TECHNICAL PROTOCOL FOR KEY COMPARISON CCAUV.A-K4

Transcription

1 EL CENTRO NACIONAL DE METROLOGÍA & THE DANISH PRIMARY LABORATORY FOR ACOUSTICS TECHNICAL PROTOCOL FOR KEY COMPARISON CCAUV.A-K4 OCTOBER 2006 DRAFT Knud Rasmussen & Salvador Barrera-Figueroa Danish Primary Laboratory for Acoustics Kgs. Lyngby Denmark Tel Fax

2 DRAFT TECHNICAL PROTOCOL FOR KEY COMPARISON CCAUV.A-K4 BACKGROUND It was agreed during the 2 nd meeting of the CCAUV in Sèvres, France on October 2001 that after finishing the first Key Comparison organised by the CCAUV, denominated as CCAUV.A-K1, concerned with pressure calibration of laboratory standard microphones LS1P, a free-field calibration of laboratory standard microphones type LS2aP should be the next step. The CCAUV defined an outline for a key comparison and it was agreed that CENAM would be the pilot laboratory with technical assistance given by DPLA. This document defines the protocol for the comparison. It should be read in conjunction with the Guidelines for key comparisons carried out by Consultative Committees by T J Quinn which includes more details on the purpose and conduct of key comparisons in general. The purpose of this document is to specify the procedures necessary for the comparison, but not the procedures used for the realization of the standards being compared. PARTICIPANTS The following laboratories will participate: BNM-LNE, France CENAM, Mexico DPLA, Denmark INMETRO, Brazil NIST, USA NMIJ, Japan NPL, UK PTB, Germany KRISS, Korea Contact details are attached. MICROPHONES TO BE CIRCULATED Two LS2aP microphones have been selected for this comparison. They are Brüel & Kjær type 4180 microphones serial numbers yyyyyyy and zzzzzzz. Each participant is responsible for the collection and return of the microphones to DPLA. Local customs formalities must be observed and if the participating laboratory requires DPLA to supply an ATA carnet for this purpose (or any other documentation) then they must give sufficient notice for DPLA to obtain that documentation. The timetable must be followed regardless of any delays caused by customs irregularities and this could cause a laboratory to loose the opportunity to participate in the comparison.

3 The microphones may be transported either by a courier company like DHL or by hand. If a courier company is chosen the microphones will be put in a thermo-jug packed in an isolated box delivered by DPLA. The microphones shall be returned using the same packing. If the microphones are transported by hand the microphones will be packed into the small box as provided by the manufacturer in order to avoid check-in problems during travelling. In this situation the microphones shall be carried only in the passenger cabin and never in the hold of an aircraft. No packaging will be supplied beyond that provided by the manufacturer of the microphones as it is thought that the best protection is the vigilance of the person carrying the microphones and this is easier to achieve when the package is small. Large temperature changes and sudden shocks must be avoided as these could cause an irreversible change in sensitivity or for the microphones to become less stable. Sudden shocks can be caused by applying sound calibrators, pistonphones or dehumidifiers to the microphones and these actions should also be avoided or performed with great care. The microphones must not be used for any purposes other than those associated with their calibration for this comparison. The microphones will return to DPLA for a check calibration after each calibration in a participating laboratory. This is so that the stability of the devices can be monitored and so that results from different laboratories can still be compared should a change occur. MEASUREMENTS This key comparison is only concerned with primary methods of calibration and will only consider results from such methods. The microphones require a polarising voltage of 200 V. Each laboratory is to report the open-circuit free-field sensitivity level of both microphones at the nominal preferred 1/3 rd -octave frequencies from 1 khz to 31,5 khz and optionally also 40 khz using their normal primary calibration method. The nominal frequencies are defined by the R10 series given in ISO 266. These frequencies are chosen in order to comply with the results of the CCAUV.A-K3 key comparison. It is recognized that the calibration technique used by the participants are quite different and may not allow calibrations to be performed at the nominal preferred frequencies but at other frequencies close to those. It is accepted that an interpolation technique is used to report the results at the preferred nominal frequencies. The interpolation technique used to derive the result at the required frequency shall be reported together with the results at the actual measurement frequencies in a separate report or as an annex to the main report. Also it may not be feasible to perform a free-field reciprocity calibration at frequencies down to 1 khz. It is accepted that the reported free-field sensitivity at the lowest frequencies are based on estimations derived by calculations or from a pressure calibration. The method used to estimate the sensitivities at the lowest frequencies shall be reported. It is recommended not to use the standard corrections given in IEC/TS since a side effect of the key comparison is to collect information to support or challenge this document. The initial free-field reciprocity calibrations at the pilot laboratory will be conducted in linear frequency steps of 120 Hz from 1-51 khz while the following performance checks will be reduced to the frequency range from 3 51 khz in addition to a pressure reciprocity calibration in the full frequency range. The microphones submitted shall only be used as receivers. Results shall be corrected to the reference environmental conditions given in IEC

4 REPORTING RESULTS Each laboratory shall report their results using the standard certificate that they would issue to a customer. This certificate should include: The environmental conditions during the calibrations. The actual distance(s) used between the microphones during the calibrations. Values of the temperature and pressure coefficients of the microphones used in the calculations. A summary of the uncertainty calculation and the overall uncertainties calculated for a coverage factor of k=2. It must be noticed that the CIPM Guidelines require uncertainty budgets to be submitted in advance of participation. Each laboratory shall submit a sufficiently detailed uncertainty budget and failure on doing so may result in the exclusion of the laboratory. The (preliminary) budget shall be submitted before the key comparison starts. However, any changes will be accepted, provided they are submitted before the laboratory receives the microphones and carries out the measurements. An additional covering letter or report should include (where necessary): Details of any deviations from the recommendations in IEC and an estimate of the effect on the reported results. The values of the acoustic centres used in the calculation. Calibration results using three decimals (if not already given in the certificate). The interpolation technique used if the actual measurements are not performed at the required frequencies. The technique used to estimate the free-field sensitivity at low frequencies if a direct calibration is not available. A recalculation of the results using a common set of acoustic centre values (to be circulated by the pilot laboratory). The results should be posted to DPLA within a maximum of four weeks of the return of the microphones. This deadline shall be strictly enforced. Failure on submitting the results within the deadline may lead to the exclusion of the participant laboratory. An or fax should be sent to announce that the results have been despatched. When all participants have finished the measurements, the reports together with the results from DPLA will be submitted to the pilot laboratory (CENAM) for analysis. If a result is found anomalous the laboratory in question will be notified and given 3 weeks to respond. The results from DPLA will then be circulated to the participants and the pilot laboratory will prepare a first draft report. FINANCE Participants are responsible for their own costs, the collection and return of the microphones and for any damage to the microphones while they are away from DPLA. When the microphones are transported by a courier company the participant shall contact the courier company and arrange for the microphones to be picked up at DPLA. In case DHL or UPS are used the laboratory may inform DPLA on their relevant import account number and full receiver address of the laboratory. DPLA will then contact the company and ask for a pick-up.

5 KEY COMPARISON REFERENCE VALUE The determination of the Key Comparison Reference Values is an important outcome of this project. It is expected that the analysis of the results can be conducted in the same way as used for the previous key comparison CCAUV.A-K3. TIMETABLE The timetable is shown below. It is essential that the microphones be returned to DPLA on time even if measurements are not complete at the participating laboratory. If a problem arises with the timetable then it may be possible for two participants to exchange their place in the timetable. If measurements cannot be completed at a laboratory then it may be possible for the microphones to go to that laboratory after the termination of the measurement round (in 2008). However DPLA cannot guarantee to perform check measurements after this date. In the event of one of the microphones failing then DPLA will attempt to find a substitute though this may make the analysis of the results more complicated. No Calibration laboratory Starting date Finishing date 1 DPLA 12 February March CENAM 5 March March DPLA 2 April April KRISS 23 April May DPLA 21 May June NPL 11 June July DPLA 9 July July NMIJ 30 July August DPLA 27 August September BNM-LNE 17 September October DPLA 15 October November PTB 5 November November DPLA 3 December December INMETRO 4 January February DPLA 4 February February NIST 26 February March DPLA 24 March April 2008 List of contact persons

6 BNM-LNE: Jean-Noel Durocher Laboratoire national de métrologie et d essais 29, avenue Roger Hennequin Trappes Cedex France Tel: Fax: jean-noel.durocher@lne.fr CENAM: Andrés Esteban Pérez Matzumoto Centro Nacional de Metrologia Vibration and Acoustics Division Km 4,5 Carretera a Los Cués, Municipio El Marqués C.P Querétaro Mexico Tel: Fax: eperez@cenam.mx DPLA: Knud Rasmussen, Salvador Barrera-Figueroa Danish Primary Laboratory of Acoustics, DFM Matematiktorvet Building 307, DTU 2800 Kgs. Lyngby Denmark Tel: ; Fax: kra@dfm.dtu.dk; sbf@dfm.dtu.dk INMETRO: Walter E. Hoffmann INMETRO - Laboratório de Eletroacústica Av. N. Sra Das Gracas, 50 Xerém CEP Duque de Caxias, RJ Brazil Tel: Fax: laeta@inmetro.gov.br KRISS: Sang Joon Suh Korea Research Institute of Standards and Science Acoustics and Vibration Group Division of Physical Metrology 1 Doryong-Dong, Yoseong Daejeon Korea, Republic of Tel: Fax: sjs@kriss.re.kr NIST: Victor Nedzelnitsky National Institute of Standards and Technology Acoustical Metrology 100 Bureau Drive, Stop 8221 Building 233, Room B140 MD , Gaithersburg United States Tel: Fax: victor.nedzelnitsky@nist.gov NMIJ: Ryuzo Horiuchi National Metrology Institute of Japan, AIST Acoustics and Vibration Metrology Division Tsukuba Central 2 Tsubuka Japan Tel: Fax: ryuzo.horiuchi@aist.go.jp NPL: Richard Barham National Physical Laboratory Quality of Life Division Hampton Road Teddington, Middlesex TW11 0LW United Kingdom Tel: Fax: Richard.barham@npl.co.uk PTB: Christian Koch Physikalisch-Technische Bundesanstalt FB 1.6 Bundesalle 100 D Braunschweig Germany Tel: Fax: christian.koch@ptb.de