Patent ID: 7201034
Filing Date: 2007-04-10
Classification: G01N

Abstract:
1. A gas concentration measurement instrument for measuring change in concentration of gas in a measurement region, comprising: ultrasonic wave transmitting means for transmitting an ultrasonic wave composed of a group of rectangular pulse waves as an ultrasonic wave generation signal; ultrasonic wave receiving means for receiving an ultrasonic wave transmitted through the gas in the measurement region and converting the ultrasonic wave transmitted through the gas in the measurement region into an electric signal to use it as an ultrasonic wave reception signal; and gas concentration measuring means for measuring a signal output time when the ultrasonic wave generation signal is outputted, generating an envelope processing signal by subjecting the ultrasonic wave reception signal to an envelope extracting process, measuring a threshold fall time when the envelope processing signal decreases below a predetermined threshold after exceeding the threshold, and measuring the difference between the threshold fall time and the signal output time as an indication of change in the gas concentration.