Vol.2 No.4 2010

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Research paper : How the reliable environmental noise measurement is ensured (R. Horiuchi)−265−Synthesiology - English edition Vol.2 No.4 (2010) ・ The system can introduce new technology fairly rapidly by reconsidering technical requirements essential for the assessment of calibration service providers whenever necessary.・ JCSS can verify the performance of acoustic measuring instruments within the audible frequency range (20 Hz to 20 kHz) while the testing of sound level meters was limited to a range of 20 Hz to 12.5 kHz.・ Calibration service providers are required to have technical performance suitable for essential players of the traceability system. Calibration service providers registered at present have years of accomplishments as a specific testing laboratory of sound level meters or specific manufacturers of them in the Japanese Measurement Law.6 Validation of measurement capability6.1 Validation of equivalence among national standardsIn 1999, mutual recognition arrangement of measurement standards was made among countries including Japan[27]. In this arrangement, national metrology institutes of the countries approve the equivalence among national standards and accept calibration certificates of each other. Institutes of signatory nations are required to establish the quality systemTerm 7 conformable to the international rule of ISO/IEC 17025[28] and to verify their measurement capability objectively by participation in international comparisons (round robin tests).NMIJ/AIST established the quality system on self-developed acoustic standards. The National Institute of Technology and Evaluation (NITE) assessed NMIJ/AIST from the point of view of conformity to ISO/IEC 17025, based on ASNITE-NMI (a program to accredit national metrology institutes). NMIJ/AIST was accredited in the field of acoustics in January 2003.As to international comparisons, CIPM/CCAUV (International Committee for Weights and Measures /Consultative Committee for Acoustics, Ultrasound and Vibration) planned four international comparisons on laboratory standard microphones and NMIJ/AIST took part in all of them. International comparisons on pressure sensitivities of LS1P and LS2aP microphones have already finished and the results revealed that uncertainties (95 % level of confidence) declared by the main institutes including NMIJ/AIST range from 0.03 dB to 0.05 dB within the main frequency range[29,30]. Difference of the results between NMIJ/AIST and other institutes was less than the uncertainty evaluated by NMIJ/AIST. Thus, NMIJ/AIST could verify its equivalence to the other national standards.The number of participants in the international comparisons organized by CCAUV is limited to around ten and all the national metrology institutes in the world cannot be included. Therefore, similar international comparisons were individually conducted in several areas of the world. In Asia and Pacific area including Japan (this area is called APMP /Asia Pacific Metrology Programme), NMIJ/AIST acted as a pilot laboratory of the first international comparison for pressure sensitivity of LS1P microphones; NMIJ/AIST prepared the technical protocol, monitored Fig. 8 Results of international comparison at 1 kHz.Acronyms of national metrology institutes which participated in the international comparison are listed along the horizontal axis. Vertical axis shows deviation of each participant’s results from the reference value, determined as the arithmetic mean of all the participants’ results. If the deviation of a participant (marked as •) is within the range of uncertainty at 95 % level of confidence (which was self-declared by the participant and denoted by a bar), it is concluded that the national standard is equivalent to the other participants. Deviation from reference value (dB)SCL(Hong Kong)NPLI(India)NML/SIRIM(Malaysia)NIMT(Thailand)NIM(China)CMS/ITRI(Taiwan)NMIA(Australia)KRISS(Korea)NMIJ(Japan)VNIFIRI(Russia)PTB(Germany)NRC(Canada)NIST(USA)GUM(Poland)DPLA(Denmark)CSIR(South Africa)CENAM(Mexico)NPL(UK)0.080.060.040.020.000.10-0.06-0.10-0.04-0.02-0.08

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