nabl 125

NABL 125

NABL

NATIONAL ACCREDITATION BOARD FOR TESTING AND CALIBRATION LABORATORIES

SPECIFIC CRITERIA for

CALIBRATION LABORATORIES IN FLUID FLOW DISCIPLINE

ISSUE NO : 04 ISSUE DATE: 28.03.2008

AMENDMENT NO : 00 AMENDMENT DATE: -`

AMENDMENT SHEET Sl

Page No.

Clause Date of No. Amendment

Amendment made

Reasons

Signature QM

Signature Director

1 2 3 4 5 6 7 8 9 10

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National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 125 Issue No: 04

Specific Criteria for Calibration Laboratories in Fluid-Flow Discipline Issue Date: 28.03.2008 Amend No: 00 Amend Date: --

Page No: i

PREFACE This document clarifies NABL’s stand on the accuracy and measurement capability levels.

NABL intends to uphold its policy of granting accreditation to laboratories as per their requirements of accuracy and measurement capability.

These criteria are applicable to laboratories, which perform repetitive calibrations in various parameters and desire accreditation from NABL. These criteria provide guidelines for use by laboratories and those who are associated with the programme of accreditation of calibration laboratories e.g. experts, assessors, officials engaged with day-to-day activities of accreditation. These criteria cover all areas/ fields of calibration.

This document provides the laboratories with necessary information on the requirements for assessment/ surveillance and to assist them in carrying out internal audit of their system.

The information in this document has been compiled in three parts.

PART – I General Guidelines for Accreditation of Calibration Laboratories This part contains relevant information on general requirements of a laboratory engaged in Calibration in the field of Fluid Flow Measurements. The laboratory seeking accreditation must comply with the requirements of ISO/ IEC 17025: 2005 and this document.

PART – II Specific Criteria for Accreditation of Calibration Laboratories This part provides information on special requirements of the laboratories, which are specific to the parameters covered in the respective fields

PART – III Guidelines Regarding Accuracy of Standards & Measurement Uncertainty in Calibration This part contains guidelines of the Specified accuracies of measurement standard and uncertainties of measurement generally achieved in laboratories using equipment and instruments of different classes of accuracies/ uncertainties for different parameters under Fluid Flow measurements.

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National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 125 Issue No: 04

Specific Criteria for Calibration Laboratories in Fluid-Flow Discipline Issue Date: 28.03.2008 Amend No: 00 Amend Date: --

Page No: ii

CONTENTS Sl.

Title

Page No.

Amendment Sheet

i

Preface

ii

Contents

iii-iv

PART - I 1

Scope

1

2

Criteria for Accreditation

2

3

Organisation

2

4

Management System

3

5

Personnel

4

6

Accommodation and Environmental Conditions

5

7

Equipment

6

8

Range, Uncertainty of Measurement & Traceability

7

9

Calibration Certificate/ Report

7

10

Proficiency Testing Programme

8

PART – II 1

Scope

9

2

Range and Uncertainty of Measurement

10

3

Environmental Conditions

10

4

Special Requirements of Laboratory

10

5

Repair and Maintenance

12

6

Storage and Packaging

12

7

Safety Precautions

13

8

Additional Requirements for the Calibration of the Instruments Used in Open Channel, Petroleum and Similar Liquids and Gases

13

Appendix: Conditions for Calibration

15

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National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 125 Issue No: 04

Specific Criteria for Calibration Laboratories in Fluid-Flow Discipline Issue Date: 28.03.2008 Amend No: 00 Amend Date: --

Page No: iii

Sl.

Table

Page No.

PART – III General Remarks and Environmental Conditions

17

1.

Water Flow Measurement

18

2.

Petroleum and other Non-aqueous Liquid Flow Measurements

18

3.

Gas Flow Measurement

18

4.

Gas velocity, range from 0.1m/s to 50 m/s

19

5.

Viscosity Measurement

19

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National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 125 Issue No: 04

Specific Criteria for Calibration Laboratories in Fluid-Flow Discipline Issue Date: 28.03.2008 Amend No: 00 Amend Date: --

Page No: iv

PART – I

GENERAL GUIDELINES FOR ACCREDITATION OF CALIBRATION LABORATORIES

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1.0

SCOPE

1.1

Calibration laboratories are accredited by NABL after it is demonstrated that a laboratory complies with the requirements of international standard ISO/IEC 17025: 2005. In view of generic nature of the standard the requirements stated there in, need to be further redefined in specific fields of calibration. This specific criteria lays down those specific requirements in the field of fluid flow calibration. This part of the document thus amplifies the generic requirements for fluid flow calibration and supplement the requirements of ISO/IEC 17025:2005. Laboratories seeking NABL accreditation in the field of fluid flow calibration must also comply with the requirements stated in this part.

1.2

Best Measurement Capability (BMC) is one the parameters that is used by NABL to define the scope of an accredited calibration laboratory, the others being parameter/quantity measured, standard/master used, calibration method used and measurement range. The BMC is expressed as ”the smallest uncertainty that a laboratory can achieve when calibrating a device that is effectively ideal”. It is an expanded uncertainty estimated at a confidence level of approximately 95% corresponding to a coverage factor k=2.

The laboratory’s ability to achieve their claimed BMC shall be evaluated based on its performance during the on-site assessment and by review of proficiency testing results, wherein the laboratory has participated.

1.3

The definition of BMC implies that within its accreditation a laboratory is not permitted to report a smaller uncertainty of measurement than the BMC endorsed on its scope of accreditation. This means that the laboratory shall be required to state a uncertainty not better than that corresponding to the BMC whenever it is established that the actual calibration process adds significantly to the uncertainty of measurement. The BMC is applicable only to the results for which the laboratory claims its status as accredited laboratory. It is therefore a realistic means for customers to select and compare accredited laboratories’ capabilities.

1.4

All the parameters for which accreditation is sought must be expressed in S.I. Units, wherever applicable.

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National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 125 Issue No: 04

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2.0

CRITERIA FOR ACCREDITATION Accreditation of a calibration laboratory will require assessment in respect of organization,

staff,

equipment

and

traceability

of

its

calibration,

laboratory

accommodation and environmental conditions, safety, handling of calibrated equipment and equipment under calibration, measurement capability and recording system, etc., as per ISO/ IEC 17025: 2005 General Requirements for the Competence of Testing and Calibration Laboratories. Some explanatory notes of this document are given in the following clauses.

3.0

ORGANISATION

3.1

The Calibration Laboratory shall be organized in such a way that all staff members are aware of both the extent and the limitations of their area of responsibility.

This

organization shall specify and document the responsibility and authority of the Head of the Calibration Laboratory/Technical Manager/Quality Manager with direct access to the top management. All personnel will perform or verify work affecting the quality of calibrations as per general guidelines and specific criteria laid down for the accredited parameters. The calibration laboratory shall be organized in such a way so as to ensure the integrity and training of its staff and operations for ensuring unbiased Calibration.

3.2

A Deputy Head/Technical Manager may also be nominated to take over the responsibility in the absence of the Laboratory Head. In case there is no Deputy-incharge, the authorities concerned may appoint a suitable person to look after the laboratory, under intimation to NABL. The laboratory shall also clearly define authorized signatory for the calibration certificates/reports issued by the laboratory.

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Specific Criteria for Calibration Laboratories in Fluid-Flow Discipline Issue Date: 28.03.2008 Amend No: 00 Amend Date: --

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4.0

MANAGEMENT SYSTEM

4.1

The calibration laboratory shall have a Quality Manual which shall be maintained up-todate and available for scrutiny, in compliance with ISO/ IEC 17025: 2005 and NABL requirements, with emphasis on following information: a)

A quality policy statement, including objectives and commitments by the top management.

b)

A statement on the organization of the calibration laboratory.

c)

Names, qualifications and experience of the persons responsible for managerial, and scientific/ technical activities.

d)

A clearly defined charter of responsibility showing the relationship between management and support services.

e)

Scope and operation together with information on measurement capability and traceability of calibration of all measuring instruments to national measurement standards.

f)

The reference of document number on detailed calibration procedures adopted in the laboratory, which should be compiled in the form of a manual for the use of calibration staff.

g)

The reference list of all national/international standards being referred to or used in the performance of calibration work (copies of such standard specifications should be available in the laboratory for the use of calibration staff.)

h)

All amendments made in any of the documents must be dated and listed in the Quality Manual and brought to the notice of NABL.

4.2

The calibration facilities established in accordance with the general guidelines and specific criteria shall be audited periodically and reviewed by or on behalf of the management to ensure the continued effectiveness of the system.

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4.3

The calibration laboratory shall clearly specify, document and make known to the customers, the administrative and other procedures to be followed for getting calibration done from the laboratory.

The procedure for redressal of technical

complaints should also be clearly specified and documented.

4.4

The laboratory shall have authorized signatories for approving and issuing calibration certificates for each calibration parameter as mentioned in the scope of accreditation.

Any officer competent to evaluate calibration results critically and occupying a position involving responsibility for the adequacy of calibration results is eligible for approval by NABL as an authorized signatory of endorsed calibration documents. Consequently approved

authorized

signatories

must

demonstrate

understanding

of

these

requirements.

5.0

PERSONNEL

5.1

The calibration laboratory shall have adequate number of qualified competent and trained personnel as follows: Laboratory personnel performing calibration: Diploma in Engineering (relevant branch) or Science graduate (with Physics, Chemistry and Mathematics) with 1 year of relevant experience or ITI with at least 5 years of experience in the field of Fluid Flow Measurements and calibration practices in the relevant parameters.

Authorized Signatory: Bachelor of Engineering/Post Graduate in Science (relevant branch) with 1 year of relevant experience or Diploma in Engineering (relevant branch) with minimum 3 years of experience in the field of Fluid Flow Measurements and calibration practices.

5.2

Arrangements for improvement of qualifications and periodic refresher courses and practical training should also exist for the staff so as to keep them in touch with latest developments in the relevant fields.

5.3

The Head of the calibration laboratory shall be at least a Post Graduate in Physical Science or Graduate in Mechanical/ Instrumentation Engineering or equivalent with specialised knowledge and adequate experience in precision Fluid Flow and other relevant parameter measurements. In exceptional cases, a graduate in physics or diploma holder in Mechanical Engineering with long experience could be accepted.

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6.0

ACCOMMODATION AND ENVIRONMENTAL CONDITIONS

6.1

Vibrations The calibration area shall be adequately free from vibrations generated by central airconditioning plants, vehicular traffic and other sources to ensure consistent and uniform operational conditions. The laboratory shall take all special/protective precautions like mounting of sensitive apparatus on vibration free tables and pillars etc., isolated from the floor, if necessary.

6.2

Acoustic Noise Acoustic noise level in the laboratory shall be maintained to facilitate proper performance of calibration work. A threshold noise level of 60 dBA is recommended unless otherwise stated.

6.3

Illumination The calibration area shall have adequate level of illumination.

Where permissible,

fluorescent lighting is preferred to avoid localized heating and temperature drift. The recommended level of illumination is 450-700 lux on the working table with glare index of 19 for the laboratory.

6.4

Environmental Conditions and Monitoring The environmental conditions for the activity of the laboratory shall be such as not to adversely affect the required accuracy of measurement. Facilities should be provided whenever necessary for recording temperature, pressure and humidity values prevailing during calibration. The atmospheric conditions maintained in the laboratory during calibration should be reported in the calibration report/certificate.

6.5

Entry to the Calibration Area As far as possible, only the staff engaged in the calibration activity shall be permitted entry inside the calibration area.

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7.0

EQUIPMENT Each calibration laboratory should have measurement standards or equipment of required accuracy in respect of each parameter covered by it in order to be able to realize and to substantiate the corresponding measurement capability claimed.

Stability of the standards, accuracy of the values realized through them and repeatability, should be regularly monitored.

Any bias resulting from ageing of standards should be precisely determined.

Instructions for operating each standard and equipment/instrument should be readily available for use by the laboratory staff members.

7.2

The standards/measuring equipment of the laboratory should be calibrated at regular intervals, with higher accuracy standards.

The calibration certificates, performance

history sheets in respect of the reference secondary/working standards and measuring equipment should be held safely by the laboratory.

7.3

7.4

Proper record shall be maintained for each standard and equipment with the following information: a)

Name of the equipment

b)

Manufacturers name and address

c)

Type, range, identification and serial number

d)

Date of procurement and commissioning

e)

Details of Calibration

f)

Details of maintenance and repairs

g)

Performance history with dates

h)

Availability of service manual

Details of periodic calibration schedule of new and old standards and measuring equipment should be worked out in consultation with higher accuracy laboratory and this schedule should be observed.

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National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 125 Issue No: 04

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7.5

Details of re-calibration of used, serviced and repaired equipment should also be available and proper precautions shall be observed to identify equipment, which are not in service.

7.6

Any alterations in the observations/data shall be signed by the calibration staff and duly authenticated.

Instructions to this effect should be printed on data sheet used for

writing observations/data in the laboratory.

8.0

RANGE, UNCERTAINTY OF MEASUREMENT AND TRACEABILITY

8.1

The level of uncertainty of measurement of the standards to be maintained by a laboratory and the measurement capabilities to be generated by it in respect of various parameters shall be as demonstrated during assessment.

8.2

All the Standard Equipment of the Laboratory shall be calibrated periodically against Calibration Standards of a laboratory accredited by NABL/ equivalent MRA partners having superior measurement capability or NPL/ other international NMIs.

8.3

In the event when the levels of uncertainty of measurement and measurement capability of an accredited laboratory are revised, the laboratory shall be required to intimate NABL secretariat and undergo surveillance / reassessment as applicable.

9.0

CALIBRATION CERTIFICATE/REPORT

9.1

The result of calibration carried out by the calibration laboratory, shall be presented in a comprehensive manner, using a standard format which shall unambiguously and objectively present the measurement results and all relevant information in order to facilitate easy comprehension and usage.

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9.2

9.3

The calibration report/certificate shall include the following additional information: a)

Date of receipt of the item and date of completion of the calibration work

b)

Environmental conditions maintained during the measurements

c)

Signature and title of authorized person (authorized signatory) accepting responsibility for the report and date of issue

d)

A statement of the accreditation measurement capability relevant to the job under calibration

e)

A symbol of NABL or statement or both clarifying the status of accreditation of the laboratory.

f)

The Uncertainty of measurement

g)

An evidence that the measurements are traceable to National/ International Standards through unbroken chain of Accredited Laboratories.

The calibration report/ certificate shall not contain any recommendation on the calibration interval except where this has been agreed with the client. This requirement may be superseded by legal regulations.

10.0

PROFICIENCY TESTING PROGRAMME

10.1

To give further assurance to the accuracy or Uncertainty of measurements, a laboratory will be required to participate, from time to time, in Proficiency Testing Programmes. The laboratory shall remain prepared to participate in the Proficiency Testing Programme through inter-laboratory, inter-comparison schemes wherever it is technically feasible. In case any abnormalities, in terms of En number are detected through these inter-comparisons, appropriate corrective action will be taken, the standards/equipment shall be replaced/ repaired and re-calibrated with a higher accuracy standard. Reports on such inter-comparisons should be documented with reference. The Proficiency Testing practice should be included in the Quality Manual.

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PART – II

SPECIFIC CRITERIA FOR ACCREDITATION OF CALIBRATION LABORATORIES IN THE FIELD OF FLUID - FLOW MEASUREMENTS

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1.0

SCOPE

1.1

An accredited laboratory shall be classified as calibration laboratory for accredited parameters in the field of Fluid Flow Measurements in accordance with its measurement capability.

1.2

A calibration laboratory seeking accreditation to offer calibration services in the field of Fluid Flow measurements will generally carry out calibration in

1.3

a.

Water Flow

b.

Petroleum and non-aqueous liquid flow

c.

Gas flow

The accredited calibration laboratory shall be mainly concerned with measurements of one or more of the following parameters

1.4

a.

Flow rate by mass

b.

Flow rate by volume (at specified temperature and pressure, for gases)

c.

Quantity by mass

d.

Quantity by volume (at specified temperature and pressure, for gases)

e.

Velocity at a point

f.

Mean velocity in close conduits for water and gases as well as in open channel for water

g.

Viscosity of liquids and gases

Measurements of the following parameters is an additional requirement of fluid fuels : a.

Flow rate of energy value associated with flowing fuel

b.

Quantity of energy associated with fuels

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2.0

Range and Uncertainty of Measurement

2.1

A calibration laboratory will be accredited according to its measurement capability expressed in terms of uncertainty.

3.0

Environmental conditions

3.1

The laboratory shall specify limits on the environmental conditions to be achieved in the laboratory. The condition shall appropriate to the level of accuracy required for calibration undertaken by the laboratory.

The environmental conditions shall be monitored at appropriate intervals and calibrations stopped when the environmental conditions fall out side of specified limits.

3.2

The acoustic noise in the laboratory area where measuring instruments are kept, shall be maintained below an accepted threshold level of 80 dBA

3.3

Temperature extremes of the working fluid must be avoided and difference between the fluid temperature and the ambient air temperature should not exceed 10째 C, where a approval is sought for better than +/- 0.5% level of uncertainty.

3.4

For obtaining desired accuracy of measurement adequate stability in temperature of medium shall be maintained.

4.0

Special requirements of Laboratory

4.1

The calibration laboratory shall make arrangement for regulated and Un interrupted power supply. The recommended regulation level is +/- 1% or better on the calibration bench.

4.2

Relevant IS Specifications (IS:1248, 4722) regarding the total harmonic content and variation in supply frequency should be followed. Voltage stabilizers of low harmonic content should be used to comply with this requirement.

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4.3

Adequate arrangements shall be made by the laboratory so as to ensure temperature gradient not exceeding 1.5째 C per hour inside the laboratory in case of power failure

4.4

The laboratory shall use, if necessary, isolation transformers and filters etc. to ensure minimization of ground current and effects of mains hum interference.

4.5

The power supply to the calibration laboratory shall be directly obtained from the substation as far as possible and shall not be on the same feeder line which is supplying power to workshops and other production areas which require operation of heavy duty machines.

4.6

Effective mains earthing provided in accordance with relevant specification IS: 3043.

This shall be periodically checked and stray couplings minimized.

4.7

Special care shall be taken about the location of magnetic field sources like, transformers, looped wires, ferrous materials etc., in order to minimize magnetic interference in the measurements.

4.8

Adequate screening of the laboratory against electro magnetic interference shall be done if necessary. By pass filters should also be provided to minimize conducted interference effect on the electronic equipment. Special shielding chambers should be provided in the laboratory for measurements, Particularly when signal to noise ratio is a disturbing factor for accurate measurements.

4.9

The reference standards shall be maintained at temperatures specified for their maintenance in order to ensure their conformance to the required level of operation and traceability. The laboratory should have specific facilities required for carrying out the calibrations of the parameters chosen.

4.10

The laboratory shall be sealed against dust and external air pressure. Positive air pressure shall be maintained inside the laboratory. Laboratory should be clean.

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4.11

Adequate protective measures, like use of transient suppressors etc shall be taken by the laboratory to ward off high current spikes and transients emanating from switching off and on of heavy machines, surges in power lines and other such reasons, from reaching the electronics equipment in general and computer based systems involving data storage facilities in particular.

5.0

Repair and maintenance

5.1

A separate repair and maintenance facility, adequately equipped with repair facilities and qualified and experienced manpower, shall be available in house or by any other means, effectively accessible to the calibration laboratory. This facility shall also assist in identifying the preventive maintenance measures which should be brought to the attention of the personnel engaged in calibration work for taking necessary action. The repair facility should also cover digital and programmable instruments.

5.2

Every repaired equipment shall invariably be recalibrated through in house facility or by higher accuracy laboratory before being used for further calibration work.

6.0

Storage and Packaging

6.1

The standards/ measuring instruments/ equipment received by the laboratory for calibration shall be safely stored in proper environmental conditions according to the instructions given by the supplier.

6.2

The laboratory shall have adequate arrangements for packaging of calibrated instruments and may assist the user, if necessary, about the procedure and precautions to be taken by them for packaging and transportation of equipment to the calibration laboratory and back.

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7.0

Safety Precautions

7.1

Relevant fire extinguishing equipment for possible fire hazards should be available in the corridors or convenient places in the laboratory. Adequate safety measures against electrical, chemical fire hazards must be available at the work place.. Laboratory rooms/areas where highly inflammable materials are stored/used should be identified.

Access to the relevant fire equipment should be assured near these rooms/areas.

7.2

Specification SP. 31-1986, a special publication in the form of a wall chart, giving the method of treatment in case of electric shock, should be followed. The chart should be placed near the power supply switch gear and at the other prominent places as prescribed under Indian electricity rules 1956.

8.0

Additional requirements for the calibration of the instruments used in open channel, Petroleum and similar liquids and gases

8.1

An appropriate gauge must be available for measuring the elevation of the water surface at the device being calibrated. Proper account must be taken of various factors which might influence water level measurements, such as surface tension, vibration, gauge well, lag etc.

8.2

Instruments and equipment must be available for datum level determinations and technique used must be such that the datum level determinations are reliable and that the levels of uncertainty obtained are compatible with the uncertainties of the gauge readings.

8.3

Precautions must be taken to ensure that materials of construction of the calibration equipment do not react chemically with the working fluid. (for example, with kerosene fuel, the presence of copper alloys can cause a significant change in physical properties with in an hour at a temperature of 120째 C.)

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8.4

For volumetric calibration of gases, the absolute temperature and the absolute pressure of the gas must both be measured to a percentage uncertainty of one fifth of the applicable approved uncertainty level of the flow rate or the quantity measurement.

Sufficient observations of absolute pressure and absolute temperature measurement must be made to take account of any unsteadiness in the gas flow. Due consideration must also be given to distance/velocity lags through the calibration system and to the speed of the response of the absolute pressure and absolute temperature measuring equipment.

8.5

Protection against fire hazards (for petroleum products) 8.5.1 Adequate means must be available with the laboratory to prevent the accumulation of toxic smoke/flammable vapour.

8.5.2 The laboratory should observe adequate safety precautions against fire hazard due to flammable liquids. It should produce evidence from the appropriate authority.

Some of the conditions normally encountered for calibration in Fluid Flow measurements are given in Appendix – I

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National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 125 Issue No: 04

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Appendix – I CONDITIONS FOR CALIBRATION 1

Permitted deviations in the consistency of the flow rate may be as follows: Uncertainty of measurement(%)

2

Corresponding permissible deviation(%)

0.1

0.3

0.3

0.5

0.5

1.0

1.0

2.0

2.0

4.0

Density of working fluid, wherever applicable, must be checked and recorded in laboratories approved for measurement uncertainties up to 0.5% level. The instrument used should be accurate enough to ensure an accuracy of Âą 0.05% of the actual value.

In case of gases, the density may be determined by direct measurement or by measurement of pressure, temperature and, if applicable, moisture content and chemical composition of the gas. Where gas law deviation coefficients are used in density determinations, the data must be taken from a recognized & stated source for which the levels of uncertainty are known.

3

The viscosity of the fluid, wherever necessary, must be measured at the temperature at which the calibration is performed and recorded. It is a common practice to check it at a recognized

reference temperature in addition to the working temperature. For

convenience, the measure of viscosity which is used may be the kinematic viscosity, rather than the dynamic viscosity.

4

The working fluid must be clean. The degree of cleanliness will depend on the type of flow meter being calibrated, for instance, turbine-type flow meter(the bearings of which can be affected) or variable area flow meters ( having fine clearances between the float and tube) need greater fluid cleanliness than venturi tubes.

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5

The working fluid must be of known and uniform composition and the temperature during measurement process should be specified.

6

The fluid used in any approved laboratory must be sufficiently free from impurities so as not to cause corrosion or erosion damage to flow meters and associated pipe work whilst the calibration is being carried out. For example, in water flow measurement, an analyst’s report on water in the laboratory may be required, and a pH check should indicate a figure between 6 and 8. A member of the staff of the laboratory should have the specific job of ensuring that the water does not damage equipment under calibration.

7

Valves must be leak proof, especially where they are used as isolating valves at pipe work junctions. Adequate arrangements for detection of leakage must be provided. The leak rate, if any, shall be sufficiently of low value, so as not to affect the calibration/accuracy.

8

The method used for controlling the flow in a closed conduit system whether upstream or downstream must be such that : a.

operation of the controlling device has no effect on the flowmeter calibration.

b.

Any drop in the pressure at the flow meter undergoing calibration does not cause air or gases to escape out of the solution or allow cavitation to occur.

c.

The flow meter and the complete calibration system must continue to run full under all conditions. These requirements must be met wherever the controlling device is placed, whether upstream or downstream.

9

Adequate straight lengths should be provided upstream and downstream of the flow measuring section as per relevant international/national standards to take care of asymmetry in the velocity distribution, swirls etc.

10

The complete flow system including the flow measuring device (for instance, the flow in open channel calibration) must be leak proof.

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PART – III

GUIDELINES REGARDING LEVELS OF ACCURACY OF STANDARDS AND MEASUREMENT UNCERTAINTY IN CALIBRATION FOR FLUID FLOW MEASUREMENTS

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GENERAL REMARKS The following pages may be referred as guidelines and not mandatory recommendations for the laboratories. The accredited calibration laboratories are no longer required to be categorized into Echelon/ level I, II, III. Part III of this document is aimed to provide guidance to the laboratories regarding the precautions they should take with respect to Environmental conditions as appropriate to respective Best Measurement Capability of the laboratories. The laboratories, on their own, should decide/ determine to have environmental conditions in their premises, for the best measurement capability claimed corresponding to their scope of accreditation applied for. Further to note that: 1)

The term Accuracy in these tables refer to Measurement Standards only, pertaining to each parameter.

2)

The measurement capability is expressed as uncertainty (±) at a confidence probability level of 95%.

3)

The term Uncertainty in these tables pertains to the corresponding measurement capability of the laboratory in respect of each parameter.

4)

The values of Accuracy/Uncertainty of measurement shown in the following tables are at 95% CL unless stated otherwise.

ENVIRONMENTAL CONDITIONS The Laboratory area where electronic measuring instruments are kept, shall be normally maintained at at the following temperature and relative humidity conditions:

Temperature Relative humidity

Level I

Level II

Level III

250C ± 1.50C

250C ± 2.50C

250C ± 4.00C

40 to 60%

40 to 60%

40 to 60%

For obtaining desired accuracy of measurement, the following stability in temperature of the medium shall be maintained:-

Stability in temperature of medium

Level I

Level II

Level III

± 10C/h

± 20C/h

± 40C/h

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National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 125 Issue No: 04

Specific Criteria for Calibration Laboratories in Fluid-Flow Discipline Issue Date: 28.03.2008 Amend No: 00 Amend Date: --

Page No: 17/ 19

1.

Water Flow Measurement

i)

Rate of Flow by Mass/Volume and Quantity of Flow Mass/Volume for all ranges Level I

Level II

Level III

Accuracy of standards

0.2%

0.5%

1.0%

Measurement Uncertainty

0.5%

1.0%

2.0%

Level I

Level II

Level III

Accuracy of standards

0.25%

0.5%

1.0%

Measurement uncertainty

0.5%

1.0%

2.0%

ii)

Velocity (magnitude) of water from 0.02m/s to 8.0 m/s

Note: Velocity Direction: All measurements in respect of Velocity Direction should be carried out within ¹3° inclination for all laboratories at different levels.

2.

Petroleum and other Non-aqueous Liquid Flow Measurements Rate of Flow by Mass/Volume and Quantity of Flow by Mass/Volume for all ranges.

Level I

Level II

Level III

Accuracy of standards

0.05%

0.1%

0.3%

Measurement uncertainty

0.1%

0.3%

o.5%

3.

Gas Flow Measurement* Rate of Flow by Mass/Volume and Quantity of flow by Mass/Volume for all ranges.

Level I

Level II

Level III

Accuracy of standards

0.2%

0.5%

1.0%

Measurement uncertainty

0.5%

1.0%

2.0%

*The temperature and pressure conditions at the time of measurements should be specified.

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National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 125 Issue No: 04

Specific Criteria for Calibration Laboratories in Fluid-Flow Discipline Issue Date: 28.03.2008 Amend No: 00 Amend Date: --

Page No: 18/ 19

4.

Gas velocity, range from 0.1m/s to 50 m/s Level I

Level II

Level III

Accuracy of standard

0.2%

0.5%

1.0%

Measurement uncertainty

0.5%

1.0%

2.0%

5.

Viscosity Measurement

i)

Accuracy of Standards

Range

Level I

Level II

Level III

1-25mm2/s

0.1%

0.3%

1.0%

25-200mm2/s

0.2%

0.6%

2.0%

200-600mm2/s

0.5%

1.5%

5.0%

Above 600mm2/s

1.0%

3.0%

9.0%

Level I

Level II

Level III

0.3%

1.0%

2.0%

25-200mm /s

0.5%

1.5%

5.0%

200-600mm2/s

1.0%

3.0%

To be worked out later

Above 600mm2/s

2.0%

6.0%

ii)

Measurement uncertainty

Range 2

1.25mm /s 2

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National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 125 Issue No: 04

Specific Criteria for Calibration Laboratories in Fluid-Flow Discipline Issue Date: 28.03.2008 Amend No: 00 Amend Date: --

Page No: 19/ 19

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