NABL 122-07

NATIONAL ACCREDITATION BOARD FOR TESTING AND CALIBRATION LABORATORIES

SPECIFIC CRITERIA for CALIBRATION LABORATORIES IN MECHANICAL DISCIPLINE : UTM, Tension Creep and Torsion Testing Machine MASTER COPY Reviewed by

Approved by

Quality Officer

Director, NABL

ISSUE No.

: 05

ISSUE DATE: 12.08.2014

AMENDMENT No.

: 00

AMENDMENT DATE:

AMENDMENT SHEET Sl no 1

Page Clause Date of No. No. Amendment

Amendment made

Reasons

Signature Signature QO Director

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National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 1 of 29

Sl. No. 1

Contents

Page No.

General Requirements

1.1

Scope

3

1.2

Calibration Measurement Capability(CMC)

3

1.3

Personnel, Qualification and Training

3-4

1.4

Accommodation and Environmental Conditions

4-6

1.5

Special Requirements of Laboratory

6

1.6

Safety Precautions

6

1.7

Other Important Points

6

1.8

Proficiency Testing

6

2

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14 3 4

Specific Requirements - Calibration of Uni-axial Testing Machines Scope National/ International Standards, References and Guidelines Metrological Requirements Terms and Definitions Selection of Reference Standard for UTM calibration Calibration Interval Legal Aspects Environmental Conditions Calibration Methods Calibration Procedures Measurement Uncertainty Evaluation of CMC Sample Scope Key Points Calibration of Tension Creep Testing Machine Calibration of Torsion Testing machine

7

7 7-8 8 8-9 9 9 9-10 10 10-11 11 11-12 12 13 14-20 21-29

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 2 of 29

1 General Requirement • The purpose of this document is to specify requirements with which a laboratory has to operate and demonstrate its competency to carry out calibration in accordance with ISO/IEC 17025:2005. • To achieve uniformity between the laboratories, assessors and assessment process in terms of maximum permissible error, CMC, measurement uncertainty etc in line with National/International standards. • To achieve uniformity in selection of equipment’s, calibration methods, maintaining required environmental conditions, personnel with relevant qualification and experience. 1.1 Scope This specific criteria lays down the specific requirements in UTM, Tension Creep and Torsion Testing Machine calibration under mechanical discipline. This part of the document thus amplifies the specific requirements for calibration of UTM, Creep and Torsion Testing Machine and supplements the requirements of ISO/IEC 17025:2005. 1.2 Calibration and Measurement Capability (CMC) 1.2.1

CMC 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 CMC is expressed as “the smallest uncertainty that a laboratory can achieve when calibrating the best existing device”. It is an expanded uncertainty estimated at a confidence level of approximately 95% corresponding to a coverage factor k=2.

1.2.2

For evaluation of CMC laboratories should be based on NABL 143 - Policy on Calibration and Measurement Capability (CMC) and Uncertainty in Calibration.

1.3 Personnel, Qualification and Training 1.3.1 Technical Personnel: 1.3.1.1 Qualification required for carrying out calibration activity: The following are only specific requirements. However, qualification and experience will not be the only criteria for the required activity. They have to prove their skill, knowledge and competency in their specific field of calibration activity. a) B.E / B.Tech or M.Sc. (having Physics as one of the subject) degree with 3 months experience in Basics of Force Metrology and Calibration of UTM, Tension Creep and Torsion Testing Machine. b) B.Sc (with Physics as one of the subject) or Diploma with 6 months experience in Basics of Force Metrology and Calibration of UTM, Tension Creep and Torsion Testing Machine. c) ITI with 1 year of experience in Basics of Force Metrology. 1.3.2

Training and experience required: a) Training may be external/ internal depending on the expertise available in the field.

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 3 of 29

b) Training in Force calibration and in Uncertainty Measurements, CMC including statistical analysis for Technical Manager. c) Experience and competence in Basics of Force metrology and calibration of UTM, Tension Creep and Torsion Testing Machine. d) Sufficient knowledge about handling of reference equipment, maintenance, traceability, calibration procedure and effect of environmental conditions on the results of calibration. e) During training calibration activity should be done under supervision. 1.3.3

Authorised Signatory 1.3.3.1 Qualification required for interpretation of results and signing the calibration certificates: The following are only guidelines. However, qualification and experience will not be the only criteria for the required activity. They have to prove their skill, knowledge and competency in analysis and interpretation of calibration results. a) B.E / B.Tech or M.Sc. (with having Physics as one of the subject) degree with 6 months experience in Force Metrology. b) B.Sc. (with Physics as one of the subject) or Diploma with 1 year experience in Basics of Force Metrology and Calibration of UTM, Tension Creep and Torsion Testing Machine. 1.3.3.2

Training and experience required: a) Training may be external/ internal depending on the expertise available in the field. b) Training, Experience and Competence in Basics of Force metrology and calibration of UTM, Tension creep and Torsion testing machine and Training in Uncertainty Measurements, CMC including statistical analysis for Technical Manager. c) Sufficient knowledge and competence in effective implementation of ISO/IEC 17025, specific criteria and NABL guidelines. d) Competency in reviewing of results, giving opinion and interpretations. e) During training the relevant activity has to be done under supervision.

1.4 Accommodation and Environmental Conditions A Laboratory may be offering calibration services under different categories i. Permanent laboratory service ii. Onsite service The above category of laboratories may provide following types of services. a) Service that intended primarily for measurement standards, reference equipments which are further used for calibration purposes or high accuracy measurements which requires high degree of accuracy and better CMC. National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 4 of 29

b) Service that intended primarily for calibration and adjustment of test, measurement and diagnostic equipments to use in such areas as product testing, manufacturing and servicing. Accommodation and environmental conditions adversely affect the results of calibration and measurement accuracy unless they are controlled and monitored. Hence, they play a very important role. The influencing parameters may be one or more of the following i. e. temperature, relative humidity, atmospheric pressure, vibration, acoustic noise, dust particle, air currents/draft, illumination(wherever applicable), voltage fluctuations, electrical earthing and direct sunlight etc., depending on the nature of calibration services provided. The variables described above can play a major factor on calibration results. The main difference between the permanent laboratory, onsite and mobile calibration services has to do with environmental conditions only. Since the onsite calibration relies on where the service is provided, it affects the results of calibration (Refer NABL 130). The laboratories are advised to follow the requirement of accommodation and environment depending on the types of services provided as recommended. • By the manufacturers of the reference equipment. • By the manufacturers of the Unit under calibration. • As specified in the National/ International Standards or guidelines followed for the calibration. The environmental monitoring equipments used should also meet the requirement of manufacturers’ recommendations and specifications as per the relevant standards followed. If, accommodation and environmental conditions are not specified either by manufacturer or by National/International standards / guidelines, the laboratory shall follow the below recommendations. 1.4.1

Vibration The calibration area shall be free from vibrations generated by central air-conditioning 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.

1.4.2

Acoustic Noise Acoustic noise level in the laboratory shall be maintained to facilitate proper performance of calibration work. Noise level shall be maintained less than 60 dBA, wherever it affects adversely the required accuracy of measurement.

1.4.3

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 250-500 lux on the working table.

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 5 of 29

1.4.4

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 shall be provided whenever necessary for recording temperature, pressure and humidity values prevailing during calibration. The atmospheric conditions maintained in the laboratory during calibration shall be reported in the calibration report/ certificate.

1.5 Special Requirements of Laboratory 1.5.1

The calibration laboratory shall make arrangements for regulated and uninterrupted power supply of proper rating. The recommended voltage regulation level is ±2% or better, and Frequency variation ± 2.5 Hz or better on the calibration bench.

1.5.2

The reference standards shall be maintained at temperatures specified for their maintenance on order to ensure their conformance to the required level of operation.

1.5.3

The laboratory shall take adequate measures against dust and external air pressure.

1.6 Safety Precautions 1.6.1

Relevant fire extinguishing equipment for possible fire hazards, shall 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.

1.7 Other Important Points 1.7.1

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

1.7.2

Space in Calibration Area: The calibration Laboratory shall ensure adequate space for calibration activity without adversely affecting the results.

1.8 Proficiency Testing 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 Program. The laboratory shall remain prepared to participate in the Proficiency Testing Program through inter-laboratory, inter-comparison schemes wherever it is technically feasible. (Ref. NABL 162, 163 and 164 for further details)

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 6 of 29

2 Specific Requirements - Calibration of Force Measuring System of Uni-axial Testing Machine 2.1 Scope

Sl. No. 1

Description

Relevant Standard

Permanent Facility

Onsite Calibration

Universal Testing Machines / Tensile Testing Machines / Compression Testing Machines

IS1828 (Part 1): 2005 ISO 7500-1:2004

√*

√

*Note 1: Calibration of UTM at permanent facility (by manufacturer) is acceptable however; verification shall be required after installation and commissioning of UTM at site. Note 2: UTM can also be calibrated as per ASTM E4-10 using Force proving instruments duly calibrated as per ASTM E 74 or any other standard. Note 3: This technical requirement is based on the standard IS 1828 (Part-1). Lab may follow any relevant standard, however care shall be taken to follow the requirements in totality. 2.2 National/ International Standards, References and Guideline •

IS1828 (Part 1): 2005 (ISO 7500-1:2004) -Metallic Materials-Verification of static uniaxial testing machines, Part 1: Tension/Compression Testing Machines-Verification and Calibration of the Force Measuring System.

•

ASTM E4-10, Force Verification of Testing Machines.

•

ISO: 376: 2011 E - Metallic materials-Calibration of Force -Proving Instruments used for the Verification of Uni-axial Testing Machines.

•

ASTM E 74- 06 Standard practices of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines.

•

OIML R 111- 1 Metrological and Technical Requirement of Weights.

2.3 Metrological Requirement 2.3.1

The standard IS:1828 (Part 1): 2005 (ISO 7500-1:2004) is for both verification and calibration of force measuring system of the Uni axial Testing machine. This specific criteria is meant for only calibration of force measuring system. If the verification is also to be included, then lab has to follow the standard completely along with Annexure -A, B and C of the standard and verification and calibration report can be issued for the machine.

2.3.2

Force Proving instruments used for calibration of uniaxial testing machines as per IS1828 (Part 1): 2005 (ISO 7500-1:2004) shall have traceability and calibration certificate as per ISO 376:2011 E (Or any other standard).

2.3.3

Proving instrument calibrated in compression mode shall not be used for calibration of the machine in Tension mode and vice versa.

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 7 of 29

2.3.4

The force proving instrument shall be calibrated along with load fittings liked loading pads for compression and ball nut, ball cup and tensile force measuring rod as per A.4 of ISO 376: 2011E.

2.4 Terms and Definition Universal Testing Machine • Uniaxial testing machine also known as Universal Testing Machine (UTM) , is used to test the tensile stress, compressive strength of materials. It is named after the fact that, it can perform any standard tensile and compressive tests on materials, components and structures. Load Frame • Usually consists of two strong supports for the machine. Some small machines have single support. Cross Head • A moveable head, controlled to move up/down at a constant speed. Electro mechanical, servo hydraulic, linear drive and resonance drive are some of the methods used for controlling the speed of cross head movement. Force Proving Instrument • A device or system consisting of an elastic member combined with a device for indicating the magnitude (or a quantity proportional to the magnitude) of deformation of the member under an applied force. 2.5 Selection of Reference Standard for UTM Calibration 2.5.1

The proving instruments used for the calibration shall have a certificate from either NMI or accredited laboratory with traceability to the SI units and shall comply with the requirements specified in ISO 376:2011.

2.5.2

The class of the instrument shall be equal to or better than the class for which the testing machine –force indicator is to be calibrated. Initially, the class of the machine may be taken as per the relative resolution of the force indicator (Preferably).

2.5.3

Proving instrument used in compression mode shall have the certificate of calibration in compression mode. Similarly used in tension mode should have certificate of calibration in tension mode.

2.5.4

The force proving instrument shall be calibrated along with load fittings like loading pads for compression and ball nut, ball cup and tensile force measuring rod as per the required application (or as per manufacturers recommendations).

2.5.5

Proving instrument (proving ring with dial) calibrated in specific forces only should be used for calibrating in the same specific force points and not in between force points. If it has to be used for in between force points, it has to have certificate of calibration with interpolation equation and the calibration certificate for the dial also.

2.5.6

All the elements of force proving instrument shall be individually and uniquely identified.

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 8 of 29

2.5.7

Required characteristics of Force Proving Instruments: Table 1(as per ISO 376:2011) Class of the Relative Error of Force Proving Instrument, % Uncertainty of Force applied Zero Creep Proving Reproducibility Repeatability Interpolation ± (f 0 Reversibility (c) calibration force, (b) (bʹ) ± (fc) (ν)* Instrument k=2 ± (%) ) 00 0.05 0.025 0.025 0.012 0.07 0.02 0.01 5 0.5 0.10 0.05 0.05 0.025 0.15 0.05 0.02 1 0.20 0.10 0.10 0.05 0.30 0.1 0.05 2 0.40 0.20 0.20 0.10 0.50 0.2 0.10 * The relative reversibility error is only determined when required

Note 1: As per IS: 1828 (Part-1) Clause 6.1 Force Proving Instrument used for calibration shall comply with ISO376:2011 only. 2.5.8

2.5.9

Maximum expanded uncertainty of the Force Proving instrument shall be as per Table -2 below:

Class of accuracy of UTM

Required Class of accuracy of force proving instrument ISO 376:2011

0.5 1 2 3

0.5 1 2 2

Force proving Instrument, Uncertainty (in %), k=2 Specific Force 0.127 0.257 0.513 0.513

With interpolation without With reversibility reversibility 0.162 0.237 0.325 0.475 0.651 0.870 0.651 0.870

Calibration using Dead Weights In case of dead weights used for calibration, the relative error of the force generated by these weights shall be ≤ ± 0.1% .These weights shall be in Newton.

2.6 Calibration Interval Reference Equipment Force proving instrument used for calibration

Interval 26 months

Dead weights

3 years

2.7 Legal Aspects Calibration of UTM done by any accredited laboratories is meant for scientific and industrial purpose only. However, if used for commercial trading, additional recognition/ approval shall be complied as required by Dept. of Legal metrology, Regulatory bodies, etc. 2.8 Environmental Conditions 2.8.1

The calibration shall be carried out between 10°C and 35°C. The temperature at which calibration is carried out shall be noted in the calibration certificate.

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 9 of 29

2.8.2

The temperature measuring equipment with a resolution 1°C shall be used for monitoring temperature during calibration.

2.8.3

Stability of temperature during measurement is to be mentioned.

2.9 Calibration Methods 2.9.1

Calibration can be carried out with constant indicated force of the machine for all the three series of measurement. When this method is not feasible, the calibration may be carried out with constant true forces. When more than one force proving instrument is required to calibrate a force range, maximum force applied to the smaller device shall be the same as the minimum force applied to the next force proving instrument of the higher capacity. Refer clause 6.5.3 of IS 1828 (part 1):2005 for agreement between two force proving instruments.

2.10 Calibration Procedures 2.10.1 Follow procedure as per IS 1828 (part 1): 2005 for static Uniaxial Testing Machine. 2.10.2 Select suitable accuracy class force proving instruments one or more depending on the class of accuracy of the testing machine (refer Table 6.1.5.8). 2.10.3 Sufficient period of time shall be provided to allow the force proving instrument to reach a stable period of temperature. The temperature of the force proving instrument shall remain stable to within ± 2°C during each calibration run. If necessary, temperature correction shall be applied to the reading as mentioned below: a. If a proving instrument is used at a temperature other than the calibration temperature (as per its certificate), the deflection of the instrument shall be, if necessary, corrected for nay temperature variation in accordance with the formula. D t = D e [1+ K( t - t e )] Where, D t =deflection at the temperature t, D e = deflection at the calibration temperature (as per the certificate), K= temperature coefficient of the instrument per °C. t e temperature (as per the certificate). Table B.2 of ISO 376:2011 gives the deflection corrections for the instruments (proving rings). These corrections are obtained with K= 0.00027 per °C. b. Most force transducers with electrical outputs are thermally compensated in the range of application, in these cases, temperature correction might not be necessary. 2.10.4 If a calibration is conducted at forces below 20% of the range, supplementary force measurements shall be made at approximately 10%, 5%, 2%, 1%, 0.5 %. 0.2 %, 0.1 % of the scale down to and including the lower limit of calibration.

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 10 of 29

2.10.5 The lower limit of discrete force to be considered before calibrating the UTM (Refer table below) Class Minimum force applied shall be 0.5 400 x r 1 200 x r 2 100 x r 3 67 x r Where r is the resolution of Indicator 2.10.6 Characteristic value of Force Measuring System of the Testing Machines as per IS 1828 (part 1): 2005 for 20% to 100% of the measuring range. Class of the Testing Machine

Maximum Permissible Values, % Relative Relative Relative Relative Accuracy ± (q) Repeatability (b) Reversibility Zero ± (f 0 ) ±(u)* 0.5 0.5 0.5 0.75 0.05 1 1.0 1.0 1.5 0.10 2 2.0 2.0 3.0 0.2 3 3.0 3.0 4.5 0.3 * The relative reversibility error is only determined when required

Relative Resolution (a) 0.25 0.5 1.0 1.5

2.10.7 Calibration Interval for Device under Calibration • As recommended in the standard - Not exceeding 12 months. 2.11 Measurement Uncertainty Possible sources of uncertainty for testing machines calibration include, but are not limited to, the following: 1. Uncertainty due to applied calibration force from calibration certificate of force proving instrument. 2. Uncertainty due to repeatability of calibration results (from 3 series of measurement). 3. Uncertainty due to zero error. 4. Uncertainty due to resolution of testing machine(only if calibration is carried out with constant true force) 5. Uncertainty due to reversibility (optional) 6. Uncertainty due to thermometer used for temperature measurement. Note: If constant indicated force method is used during calibration, uncertainty due to resolution is not required as it reflects in repeatability measurements. If the results obtained are not corrected for accuracy error the maximum possible deviation may also be reported as ‘max accuracy error plus the uncertainty so obtained’ (Not for CMC evaluation). 2.12 Evaluation of CMC 2.12.1 Refer NABL 143 for CMC evaluation. National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 11 of 29

2.12.2 CMC value is not the same as expanded uncertainty reported in the calibration Certificate/Report. CMC values exclude the uncertainties which are attributed to the UUT (Unit under Test/Calibration). 2.12.3 For the purpose of CMC evaluation the following components should be considered: • Uncertainty due to applied calibration force from calibration certificate of force proving instrument. • Uncertainty due to repeatability of calibration results (from 3 series of 10 measurement both minimum and maximum). • Uncertainty due to resolution of testing machine (only if calibration is carried out with constant true force). 2.12.4 Uncertainty due to thermometer used for temperature measurement. 2.13 Sample Scope An illustrative example: Correct Presentation of Scope Laboratory: XYZ

Date(s) of Visit:

Discipline: Mechanical Sl

1

Parameter* / Device under calibration

Force measuring system of UTM

Master equipment used

Range(s) of Calibration and Measurement Capability Remarks+/ Method measurement ** used Claimed by Observed by Recommended Laboratory Assessor by Assessor

Proving Rings / Load Cells with display (Class-II accuracy)

For UTM of accuracy Class II and coarser as per IS 1828 (Part 1): 2005

Compression

Tension

50N to 3000kN

0.49 %

0.45 %

0.49 %

3N to 50kN

0.69 %

0.65 %

0.69 %

* Only for Electro-technical discipline; scope shall be recommended parameter wise (where applicable) and the ranges may be mentioned frequency wise. ** NABL 143 shall be referred for the recommendation of CMC +

Remarks shall also include whether the same scope is applicable for site calibration as well. NABL 130 shall be referred while recommending the scope for site calibration.

Signature, Date & Name of Lab Representative

Signature, Date & Name of Assessor(s)

Signature, Date & Name of Lead Assessor

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 12 of 29

2.14 Key Points Required Class of accuracy of force proving Class of instrument accuracy of ISO 376:2011 UTM

0.5 1 2 3

Note1:

Uncertainty (%) of Force proving Instrument k=2

Class of accuracy

Specific Force

0.5 1 2 2

0.127 0.257 0.513 0.513

Limit of combined uncertainty(%) of UTM as per IS 1828 (part 1):2005 k= 2

(Includes repeatability and applied force) Without With Specific Without With Reversibility Reversibility Force Reversibility Reversibility 0.162 0.237 0.315 0.331 0.374 0.325 0.475 0.632 0.663 0.748 0.651 0.870 1.264 1.326 1.446 0.651 0.870 1.806 1.850 1.938 With Interpolation

Laboratory shall comply with the applied uncertainty of force proving instrument required for different class as per the table above.

Note 2: The cut off CMC value for class 3 or better, the lab shall comply with the uncertainty. For specific forces: ≤ 1.81% with k=2, with interpolation without reversibility≤ 1.85%, with interpolation with reversibility ≤ 1.94%. Beyond this accreditation cannot be granted. Note 3: Lab shall comply with any CMC values doesn't automatically qualify for accreditation until the lab satisfies the stipulated requirement given above.

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 13 of 29

3 Calibration of Tension Creep Testing Machine Sl.No.

Contents

Page No

3.1

Scope

15

3.2

National/ International Standards, References and Guidelines

15

3.3

Metrological Requirements

15

3.4 3.5 3.6

Terms and Definitions Selection of Reference Standard for Tension Creep Testing Machine Calibration Calibration Interval

3.7

Environmental Conditions

3.8

Calibration Procedures

3.9

Measurement Uncertainty

3.10

Evaluation of CMC

3.11

Sample Scope

19

3.12

Key Points

20

15-16 16 17 17 17-18 18 18-19

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 14 of 29

3.1 Scope: Calibration of Tension Creep Testing Machine Sl. No 1

Parameter-Force

Relevant Standard

Permanent Facility

Onsite Calibration

Tension Creep Testing Machines

IS1828 (Part 2): 2002 (ISO7500-2:1996)

√*

√

*Note 1: Tension creep testing machine can also be calibrated as per relevant ASTM standard using Force proving instruments duly calibrated as per ASTM E 74. Note-2:

This technical requirement is based on the standard IS 1828 (Part-2). However, lab may follow any other relevant standard/guideline in totality.

3.2 National/ International Standards, References and Guideline • IS1828 (Part 2) : 2002 (ISO7500-2:1996) / ISO 7500-2:2006 - Metallic Materials-Verification of Static Uniaxial Testing Machines- Part-2: Tension Creep Testing Machines-Verification of the Applied Force. • ISO 376:2011(E) - Metallic Materials-Calibration of Force-Proving Instruments used for the Verification of Uniaxial Testing Machines. • OIML R 111- 1 Metrological and Technical requirement of Weights. • ASTM E 74- Standard practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines. 3.3 Metrological Requirement 3.3.1

Force Proving instruments used for verification of applied load in Tension Creep Testing Machines as per: 1828 (Part 2): 2002 (ISO 7500-2:1996) shall have traceability and calibration certificate as per ISO 376:2011 E.

3.3.2

Proving instrument calibrated in Tension Mode.

3.3.3

The force proving instrument shall be calibrated along with load fittings like ball nut, ball cup and tensile force measuring rod as per the required application.

3.4 Terms and Definition Tension Creep Testing Machine • A creep testing machine measures the creep (the tendency of a material after being subjected to high levels of stress of an object (i.e. like high temperature to change its form in relation to time). It is a device that measures the alteration of a material after it has put through different forms of stress. Creep machines are important to see how much strain (load) an object can handle under pressure. So engineers and researchers are able to determine what materials to use. The device generates a creep time dependent curve by calculating the steady rate of creep in reference to the time it takes for the material to change.

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 15 of 29

Creep • The time dependent deformation under constant load at high temperature is called creep and the resulting strain is a function of applied stress, temperature and time. Creep Test •

The main objective in a creep test is to measure how a given metal or an alloy will perform under constant load at elevated temperatures. In a creep test, a tensile specimen (with similar specimen as a tensile test specimen) is subjected to a constant load inside a furnace where the temperature is maintained constant.

Force Proving Instrument •

A device or system consisting of an elastic member combined with a device for indicating the magnitude (or a quantity proportional to the magnitude) of deformation of the member under an applied force.

3.5 Selection of Reference Standard for Tension Creep Testing Machine Calibration 3.5.1

The proving instruments used for the calibration shall have a certificate from either NMI or accredited laboratory with traceability to the SI units and shall comply with the requirements specified in ISO 376:2011.

3.5.2

The class of the instrument shall be equal to or better than the class for which the testing machine is to be calibrated. Initially, the class of the machine may be taken as per the relative resolution of the force indicator of machine.

3.5.3

Proving instrument should have the certificate of calibration in Tension mode.

3.5.4

The force proving instrument shall be calibrated along with load fittings like ball nut, ball cup and tensile force measuring rod as per the required application.

3.5.5

Proving instrument (proving ring with dial) calibrated in specific forces only should be used for calibrating in the same specific force points and not in between force points. If it has to be used for in between force points, it has to have certificate of calibration with interpolation equation and the calibration certificate for the dial also.

3.5.6

All the elements of force proving instrument shall be individually and uniquely identified, like for proving rings, the ring, dial gauge / micrometer, vibrating reed or fulcrum, tension shackles etc and in case of load cells the indicator, connecting cables etc.

3.5.7

Required characteristics of Force Proving Instruments :Table 1(as per ISO 376:2011) Class of the Uncertainty Relative Error of Force Proving Instrument, % Force Creep of applied Proving Reproducibility Repeatability Interpolation Zero Reversibility (c) calibration Instrument force, (b) (bʹ) ± (fc) ± (f 0 ) (ν)* k=2 ± (%) 00 0.05 0.025 0.025 0.012 0.07 0.025 0.01 0.5 0.10 0.05 0.05 0.025 0.15 0.05 0.02 1 0.20 0.10 0.10 0.05 0.30 0.1 0.05 2 0.40 0.20 0.20 0.10 0.50 0.2 0.10 * The relative reversibility error is only determined when required

Note 1: As per IS1282 (Part-2) Clause 5.1 Force Proving Instrument used for Calibration should comply with ISO376:2011. National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 16 of 29

3.6 Calibration Interval Reference Equipment Force proving instrument used for calibration

Interval 26 months

3.7 Environmental Conditions The temperature measuring equipment with a resolution 1°C should be used for monitoring temperature during calibration. 3.8 Calibration Procedures 3.8.1

Follow procedure as per IS 1828 (part 2): 2002 for Tension Creep Testing Machine.

3.8.2

Select suitable accuracy class force proving instruments one or more depending on the class of accuracy of the testing machine. Class of accuracy of Tension Creep Testing Machine 0.5 1 2

3.8.3

Class of Accuracy of Force Proving Instrument as per ISO 376 0.5 1 2

Sufficient period of time shall be provided to allow the force proving instrument to reach a stable period of temperature. The temperature of the force proving instrument shall remain stable to within ± 2°C during each calibration run. If necessary, temperature correction shall be applied to the reading as mentioned below: a. If a proving instrument is used at a temperature other than the calibration temperature (as per its certificate), the deflection of the instrument shall be, if necessary, corrected for nay temperature variation in accordance with the formula. D t = D e [1+ K( t - t e )] Where, D t =deflection at the temperature t, D e = deflection at the calibration temperature (as per the certificate), K= temperature coefficient of the instrument per °C & t e =temperature (as per the certificate) Table B.2 of ISO 376:2011 gives the deflection corrections for the instruments (proving rings). These corrections are obtained with K= 0.00027 per °C. b. Most force transducers with electrical outputs are thermally compensated in the range of application, in these cases, temperature correction might not be necessary.

3.8.4

Determination of the discrimination threshold at 20%, 60% and 100% of the max. load of the force measuring range. •

The discrimination threshold‘d’ of the machine is defined as the smallest increment of the force that can be applied and detected during the verification procedure.

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 17 of 29

•

The relative discrimination threshold a = d/F *100 and shall remain within the limits given in the table below for the class of machine considered.

•

The discrimination threshold‘d’ shall be expressed in Newtons.

•

Determination of lower limit of verification : the limit of verification Fv shall be specified according to table below: Class Minimum force applied shall be 0.5 400 x d1 1 200 x d1 2 100 x d1 Where d1 is the discrimination threshold corresponding to 20% of the force.

3.8.5

Three series of at least 5 approximately equi-spaced loads starting at 20% of range as the lowest force range or the lower limit of verification whichever is greater shall be applied.

3.8.6

Characteristic values of Tension Creep Testing Machine as per IS 1828 (part 2) for 20% to 100% of the measuring range Accuracy Class of Machine 0.5 1 2

3.8.7

Maximum Permissible Values, % Relative discrimination Relative error of Relative error of threshold repeatability accuracy A B Q 0.25 0.5 ± 0.5 0.5 1 ± 1.0 1 2 ± 2.0

Calibration Interval for Device under Calibration • As recommended in the standard - 5 Years

3.9 Measurement Uncertainty Possible sources of uncertainty for testing machines calibration include, but are not limited to, the following: 1. Uncertainty due to applied calibration force from calibration certificate of force proving instrument. 2. Uncertainty due to repeatability of calibration results (from 3 series of measurement). 3. Uncertainty due to resolution of the testing machine. 4. Uncertainty due to relative discrimination threshold. 5. Uncertainty due to thermometer used for temperature measurement. 6. If the results obtained are not corrected for accuracy error the maximum possible deviation may also be reported as ‘max accuracy error plus the uncertainty so obtained’ (Not for CMC evaluation). 3.10 Evaluation of CMC 3.10.1 Refer NABL 143 for CMC evaluation. National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 18 of 29

3.10.2 CMC value is not the same as expanded uncertainty reported in the Calibration Certificate/Report. CMC values exclude the uncertainties which are attributed to the UUT (Unit under test/calibration). 3.10.3 For the purpose of CMC evaluation the following components should be considered: • Uncertainty due to applied calibration force from calibration certificate of force proving instrument. • Uncertainty due to repeatability of calibration results (from 3 series of 10 measurements both minimum and maximum). • Uncertainty due to resolution of testing machine. • Uncertainty due to thermometer used for temperature measurement. 3.11 Sample Scope An illustrative example: Correct Presentation of Scope Laboratory: XYZ

Date(s) of Visit:

Discipline: Mechanical Sl

1

Parameter* / Device under calibration

Master equipment used

Force measuring system of Creep Testing

Proving Rings / Load Cells with display (Class-I accuracy)

Tension

Range(s) of Calibration and Measurement Capability Remarks+/ Method measurement ** used Claimed by Observed by Recommended Laboratory Assessor by Assessor

1 kN to 10 kN

0.25 %

0.28 %

0.28 %

For Tension Creep testing machine of accuracy Class I and coarser as per IS 1828 (Part 2): 2005

* Only for Electro-technical discipline; scope shall be recommended parameter wise (where applicable) and the ranges may be mentioned frequency wise. ** NABL 143 shall be referred for the recommendation of CMC +

Remarks shall also include whether the same scope is applicable for site calibration as well. NABL 130 shall be referred while recommending the scope for site calibration.

Signature, Date & Name of Lab Representative

Signature, Date & Name of Assessor(s)

Signature, Date & Name of Lead Assessor

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 19 of 29

3.12 Key Points

Class of accuracy of TCTM

Required Class of accuracy of force proving instrument ISO 376:2011 Class of accuracy

0.5 1 2

0.5 1 2

Uncertainty (%) of Force proving Instrument k=2 Specific Force 0.127 0.257 0.513

With interpolation 0.162 0.325 0.651

Limit of CMC of combined uncertainty (%) k=2, for Tension Creep Testing machine as per IS 1828 (part 2):2002 (Includes repeatability and applied force) 0.347 0.700 1.345

0.374 0.748 1.446

Note 1: Laboratory shall comply to the applied uncertainty of force proving instrument required for different class as per the table above. Note 2: The cut off CMC value for class 2 or better, the lab shall comply the uncertainty. For specific forces: ≤ 1.345% with k=2 and with interpolation ≤ 1.446 % .Beyond this accreditation cannot be granted Note 3: Lab shall comply to any CMC values doesn't automatically qualify for granting accreditation until the lab satisfies the stipulated requirement given above.

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 20 of 29

4 Calibration of Torsion Testing Machine Sl.No.

Contents

Page No

4.1

Scope

22

4.2

National/ International Standards, References and Guidelines

22

4.3

Metrological Requirements

22

4.4

Term and Definitions

23

4.5

Selection of Reference Standard

4.6

Calibration Interval

24

4.7

Legal Aspects

24

4.8

Environmental Conditions

25

4.9

Calibration Procedures

25

4.10

Measurement Uncertainty

4.11

Evaluation of CMC

28

4.12

Sample Scope

29

4.13

Key Points

29

23-24

25-28

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 21 of 29

4.1 Scope: Calibration of Torsion Testing Machine Sl. No 1

Parameter-Force

Relevant Standard

Permanent facility

Torsion testing Machine

ASTM E 2624-09

√

Onsite calibration √*

*Note-1: Using torque transducer or load cell with calibrated arm. Note-2:

This technical requirement is based on ASTM E 2624-09. However, lab may follow any other relevant standard/guideline.

4.2 National/ International Standards, References and Guideline • BS 7882:2008: Method for calibration and classification of torque measuring devices. • EURAMET cg 14: Static Torque measuring devices. • ASTM E 2428-08 Practice for calibration of torque measuring instruments for verifying Torque indication of Torque testing machines. • ASTM E 2624-09 Standard procedure for torque calibration of testing machines and devices. • ISO 376:2011(E) - Metallic materials-calibration of force -proving instruments used for the verification of Uniaxial testing machines. • OIML R 111- 1 Metrological and technical requirement of weights. • ASTM E 74- Standard practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines. 4.3 Metrological Requirement 4.3.1

For Each weight, the expanded uncertainty, U, for k=2, of the true mass.

4.3.2

All weights used for verification of force shall be in Newton.

4.3.3

Preferably all weights shall be equivalent or better than F2 standard as per OIML R-111.

4.3.4

'g' value shall be known with sufficient accuracy either by Geological Survey of India or any other relevant source for finer CMC.

4.3.5

Laboratory may also calculate 'g' value knowing latitude and height as per the formula. However, same shall be validated (refer 6.3.8.4).

4.3.6

Since mass has to be calibrated in true mass basis, the air buoyancy correction shall be applied.

4.3.7

Knowing the true mass and 'g' value, Newtonian value will be determined after applying buoyancy correction.

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 22 of 29

4.4 Terms and Definition Torque • Torque is the vector product of tangential force and length applied about a known centre of rotation. Torque Measuring Device • A system comprising of an Electrical, Mechanical, Hydraulic or Optical Torque Transducers with associated instrumentation including the automated logging of data when part of the device Instrumentation can be a electronic instrument, a mechanical device is a scale and pointer system or a bourdon tube instrument. Relative Reversibility • Difference between the deflection obtain from the last given torque value both in increasing and increasing order. Relative Residual Deflection • Maximum residual deflection obtained from all the series of torque. Acceleration Due to Gravity ‘g’ • It is the acceleration of a body due to the influence of the pull of gravity alone, usually denoted as ‘g’ and unit of measurement is m/s2. Force Proving Instrument • A device or system consisting of an elastic member combined with a device for indicating the magnitude (or a quantity proportional to the magnitude) of deformation of the member under an applied force. 4.5 Selection of Reference Standard for Calibration of Torque Testing Machine Calibration of torque testing machines will generally be carried out in accordance with a documented procedure such as ASTM E2624 and the uncertainty of the calibration results will be dependent on the maximum permissible uncertainty of calibration torque applied, as well as on the performance of the torque testing machine. The reference calibration equipment shall be capable of calibrating the machine in clockwise/anticlockwise, application of torque in both increasing and decreasing steps. It should ensure axial application of torque. 4.5.1

The methods of calibration of Torque Testing Machines a. Use of standard weights and lever arms. b. Elastic Torque measuring device (Torque transducer). c. Elastic Force measuring device (Load cell) and lever arms.

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 23 of 29

d. Any other methods require a specific uncertainty of measurement and a traceability derived from national standards of mass and length. 4.5.2

Most of the torque testing machines are of ±1 % of the reading accuracy. The accuracy class of the applied torque should be at least 1/3 i.e. 0.3 % including its uncertainty. So normally the uncertainty of applied torque should be ± 0.1 % which is 1/3 of the 0.3% accuracy.

4.5.3

Torque calibration machines calibration can be done either at permanent facility or onsite as follows: a) Permanent facility: Using calibrated weights and calibrated lever arm. The local ‘g’ value, air density and density of weights should be known to sufficient accuracy. b) Onsite Calibration: Using torque transducer or load cell with calibrated lever arm.

4.5.4

Calibration by the application of standard weights using lever arm to the torque sensing mechanism of the testing machine, where practicable is the most accurate method. Its limitations are 1) small range of torque that can be calibrated 2) non portability of any high capacity standard weights 3) the analysis of all parasitic torque components.

4.5.5

Expanded measurement uncertainty with k=2 for weights should not exceed 0.1%.

4.5.6

Lever arm or wheel shall be calibrated to determine length or radius within a known uncertainty i.e. traceable to National Standards. The expanded uncertainty with k=2 shall not exceed 0.1%.

4.5.7

The second method of calibration of torque testing machines, involves the measurement of elastic strain or rotation under the torque of a torque transducer or a force transducer with lever arm combination. Elastic calibration devices are less constrained than the system mentioned at 6.3.5.4.

4.5.8

The design of fixtures and interfaces between the calibration device and the machine are critical. When using elastic torque or force measuring devices use class A or better of Torque transducer as per ASTM E 2428 or class 0.2 of BS7882: 2008 and Force sensor (Load cell) Class A of ASTM E74 or Class 0.5 of ISO 376.

4.6 Calibration Interval Reference Equipment Mass Lever arm Torque Transducer Load cell

Interval 3 years 2 years 1 year 26 months

4.7 Legal Aspects Calibration of weights done by any accredited laboratories is meant for scientific and industrial purpose only. However, if load cell is used in equipment for commercial trading, additional recognition/ approval shall be complied as required by Dept. of Legal metrology, Regulatory bodies, etc.

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 24 of 29

4.8 Environmental Conditions (for Permanent Facility) Lab is advised to follow Manufacturer’s recommendation for environmental conditions, operations and maintenance. Otherwise, Laboratory using torque testing machine shall fulfill the following conditions for realization of applied force. 4.8.1

The temperature shall be maintained in the range of 18°C to 28°C. The temperature shall not vary more than ± 1°C throughout a measurement series.

4.8.2

The relative humidity shall be maintained at 50% RH ± 15% RH.

4.8.3

For measurement uncertainty of applied force, ‘g’ value shall be known. For realization of applied force more than 0.01%, ‘g’ value shall be calculated using the formula given in below For better than 0.01%, ‘g’ value shall be measured by appropriate authority.

4.8.4

Validation of local ‘g’ and its Uncertainty Formula for calculation of Acceleration due to gravity. An approximate value for g, at given latitude and height above sea level, may be calculated from the formula:

g = 9.780 327 (1 + Α sin2 L - B sin2 2L) - 3.086 × 10-6 H m·s-2 where: A = 0.005 302 4, B = 0.000 005 8, L = latitude, H = height in meter above sea level 4.8.5

Recommended Environment monitoring equipments at calibration laboratory • Temperature with a resolution of 0.1C. • Humidity with a resolution of 1% RH. • Barometer with 1 mbar However, laboratory shall evaluate the requirement of accuracy, resolution and uncertainty depending on the CMC aimed at.

4.9 Calibration Procedures 4.9.1

Follow procedure as per ASTM E 2624-09 for calibration of torque testing machine.

4.9.2

Calibration Interval for Device under Calibration. • As recommended in the standard - 18 months

4.10 Measurement Uncertainty 4.10.1 Components of Uncertainty for Applied Torque with Lever Arm & Dead Weights 4.10.1.a Equation for realization of Torque using Dead Weight and Beam National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 25 of 29

Torque =

Force x Distance x (cos α)

T=

F x D x cos α

F= Where, T= F= D= α= mt = g= ρa = ρm =

m t x g L x [1-ρ a /ρ m ] Torque in Newton- meter Force in N Nominal Length of the Lever Arm in metre Angle True Mass used for generating the force Local acceleration due to gravity in m/sec2 Density of Air in kg/m3 Density of Mass in kg/m3

4.10.1.b Formula for applying Temperature correction to the length L=

l 0 *(1+β T *δ T )

l0 =

length at calibration temperature, T 0 =20ºC

βT =

Coefficient of linear Expansion for the material of Arm length Difference between the Temperature at calibration and during calibration

δT =

Major sources of Uncertainty of Applied Torque Uncertainty contribution of Force: • Uncertainty of Mass, error in Mass, drift or stability in Mass and Mass stack. • Uncertainty due to gravity and Uncertainty of gravity due to height of the mass stack. • Uncertainty due to Air Density. • Uncertainty due to Density of Mass. 4.10.1.c Formula for calculation of uncertainty contribution of generated force. [σ(F)/F]2 = [σ(m t )/m t ]2 +[σ(g)/g]2 +[(ρ a /ρ m )2 * ((σ(ρ m ) /ρ m )2+(σ(ρ a )/ρ a )2 )] Uncertainty contribution of Beam Length: • Uncertainty of beam length u(l 0 ) • Uncertainty due to angle measurement u(α) • Uncertainty due to thermal expansion coefficient u(β T ) • Difference in temperature of the beam between calibration and usage at lab (θ) • Uncertainty in temperature measurement u(θ) National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 26 of 29

4.10.1d Formula for Calculation of Uncertainty contribution of Beam Length: (u(l)/l)2 = (ul 0 /l 0 )2 + u2(α) + (β T θ/(1+β T θ))2 *

(uβ T /β T ) 2 + (uθ/ θ)2

4.10.1.e Uncertainty of applied Torque is calculated as below: (u(T)/ T)2

= (u(F)/ F)2

+

(u(l)/ l)2 + u2(α)

Where, uT is uncertainty of Torque, uF is uncertainty of Force, ul is the uncertainty of length of the beam u(α) is uncertainty of cosine error • Uncertainty due to bending if any should also be taken into account along with above. 4.10.2 Effect of Weight, Gravity, Buoyancy and Temperature on Generated Force 4.10.2.a Weight Consideration Weights should be calibrated in terms of Newton. If the weight is in terms of kg and converted in terms of force using the formula [F= m*g] For example: for m = 1 kg the generated force =1*9.80665= 9.80665 N For Force of 10N, we require denomination of weights 1kg, 10g, 5g, 2g, 2g, 500mg, 200mg, 10mg & 1mg to get 1.019716 kg. The shape of the weights used in the calibration machine should be such that, it doesn’t affect verticality of the measuring axis and concentric to the applied force. Otherwise, the magnitude of error of applied force will be more and hence the uncertainty since, force is a vector quantity. 4.10.2.b Gravitational Effects Consideration It is very important to establish the gravitational value of the laboratory since it is one of the major quantity during realization of force. The effect of not doing this could be a variation in force produced by the weight perhaps 0.5% of the force. It is therefore recommended that, the Force calibration laboratory establishes local value of gravity (g) and use weights that have been calibrated at that gravitational constant. 4.10.2.c Buoyancy Effect Consideration The weights are used to generate a downward force in air during force calibration (not in Vacuum). This means that, Archimedes’s principle applies i.e. air pressure under the weights causes an upward force. This reduces the effective force generated by the weights and therefore the mass must be increased to allow for this. If the weights are calibrated on conventional mass basis under standard conditions of air density of 1.2 kg/m3 at 20°C and density of weight 8000 kg/m3. The increase is required by a factor National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 27 of 29

of 0.012% - 0.015%. Because, realization of force is a product of true mass local g and local air density. 4.10.2.d Effect of Change in Temperature on Calibration Results • The weights and the hanger used are of steel material. The variation of temperature changes the volume of the material due thermal expansion and affects the value of mass as it is a function of density and volume. • The variation of temperature affects the air density, which is used in buoyancy correction. Hence, change in temperature affects in realization of force values. • Apart from the above, it affects change in length also in a lever multiplication system and there by uncertainty due to thermal expansion depending on the material used. 4.10.3 Uncertainty Components for Lever Arm and Force Transducer • Uncertainty of reference force transducer with indicator including error. • Uncertainty of lever arm length or radius including error. • Uncertainty due to coefficient of thermal expansion. • Uncertainty due to cosine error. • Type A uncertainty. 4.10.4 Uncertainty Components Torque Transducer • Uncertainty of reference Torque transducer with indicator including error. • Type A uncertainty. 4.11 Evaluation of CMC 4.11.1 Refer NABL 143 for CMC evaluation. 4.11.2 CMC value is not the same as expanded uncertainty reported in the calibration Certificate/Report. CMC values exclude the uncertainties which are attributed to the UUT (Unit under test/calibration). 4.11.3 For the purpose of CMC evaluation the uncertainty calculated along with Type A (10 readings with minimum and maximum) uncertainty is considered.

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 28 of 29

4.12 Sample Scope An illustrative example: Correct Presentation of Scope Laboratory: XYZ

Date(s) of Visit:

Discipline: Mechanical Sl

1

Parameter* / Device under calibration

Torque measuring system Torque Testing Machine

of

Master equipment used

Range(s) of Calibration and Measurement Capability Remarks+/ Method measurement ** used Claimed by Observed by Recommended Laboratory Assessor by Assessor

Torque Sensor with display (Class 0.2 accuracy)

Torque

For Torque testing machine as per ASTM E 2624-09

10 Nm to 100 Nm

0.25 %

0.28 %

0.28 %

* Only for Electro-technical discipline; scope shall be recommended parameter wise (where applicable) and the ranges may be mentioned frequency wise. ** NABL 143 shall be referred for the recommendation of CMC +

Remarks shall also include whether the same scope is applicable for site calibration as well. NABL 130 shall be referred while recommending the scope for site calibration.

Signature, Date & Name of Lab Representative

Signature, Date & Name of Assessor(s)

Signature, Date & Name of Lead Assessor

4.13 Key Points •

The design of fixtures and interfaces between the calibration device and the machine are critical. When using elastic torque or force measuring devices use class A or better of Torque transducer as per ASTM E 2428 or class 0.2 of BS7882: 2008 and Force sensor (Load cell) Class A of ASTM E74 or Class 0.5 of ISO 376 :2011(E).

•

Demonstration of any CMC values doesn't automatically qualify for granting accreditation until the lab satisfies the stipulated requirement given in this document.

National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 122-07 Specific Criteria for Calibration Laboratories in Mechanical Discipline –UTM, Tension Creep and Torsion Testing Machine Issue No: 05 Issue Date: 12.08.2014 Amend No: 00 Amend Date: Page No: 29 of 29

National Accreditation Board for Testing and Calibration Laboratories NABL House Plot No. 45, Sector- 44, Gurgaon – 122002, Haryana Tel.: +91-124 4679700 Fax: +91-124 4679799 Website: www.nabl-india.org