Abstract: An ultrasonic distance measuring device retrieves an ultrasonic wave propagation speed from a correlation between an output of a medium sensor and a corresponding ultrasonic wave propagation speed. The ultrasonic distance measuring device sets a propagation path detection period for detecting a detection signal, which corresponds to the ultrasonic wave reflected by a liquid surface, based on a longest propagation path length and a shortest propagation path length between the liquid surface and the retrieved propagation speed of the ultrasonic wave. The ultrasonic distance measuring device calculates a distance of the propagation path based on a time difference between a detection timing of the detection signal and an output timing of the ultrasonic wave in a propagation path detection period, and the propagation speed of the ultrasonic wave.

Abstract: An ultrasonic distance measuring device retrieves an ultrasonic wave propagation speed from a correlation between an output of a medium sensor and a corresponding ultrasonic wave propagation speed. The ultrasonic distance measuring device sets a propagation path detection period for detecting a detection signal, which corresponds to the ultrasonic wave reflected by a liquid surface, based on a longest propagation path length and a shortest propagation path length between the liquid surface and the retrieved propagation speed of the ultrasonic wave. The ultrasonic distance measuring device calculates a distance of the propagation path based on a time difference between a detection timing of the detection signal and an output timing of the ultrasonic wave in a propagation path detection period, and the propagation speed of the ultrasonic wave.