Two 4-20mA signals from a single 4-20mA signal


Thread Starter

Andrew Ng

Looking for a cheap device that can re-transmit a single 4-20mA signal to two 4-20mA signals. Something like a repeater device that can split the 4-20mA signal into 2 streams without signal degradation.

Junaid Zafar

There are numerous devices like that in the market. Check (for example) with Moore Industries. Split ranging is also done in DCS/PLC software blocks where one split ranging block drives two 4/20 mA outputs. Depends on what your application is.


Chris Parrish

Um, how many devices are on the loop? Have you tried putting them in series on the one loop? That's one of the benefits of current loops. Good luck.

The cheapest way is buy double out put isolator.
The specification : input : 4 - 20 ma
Outpurt : dual channel : 4 - 20 ma
Supply voltage : 24 V Dc/ or 230 v AC

Entech Consultancy, Madras. India.
Teletherm Instruments, Madras, India

Frank Rytkonen

Why do you want to do this? If you're trying to send the signal to more than one passive device for control or display, connect them in series on the loop. The active transmitter will be the only thing controlling the current in the loop, but all the passive receivers can monitor it. Little, if any, signal degradation should occur.

If you've got some other need in mind, please post it.

You may look into a signal splitter. There is one from Action Instruments. One 4-20 ma input, two 4-20 ma output.

Check out Action Instruments, ActionI/Q series signal conditioners. You would be interested in the model Q406 unit, this can give you (2) 4-20ma outputs from 1 input signal. They work great and come either AC or DC powered.

Action Instruments
8601 Aero Drive.
San Diego, CA 92123

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Richard O'Donnell

Hello: I will need some details regarding your existing 4/20 mA loop, and the two (2) secondary loops you are trying to feed.

(1) is your existing 4/20 loop from a 2-wire or a 4-wire transmitter?

(2) What is the total current Shunt resistance of each of the 'secondary 4/20 loops'?

I will asume that you have already evaluated these factors and will advise accordingly:

My understanding is that your present device is only capable of feeding one device (you are not able to put two devices in your existing 4/20 loop because the combined series resistance (input shunt Zt) of the two devices is too large.

To answer your question directly, AGM Electronics (Tucson, Arizona) used to make several 'modules' that would solve your problem: You can ask for a

(1). single 4/20 input, Dual 4/20 out module
(2). single 4/20 input, Single 4/20 out (high power (i.e., the output can source 4/20 mA into a total Z of 1300 ohms.

I beleive you even have the option of "Isolated" or "Non-Isolated" modules (transmitters)

I used to be an Engineer for AGM (12 years ago) and I like their "7-year" no-questions asked warranty. Also, their standard input resistance for a 4/20 device used to be only 50 Ohms (unlike the majority who use 250, 500 or more.

Their Telephone number is (520)722-1000

A second aproach is to examine all of your options; For example, do you have the option of selecting a voltage output and removing the input shunt resistors from the secondary devices (design permitting of course)?

likewise, if you can "re-span" your devices, is it possible to put the two inputs of the secondary devices in Parallel ? If the world were perfect, and each had identical values of input shunt resistors, 0 to 100% input would yield 0 to 50% output of the secondary devices.

Hope this helps!


Richard O'Donnell
VP, Engineering
Clean Technologies International Corporation.
My name is B.R Sandeep and working as Deputy Manager (Controls Engg) in Triveni Engg. Industries Ltd., Bangalore India.
I have used ICC-312(Isolating Interface) of MTL Instruments make for similar application in one of my project. This has costed us around Rs.5000/ . You can get more information if you log onto My normal e-mail ID is [email protected]

I'm having a problem involving putting two devices in series on a 4-20mA current loop. Both devices have connections to ground through
their common terminal. The current goes into one of the analog inputs of the first device then rather than go out the first devices common
terminal and into the input of the secondn device, the current goes straight to ground skipping the second device and comes out the second devices common terminal which is tied to ground. Does anybody have anyone know of any way of getting around such a problem?
From my instrument I have one two wire 4-20mA O/P. I need to provide this signal to two different instruments. What can I do? please suggest
It will depend on where isolation is needed and present, and the drive capability of the transmitter. You could wire the two instruments in series, wire one of the instruments in series with a transmitter or isolator, wire to a transmitter that has two output channels, or two isolators in series with their outputs going to the instruments.
Simply putting them in series may work, provided the source has enough
compliance and they are both isolated. That's kinda the idea of a current loop.

With somewhat less potential accuracy, there are splitters for this as well.