ECN Forum Forums General Topics of the Trade General Discussion Area 4-20ma Pressure Transmitter

Does anyone have any industrial experience with pressure transmitters. My question is this: If the voltage is 10 - 30 V DC and the output is 4-20ma, would this require 4 wires to connect( 2 for the voltage and 2 for the 4-20ma output). Can the transmitter run on only 2 wires?

Yes it can work with only two wires. This is fairly common.

Positive transducer lead to positive of power supply. Negative of power supply to negative side of "load" . Positive side of load to negative lead on transducer.
So essentially it is just a loop.

The load could be many things such as a plc controller a meter or readout of some type etc.

4-20 mA control loops are very common in industrial control gear. In the 2-wire configuration, the transmitter is actually powered by the voltage drop across it.

A good introduction to current loop sensors here:

http://www.datel.com/data/meters/dms-an20.pdf

How many terminals do you have on the transducer? And do you have the wiring diagram for it? Normally you will have an input 2 wires (10-30vdc) and an output 2 wires (4-20ma). Two in. Two out. No common. To test the output MA, put meter in series with one output conductor. Use the MA setting on the meter. Depending on how sensitive you need this, you may need to adjust the DC input or if provided the adjustment screw on the transducer.