Gas detection method using laser generated frequency modulated light

摘要

The method uses a gas detector (10) comprising a laser transmitter (12) for sending out a frequency-modulated light beam of a wavelength absorbed by the gas, a reflector (18) and a receiver (14) which evaluates the light returned through the area (16) under examination. The equipment is fixed in an explosion-proof housing (52). Within the receiver are a reference generator (24) and a switching system consisting of a bandpass filter (26), an amplifier (18), a phase-regulating circuit and a phase-shifter. This blends the received signal with a reference signal using one of the modulation frequencies from the laser which has also traversed the gas area. Etalon strips filter out unwanted frequencies. A signal analyser connected to the blending switch system determines the presence of gas from analysis of its output.