Communication Errors

[Evilbeard]

I have two Do-More PLCs on a machine I designed. The PLC in the rewind is a H2-D1ME, and I installed a BRX 20 point on the unwind of the machine to contol the motor on the shaft via PID. I connected the two via ethernet (through a switch). I ran into a problem yesterday (it's been about a year of the PLC being installed in the unwind), where the machine would start, and the unwind wouldn't run. it started, but it got no frequency command (analog out from the PLC). I logged into the PLC via ethernet, and it showed the PID loop was operating properly, and it showed that RY0 was changing. I checked and I was not getting an analog output. Furthermore, I noticed that the RX instruction I was using to read the values from the Rewind PLC was failing and timing out. I powered down the machine and restarted it, and everything was fine.

It ran for a few hours and the problem repeated. This time, I tried disconnecting/reconnecting the ethernet cables, and I even tried different ports on the switch. Nothing changed. I power cycled the rewind PLC and nothing changed. I power cycled the unwind plc and communication resumed. I tested the ethernet cables also, all 4 pairs tested good. I never show any faults or warnings (other than the communication error timeout). I can still connect to the PLC via ethernet, but it won't talk to the other PLC (and I can communicate to the other PLC via PC also). I don't know what fault would cause this and the analog output issue. I don't know whether the timeout is causing the analog output issue (it still sees the analog input just fine).

I ended up swapping the PLC out, as I had a smaller BRX that had enough connections. It was very easy to switch the CPU type and upload, so thanks for that. Any help on why this could be happening would be appreciated.

[BobO]

So you're getting RX comm errors and the physical analog out drops out, but the unit is still in run and doing everything else? Odd. I can't think if anything I know that would cause just those two things while everything else worked. I would probably start with clearing just the retentive memory, and if it still fails, clearing the entire unit and starting again. It is still fails, we could test it here and see if there is any kind of hardware issue.

We're happy to work with you to get answers.

[Evilbeard]

So you're getting RX comm errors and the physical analog out drops out, but the unit is still in run and doing everything else? Odd. I can't think if anything I know that would cause just those two things while everything else worked. I would probably start with clearing just the retentive memory, and if it still fails, clearing the entire unit and starting again. It is still fails, we could test it here and see if there is any kind of hardware issue.

We're happy to work with you to get answers.

Yeah, the unit was in run, and all the inputs and outputs function except the analog out. Rebooting it via a power cycle fixed the issue for a short period of time. I might hook it to a test PLC to attempt to replicate it on my bench.

[BobO]

Yeah, the unit was in run, and all the inputs and outputs function except the analog out. Rebooting it via a power cycle fixed the issue for a short period of time. I might hook it to a test PLC to attempt to replicate it on my bench.

If you can reduce it to something we can dupe here, we're more than happy to dig into it.