Troubleshooting Serial Port Configuration - iTools Control Panel

I have an iTools OPC server that has suddenly lost serial communications to one set of 2204e temperature controllers (8 daisy-chained together).
I've switched serial ports and the problem seems to travel with the wiring and devices. However the wiring seems okay (as checked with an ohmmeter). Do you have any advice for troubleshooting the problem. Should I try to minimize the set-up to one device?
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  • Usual troubleshooting techniques apply really. I would remove all but one unit from their sleeves then try to communicate with that one instrument. If that works then progressively introduce more instruments until things fail, which may indicate the sleeve at which a problem in wiring has been introduced, or a faulty instrument. To diagnose a faulty instrument if you get a failure in this method, swap it for another in the same physical sleeve if possible (obviously beware of any possibility of incorrect heating or other control to your plant while doing this).

    The sorts of things that could have gone wrong are as follows:

    1) Wire has become dislodged or is not connecting (solder joint in a connector, screw terminal loose)
    2) Fault on a single instrument loading the RS422/485 bus and preventing others from communicating
    3) Fault on serial port on PC (you seem to have eradicated this)
    4) Some sort of electrical fault on the serial lines that has overloaded the serial interface cards in the instruments (could break all of them at once)
    5) bad termination resistor - only really likely to be a problem if there's a very extended line length
    6) Something I haven't thought of...

    So work systematically through swapouts and checks on this basis and you should be able to get to the root cause. The most difficult problem to diagnose is probably 4 - if you have any spares or instruments in a different line you can cross check with then that will help. In my experience that fault is very unusual as the units are designed to be robust in normal use, so transient high voltages are usually OK although connecting mains to the comms would probably do some damage.

    The units are reliable in general use and there are no stock faults with comms, normally they work for very long periods without failures.
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  • I was back on-site today and isolated the controllers and was surprised that I still didn’t have communications.

    I also realized that my test of the serial card was invalid since I had only really tested the software and drivers. As it turned out one of the card’s serial port hardware was not working properly but not reporting an error.

    I’m communicating again after replacing the card.

    Thanks for your help.
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