2 plcs's sharing 1 4-20ma signal??

I have a SLC 5/04 and a controllogix that need to read the same analog input. Can you put them in series with each other? We have two processes with two controllers. System #1 and system #2. The 5/04 controls #1 and the controllogix is for #2. They both have their own return flow temp sensor (4-20ma). We are looking for redundancy, if one skid dies, we can use the other for either process. The problem: How to share the return flow temp signal with both skids? We could install two RTD's on each side, but that would involve more cabeling and more sensors(and welding bungs in the piping). How would you isolate the power supplies for the loops in each skid? I know this is confusing, but the project engineer doesn't have an answer for this. Help me out here!

Yes, as long as the sum of the loads on the loop doesn't exceed the maximum loading for the transmitter.

You may also have a problem if one (or both) of the analog inputs are physically referenced to common. Generally that isn't the case.

Yes, you can put them in series with each other. Just make sure that the power(24VDC) to the temperature sensor comes from only one source and the 24 VDC common is the same for both PLC's.

I've run into a similar situation and was instructed that the input needed to be adapted to voltage in order to work with parallel inputs...

ELake20 said:

I've run into a similar situation and was instructed that the input needed to be adapted to voltage in order to work with parallel inputs...

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Parallel inputs require voltage signal.

Series inputs require current signal.

Save yourself a headache and go for something like this.

Bryan