ML1000 Retentive Data Lost??

I witnessed an issue today with a ML1000, faulting on Retentive data lost (S:5/8).

We could not establish exactly what 'retentive data' was lost, but we had to manually
reset the bit, to clear the fault.
I have since added an OTU to the last rung of the program for this bit to overcome this
error happening again.

What I don't know, and cannot ascertain, is what was causing this to happen. What causes
this bit to be set?

0005: Retentive data is lost. This recoverable error occurs when going to Run.

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Based on this comment from the help, I would 'assume' that it happens if a bit (for example) has been set
before the PLC went off, OR out of run mode, and then when it came back on OR back to Run mode, that
this bit could no longer be set (As it was an output bit), then the S:5/8 bit would be set?

I was going to try and do some testing based on this theory.

Probably the other thing that we need to understand, is what is classified as retentive data, in relation
to this error? I'm pretty sure that anything that uses the OTL instructions is classified as retentive, is
also the OTU? There are also a couple of timers in this small program as well, are they also classified
as retentive?

All the numeric data is retentive. Did you check if any of those changed?

All the numeric data is retentive. Did you check if any of those changed?

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When you say numeric data, do you mean the complete data table?

I have not checked that yet, this is a pretty small program, so how can this happen?

My only thoughts are that when the PLC saves the 'retentive data' when down-powering, something alters this after this save, or on power up...

Power problems (brownouts or quick dips) may cause this. Check for power line filtering.

Power problems (brownouts or quick dips) may cause this. Check for power line filtering.

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So my 'assumption' is correct, in that it is that the PLC must be being switched off, or the supply voltage is at a point where the shutdown routine does its thing, but does not shutdown completely.?

It could be symptomatic of a large load starting nearby then? Is there anyway to simulate this?

Have you had experience with this before Bernie?

bernie_carlton said:

Power problems (brownouts or quick dips) may cause this. Check for power line filtering.

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I agree with bernie, install a UPS along with line filtering it will always help.

And check and double check your ground.