which state that the volume of a given mass of a gas is inversely proportional to its pressure at a constant temperature.“Simply put, pressure × volume, or pressure × capacity, is constant. Our measurement method involves using sound emitted by a speaker to induce changes in pressure, then sensing the change with microphones inside the instrument. To be more precise, the value is calculated based on information from the calibrator. We can then deter-mine volume or capacity by dividing the calculated value by the value of the articially applied pressure. Try to imagine forcing the pressure inside an enclosed space to change, then using an acoustic sensor to detect the change.”How to understand and overcome dierences in temperature characteristics of microphonesese acoustical capacity and volume meters rst appeared on the market in the latter half of the 1990s. roughout their history, the functions they oer have been steadily updated. One signi-cant change in their functionality involved handling changes in tempera-ture. Iseki explains how the functions for correcting for temperature changes were added.and volume meters have two micro-phones installed in each unit. To prevent unwanted variations in measurement results, we need to select a pair of micro-phones with minimal dierences in temperature characteristics.”What Iseki attempted to do was to investigate the pairing of microphones exhibiting nearly identical temperature sensitivity characteristics.“e task involved nding two microphones with similar temperature characteristics from, say, 30 micro-phones, and pairing them. A good pairing generates minimal errors, even when temperatures uctuate. e improvement reduced deviations in measurement results to within 0.1 mL for a temperature change of 1 °C. Selecting microphones based on tem-perature characteristics enabled high precision measurement.”e original purpose was to measure the volume of a babye mechanism of the acoustical capac-ity and volume meters was originally conceived by Professor Ishii at the Acoustics Laboratory, Faculty of Engineering, University of Tokyo and his group. Ph.D. Yoshihiro Hirao, who currently specializes in sound and “Around 15 years ago, while I was still a member of the custom order sec-tion that produced these acoustical capacity and volume meters, the main issue was how to handle temperature changes. e issue was that the results of measurement changed when tem-peratures changed. My duties involved performing various tests and reexamin-ing the design at the component level in order to overcome this problem. It took nearly six months to realize the impr-ovement. My predecessor came up with an idea to solve the problem. I was tasked with nding a way to implement the idea as an actual product.”Each instrument incorporates two microphones. e issue was traced to dierences in the temperature charac-teristics of the two microphones. To improve performance, Iseki had to nd a way to overcome the problem of these dierences.“Even microphones made from identical parts and assembled in the same way can have dierent tempera-ture characteristics. ey can look exactly the same, but they can still have slight dierences in how they react to temperature changes. at doesn’t matter with sound level meters, for example, because each unit has just one microphone. But acoustical capacity Cross-sectional diagram of an acoustical capacity meterCross-sectional diagram of an acoustical volume meterReference chamber capacity V1Communicating tubeAttachmentMeasurement enclosureTarget object (Volume V)e1e2V2⊿P2ｰ⊿P1GripMicrophone 1Microphone 2ControllerComputerUSBSine wave signalSpeakerControllerReference chamber capacity V1Sine wave signalCommunicating tubeAttachmentGripMicrophone 1Microphone 2SpeakerCombustion chamber VCylinder headComputerUSBe1e2V2＝V0 +VV0⊿P2ｰ⊿P14
元のページ ../index.html#6