CRITERIA FOR LABORATORY ACCREDITATION IN THE FIELD OF TORQUE METROLOGY (Torque Generating Device Calibration)

Transcription

1 CRITERIA FOR LABORATORY ACCREDITATION IN THE FIELD OF TORQUE METROLOGY (Torque Generating Device Calibration) Approved By: Chief Executive Officer: Ron Josias Executive - Accreditation: Mpho Phaloane Author: Calibration STC Members Date of Approval: Date of Implementation: SANAS Page 1 of 8

2 CONTENTS: 1. Purpose and Scope References, Definitions and Abbreviations Environmental Requirements Laboratory Calibration General Requirements Calibration Calibration Certificates Procedures and Standards... 6 ADDENDUM 2: Amendment Record... 8 SANAS Page 2 of 8

3 1. Purpose and Scope The purpose of this document is to define the minimum technical requirements to be met by accredited Laboratories in the field of Torque metrology. This document is applicable to South African National Accreditation System (SANAS) accredited laboratories performing calibration of Torque Generating Devices for the use of the controlled tightening of bolted connections. 2. References, Definitions and Abbreviations 2.1 References [1] PM SANAS Policy Manual [2] A01 References, Acronyms and Definitions. [3] ISO 6789 Assembly Tools for Screws and Nuts. Hand Torque Tools Requirements and Test Methods for design conformance testing, quality conformance testing and re-calibration procedure. 2.2 Definitions Torque Generating Devices indicating torque tool (Type I) Tool that indicates by means of a mechanical scale, dial or electronic display, the value of torque exerted by the tool at the output drive. [3] setting torque tool (Type II) Tool that is preset to a certain torque value, so that, when the prescribed value of the torque is exerted by the tool at the output drive, a signal is released (e.g. audibly, visibly or perceptibly). [3] adjustable graduated torque tool (Type II) Tool designed to be adjusted by the user, which has a scale or display to assist adjustment. [3] adjustable, non-graduated torque tool (Type I) Tool designed to be adjusted by the user with the aid of a calibration device. [3] torque tool with fixed adjustment (Type II) Tool not designed to be adjusted by the user i.e. having a single setting. [3] SANAS Page 3 of 8

4 2.3 Abbreviations Calibrating Device The device used for the calibration of torque tools. Typically, a torque transducer with readout device. [3] CMC UUT CW Calibration Measurement Capability Torque measuring device being calibrated. (Unit Under Test) Clockwise rotational direction when viewed from the end of the torque measuring device to which the torque is applied. CCW Counter-clockwise rotational direction when viewed from the end of the torque measuring device to which the torque is applied. UOM Uncertainty of Measurement 3. Environmental Requirements 3.1. Laboratory Calibration The ambient temperature shall be maintained in the range 18 C to 28 C. The temperature shall not vary by more than ±1 C throughout a measurement series. The temperature at the start of a calibration, and the temperature at the end of the calibration shall be recorded The Relative Humidity requirements are not specified other than they should be high enough to reduce the static which could damage electronic readout instruments and below condensation which would aggravate the rusting of steel components. They shall be recorded The magnitude of vibration, shock or other disturbing conditions shall be such that they will have a negligible effect on the measurement results On-Site Calibration If a calibration is conducted on-site and the ambient temperature variation exceeds the range as specified in Para 3.1.1, the maximum and minimum temperatures during the calibration shall be recorded and reported on the calibration certificate. The influence of the temperature variation shall be taken into account when estimating the uncertainty of measurement. 4. General Requirements 4.1. Unique identification or serial number and maximum torque All UUTs shall have a unique identification number or serial number. This unique number shall be reported on the calibration certificate. The maximum working torque and a serial number shall be marked on the UUT Calibration to other standards. Should the calibration laboratory perform the calibration according to a recognised national or international standard, in preference to following the guidelines in this document, the standard used shall become the mandatory document and all tests and measurements, as SANAS Page 4 of 8

5 required by the standard, shall be performed and the results reported. The relevant standard used shall be referred to in the calibration certificate. In addition, any clauses/requirements of the standard complied with by the calibration laboratory, shall be clearly identified on the calibration certificate. 5. Pre-calibration Requirements 5.1 Orientation of the UUT. Torque generating devices may be calibrated either in the horizontal or vertical plane. When calibrating torque wrenches, great care should be taken to ensure that the handle is kept perpendicular to the torque axis. When calibrating torque screwdrivers, great care should be taken to ensure that the handle is kept in line with the principal torque axis. 5.2 Torque Loading When calibrating Type I torque tools: - the tool shall be loaded on the calibration device with increasing torque until the torque tool indicates the respective torque value. If the torque value has been exceeded, the calibration stage shall be repeated from the zero position. When calibrating Type II torque tools: - the tool shall be loaded on the calibration device with increasing torque up to approximately 80 % of the respective target torque value. From 80 % to the final target torque value, the load shall be applied slowly and uniformly. The setting of the target torque value shall be incremented from the lowest value. 5.3 Pre-loading When calibrating Type I torque tools: - a minimum of three pre-loads up to the maximum value must be carried out in the direction of calibration and after the release of load, the pointer or electronic display shall be set to zero When calibrating Type II torque tools: - five pre-loads up to the maximum value must be carried out in the direction of calibration. 6. Calibration. 6.1 Calibration Sequence As a minimum, torque tools shall be calibrated at approximately 20%, 60%, and 100% of the torque tools maximum torque range. If the scale mark of 20 % of the maximum torque value is not indicated on the torque tool, the permissible deviation shall be determined at the next lower scale mark. OR As specifically requested otherwise, by the customer during contract review. When calibrating torque tools, the number of measurements shall be as follows:- Type I Five times in a row, for every calibration point for Indicating torque tools Type II Five times in a row, for every calibration point for setting torque tools OR Five times at the nominal/set value for setting torque tools SANAS Page 5 of 8

6 OR Ten times in a row for adjustable non-graduated torque tools, 6.2 Indicated value The torque value reported on the calibration certificate is the value as displayed/indicated by the calibration device and not the torque tool (UUT). To determine the indicated value, the torque tool must be set to the nominal required torque value, and the measured value recorded from the display of the calibration device. 7. Calibration Certificates In addition to the SANAS requirements and those of ISO/IEC for calibration certificates the following shall also be reported on calibration certificates for Torque Generating Devices:- - Measurement results obtained at each point, in each rotational direction, the calculated mean value, and the associated expanded measurement uncertainties, - Details of the unique identification of the torque tool, - Details of the setup configuration of the torque tool where applicable, Maximum and minimum temperature 8. Procedures and Standards The calibration laboratory shall have detailed procedures for each measured quantity or type of torque generating device it is accredited for according to the SANAS accreditation schedule, as well as the relevant traceable calibration standards. 9. Authorship The revisions to this Technical Requirement document were prepared by the following members of an approved subcommittee of the SANAS Force, Torque and Hardness STC:- B Reynolds Denel Dynamics B Burke NMISA E Tarnow NMISA E Smit - SANAS J Petzer - SAA SANAS Page 6 of 8

7 ADDENDUM 1: Schedule of Accreditation S C H E D U L E O F A C C R E D I T A T I O N TORQUE METROLOGY Laboratory Accreditation Number 4321 Permanent Address of Laboratory: Petes plumbing for perfectly placed pipes 104 Piet Pompies str Pompiesville Ververlatevlakte Postal Address Private Bucket at the farm gate Pompiesville 9081 Tel : (012) Fax : (012) pete@pppp.co.za Technical Signatories Nominated Representative Issue Number Date of Issue Expiry Date : Pete Plumber : Pete Plumber : 01 : September 2006 : August 2008 ITEM MEASURED QUANTITY OR TYPE OF GAUGE OR INSTRUMENT RANGE OF MEASURED QUANTITY CALIBRATION MEASUREMENT CAPABILITY EXPRESSED AS AN UNCERTAINTY (±) 5. 1 TORQUE Torque Generating Devices Torque Wrenches 1 N m to 10 N m or 0 N m to 10 N m etc. 0,03 N m or T ( T+0,1 N m) etc Torque Screw Drivers Torque Impact Wrenches Torque Multipliers Note: Number according to the BIPM Classification of Services in Mass and related quantities Original date of accreditation: August 2003 Page 1 of 1 The CMC, expressed as an expanded uncertainty of measurement, is stated as the standard uncertainty of measurement multiplied by a coverage factor k = 2, corresponding to a confidence level of approximately 95% SANAS Page 7 of 8

8 ADDENDUM 2: Amendment Record Proposed by STC, FM Section Change Date New document aligned to ISO 6789: 2003 E SANAS Page 8 of 8