Acoustic Probe for Temperature Measurement Suitable for Audio Interfaces Having Random Input/Output Delays

Abstract

The technique of measuring temperature distribution is essential across various fields. An acoustic probe, emitting sound waves and measuring their time-of-flight (ToF) to reach a microphone, can measure the average temperature along the sound propagation path. Moreover, deploying multiple acoustic probes in the measurement space allows temperature distribution measurement with fewer sensors than conventional point-type sensors. The accuracy of temperature measurement using acoustic probes depends on precise ToF measurement. However, the impact of ToF measurement errors on temperature distribution remains thoroughly explored. Acoustic probes require a DAC/ADC with minimal input/output delay or the capacity to synchronize operations via an external trigger. This poses challenges in utilizing existing platforms like audio interfaces on single-board computers. In this study, we proposed a method to accurately measure ToF, even when random delays occur in the operation's timing. This method is achieved by transmitting loopback signal from DAC to ADC and canceling the delay between input and output. Experimental evaluations demonstrate that the proposed method exhibits an error of 0.36° C, while substracting offset of delay demonstrates an error of 0.93° C when the length of acoustic path is 2.48m. These results shows that the proposed method can eliminate the impact of audio input/output delays and precisely measure air temperature.