Speed of Sound Measurement Using an Ultrasonic Motion Detector

Abstract

We propose a method to measure the speed of sound in air using a motion detector. The experiment is based on the principle of a motion detector used to measure distances. This device measures the time of flight of alternating ultrasonic waves between the observer and the target. By assuming a fixed speed of sound, the time of flight can be converted into a distance. The medium, including its temperature through which the sound travels, influences the speed of sound. A motion detector has been used to show the effect of CO2 concentration on the resulting distance measurement, and to estimate the linear change in speed of sound per degree Celsius. The distance measurement using a motion detector has to be calibrated according to the medium’s condition. The Logger Pro 3 features allow adjustment of the temperature setting and addition of an offset value to correct the motion detector reading.