Abstract: This experiment improves the ultrasonic velocity measurement instrument using a capacitive sensor ranging system．By controlling the capacitive sensor measures the data at the threshold voltage position through the output voltage of the piezoelectric transducer receiving sound waves，it achieves precise and automatic wavelength measurement，reducing human error and improving measurement efficiency． It is particularly advantageous when measuring the speed of sound in media with real-time changes in state．In the experiment，the first step was to investigate the impact of the threshold voltage on the experimental results．The results show that increasing the threshold voltage can improve measurement accuracy．When the threshold voltage is 11 V，the propagation speed of sound in air is，the relative uncertainty is，and the percentage deviation is．Compared to before the improvement，the relative uncertainty has decreased by，and the percentage deviation has decreased by．This experiment will provide strong support for research and application in related fields．
