connecting AO --> AI

isiah_s · Mar 9, 2018

I want to use the analog output of one PLC and send it as an analog input to another PLC.

Do I need a signal isolator? Is there a better way to do besides a signal isolator?

Bit_Bucket_07 · Mar 9, 2018

isiah_s said:
I want to use the analog output of one PLC and send it as an analog input to another PLC.

Go ahead.

isiah_s said:
Do I need a signal isolator?

Probably not. What kind of PLCs? What kind of Analog Modules? How are they wired?

isiah_s said:
Is there a better way to do besides a signal isolator?

Yes. You could possibly transfer the data between the two PLCs via messaging and not have to worry about either calibration errors or electronic isolation, but that would depend upon the type(s) of PLCs involved and their communications capabilities.

James Mcquade · Mar 9, 2018

I would advise a signal isolator.

if you don't, you will need to provide the + and - signals to the plc.
this might introduce feedback or a dc loop in the backplane.
we had an issue years ago doing something similar.

any way you can do a bench test?
if I am wrong, someone please correct me

james

janner_10 · Mar 9, 2018

I would advise waiting to see what the 2 PLCs are.

Impacts the answer greatly.

DwSoFt · Mar 9, 2018

Yes you can do this. I have many times. If you are do do a signal isolator then you.may be better off just using a splitter. It saves an analog output then.

OkiePC · Mar 9, 2018

Sidenote:

I have been getting the DIN3 ISO 4-20mA from http://www.scontrolsolutions.com/isolation-amplifiers.html

It is unbelievably cheap and we have about a dozen of them in the field with no issues. There are no trim pots which is usually a good thing for my end users, and it is quite compact.

We still don't know if the analog signals the OP needs to connect are voltage or current or whether the analog input of his PLC might already be isolated...

ivo.maenen · Mar 10, 2018

isiah_s said:
I want to use the analog output of one PLC and send it as an analog input to another PLC.

Do I need a signal isolator? Is there a better way to do besides a signal isolator?

Don't forget to connect the 0Vdc of the two systems together if you don't use the isolator.

connecting AO --> AI

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