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PLC rs485 communication to 2 devices

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  • PLC rs485 communication to 2 devices

    I'm trying to build an automated vacuum furnace. This should be controlled by a plc that will interface with one SOLO temperature controller (where I will need to read process value, write set point values) and 1 MKS® Granville-Phillips® 390 Micro-Ion® ATM Vacuum Gauge Module ( where I would need to get pressure reading, turn ion gage on/off. I'll be using a couple of doze I/O for valve control, and an ethernet connection to a Cmore panel for HMI. I've never done any sort of PLC rs485 communication, so could use some assistance with how to best get the communication to work, as well as picking out the right hardware to get me started. I'm partial to the BRX PLCs as I found them easy to work with in the past, but could work with something else if necessary.
    Thanks in advance

  • #2
    BRX will work fine. Modbus? If you can multidrop, just use the internal port. If you cannot multidrop, you can use a 485POM for the second port.

    If multidropping, just make sure that each slave device is set to a difference slave ID number. The default is generally 1.

    Others can comment on wire choices, but wiring itself is easy...D+ to D+ and D- to D-. Some get confused and go D+ to D-.

    If Modbus, use MRX and MWX to read and write.


    • #3
      The vacuum module works both rs485 and analogue. Analogue is faster, while rs485 requires both hard and soft support. The software is straightforward, with one caveat: make sure that the transfer (either send or receive) is exclusive, meaning it is only initiated if no other transfer is in progress.

      i don’t know the solo. If you need to setup the pid controller, that is a trial and error process. Figure out how much heating you need to bring the temperature close but below your set value and fiddle with the proportional coefficient until you get stable temp at set point.

      for the thernet, there are rs485/Ethernet interfaces which allow one modbus network over multiple hardware lines ( Ethernet and rs485). In that case, your plc is master in one modbus network. Otherwise you will need to build different modbus networks, which will require two com ports on plc: rs485 and Ethernet.