Calibration Intervals

General Equipment - Calibration and Checks June 2013

© Copyright National Association of Testing Authorities, Australia 2013

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General Equipment - Calibration and Checks

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General Equipment- Calibration and Checks

All parameters that contribute to the overall quality of a test or calibration require measurement traceability. This includes measurements that have a significant effect on the accuracy or validity of the result being reported. Therefore equipment that is used to provide a measurement of these parameters must be calibrated.

A facility must demonstrate how it has determined which parameters are critical (and non critical) to the overall quality of test and calibration results. As an example, critical parameters may be analytical or quantitative data, or measurements which have a significant contribution to the final result and associated measurement uncertainty.

Definitions

‘Metrological Traceability’ is the property of a measurement result whereby

the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty (ISO/IEC

Guide 99 (2007) – 2.41).

Applying this definition, the measurement uncertainty must be determined for each link of the traceability chain back to a realised standard. The last step of the link must also be included e.g. equipment calibrated in-house through use of a reference item or reference material.

To demonstrate evidence of measurement traceability, each link of the traceability chain, including its measurement uncertainty, must be reviewed.

NATA’s policy for measurement traceability is detailed in Policy Circular 11.

‘Calibration’ is an operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication (ISO/IEC Guide 99 (2007) – 2.39).

As detailed in Policy Circular 11 and under clause 5.6, of the ISO 17025 Standard Application Document, calibrations are normally carried out by an external calibration authority and an endorsed test report is obtained for this work. For calibrations performed in-house, a facility must demonstrate the capability to do so according to the criteria set out in ISO/IEC 17025 sub-clause 5.6.2.1 and NATA Policy Circular 12.

Note: Some items of equipment such as sound level meters are designed to have a level adjustment before each use by applying a known source to the input of

the instrument. Although sometimes called a ‘calibration’ or ‘internal calibration’ by the manufacturer, it is a single point level adjustment and is not to be confused with a full calibration which provides measurement traceability across the instruments full measurement range.

‘Check’ is a measurement of at least one point in a range of a measuring instrument or system or material against a known value to confirm that it has not deviated significantly from its original calibrated value. It is also an examination of the condition of an artefact i.e. the reference of known value, to determine that it has not been adversely affected by constant use.


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Checks are usually carried out in-house by the facility staff. If, however, the checks are carried out by an external authority then an endorsed report must be obtained.

By performing a check on an instrument, a facility is able to determine if the instrument has changed since its last calibration. By performing regular checks, the interval between periodic calibrations may be extended.

Alternatively, in some applications, where an instrument is used for comparative results and it has been determined that measurement traceability is not required, a check of the instrument’s measurement functionality may be deemed acceptable.

Calibration and checking intervals

Facilities are responsible for establishing their own equipment assurance program. This is to ensure that all equipment used satisfies the need to produce consistent and reliable and where appropriate, traceable results.

When establishing an equipment assurance program, consideration must be given to the following:

history of stability;

frequency of use;

accuracy required;

requirement for traceability of measurement;

ability of staff to perform in-house checks;

successful participation in proficiency testing programs.

Equipment assurance programs move the emphasis from a high reliance on demonstration of equipment conformance at the time of calibration to:

having a greater contribution from more frequent checks against reference items or materials;

cross-checking against similar systems;

the checking of particular critical features.

Equipment calibration and check programs should cover:

commissioning of new equipment (including initial calibration and checks after installation);

operational checking (checking during use with reference items or materials*);

periodic checking (interim but more extensive checking, possibly including partial calibration);

scheduled maintenance by in-house or specialist contractors;

complete recalibration.

Note: * If no appropriate reference items or materials are available, then the facility shall demonstrate that the alternatives used have sufficient traceability, stability, homogeneity and accuracy such that the method and subsequent results can be deemed fit for purpose.

Where an equipment assurance program is not established by the laboratory,


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then the minimum intervals for calibrations and checks are as detailed in the following table.

The table includes the most common items of equipment and it should not be assumed that measurement traceability, and thus calibrations (and checks), are not applicable for equipment not listed.

The intervals indicated in the table are based on the assumption that:

typical uses of the equipment and the required accuracy have been considered;

the equipment is of good quality, of proven adequate stability and is properly used and housed;

the facility has both the equipment capability and staff expertise to perform the requisite in-house checks;

all of the subsidiary checks indicate satisfactory operation.

Shorter intervals between calibrations and/or checks may be required when the equipment operates under less than ideal conditions. If any suspicion of damage arises, the equipment must be recalibrated immediately and thereafter at reduced intervals until it is shown that stability has not been impaired. Furthermore, reduced intervals between calibrations and/or checks may also be required in particular testing applications or with particular equipment configurations.

An interval may be extended if the facility is able to justify the extension, subject to statutory, contract, specification or test standard requirements.

In order to assist facilities to demonstrate good control of their tests and measurements and to reduce their operating costs, NATA encourages facilities to develop equipment assurance programs.

Details of the documents referenced may be found within the body of the following table.


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General Equipment Table

Item of equipment Calibration

interval (years)

Checking interval

(months)

Procedures and references

Accelerometers

Piezoelectric types 3

12 Intercomparison.

On use Check against vibration calibrator.

Servo, strain gauge and piezoresistive types (CD or 0Hz response

2 On use Check by inversion

Air flow nozzles Initial

12 Check throat diameter.

Anemometers 1

Angle gauges 2 then 4

Balances 3 The Calibration of Weights and Balances EC Morris and KMK Fen

12 Service.

6 Repeatability check. NATA Technical Note 13.

1 One point check. NATA Technical Note 13.

Barometers Initial NATA Technical Note 8.

Biological safety cabinets (BSC)Class I and Class II for

personnel and environment protection

1 AS 2252.4

Callipers 2 AS 1984

Dial gauges 2 AS 2103

Digestion blocks e.g. blocks or mantles used for Kjehldahl Nitrogen, Chemical Oxygen Demand or metal digestions

Initial, then 12 and after repair or maintenance

Temperature variation check across working spaces or recovery check with a difficult to digest standard/sample e.g. nicotinic acid for TKN digestion.

Dimensional Measuring machines

Precision scales 10

Geometric tests 5

Micrometer heads 3

Coordinate Measuring Machines (CMMs)

2


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interval (years)

Checking interval

(months)


6 Intermediate volumetric check (eg ball bar).

Displacement transducers (LVDT)

2

On day of use

Against length standard.

Electrical instruments

Digital multimeters

(DMM), and other types of meters which measure electrical parameters such as volts, resistance, current, capacitance etc. Including: Analog meters, Data loggers, Chart recorders, Watthour and Varhour meters.

1 Calibrate over all ranges and parameters of use including calibration across frequency (Hz) of use.

6 Compare with meters of similar resolution.

Environmentally controlled enclosures including

Incubators, Ovens, Furnaces, Conditioning enclosures (ageing), Refrigerators and Freezers, Water baths

Temperature 3 Spatial uniformity, IEC 60068-1; 60068-2-38; 60068-2-39; AS 2853

On use Monitor temperature at at least one point

Humidity 3

12 Spatial uniformity of temperature.

CO2 On use Monitor level.

Infra Red, Ultraviolet and Visible

3

On use Check operation of the lamps.


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interval (years)

Checking interval

(months)


Pressure / Vacuum On use Monitor level.

Extensometers

Contact and Optical 2 AS 1545. Grading requirements apply.

Feeler gauges 2 AS 1665

Flowmeters

Differential Pressure meters, orifice meters, venturi meters and Anubar

2

6 Flow or dimensional calibration plus inspection for wear and damage. Pressure to be calibrated as appropriate.

Electronic Thermal, Mass Flow

1 Where high temperature or corrosive gases are monitored a shorter interval is recommended.

Laminar flow meters 2

6 Inspect for damage or contamination

Sonic Nozzle

Reference 0.1% 3 6 Inspect and clean.

Working 0.5% 6 6 Inspect and clean.

Soap Film 2

Positive Displacement Meters

2

Provers 2

6 Thermometer ice points and pressure readout checks for stability

Rotary meter 2

6 Inspect for contamination or damage

Rotameters Variable area meters

2

3 Visual inspection for damage to float edges or ball float for pitting

Turbine meters 2

6 Inspect for contamination or damage of turbine blades

Turbine meters (Pelton Wheel/Miniature)

1

Vortex shedding 2

6 Inspect for contamination of the bluff body


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interval (years)

Checking interval

(months)


Wet test meters 2

Before use Set water level before use

Force testing machines

Dead Weight 5 AS 2193

Elastic Dynamometer 2 AS 2193

Hydraulic, pneumatic 2 AS 2193

6 Cross head speed (for constant rate of extension machines) and pressure

Fume cupboards (cabinets)

2 Depending on cabinet type either AS/NZS 2243.8 or AS/NZS 2243.9

Gauge blocks 2 then 4 subsequent

AS 1457

Hygrometers

(Assmann and sling psychrometers)

10

6 Compare thermometers at room temperature with wick dry. AS 2001.1 Appendix C

Thermohygrographs (hair)

1

Weekly Check against a calibrated psychrometer.

Electronic types (eg. digital psychrometer)

1

Digital psychrometers (not electrical impedance sensors)

3

6 Check against a calibrated thermometer at ambient temperature.

Electrical impedance humidity probes

1 2 yearly if used only under ambient conditions.

Dew or frost point hygrometers

2

Levels (precision) 4

12 12- monthly single point check for electronic levels

Load cells and Large scale weighing devices

2 AS 2193

On day of use

If amplification is variable, perform shunt calibration check.

Luminance meters &


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interval (years)

Checking interval

(months)


Illuminance meters

Digital 1

Analogue 2

Manometers

Liquid 10

Electronic 1

Masses

Stainless steel, nickel chromium alloy

3

Other alloy and iron Class III

2

For proof loading purposes

5 Against calibrated load cell (in house) or weighing device, which achieves the specified accuracy.

Micrometers 5 AS 2102

1 Zero, one point (against gauge block) and condition of anvils.

Optical electronic distance measurement equipment

2

Optical projectors 5

pH meters Daily or on use

Check against two buffer solutions as per manufacturer’s instructions.

Pipettes (POVAs) * * *Equipment calibration and/or checking requirement will be dependent on the criticality of volume dispensed and/or the repeatability of dispensed volume required by the test method.

Pressure equipment

Test gauges used for calibration of industrial gauges

1 AS 1349 for Bourdon tube types

Industrial gauges not subject to shock loading

1 AS 1349 for Bourdon tube types

Industrial gauges subject to shock loading.

6 months AS 1349 for Bourdon tube types

Digital pressure gauges

1

Pressure transducers 1


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interval (years)

Checking interval

(months)


Pressure transmitters 1

Calibrators 1

Radiation thermometers including Visible and Infrared Pyrometers

2 Initial test of target size dependence should be performed Initial calibration should include sufficient points to confirm linearity

12 Check at one point in range or at ice point

Disappearing filament pyrometers

3

Pyrgeometers 3

Sieves Initial Compliance certificate to AS 1152, BS 410.

12 More or less frequent checks may be required against a reference set or a suitable reference material.

Sound measuring devices Including Sound level meters & Noise dosimeters

2

On use Check against acoustic calibrator or pistonphone

Acoustic calibrators including Pistonphones and sound sources

1 AS/IEC 60942

6 Intercompare

Spectrophotometers and Spectroradiometers

6 Wavelength accuracy, bandpass, absorbance, stray light error, linearity of response, repeatability and matching of cells.

On use A blank and at least 2 points on the calibration curve must be checked.

Tape measures, rules

Tape measures and retractable pocket rules

Initial AS 1290.4

24 to 60 Check at maximum length, depending on use and accuracy required.

Steel rules Initial BS 4372

6 1 point check within operating range.

Thermocouples

‘Base metal’ type, sheathed

2 For use up to 400°C. For use from 400°C to 1300 °C the same immersion depth must always be used


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interval (years)

Checking interval

(months)


(or a greater depth of immersion). Homogeneity must be assessed as part of their recalibration.

‘Base metal’ type, wire 2 For use up to 300o C. Replace if used

above 300o C.

Stored reels 10 Reel of wire – 4 samples of wire from end points and middle of reel.

‘Rare metal’ type 3 3 years or after 100 hours above 500o

C whichever is sooner.

Thermocyclers * 12 *Equipment calibration and/or checking requirement will be dependent on test method/kit. When performing a verification, measure temperature uniformity across the block for a number of cycles, logging time spent at temperature using a measurement frequency of at least 2 Hz; Check for excessive overshoot and undershoot (recovery rate) of temperature between temperature point. Perform verification of digital display accuracy as required.

Thermometers

Liquid–in–glass

5

6 Check at ice point. NATA Technical Note 19 or against reference thermometer at 1 point in range

Resistance

-40°C to 250°C 5

6 Check at ice point.

<-40°C and >250°C 2

6 Check resistance at ice point.

Measuring instrument AC Bridge type, Reference and Working

5

Measuring instrument DC Bridge type

2

6 Check at ice point.


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interval (years)

Checking interval

(months)


Digital indicating systems, with or without a temperature sensor, hand held or bench type, single and multichannel. (Includes temperature loggers)

2

6 Check against a reference device at the temperature of use. If used at more than one temperature, choose the most critical temperature. Check at ice point if the facility does not have a reference device. (For data loggers the reference device can not be another data logger of the same type).

Timing devices

Stop watches, clocks (mechanical and electrical devices)

6 Check using Telephone Speaking Clock or GPS signal

Torque wrench and transducers, Screwdrivers

1

6 In house cross check of overlapping ranges if possible.

Velocity transducers 3

24 Check frequency response and sensitivity.

Volumetric glassware Initial (on commissioning and subject to nature of intended use)

AS 2162.1; BS 1797


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REFERENCES

This section lists publications referenced in this document. The year of publication is not included as it is expected that only current versions of the references shall be used.

Australian Standards

AS 1152 Specification for test sieves

AS 1290.1 Linear measuring instruments used in construction - General requirements

AS 1290.4 Linear measuring instruments used in construction - Retractable steel pocket rules

AS 1349 Bourdon tube pressure and vacuum gauges

AS 1457 Geometrical Product Specifications (GPS) - Length standards - Gauge blocks

AS 1545 Methods for the calibration and grading of extensometers

AS/NZS 1665 Welding of aluminium structures

AS 1984 Vernier callipers (metric series)

AS 2001.1 Methods of test for textiles - Conditioning procedures

AS 2102- Micrometer callipers for external measurement

AS 2103 Dial gauges and dial test indicators (metric series

AS 2162. Verification and use of volumetric apparatus - General - Volumetric glassware

AS 2190 Clinical maximum thermometers - Mercury-in-glass

AS 2193 Calibration and classification of force-measuring systems

AS/NZS 2243.8 Safety in laboratories - Fume cupboards

AS/NZS 2243.9 Safety in laboratories - Recirculating fume cabinets

AS 2252.1 Biological safety cabinets - Biological safety cabinets (Class I) for personnel and environment protection

AS 2853 Enclosures - Temperature-controlled - Performance testing and grading

AS IEC 60942 Electroacoustics - Sound calibrators

Other Standards

BS 410. Stainless steel test sieves

BS 1797 Schedule for tables for use in the calibration of volumetric glassware

BS 4372 Specification for engineers' steel measuring rules

IEC 60068-1 Environmental testing. Part 1: General and guidance;

IEC 60068-2-38 Environmental testing - Part 2-38: Tests - Test Z/AD: Composite temperature/humidity cyclic test;

http://www.saiglobal.com/online/script/Details.asp?DocN=stds000012892


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IEC 60068-2-39 Environmental testing - Part 2: Tests. Test Z/AMD: Combined sequential cold, low air pressure, and damp heat test

ISO/IEC Guide 99 International vocabulary of metrology -- Basic and general concepts and associated terms (VIM)

ISO/IEC 17025 General Requirements for the competence of calibration and testing laboratories

NATA Publications

NATA Policy Circular 11 Policy on Metrological Traceability

NATA Policy Circular 12 NATA Requirements for the Performance of Calibrations In-house

NATA Technical Note 8 The in-situ calibration of Barometers

NATA Technical Note 13 User Checks of Balance Calibration

NATA Technical Note 19 Liquid-in-Glass Thermometers – Selection, Use and Calibration Checks

Other Publications

The Calibration of Weights and Balances EC Morris and KMK Fen

Amendment Table

The table below provides a summary of changes made to the document with this issue.

Section Amendment

Equipment table

Thermocyclers * 12 *Equipment calibration and/or checking requirement will be dependent on test method/kit. When performing a verification, measure temperature uniformity across the block for a number of cycles, logging time spent at temperature using a measurement frequency of at least 2 Hz; Check for excessive overshoot and undershoot (recovery rate) of temperature between temperature point. Perform verification of digital display accuracy as required.

Equipment table

Pipettes (POVAs) * * *Equipment calibration and/or checking requirement will be dependent on the criticality of volume dispensed and/or the repeatability of dispensed volume required by the test method.

Additional guidance as above inserted into the body of the equipment table. Guidance for thermocyclers as above replaced earlier text in the previous version.

Calibration Intervals

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