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PVBad_ALM from a temperature control module consisting of AI input, PID, AO, CALC blocks. alarm is configured critical and comes up at any time when the module is running

I have a temperature control module  26TCA431B for a thyristor control panel. The module is always flagging PVBad_ALM when the thyristor is heating up. I checked the input IN which is AI/OUT of another module 26TI-431B and the module is OK. Process History view shows the PID PV value is fine.l Alarms configured for the 26-TCA431B are Hi-Warning, Lo-Warning and PVBad-Critical.

The blocks in the 26 TCA431B module are:PID1,CALC1, CALC2,RTLM, AO1, AI1.. The CALCs have expressions to decide how the PID/OUT is used to control the thyristor in the field depending on availability of generators

On the PID The OUT_SCALE is 0-100% and PV is 0-250DegC on the 26TCA-431B.I have checked diagnostics and nothing seems to be wrong. MERROR is Module Ok, MSTATUS is Abnormal Active and BLOCK_ERR is Simulate Active which I confirmed is due to Simulate -IN enabled for an AI block as part of the configuration.

The faceplate keeps flagging PVBad_ALM whatever the value of the PV on the PID. I checked the input module to the PID, a 26TI-431B and it appears fine.

Can someone tell me what conditions can result to this kind of Alarm. Every thing is running fine but this alarm will spoil my alarm rates after each shift.

 

 

 

chigarthur

1 Reply

  • Andre Dicaire
    The PVBAD alarm is typically based on MERROR, which is a role up of the module health including block error. It may have nothing to do with the PV value. Check which parameter sets the alarm and the verify the associated mask.

    The AI block's input status is typical but the make selection can drive the MERROR or BLOCKERROR status due to a variety of reasons.

    Once you know water is driving the PVBAD alarm you can determine how to address it.

    Andre Dicaire

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