Analog Signal Multiplexer


Thread Starter

Bob Munch

Hello List: I have a PLC application that requires me to read twenty four 4-20ma temperature signals.(differential) Speed is not an issue so I would like to use a MUX that will take 6 signals and give me 1 output. There should be a digital input that triggers which Analog input is being passed through the MUX. This approach would allow me to use just 1 analog card in my PLC instead of 6 analog cards and save $$$. Does anyone on the list know who Mfgs something like this ? I could build it myself but it would be better if it were a commercial item. Thanks

Gerald Moore

I would go to and buy three analog inputs that each have 8, 4-20's, 200 or 400 series. The total cost would be less than $2k. The analog input card will probably have a mux built into it. Then you won't have to goof around with something external.

Jody Gallant

We do almost the same thing with an Analog output signal. We are controlling 25 different pieces of equipment (no simultaneously) using the output from a single analog card. The way we do it is with a Relay output card. Feed the Iout from the analog card into the common of the relay card, or cards. Then, we built a PLC program to make whichever output we want to control go active. Each piece of equipment is hooked to the other terminal on the output card and the common of each piece of equipment is tied together and then back to the common on the analog card. It is very simple to wire and works really slick. We have been using it this way for almost 5 years on one system, so reliability isn't a problem. You could do the same for the analog input. Hook it to the common of the set of relay outputs you want to use, and then run each 4-20ma signal into the other terminals. You may need to program in a bit of a delay to allow the signal to stabilize, but that is pretty simple. I can send you a set of drawings if you want, to make it clearer. good luck Jody Gallant CET Shadcomm Ltd.
There is an Israel company that makes a 16 channel multiplexer for $350. Check out: or email: [email protected] Since they are one of those preferred trade countries, there is NO duty on items they make in Israel and with Fedex, the delivery is pretty fast and not too expensive. Good Luck, Robert Phillips Cypress Water Plant Wichita Falls, Tx

Alastair Fordyce

Try for their 2100-A16 series of multiplexers. You can get thermocouple, V, I, Pt100 options. 16 inputs multiplexed to one analog output. Inputs can selected by PLC logic or clocked and demultiplexed in the PLC. You define which input is selected rather than the device telling you. Alastair Fordyce A.IPENZ, REA, NZCE,CQA Systems Engineer Bremca Industries Limited PO Box 7169 Christchurch NEW ZEALAND tel +64 (3) 332 6370 fax +64 (3) 332 6377 e-mail [email protected]

Johan Bengtsson

Similar topics have been up at the list before, you might want to check the archives as well as the answers to your question. (I don't know the answer, I just remembers similar topics) /Johan Bengtsson ---------------------------------------- P&L, Innovation in training Box 252, S-281 23 H{ssleholm SWEDEN Tel: +46 451 49 460, Fax: +46 451 89 833 E-mail: [email protected] Internet: ----------------------------------------
Hello Bob... I don't think you are looking for a MUX. You are looking for a device that will select (on command) an input to pass through to the device's output terminals. This unit would have to be specific with respect to the type of signal being passed along. These devices exist for many applications... keyboard and monitor switches for a server farm, a buffer unit that connects several PCs to one printer, a RS-232 switch that connects many serial devices to one terminal... are just a few that come to mind. I can't recall one that is set up to handle 24 channels of 4-20ma analog data, but... that does not mean one does not exist. If you find one... I am willing to bet that it will cost you more $$ for this device then what the analog input cards would have. Best Regards... Rick Kelly Chief Electrical Technician Natural Cuts, Cheese Operations Kraft Canada Inc. [email protected] (613) 537-8069 (V) (613) 537-8044 (F)

List Manager

Cheap and dirty..... speed is not an issue........why not use relay switching......4-20ma is real easy on contacts???? Gerald Beaudoin
TO: BOB MUNCH - Take a look at the 24 channel AMUX at "": . This is Tritech Enterprises 24 channel analog multiplexer built to interface directly to PLC's, but can work separately as well. For 24 ea differential signals, you might need two AMUX's.