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I have 2 P2k on a network and need to know if they quit talking

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  • I have 2 P2k on a network and need to know if they quit talking

    Slave is sending info to master and if 3 minuets go by with no communication i want to set error on master , any ideas would be great

  • #2
    You could use a "heartbeat" bit. set the slave to flash a bit 10x per second, transmit that bit and your master could monitor it.

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    • #3
      i am really new to plc and could use a little more help on the ladder logic for this bit

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      • #4
        What protocol do you plan on using?

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        • #5
          There are a couple ways to accomplish this, here's a simple method.
          The Slave generates a heart beat on a bit, which gets transferred to the master via say Modbus,
          The Master monitors that bit and sets a alarm bit if it hasn't seen a heart beat in 3 seconds.
          Attached Files

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          • #6
            I am using the RX and WX instructions for other data transfers

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            • #7
              You could have any of the error tags for the network instructions start a timer, if a success tag is then seen on the instruction that was giving the error then the error is reset and the timer goes back to 0. If the timer ever reaches 3 seconds it gives an error to the operator.

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              • #8
                Originally posted by highvoltage50 View Post
                I am using the RX and WX instructions for other data transfers
                You could include the heartbeat bit in your transfer or do what MikeN suggested with the error bits.
                Personally, I prefer the heart beat method because say we have the master retrieving values from the slave via Modbus. The comm operation would continue without errors even if the slave PLC is in stop mode and not executing any logic.
                Whereas with the heartbeat method, if for whatever reason the PLC stops execution, the Master PLC has a way to detect it and act accordingly.
                Also if you have (as you stated) the slave sending to the Master, and the master is not initiating any of the transfers it has no way of knowing if a network error occurred without a heartbeat bit of some type.
                Last edited by pbw; 08-14-2018, 04:10 PM.

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                • #9
                  Some people use an incrementing value from one plc and the other plc monitors that the value is NOT stuck.
                  the reverse of this is also true

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                  • #10
                    thanks for all the info i used a heart beat on slave and a timer with a no on edge looking at heart beat for timer reset

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