| 摘要 |
PURPOSE:To detect concentration of air-pollutant gas by comparing a reference signal with a signal representative of the quantity of absorption in the gas to be detected. CONSTITUTION:A beam of variable-wavelength laser, after passing through a space where a certain gas to be detected exists, is received by a light-receiving element 40, where gas concentration is obtained from the quantity of absorbing the laser beam by the gas. In this case, the circuitry 45-47 is provided to produce a reference signal which varies in accordance with the product of the length of light path employed for this detecting method by the gas concentration to be detected. The reference signal is compared with the signal representative of the laser absorption quantity by the gas to be detected which is obtained based on the output of photo-electric conversion of the laser beam received. The gas concentration is obtained from the reference signal level to be given when these two signals coincide with each other. |
