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PLC loses communication (Modbus and VNC)


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We use Unistream 7in panels in our machines and access the HMI remotely via VNC viewer. We also have a modbus tcp slave setup to read some registers.

The plc is directly connected to a router using an ethernet cable and this router is connected to our network. We can then access the panel by its static ip address using a pc connected to the same network. This has worked fine for over a year until recently where the connection drops with seemingly no cause.

The first to go is the vnc connection while the modbus data is still received, but sooner or later the modbus comms stop as well. The only way to re-establish connection is to turn the plc off and back on. This enables vnc and modbus comms again until eventually it happens again.

One suspicion that we have is that this issue started after updating the firmware on the plc. I say this because we just had to update the project on a plc but since it was made in a newer version of unilogic it also required updating the firmware of the unit. After updating the firmware and loading the newest project the communication issues started on this unit which never had them before. The other unit we have that also has this issue also has the same firmware and we never experienced this issue before on older firmwares.

Our latest projects are made in unilogic v1.33.373 and the PLCs with these projects have the firmware required for that version.

The previous projects without the comms issues were made in unilogic v1.33.236 and those PLCs had the firmware required for that version.

Has anyone experienced something like this?

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  • MVP 2023

I recommend that you take a PLC that has a communication problem with the new firmware and downgrade the firmware version to the previous one for the test. Use an older program accordingly.

If everything works properly, you need to contact support to identify problems in the environment or new firmware.

If problems in the controller with a reduced version of the firmware remain, the problem is in the PLC and you should contact the distributor about the warranty.

P.S. The only question is whether your machine  has any new  sources of electromagnetic noise, grounding or power issues with the software update. Sometimes an imperceptible design change fuels our desire to wrestle with firmwares and programs. :)

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