光离子化检测器中新型微电流检测电路设计

光离子化检测器(photoionization detector, PID)中需要微电流检测电路模块，而传统的跨阻式微电流检测电路稳定性差，测量范围小，设计成本高，且整体结构较为复杂。采用对数放大器LOG112与微处理器STM32F103VCT6相结合，设计一种宽范围对数式微电流检测电路。通过TINA-9软件仿真，所设计对数前置放大电路应用于500 pA~8 nA的微电流检测，误差低于1%。搭建实验系统，将所设计检测电路检测结果与直接用商用皮安表(吉利时6485型)搭建的检测系统实验结果对比，2种测量方法具有较高的重复性，且整个检测系统线性度良好，拟合优度达到0.987。利用所设计系统与购置的空气检测仪在相同环境下分别测试同种浓度的异丁烯气体，发现所设计系统响应时间更快，准确度更高。实验测得系统响应时间小于6s，系统短期重复性约为±1.37%，长期测试的重复性约为±2.28%。实验结果表明，所设计宽范围对数式微电流检测电路能够应用于光离子化检测器中。

Design of a novel weak current detection circuit in photoionization detector

Weak-current detection circuit module is required in photoionization detector. However, the traditional cross-resistance micro-current detection circuit has poor stability, small measurement range, high design cost and complex overall structure.Therefore,a wide-range logarithmic weak-current detection circuit is designed by using logarithmic amplifier LOG112 and microprocessor STM32F103VCT6.Through the TINA-9 software simulation, the designed logarithmic preamplifier circuit is applied to the microcurrent detection of 500 pA~8 nA, and the error is less than 1%. The experimental system is built to compare the test results of the designed detection circuit with those of the detection system directly built with picoammeter(Keithley6485). The two measurement methods have high repeatability, and the linearity of the whole detection system is good,and the goodness of fit reaches 0.987. Using the designed system and the purchased air detector to test the same concentration of isobutylene gas in the same environment,it is found that the designed system has faster response time and higher accuracy.The experimental results show that the response time of the system is less than 6s,the short-term repeatability of the system is about ±1.37% and the long-term repeatability of the system is about ±2.28%. Therefore, the designed wide range logarithmic microcurrent detection circuit can be used in photoionization detector.