Design of a Photoelectric Precision Detection Circuit of Dual Channel for the NH3 Concentration

摘要

Ammonia(NH3) is the most abundant alkaline gas in the atmosphere. It is the root cause of the formation of most secondary particulates in PM2.5 and the accelerator of the haze pollution formation in the atmosphere. Therefore the monitoring of the NH3 concentration is very important to the environmental protection. In this paper, the principle of NH_3 concentration detection based on Lambert-Beer law has been introduced. A dual-channel modulated ultraviolet photoelectric signal detection circuit for NH_3 concentration has been designed and its performance index has been studied. And then a precision detection circuit is designed, which is composed of a trans-impedance amplifier and a lock-in amplifier, with which the output of the UV photoelectric detector can be amplified to a suitable voltage range, and the DC noise of the pre-stage amplifier is effectively removed by the lock-in amplifier. The designed circuit has been tested for the NH_3 concentration quantitative measuring in the laboratory, with the exchange calibration method being used to ensure the consistency of the two channels. It can be drawn from the test results that the designed circuit is of high SNR, measuring accuracy and a large dynamic range. The NH_3 concentration detection limit of vehicle emissions can reach 2ppm, while the detection precision is ±19ppm.