一种信号隔离电路设计及故障模式分析

A Signal Isolation Circuit Design and Fault Mode Analysis

摘要:

隔离电路是工业生产现场智能监测设备、显示仪表等之间连接不可或缺的组成部分，能够去除共模电压和外界电磁干扰，对整个系统的测量精度和运行状态有着至关重要的作用。首先研究现有的隔离电路，并设计一种将1路4~20mA输入信号转换为2路1~5V输出信号的高可靠隔离电路。该电路由1路输入、单片机、2路输出以及隔离电源组成。其中，输入电路负责将输入的电流信号转换为电压信号并进行滤波；单片机负责对AD转换、误差补偿以及输出组态选择；输出电路负责光耦隔离、信号整形和DA转换。经过上述处理，输出2路相同的电压信号。该电路能够将干扰源和易干扰部分隔离，从而保证设备与操作安全。典型故障模式下的评估结果标明，该隔离电路能够有效消除串扰和降低外部干扰,能够满足不同监测平台隔离要求，适用于高精度测控系统。

Abstract:

Isolation circuit is an essential part of the connection between intelligent monitoring equipment and display instrument in industrial production site. It is able to reject the common-mode voltage (CMV) and external electromagnetic interference (EMI), and therefore is significant to the measurement accuracy and the performance of the whole system.Firstly,we investigate the current work and design a high reliable isolation circuit to change one4~20mA input to two 1~5V outputs. The isolation circuit is mainly consisted of four parts, including isolated power, one input, MCU, and two outputs, where the isolated power is used to supply the system energy; the input circuit is responsible for transforming the input current signal into voltage signal and filtering; MCU is responsible for AD conversion, error compensation and output configuration selection; the output circuit is responsible for optocoupler isolation, signal shaping and DA conversion. After the above procedure, it outputs two identical voltage signals. The designed circuit can isolate the interference source from the vulnerable part, so that to ensure the safety of equipment and operation. Evaluation with typical fault modes demonstrates that the proposed isolation circuit is more effective in eliminating crosstalk and reducing external interference. Therefore, the proposed isolated circuit is able to satisfy the isolation requirement of different monitoring platform and is applicable to measuring and controlling system with high measurement accuracy.