Bi-lateral comparison of pistonphone calibration between INMETRO and INTI

Transcription

1 PROCEEDINGS of the 22 nd International Congress on Acoustics Acoustical Measurement and Instrumentation (others): Paper ICA Bi-lateral comparison of pistonphone calibration between INMETRO and INTI Jorge Martín Riganti (a), Federico Ariel Serrano (b), Thiago Antônio Bacelar Milhomem (c), Zemar Martins Defilippo Soares (d) (a) INTI Instituto Nacional de Tecnología Industrial, Argentina, (b) INTI Instituto Nacional de Tecnología Industrial, Argentina, (c) INMETRO Instituto Nacional de Metrologia, Qualidade e Tecnologia, Brazil, tbmilhomem@inmetro.gov.br (d) INMETRO Instituto Nacional de Metrologia, Qualidade e Tecnologia, Brazil, zmsoares@inmetro.gov.br Abstract In , Instituto Nacional de Tecnología Industrial - Unidad Técnica Acústica - INTI (the National Metrology Institute of Argentina) and Instituto Nacional de Metrologia, Qualidade e Tecnologia - INMETRO (the National Metrology Institute of Brazil) participated in a comparison of pistonphone calibration within the Inter-American Metrology System called SIM.AUV.A-S1. However, since that time no other comparison was performed. Therefore, it was agreed between INTI and INMETRO that a new comparison of pistonphone calibration could be performed between these institutes with the aim to keep the support to the sound pressure level quantity. Each laboratory used its own procedure for the measurement of sound pressure level, frequency and total harmonic distortion. INMETRO was the pilot laboratory and the international standard IEC guidelines were followed. The institutes results were collected throughout the project and were calculated the module of normalized error which are all less than 1, i.e. the results are satisfactory. Keywords: comparison, pistonphone, calibration

2 Bi-lateral comparison of pistonphone calibration between INMETRO and INTI 1. Introduction All metrologists know the importance of a stable standard in all metrologies areas and they look for to achieve it. Since 1875, when the International Bureau of Weights and Measures (BIPM) was created [1], this search has been more structured. Furthermore, the modern global economic needs better measurements: more accuracy and lower uncertainties. After the creation of the Inter-American Metrology System (SIM), who aims to organize and improve the cooperation between the Inter-American National Metrology Institutes (NMIs) [2], all its members measurements and uncertainties are made based on international standards. To qualify and prove that the individual measurements are consistent, it is required to compare measurements and uncertainties between NMIs. Thus, the international comparisons are a bridge to achieve this proposal with a methodic technical work. The basic structure of an international comparison is to measure a known and very stable standard with the better uncertainty as possible, then, transport the standard to a NMI who measures it and, finally, get it back to the pilot laboratory where it is measured for last time (if doesn t travel to another NMI). The travel always implies stress to the standard so the pilot laboratory needs to measure it again and expects that the results after and before the travels are within the declared uncertainties. Before the start of the measurements, a technical protocol must be prepared and agreed between the participants. This document should include, among other things, the standard to be circulated, the method to be used, the measurements treatment to be applied, the pilot laboratory (responsible to calculate the comparison results and prepare a final document) and the schedule to be followed. This paper presents the first bilateral comparison in acoustics organized by Instituto Nacional de Metrologia, Qualidade e Tecnologia (INMETRO) and Instituto Nacional de Tecnología Industrial Unidad Técnica Acústica (INTI) aiming to support the sound pressure level. 2. Comparison protocol In March 2015, a protocol was agreed between INMETRO and INTI containing the practical procedure to circulate the standard and a general framework for the measurements. The standard circulated was a pistonphone, the calibration method used was the inserted voltage technique, the measurements were compared using the module of normalized error and INMETRO was the pilot laboratory [3]. 3. Traveling pistonphone 2

3 The pistonphone circulated in this comparison was supplied by INMETRO. The stability of the standard was verified by measurements performed at INMETRO before and after its circulation. Table 1 shows the deviation between the measurements after and before the circulation. It was verified with the one inch to half inch adaptor ( half inch ) and without the adaptor ( one inch ). Table 1: Deviation between measurements performed at INMETRO after and before the standard circulation. Nominal Sound Pressure Level [db re. 20 Pa] Sound Pressure Level [db re. 20 Pa] Frequency Total Harmonic Distortion (one inch) (half inch) The results in Table 1 are lower than INMETRO declared uncertainty and endorse the stability of the standard during the circulation. 4. Measuring systems Figures 1 and 2 show blocks diagrams of INMETRO and INTI measurement systems [4, 5]. PISTONPHONE LS MICROPHONE PREAMPLIFIER (WITH INSERT VOLTAGE FACILITY) INSERT VOLTAGE JUNCTION UNIT MEASURING AMPLIFIER MULTIMETER SINE GENERATOR AUDIO ANALYZER Figure 1: Blocks diagram of the measuring system used by INMETRO. PISTONPHONE LS MICROPHONE PREAMPLIFIER (WITH INSERT VOLTAGE FACILITY) INSERT VOLTAGE JUNCTION UNIT POWER SUPPLY ATENUATOR BOX SINE GENERATOR MULTIMETER DISTORTION METER Figure 2: Blocks diagram of the measuring system used by INTI. 3

4 5. Results The results of the sound pressure level generated by the pistonphone were obtained measuring the open circuit voltage of the laboratory standard microphone using the inserted voltage technique. Those values were corrected taking in account the influence of the barometric pressure, the temperature, the humidity and the frontal volume of the microphone [4, 5]. The reported sound pressure level (), frequency and total harmonic distortion (THD) according to the international standard IEC 60942:1988 [6] for the pistonphone for both laboratories are shown in Tables 2 and 3. Table 2: Reported sound pressure level, frequency and total harmonic distortion by INMETRO. Nominal (one inch) (half inch) 1 re. 20 Pa. Frequency THD Table 3: Reported sound pressure level, frequency and total harmonic distortion by INTI. Nominal (one inch) (half inch) 1 re. 20 Pa. Frequency THD Analysis of the results The statistical analyses of the results were carried out by the pilot laboratory using the module of the normalized error E n [7], given by the following equation: (1) where M INTI are the measurements reported by INTI, M INMETRO are the measurements reported by INMETRO, U INTI are the expanded uncertainty of measurements reported by INTI and U INMETRO are the expanded uncertainty of measurements reported by INMETRO. The modules of the normalized error are shown in Table 4 and Figure 3 [8]. 4

5 E n 22 nd International Congress on Acoustics, ICA 2016 Table 4: Modules of normalized error. Nominal Frequency THD (one inch) (half inch) re. 20 Pa " 1/2" 1" Frequency 1/2" Frequency 1" THD 1/2" THD Figure 3: Modules of the normalized error. The results are less than 1 and so the performances of both participants are considered satisfactory. 7. Conclusions Several factors have influence in the sound pressure level generated by the pistonphone. The front volume of the microphone and the barometric pressure are the main source of the corrections. The agreement in the results shows that both factors are well defined. For the frequency measurement, the 0.0 Hz difference between the institutes needs no further commentaries. Regarding the distortion measurements, it is well known the difficulties involved in their calibration. Nevertheless, for the two setups (with and without the one inch to half inch adaptor) it was possible to note a close the agreement. So, it is possible to conclude that the results of the comparison are in general quite satisfactory. References [1] BIPM, The Metre Convention, Available in: Access in: June [2] SIM, Available in: Access in: June

6 [3] Milhomem, T.A.B.; Soares, Z.M.D.; Serrano, F.A.; Riganti J.M., INTI-INMETRO Technical protocol for bi-lateral comparison, March, [4] INMETRO, NIT-LAETA-010 Pistonphone calibration by the inserted voltage technique, July (In Portuguese). [5] INTI, PEA08 Pistonphones Technical characteristics verification as per IEC 60942, August [6] IEC, International Standard IEC Sound calibrators, [7] ISO/IEC, International Standard ISO/IEC Conformity assessment -- General requirements for proficiency testing, [8] Milhomem, T.A.B.; Soares, Z.M.D.; Serrano, F.A.; Riganti J.M., Final report on the pistonphone bilateral comparison INMETRO-INTI, September,