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.
