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化学发光法是测量低浓度的大气氮氧化物含量的有效方法,可用于24h连续自动分析的大气环境监测系统。然而该方法需要高温转换室、高压臭氧发生模块、高温反应室等模块,使得仪器内的环境分布极为复杂,仪器在长时间运行后容易出现灵敏度下降、信噪比降低等现象。针对上述现象,设计了用于仪器的光信号探测模块的温度控制系统。该温控系统基于PID控制原理,通过AVR单片机ATMEGA16对半导体制冷片(Thermo-Electric Cooling,TEC)的闭环控制来实现温度的精密控制。实验结果表明,该系统可以使光信号探测模块的温度控制在5℃±0.1℃,光电倍增管的暗噪声从25℃时的363个/s下降到5℃时的8个/s光子数,噪声波动标准差也从22降到3,能够很好地满足系统对信号探测稳定性的要求。
Chemiluminescence is an effective method to measure the content of atmospheric nitrogen oxides in a low concentration and can be used in the atmospheric environment monitoring system for 24-hour continuous automatic analysis. However, the method requires modules such as a high-temperature conversion chamber, a high-pressure ozone generating module, and a high-temperature reaction chamber, which make the environment in the instrument extremely complicated. The sensitivity of the instrument is liable to drop and the signal-to- noise ratio decreases after a long time operation. In view of the above phenomenon, a temperature control system for the optical signal detection module of the instrument is designed. The temperature control system based on PID control principle, through the AVR microcontroller ATMEGA16 on the semiconductor cooling sheet (Thermo-Electric Cooling, TEC) closed-loop control to achieve precise temperature control. The experimental results show that the system can control the temperature of optical signal detection module at 5 ℃ ± 0.1 ℃ and the dark noise of photomultiplier tube decreases from 363 / s at 25 ℃ to 8 / s photons at 5 ℃. The standard deviation of noise fluctuation is also reduced from 22 to 3, which can well meet the requirements of the system for signal detection stability.