How to re-transmit and isolate 4-20mA Signals

How to re-transmit and isolate 4-20mA Signals

This application blog on how to re-transmit and isolate 4-20mA signals from remotely mounted 3-Wire Gas Detection Sensors is provided by our friends at Acromag.  To see the original blog, click here.  For more information on this application or the product used, contact us.

What’s the problem?

Firstly, signals from 3-wire remote sensors that monitor gases are usually transmitted directly to the remote gas monitor or controller.  However, sometimes the signal needs to reach more than one destination.  This is achievable by two methods:

  1. Retransmit the existing signal to additional locations
  2. Isolating the signal and then sending it on to multiple locations.

System Requirements to allow Re-transmit and Isolate 4-20mA Signals

Secondly, a 3-wire remotely mounted gas detection sensor transmits a 4-20mA Signal.  Note that the 3-wire loop is where the sensor and receiver share a ground connection with power.  The sensor uses a third wire to connect to power outside the current loop.

Use a 2-wire or 4-wire isolator to re-transmit and isolate a loop to a single location.


Use a 2-wire or 4-wire splitter to re-transmit the loop to two separate locations and maintain isolation on all three loops.

The Solution

  1. Acromag signal isolators will take a 4-20mA field input and provide an isolated 4-20mA output signal. Each Splitter channel operates independently.  Therefore, it is isolated from others to prevent interaction between channels.
  2. The 600T Series of isolators and splitters are field adjustable. Meaning zero and pan trim pots on the front of the units
  3. TT Series isolators are factory calibrated for 4-20mA in and out.
  4. Recalibration is simple. Use Acromag’s Windows Software on a desktop PC or the Acromag Agility Mobile App for Android.
  5. Follow the proper wiring practices as detailed in the user manual. Connect earth ground as indicated.

Why choose these Acromag Isolators and Splitters?

Finally, Gas detectors installed in hazardous areas.  Designed for UL/cUL Class 1 Division 2 safety rating for hazardous environments.  They provide a 4-20mA input and output.  Therefore, making installation simple with up to 1500V of isolation.  Protection is excellent.

Video of application note is below: