Sensor (4-20mA) To Two PLCs

randheerp · Nov 1, 2012

Hi,

I have 10 sensors whose output is 4-20mA connected to a S7-200 PLC. This is an existing system. Now, I want to take this 10 sensors output to another PLC also. How to do this? Should i split the sensor output or I need to loop it from S7-200? Is there any problem to do like this?

Thanks,
Randheer

BobB · Nov 1, 2012

Use an analogue splitter otherwise the PLCs will almost certainly interfere with each other with respect to the analog signals.
Only ever connect one analogue to one input.

curlyandshemp · Nov 1, 2012

randheerp said:
Hi,

I have 10 sensors whose output is 4-20mA connected to a S7-200 PLC. This is an existing system. Now, I want to take this 10 sensors output to another PLC also. How to do this? Should i split the sensor output or I need to loop it from S7-200? Is there any problem to do like this?

Thanks,
Randheer

Or , if you have analog outputs available, scale each input to an output. Or in you have any type of PLC Network setup, message the analogs to the other PLC.

JesperMP · Nov 1, 2012

For 10 signals, using 10 isolation amps to split to 2 PLCs will be a bit costly. Also remember that you have to have double the number of analog inputs.
Using S7-1200 or IM151-8 in stead of the obsolete S7-200 will mean you can send the data via ethernet, and the cost will not be more than going by the oldfashioned way. The two newer PLCs will be much better than the old one for a number of reasons.

randheerp · Nov 1, 2012

The existing system is done by one system integrator. They won't give any help us to get out of their PLC, they won't allow us to touch their system in first place.

randheerp · Nov 1, 2012

The existing system is done by one system integrator. They won't give any help us to get data out of their PLC, they won't allow us to touch their system in first place.

We don't want to disturb their existing system also. So I thought of buying a new PLC and connecting those 10 input to this PLC.

From your advice i feel it is not that easy, rgt?

Ok, now you guys tell me how this redundant PLC concepts works then?

CalleLundin · Nov 1, 2012

the easy way is to buy an old fashion analog signal splitter, then you dont need to interfeer with the existing system at all, just put the splitter on the cable and you are done...

Lancie1 · Nov 1, 2012

Except that if something does go wrong, then the system integrator will be allowed to say "yes, the entire problem was caused by nothing except those signal splitters added by the customer". You have to make your choice and take your best shot.

amitss_sam · Nov 1, 2012

which sensors you are using? I recently tried taking signals from temperature transmitters (E&H) to PLC & separate indicator in series. At first I was little bit scared, but then it settled. Now I am getting temperature values same in PLC as well as same in indicator. Try in series.

randheerp · Nov 1, 2012

Fine, but can anybody tell me how this sensor wiring is done in redundant PLC concept?

Mickey · Nov 2, 2012

randheerp said:
Fine, but can anybody tell me how this sensor wiring is done in redundant PLC concept?

See pictures below one is when wiring the two PLC's in series and the other is using a signal splitter.

Make sure your transmitters will support the extra load if you wire them in series.

randheerp · Nov 2, 2012

Thanks Mickey, So, sensor wiring is always done in redundant PLC concept using Analog splitter, got it.

Mickey · Nov 2, 2012

randheerp said:
Thanks Mickey, So, sensor wiring is always done in redundant PLC concept using Analog splitter, got it.

That's what I would recommend.

Sensor (4-20mA) To Two PLCs

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