4-20 mA Current Loop Primer

This application note’s primary goal is to provide an easy-tounderstand primer for users who are not familiar with 4-20mA current-loops and their applications. Some of the many topics discussed include: why, and where, 4-20mA current loops are used; the functions of the four components found in a typical application; the electrical terminology and basic theory needed to understand current loop operation. Users looking for product-specific information and/or typical wiring diagrams for DATEL’s 4-20mA loop- and locallypowered process monitors are referred to DMS Application Note 21, titled “Transmitter Types and Loop Configurations.”

Despite the fact that the currents (4-20mA) and voltages (+12 to +24V) present in a typical current loop application are relatively low, please keep in mind that all local and national wiring codes, along with any applicable safety regulations, must be observed. Also, this application note is intended to be used as a supplement to all pertinent equipment-manufacturers’ published data sheets, including the sensor/transducer, the transmitter, the loop power supply, and the display instrumentation.

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