the indicating devices or the

counting of the events of different pulse generators (high-frequency, low-frequency and combinations thereof) are

essential. The determination of the increments, of the pulses and of the testing time can be made manually or

automatically. In the case of manual start-stop in particular, compliance with the permissible measurement

uncertainty is to be evidenced by repeated measurements.

The comparison method using the flowrates is of advantage if both the meter under test and the standard (e.g.

standard drum-type meter, bell prover) are not equipped with a high-frequency pulse generator. The flowrate here

needs to be kept constant and the time measurements on meter under test and standard must take place almost

synchronously. If the features of the standard or the meter under test allow several single measurements to be

carried out during the overall measurement time which is determined by the pulse generator with the lowest

frequency, a mean value can be formed from the single values provided that the evaluation software of the

computer allows the single measurement values to be compared and that their differences are smaller than 0.05 %.

6.3.1.3 Minimum test volumes

The minimum test volumes depend on the features of the meter under test and the test rig. They are specified in

the approval by the verification authority.

If - with the exception of diaphragm gas meters - the volume is determined from the reading or scanning of the

last index drum of the mechanical indicating device, the test volume must be an integer multiple of the constant

of the last drum. For the maximum permissible uncertainty to be complied with, the testing time must typically be

at least 120 s.

If drum-type gas meters are used, the test volume depends on the minimum number of revolutions of the standard.

6.3.1.4 Flowrate adjustment

The test flowrates are to be adjusted with an accuracy as given in Table 7.

Table 7: Maximum permissible errors of flowrate adjustment

Flowrate Maximum permissible errors

> 0.5 m³/h + 5 %

< 0.5 m³/h -10 % to +5 %

6.3.1.5 Pulse counting

51

As a rule, the minimum measurement time should be 60 s.

If the measurement values are electronically determined via higher-frequency pulse generators, shorter testing

times are permitted if the measurement uncertainty can be proved to be the same.

If the pulse generators are driven via a mechanical gearing, it is to be ensured that the result of the metrological

examination is not falsified by transmission effects.

If magnetically operated pulse generators are used, the test quantity is to be selected such that the start and the

stop of the measurement are always triggered by the same magnet.

Besides the determination of the volume passed by counting the volume-proportional pulses, testing with

preselection of a theoretical number of pulses and automatic starting and stopping of the meter controlled is also

permitted.

To determine the indicated volume or flowrate, respectively, on a meter (standard or meter under test), it is

always the pulse generator with the highest frequency which is to be evaluated.

In test rigs with a common time window for the pulse counting for meter under test and standard, from among the

pulse generators to be evaluated that with the lowest frequency is to be used for triggering the time window. This

allows as small a measurement uncertainty as possible to be attained.

If several meters under test are tested simultaneously using one or several standards, there are two possibilities of

pulse counting:

• For each meter under test a separate pulse detection unit is provided generating a time window for pulse

counting for meter under test and standard.

• For one meter under test a pulse detection unit is provided generating the time window for pulse counting for

meter under test and standard. For each further meter under test, one pulse detection unit is employed to

determine the indicated flowrate of the meter under test only. The measurement errors of the meters under test

are determined by means of the measured flowrates. This procedure implies a constant volume flow

throughout the time of measurement.

Each pulse generator is, as a matter of principle, to be subjected to a functional check.

6.3.1.6 Adjustment

It is the aim of the adjustment that the error curve is as close to zero as the adjustment steps and the maximum

permissible errors permit.

52

For the adjustment either individual measurement errors or the measurement errors of all test points can be used.

Method of adjustment using the measurement results for individual measuring points

After having been tested the meters are adjusted at individual flowrates using the experience gained with the error

curve for measuring devices of identical type. For all other test points, it remains to be seen whether all

measurement errors lie within the maximum permissible errors and whether the one-sidedness clause is complied

with.

Method of the weighted mean error WME

After all test points have been handled, the meters are adjusted according to equation (3). The mean error WME

must not exceed ± 0.4%.

In the initial verification of diaphragm gas meters, adjustment wheels with a maximum spacing from the standard

pair of ± 5% - e.g. according to the table in Annex 3 - are to be used for this purpose. In subsequent verification,

adjustment wheels from the whole table may be used. For other gas meter types, other adjustment wheel pairs or

other adjustment methods are applied as well.

6.3.1.7 Check of pulse value and indicating device

The check of the pulse value and of the indicating device aims to assure the values of all pulse outputs and the

correctness of the indication of the indicating device after the test and, where appropriate, after the adjustment. As

the pulse value of all pulse outputs derives from mechanical quantities of the gas meter such as gear ratio, number

of blades and ratios of adjustment wheel pair and indicating device wheel pair, the pulse value check can be

carried out only after selection and mounting of the indicating device wheels and the adjustment wheels. A pulse

value and indicating device check is to be carried out each time the adjustment is changed.

Meters can have high-frequency pulse outputs which are to be used for the metrological examination in

accordance with section 6.3.1.5. Furthermore, meters with a mechanical indicating device can have a low-

frequency pulse output or, for the metrological examination, a test element.

For low-frequency pulse outputs or the test element, respectively, the manufacturer has stated design-specific

pulse values cIW,NF or an output constant tr. For high-frequency pulse outputs, pulse values are determined

depending on the adjustment. The pulse value is always determined accurate to seven digits and rounded to six

digits (e.g. 1 m³ ^= 11,264.3 imp/m³).

The relation emerges from the following equations which are generally valid.

For the low-frequency pulse value and the output constant the following relations are valid:

53

( ) ( )12Gzr12GzNFIW, *or * /J*JIVt/J*JIVc == (32)

with:

Vz – cyclic volume

IG – total gear ratio

J2/J1 – adjustment wheel pair

Between the cyclic volume Vz and the associated number of pulses of a high-frequency pulse generator there is a

design-specific ratio nImp,Vz.

For the pulse value of the high-frequency pulse generator, the following is thus obtained:

zV Vnc =⋅zImp,HFIW, (33)

From this the following relations between low-frequency outputs and test element ensue:

( ) ( )12GImp,HFIW,r12GImp,HFIW,NFIW, zzor /J*JInct/J*JIncc VV ⋅=⋅= (34)

For a meter under test the applicable formula is to be taken from the approval documents or from the

manufacturer's specifications.

Pulse value check

For the check of the low-frequency pulse values with the aid of high-frequency pulse outputs, the following

conditions are to be met:

%05.0%1001HFIW,HFImp,

NFIW,NFImp, <⋅⎟⎟⎠

⎞⎜⎜⎝

⎛−

cncn

(35)

or

%05.0%1001HFIW,HFImp,

rtrImp, <⋅⎟⎟⎠

⎞⎜⎜⎝

⎛−

⋅

cntn

(36)

The start and the stop of the pulse counting operation is triggered by a low-frequency pulse generator. The

number of low-frequency pulses nImp,NF or the number of revolutions of the test element shall correspond to a

working volume VG passed during approx. 8 minutes at Qmax.

Furthermore, the number of counted pulses must allow a measurement uncertainty of 0.05 %.

54

If the required accuracy according to equation (35) or (36), respectively, is not reached, an increase in the

working volume VG passed during the pulse value check may yield better agreement.

Should the meter under test have different pulse generators at the same time, the pulse value check is performed

with the pulse generator with the highest frequency. The pulse values of the other high-frequency pulse

generators are determined by computation. During the meter test, the plausibility check of these pulse values must

be performed in metrological terms by pulse counting and comparison of the volumes corresponding to the

number of counted pulses.

Check of indicating device

If the meter is tested with the aid of the test element or with a pulse output, a check of the mechanical indicating

device is necessary. This check can be performed by repeating at least one test flowrate with the indicating device

using a button or another starting / stopping switch and complying with the following requirement:

%2.0%1001G

IWImp <⋅⎟⎟⎠

⎞⎜⎜⎝

⎛−

Vcn

(37)

6.3.1.8 Data interfaces

In the verification of the meters, digital data interfaces for reading out or transmitting the measurement values

(e.g. DSfG, encoder-type indicating device) may be used.

If the accuracy check is not carried out via the indication but exclusively via digital data interfaces, it is to be

ensured at least once by a comparison of values within the scope of the accuracy check that the register contents

read out and the associated register contents indicated are in keeping at least as regards the digits which can be

seen in the display.

For meters which have a special mode for testing (e.g. a higher resolution of the display), the comparison must be

performed at least once prior to the beginning and once after completion of all tests.

As a matter of principle, each digital data interface is to be subjected to a check (comparison of values).

6.3.2 Testing of diaphragm gas meters

6.3.2.1 Test flowrate and test volumes

55

The meters are to be tested for compliance with the maximum permissible errors at the following flowrates:

• Qmin

• 0.2 Qmax

• Qmax

Test volume, with indicating device

Unless otherwise specified in the approval of the test facility or in the test certificate for the standard, the

following minimum test volumes are to be complied with in the testing of the diaphragm gas meters with attached

indicating device:

Table 8: Test flowrates and test volumes for the testing with indicating device reading

Qmax

in m³/h

Meter size acc. to

EEC Directive

Qmin

in m³/h

Test vol. in

m³

at Qmin

Test vol.

in m³

at 0.2 Qmax

Test vol.

in m³

at Qmax

2.5 G 1.6 0.016 0.02 0.10 0.2

4.0 G 2.5 0.025 0.02 0.10 0.2

6.0 G 4 0.04 0.03 0.10 0.3

10 G 6 0.06 0.03 0.20 0.5

16 G 10 0.10 0.15 0.30 0.9

25 G 16 0.16 0.15 0.45 1.3

40 G 25 0.25 0.2 0.70 2.0

65 G 40 0.40 0.3 1.2 3.5

100 G 65 0.65 0.5 1.8 5.0

160 G 100 1.0 1.5 3.0 8.0

250 G 160 1.6 1.5 4.5 13.0

400 G 250 2.5 3.0 7.0 20.0

650 G 400 4.0 6.0 14.0 35.0

If the approved working ranges differ from those given in the table (1:160), the test volume at Qmin is to be

selected from the table according to the Qmin, stated on the meter.

Test volume, without indicating device

To minimize the test volume and the testing time, diaphragm gas meters can be tested without indicating device.

In this case, in the place of the indicating device, a test element (e.g. cross, star) is to be mounted which is

scanned optically or by magnetic-inductive means.

56

To reduce periodic errors of the device to be tested, the test volume to be defined must correspond to an integer

multiple of the test volume of the gas meter.

The sampling uncertainty of the test elements must not exceed 0.2 %. The permissible minimum test volume is

stated in the approval for the test rig.

The procedure may be applied on condition that

• the shaft of the measuring device is accessible after the indicating device has been removed

• starting of the measurement in the reversal point of the measuring device is avoided

• the transmission ratio in the measuring device is 1 : 1

• the input torque of the indicating device influences the measurement error at Qmin only insignificantly.

After termination of the individual test runs, the adjustment wheels determined and the indicating device are to be

mounted and a plausibility check at a test flowrate is to be carried out. The maximum deviation from the

measurement value ascertained beforehand must not exceed 0.6 %.

6.3.2.2 Maximum permissible errors

The measurement errors calculated according to equation (26) or (29) are compared with the maximum

permissible errors for which different values are provided in DIN EN 1359 and EEC Directive 71/318/EEC. They

are:

Table 9: Maximum permissible errors for diaphragm gas meters

according to 71/318/EEC according to DIN EN 1359 Flowrate range Max.perm.error on

verification Flowrate range Max.perm. error

Qmin ≤ Q <2·Qmin ± 3.0 % Qmin ≤Q <0.1.Qmax ± 3.0 % 2·Qmin ≤ Q ≤Qmax ± 2.0 % 0.1Qmax ≤ Q ≤Qmax ± 1.5 %

In the verification the measurement errors of a meter at flowrates between 2·Qmin and Qmax must not all exceed ±1

% if they all have the same sign.

6.3.2.3 Pressure measurement

The pressure loss is determined as the pressure difference between inlet and outlet of the meter. It varies

periodically with the filling and discharging of the measuring compartments. A distinction is made between

mechanical pressure loss and total pressure loss.

Mechanical pressure loss

57

The mechanical pressure loss is determined at flowrates between Qmin and 2 Qmin as the maximum value of the

four pressure peaks of one revolution of the measuring device. For this determination pressure gauges with

maximum device or off-limit monitoring or appropriate pressure recorders are to be used and the following

maximum values are to be complied with:

Table 10: Maximum permissible values of the mechanical pressure loss for diaphragm gas meters

Maximum permissible values of mechanical pressure loss acc. to EEC Directive

Meters with Qmax

N/m² mbar up to 65 m³/h 60 0.6

> 65 m³/h to 400 m³/h 100 1.0

Total pressure loss

The total pressure loss is determined at the flowrate Qmax as the mean value of the pressure variation of one

complete revolution of the measuring device. It must not exceed the following values:

Table 11: Maximum permissible values of the total pressure loss for diaphragm gas meters

Maximum permissible mean pressure loss values Meters with Qmax N/m² mbar

up to 10 m³/h 200 2 > 10 m³/h to 65 m³/h 300 3

> 65 m³/h to 400 m³/h 400 4

6.3.2.4 Testing of diaphragm gas meters with mechanical temperature conversion

The gas meters are to be tested on a test rig for diaphragm gas meters equipped with a temperature conversion

device. Prior to the metrological examination, the meters under test are to be subjected to a preparatory run with

at least 50 test volumes each time the temperature has changed.

The temperatures are stabilized after each temperature change so that the temperatures of the test gas (dry air) and

the meter as well as the inside temperature of the temperature-regulated cabinet are within 2 K. During the time of

measurement, the temperatures must not change by more than 2 K.

The calculation of the measurement errors is made using equation (26) and inserting the billing temperature Tb in

the place of the temperature of the meter under test TP. Two different procedures are available:

National initial verification - procedure A - overall testing of all meters

All meters are tested at the permissible test room temperature at the flowrates Qmin, 0.2 Qmax and Qmax. At the

temperature limits tmin (lower temperature limit) and tmax (upper temperature limit), only the flowrate 0.2 Qmax is to

be tested. The maximum permissible errors on verification according to Table 12 are to be complied with:

58

Table 12: Maximum permissible errors on verification for diaphragm gas meters with mechanical temperature

conversion

Flowrate

Test temperature Qmin 0.2 Qmax Qmax

Room temperature 3.5 % 2.5 % 2.5 %

tmin ± 2 °C / tmax ± 2 °C - 3.0 % -

If at 0.2 Qmax and Qmax the measurement errors are of the same sign at test room temperature, both measurement

errors must lie within +1 %.

National initial verification - procedure B - testing by a sampling procedure

As an alternative to procedure A, a simplified test procedure can be used in initial verification for testing the

meters if the temperature behaviour of the meters coming into question has been checked beforehand by the

following sampling procedure:

Meters of the same type are combined into lots. The meters must stem from continuous production and be

designed for the same temperature range. Following DIN ISO 2859 part 1, lots of a maximum size of 500 meters

are to be formed, and five sample meters are to be randomly selected from each lot. For testing at test room

temperature, an additional two meters may be taken as reserve.

To start with, the sample meters are tested at test room temperature and must comply with the limited error limits

for testing in Table 13. If a sample meter does not comply with these limits, a reserve meter can be used. If at test

room temperature the measurement errors have the same sign at 0.2 Qmax and Qmax, both measurement errors must

lie within +1 %.

Table 13: Maximum permissible errors for the testing of sample meters of a tested lot

Flowrate

Test temperature Qmin 0.2 Qmax Qmax

Room temperature 2.5 % 1.5 % 1.5 %

tmin ± 2 °C / tmax ± 2 °C - 2.5 % -

Subsequently, the sample meters are additionally tested at 0.2 Qmax at the temperature limits tmin and tmax and must

also comply with the error limits for testing in Table 13. For this test one-sidedness is not mandatory.

Readjustment after the test at the temperature limits tmin and tmax is not permitted.

59

When tested at the temperature limits tmin and tmax, no sample meter must fail as otherwise the lot will be rejected

or is to be subjected to overall testing according to procedure A1.

The results of the sampling inspection are to be kept in a suitable form for quality assurance according to the

example in Table 14.

Table 14: Example of quality assurance for diaphragm gas meters with mechanical temperature conversion

Table 15: Error limits for testing the other meters of a lot subjected to sampling

Flowrate

Test temperature Qmin 0.2 Qmax Qmax

Room temperature 2.5 % 1.5 % 1.5 %

If the measurement errors at 0.2 Qmax and Qmax are of the same sign, not both may exceed 1% in amount.

Meters which in this test do not comply with the limited error limits for testing have successfully passed the test

only if they are tested by procedure A.

Subsequent verification

For subsequent verification the meters are to be tested at test room temperature at the flowrates Qmin, 0.2 Qmax and

Qmax. Prior to this test a preparatory run at approx. 0.2 Qmax with at least 30 Vz is to be provided. The maximum

permissible errors stated for initial verification are valid.

6.3.2.5 Sampling inspection to extend the period of validity of verification, with reduced

test volume

The procedure described below serves to carry out the sampling inspection of diaphragm gas meters up to

Qmax=10 m³/h without indicating device with reduced test volume as follows:

Q u a lity a s su ra n c e Q u a litä tsn a c h w e is fü r d ie E rste ic h u n g vo n H a u sh a ltsb a lg e n g a szä h le rn m it m e c h a n isc h e r T e m p e ra tu ru m w e rtu n g n a c h V e rfa hre n B Z ä h le rlos : tm in = ...°C P rü fs te lle : L o sg rö ß e: tm ax = ..

°C P rü fda tu m :

Z ä h le rtyp : P rü fs ta nd :

S p an ne d e r M e ssab w e ich un ge n

H e rs te lle r: P rü f te m pe ra tu r: 2 0 °C 2 0 °C 2 0 °C tm in tm ax 0 ,2 Q m ax 0 ,2 Q m ax 0 ,2 Q m ax Z u l.-Z e ich en :

D u rch f lu ss : Q m in 0 ,2 Q m ax Q m ax 0 ,2 Q m ax 0 ,2 Q m ax f(tm in) - f(tm ax) %

f(tm in) - f(tm ax) %

f(2 0 °C ) - f(tm ax) %

L fd .N r. Z ä h le r-n u m m e r

K u nd e Z ä h le rn u m m e r V o n ... b is ...

M e ssa b w .%

M e ssa b w .%

M e ssa b w .%

M e ssa b w . %

M e ssa b w . %

60

a) mounting of the gas meter in the test facility and preparatory run

b) testing of the meter at 0.2 Qmax with indicating device (test volume 40 times the test volume of the meter or at

least 80 l, reading when indicating device stands still).

The result can be as follows:

• The maximum permissible error for the sample is complied with.

• The maximum permissible error of the sample is exceeded by more than 0.5 %, so the meter is defective.

• The maximum permissible error of the sample is exceeded by up to 0.5 %, so the test must be repeated. If the

mean value of the two tests does not comply with the maximum permissible error for the sample, the meter is

considered defective.

c) removal of cap of indicating device and then of the indicating device, testing of indicating device

If, according to b), the meter has been assessed as defective, the test is to be terminated.

d) testing of meter with pulse generator (flying start-stop) at the flowrates 0.2 Qmax and Qmax accounting for the

built-in adjustment wheel pair. The test volume is to be selected according to the approval of the test facility.

e) determination and evaluation of the test results

The result for the flowrate 0.2 Qmax is obtained from the mean value of the measurement error with and without

indicating device.

The result at flowrate Qmax is to be corrected if at the flowrate 0.2 Qmax the difference between the measurement

errors with and without indicating device is greater than 0.6 %. It is to be assumed that the test points are

staggered in parallel.

6.3.3 Testing of rotary piston gas meters

The meters are to be tested at the following flowrates for compliance with the maximum permissible errors:

Table 16: Test flowrates for rotary piston meters

National context, according to EO 7 or 71/318/EEC according to DIN EN 124 80

Qmin, 0.05·Qmax , 0.1·Qmax, 0.25·Qmax, 0.4·Qmax, 0.7·Qmax and Qmax Qmin, 0.25·Qmax and Qmax

In the case of meters which can be operated in changing directions of flow, compliance with the measurement

errors ascertained must be additionally checked at least in one test point. For this check, no difference greater than

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0.3 % must occur in the flowrate range from 0.2 Qmax to Qmax. Otherwise testing must be carried out in all test

points and in both directions of flow.

The minimum flowrate Qmin is obtained as a function of the working range from Table 17.

Table 17: Minimum flowrate in dependence on the working range for rotary piston meters

Working range

1:10 1:20 1:30 1:50 1:65 1:80 1:100 1:160 1:200 1:250

Qmax [m³/h] Qmin [m³/h]

16 1.6 0.8 0.5 0.3 0.2 0.2 0.2 0.1 0.1 0.1

25 2.5 1.3 0.8 0.5 0.4 0.3 0.3 0.2 0.1 0.1

40 4 2 1.3 0.8 0.6 0.5 0.4 0.3 0.2 0.2

65 6 3 2 1.3 1 0.8 0.7 0.4 0.3 0.3

100 10 5 3 2 1.5 1.2 1 0.6 0.5 0.4

160 16 8 5 3 2.5 2.0 1.6 1 0.8 0.6

250 25 13 8 5 4 3 2.5 1.6 1.3 1

400 40 20 13 8 6 5 4 2.5 2 1.6

650 65 32 20 13 10 8 7 4 3 3

1000 100 50 32 20 15 12 10 6 5 4

1600 160 80 50 32 25 20 16 10 8 6

...

In the case of working ranges >1:250, the Qmin value is an appropriate decimal fraction of the values stated.

The pressure loss of the meter under test must be measured and recorded.

Graphical recording is not prescribed but facilitates recognition of resonant phenomena which may substantially

falsify the error behaviour of rotary piston meters. If resonances occur, representative equivalent test flowrates are

to be selected. As resonances depend both on the meter under test and on its mounting conditions, no

specification can be made for the position of the equivalent test points.

The maximum permissible errors are at present defined as follows:

Table 18: Maximum permissible errors for rotary piston meters

Maximum permissible errors on verification acc. to 71/318/EEC acc. to DIN EN 124 80

Flowrate range Perm. measurement error Flowrate range Perm. measurement error

Qmin ≤ Q < 2·Qmax ± 2.0 % Qmin ≤ Q < Qt ± 2.0 %

0. 2·Qmax ≤ Q ≤ Qmax ± 1.0 % Qt ≤ Q ≤ Qmax ± 1.0 %

62

According to the EEC Directive, measurement errors must not all exceed half the above-mentioned maximum

permissible errors if they are of the same sign.

The transitional flowrates Qt are defined as follows in dependence on the working range:

Table 19: Transitional flowrates for rotary piston meters

Working range Transitional flowrate Qt

acc.to 71/318/EEC / EN 12480 1:10 0.20·Qmax

acc.to 71/318/EEC / EN 12480 1:20 0.20·Qmax

national context, acc. to EO 7 / EN 124 80 1:30 0.15·Qmax

national context, acc. to EO 7 / EN 124 80 1:50 0.10·Qmax

acc. to DIN EN 124 80 >1:50 0.05·Qmax

6.3.4 Testing of turbine gas meters

In dependence on the working range, turbine gas meters are to be tested for compliance with the maximum

permissible errors at the following flowrates (statements in % of Qmax):

Table 20: Test flowrates for turbine gas meters

Working range

1:10 1:20 1:30 1:50

2 %

3 %

5 % 5 % 5 %

10 % 10 % 10 %

25 % 25 % 25 % 25 %

40 % 40 % 40 % 40 %

70 % 70 % 70 % 70 %

100 % 100 % 100 % 100 %

The maximum permissible errors are at present fixed as follows:

Table 21: Maximum permissible errors for turbine gas meters

Max.perm. errors on verification acc. to 71/318/EEC acc. to EN 122 61

Flowrate range Permissible measurement error Flowrate range Permissible measurement error

Qmin ≤ Q< 2·Qmax ± 2.0 % Qmin ≤ Q < Qt ± 2.0 %

2·Qmax ≤ Q ≤ Qmax ± 1.0 % Qt ≤ Q ≤ Qmax ± 1.0 %

63

According to the EEC Directive, the measurement errors must not all exceed half the above-mentioned maximum

permissible errors if they are of the same sign.

Depending on the working range, the transitional flowrates Qt are defined as follows:

Table 22: Transitional flowrates for turbine gas meters

Working range Transitional flowrate Qt

acc.to 71/318; EEC /EN 122 61 1:10 0.20·Qmax

acc.to 71/318; EEC / EN 122 61 1:20 0.20·Qmax

national context, acc.to EO 7; EN 122 61 1:30 0.15·Qmax

national context, acc.to EO 7; EN 122 61 1:50 0.10·Qmax

acc.to EN 122 61 >1:50 0.05·Qmax

6.3.5 Testing of vortex and swirl gas meters

Just as turbine gas meters, vortex and swirl gas meters are to be tested for compliance with the maximum

permissible errors at the following flowrates (statements in % of Qmax):

Table 23: Test flowrates for vortex and swirl gas meters

Working range

1:5 1:10 1:20

5 %

10 % 10 %

20 % 25 % 25 %

40 % 40 % 40 %

70 % 70 % 70 %

100 % 100 % 100 %

The following maximum permissible errors on verification are valid:

Table 24: Maximum permissible errors for vortex and swirl gas meters

Flowrate range Perm. measurement error

Qmin ≤Q<2·Qmax ± 2.0 %

2·Qmax ≤ Q ≤ Qmax ± 1.0 %

The measurement errors must not all exceed half the above-mentioned maximum permissible errors if they are of

the same sign.

64

6.3.6 Testing of ultrasonic gas meters

Testing of ultrasonic gas meters with maximum flowrate up to 10 m³/h is carried out in analogy to the testing of

diaphragm gas meters according to section 6.3.2 heeding the following particular features:

� For testing, the ultrasonic gas meters are to be switched to the test mode in order to ensure the necessary higher

scanning rate and resolution (digits behind decimal sign).

� In the external inspection, the software version, its checksum and the condition of the battery are also to be

checked.

� To obtain reliable measurement results, test volumes according to Table 8 are to be used. For smaller test

volumes it is to be proved that the interface of the test rig is compatible with that of the ultrasonic gas meter and

that the uncertainty of the pulse detection does not exceed 0.2 %. The permitted minimum test volume must be

stated in the operating license for the test rigs.

For larger ultrasonic gas meters, the test flowrates are fixed as a function of the working range according to the

following table (statements in % of Qmax):

Table 25: Test flowrates for ultrasonic gas meters with Qmax > 10 m³/h

Working range

1:10 1:20 1:30 1:50

2%

3,5%

5% 5% 5%

10% 10% 10%

25% 25% 25% 25%

40% 40% 40% 40%

70% 70% 70% 70%

100% 100% 100% 100%

The following maximum permissible errors on verification are applicable:

Table 26: Maximum permissible errors on verification for ultrasonic gas meters with Qmax > 10 m³/h

Flowrate range Perm. measurement error

Qmin ≤Q < Qt ± 2.0

Qt ≤ Q ≤ Qmax ± 1.0

65

The measurement errors must not all exceed half the above-mentioned maximum permissible errors if they are of

the same sign.

The transitional flowrates Qt are fixed in dependence on the working range as follows:

Table 27: Transitional flowrates for ultrasonic gas meters with Qmax > 10 m³/h

Working range Transitional flowrate Qt

1:10 0.20·Qmax

1:20 0.20·Qmax

1:30 0.15·Qmax

>1:50 0.10·Qmax

6.4 Metrological evaluation

6.4.1 Measures prior to testing

The agencies entrusted with the dismantling and transport are to be urged to handle measuring instruments to be

subjected to metrological evaluation with utmost care.

Any unfavourable influences prevailing at the place of use as well as operating conditions which may have an

effect on the measurement result for the meter under test shall be stated in the delivery note. As soon as the meter

is removed from the system, the meter sockets are to be sealed so that they are tight. The meters must not be

excessively stressed during transport. Violation of the marks is not admissible. Between the dismantling and the

tests, the meter shall be stored, if possible, for two weeks at most at test temperature.

6.4.2 Performance of testing

Metrological evaluations must be carried out with particular care. The specific requirements to be met by the

testing staff pursuant to section 60 (3) of the Verification Ordinance for metrological evaluations at test centres

are to be complied with. On request, the applicant shall be permitted to be present in the test rooms when the tests

are carried out.

For the metrological evaluation of verified measuring instruments, prior to or after expiry of the period of validity

of verification, the maximum permissible errors in service and the other requirements applicable at the date of

verification are valid. If necessary, the tests are to be carried out on the basis of regulations which are no longer

valid. For measuring instruments which have not yet been verified, the regulations applicable at the date the

metrological evaluation has been applied for are valid.

The evaluation covers

66

� the external inspection

� the metrological examination

� the internal inspection.

First the external inspection is carried out with the meter not being opened.

For the internal inspection following the metrological examination, the indicating device is opened and its

condition is checked. Destruction of the measuring instrument shall be avoided.

In exceptional cases, the internal inspection may be dispensed with if the applicant has applied for or agreed to

testing without the measuring instrument being opened. This is to ensure the investigation by further experts. In

the case of any pending or threatened legal proceedings in particular, the applicant shall be advised that testing

without the measuring instrument being opened might be possible. Such a limitation of the scope of testing is to

be stated in the test certificate.

Prior to the metrological examination, a preparatory run is to be provided at the flowrate 0.2 Qmax. For

diaphragm gas meters, the quantity of gas supplied shall be of the order of approx. 30 l, and for other meter types

a preparatory run shall be conducted until stable temperature conditions have been reached. Then all test flowrates

are adjusted beginning with Qmin in ascending order according to the testing instructions to be applied.

6.4.3 Result of metrological evaluation and test certificate

To the evaluation of the results of the metrological examination the maximum permissible errors in service

according to the Verification Ordinance - General Provisions - are applicable. For gas volume meters they are

twice the maximum permissible errors on verification. The one-sidedness of measurement errors is of no

significance.

The results of the metrological evaluation are to be recorded. On this basis, the decisions stated in the Verification

Instruction - General Provisions - for the further handling and use of the measuring instrument are to be taken.

The result of a metrological evaluation is to be laid down in a test certificate (see format in Annex 4.3). The

content of the indicating device read off prior to the test as well as the associated unit are to be entered into the

test certificate.

6.4.4 Particular regulations for limited test volume

Partial test without indicating device

If the type of the test facility available does not allow the test volumes necessary for testing with indicating device

to be reached and the applicant has agreed to the meter being opened, the metrological evaluation of diaphragm

gas meters with a maximum flowrate of 10 m³/h may in part be carried out without indicating device.

67

The test is to be performed in the following steps a) to e):

a) If in the preliminary run after mounting of the gas meter into the test facility it turns out that the indicating

device

� operates, the test is continued with b)

� does not operate, the test is continued with c).

b) Testing of the meter at 0.2 Qmax with indicating device (test volume 40 times the test volume of the meter or

at least 80 l, reading when indicating device stands still)

The result may be the following:

� the maximum permissible error in service is complied with

� the maximum permissible error in service is exceeded by more than 0.5 %, thus the meter is defective

� the maximum permissible error is exceeded by up to 0.5 %, thus the test must be repeated. If the mean value

for the two tests does not comply with the maximum permissible error in service, the meter is considered

defective.

c) Removal of indicating device cap and indicating device, testing of indicating device.

If the meter has turned out to be defective according to b), the test is to be terminated.

d) Mounting of pulse generator, testing of meter with pulse generator (flying start-stop) allowing for the built-in

pair of adjustment wheels at the flowrates Qmin, 0.2 Qmax and Qmax. The test volume adjusted must be in

compliance with the approval for the test rig.

e) Classification of the meter including all four test points and the comparison between the results obtained with

and without indicating device at the flowrate 0.2 Qmax as follows:

� The maximum permissible error in service is exceeded in none of the four test points and the difference

between the tests with and without indicating device at 0.2 Qmax is not greater than 0.5 %. Thus the meter is in

order.

� The maximum permissible error in service is exceeded in none of the four test points and the difference

between the tests with and without indicating device at 0.2 Qmax is greater than 0.5 %. Thus the meter is in order;

the test certificate must refer to potential effects of the indicating device.

� The maximum permissible error in service is exceeded in one or several of the four test points. Thus the meter

is not in order.

6.4.5 Diaphragm gas meters with mechanical temperature conversion

68

In the metrological evaluation of diaphragm gas meters with mechanical temperature conversion, the meters are

first to be tested at test room temperature at the flowrates Qmin, 0.2 Qmax and Qmax. Prior to this test, a

preparatory run at approx. 0.2 Qmax with approx. 30 Vz is to be provided.

If the measurement results are outside the limited maximum permissible errors in service but lie within the

maximum permissible errors in service, the applicant can additionally require testing at tmin and tmax.

Table 28: Limited maximum permissible errors in service for diaphragm gas meters with mechanical temperature

conversion

Test temperature Flowrate

Qmin 0.2 Qmax Qmax

Room temperature 6 % 4 % 4 %

Table 29: Maximum permissible errors in service for diaphragm gas meters with mechanical temperature

conversion

Test temperature Flowrate

Qmin 0.2 Qmax Qmax

Room temperature 7 % 5 % 5 %

tmin ± 2 °C

tmax ± 2 °C - 6 % -

6.5 Testing of volume standards

Testing of sonic nozzles as working standards is carried out as described in the PTB Testing Instructions, volume

25 “Measuring Instruments for Gas - Test Rigs with Sonic Nozzles."

For the testing of standard drum-type gas meters, the special features referred to in Annex 5 are to be allowed for.

6.5.1 General

In Germany, the realization of the unit of volume takes place in two traceability chains, separate for air in the

low-pressure range (up to 4 bar) and natural gas under high pressure (more than 4 bar).

The primary and secondary standards for the unit of volume of atmospheric air from which all measurements for

this field are derived are kept at the PTB.

Testing of volume standards is carried out with the aid of volume measuring facilities of higher accuracy

(reference standards of the PTB, standards of the next higher order of the verification supervising authorities).

69

Standard devices can be tested as working standard devices and as standards of the next higher order. The

working standards for low pressure are tested either by the PTB or by the verification authorities which have

suitable testing means or test rigs at their disposal. The testing of the standards of the next higher order is the task

of the PTB.

The testing of working standards can take place not only at the PTB or at the verification authorities but also with

portable standards at the place of use (transfer standards).

The measurement uncertainty achieved in the testing of the working standards as well as in their use must be

separately determined on every test rig in compliance with Annex 3.

To realize a load for the testing of working standards, which cannot be achieved with a single standard of the next

higher order, two or several standards of the next higher order may be arranged in parallel.

If it is intended to use a working standard with a detachable test element, this must have been mounted for testing.

If it is intended to use working standards with pulse generators or pulse scanning, these must have been mounted

and are to be included in the testing.

6.5.2 Connection of supplementary and auxiliary devices

Supplementary devices must be so designed and mounted that they do not affect the mode of action and the

reading of the working standards.

Working standards can be provided with non-interacting double pulse generators which must be fail-safe as

regards their function. If they are of single-channel design only, it must be possible to periodically check them in

a simple way using an additional low-frequency pulse generator.

The pulse value is to be selected as a function of the minimum test volume so that a resolution equal to or better

than 0.1 % is reached.

Other integrated auxiliary measuring devices must meet the requirements in section 4.3.

6.5.3 Particular requirements for test rooms and testing means

Test rooms must meet the requirements in section 5. The temperature must not, however, vary by more than 0.5 K

per hour.

For the testing of working standards in situ, the portable standard of the next higher order must have a

measurement uncertainty of 0.15 % at most.

70

For volume determination, volume standards of higher order are suitable depending on the nominal flowrate of

the working standards.

Piston measuring devices and bell provers must be provided with precise path difference measuring devices. Gas

meters with Qmax > 40 m³/h must be equipped with NF and/or HF pulse generators. Drum-type gas meters need

devices for the detection of complete drum revolutions. When rotary piston gas meters are used, care must be

taken to ensure appropriate dampening.

The test medium must be clean and free from oil (except for measuring systems with oval gear meters and drum-

type gas meters) and dust. If air at almost atmospheric conditions is used as test medium, the relative air humidity

must be such that no condensation occurs.

When using the standards of higher order, the information contained in the test certificates (oiling, occurrence of

vibrations, filling with sealing liquid) is to be noted.

Upstream of inferential gas meters used as working standard, straight inlet pipes with the same inside diameter as

at the gas meter inlet are to be provided in the test rig. If these mounting instructions are deviated from for the test

rig for reasons of space and the working standard is tested on an external test rig, the standard is to be tested with

the appurtenant inlet pipe.

Furthermore, testing means and testing aids are required as are also necessary for the application of the volume

standards in test rigs and described in section 4.3.

6.5.4 Preparation of test

The temperature of the working standards (of the test rig, if applicable) is to be appropriately adjusted to that of

the standard of higher order. This is generally ensured if the standards are brought to the test room the day before

the test.

For the stabilization of their measurement properties, new or refurbished (new bearings, new gears) drum-type,

turbine, rotary piston and rotary vane gas meters which are intended to be used as working standards require gas

being supplied for at least 50 hours at Qmax. All other working standards require gas supply for at least five

hours at Qmax.

During the period of validity of the test, it is not permitted in turbine gas meters to use the lubricator.

The tightness of the connection between the standard of next higher order or the test rig, respectively, and the

working standard or the test rig (external tightness) - and possibly also the tightness of parallel lines with respect

to one another (internal tightness) is to be ensured as described in section 6.2.5.

6.5.5 Scope of testing and test sequence

71

The measurement errors of working standard meters must be determined at at least 12 flowrates, usually in

decreasing order. At the same time repeat measurements (also at increasing flowrate) are to be carried out to

determine the reproducibility. Both below and above the flowrate range, one test point is to be provided. On the

basis of the results, the permissible flowrate range is fixed (as a rule, >1:10).

When bell provers and piston/cylinder systems are tested, the measurement errors of which do not depend on the

flowrate, tests are carried out in the possible start and stop positions with different volumes at arbitrary flowrates.

For the verification of the reproducibility, at least three tests and additional repeat measurements are necessary for

each section. To confirm independence of the flowrate, the flowrates are varied and, if possible, also adjusted at

the boundaries for the intended use of the working standards. In particular cases, for particularly high flowrates in

particular, testing can also be carried out by step-by-step measurements (parallel arrangement of working

standards). In these cases, the PTB is to be informed, which will decide whether a PTB representative will take

part in these measurements.

In accordance with the deviations permitted in the test certificates, the pressure loss of the standards of the next

higher order must comply with the theoretical values which are to be taken from the test certificates for the load

in question.

The differential pressure between working standard and standard or standards of higher order, respectively, must

be measured or determined with a measurement uncertainty of at least < 0.3 mbar.

The pressure loss is measured by connecting the pressure tappings at the inlet and outlet of each meter back to

back; its value is to be rounded to 0.05 mbar and entered into the test report; if major variations (resonant range)

occur, the boundary values are to be entered as well.

6.5.6 Measurement errors of volume standards

The measurement errors are calculated by equations (26) and (27). They relate to the measurements with air with

a reference density of 1.2 kg/m³. Under normal atmospheric conditions it can be assumed that the air in the test

room meets these requirements.

In the initial testing of a standard meter the adjustment shall be carried out with a mean WME of � 0.2 %.

To attain the required measurement uncertainty, it would be advisable to meet the following requirements for the

error curve of the working standards:

� curve of measurement errors of the shape typical of the type

� span of measurement errors max. 2 %

� reproducibility of measuring points < 0.1 %

72

� for rotary piston, rotary vane and turbine gas meters:

- slope of error curve in the range

Q � 0.2 Qmax: �f / �Qrel � 5 (�f in %)

- slope of error curve in the range

Q ≤ 0.2 Qmax: �f / �Qrel � 3 (�f in %)

If the measurement errors ascertained in the testing of a working standard in the overlap region of two standards

of the next higher order differ from one another by more than 0.2 %, the cause is to be found and eliminated. In

the case of errors up to 0.2 %, the measurement errors are to be averaged.

6.5.7 Identification of volume standards

Volume standards which are used for the testing of gas meters must have had a calibration still valid. The

individual measurement errors found are documented in the test certificate (for an example, see Annex 4.4) and

are binding for the operation of the standards. Test certificates and volume standards must therefore be clearly

identified so that they can be assigned and are readable without technical aids.

For the identification of each volume standard, at least the following information must be available:

� manufacturer's identification

� year of manufacture

� serial number

� type of standard device

� meter size, if appropriate

� nominal value of test volume, if appropriate

� nominal diameter of connecting flanges, if any

� maximum working gauge pressure

� direction of flow

These statements must be directly visible, well readable and permanently applied for normal operating conditions.

For turbine gas meters the following information is to be given on a particular plate: "Use of the lubricator is

inadmissible during the period of validity of the test."

Volume standards whose case or measuring device is not resistant to or protected from the exposure to gases must

be provided with the information "For air only" on a particular plate.

6.5.8 Marking

The stamping locations are to be so selected that any dismantling of the marked part leads to the marks being

destroyed.

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(Test) marks are to be applied, among other things, to

� all plates carrying a mandatory marking

� parts of the case which are not otherwise protected against manipulations by which the accuracy of

measurement may be affected

� connecting points between the volume standard and the auxiliary and supplementary equipment connected for

testing.

In addition, the volume standards are to be marked after the test with the year of the test (mark consisting of test

mark and year).

6.5.9 Test certificate and period of validity of test

A test certificate is to be made out stating the results. It must contain the following information:

� agency performing the test

� type and class of volume standards used for testing

� place where test is carried out

� whether the test is carried out on the test rig or on an external test rig of the agency performing the test

� applicant

� type of volume standard tested

� manufacturer's identification

� year of manufacture

� serial number

� meter size, if appropriate

� nominal value of test volume, if appropriate

� nominal diameter of connecting flanges, if any

� type of oil filled, if any

� for turbine gas meters the information: "Use of the lubricator is inadmissible during the period of validity of the

test"

� maximum working gauge pressure

� intended use (working standard)

� values specified for Qmin and Qmax

� measurement errors determined for the individual flowrate values

� measurement uncertainty attained in the test and, where appropriate, for application

� period of validity or time interval until the test is repeated

� where appropriate, equation(s) for the calculation of the measurement errors versus the flowrate

According to the Administrative Regulation GM-AR, the period of validity of the test of the working standards is

fixed as in Table 30.

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In well-founded cases (e.g. another manufacturer) and in agreement with the PTB, it is also possible to specify

shorter periods of validity. The initial testing of novel working standards is carried out by the PTB.

A repetition of the test is necessary after each repair and if in comparison measurements using portable standards,

deviations of more than 0.3 % are determined or when the validity of the test certificate has expired.

Repeat measurements are advisable if the deviations in the comparison measurements exceed 0.2 %.

Table 30: Period of validity of the test of working standards

Kind of volume standard Meter size Period of validity in years

Bell prover (gauging apparatus) 5

Drum-type gas meter 5

Rotary piston gas meter up to G 1000

from G 1600 5

8

Rotary-vane gas meter up to G 250

from G 400 3

5

Turbine gas meter up to G 1000

from G 1600 3

5

Piston-cylinder measuring system 5

Measuring system with oval gear meter up to G 6 5

6.5.10 Comparison measurements on test rigs for gas meters with Qmax > 40 m³/h

To verify the durability of the working standards, comparison measurements are to be carried out using suitable

reference meters. The desired measurement uncertainties of these reference meters, including the drift and

including the uncertainty in volume conversion due to measurement uncertainties in pressure and temperature

measurement, shall be smaller than or equal to 0.3 %.

For reference meters no official test certificates are required; they must, however, be of an approved type.

Internal comparisons

When a test is carried out, exact comparisons of the working standards are to be made in the overlap regions (> 10

%) at least monthly. If standard meters of the same size are available, these are to be indirectly compared with one

another at least once quarterly testing a meter under test with them at identical flowrates.

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The results of these comparison measurements are to be documented. In the case of deviations exceeding 0.3 %,

investigations must be carried out to identify and eliminate their causes.

External comparisons

At least yearly external comparison measurements shall be carried out with the supervising verification authority

or other test facilities. These measurements need not cover the entire flowrate range. After three years at the

latest, the entire range of flowrates of the test rig shall be checked.

6.6 Acceptance and monitoring of test facilities

6.6.1 Preparation for acceptance

For the acceptance by the supervising verification authority, the test facility is prepared ready for operation. It

must be ensured that the auxiliary measuring devices used meet the requirements defined in section 4.3. The test

rig documentation (description of hardware and software, calculations, test rig manual and, where appropriate,

test certificates) is to be kept ready for inspection. It must, if required, be made available to the supervising

verification authority before the date of acceptance.

Acceptance

The acceptance is carried out by the appropriate authority at the test centre at the place where the test facility is

used. Within the scope of the acceptance, the documentations and the calculations, specifications and certificates

in particular are inspected.

System identifications (such as nameplate, sensor inscriptions) are to be checked.

The volume standards are checked with respect to identification, material and condition. The design and

construction of the test facility is to be investigated for danger of bypass formation. For volume standards without

sealing liquid (e.g. rotary piston gas meters), double sealing must be provided. Furthermore, it must be proved

that all flowrates necessary for official tests can be realized within the specified bounds of the nominal flowrate.

This applies both to the use of individual standards and for combinations of standards. The overlap of the working

ranges of the standards is to be verified. In the case of impairments of the mode of action of the volume standards

by existing supplementary and auxiliary measuring devices, the condition and the mounting of the latter into the

test facility are to be checked and, if need be, remedied.

Unless the auxiliary measuring devices according to section 4.3 or the sensors, respectively, have already been

checked with the signal processing of the test rig, this must be done within the scope of acceptance. If necessary,

the overload stability of difference pressure sensors is to be proved.

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The facility is to be tested with respect to the function and for external and internal tightness (with pipe prover).

Inlet and outlet pipes for the volume standards and/or meters under test are to be tested, among other things, for

their length, their inside diameter and the radius on the inner edge of the flange. The heat given off by the blower

must not lead to any undesired heating of the test air in the test rig. The sensitivity of the flowrate control valves

is also to be tested.

If the determination of the test volume entails a time measurement, either the internal quartz frequency used or,

still better, the time measurement is to be checked over the entire measurement chain from the pulse detection at

the test assembly to the evaluation. For this purpose, in the place of the meter under test, a pulse generator radio

controlled by DCF77 or indirectly tested can be used on any test assembly, and its signals which are output by the

measurement software can be measured.

The software is to be verified with respect to the test sequences, the boundary value inputs, the measurement

uncertainty calculations, logging, data security and access authorization. If this has already been done on test

facilities of identical design, this inspection can be referred to. The prerequisites for the recognition of identical

software is the identification of the version. It is to be made sure that all measurement data necessary for

calculating the measurement error can be recalled and that logging is carried out according to the requirements in

section 4.4.3.

To check the correctness of measurement and the repeatability of the test facility, repeat measurements are to be

carried out. The meters under test used for this purpose should be of very high measuring stability and their

measurement properties should be sufficiently well known. At least ten repeat measurements with the necessary

test steps and test parameters are to be carried out.

Subsequently, the uncertainty in the determination of the advance of the indicating device at the adjusted test

volumes is to be determined on the meter types usually tested at the owner's in at least ten repeated tests, and, if

necessary, the test volumes are to be adjusted. These tests must cover the scanning devices to be used for volume

determination.

From the repeated tests the double standard deviation is determined. The uncertainty in volume determination

corresponding to this value must not exceed one fifth of the relevant maximum permissible error on verification.

In the case of series test rigs it is to be checked whether the meters interact in the series test. For this purpose,

measurements with the meters used for the determination of the uncertainty in volume determination are to be

carried out. The individual meters are tested in the completely fitted test series at different test benches. For

domestic meters the mean values for the measurement errors must not differ by more than 0.4 % from the mean

values from the repeated tests at the test points 0.2 Qmax and Qmax.

For single test rigs the acceptance must encompass internal and external comparison measurements according to

section 6.5.10.

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The test sequences and test volumes necessary for the meter types to be tested as well as boundary values which

might be required (e.g. permissible leakage rate) are to be definitely defined. Furthermore, the time sequence for

checking the auxiliary measuring devices is fixed upon acceptance.

When rotary piston meters with four chamber volumes (standard rotary piston meters) are used as standards or

meters under test, the following is to be additionally heeded:

As a rule, acoustic oscillations and any ensuing resonances are accompanied by an increase in the pressure loss of

the volume meters at the respective flowrate. By exact measurement and recording of the pressure loss values

versus the flowrate, these can generally be detected and reduced.

a) Tests with common rotary piston gas meters

After initial testing, the curve of the measurement errors and of the pressure loss of common rotary piston meters

which shall be used as standards is also to be determined by comparison with a transfer standard (if possible, no

common rotary piston meter) with the meter mounted in the test rig. For this purpose, measurements need to be

carried out over the whole measurement range in steps of 0.05 Qmax. Pressure loss deviations > 0.15 mbar from

the pressure loss curve determined suggest resonant phenomena which in part are linked with considerable jumps

of the measurement errors (> 0.25 %), as a rule towards minus. Such disturbing influences are to be reduced by

dampening measures.

b) Tests with common rotary piston gas meters as meter under test

After the test rig according to a) is practically free from resonant influences from standard common rotary piston

gas meters, each size of common rotary piston gas meter under test must be exemplarily tested for disturbing

influences. Also, pressure loss increases and associated jumps of the measurement errors are determined in

flowrate steps according to a).

If these jumps are greater than 0.15 mbar or 0.25 %, dampening measures must be taken or those already taken

must be improved so that at least these boundary values are complied with.

If the sound reduction measures are not sufficient or not successful, the area around the point of resonance is

considered unsuitable for the testing of common rotary piston gas meters. The usability of the test rig is to be

limited accordingly unless it is possible to achieve usable measurement results by varying the flowrate around the

test point.

Alternatively, standard rotary piston meters other than the common ones should be used. If the buffer volume is

sufficient, standard turbine gas meters may be used as well. It is, however, to be investigated within the scope of

the above-mentioned tests whether standard turbine gas meters will furnish reproducible results for meters under

test whose error curves are well known. If this is so, one may assume for the meter sizes tested that the pulsations

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are appropriately reduced. If - when common standard rotary piston gas meters are used - there are points of

resonance which cannot be eliminated, the selective use of standard turbine gas meters may also be investigated.

6.6.3 Monitoring

The owner has to ensure surveillance of all auxiliary measuring devices at regular intervals pursuant to the

specifications laid down upon acceptance.

7 Marking, identification and certification

7.1 Marking

As a rule, the principal mark (consisting of the verification mark and the year affixed side by side) is applied to

the dataplate of the gas meter or in its immediate vicinity after the metrological examination has been completed.

The principal mark may also consist of a seal whose front side shows the verification mark and to the rear of

which the year mark is applied.

If necessary, the marks can also be applied to two separate seals.

If the verification is carried out in steps, including a preliminary inspection of the components (e.g. the measuring

device of a vortex gas meter) or in the case of meters which shall in addition be tested under high pressure, only a

protective mark (verification mark without year mark) is applied to the principal stamping location.

Gas meter components such as measuring device, indicating device, pulse generator, etc. are protected with

protective marks from being separated from the measuring device and against interventions.

Protective marks applied to prevent components from being detached can be dispensed with if it is ensured by the

design of the gas meter that tampering is permanently visible or leads to uselessness of the measuring device.

Plates with inscriptions or designations which are not permanently affixed to the gas meter or are not destroyed

when detached from the gas meter are also to be protected with official marks.

In all other respects, the marking of gas meters is to be made according to the specifications in the relevant type

approval.

7.2 Identification

If the gas meter does not bear inscriptions which are prescribed by No. 4.1 of Chapter I of the EEC Directive for

gas volume meters or by the relevant type approval, or if these inscriptions are no longer readable or are damaged,

they are to be applied prior to completion of the verification.

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7.3 Certification

The verification of gas meters at atmospheric pressure can be certified on request by issuing a verification

certificate with or without a list of the measurement errors according to the format in Annex 4.2.

The results of metrological examinations by foreign verification authorities for which test certificates are

available can be used for issuing national certificates without the measurements being repeated.

For the preliminary inspection of components of an electronic gas meter (e.g. the measuring device of a vortex

gas meter), a preliminary inspection certificate as shown in Annex 4.1 is then to be made out if the components

are not assembled and verified immediately after the individual test.

A preliminary inspection certificate is also to be made out if it is intended to subject the meter to an additional

high-pressure test. This preliminary inspection certificate will subsequently be kept by the test centre carrying out

the high-pressure test and making out a verification certificate allowing for changes in the adjustment, if any.

As to the result of metrological evaluations, a test certificate is to be made out with or without stating the

measurement errors (depending on the test result) (see format in Annex 4.3).

8 Transitional provisions

The provisions contained in these Instructions are applicable from the date they have been put into force by the

appropriate authorities of the federal states.

Should the new requirements make changes of a test facility necessary, any test facility set up and put into service

before December 31, 2001, in compliance with the PTB Testing Instructions, Volume 4, can nevertheless be

further operated without alterations until December 31, 2004.

The relief these Instructions offer compared to Volume 4 of the PTB Testing Instructions can be profited from for

existing test facilities only if the technical and organizational prerequisites are fulfilled and the test facilities have

been accepted in this respect by the appropriate authority.

Annex 1

Designs of gas meters and their measurement properties

In the following, an overview of the gas volume meter types at present available will be given.

For gas volume meters, a distinction between displacement gas meters and inferential gas meters can be made. In

displacement gas meters, volume measurement takes place directly by periodically filling and emptying one or

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several measuring chambers: They are therefore also referred to as volumetric gas meters. The displacement gas

meters cover meters with:

� sealing liquid (drum-type gas meters)

� deformable walls (diaphragm gas meters) and

� rotating walls (rotary piston gas meters, rotary vane gas meters)

In contrast, inferential gas meters are gas meters in which the volume is measured indirectly using some flow-

physical action or impact, the effects of the flowing gas being detected with the aid of specifically adapted

measuring devices or sensor systems. Among the inferential gas meters are:

� differential pressure gas meters

� turbine gas meters

� vortex gas meters

� ultrasonic gas meters

� Coriolis-type gas meters.

Differential pressure and Coriolis-type gas meters will in the following not be dealt with as they are of no interest

for these Testing Instructions.

Drum-type gas meters, rotary vane gas meters

Drum-type gas meters and rotary vane gas meters today are of practical importance as standard measuring devices

only. But for this application, too, they are increasingly replaced with sonic nozzles and other gas volume meters.

Diaphragm gas meters

Diaphragm gas meters are volumetric meters with four measuring chambers every two of which form a unit

separated by a deformable wall, the diaphragm. The diaphragms of the two units are connected with each other

via levers and rods and drive the valves and the indicating device via a crank assembly (Figures A1-1 and A1-2).

Figure A1-1: Schematic sketch of a diaphragm gas meter

During the measuring operation, the gas is supplied from the inlet socket through an opened valve into a

measuring chamber and fills the latter. Hereby the gas is conveyed from the opposite measuring chamber to the

outlet socket. After the bellow has reached its final position during filling, the rods switch the valves - which are

designed as slides - so that the measuring chamber which has just been emptied is filled and the gas from the

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filled measuring chamber is supplied to the outlet socket. The other unit operates in the same way but with a

"phase shift." As a result, the forces required for switching over the slides at the end of the filling / emptying

operation can be supplied by the other unit. The test volume is obtained from the sum of the cubic contents

displaced by the two bellows during one measuring cycle.

Figure A1-2: Sectional view of a diaphragm gas meter

In the course of the development of diaphragm gas meters, the material for the diaphragms has been changed

from leather to plastics and on the other hand, the diaphragm gas meter with fixed stop has been replaced by the

diaphragm gas meter without fixed stop. Fixed stop means that the final position of the deformable walls is

defined by stops in the measurement units. Owing to the use of gummed plastics diaphragms, the long-time

behaviour could be improved compared to the meters with leather diaphragms.

If diaphragm gas meters are used in locations with great temperature variations, temperature-converting designs

can be used. These meters have temperature-sensitive elements, e.g. bi-metal levers adjusting the measuring

chamber volume as a function of temperature. As this mechanism has additional effects on the measuring

behaviour, increased maximum permissible errors on verification were specified for temperature-converting

diaphragm gas meters.

Leakages in the sliding faces of the valves and leaky bellows are the main causes for measurement errors of

diaphragm gas meters. The leakage due to porous bellows or caused by the sliding faces of the valves leads to slip

which has its greatest effects in the lower part of the flowrate range (reduced indication).

Diaphragm gas meters which excel by a particularly large working range are used in great numbers in private

households.

Like other gas meters, diaphragm gas meters can in part be equipped with very different systems for transmitting

counter contents (usually magnetic pulse generators) to conversion or supplementary devices. For use in official

and commercial transactions, these must comply with the requirements of the Verification Ordinance.

Rotary piston gas meters

Rotary piston meters are volumetric meters in which two rotating pistons roll off against each other in a case. The

section of the pistons vertical to the rotation axis is such that the clearances between the pistons themselves and

the case are small, irrespective of the position (Figure A1-3).

Figure A1-3: Sectional view of a rotary piston meter

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The pistons are synchronized by a gearing with a small backlash so that they do not come into contact with each

other when rotating (Figure A1-4). The measured volume is conveyed between the pistons and the case wall. At

each complete revolution of the pistons (measuring cycle), the test volume M per piston is pushed out twice and,

thus, four times on the whole.

Figure A1-4: Construction of a rotary piston meter

To the synchronizing gear the indicating device and the pulse generator are connected. The dimensions of the

clearances can be kept small owing to modern manufacturing methods so that it is possible to achieve very great

flowrate ranges of Qmax/Qmin = 250. On the other hand, the small clearance dimensions result in high sensitivity

to foreign matter particles. To avoid damage to the pistons which frequently are made from light metal, suitable

devices such as filters are therefore to be provided.

The typical error behaviour of the rotary piston gas meter is shown in Figure A1-5. The error curve is determined

by the clearance losses between the rotary pistons as well as between rotary pistons and case and increases

approximately hyperbolically with increasing flowrate.

Figure A1-5: Typical error curve of a rotary piston meter

Due to the clearance losses and the friction of the gears and bearings, a rotary piston meter needs a minimum

flowrate for starting.

In the lower working range, due to the clearance losses, part of the gas can flow through the meter without being

measured. With increasing load, due to the increasing relative velocity with which the walls limiting the

measurement space move past one another, part of the measured gas is conveyed back to the inlet end of the

meter and is measured once again.

The clearance losses and the amount conveyed back are dependent on the clearance widths, on the viscosity of the

gas and on whether the clearance flow is laminar or turbulent.

During gas volume measurement, the gas does not continuously flow through the rotary piston meter. As a result,

pulsations occur which in an unfavourable pipework configuration can lead to oscillating gas columns and thus to

considerable measurement errors. In order to avoid breaks in the measured error curve due to pulsations when

testing meters, the latter are frequently tested with silencers. When using the meters in practice, suitable measures

may have to be taken (e.g. change of the meter size in the case of resonances) to avoid pulsation-related

measurement errors.

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Turbine gas meters

Turbine gas meters consist of a pressure-proof case, a displacement body, the turbine wheel and a gearing which

drives the indicating device (Figures A1-6 and A1-7).

Figure A1-6: Schematic representation of a turbine gas meter

Under the action of the gas flow, the turbine wheel is set into rotation; by optimizing the meter design with

respect to the flow, it was possible to achieve that the rotation frequency is approximately proportional to the

mean velocity of flow. The error curves show a flat shape and a slight pressure dependence.

Mechanical friction losses in the bearings and in the gearing parts as well as boundary layer flow in the annular

nozzle as well as at the turbine wheel, which are a function of the velocity of flow and the viscosity of the gas to

be measured, lead to deviations of the error curve from the flat shape aimed at. For high-pressure applications it is

therefore expedient to test the meters in the entire pressure range used. For the comparison of low-pressure and

high-pressure error curves, it is possible to represent the error curves as a function of the Reynolds number, as

boundary layer effects are subject to the Reynolds similarities.

Turbine gas meters are mainly used for the measurement of large gas quantities in the medium and high-pressure

range. The meters have one or several pulse outputs which furnish high and low-frequency pulses. The high-

frequency pulse generators frequently use the blade ends of the turbine wheels or toothed disks to generate pulses.

By a second pulse generator a phase-shifted pulse signal can be generated. Suitable signal evaluation allows

disturbances to be suppressed and perfect function of the turbine gas meters to be ensured.

While the low-frequency pulses mostly have integer pulse values, the value of high-frequency pulses is a

fractional number which is influenced by the adjustment of the indicating device gearing and determined when

the meters are tested.

Figure A1-7: Sectional view of a turbine gas meter

As all other inferential gas meters, turbine gas meters are sensitive to disturbed upstream flow profiles. In the

Technical Guideline G 13, mounting instructions have therefore been specified which are to be followed when

using the meter. In dependence on the stability of the meters with respect to inlet disturbances which is

investigated in the approval with the aid of defined inlet disturbance configurations (see OIML Recommendation

R 32), it is admissible to specify deviating mounting instructions in the approval.

84

Another problem in the use of turbine gas meters can ensue from the temporal variation of the flowrate. In

intermittent operation, i.e. in the case of periodic changes between gas at rest (no flow) and a high flowrate in

particular, it can be observed that the turbine wheels run on for a much longer time than it takes to start for a

speed proportional to the flowrate. As this effect can lead in unfavourable cases to the maximum permissible

errors in service being considerably exceeded, the Technical Guideline G 13 prescribes that the meters must not

be used in this way, or that additional technical measures are to be taken. These may be mechanical overrun

brakes or overrun recorders which must have been approved.

Vortex gas meters

Vortex gas meters use the effect of the separation of a Kármán vortex street on a body exposed to an upstream

flow. The meter consists of a case of circular section and flanges as well as of an incorporated sharp-edged bluff

body with T-like section. The flow arrives vertical to the front side of this bluff body (crossbar of the T-section)

so that a Kármán vortex street forms downstream of this front side, with vortexes on both sides of the longitudinal

edge (see Figure A1-8). The frequency of the separations of vortexes is proportional to the mean velocity of flow

in the pipe.

For the detection of vortex separation, pressure oscillations in the area of the bluff body can be used. So in one

design, in two borehole / pipework systems appropriately arranged in this flow region, the pressure oscillations

lead to two flowrate fluctuations phase-shifted by 180° being produced.

Figure A1-8: Formation of the Kármán vortex street

The flowrate fluctuations in the two pipework systems are converted by means of thermistors into voltage

fluctuations which are used to generate rectangular pulses. Via two channels the pulses are supplied to an

electronic indicating device provided with an error detection unit (pulse failure). The pulses counted by the

volume indicating device are proportional to the volume having flowed through the meter.

Figure A1-9: Schematic sketch of a vortex gas meter

To limit the influence of upstream disturbances, the meter must be integrated into a meter run of the same inside

diameter. The length of the necessary inlet section with, for example, an overall length of 20 inside pipe diameters

D (with built-in pipework straightener) and the outlet section with, for example, at least 5 D is fixed in the

approval.

Ultrasonic gas meters

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Ultrasonic gas meters are manufactured both for measurements in households and for measurements in pipelines

with a large inside diameter. It is an advantage of ultrasonic gas meters that - as in vortex gas meters - there are no

moving parts subject to mechanical wear. The principle consists in using the influence of flowing gas on sound

propagation. If an acoustic pulse is emitted by transducer A, it reaches transducer B - as a consequence of the

flow velocity um - more rapidly than it would if the flow were at rest (Figure A1-10). If, however, the acoustic

pulses run from B to A, the time delay tba is longer than without flow. By measurement of the time delays tab and

tba, the sound velocity c can be eliminated from the conditional equation for the mean path velocity um so that

the mean velocity of flow along a path follows only from geometrical quantities and the time delay difference of

the acoustic pulses.

(A1-1)

(A1-2)

(A1-3)

Figure A1-10: Principle of an ultrasonic gas meter

If it is made sure - just as for domestic ultrasonic gas meters - that the flow profile always develops in the same

way irrespective of the upstream flow conditions, it will be sufficient to use a single path.

For industrial gas meters with nominal diameters DN 80 and greater, a developed flow profile cannot, however,

be assumed even at a straight inlet length of 10 D. To achieve sufficient "scanning" of the flow, approved

industrial ultrasonic gas meters are equipped with at least three paths. The volume flow Q is determined from the

path velocities um by weighted summation. As the measured delay times also allow the sound velocity to be

calculated, monitoring of the meters can take place by comparison with the sound velocity values which may

have been determined from gas condition measurements.

For domestic use of ultrasonic gas meters, a battery serves for power supply. To achieve an appropriate period of

use for the meters without the battery being changed, the measuring frequency (frequency of emission of acoustic

pulses) is relatively low in normal operation. For testing, domestic ultrasonic gas meters can be switched to a test

mode in which the measuring frequency is increased.

Approved ultrasonic gas meters with several paths in most cases allow the transducers to be changed without

relief of the pipework and without subsequent verification providing the work and the updating of the transducer-

specific data are carried out under the supervision of the verification authority.

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The measured values are transmitted to volume correctors and supplementary devices via pulse or serial interfaces

with manufacturer-specific protocols. Also, compared to testing using the indication, a reduction of the testing

times is possible owing to the serial interface with which domestic ultrasonic gas meters are provided.

Annex 2

Test examples

2.1 Domestic diaphragm gas meters

Five size G 4 diaphragm gas meters of identical type shall be tested metrologically.

For these tests, a series test rig with working standard drum-type gas meters of sizes NB 2 and NB 15 according

to the following sketch are available for operation under suction conditions:

ΔpP1

p1=pamb p2=p1 1-dp p3=p2 2-dp p4=p3 3-dp p5=p4 4-dp

pN=p5 5-dp

ΔpP2 ΔpP3 ΔpP4 ΔpP5pPEin

pN

Prüfling 1

Gebläse Normal

tPEin

tNEin

tPAus

tNAus

Prüfling 2 Prüfling 3 Prüfling 4 Prüfling 5

20,6°C

20,6°C 20,5°C

20,4°C

Figure A2-1: Sketch of diaphragm gas meter arrangement for series testing

For the metrological examination with manual operation, the following sequence is to be followed after the

meters under test have been mounted and a preparatory run has been carried out:

1. Tightness test

Over a testing time of 10 min, a pressure drop of 0.2 mbar is observed.

The volume VE enclosed between the shut-off devices of the test rig is composed as follows:

- the test volume of the standard (NB 15): 50 dm³

- the volume of the meters under test (5·4 dm³): 20 dm³

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- the volume of the connecting pipework: 30 dm³

VE thus amounting in total to 100 dm³

For meters of size G 4 with Qmin = 40 dm³/h, the admissible leakage rate is:

According to equation (31), the actual leakage rate is:

The tightness requirement is thus complied with.

2. Test at Qmax = 6 m³/h

In the test carried out with the standard drum-type gas meter NB 15, the following measured values are recorded:

• volume indication on the standard (default value): VN = 300 dm³

• measurement error of the standard according to test certificate: fN = - 0.15 %

• volume indications on meters under test P1 to P5:

P1 P2 P3 P4 P5

Start of test dm³ 657.4 518.2 422.0 321.3 524.2

End of test dm³ 951.8 816.0 720.2 619.2 821.8

• differential pressures Δp:

ΔpP1 ΔpP2 ΔpP3 ΔpP4 ΔpP5 ΔpN mbar 1.60 1.80 1.50 1.50 1.60 0.15

• temperatures:

at inlet of standard NB 15: 20.6 °C

at outlet of standard NB 15: 20.5 °C

at inlet of series test rig: 20.6 °C

at outlet of series test rig: 20.4 °C

From this the following provisional results are calculated:

dm³/min002.01000min101002.0 == ⋅⋅

mbardm³mbar

LQ

dm³/min002.0003.0 min6040 =⋅= dm³

LzulQ

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• advance of indicating device at meters under test (end - start of test):

VP1 VP2 VP3 VP4 VP5

dm³ 294.4 297.8 298.2 297.9 297.6

• rough measurement errors from fr = ( VP/VN - 1 ) · 100 %:

frP1 frP2 frP3 frP4 frP5

% -1.87 -0.73 -0.60 -0.70 -0.80

• assigned pressures according to sketch of test arrangement:

pP1 pP2 pP3 pP4 pP5 pN

mbar 1000.0 998.4 996.6 995.1 993.6 992.0

• pressure correction according to kp = 0.1 · ( pP - pN) %:

kp1 kp2 kp3 kp4 kp5

% +0.80 +0.64 +0.46 +0.31 +0.16

• assigned temperatures:

tP1 tP2 tP3 tP4 tP5 tN

°C 20.6 20.55 20.5 20.45 20.4 20.5

• temperature corrections according to kt = 0.34 (tN - tP) %:

kt1 kt2 kt3 kt4 kt5

% -0.03 -0.02 0 +0.02 +0.03

The calculation of the measurement results for test point Qmax according to fP = fr + fN + kp + kt yields:

fP1 fP2 fP3 fP4 fP5

% -1.25 -0.26 -0.29 -0.52 -0.76

3. Test at 0.2 Qmax = 1.2 m³/h

89

In the test carried out with the standard drum-type gas meter NB 2 (the smaller standard with higher resolution

and smaller measurement uncertainty is to be preferred), the following measurement results are obtained:

• volume indication on standard (default value): VN = 100 dm³

• measurement error of standard according to test certificate: fN = -0.15 %

• volume indications on meters under test P1 to P5:

P1 P2 P3 P4 P5

Start of test dm³ 951.8 816.0 720.2 619.2 821.8

End of test dm³ 1053.0 916.4 821.0 720.1 923.0

• differential pressures Δp:

ΔpP1 ΔpP2 ΔpP3 ΔpP4 ΔpP5 ΔpN mbar 0.20 0.30 0.20 0.20 0.30 0.20

• temperatures:

at inlet of standard NB 2: 20.7 °C

at outlet of standard NB 2: 20.6 °C

at inlet of series test rig: 20.6 °C

at outlet of series test rig: 20.4 °C

From this the following provisional results are calculated:

• advances of indicating device on meters under test (end - start of test):

VP1 VP2 VP3 VP4 VP5

dm³ 101.2 100.4 100.8 100.9 101.2

• rough measurement errors from fr = ( VP/VN - 1 ) · 100 %:

frP1 frP2 frP3 frP4 frP5

% +1.20 +0.40 +0.80 +0.90 +1.20

• assigned pressures according to sketch of test arrangement:

pP1 pP2 pP3 pP4 pP5 pN

mbar 1000.0 999.8 999.5 999.3 999.1 998.8

90

• pressure correction according to kp = 0.1 · ( pP - pN) %

kp1 kp2 kp3 kp4 kp5

% +0.12 +0.10 +0.07 +0.05 +0.03

• assigned temperatures:

tP1 tP2 tP3 tP4 tP5 tN

°C 20.6 20.55 20.5 20.45 20.4 20.6

• temperature corrections according to kt = 0.34 · (tN - tP) %

kt1 kt2 kt3 kt4 kt5

% 0 +0.02 +0.03 +0.05 +0.07

The calculation of the measurement results for test point Qmax according to fP = fr + fN + kp + kt yields:

fP1 fP2 fP3 fP4 fP5

% +1.17 +0.37 +0.75 +0.85 +1.15

4. Test at Qmin = 0.04 m³/h with standard drum-type gas meter NB 2

In the test which is possible only with the standard drum-type gas meter NB 2, the following measurement values

are obtained:

• volume indication on standard (default value): VN = 30 dm³

• measurement error of standard according to test certificate: fN = + 0.05 %

• volume indications on meters under test P1 to P5:

P1 P2 P3 P4 P5

Start of test dm³ 53.0 916.4 821.0 720.1 923.0

End of test dm³ 82.8 946.0 850.6 749.8 952.7

91

• differential pressures Δp:

ΔpP1 ΔpP2 ΔpP3 ΔpP4 ΔpP5 ΔpN mbar 0.20 0.10 0.15 0.20 0.20 0.03

• temperatures:

at inlet of standard NB 2: 20.7 °C

at outlet of standard NB 2: 20.6 °C

at inlet of series test rig: 20.6 °C

at outlet of series test rig: 20.4 °C

From this the following provisional results are calculated:

• advances of indicating device on meters under test (end - start of test):

VP1 VP2 VP3 VP4 VP5

dm³ 29.8 29.6 29.6 29.7 29.7

• rough measurement errors from fr = ( VP/VN - 1 ) · 100 %:

frP1 frP2 frP3 frP4 frP5

% -0.67 -1.33 -1.33 -1.00 -1.00

• assigned pressures according to sketch of test arrangement:

pP1 pP2 pP3 pP4 pP5 pN

mbar 1000.0 999.8 999.7 999.5 999.3 999.1

• pressure correction according to kp = 0.1 · ( pP - pN) %

kp1 kp2 kp3 kp4 kp5

% +0.09 +0.07 +0.06 +0.04 +0.02

• assigned temperatures:

tP1 tP2 tP3 tP4 tP5 tN

°C 20.6 20.55 20.5 20.45 20.4 20.6

• temperature corrections according to kt = 0.34 · (tN - tP) %

92

kt1 kt2 kt3 kt4 kt5

% 0 +0.02 +0.03 +0.05 +0.07

The calculation of the measurement results for test point Qmax according to fP = fr + fN + kp + kt yields:

fP1 fP2 fP3 fP4 fP5

% -0.53 -1.20 -1.19 -0.86 -0.86

The measurement results are compiled in the test report format in Appendix 1.

2.2 Turbine gas meters

In the following, the tests for a turbine gas meter of size G 4000 in five points will be described. First the tests at

Qnenn = 2600 m³/h with one standard and at Qnenn = 4500 m³/h with two standards arranged in parallel will be dealt

with. The results of the test in the other points at Qnenn = 6500 m³/h, 1625 m³/h, 650 m³/h and 325 m³/h are given

in tabular form. Subsequently, the calculation of the mean weighted measurement error WME is carried out for

this example.

2.2.1 Testing with one standard

Figure A2-2 shows the test rig configuration with the meter under test and the two standards arranged in parallel,

only standard 1 being involved in the measurement.

Figure A2-2: Arrangement sketch for the testing of a turbine gas meter with one standard

The measurement error fP of the meter under test shall be determined at a nominal test flowrate Qnenn = 2600 m³/h.

There are measuring points on meter under test and standard for the detection of the inlet and outlet temperature

pP=1009,38mbar

pa=1010,98mbar

pN1=996,35mbar

impP=17500

impN1=41600

cIW,P=374,182 Imp./m³

=876,960 Imp./m³cIW,N1

Prüfling

Normal 2

Normal 1tPEin=20,50°C

t=65,702sec

tN1Ein=20,45°C

tPAus=20,54°C

tN1Aus=20,49°C

93

tEin and tAus as well as of the reference pressure p. The volume V having passed through the configuration during

the testing time t is calculated with the sum of the detected pulses imp and the relevant associated pulse value cIW.

The following table shows all measurement values acquired:

Inlet temperature of meter under test tPein 20.50 °C Outlet temperature of meter under test tPaus 20.54 °C Reference pressure at meter under test pP 1009.38 mbar Pulses from meter under test ImpP 17500 1 Pulse value of pulses from meter under test cIW,P 374.182 Imp/m³ Inlet temperature at standard 1 tN1Ein 20.45 °C Outlet temperature at standard 1 tN1Aus 20.49 °C Reference pressure at standard 1 pN1 996.35 mbar Pulses from standard 1 ImpN1 41600 1 Pulse value of pulses from standard 1 cIW,N1 876.960 Imp/m³ Measurement error of standard 1 fN1 0.08 % Atmospheric pressure pa 1010.98 mbar Testing time t 65.702 s

The temperature value TP or TN at the meter under test or standard, respectively, which is required for the

calculation of the measurement error fP is obtained from the arithmetic mean of inlet and outlet temperature tEin

and tAus at the meter under test or the standard, converted into kelvin (equation A2-1).

K15.2732

AusEin ++

=tt

T (A2-1)

The volume V or VN contained in the meter under test or the standard is obtained by division of the pulse sum imp

counted during the testing time t by the relevant pulse value cIW (equation A2-2).

IWc

ImpV = (A2-2)

The measurement error fN of the standard at the appropriate flowrate Q is calculated either from a polynomial

given in the test report for the standard or from linear interpolation among the individual measurement errors. The

required load QN of the standard is obtained by division of the volume VN at the standard by the testing time t

(equation A2-3). As the testing time is usually measured in seconds and the flowrate is generally given in m³/h,

the factor 3600 s/h is used here for conversion.

hs3600⋅=

tVQ (A2-3)

According to the following table, the provisional results calculated for use in equation (26) are as follows:

94

Reference temperature at meter under test

TP 293.67 K

Volume indication of meter under test VP 46.77 m³ Load of meter under test QP 2562.59 m³/h Reference temperature at standard 1 TN 293.62 K Volume indication of standard 1 VN 47.44 m³ Load of standard 1 QN 2599.19 m³/h

The measurement error fP of the meter under test is obtained with the aid of equation (26). As equation (A2-4)

shows, a measurement error fP = - 0.06 % is calculated for this example:

%06.0

%1001K67.293mbar35.996m³44.47

K62.293mbar38.1009%100%08.01m³77.46

−=

⋅

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡

−⋅⋅

⋅⋅⎟⎠⎞

⎜⎝⎛ +⋅

=

P

P

f

f (A2-4)

95

2.2.2 Test with two standards used in parallel

In contrast to example 2.2.1, two standards are operated here in parallel to test the meter under test at a nominal

flowrate Qnenn = 4500 m³/h, the total flow

Figure A2-3: Arrangement sketch for the testing of a turbine gas meter with two standards operated in parallel

being assigned to each of the two standards more or less in equal parts. The sketch below shows the configuration

of the test rig assumed for this exemplary calculation.

In the following table all measured values acquired for the calculation of the measurement error fP are given:

Inlet temperature at meter under test tPEin 20.63 °C Outlet temperature at meter under test tPAus 20.67 °C Reference pressure at meter under test pP 1005.78 Mbar Pulses from meter under test ImpP 30700 1 Pulse value of pulses from meter under test

cIW,P 374.182 Imp/m³

Inlet temperature at standard 1 tN1Ein 20.54 °C Outlet temperature at standard 1 tN1Aus 20.58 °C Reference pressure at standard 1 pN1 997.49 Mbar Pulses from standard 1 ImpN1 35861 1 Pulse value of pulses from standard 1 cIW,N1 876.960 Imp/m³ Measurement error of standard 1 fN1 0.09 % Inlet temperature at standard 2 tN2Ein 20.21 °C Outlet temperature at standard 2 tN2Aus 20.25 °C Reference pressure at standard 2 pN2 993.96 Mbar Pulses from standard 2 ImpN2 37930 1 Pulse value of pulses from standard 2 cIW,N2 907.214 Imp/m³ Measurement error of standard 2 fN2 -0.49 % Atmospheric pressure pa 1010.98 Mbar Testing time t 65.640 s

pP=1005,78mbar

pa=1010,98mbar

pN1=997,49mbar

pN2=993,96mbar

impP=30700

impN1=41600

impN2=37930

cIW,P=374,182 Imp./m³

=876,960 Imp./m³cIW,N1

=907,214 Imp./m³cIW,N2

Prüfling

Normal 2

Normal 1tPEin=20,63°C

t=65,640sec

tN1Ein=20,54°C

tN2Ein=20,21°C

tPAus=20,67°C

tN1Aus=20,58°C

tN2Aus=20,25°C

96

As in example 2.2.1, the reference temperature T, the volume V and the load Q at meter under test and standards

are calculated by the equations (A2-1) to (A2-3).

The provisional results following for the calculation of the measurement error fP are given in the table below:

Reference temperature at meter under test TP 293.80 K Volume indication of meter under test VP 82.05 m³ Load at meter under test QP 4499.76 m³/h Reference temperature at standard 1 TN1 293.71 K Volume indication at standard 1 VN1 40.89 m³ Load at standard 1 QN1 2242.73 m³/h Reference temperature at standard 2 TN2 293.38 K Volume indication at standard 2 VN2 41.81 m³ Load at standard 2 QN2 2293.02 m³/h

As two standards are used here, according to equation (27), the volumes VN measured by the standards must be

separately calculated and converted to the thermodynamic conditions at the meter under test. The sum of the

partial volumes VN1 and VN2 then serves to calculate the measurement error fP of the meter under test. For this

example, a measurement error fP = -0.07% is calculated.

%07.0

%1001

K38.293mbar96.993

%100%49.01

m³81.41K71.293

mbar49.997

%100%09.01

m³89.40

K80.293mbar78.1005m³05.82

−=

⋅

⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢

⎣

⎡

−

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

⋅⎟⎠⎞

⎜⎝⎛ −+

+⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

⋅⎟⎠⎞

⎜⎝⎛ +

⋅=

P

P

f

f

(A2-5)

The table below shows a summary of all measurement errors measured:

No. Test flowrate Measurement error

6 100% Qmax Q6=6500 m³/h fP6 = -0.26%

5 70% Qmax Q5=4500 m³/h fP5 = 0.06%

4 40% Qmax Q4=2600 m³/h fP4 = -0.07%

3 25% Qmax Q3=1625 m³/h fP3 = 0.11%

2 10% Qmax Q2=650 m³/h fP2 = 0.40%

1 5% Qmax Q1=325 m³/h fP1 = -0.06%

97

From the measurement errors fP i of the meter under test measured at the individual test flowrates Qi the mean

weighted error WME is calculated for this example by equation (3):

6500325

6500650

65001625

65002600

650045004.0

)06.0(650032540.0

650065011.0

65001625)07.0(

6500260006.0

65004500)26.0(4.0

+++++

−⋅+⋅+⋅+−⋅+⋅+−⋅=WME

WME = - 0.014 %.

The calculation of the measurement results is to be documented in a report according to the format in Appendix 2.

98

Annex 3

Measurement uncertainty

When determining the measurement uncertainty, it is, as a rule, to be ensured that the overall measurement

uncertainty of the test rig does not exceed one third of the maximum permissible error on verification of the meter

under test.

The overall measurement uncertainty is obtained from the uncertainty of the standard devices and the test rig

specific uncertainties. The latter must be determined for the particular test rig.

3.1 Influence quantities

The influence quantities act on

• the standard

• the meter under test

• the measuring procedure (measuring operation).

This subdivision is advantageous both for systematic reasons (separation of the three main influence groups) and

for reasons of straightforward quadratic summation, as these components are frequently uncorrelated with one

another.

Quantities influencing the standard

• uncertainties of the measurement errors according to test certificate (in this value the

following three influence quantities are already contained): - type

- reproducibility

- long-time stability

• kind and reliability of detection of volume advance

• uncertainty of adjustment (in the case of drum-type gas meters)

• temperature regulation (adjustment to test room temperature)

• operating condition (e.g. preparatory run, oil filling for drum-type gas meters, lubricating

system)

Quantities influencing the indicated volume on the meter under test

• measurement principle

• reproducibility

• kind and reliability of detection of volume advance

99

• temperature regulation (adjustment to test room temperature)

• operating condition (e.g. preparatory run, oil filling for drum-type gas meters, lubricating

system)

Influence quantities of the test procedure (test rig)

• temperature sensing (standard and meter under test): - kind and accuracy of the sensors

- uncertainty of the measurement error of the sensors

- inclusion of the measurement error of the sensors (if no correction is made)

- inertia in case of variation of the measurement value

- reaction to upstream flow (flowrate)

- self-heating due to measurement current

- long-time drift

- frequency of measurement value sensing

- signal evaluation electronics (conversion error, drift)

• pressure sensing (standard and meter under test): - kind and accuracy of the sensors

- uncertainty of the measurement error of the sensors

- correction of the measurement error of the sensors

- mobility, hysteresis, long-time drift

- reaction to pressure variations

- frequency of measurement value sensing

- signal evaluation electronics (conversion error, drift)

Further influences

• temperature level and stability during the measurement

• flowrate (accuracy of adjustment or calculation, respectively)

• air pressure (recording, correction, variations)

• density of test medium (air, gas)

• humidity of test air

• interaction between standard and meter under test and/or between the meters under test

when tested in series (resonances, swirl, upstream flow profile etc.)

• kind and accuracy of the evaluation of measurement results (rounding error).

Almost all influence quantities mentioned lead to temperature, pressure and, thus, to indirect or direct volume

variations.

3.2 Inclusion of the influence quantities

100

The essential influence quantities which must in any case be taken into account when determining the

measurement uncertainty are:

Volume at the meter under test and at the standard

The measurement uncertainty is mainly influenced by how and with what accuracy the volume is determined. As

a rule, the measurement uncertainty stated in the test certificate can be assumed for the standard providing the

latter is operated in keeping with the conditions prevailing during its test. This applies in particular if the standard

was checked on the test rig using a transfer standard.

If only the minimum requirements are complied with when defining the test volume, the uncertainty stated in the

following exemplary calculation (0.05 %) for the meter under test is to be included in the calculation. In the case

of reduced test volumes and using particular auxiliary devices such as pulse generators, an appropriate number of

repeat measurements are to be carried out to see whether at least the same uncertainties are attained.

Temperature measurement on the meter under test and on the standard

Here not only the type of temperature sensor (sensitivity, inertia) is decisive but also the design of the temperature

measuring points, the frequency of the measurements and their evaluation. If for practical reasons (e.g. difficulty

of reading) the measurements are not carried out in the measuring points specified but elsewhere, it is to be

ensured when the test rig is accepted that the uncertainties given in Table 2 of section 4.3 are complied with

nevertheless.

Metering pressure at the meter under test and at the standard

The direct measurement of the differential pressure between the tappings for the metering pressure of meter under

test and standard generally yields the smallest measurement uncertainty.

In indirect measurements, e.g. via the pressure loss of meters connected in series, it is to be ensured when the test

rig is accepted that the measurement uncertainty does not exceed the value stated in Table 2 of section 4.3.

3.3 Calculation example

3.3.1 Method A

Application of the computational variation of the influence quantities within the bounds of the estimated

uncertainty and determination of the ensuing variation of the result quantity according to DIN 1319 part 3.

Realization:

Following equations 24 to 27, the following is obtained for the absolute measurement error eP of the meter under

test:

101

(Formel)

and for the relative measurement error:

%1001P ist,

PP ⋅⎟

⎟⎠

⎞⎜⎜⎝

⎛−⋅⋅

=VV

f

Meter under test:

VP = 1000 dm3 = 1000 l

pP = 990 mbar

tP = 20.0 °C or TP = 293.15 K

Standard:

VN = 1011 dm3 = 1011 l

pN= 980 mbar

tN = 20.0 °C or TN = 293.15 K

fN = + 0.10 %

If these values are inserted into the equations, an absolute measurement error of the meter under test of eP = 0.212

l or a relative measurement error fP = 0.02 % is obtained.

In the following calculation example the standard uncertainties of all input quantities are determined from the

statements of the expanded uncertainty in the test certificates of the measuring devices used for measuring the

input quantities. The standard uncertainty of the measurement value for the volume on the standard u(VN)

contains already the standard uncertainty of the measurement error fN according to the test certificate:

Input quantity Expanded uncertainty

U*(k = 2)

Standard uncertainty**

u = U/2

Indication of standard gas meter VN 0.20 % = 2.02 l 0.1 % = 1.01 l

Indication of meter under test VP 0.05 % = 0.50 l 0.025 % = 0.25 l

Pressure measurement on standard PN 0.3 mbar = 0.03 % 0.15 mbar = 0.015 %

Pressure measurement on meter under test pP 0.3 mbar = 0.03 % 0.15 mbar = 0.015 %

Temperature measurement on standard TN 0.2 K = 0.07 % 0.1 K = 0.035 %

Temperature measurement on meter under test TP 0.2 K = 0.07 % 0.1 K = 0.035 %

* according to the test or calibration certificates for the measuring devices used

**Normally, the measurement uncertainty of a measuring device stems from a calibration with a great number of influencing

factors so that a normal distribution of the influencing factors can be assumed for the final result. In the case of measuring

devices for which a uniform distribution with the interval width 2a must be started from (e.g. when maximum permissible

errors are used for the measurement uncertainty), the standard uncertainty is obtained as u = al√3.

102

The expanded uncertainty U is obtained by multiplication of the standard uncertainty u by the factor k=2: The measurement error f of the meter under test is in l: in %

When the values of these influence quantities are varied in the conditional equation for eP by half the absolute

value of the assumed measurement uncertainty in the positive and in the negative direction in accordance with

section 6.3.2 of DIN 1319-3, the values given in the table above are obtained.

The overall measurement result thus reads eP = 0.212 l ± 2.3141 l or

fP = 0.02 % ± 0.23 %.

3.3.2 Method B

Determination of the sensitivity of the system of equations considered, by mathematical differentiation of the

conditional equation with respect to the individual influence quantities for determining the respective

proportionality factor (sensitivity coefficient) with which the uncertainty of the input quantity is converted into

the uncertainty component of the result quantity (approximation method).

Realization:

Gas meter test using a volumetric standard meterDetermination of measurement unceertainty by variation of the input quantities

Variable VP VN pP pN TP TN f N eP Differencel l mbar mbar K K % l upper/ squared

Output data lower (variance)Variation of output data value

Sum of sqQuadrate: Root

)100/1(PPPNNP

PNNfTpTpVVVVe

103

By partial differentiation of the initial equations

with respect to the individual influence quantities, the sensitivity coefficients can be determined as follows:

The overall standard uncertainty u(eP) of the measurement error eP of the meter under test in the case of i

influence quantities xi is

( )( )∑ ⋅⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

=2

2

)( ii

xuxeeu

u(xi) being the standard uncertainty of the particular influence quantity and assuming that the input quantities are

uncorrelated.

Applied to the above equation, this yields:

( ) ( )( ) ( )( ) ( )( ) +⋅⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

+⋅⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

+⋅⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

= 2N

2

N

2P

2

P

2N

2

N

pupePVu

VePVu

VePePu

( )( ) ( )( ) ( )( )2P

2

P

2N

N

2P

2

P

TuTePTu

TePpu

peP

⋅⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

+⋅⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

+⋅⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

+

For the calculation example the same numerical values as above for method A are used:

Meter under test Standard

VP = 1000 dm³ = 1000 l

pP = 990 mbar

tP = 20.0 °C or TP = 293.15 K

VN = 1011 dm³ = 1011 l

pN = 980 mbar

tN = 20.0 °C or TN = 293.15 K

fN = +0.10 %

Input quantity Expanded uncertainty U

(k = 2)

Standard uncertainty u =

U/2

Indication of standard gas meter VN

Indication of meter under test VP

Pressure measurement on standard pN

Pressure measurement on meter under test pP

Temperature measurement on standard TN

Temperature measurement on meter under test TP

0.20 % = 2.02 l

0.05 % = 0.50 l

0.3 mbar = 0.03 %

0.3 mbar = 0.03 %

0.2 K = 0.07 %

0.2 K = 0.07 %

0.1 % = 1.01 l

0.025 % = 0.25 l

0.15 mbar = 0.015 %

0.15 mbar = 0.015 %

0.1 K = 0.035 %

0.1 K = 0.035 %

)100/1(PPP NNP

PNNfTpTpVVVVe +⋅⋅⋅⋅−=−=

104

Using the numerical values stated above, the individual differential quotients are obtained as follows:

( ) 98891.0100/1 NNP

GN

N

−=+⋅⋅⋅

−=∂∂

fTpTp

VeP

1P

=∂∂Ve

( ) dm³/mbar0202.1100/1 NNP

PN

N

−=+⋅⋅⋅

−=∂∂

fTpTV

pe

( )dm³/mbar00989.1

100/1 NN2

G

PNN

P

=+⋅⋅⋅⋅

=∂∂

fTpTpV

pe

( )

dm³/K407093.3100/1 P

2N

2N

PNN

N

=⋅+⋅

⋅⋅=

∂∂

pfTTpV

Te

( ) dm³/K410500.3100/1 NNP

NN

P

−=+⋅⋅⋅

−=∂∂

fTppV

Te

Testing of a gas meter using a volumetric standard gas meter Determination of the measurement uncertainty by differentiation of the initial equation Formel = 0.212 dm³ fN = 0.1 % fP = eP/VIst,P = 0.021 % Input quantity Standard

uncertainty Sensitivity coefficient

Variance

xi u(xi) deP/dxi (deP/dxi)u(xi) (dm³) VN (dm³) 1011.00 1.01 -0.98891 -0.998799 9.98E-01 VP (dm³) 1000.00 0.25 1.0000 0.250000 6.25E-02 pN (mbar) 980.0 0.2 -1.02019 -0.153029 2.34E-02 pP (mbar) 990.0 0.2 1.00989 0.151483 2.29E-02 TN (K) 293.15 0.1 3.40709 0.340709 1.16E-01 TP (K) 293.15 0.1 -3.41050 -0.341050 1.16E-01 Sum ∑: 1.3389 Standard uncertainty u(eP): (dm³) 1.157 Expanded uncertainty U(eP) (k = 2): (dm³) 2.314

Overall measurement result: The measurement error eP in dm³ is: 0.212 ± 2.314 or the relative measurement error fP in % is: 0.02 ± 0.23

105

With U(eP) = 2.314 or U(fP) = 0.23 %, practically the same result as calculated by method A is obtained. The

overall measurement result here reads:

eP = 0.212 dm3 ± 2.314 dm3

fp = 0.02 % ± 0.23 %.

Since - as demonstrated - the two methods A and B yield the same result, method A will in most cases be

employed in practice using a spreadsheet program so as to avoid partial differentiation which is necessary for

method B and - in the case of complicated equations - often irksome.

106

Annex 4

Recommendations for reducing resonant vibrations

To dampen resonant vibrations in test rigs in which standard rotary piston gas meters are used as standards or

meters under test, it is always possible to choose among a great number of possibilities.

As silencers filters incorporated in the meter run, large-volume risers, hoses, throttles, diverters and pipe sections

with a wavy internal face can be used. A well-targeted attenuation of disturbing resonances can be achieved, for

example, using noise absorption silencers or damping cups. The use of throttle-type silencers cannot be

recommended as they produce little effect and show a high resistance to flow.

Sound attenuation using absorption silencers

The absorption silencer consists of an element whose through channel or tube is lined with sound-absorbing

materials. By friction losses the acoustic energy is transformed into heat. The effect is dependent on the length of

the absorption range, the thickness of the absorbing material, the circumference and the cross section of the

passage. The sound attenuation increases with the ratio of the length, multiplied by the circumference, to the cross

sectional area taking the occurring wavelengths into account.

Figure A4-1 shows a schematic sketch of an absorption silencer.

For the application in test rigs for rotary piston gas meters, it is necessary to know the rotational frequency of the

rotary piston gas meters to be tested and of those to be used as standard, as well as of the blowers used.

107

Figure A4-1: Schematic sketch of an absorption silencer

The set-up of a test facility with rotary piston meters as meter to be tested and as standard device using absorption

silencers is shown in Figure A4-2 in a simplified form.

%07.0

%1001

K38.293mbar96.993

%100%49.01

m³81.41K71.293

mbar49.997

%100%09.01

m³89.40

K80.293mbar78.1005m³05.82

−=

⋅

⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢

⎣

⎡

−

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

⋅⎟⎠⎞

⎜⎝⎛ −

++

⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

⋅⎟⎠⎞

⎜⎝⎛ +

⋅=

P

P

f

f

Figure A4-2: Schematic representation of a test facility with absorption silencers

In the place of the silencer at the inlet of the meter under test, it is also possible to provide a low-reflection closure

or an open inlet into the test facility without inlet pipe providing the metrological influence of sonic vibrations is

sufficiently feeble and the test facility is operated under suction conditions. The same applies in analogy to the

last silencer of the test facility if the latter is operated under pressure conditions.

It is the advantage of absorption silencers that they are very effective. Also, their use according to the figure

above can serve to reduce the noise in the test room so that additional noise protection needs to be provided for

the operating staff only in exceptional cases. Disadvantages are the high costs of planning and construction and

the fact that their application is limited to particular frequency ranges.

Sound attenuation using damping cups

Attenuation of sonic vibrations can also be achieved by the use of damping cups to be arranged, if possible,

directly upstream and, if need be, downstream of the meter.

The cup shall be of cylindrical form, the connecting sockets of the meters being arranged as close to one another

as possible. The size is to be selected such that its volume corresponds to a multiple of the test volume of the

meter. The effectiveness can be enhanced by increasing the volume and, for example, by the use of plates

arranged parallel to the front faces, thus subdividing the cup into spaces of more or less identical size and

SchallschluckstoffDämmaterial

schalldurchlässige Abdeckung

MantelrohrStrömungskanal/Rohr

108

diverting the volume flow several times. Attenuation can also be achieved by carrying the test air through

perforated plates and (perforated) hoses. In addition, the cup walls are lined with sound absorbing material (e.g.

mineral wool, foamed plastic).

Figure A4-3 shows the schematic set-up of a test facility with damping cup.

Prüfling NormalDämpfungs-behälter

Dämpfer

Gebläse

Figure A4-3: Schematic representation of a test facility with damping cup

Under suction conditions, the meter under test can altogether be operated without inlet pipe (suction from the

semispherical space) or also with damping cup or absorption silencer upstream of the inlet. Under pressure

conditions, the same applies in analogy to the outlet side of the standard device. Damping cups allow resonant

vibrations to be easily reduced or eliminated at relatively low cost. A reduction of offending noise will not be

reached if meters under test are operated under open suction conditions without silencer at the inlet end.

109

5 Additional and deviating requirements for drum-type gas meters as volume

standards (section 6.5)

For drum-type gas meters used as volume standards, not only the requirements of section 6.5 "Testing of volume

standards" but also the following additional and deviating requirements are to be complied with.

5.1 Working ranges

Drum-type gas meters of the following sizes with the appurtenant working ranges are permissible:

Size NB

Test volume V (dm³)

Min. flowrate Qmin (m³/h)

Max. flowrate Qmax (m³/h)

2 3 6

15 30 50

100 150 300

5 10 20 50

100 200 500

1000 2000

0.015 0.030 0.060 0.150 0.300 0.600 1.500 3.000 6.000

2.0 3.0 6.0 15.0 30.0 50.0 100.0 150.0 300.0

In the test, the range of use for the working standards can be fixed deviating from the above-mentioned working

ranges.

5.2 Requirements for design and construction

The case and all components important for measurement must consist of an impervious, sufficiently strong and

non brittle material. As far as they come into contact with the sealing liquid or with lubricants, they must be

sufficiently resistant to these.

The drum-type gas meters must be set up such that the gas flows from the case through the drum to the elbow.

The inlet socket shall be in the back-end plate or in its vicinity in the case jacket, and the outlet socket on the rear

side in the direction of the drum axis. The elbow must extend so far upwards that no sealing liquid can penetrate

when the meter is operated.

The case must reliably withstand a gauge pressure of at least 50 mbar without being deformed and the

measurement properties being affected as a result.

For cleaning and repair purposes, it must be possible to dismantle the drum. The position of removable plates

with respect to the case must be maintained using fitting pins or the like. For inspection of the inside of the drum,

large cases may have manholes.

110

The drum must contain at least five measuring chambers of equal size. The axial alignment of the drum must be

good, and it must be statically balanced.

When running forward, the drums must rotate clockwise.

The walls closing the measuring chambers must extend so deep into the sealing liquid that safe sealing is ensured

even at the highest differential pressures to be expected in the meter.

The drum shaft must be properly carried in bearings. If it extends outside through the front-end plate to drive a

pointer or indicating device arranged outside the meter case, the exit hole must be tight but exhibit as little friction

as possible. Preference is to be given to magnetic couplings.

Only a thin-bodied, sparingly evaporating oil may be used as sealing liquid.

The fill hole in the case must be arranged above the limit defined by the rated level; it must be possible to shut it

off so that it is gas-tight. For drawing off sealing liquid, a cock arranged below the rated level shall be available,

and for completely emptying the drum, a drain cock must be provided in the front-end plate at the lowest point.

The outlet socket must be provided with a device indicating whether oil has overflowed. At the lowest point a

cock must be available to discharge the liquid having overflowed.

To obtain the proper filling level, a device (level indicator) must be available allowing the sealing liquid level to

be adjusted such that the test volume is obtained with an uncertainty of ± 0.1 % at most.

For drum-type gas meters, the use of level indicating pipes or hook gauges is permitted. Particular provisions for

devices for testing the proper filling level in large drum-type gas meters are reserved.

The level indicating pipe or the hook gauge device must be vertically adjustable via a fine thread. It must be

possible for the adjustment to be secured by a check nut or the like. The edge of the level indicating pipe must be

horizontal. The adjustment of the adjustment device must be sealable.

The adjustment device must be separately lockable. It must be possible to cover the level indicating pipe with a

hinged cap. The adjustment device must be provided with a collecting device for overflowing liquid with a

lockable discharge.

The edge of the level indicating pipe must be sharp and shall be approx. 30 mm in diameter.

The inlet and outlet sockets of the drum-type gas meters must have sealable openings for drum ventilation.

The meter must be equipped with a cross level with a sensitivity of at least 1 mm deflection at an inclination of

1/2000.

111

Portable drum-type gas meters must have at least three feet with adjusting screws. The screws shall end in cones

with semispherical tips.

At the inlet and outlet socket, pressure measuring sockets must be available. The holes shall be 3 mm to 5 mm in

diameter and be internally flush.

Temperature measuring sockets must be available at the inlet and outlet socket as well as in the front-end plate

below the provided filling level.

The mechanical pressure loss of a drum-type gas meter, i.e. the pressure loss at a flowrate of approx. four times

the minimum flowrate as measured with a differential pressure gauge with appropriately small inertia, may vary

around its mean value during one revolution of the drum by 0.1 mbar at most. Negative pressure losses must not

occur.

5.3 Indicating device and test element

The requirements of the EEC Directive for Gas Volume Meters (71/318 EEC), chapter I No. 5 – Indicating

devices and test element – are also applicable to drum-type gas meters.

Only drum registers are permitted. In addition to the drum register, a pointer linked without clearance to the drum

shaft or - if the pointer is of the stationary type - a dial fixed to the drum must be available.

The lowest element of the drum register must have a division of at least 0.2 l and float uninterruptedly with the

measuring device.

If the pointer or the zero scale marking of a dial applied to the drum, respectively, points vertically upwards, the

drum must be in the middle of an angular section in which the surfacing chambers are connected either with the

inlet or with the outlet. The linkage of the pointer with the drum shaft must be such that the pointer can be placed

only in this position. The pointer must have been balanced.

The diameter of the circle described by the pointer tip or of the dial fixed to the drum, respectively, must not be

smaller than 200 mm. The last 5 cm of the pointer tip may be max. 2 mm in width. It must taper to a point.

The alidade or the dial fixed to the drum, respectively, must be provided with a uniform, centered line graduation.

On the alidade or dial fixed to the drum, the drum positions in which a surfaced chamber is linked neither with the

inlet nor with the outlet must be marked with red circles over its whole length. As the drum position in which the

level is checked, the zero line must additionally be designated "filling position."

112

5.4 Scope of testing

Not only for the test points which are first determined at decreasing loads and then are in part repeated at

increasing loads but also for certain test points in which the standard shall be used, measurement errors can be

determined for additional loads.

If it is intended - deviating from the specifications in the table - to extend the working range of the standard meter

towards higher values, additional tests must be carried out at this peak load. The measurement errors which were

measured at the Qmax value according to the table and at the higher value of the peak load, may differ from each

other by 0.3 % at most.

If a check confirms the original error curve, the determination of the measurement errors for additional test points

can be dispensed with.

5.5 Test volume

The test volume must meet the requirements of section 6.3.2. In addition, it must amount to at least three times the

test volume of the drum-type gas meter.

5.6 Temperature measurement

The temperature is to be measured not only according to the requirements in section 4.4 but also in the sealing

liquid of the drum-type gas meters.

The temperature at the inlet socket of drum-type gas meters may differ from the temperature of the sealing liquid

by 0.3 K at most.

In the case of drum-type gas meters, the outlet temperature is the metering temperature.

5.7 Permissible measurement errors

Deviating from section 6.5.6, drum-type gas meters must meet the following requirements as regards the

measurement errors:

• For testing as working standards, the permissible measurement errors are ±0,5 %. The maximum permissible

span for the measurement errors is 0.8 %.

• The differences of the measurement errors between measurements at decreasing and increasing loads may

amount to 0.1 % at most.

113

• The volume values for ten numbered scale intervals corresponding each to 1/10 drum revolution must not

deviate from their mean value by more than ± 0.5%.

• In the test certificate for a drum-type gas meter to be used as working standard, the

minimum test volume for test runs with fractions of drum revolutions is to be specified in

such a way that the maximum periodic measurement error obtained by addition of the

measurement errors of arbitrary neighbouring scale intervals does not exceed 0.2 % of the

test volume.

5.8 Adjustment of the drum-type gas meters

Experience has shown that at the flowrate Qmax, a drum-type gas meter must be adjusted to -1 % to -0.2 %. The

adjustment (e.g. in the minus direction) is performed at Qmax as follows:

• From the meter ready for operation an exactly defined amount of sealing liquid is to be discharged (for a

meter NB 15, for example, 0.5 litre).

• The level indicator is to be exactly adjusted to the new sealing liquid level.

• After having discharged the sealing liquid, the meter is to be tested again.

• The measurement errors ascertained minus the original measurement errors are the

measure of the caused change in the measurement error, related to the volume of the

sealing liquid discharged.

• The sealing liquid less the amount corresponding to the change in the measurement error

aimed at is filled again into the meter and the level indicator is properly adjusted.

• Then the measurement errors over the whole flowrate range are recorded.

5.9 Identification of drum-type gas meters

In addition to the details given in section 6.5.7, the "filling rule" must be given in the vicinity of the level

indicator as follows:

"For correct filling, the meter must be aligned, the drum completely wetted and brought into filling position, the

draining time complied with and the ventilation sockets at the inlet and outlet opened.“

5.10 Correct filling of drum-type gas meter

Prior to use and after a change in temperature of the sealing liquid of 0.5 K at most, the oil level must be

readjusted. The drum-type gas meter must have been aligned. After approx. three revolutions, the meter is

114

stopped and the dripping time specified in the test certificate with at least two minutes must be complied with.

Subsequently, the oil level is exactly adjusted by discharging or refilling oil.

115

Appendices 1 Report format for diaphragm gas meters 2 Report format for turbine gas meters 3 Adjustment wheel table 4 Certificate formats 4.1 Preliminary Inspection Certificate 4.2 Verification Certificate 4.3 Metrological Evaluation Certificate 4.4 Test Certificate

Anlagen in separater Datei

Appendices 1 Report format for diaphragm gas meters 2 Report format for turbine gas meters 3 Adjustment wheel table 4 Certificate formats 4.1 Preliminary Inspection Certificate 4.2 Verification Certificate 4.3 Metrological Evaluation Certificate 4.4 Test Certificate

116

Appendix 1 Prüfprotokoll Haushalts-Balgengaszähler Test report for domestic diaphragm gas meters Bauartzulassungs-Nr. Type approval No. Größe Size Messraum Measurement room Membran Kunstst

Diaphragm plast.

Hersteller Manufacturer Fabrik-Nr./Baujahr Serial No./year of manuf. Messpunkt bei Q Measuring point at Q Durchfluss Flowrate Prüfling Ablesung Prüfende Ablesung Prüfanfang Fortschritt

Meter under test Reading - end of test Reading - start of test Advance

Normal Fortschritt

Standard Advance

Rohe Messabweichung absolute relativ

Rough measurement error absolute relative

Druck Verlust zulässig am Normal am Prüfling Differenz Korrektur

Pressure Loss admiss. at standard at meter under test Difference Correction

Temperatur am Normal am Prüfling Differenz Korrektur

Temperature at standard at meter under test Difference Correction

Messabweichung des Normals Measurement error of standard Korrektursumme Correction sum Messabw. des Prüflings Measurement error of meter under test Fehlergrenze Error limit Prüfamt Test office Prüfdatum Date of test Prüfer Test engineer Unterschrift Signature Bemerkungen Remarks

117

Appendix 2 Test Report for Turbine Gas Meters Bauart: Turbinenradgaszähler Type: turbine gas meter Zulassungs-Nr. Approval No. Justierradpaar Adjustment wheel pair Hersteller Manufacturer Größenbezeichnung Designation of size NF-Impulswert NF pulse value Fabrik-Nr. Serial No. HF-Impulswert HF pulse value Baujahr Year of manufacture Luftdruck Air pressure Anlass der Prüfung: Nacheichung nach Reparatur Reason for test: subseq. verif. after repair Bemerkungen: justiert nach 26/33, neuer HF-IW Remarks: adjusted to 26/33, new HF pulse value Gebrauchsnormal Working standard Messpunkt Measuring point Durchfluss Flowrate Temperatur Normal

Temperature standard

Temperatur Prüfling

Temperature meter under test

Druck Normal Druckverlust Solldruckverlust

Pressure standard pressure loss theor. pressure loss

Druck Prüfling Druckverlust

Pressure meter under test pressure loss

Messzeit Measurement time Volumen Normal Impulswert Impulse

Volume standard pulse value pulses

Volumen Prüfling Impulswert Impulse

Volume meter under test pulse value pulses

Messabw. des Normals (Prüfschein) Meas. error of standard (test certificate) Messabw. des Prüflings (Gleichung) Meas. error of meter tested (equation) Messabw. des Prüflings (nach Just.) Meas. error of meter tested (after adjustm) Fehlergrenze Error limit Prüfamt Test office Prüfdatum Date of test Prüfer Test engineer Unterschrift Signature

118

Appendix 3 Adjustment wheel table Zähneanzahl Number of teeth treibendes Rad Driving wheel getriebenes Rad Driven wheel Damit erzielter Übers.faktor Gearing factor achieved Abstand vom Grundpaar Spacing from standard pair Einzelabstand Single spacing Modul Modulus Radsatz-Nr. Wheel set No. Farbe Colour braunbeige brown beige weißgrün pastel green lichtblau light blue pastellorange pastel orange olivgrün olive green hellrosa light pink staubgrau dusty gray grünblau greenish blue enzianblau gentian blue reinweiß pure white rehbraun fawn brown tiefschwarz jet black maigrün may green schwefelgelb sulphur yellow feuerrot flame red rotlila red lilac granitgrau granite gray erdbeerrot strawberry red The adjustment wheel table shown above and other such tables are to be used according to the following example. After measurement errors have been ascertained for a gas meter with the adjustment wheel pair 33/42 currently used, the meter shall be adjusted by 0.8 % in the plus direction. With the adjustment wheel pair 33/42, the meter is adjusted by -1.82 % with respect to the standard pair 32/40. For a correction by +0.80 %, an adjustment wheel pair should be chosen which is -1.82 % + 0.8 % = -1.02 % from the standard pair 32/40. For this purpose, only the adjustment wheel pair 38/48 with a spacing of -1.05 % from the standard pair comes into question.

119

Appendix 4.1 Mess- und Eichwesen Neuland - Eichdirektion Legal Metrology Office of the Federal State of Neuland (Germany) THE STANDARDS USED FOR THE MEASUREMENTS ARE TRACEABLE TO THE NATIONAL STANDARDS AT THE PHYSIKALISCH-TECHNISCHE BUNDESANSTALT. Vorprüfschein Preliminary Inspection Certificate Number 123/2001 Gegenstand Measuring device of vortex gas meter Object Identifikation Serial No. 1234567 Identification Hersteller Neuding Manufacturer Antragsteller GVU Applicant Anzahl der Seiten der Anlage 1 Number of pages of Addendum Ort und Datum der Vorprüfung Neustadt, January 8, 2002 Place and date of preliminary inspection This Preliminary Inspection is valid until January 8, 2003 Marking E

Vorprüfscheine ohne Unterschrift und Dienststempel haben keine Gültigkeit. Dieser Vorprüfschein darf nur unverändert weiterverbreitet werden.

Preliminary Inspection Certificates without signature and official stamp are not valid. This Preliminary Inspection Certificate may only be reproduced unaltered. Ort und Datum Stempel Im Auftrag Place and date Official stamp On behalf of Neustadt, 08-01-2002 (Name)

Page 1 of Addendum to Preliminary Inspection Certificate No. 001/02 Additional details of the object Measuring device of a vortex gas meter with the national pattern approval No. 7.222/01-XX of size G 1600. Test procedure The measuring device was tested on the test rig of the manufacturer at the flowrates given below. It was compared in series with standard gas volume meters of the manufacturer using the pulse generators at the standard and at the meter under test. For the condition of the test air, the pressures at the pr socket and the temperatures at the meter outlet were decisive. Ambient conditions Air pressure: 995 mbar / test room temperature: 20.3 °C to 20.6 °C Result The requirement of Appendix 7-1 to the Verification Ordinance and in the type approval referred to on page 1 of Addendum 1 are complied with. On the basis of the pulses emitted by the measuring device, the following measurement errors were determined for the pulse value of 345.123 imp/m³ fixed according to the test results: Test flowrate Qmin 0.1 Qmax 0.25 Qmax 0.4 Qmax 0.7 Qmax Qmax

Flowrate /m³/h Measurement error (%) Measurement uncertainty (%)

Error limit /%) Measurement uncertainty The measurement uncertainty stated is the expanded uncertainty which is obtained from the standard uncertainty by multiplication by the coverage factor k = 2. It has been determined in accordance with the "Guide to the Expression of Uncertainty in Measurement“ (DIN V ENV 13005). In the case of normal distribution, the value of the measurand lies with a probability of 95 % within the interval of values assigned. Notes With this, the measuring instrument is not verified. It can be subjected to verification in conjunction with a display device approved for this purpose, e.g. an electronic corrector. The verification mark will be applied to the display after the metrological overall examination.

The validity of the preliminary inspection will terminate prematurely if one of the changes described in section 13 para. 1 of the Verification Ordinance has occurred.

End of Addendum

Appendix 4.2 Mess- und Eichwesen Neuland Eichdirektion - Legal Metrology Office of the Federal State of Neuland (Germany) THE STANDARDS USED FOR THE MEASUREMENTS ARE TRACEABLE TO THE NATIONAL STANDARDS AT THE PHYSIKALISCH-TECHNISCHE BUNDESANSTALT. Eichschein Verification Certificate Number 002/02 Gegenstand Gas meter Object Identifikation Serial No. 1234567 Identification Hersteller Neuding Manufacturer Antragsteller GVU Applicant Anzahl der Seiten der Anlage 1 Number of pages of Addendum Ort und Datum der Eichung Neustadt, January 8, 2002 Place and date of verification This verification is valid until December 31, 2010 Marking e 02

Eichscheine ohne Unterschrift und Dienststempel haben keine Gültigkeit. Dieser Eichschein darf nur unverändert weiterverbreitet werden.

Verification Certificates without signature and official stamp are not valid. This Verification Certificate may only be reproduced unaltered. Ort und Datum Stempel Im Auftrag Place and date Official stamp On behalf of Neustadt, 08-01-2002 (Name)

Page 1 of Addendum to Verification Certificate No. 001/02 Additional details of the object Turbine gas meter with EEC pattern approval No. D01/7.211/XX of size G 650 without lubricating device. Test procedure The turbine gas meter was tested on the test rig of the verification authority at the flowrates given below. It was compared in series with working standard gas volume meters of the verification authority using the pulse generators at the standard and at the meter under test. For the condition of the test air the pressures at the pr socket and the temperatures at the meter outlet were decisive. Ambient conditions Air pressure: 990 mbar / test room temperature: 21.8 °C to 22.2 °C Result The requirements of Appendix 7-1 to the Verification Ordinance and in the type approval referred to above are complied with. The following measurement errors were determined: Test flowrate Qmin 0.1 Qmax 0.25 Qmax 0.4 Qmax 0.7 Qmax Qmax

Flowrate (m³/h) Measurement error (%) Measurement uncertainty (%)

Max.perm.error on verification (%)

Measurement uncertainty The measurement uncertainty stated is the expanded uncertainty which is obtained from the standard uncertainty by multiplication by the coverage factor k = 2. It has been determined in accordance with the "Guide to the Expression of Uncertainty in Measurement“ (DIN V ENV 13005). In the case of normal distribution, the value of the measurand lies with a probability of 95 % within the interval of values assigned. Notes The validity of the verification will terminate prematurely if one of the changes described in section 13 para. 1 of the Verification Ordinance has occurred.

End of Addendum

Appendix 4.3 Mess- und Eichwesen Neuland - Eichdirektion Legal Metrology Office of the Federal State of Neuland (Germany) THE STANDARDS USED FOR THE MEASUREMENTS ARE TRACEABLE TO THE NATIONAL STANDARDS AT THE PHYSIKALISCH-TECHNISCHE BUNDESANSTALT. Befundprüfschein Metrological Evaluation Certificate Number 003/01 Gegenstand Gas meter Object Identifikation Serial No. 1234567 Identification Hersteller Neuding Manufacturer Antragsteller GVU Applicant Anzahl der Seiten der Anlage 1 Number of pages of Addendum Ort und Datum der Befundprüfung Neustadt, January 8, 2002 Place and date of Metrological Evaluation Marking e 98

Befundprüfscheine ohne Unterschrift und Dienststempel haben keine Gültigkeit. Dieser Befundprüfschein darf nur unverändert weiterverbreitet werden.

Metrological Evaluation Certificates without signature and official stamp are not valid. This Metrological Evaluation Certificate may only be reproduced unaltered. Ort und Datum Stempel Im Auftrag Place and date Official stamp On behalf of Neustadt, 08-01-2002 (Name)

Page 1 of Addendum to Metrological Evaluation Certificate No. 003/01 Additional details of the object Diaphragm gas meter with national type approval No. 7.122-XX, size G 4, principal mark of Neustadt Verification Office from the year 98 applied, counter contents prior to test: 12345.2 m³, counter contents after completion of test: 12345.7 m³. Test procedure After examination of the external condition, the gas meter was metrologically examined in the test facility of the verification authority after a preparatory run at 0.2 Qmax of 30 dm³ at the flowrates mentioned below, in ascending order. The meter was compared in series with working standard gas volume meters of the verification authority using the scale indications. For the condition of the test air, the pressures at the inlet socket and the temperatures at the outlet socket of the meters were decisive. Within the scope of the internal inspection, the indicating device was checked. / The internal inspection was dispensed with in accordance with the applicant's application.* Ambient conditions Air pressure: 998 to 1000 mbar / test room temperature: 20.0 °C to 20.3 °C Result The requirements for the external inspection are - not - complied with.* The measurement errors - do not - lie within the maximum permissible errors in service.* Test flowrate Qmin 0.2 Qmax Qmax

Flowrate (m³/h) Measurement error (%)**

Measurement uncertainty (%)

Error limit (%) The indicating device is - not - in order.* Other findings and assessments: strong noise at Qmax.*** Measurement uncertainty The measurement uncertainty stated is the expanded uncertainty which is obtained from the standard uncertainty by multiplication by the coverage factor k = 2. It has been determined in accordance with the "Guide to the Expression of Uncertainty in Measurement“ (DIN V ENV 13005). In the case of normal distribution, the value of the measurand lies with a probability of 95 % within the interval of values assigned. Notes With the Metrological Evaluation Certificate a supplementary sheet with additional legal information is enclosed.

End of Addendum * delete what is not applicable ** This line does not apply if the maximum permissible errors in service are complied with. *** not applicable if no further findings are made.

Appendix 4.4 Mess- und Eichwesen Neuland - Eichdirektion Legal Metrology Office of the Federal State of Neuland THE STANDARDS USED FOR THE MEASUREMENTS ARE TRACEABLE TO THE NATIONAL STANDARDS AT THE PHYSIKALISCH-TECHNISCHE BUNDESANSTALT. Prüfschein Test Certificate Number 004/01 Gegenstand Drum-type gas meter Object Identifikation Serial No. 1234567 Identification Hersteller Neuding Manufacturer Antragsteller GVU Applicant Anzahl der Seiten der Anlage 1 Number of pages of Addendum Ort und Datum der Prüfung Neustadt, January 8, 2002 Place and date of test This test is valid until January 8, 2007 Marking e 02

Prüfscheine ohne Unterschrift und Dienststempel haben keine Gültigkeit. Dieser Vorprüfschein darf nur unverändert weiterverbreitet werden.

Test Certificates without signature and official stamp are not valid. This Preliminary Inspection Certificate may only be reproduced unaltered. Ort und Datum Stempel Im Auftrag Place and date Official stamp On behalf of Neustadt, 08-01-2002 (Name)

Page 1 of Addendum to Test Certificate No. 002/02 Additional details of the object Turbine gas meter with EEC type approval No. D01/7.211/XX of size G 650 without lubricating device. Test procedure The turbine gas meter was tested on the test rig of the verification authority at the flowrates given below. It was compared in series with working standard gas volume meters of the verification authority using the pulse generators at the standard and at the meter under test. For the condition of the test air the pressures at the pr socket and the temperatures at the meter outlet were decisive. Ambient conditions Air pressure: 990 mbar / test room temperature: 21.8 °C to 22.2 °C Result The requirements of Appendix 7-1 to the Verification Ordinance and in the type approval referred to above are complied with. The following measurement errors were determined: Test flowrate Qmin 0.1 Qmax 0.25 Qmax 0.4 Qmax 0.7 Qmax Qmax

Flowrate (m³/h Measurement error (%) Measurement uncertainty (%)

Error limit (%) Measurement uncertainty The measurement uncertainty stated is the expanded uncertainty which is obtained from the standard uncertainty by multiplication by the coverage factor k = 2. It has been determined in accordance with the "Guide to the Expression of Uncertainty in Measurement“ (DIN V ENV 13005). In the case of normal distribution, the value of the measurand lies with a probability of 95 % within the interval of values assigned. Notes The validity of the verification will terminate prematurely if one of the changes described in section 13 para. 1 of the Verification Ordinance has occurred.

End of Addendum

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Bildbeschriftungen Die Seitenzahlen beziehen sich auf den deutschen Text. Seite 27 bis 29 Flowcharts (Eichung) Verification nein no ja yes ausschl. mit HD-Gas? exclusively with high-pressure gas Start start EWG-Ersteichung EEC initial verification organ.+ techn. Voraussetzungen erfüllt? organiz. and techn. conditions fulfilled? Beschaffenheitsprüfung external inspection Anforderungen erfüllt? requirements fulfilled? Messtechn. Prüfung metrol. examination Anforderungen erfüllt? requirements fulfilled? Auslieferung ohne HD-Prüfung? delivery without HD test? Stempelung marking Bescheinigung beantragt? certificate applied for? Zertifikat, Bescheinigung certificate Gebührenerhebung levying of fees Ende end Stempelung marking Vorprüfschein preliminary inspection certificate Gebührenerhebung levying of fees Durchführung der Eichung mit HD-Gas performance of verification with HD gas Rückgabe return ggf. Entwertung obliteration, if necessary Mitteilung notification Bemerkungen, Verweise remarks, references Abschnitt section Anlage annex EKVO Ordinance on verification fees Bearbeitgung gemäß… handling acc. to Testing Instructions for HP

testing

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(Befundprüfung) Metrological evaluation nein no ja yes Start start Antrag auf Befundprüfung application for metrological evaluation organ.+techn. Voraussetzungen … organ. and techn. conditions fulfilled? äußere Beschaffenheitsprüfung external inspection Anforderungen erfüllt requirements fulfilled? messtechnische Prüfung metrological examination Anforderungen erfüllt? requirements fulfilled? innere Beschaffenheitsprüfung internal inspection Öffnung, Untersuchung opening, investigation Prüfschein test certificate Gebührenerhebung levying of fees Ende end Fortsetzung möglich? continuation possible? Entwertung obliteration besonderer Hinweis im Prüfschein particular reference in test certificate Bemerkungen, Verweise remarks, references gemäß… acc. to Abschnitt section Mitteilung notification gemäß EKVO acc. to EKVO (Sonderprüfung und sonstige Prüfung) Special examination and other examinations Mitteilung notification nein no ja yes Start start organ.+techn. Voraussetzungen… organ. and techn. conditions fulfilled? Auswahl vergleichbarer… selection of comparable meters acceptable for

verification to define the test program Beschaffenheitsprüfung external inspection Anforderungen erfüllt? requirements fulfilled? Messtechn. Prüfung metrological examination Anforderungen erfüllt? requirements fulfilled? Bescheinigung beantragt? certificate applied for? Bescheinigung, Sonderprüfschein certificate, special examination certificate Sonderprüfung beantragt? special examination applied for? Stempelung marking Gebührenerhebung levying of fees Ende end Bemerkungen, Verweise remarks, references gemäß … according to Abschnitt section EO Anlage Appendix to EO Kennzeichnung gemäß… identification acc. to EA-AV Nr. EA AV No. Seite 43 Bild 1

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Einlauf inlet pipe Prüfling meter under test Auslauf outlet pipe Seite 45 Bild 2 Klimaschrank climatic chamber Prüfling meter under test vorgetrockete Prüfluft pre-dried test air Seite 46 Prüfling meter under test Normal standard Gebläse blower Seite 69 Tabelle 14 Qualitätsnachweis… Quality assurance for initial verification of domestic

diaphragm gas meters with mechanical temperature conversion acc. to method B

Zählerlos meter lot Losgröße lot size Zählertyp meter type Hersteller manufacturer Zulassungszeichen approval mark Lfd. Nr. cons. No. Prüfstelle test centre Prüfdatum date of test Prüftemperatur test temperature Durchfluss flowrate Spanne der Messabweichungen span of measurement errors Zählernummer meter No. Kunde customer von bis from - to Messabw. meas. error Seite 100 Bild A1-1 a Zählwerk indicating device b Kurbeltrieb crank assembly c Anschluss für Prüfzählglied connection for test element d Justierung adjustment e Schiebersteuerung slide control f max. Auslenkung der Trennmembran max. deflection of diaphragm g Trennmembran (Balg) diaphragm (bellow)

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h Messkammergehäuse measuring chamber case I Zählergehäuse meter case Seite 103 Bild A1-3 Drehkolben rotary piston Spalt clearance Messkammerinhalt volume of measuring chamber Gehäuse case Seite 105 Bild A1-5 Druckverlust ohne Resonanzschwingungen pressure loss without resonant vibrations Druckverlust mit Resonanzschwingungen pressure loss with resonant vibrations Abweichung ohne Resonanzschwingungen error without resonant vibrations Abweichung mit Resonanzschwingungen error with resonant vibrations Seite 106 Bild A1-6 a Verdrängungskörper displacement body b Gehäuse case c niederfrequenter Impulsgeber low-frequency pulse generator d Justierung adjustment e Zählwerk indicating device f Getriebe gearing g Flügelrad impeller h Impulsgeber pulse generator I Strömungskanal flow channel Seite 110 Bild A1-9 a Sensor sensor b Absperrventile shut-off valves c Testkopf test head d Druckbohrungen pressure holes e Störkörper bluff body f Gehäuse case g Sensorleitungen sensor lines h Epoxyd-Harz epoxy resin I oberes Fühlerrohr upper feeler pipe j unteres Fühlerrohr lower feeler pipe k Thermistor, Spitze glasüberzogen thermistor, tip glass-covered Seite 111 Bild A1-10 a Gehäuse case b Transducer A transducer A c Transducer B transducer B

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Seite 113 Bild A2-1 Prüfling meter under test Gebläse blower Normal standard Seite 119 Bild A2-2 Normal standard Prüfling meter under test Seite 122 Bild A2-3 Normal standard Prüfling meter under test Seite 130 Tabelle Formel Summe der Quadrate = sum of squares Seite 132 Formel Seite 135 Bild A4-1 Schallschluckstoff pressure-absorbing material Dämmmaterial insulating material schalldurchlässige Abdeckung cover permeable to sound Mantelrohr jacket tube Strömungskanal/Rohr flow channel / pipe Seite 135 Bild A4-2 Dämpfer silencer Prüfling meter under test Normal standard Gebläse blower Seite 136 Bild A4-3 Prüfling meter under test Dämpfungsbehälter damping cup Normal standard Gebläse blower

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