stickman47

Communicating with other PLC's

9 posts in this topic

Is it possible to monitor a tag, in another PLC on the network, and use that tag status in a different PLC?

I have a number of Compact Logix PLC's that are all connected via Ethernet.

I need to monitor an input on each node and use that input status in another program.

I would have to run a lot of wiring if this is not possible. Is there a protocol that would allow this? 

I am using RSLogix Enterprise and I can "see" all the processors I need to monitor in "Who Active".

 

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You can use Produced / Consumed tags (not my favorite way to move data between PLC's)

Or a Message block. Message blocks are simple to do and fast. I can send an example (or attach it here) but you'll need to be able to open a structured text routine to see the complete picture. I vaguely remember doing a step by step writeup for a tech to do this. I'll look for that instead. 

Personally, I don't do safety related data moves "softly". I always have those hard wired (motor start / stop, ESD, etc). 

Edited by Michael Lloyd

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Thanks for the info.. I have found a method, but it requires that both processors have ENB for the communications. I have an L32E, which has the ENB built in, and an L24ER, which does not. The question is, is it worth the $1500.00 to add the 1768-ENBT to the L24ER, or run the wires and isolation relays. I'll have to make up quotes for each and see what my boss says... 

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How is the L24RER on the network? I am not familiar with that model but looking online it's supposed to have two Ethernet I/P ports. This is jogging my memory. I think I had a similar problem but I found a workaround. I need to dig through some of my programs and see if it's the same issue.

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On the I/O Configuration tab it shows the processor but it doesn't have the Ethernet Port Local ENB. Some of the processors have  it built in, others do not, but they have Ethernet ports.

Sounds confusing but the ENB allows you to communicate with other processors by adding them to the Ethernet tab.

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" I need to monitor an input on each node and use that input status in another program. "

 

An actual physical input (to an input module)?

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Yes, I need to monitor the status of an input on another plc in the network. I can't use messaging because the second plc does not have ENB built in, and to do so would cost $1500 for an ENBT module.

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Have you tried setting up a message read in the PLC with the ENBT to the model that doesn't have an ENBT? I have done a lot of messaging to / from PLC's across cell modems and I vaguely remember having to do that with one of the newer PLC's

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If you're talking about CLX controllers, you an map the input modules that you need the data from into the configuration of the CLX that needs that data.

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