Policy on Measurement Traceability

Transcription

1 Policy on Measurement Traceability Date of Issue: January 1, 2006 Voluntary EMC Laboratory Accreditation Center, Inc. (VLAC) This document is copyrighted under the Copyright Act. Unauthorized reproduction, transcription, or any other unauthorized duplication of this document in whole or in part, with the exception of reproduction for private use, may constitute an infringement of the copyright and other rights 1

2 Policy on measurement traceability Introduction This document is for the Voluntary EMC Laboratory Accreditation Center (hereinafter referred to as VLAC) to use as a part of evaluation criteria for accreditation of testing laboratories engaged in the field of Electromagnetic Compatibility (EMC) testing. The purpose of this document is to give an operational interpretation of requirements specified in article 5.6 Measurement traceability of VR101 General requirements for the competence of testing laboratories (ISO/IEC version). As such this document contains no requirements that exceed the general requirements. 1. Scope of application This document lays out policy for laboratories that seek accreditation for competence in performing electromagnetic compatibility testing (interference and immunity testing) on measurement traceability of their testing facilities. This document also applies to laboratories already accredited by VLAC at the effective date. 2. Normative references 2.1Quoted standards In addition to the standards referenced in VR101 and related standards referenced in VR102, the following standards are referenced. GUM: Definition of terms 3.1 Traceability The property of a result of a measurement whereby it can be related to appropriate standards, generally international or national standards, through an unbroken chain of comparisons in which all uncertainties are indicated(vim: 1993) 3.2 Calibration The set of operations which establish under specified conditions, the relationship between values indicated by a measuring instrument or measuring system, or values represented by a material measure or reference material and the corresponding known values of a measurand (VIM:1993) 3.3 Measurement Set of operations having the object of determining the value of a quantity reference: VIM:1993) 3.4 Uncertainty of measurement Parameter associated with the result of a measurement that characterizes the dispersion of the values that could reasonably be attributed to the measurand (VIM: 1993, GUM: 1993). Examples are the standard deviation and an estimate which characterizes the range of values within the true value. 3.5 Test Activities to determine characteristics of an object by using a given procedure. 3.6 Verification Deed of confirmation by presenting objective evidences that specific requirements are met. 2

3 3.7 Reference standard A standard, generally of the highest metrological quality available at a given location or within an organization from which measurements made at that location are derived (VIM-6.6). 4 Basic policy 4.1 Basic principle: For all testing facilities that employ measurement facilities and functions and reference standards (all collectively referred to as subject equipment hereafter) that have potential to significantly impact the precision of test results and its effectiveness, the testing laboratory shall evaluate their potential, and establish a procedure and plan for calibration of the equipment, if the potential is not negligible. Before putting the subject equipment in actual test operations the laboratory shall carry out the calibration based on the plan, verify the result and keep records on this action. Note 1: Note 2: Certificates or records of calibrations shall bear an indication that subject equipment is traceable to national meteorological standards. In addition, those documents shall contain measurement results including uncertainty of measurement. In principle, uncertainty of measurement should be presented based on the guide for presentation of uncertainty of measurement (GUM). If calibration service does not cover issuance of calibration certificates but does cover verification of calibration, then supplemental information (such as criteria for tolerance) together with a record of such verification of calibration can give a similar effect to what described in note Selection of equipment needing calibration Testing laboratory shall first select subject equipment that needs calibration through evaluation of need. In the record of selection the exclusion of equipment from the selection is not justified unless the following conditions are met. (1) Contribution of uncertainty of the subject equipment is negligibly small to uncertainty of test result. 4.3 Calibration Calibration of subject equipment selected in accordance with item 4.2 above can either be get done using outside calibration services or in-house self-service. In either case it is necessary to develop and follow a calibration plan in order to be able to demonstrate appropriateness of operations, competence in measurement and traceability. When using outside calibration services the laboratory shall use a JCSS accredited company or domestic or overseas calibration machinery accredited by national standards institutes and the like or signatories of Mutual Recognition Arrangement of such organization as APLAC and ILAC, as long as they are available. 4.4 Records on calibration and verification to demonstrate appropriateness of operation How to carry out calibrations (or verifications rendering equivalent results) on subject equipment varies depending on the nature and degree of precision (uncertainty) and other factors of testing performed by the laboratory. Therefore, it is up to testing laboratories to identify and control subject equipment considering intended purpose of use and to keep record of matters in an appropriate way Followings are guidelines for required record keeping on calibration of subject equipment Calibration substantiated with calibration certificate that includes necessary information a) Calibrations by Japan Calibration Service System (JCSS) 3

4 Calibration certificates with an accreditation symbol issued by a JCSS accredit laboratory within its scope of accreditation are an appropriate record of calibration meeting requirements in item 4.1. b) Calibrations by a national standards institute and the like (see note below) Calibration certificates issued by national standards institute and the like are an appropriate record of calibration meeting requirements in item 4.1. Note: The following organizations are all national standards institute. They are, Meteorological and Standards Department of National Institute of Advanced Industrial Science and Technology (Independent Administrative Agency of Japan), National Institute of Information and Communications Technology (Independent Administrative Agency of Japan) and Japan Electric Meters Inspection Corporation, and JCSS Designated Laboratories c) Calibrations by calibration laboratories accredited in accreditation schemes other than JCSS s scheme Calibration certificates with an accreditation symbol issued by calibration laboratories accredited by signatories of Mutual Recognition Arrangement of APLAC and ILAC and the like are an appropriate record of calibration meeting requirements in item 4.1. d) Calibrations by other calibration laboratories If one of calibration certificates such as those listed below is to be used, it shall include supplementary information that demonstrates traceability to SI units. In concrete terms, the information shall cover calibrated value and uncertainty of calibration and prove that there is a chain of traceability up to national standards as the primary standards to realize SI units. In this case, certificate-using laboratories shall ascertain and keep record that the issuer of the certificate has adequate Quality System and enough technical competence to perform the calibration Calibration certificates issued outside the accreditation scope by JCSS Accredited Laboratories Calibration certificates issued by suppliers of measuring instruments/test equipment e) In-house calibration A testing laboratory that performs calibrations by itself shall basically meet requirements imposed to calibration laboratories. In other words, self-calibrating test laboratories are required to have calibration performed by appropriately trained staff using reference standards and facilities with adequate traceability in accordance with documented procedures. Also the laboratory shall keep record of all related matters (for example materials for estimates of uncertainty) including calibration data and estimates of measurement uncertainty. Note 1: Calibration of type d) or e) above shall not be performed unless it is the last resort when calibration of either type a) b) or c) is not possible for some reason. Note 2: Calibration described in e) above is the one performed by laboratories accredited by VLAC (accredited laboratories). In case an accredited laboratory is part of a larger organization that has a calibration department under it independent of the accredited laboratory, calibration performed by the calibration department is not in-house calibration. If the calibration department is qualified as per a) d) above, then calibration performed by it is considered legitimate. If the calibration department is not qualified as such, then the calibration performed by it is not considered legitimate Points of concern about practice on the use of verification services 4

5 In most of the cases, the results of verification (verification certificate and verification mark etc) do not describe measurement data and uncertainty of measurement. If this is the case it is necessary to acquire supplemental information (such as on the common difference used, measurements and declaration of conformity going with them) to satisfy traceability requirement. 5