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PAC8000 safety controller, Analog module goes in failsafe

We are using 8851 in redundant mode and have analog module 8101-HI-TX (two nos in rack1 and another two in Rack2)...Total 4 racks.
After some time, suddenly all the analog input module goes in failsafe mode..., the error seen in module diagnostic (workbench 8.4 sim8), shows "railbus comms mode" : short, under the "module diagnostic Data - Device status registers".
Also other status seen are : 
-> module state : BIM in failsafe mode
-> Last comms error : CNACK
After recycling power to the IO base plate , the module is OK /or by using reset command from the workbench....
But this problem reappears after few minutes again.


Could you please help what could be the issue!

regards
Vikram

Vikram Pungaliya (Prime Controls)
  • Steve Ward
    There are several possibilities here:

    Faulty chassis
    Faulty cables or loose connection between chassis
    Faulty CPU
    Faulty I/O module
    Faulty earthing/grounding

    You can  “Divide and conquer” – eliminate possible causes one by one to find the fault, ie replace components one-by-on to see if you can resolve the issue.
  • Vikram Pungaliya (Prime Controls)

    In reply to Steve Ward:

    Hi Steve,
    did all above...but problem persists.
    We observed on thing, one of the Ai module shows scan time of 4666ms, (when not in failsafe)....This is spare module and all its channels are configures as inactive.
  • Steve Ward

    In reply to Vikram Pungaliya (Prime Controls):

    The system will trip when an error state persists for 5 seconds, so the 4666ms scan time looks suspicious. What if you remove this module? Is there a scan setting for this module? You don't say if this is a new problem or has always occured, if a new problem in an existing system then a faulty module is most likely. SafetyNet is now discontinued and no longer officially supported so there is a limit to how much I can help, you could try our support team at www.emerson.com/iac-support.

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