| 摘要 |
<p>PURPOSE:To prevent the deterioration of S/N of a photodetecting signal and to prevent the detection accuracy of gas concentration from lowering, by controlling the photodetecting signal of the measuring gas side in a constant level by a signal for measuring a reference gas outputted from an amplifying part regardless of sensitivity variation of a photodetecting part basing on a temperature variation. CONSTITUTION:In an infrared absorptiometric type gas concentration measuring apparatus, a bias electric current of a power source 6b is supplied to a photodetecting element 5 through a resistance 7b for bias and also, each photodetecting signal of the reference gas side and that of the sample gas side is outputted from the element 5 to a noninverting input terminal + of an amplifier 19 provided to an amplifying part 9a through a capacitor 8b for decoupling. At this time, the variation of the bias electric current is detected by an amplifier 26 and the luminous quantity of a light emission diode 28 is increased at the time of increasing the bias electric current as the temperature rises and on the contrary, the luminous quantity is lowered as the temperature lowers and then, gains of the amplifier 19 are controlled by varying the inner impedance of a photodetecting body 29. Hereby, the photodetecting signals of the reference gas side and that of the measuring side, are controlled to be constant regardless of a sensitivity variation of the element 5 basing on a temperature variation and especially, deterioration of S/N of both photodetecting signals at a high temperature is prevented.</p> |
