Multi PLC lock ups!

[skj1402]

I have a similar problem as Monty K below whereby I also have a master & 9 slave T100MD's all connected together via their RS485 ports, though in my case each of them are connected to an ethernet network via individual nPort express RS485 to ethernet converter server units.
The problem I have is that the system will function happily for over a day without incident and then for no apparent reason all the slaves will lock up!
I've incorporated a MaRST facility into each slave where if I press two buttons simultaneously the PLC will reset (which normally works OK),  but when I get these lockup conditions occuring the MaRST doesn't work. Only a complete power down/power up cycle works, which is far from  ???ideal!
Do you have any idea as to what maybe causing these simultaneous lockups occuring, and why the MaRST facility doesn't work when it happens? ?

[support]

If the PLC do not respond to the ladder logic input (the two buttons your mentioned), there are two possibilities:

1) The PLC could be trapped in a WHILE loop or endless GOTO loop within a custom function and therefore is not processing the regular physical inputs.

2) The CPU hangs because of electrical noise coupled in from the power supply. If all PLC hangs at the same time due to noise it got to be a pretty large dose of electrical impulse. You can check if the CPU hangs by turning on the DIP switch #4 when the slave does not seems to respond to your reset input. If the CPU is still running, then turning on DIP switch #4 would cause the "PAUSE" LED to light up and turning it off would cause the "PAUSE" light to go OFF. If the PAUSE light does not react to the state of DIP switch #4 then the CPU probably hangs. You should check the power supply to the PLC. Try to add surge suppressor on the AC side of the power supply and try to add the "diode+capacitor" pair shown on the installation guide to eliminate the cause of problem.