CRITERIA FOR LABORATORY ACCREDITATION IN THE FIELD OF PRESSURE METROLOGY Approved By: Chief Executive Officer: Ron Josias Senior Manager: Mpho Phaloane Revised By: Specialist Technical Committee Date of Approval: 2014-10-21 Date of Implementation: 2014-10-21 SANAS Page 1 of 7
TR17-03 CONTENTS: 1. Purpose and Scope... 3 2. References, Definitions and Abbreviations... 3 3. Environmental Requirements... 4 4. General Requirements... 4 5. Technical Requirements... 5 Appendix 1: Schedule of Accreditation... 6 Addendum 1: Amendment Record... 7 SANAS Page 2 of 7
1. Purpose and Scope The purpose of this document is to define the specific environmental, general and technical requirements to be met by accredited laboratories in the field of pressure and vacuum metrology. This document is applicable to South African National Accreditation System (SANAS) Accredited Laboratories in this field. 2. References, Definitions and Abbreviations 2.1 References [1] OHS Act, 1993 Environmental Regulations 1987 - Lighting [2] OHS Act, 1993 General Admin Regulations 1994 Handling of Hazardous Chemical Substances [3] ISO 17025:2005 General requirements for the competence of testing and calibration laboratories. [4] NPL Guide 101 Guide to the Measurememt of Pressure and Vacuum (ISBN 0 904457 29 X) [5] BIPM Classification of Services in Mass and related quantities [6] Local value of Gravitational Acceleration National Physical Laboratory (UK) http://www.npl.co.uk/reference/faqs/how-can-i-determine-my-local-values-ofgravitational-acceleration-and-altitude-(faq-pressure) 2.2 Definitions 2.2.1 Absolute Pressure If a vessel were to contain no molecules the pressure would be zero. Pressures measured on the scale which uses this zero value as its reference point are said to be absolute pressures. [4]. 2.2.2 Atmospheric Pressure Atmospheric pressure is the force exerted on a surface area caused by the earth s gravitational attraction of the air vertically above that area. Atmospheric pressure is subject to change in air density caused by changes in temperature and global weather patterns. Atmospheric pressure decreases with increasing altitude. Atmospheric pressure is synonymous with barometric pressure. [4] 2.2.3 Gauge Pressure The value of pressure measured with reference to atmospheric pressure. Pressure excursions below atmospheric pressure are sometimes known as a negative gauge pressure [4] 2.2.4 Pressure Balance An Instrument consisting of a finely machined piston mounted vertically in a close fitting cylinder used for maintaining a calculable pressure; also known as a piston gauge. When fitted with a means of pressure control, additional pressure ports, masses etc, the complete system is commonly known as a dead-weight tester. [4] 2.2.5 Vacuum Vacuum is commonly known to imply any pressure below atmospheric pressure. [4] 2.3 Abbreviations CMC Calibration and Measurement Capability MSDS Material Safety Data Sheet OHS Act Occupational, Health and Safety Act SANAS Page 3 of 7
TR17-03 3. Environmental Requirements 3.1 The temperature in any laboratory where pressure or vacuum calibration is conducted must be maintained at 22 C ± 3 C however no temperature control is necessary when quoting uncertainties of larger than ± 0,25 %. 3.2 Laboratories quoting uncertainties of equal to or less than ± 0,10 % shall ensure that temperature gradients within the laboratory are limited to less than 1ºC per Hour. 3.3 Where necessary the laboratory shall maintain appropriate records to demonstrate and confirm the temperature and temperature gradients within the laboratory. 3.4 Lighting within the laboratory shall be adequate to facilitate the correct performance of the calibration work undertaken. Cognisance shall be taken of the minimum levels of lighting as specified in the environmental regulations of the OHS Act.[1] [3] 3.5 Vibration levels in the laboratory, shall be such that they do not have an adverse effect on the measurement results. 3.6 Draughts in the laboratory caused by doors, fans and/or air conditioners should be such that they do not have an adverse affect on the measurement results. Where necessary local isolation in the form of draught shields shall be utilized. 3.7 Thermometers and/or temperature recorders used for the measurement and recording of the ambient temperature in the laboratory and onsite, shall be calibrated. 4. General Requirements 4.1 All cotton and chamois leather gloves used for the handling of pressure balance weights shall be kept clean. 4.2 Weighing of pressure balance weights, and the use, or calibration of a pressure balance in the laboratory must take place on a work bench of adequate construction, which will facilitate the stable and correct operation of the balance. The work bench design shall take cognisance of vibration, stability, and support. 4.3 Raw data shall not be recorded in pencil, erasable ink or amended using correction fluid. 4.4 The laboratory shall have MSDS available for all chemicals used in the laboratory, including fluids used in pressure balances. [2] 4.5 Where the laboratory uses or calibrates mercury manometers, or barometers, the laboratory shall have a MSDS available, that shall include all the details of the necessary action to be taken in the event of a mercury spill. [2] 4.6 Laboratory procedures shall address temperature stabilization times for all equipment received by the laboratory for calibration. 4.7 Laboratory procedures shall address the use of various types of tubing and connectors used to interconnect equipment during calibration. Particular attention shall be paid to the applicable maximum pressure rating of the tubing used. 4.8 Where appropriate localized temperature measurement shall be performed and the temperature recorded during calibration, e.g. for Piston Cylinder units or Mercury columns. 4.9 Whenever Pressure Balances are either calibrated or used during a calibration and an uncertainty of ± 0,005 % is quoted, the air density must be determined and a buoyancy correction applied. SANAS Page 4 of 7
4.10 The calibration certificate shall provide all relevant information necessary for intelligent interpretation, and the application of appropriate corrections by the user. 5. Technical Requirements 3.1 Local Gravity Whenever a pressure or vacuum calibration laboratory calibrates or uses a pressure balance or liquid column manometer in the laboratory, the laboratory shall have determined, or calculated, the local gravity at the location of the laboratory. The NPL (UK) has recommended the following formula for the calculation of an approximate value for local gravity [6] where: g = 9,780 327 (1 + A sin 2 L - B sin 2 2L) 3,086 10-6 H m s -2 A = 0,005 302 4 B = 0,000 005 8 L = latitude H = height in metres above sea level The uncertainty in the value of g so obtained is generally less than ± 5 parts in 10 5. 5.2 Calibration of Pressure Balances Laboratories conducting the calibration of pressure balances, shall be accredited for pressure balance calibration as a separate entry on their accreditation schedule. The laboratory will require a CMC of at least 0,05% in order to be accredited for this function. The standard used to perform the calibration shall be appropriate in order to achieve the desired uncertainty. 5.3 Calibration of Pressure Balance Weights 5.3.1 The calibration laboratory shall report in the calibration certificate at least the conventional mass, the associated uncertainty of measurement, nominal pressure (where indicated on the pressure balance weight), and the calculated pressure determined from the mass, standard gravity, nominal piston area (where available), and measured or assumed air and metal densities. 5.3.2 Pressure calibration laboratories are limited in the CMC they may report for the calibration of pressure balance weights to 0,005% + 2 mg. Calibration of pressure balance weights to a smaller uncertainty should be referred to a laboratory accredited for mass calibration. 5.4 Calibration of effective Area of Piston / Cylinder Where a laboratory reports the effective area of a piston cylinder unit, the area shall be referenced to zero pressure at 20 C. A (0,t) 5.5 Calibration of Pressure Gauges The laboratory shall have a procedure/s that address the calibration of pressure gauges reserved for oxygen use. This procedure/s shall describe the steps to be undertaken in order to avoid the contamination of these gauges with oil. SANAS Page 5 of 7
TR17-03 APPENDIX 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 PRESSURE METROLOGY Facility Accreditation Number 299 Permanent Address of Laboratory: Special Metrology cc Upper Johannesburg Road Randville Johannesburg Postal Address: PO Box 12345 Randville 1699 Tel : (011) 622-1234 Fax: : (011) 622-5678 E-mail : pressure@special.co.za Technical Signatory Nominated Representative Issue No. Date of issue Expiry date : Ms M Pressure : Mr Vacuum : 01 : Sept 2004 : Sept 2009 ITEM MEASURED QUANTITY or TYPE OF GAUGE OR INSTRUMENT 1.1 Mass Standard RANGE OF MEASUREMENT QUANTITY CALIBRATION AND MEASUREMENT CAPABILITY EXPRESSED AS AN UNCERTAINTY (±) Pressure Balance Weights 10 g to 10 kg 0,02% + 5 mg 3.1 Absolute Pressure Gas Medium Barometer Digital Piston Manometer Altimeter 3.2 Gauge Pressure 3.2.1 Gas Medium Pressure Gauge Pressure Balance Pressure Transducer 3.2.2 Liquid Medium Pressure Gauge Pressure Balance Pressure Multiplier Manometer 3.3 Differential Pressure 0,01 Pa to 1 000 Pa 1 kpa to 260 kpa - 80 kpa to 0 kpa 0 kpa to + 85 kpa + 85 kpa to 175 kpa 175 kpa to 4 Mpa 0,1 MPa to 60 MPa 60 MPa to 70 MPa 5 % 15 Pa 15 Pa 10 Pa 15 Pa 0,01 % + 100 Pa 0,01 % + 100 Pa 0,03 % + 100 Pa 3.3.1 Gas Medium Pressure Measuring Device - 400 kpa to + 400 kpa 0,05 % + 10 Pa Liquid Medium Pressure Measuring Device - 400 kpa to + 400 kpa 0,05 % + 10 Pa 4 On-site for item 3.2 above Note Unless otherwise specified all references to percentage represent percentage of reading rather than percentage of range. Original date of accreditation: 2004 Page 1 of 1 ISSUED BY THE SOUTH AFRICAN NATIONAL ACCREDITATION SYSTEM SANAS Page 6 of 7
Addendum 1: Amendment Record Proposed By: Section Change TR 17-01 CEO Section 2 Changed QM to PM CEO Page 1 Changed to new logo & Front page FM Changed from R 17 to TR 17 (Technical Requirement) document. TR 17-02 STC 3.2 0,25% changed to 0,10% 4.3 Or correction fluid added. 4.8 Clause added 5.2 Clause amended 5.3.4 0,01% changed to 0,05% Appendix 1 Amended numbering to comply with adopted BIPM numbering TR 17-03 FM Section 2.3 MC changed to Calibration and Measurement Capability CMC FM Appendix 1 Changed to new format, CMC replaced MC STC 2.1 Reference [4] changed to NPL document Guide 101 STC 5.3 Clause 5.3.1 moved to general requirements Clause 5.3.4 moved to general requirements STC 5.1 NPL formula added for the calculation of local gravity STC Appendix 1 Added note to Schedule of Accreditation SANAS Page 7 of 7