analog signal duplication

  • Thread starter fereydoun ataei
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fereydoun ataei

I have a transmitter with 4-20 mA analog output. Can anybody tell me how to connect this single analog signal to two seperate control panel? Is there any device to duplicate the analog signal?

Alan Hartwell

One inexpensive way is to convert the current into a voltage using a resistor. A 250 ohm resistor converts 4-20 mA into 1-5 volts. Feed this voltage to high impedance voltage inputs in the two (or more) control panels. The drawback here is that you may introduce ground loops with the potential for picking up noise.

A better way would be to use two signal isolators with the inputs in series, and the outputs tied to the separate control panels. The Action Instruments G408 is one possibility. It has low input resistance because it is powered by
separate terminals.

Be aware that many other signal isolators are powered from the input signal. More than one in series would introduce more resistance than most transmitters could drive.


You may not need any isolators or resisters to do this. 4-20 ma is designed to run in a loop. simply route the 2 panel devices in series with your loop.
A couple of obstacles may keep you from doing this.
1. Do not exceed maximum loop resistance for your transmitter (Usually 600-1000 ohms) Able to drive 2-3 typical 4-20ma loads.
2. Make sure that the devices in your loop are isolated. Sometimes a PLC analog input module may have the common(-) side of all the inputs tied
together. If this is the case, see if you can make this the most negative point in the loop.

Good luck
James Johnson
[email protected]
The device that I would suggest to "duplicate" you analog signal into two isolated and "cleaned up" signal is from Phoenix Contact. The
part number is MCR-FL-C-UI-2UI-DCI-NC order# 2814867. You can find more info at "": This device take an input of any type of analog signal and the retransmits the data out of two analog outputs that are isolated and can even be of a different analog type (4-20ma, 0-20ma, 0-10V, etc) The device is fairly inexpensive for what it does.
you could turn the signal into 1-5V with a precision 250 ohm resistor and connect the control panels to that, if the analog inputs in the panels have sufficiently high input impedance, and the wires connecting them arent too long. You could buffer the 4-20ma signal with an amplifier and connect the output of that to the panels. Dataforth corporation's 5B modules should be able to handle that.

Rick Daniel

Michael R. Batchelor

I can't believe we're going through this again. There's a huge discussion about it in the archives from just a few weeks ago. And there's about a hundred ways to do it. The easiest way to do it, assuming you have decent receiver instruments with isolated inputs, is to just loop the devices in series and let the same signal pass through both receivers. If either of the receiver instruments is a common mode device which references it's local ground then you'll need to isolate it, and there were *LOTS* of
decent suggestions.

yonca yesilipek

Yu can duplicate an analog input with MTL ICC312.
It has one 4-20ma input and two 4-20 ma outputs.
It should be powered with 24Vdc and inputs and outputs are isolated.

Richard A Wolf / Abb Inc.

Connect the signal wire in series. Make sure that the total loop impedance does not exceed the load limits of the transmitter.

There are several source strategies for "splitting " and isolating the signal....Indicating, non-indicating, Control devices with retransmission et al