| 摘要 |
An apparatus 100 for measuring a gas concentration comprises a conduit 102 through which an objective gas to be measured flows, a ultrasonic transmitting and receiving element 118 fixed in a straight portion 108 of the conduit, a reflecting plate 122 fixed in the straight portion to face to the ultrasonic transmitting and receiving element, a transmit-receive switching element 124 for switching the operational mode of the ultrasonic transmitting and receiving element between a transmitting mode and receiving mode. The apparatus further comprises a calibration gas source 114 for supplying a calibration gas of which components and component ratio are preliminarily known, temperature sensors 116, 120 for measuring the temperature of the calibration gas flowing through the conduit, a propagation time calculating means 126 for calculating the time period for propagation of the ultrasonic through the calibration gas in the conduit, a calibration means for calibrating the reference distance between the ultrasonic transmitting and receiving element and the reflecting plate based on the calculation results of the propagation time calculating means.
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