Formation of reference signals in laser-type gas analyzers with mechanical switching of optical channels

A gas analyzer of the laser-absorption type consists of mechanically switched optical channels and a signal detecting electronic converter. A method of forming reference signals is proposed which will ensure exact synchronization of both components for maximum sensitivity and interference immunity during channel switching and signal detection. This method is applicable specifically to such a gas analyzer with two-beam, two-wave measurement of low light absorption levels. The intensity of radiation impinging on the data gathering photoreceiver is converted to an electric signal of a certain amplitude in the case of an analog converter or to a pulse repetition rate in the case of a digital one. In each case the reference signal is formed by a rotating disk with slots spaced in a certain sequence. The main function of the converter is to determine the ratio of the intensity drop to the intensity in the optical etalon channel. In the analog mode the photoreceiver output voltage is alternately sampled and stored, its magnitude being proportional to the duration of the reference pulses and thus to the disk speed. In the digital mode the reference signals define the instants of time at which individual converter elements are switched on, this being more practical than ensuring equal time intervals of pulse counting.