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8+ HMI's Communicating through PLC Slave serial port to Intercom

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  • 8+ HMI's Communicating through PLC Slave serial port to Intercom

    Our new install of a Pak3k on an old system required us to use a slave as the go-between for the HMI's and an old Jeron intercom system.

    The job required us to use the ascii POS callups the Jeron uses as signals in the HMI and PLC system to alert when there was a call going over the intercoms.

    The problem we are running into is that 1, the Pac3k does not like having 8 HMI systems trying to talk to it at once and even with slowing down the refresh on the HMI we sometimes run into issues with the intercoms not working and 2, all of the intercom usage through the HMI will drop out occasionally and random luck from restarting the systems has gotten through so far but if we could nip it in the bud and not have it happen anymore it would be great.

    The HMI we use is Indusoft. Like I said, there are around 8 and for the general PLC usage (doors mostly, as well as a few alarms) the Pac3k works perfectly, the problem we are having is with the serial ports.

    The Master CPU serial port is being used as well as a slave.
    Both are communicating over RS-232 with seperate baud rates and settings aside from both using ASCII.

    I can upload the program once I have clearance from the customer if it's needed.

    Does anyone have any suggestions to clear up this problem?
    We don't have a way to reprogram the intercoms since it is so old and a license is needed from the manufacturer and parts and pieces are near impossible to acquire so if there's any suggestions we can do on the PLC side that would be great.


  • #2
    Can you add in serial ports on the PAC for the HMI's?
    P3-SCM Productivity3000 communication module, 4 ports, (3) RS-232 (RJ12) and (1) RS-232 (RJ12) or RS-485 (4-pin terminal) port(s).


    • #3
      the serial ports should only interface with the intercom itself....not the hmi if you can help it. id look into moving the hmi's onto an ethernet conection to the pac3k


      • #4
        I should have clarified. The HMI's are communicating over ethernet, but there's only one serial connection to the intercom, which is where the bottleneck is.


        • #5
          Im not really understanding how everything is connected then. Could you draw up a diagram in Paint and post it?

          edit: something like this but draw in how everything is connected:

          Click image for larger version

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          Last edited by MikeN; 09-05-2019, 08:51 AM.


          • #6
            Click image for larger version

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            • #7
              Only one serial connection is used on the PLC, the intercom system is self contained in processing it's own calls and issues commands internally via ASCII.

              There is only one possible monitoring point on this system which is a serial connection connected to the PLC.

              The PLC is then connected via network to all of the individual HMI's.


              • #8
                Also Im thinking about it more, and RS232 is single device, point to point connection only. So why do you need to care at all whether an intercom is going for traffic to HMIs? It just doesnt seem like traffic contention would matter at all in this case since they are completely different systems.


                • #9
                  The traffic issue is related to the HMI's communicating with the PAC3k we have connected to the intercom system.

                  In talking with support they said 8-10 is a soft limit for the Pac3k to talk to HMI's and we've alleviated some of that problem, but we still run into issues with commands not working properly and the intercoms not working.

                  We also cannot separate the HMI's from this PLC because they HAVE to talk to the intercom system for safety reasons so I was hoping for a way to clear up traffic and make it more reliable.


                  • #10
                    I would try setting the HMIs to a different prime number for each of them on the poll time. If you have more important screens those could have the lower prime number, and the less important screens could have the later, higher prime numbers. That way they should not have traffic contention except in extremely rare circumstances. Dont start with too low a number, maybe do: 5, 7, 11, 13, 17, 19, 23, 29. Or maybe even shift those and leave 5 out and the last screen would be 31. That should alleviate timeouts on that end

                    If the issue with intercom dropping out is simply a matter of traffic saturating the P3k, this might solve that issue too. Though it seems strange to me that the designers would have Ethernet and both serial ports all on the same communication bus inside the CPU.

                    For the intercom itself, what commands are you sending or receiving? Just an "in use" flag and thats it? Or other stuff?
                    Last edited by MikeN; 09-05-2019, 09:09 AM.


                    • #11
                      Ok, I'll have to look into how to do that with the Indusoft HMI. Some of their functions are buried pretty deep.


                      • #12
                        Oh thats right I forgot these arent CMore HMIs.

                        Also set a tag for the CPU's "ethernet port is 95% full" bit and monitor that. Most likely you are sending/receiving so much traffic that it is filling the buffer and then causing timeouts as traffic gets dropped. So this tag will tell you if your traffic speed is too high. It should never get to the 95% full.
                        Last edited by MikeN; 09-05-2019, 09:20 AM.


                        • #13
                          You can probably use Ethernet/IP as driver. P3K can have up 32 adapters.
                          EIP communication is very efficient