| 摘要 |
PROBLEM TO BE SOLVED: To provide a gas concn. sensor capable of measuring the concn. of gas with high accuracy. SOLUTION: Since the propagation time T1' of the first reflected wave (first reflected wave) of a deteriorated product becomes longer than the propagation time T1 of the first reflected wave of a new product, when the concn. of a specific gas is measured on the basis of the propagation time T1 of the first reflected wave of the new product, the concn. of the gas cannot be accurately detected. Since the reflected wave (e.g.; second reflected wave) after the first reflected wave is merely reflected from the surface of an ultrasonic element and not affected by the internal structure of the element, even if a sensor is deteriorated, the fluctuations of the propagation times T2, T2' thereof are reduced and the influence of deterioration is reduced. Then, the concn. of the specific gas is detected based on the propagation time of the second reflected wave hard to receive the influence of deterioration but not based on that of the first reflected wave easy to receive the influence of deterioration. By this constitution, the concn. of gas can be measured highly accurately. |
