4-20ma---to split or not to splt

cjd1965 · Feb 12, 2014

Hi
I have an existing device with a 2 wire pressure transmitter, 24V 4-20mA feeding a existing BMS device

I need to take that into a new separate PLC panel (Siemens S7 ET200s)

I want to split the signal but my boss wants to take the 4-20 into the ET200 and retransmit

The power supply at each panel is different

So,,opinions pls

diat150 · Feb 12, 2014

I would think that you would want to use a splitter that has isolation since they are on separate power sources. Pretty sure we use a weidmuller brand... I can get a part # tomorrow.

cjd1965 · Feb 12, 2014

Yes that what I was thinking...

Power the splitter from the new panel and bring exising 4-20 into it and feed the bms and PLC seperatly

My boss is thinking ET200 route is cheaper but because PSU are different it becomes more of a problem

Part# would be useful thanks

RheinhardtP · Feb 12, 2014

S406 WavePak Loop Splitter

The Bottom one under Brochures and Datasheets.

shooter · Feb 13, 2014

Try to put them in series as a lot of inputs are isolated from power supply, at least the ones i use (WAGO).
otherwise use a repeater with two outputs (best solution), this way the PLC can stop without problems on the BMS and other way around.

BryanG · Feb 13, 2014

I have been using the range from a company called Status, they were an American company but seem to have been bought out by a UK firm. The price seems right and Farnell have them in stock.

http://www.status.co.uk/product/25_current--loop-splitter.html

http://uk.farnell.com/status/sem1200/isolator-signal-splitter/dp/898107?Ntt=898107

Farnell Part No. 898107

Tom Jenkins · Feb 13, 2014

The separate power supplies shouldn't be a problem - I've done that before. Just make sure that neither input is tied to ground. If one is then you will need an isolator to avoid a ground loop.

DamianInRochester · Feb 13, 2014

I don't see and issue with just repeating the signal through the ET200. A splitter/isolator would be a more robust solution. Shooter's point about the PLC being able to stop without losing the signal downstream is definitely a valid one.

cjd1965 · Feb 13, 2014

Hi All
I don't want to disrupt the existing installation or disconnect ground loops etc so have found a mA loop powered splitter from Status instruments which I can insert into the existing loop and then feed my PLC from that. Cheap too at approx. £100 each

4-20ma---to split or not to splt

cjd1965

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