Effect of noise and vibration on the performance of a particle concentration laser meter and optimization of its parameters

Spurious illumination penetrating into a gas duct adversely affects the performance of a laser gage measuring the concentration of solid particles dispersed in the air flow. The noise and gas duct vibration caused by the noise and vibration of the flow driver and other sources mechanically connected to the gas duct modulate the spurious radiation so that it may generate a signal that is perceived as a useful one by a photodetector. The noise-and vibration-modulated spurious illumination, as well as its optical-to-electric conversion with consideration for the spectral characteristics and the connection of the photodetector to the laser gage, is analyzed. From the amplitude and frequency properties of real noise and vibration sources causing the gas duct walls, on which the laser gage is mounted, to vibrate, the effect of the parasitic illumination is estimated. The operating parameters of a laser gage with double amplitude modulation and subsequent double synchronous detection, which make it possible to considerably improve its noise immunity, are proposed.