Definition - Pressure

• Pressure

• Force = Mass x Acceleration

• Area

SI Unit ⇒ Pascal = Newton/m2

= (m • kg • s-2)/m2

FFPP == ________

AA

Influences on Force

• Mass Load

• Local Gravity

• Air Buoyancy

• Verticality (Level)

• Surface Tension

• Other (Environment)-- Magnetism, Air Drafts, Mass

Rotation

ΣΣ FFP =P = ________

AA

Influences on Area

• Pressure Dependence

– Distortion

– Operating Fluid

– Geometric Uniformity

• Temperature

FFP =P = ________

AA

Reference Modes

ACCURACY TERMSACCURACY TERMSACCURACY TERMS

LINEARITY TSLLINEARITY TSL

• Draw a line through zero and full scale pressure point

• Error is either positive or negative• Typically nearly twice the BSL fig

ure

O/P

P

LINEARITY BSLLINEARITY BSL

• Draw a best straight line through all the points (least square error)

• Error is + and -

O/P

P

FORCED ZERO BSLFORCED ZERO BSL

O/P

P

• Fix the zero • Slope is BSL

REPEATABILITYREPEATABILITY

• Definition - the spread of readings when taking consecutive measurements without changing the pressure, temperature or other external environmental conditions e.g. EMC

• This is not easy to measure because the noise is masked by changes in the environmental factors

• Our best estimate comes from noise measurements which give <<0.1 uV in the frequency range 0.1 to 10 Hz.

PRESSURE HYSTERESISPRESSURE HYSTERESIS

• The changes in measured pressure as a percentage of full scale when the pressure is changed then returned to the original value whilst keeping all other environmental conditions the same or compensating for them.

• Again difficult to measure, changing pressure changes the temperature of the pressure media.

• Current design show pressure hysteresis lower than our measurement threshold.

TEMPERATURE ERRORSTEMPERATURE ERRORS

• TEB (Thermal error band)

• RTE (Referred temperature error)

• Thermal hysteresisGood design and temperature cycle out hysteresisCreep

RTE: REFERRED TEMPERATURE ERRORRTE: REFERRED TEMPERATURE ERROR

• Error is with respect to the room temperature error• Not necessarily a linear relationship.

TEB: TEMPERATURE ERROR BANDTEB: TEMPERATURE ERROR BAND

• Measure performance at all temperatures• Plot all errors and put a band around them, take the spread say 2%Fs and h

alve the figure quoting +/-1%FS TEB

Why Calibrate ?•Every day we make decisions based on the information we have acquired.

•Whether we make the right decisions depends largely on whether the information is correct.

•We often acquire information by way of measurement.

Equipment Categories•Product Critical Instruments - have a direct effect on QUALITY

•Process Critical Instruments - have a direct effect on QUANTITY

•Safety Critical Instruments - have a direct effect on plant and personnel SAFETY

•Non Critical Instruments

Calibration Hierarchy•NATIONAL STANDARDS LABInternational/National Primary Standard & Secondary Standard

•CALIBRATION LABORATORY Reference Standard & Working Standard

•INDUSTRYIndustrial Standard & Measuring Device

PRESSURE STANDARDS

1. Primary Pressure Standard : -. Dead weight Tester

ex) Model : 2465 ( RUSKA)…

2. Secondary Pressure Standard-. Portable Pressure Calibrator

ex) DPI 610 series, DPI605 series…

-. Digital Pressure Controllerex) DPI 515, DPI520, 7250 series ….

PRESSURE CALIBRATIONPRESSURE CALIBRATION

WHYCALIBRATE ?

SAFETY

ISO 9000TRACEABILITY

OF ALLMEASUREMENTS

MEASURINGINSTRUMENTS PRODUCTION

QUALITY

PRODUCTIONCOST

LEAKAGEPLANT FAILURE

SHUT-DOWN

DRIFT

WHY USE A DEADWEIGHT TESTER?WHY USE A DEADWEIGHT TESTER?

• LOSE USE OF INSTRUMENT FOR LONGER• RISK CHANGE IN STATUS AFTER CAL

• SHORTSIGHTED TO BU Y EXPENSIVE ACCURATE PRESSURESENSING DEVICES W ITH NO MEANS TO CHECK O R VERIFYACCURACY.

• PRIMARY REFERENCE FOR PRESSURE.

• MOST ACCURATE AND STABLE MEANS O F PRESSUREMEASUREMENTS.

• D IRECTLY TRACEABLE TO INTERNATIONA L PRESSURESTANDARDS.

• SELF-CONTAINED W ITH OW N PRESSURE GENERATOR (NOTHIGH PRESSURE AIR MODELS).

• ISO 9000

• SAVE M ONEY BY HAVING THE ABILITY TO CALIBRATE OW NSECONDARY STANDARDS

• U S E O F E XT E R N A L LA B O R A TO R IE S

• SAVE MONE Y B Y HAV IN G VER Y ACCURATE MEASURE MENTS :F ISCAL METER ING / CUSTOD Y TRANSFE R

• INTR INS ICALLY SAFE

DEADWEIGHTTESTERS

PRIMARYSTANDARDS

• SIMPLE TO USE

• STABLE

• ACCURATE

• INTRINSICALLY SAFE

SPECIFICATIONSAVAILABLE

• ACCURACY FROM:0.005% to 0.1% OF READING

• RANGES FROM:-1 to 4000 bar

• OPERATING MEDIA:OIL, GAS, WATER

• OPERATING ENVIRONMENT:LABORATORY, INDUSTRIAL, ON-SITE

PRESSUREMODES

• POSITIVE GAUGE PRESSURE

• NEGATIVE GAUGE PRESSURE

• ABSOLUTE PRESSURE

• DIFFERENTIAL PRESSURE

TYPES OF DEADWEIGHT TESTERTYPES OF DEADWEIGHT TESTER

GAUGE PRESSUREGAUGE PRESSURE

AREA

FORCE

PRESSURE PRESSURE = FORCEAREA

VACUUMVACUUM

FORCE

AREA

VACUUM

ABSOLUTE PRESSUREABSOLUTE PRESSURE

REFERENCE PRESSURE (RP)

VACUUMPUMP

AREA

FORCE

ABSOLUTE PRESSURE

= AREA + RPFORCE

DIFFERENTIAL PRESSUREDIFFERENTIAL PRESSURE

P

DIFFERENTIAL PRESSURETRANSMITTER

CROSS CONNECTING VALVE

HIGHLOW

MEASURINGPISTON

BALANCEPISTON

WHICH DEADWEIGHT TESTER?WHICH DEADWEIGHT TESTER?

WHAT PRESSURERANGE IS

REQUIRED ?

WHICHDEADWEIGHT

TESTER ?WHAT OPERATING

MEDIA ISREQUIRED ?

WHAT ACCURACYIS

REQUIRED ?

WHICH DEADWEIGHT TESTER?WHICH DEADWEIGHT TESTER?

WHAT MEDIA ? G E N E R A L L Y :• H I G H P R E S S U R E S – H Y D R A U L I C• L O W P R E S S U R E S – P N E U M A T I C

T h e d e a d w e ig h t te s te r is a c c u ra te w h ils t th e p is to n a n d w e ig h ts a re f lo a tin g a n d s p in n in g .T h e p is to n m u s t s p in to e lim in a te fr ic tio n .O il d e a d w e ig h t te s te rs w ill n o t s p in a t lo w p re s s u re s d u e to th e d ra g o f o il .

OIL1 to 4000 bar

•ROBUST•GOOD LUBRICANT•LARGE GAP BETWEEN PISTON & CYLINDER•TOLERATE SMALL DEGREE OF CONTAMINATION (NOT RECOMMENDED)•LITTLE USER MAINTENANCE REQUIRED

WATER0.5 to 700 bar

•CARE REQUIRED

•POOR LUBRICANT•SMALL GAP BETWEEN PISTON & CYLINDER•ENSURE WATER FILM EXISTS AROUND PCU BEFORE USE•DISTILLED / DEIONISED WATER ONLY•DO NOT CONTAMINATE•PERIODICALLY CLEAN PCU

•POOR LUBRICANT•SMALLEST GAP BETWEEN PISTON & CYLINDER•DO NOT CONTAMINATE•GAS SUPPLY MUST BE CLEAN & DRY•DEVICE UNDER TEST MUST BE INTERNALLY CLEAN•FREQUENTLY CLEAN PCU

•GREATER CARE REQUIRED

GAS0.0002 to 140 bar

WHICH INSTRUMENT?WHICH INSTRUMENT?W H A T A C C U R A C Y ?

IF U N C E R T A IN , U S E T H E ‘R U L E O F T H U M B ’ :

• 1 0 T IM E S M O R E A C C U R A T E T H A N T H E D E V IC E T O B E C A L IB R A T E D IF AM A N U F A C T U R E R

• 4 T IM E S M O R E A C C U R A T E T H A N T H E D E V IC E T O B E C A L IB R A T E D IF A N E N DU S E R

2%

1%

0.5%

0.25%

0.1%

0.05%

0.025%

0.01%

BOURDON TUBEPRESSURE GAUGE

COMPARITOR

ELECTRONICTRANSFERSTANDARD

DEADWEIGHTTESTER

ENVIRONMENTAL INFLUENCESENVIRONMENTAL INFLUENCES

INFLUENCE STANDARD / REFERENCE VARIANCE / EFFECT

PRESSURE = FORCEAREA

FORCE

AREA

PRESSURE

G R A V IT Y (F O R C E ) 9 8 0 .6 6 5 c m /s ² 0 .5 %

T E M P E R A T U R E (A R E A ) 2 0 °C 0 .0 0 1 6 % /°C

A IR D E N S IT Y (F O R C E ) 0 .0 0 1 2 g /m l 0 .0 0 1 3 % / 0 .0 0 0

N O T E : A IR D E N S IT Y V A R IE S T Y P IC A L L Y F R O M 0 .0 0 1 0 T O 0 .0 0 1 3 g /m l

A L L O F T H E A B O V E IN F L U E N C E S C A N B E C O M P E N S A T E D F O R .

LOCAL GRAVITYLOCAL GRAVITY

1. SITE SURVEY2. GRAVITY CALCULATION

THE CALCULATION IS BASED UPON THE FOLLOW ING DATA:• SITE LATITUDE IN DEGREES (L)• SITE ALTITUDE IN METRES (H)

THE EQUATION USED FOR SEAL LEVEL IS AS FOLLOW S:

LOCAL GA = 980.616(1 - 0.0026373 x cos2L + 5.9 x 10-6 x cos2L x cos2L)

THE EQUATION USED FOR HEIGHT ABOVE SEA LEVEL IS AS FOLLOW S:

LOCAL GRAVITY = GA – 0.0003086 x H

FOR EXAMPLE:

SITE LATITUDE IN DEGREES (L) = 13.44SITE ALTITUDE IN METRES (H) = 100

LOCAL GRAVITY AS CALCULATED ABOVE = 978.283 cm/s²

1. NEAREST LOCAL SITE

THE FOLLOW ING GENERALLY HAVE LOCAL SITE GRAVITY SURVEYS:

• METROLOGY INSTITUTE• UNIVERSITY• AIRPORT

PISTON GAUGE SELECTION CHART N o Y e s O i l A u t o m a t i c B M a n u a l o G a s t h N o Y e s Y e s N o Y e s N o

A c c u r a c y : < 0 . 0 1 %

S e e P r e s s u r e m e n t sD e a d w e i g h t G a u g e s

M e d i a : O i l G a s B o t h

A u t o m a t i c o r M a n u a l

M o d e l 2 4 9 24 0 , 0 0 0 p s i M a x i m u m

P r e s s u r e R a n g e :≤ 1 , 0 0 0 p s i

P r e s s u r e R a n g e : ≤ 2 0 , 0 0 0 p s i

M o d e l 2 4 8 5H i g h P r e s s u r e S y s t e m7 2 , 5 0 0 p s i R a n g e S e l e c t A n y P i s t o n A s s y .

M o d e l 2 4 8 5L o w P r e s s u r e S y s t e m S e l e c t P i s t o n A s s y . 1 0 – 1 , 0 0 0 p s i 1 0 0 – 1 0 , 0 0 0 p s i 2 0 0 – 2 0 , 0 0 0 p s i

M o d e l 2 4 8 5 - 6 2 6 S y s t e mG a s t o 1 5 , 0 0 0 p s i O i l t o 2 0 , 0 0 0 p s i S e l e c t A n y P i s t o n A s s y . t o 2 0 , 0 0 0 p s i

P r e s s u r e R a n g e : ≤ 3 , 0 0 0 p s i

M o d e l 2 4 7 51 7 0 – 1 5 , 0 0 0 p s i gH e l i u m G a s

M o d e l 2 4 6 50 . 2 – 1 , 0 0 0 p s iG a u g e & A b s .

M o d e l 2 4 7 01 0 0 – 3 , 0 0 0 p s i g

Ruska 2465 Gas Piston Gauge

Model 2485 Hydraulic DWG

2485 Key Features

• Accuracy

– 0.0024% of Reading to 70 bar

– 0.0035% of Reading to 1400 bar

– 0.01% of Reading to 5000 bar

• Protected Piston/Cylinder Design

• Easy to Install Piston/Cylinder - No Tools Required

• Easy to Operate (Isolation Valve, 3 Point Level)

Secondary StandardsSecondary StandardsSecondary Standards

WHAT IS A CONTROLLER/CALIBRATOR?WHAT IS A CONTROLLER/CALIBRATOR?

• Secondary or transfer standard

• Visual display of controlled pressure output

• Electrical input/output

• Digital input/output

• Pressure output

BASIC CONCEPT OF A PRESSURE CONTROLLERBASIC CONCEPT OF A PRESSURE CONTROLLER

+

-

Source

Setpoint

Feedback

Input Output

PressureController

DeviceUnderTest

+

-

DRUCK CONTROLLERS/CALIBRATORS

DPI 515

DPI 520

DPI 530

DPI 515 MAIN FEATURESDPI 515 MAIN FEATURES

• 0.01% FS Precision(0.03% FS below 700 mbar)

• 0.02% Reading 12 monthmeasurement stability

• Wide choice of pressure ranges25 mbar FS to 210 bar FS

• RS232 and IEEE-488 commsas standard

• Fast control to setpoint,typically less than 10 seconds

• Control stability better than10 ppm at setpoint

• Easy to learn, user friendly interface

DPI 515 AERONAUTICAL OPTION C

• Control in Aerospace units feet, metres, Knots, Km/h, Mph or Mach

• Altitude control/measure to 0.13 mbar

• Airspeed control/measure to 0.2 mbar

• Timed or instant Rate of Climb

• Settable R.O.C. and rate of speedto protect sensitive instruments

• Compatible with current RVSM requirements for Altitude

• Different configurations available(C1: Altitude, C2: Airspeed, C3: Both)

DPI 515-2892 NATO CODIFIED

• Special 5 range version

• Primary manifold- 35 bar g/36 bar abs (Engine pressure)- 750-1150 mbar abs (Barometric ref.)

• Secondary manifold- 2.5 bar gauge (Airspeed)- 1.3 bar absolute (Altitude)- 0.3 bar differential

• All Aeronautical ranges on one manifold

• Includes soft carry case and user manual

• Calibration and service manuals available

• Fully NATO codified (NSN-6685-99-227-8159)

• 300 bought by UK MOD for RAF

DPI 515 ENHANCED STABILITY OPTION E

• Absolute pressure control to 0.01% FS • 750 - 1150 mbar abs• 35 - 1310 mbar abs• 35 - 2700 mbar abs

• 12 month measurement stability 0.01%• Utilises Druck RPT as control sensor,

(no zeroing required!)• Replaces the old DPI 501 for low pressure

absolute application• E1: Single range, can be combined with

any other range/option• E2: Dual range, available with any option

except the barometric reference (A)

LABVIEW DRIVER FOR DPI 515

• Free Labview 6.0 Driver and example VI availableat www.Druck.com

• Easy interface with PC via Labview

• IEEE or RS232 compatible

LABVIEW SCHEMATICS

LABVIEW VIRTUAL INSTRUMENT

DPI 515 SENSOR CALIBRATION MODULE

Basic task modified with SCM feature

Units

Vent

Range

Process

Range

Gauge/abs

999.99 mbar

Set point: 999.99 mbar

Rate:Or Pre-Set/Divider

SCM: 100.0100 mVA

PressureWindow

Pressure Set Point

SCM Window

AutoRange

SCM

1barg

7barg

---

More

135mVA

135mVC

11V

25nA

SCM Off

• Accurate electrical measurementof sensor outputs

• Ranges 0-25 mA, ± 135 mV, 0-11V

• Excitation output +10 V reg, +24 V unreg

• Integral to DPI 515, all in onepressure calibration

• Easy connection with special SCM lead and probe

• Dual screen display of pressureand electrical values

DPI 515 SOFTWARE UPGRADES

• New software in development for improvement

• Downloaded via RS232

• Present release 4.3

• Next release 5.0, due early 2002

• Includes:• Improved control• Jog in Divider/Present Tasks• Test programs (similar to

RUI 100 on DPI 520). Stores15 programs

DPI 515 TECHNOLOGY

• Utilises Druck PDCR 2200 low dopedgrade A sensor

• Fully temperature characterised toprovide enhanced performance

• Barometric reference via Druck RPT• Highly reliable internal PSU, same as

DPI 520 (excellent MTBF) • Manifolds machined from a single

block of metal with latest pick ‘n’ place,surface mount technology

• Extruded aluminum chassis and steel plates for body strength

• Moulded ABS front panel for ergonomically pleasing look and mechanical strength

DPI 515 APPLICATIONS DPI 515 APPLICATIONS

DPI 520 APPLICATIONSDPI 520 APPLICATIONS