4-20 mA Current Loops

A 4-20 mA current loop is more imune to electric noise than any other voltage signal (0-10 VDC, 1-5 VDC, ..) and it can work at distances of more than 1 kM if the nominal power is 24 VDC.   Typical DC power supply voltages are 36 VDC, 24 VDC, 15 VDC, and 12 VDC.   NOTE: the power supply voltage must be at least 10% greater than the total voltage drop of the attached components (the transmitter, receiver and wire).   Note that the range of 4 to 20 mA has a 1:5 ratio.  

Converting a 4-20 mA signal back into a voltage is as simple as putting a resistor in the loop and measureing the voltage drop across it.   A 220 ohm resistor provides a 0.88 to 4.4 V range (0 to 5 V microcontroller).   A 470 ohm resistor provides a 1.9 to 9.4 V range (0 to 10 V DAQ).  

Related Links

The 4-20 mA Current Loop

NI current loop fundamentals

How To Make 4-20 mA Current Loop Measurements

Fundamentals of 4-20 mA Current Loops

 

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