Chemical Testing ISO/IEC 17025 Application Document Annex H: Calibration of gas analysers July 2013
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Chemical Testing Annex H: Calibration of gas analysers (except for motor vehicle emission testing to Australian design rules (Annex I)) This document provides additional interpretative criteria and recommendations for the application of ISO/IEC 17025 in the field of Chemical Testing for both applicant and accredited facilities conducting calibration of gas analysers, except for motor vehicle emission testing to Australian design rules which is covered in Chemical Testing Annex I. Applicant and accredited facilities must also comply with the ISO/IEC 17025 standard and Chemical Testing field application documents and any field annexes, policies and/or technical circulars (refer to NATA procedures for accreditation). The clause numbers in this document follow those of ISO/IEC 17025 but since not all clauses require interpretation the numbering may not be consecutive. 5.5.2 Common equipment performance checks Facilities are responsible for establishing their own equipment assurance program. This is to ensure that all equipment used satisfies the need to produce consistent and reliable and where appropriate traceable results. In doing so facilities must ensure that where methods writing bodies have included equipment calibration and checking intervals in standard methods that these intervals must be followed if the methods are covered by the accreditation. Facilities should refer to the guidance documents available for equipment (General Equipment Table) for further information on calibrations and checks on equipment. The following supplementary information pertains to equipment items having specific application to the calibration of gas analysers and may not be directly described within the General Equipment Table. Item of equipment Gas detection Instruments Maximum period between successive checks/ calibrations Prior to use check Weekly check Monthly check Procedures and comments Physical damage, zero and single point span check on individual sensors on portable devices at approximately 60%-90% of full scale of range being used. Physical damage, zero and single point span check at approximately 60%-90% of full scale of range for fixed monitors used for continuous monitoring on mobile equipment. (See note vii) Physical damage, zero and single point span check at approximately 60%-90% of full scale of range for fixed monitors used for continuous monitoring on non-mobile equipment. (See note vii) July 2013 Page 3 of 6
Item of equipment Maximum period between successive checks/ calibrations 6 Monthly calibration Procedures and comments Physical damage, zero and six point span check for NDIRS (with recommended values of 15, 30, 45, 60, 75 and 90% of the full range being used) (See note xii) Physical damage, zero and three point span calibration (see note vi) for other fixed or portable sensor types including UV, chemiluminescence, interferometer, refractive index, catalytic, FID, electrochemical, thermal conductivity, paramagnetic and zirconium oxide detectors. Physical damage, zero and two point span calibration (see note vii) for fixed or stationary instruments with combustible sensors used in explosive or potentially explosive atmospheres a with an output scale of zero to 100% lower explosive limit. Reference gases Reactive reference Gases Non-reactive reference gases at a concentration greater than 0.01% (100ppm) Non-reactive reference gases at a concentration of 0.01% (100ppm) or less 2 years or once the cylinder pressure drops below 700kPa (100psi) whichever comes first. 4 years or once the cylinder pressure drops below 700kPa (100psi), whichever comes first. 2 years or once the cylinder drops below 700kPa or less whichever comes first. One point for single point alarm instruments (see note viii). July 2013 Page 4 of 6
Notes (i) (ii) Frequency given is the MAXIMUM periods between checks/ calibrations. Instruments must be completely recalibrated after significant maintenance. (iii) The calibration history for each instrument must be recorded and retained. (iv) (v) (vi) The initial calibration must check interferences. The laboratory should be aware of the contaminants that may create cross-sensitivities. Calibrations must be performed more frequently if poisons/ contaminants are likely to be present in the atmosphere that is monitored by a catalytic sensor. Calibrations at three points (and zero) must adequately cover the full scale of the range. One point must be between approximately 60% and 90% of full scale, except for fixed or stationary flammable sensor instruments that are calibrated in situ in explosive or potentially explosive atmospheres with scales of 0-100% lower explosive limit (see note vii). (vii) Calibrations at two points may be used for calibration of in situ fixed or stationary flammable sensor instruments in explosive or potentially explosive atmospheres with scales of 0-100% lower explosive limit. In these situations a highest calibration point of approximately 50% lower explosive limit may be used. For weekly/ monthly single point span checks, a span gas concentration of approximately 50% lower explosive limit may be used. (viii) For single point instrument alarms, a one-point calibration is performed at the level at which the instrument alarms. (ix) (x) (xi) Fixed instruments with a remote sensor head should be calibrated in-situ where possible. If these devices are removed for calibration (i.e. in a laboratory), suitable connection leads with the same impedance must be used. For remote sensors that do not permit calibration adjustment at the actual head/sensor, and the calibration adjustment is performed at the transmitter/ readout unit, the sensor head and transmitter/ readout unit must be calibrated as a matched system. The gas flow rates necessary for optimum response of flame ionisation detectors should be checked regularly. Zero checks must be made with high purity gases (depending on precision and accuracy required). Oxygen-quenching effects must be determined on commissioning. For low level alarms (and semiconductor type detectors) all operating parameters must be included on the calibration certificate and the instrument must be calibrated with the gas type that the instrument is to measure. (xii) A non-dispersive infrared analyser, which has a linearising circuit, is not considered to be a linear instrument. A nominally linear instrument is linear if its response is within 2% of linearity over its full range of detection. (xiii) Wosthoff pumps, mass flow controllers and gas dividers must be checked annually. The checks should cover the full range of the devices. This should preferably be carried out by an accredited laboratory. 5.10 Method of reporting Test documents relating to the calibration of gas analysers must meet NATA s accreditation requirements set out in the Chemical Testing Application Document. The conditions of tests (temperature, gas mixtures, laboratory, insitu, etc.) must be clearly stated and the meaning of the test result must be unambiguous. July 2013 Page 5 of 6
Endorsed test documents must only relate to the calibration of the instrument. Any opinions on the performance of the instrument must appear on a separate, non-endorsed attachment. However, brief comment on any service or repair that does not offer opinions may be included provided that a disclaimer is made on the report stating that these comments are not part in the endorsed test document information. In addition, there must be traceability to the reference gases used for calibration or the method of generating references (e.g. Wosthoff Pump). This must be stated, either on the report or on the relevant work sheets. Amendment Table The table below provides a summary of changes made to the document with this issue. Section or Clause Amendment 5.5.2 Clarification regarding facility s responsibility for establishing their own equipment assurance program July 2013 Page 6 of 6