To provide an ultrasonic wave propagation time measuring method and a gas concentration sensor capable of recognizing an accurate propagation time.
A received wave transmitted by an ultrasonic element 5 and received is subjected to full-wave rectification, and integrated by an integration circuit 37, and a peak value is retained in a peak hold circuit 39. As for detection of gas concentration, a determination value is set based on the peak value in a threshold level calculation part 21e, and the time when a comparator 43 determines that the amplitude of the received wave subjected to the full-wave rectification reaches a set value is used as an arrival time, and the gas concentration is detected based on a period from the transmission time to the arrival time.
ISHIKAWA HIDEKI
SATO YOSHIKUNI
ISHIDA NOBORU
OSHIMA TAKAFUMI
