Cimplicity 7, RS422 multidrop Versamax

Hi all,
I have a serious problem, and I'm without any leads how to overcome it.
We are trying different solutions for almost a month now.

The thing is like this, we have two GE Versamax PLCs in multidrop configuration, from them, we read in cimplicity some data from both PLCs, make some graphics and make a write to the DB every 40 seconds.
It works almost everything perfect, except that... we have drop off communications for 40 seconds with the PLCs at random times, and not both together. It can be any of the two, almost never the two together. Sometimes, the drop off can be a bit longer (up to 5 minutes), and once in a very while, we had dop off communication that didn't come back to life.

Does someone encounter something similar?
Any ideas? I think we tried everything... but it must be something that we still didn't.

Thanks for your help

Hi have you checked the project status logs for any error messages?

Can you try removing a drop from the system and see if the problem remains with just 1 plc connected.

My gut feeling is that it is a comms problem, is everything grounded etc?



Cheers

hi,
No error logs in cimplicity, or in windows.
We didn't check without the multidrop. It is a project that was previously running with a single plc, but there was an extension of the project.
We try it with 2 PCs. Same problem.
One of the PLCs was changed because of a comm port.
The cable was also changed.
The RS422 to RS232 to the PC port was also replaced twice.
The system was tested at 4800, 9600 and 19200 with the same results.
We are now going to try a new solution, changing the multidrop for 2 RS232 connections (that will be between today and tomorrow).

...

Do you use shielded and twisted pair cables? Is a terminator used? This are the most happen physical problems using RS-485.