This article describes the signal acquisition interface types and features used by sensor in industrial automation, it includes three common electronic interfaces these are 4 ~ 20mA current output, Hart communication output and MODBUS output. Through these two aspects whether explosion and two or four-wire ,the article describes the different characteristics and practical applications of 4 ~ 20mA current output in five cases as the basic signal output of radar, ultrasonic level meter, understanding these signal interface technology from the source can help us solve various problems in practical applications quickly and accurately .%本文介绍了在工业自动化中，传感器常用的信号采集接口类型及特点，包括3种常用电子接口，即4～20mA电流输出、Hart通讯输出、MODBUS输出。通过从是否防爆和二/四线制的角度，重点讲述了作为雷达、超声波物位计最基本的信号输出4～20mA接口在5种情况下，不同接线图的原理及实际应用特点，以便从源头上理解这些信号接口技术，有助于快速精准地解决实际应用中的各种问题。
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