A sound level meter and acoustic couplerThe sound level meter is inserted into the coupler as shown above. One technical advantage offered by RACS is that the sound level meter can be precisely calibrated, regardless of the direction in which the sound level meter faces.Morikawa’s boxThe box of secret tools used personally by Morikawa. Inside are materials like clay, felt, and cushioning.PatentInternal structure of the coupler forming the base of the acoustic coupler (JP6420014)A design proposed for the internal structure of the couplerMorikawa’s pursuit of symmetry and robustness produced parts having complex shapes like this.the e ort re ectively, as a cra sman might. “You could say it was labor-in-tensive. I knew that all I could do was take one step a er another uphill to the goal line. at’s what programming is all about.”Funaki makes no e ort to exagger-ate the di culties, but as the interview proceeds, the not-so-small obstacles become evident.“Come to think of it now, the path was indeed long and arduous, with dif- culties making up most of the land-marks along the way. I think the most enormous obstacle was determining the optimum timing for measurement.”Timing is essential in connecting a target device like a sound level meter to RACS and taking measurements to con rm the target device functions cor-rectly. A noise present just at that moment measurement takes place can make the target fail the test. Conversely, a target device that isn’t functioning pro perly might just happen to produce normal readings. In other words, some thing had to be put in place to determine whether or not the target device was operating correctly at all times. rough trial and error, Funaki arrived at the solution: he came up with a method for determin-ing whether the target device was oper-ating correctly by introducing a wait time in the measurement.“When measurements are being carried out manually by an operator, he might realize, ‘Hey wait. is isn’t working properly.’” And then he’ll sim-ply repeat the measurement process. But with automatic measurement, in some cases, the timing of the measure-ment itself can generate incorrect read-ings. So I programmed the measure-ment to incorporate a wait time to increase the certainty of the readings on the target device. You could say I gave the so ware the ‘Hey wait, let’s try that again’ judgment a skilled worker would have. I felt this was one of the major achievements of the extensive develop-ment e ort.”Developing a Coupler to Guarantee Measurement Reliability e development of the acoustic coupler took place alongside the pro-gramming work. Despite the major issues that needed to be overcome, the development also reached its goal. A coupler is a socket-like component for connecting the devices to be measured to RACS—for example, sound level meters or microphones. In the initial stages of RACS development, there were major shortcomings in the acous-tic coupler. Masato Morikawa at the Technical Development Center took over the task of completing the coupler from his predecessor.“Measurement is always associated with uncertainty. Put simply, uncer-tainty is the error or dispersion of a val-ue obtained from actual measurement from the true value. eoretically, if the error is 1 dB, then the true value can be calculated by correction, meaning sub-tracting this error of 1 dB from the measured value. But correction isn’t possible because no one knows the true value. A major factor in this uncertain-ty is repetition reproducibility of mea-surements. e more the repetition reproducibility contributes to increas-ing uncertainty in measurements, the lower the reliability of an acoustic cou-pler will be. So nding ways to reduce the uncertainty associated with the rep-etition reproducibility of measurements signi cantly a ects the development of a successful calibration system. My approach to tackling this problem was to develop a new acoustic coupler.”To measure sound level meters, microphones, and other target devices with RACS, they’re inserted into the acoustic coupler. Dispersion in mea-surements was known to be caused by A prototype of the couplerOne of several coupler prototypes. The design of the final coupler was determined through the design and validation of these prototypes.4Masato MorikawaS&V Sensor Development Section, Compo-nent Technology Development Department, Technical Development Center. He contrib-uted to the development of microphones and sound calibrators associated with sound and vibration measuring instru-ments. In the development of RACS, he played a central role in the design and pro-duction of the acoustic coupler.

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