Patent ID: 6418782
Filing Date: 2002-07-16
Classification: G01N

Abstract:
A gas concentration sensor which detects the gas concentration of a specific gas, comprising:a measurement chamber having a space into which the specific gas is introduced and having a reflection surface inside the chamber; an ultrasonic element for transmitting an ultrasonic wave toward the reflection surface that is located inside the measurement chamber and at a predetermined distance away from the ultrasonic element; and a drive circuit for driving the ultrasonic element so as to transmit an ultrasonic wave having at least two frequency components; wherein the transmitted ultrasonic wave propagates through the gas and reflects off the reflection surface to form first and second reflection waves, the first reflection wave being the transmitted ultrasonic wave reflected at the reflection surface, the ultrasonic element reflecting the first reflection wave toward the reflection surface, and the second reflection wave being the first reflection wave reflected at the reflection surface, wherein the concentration of the specific gas is determined on the basis of an arrival time difference between the first and second reflection waves reflected at the reflection surface and arriving at the ultrasonic element, and wherein the transmitted ultrasonic wave and the first and second reflection waves each has an antiphase component, and the arrival time difference is determined by measuring a time period between the antiphase component of the first reflection wave and the antiphase component of the second reflection wave.