[foxboro] ACCUM inaccuracy

From: Kevin Fitzgerrell <fitzgerrell@xxxxxxxxx>
To: foxboro@xxxxxxxxxxxxx
Date: Wed, 21 Apr 2010 13:13:31 +0900
Hi all,
Just wanted to see if anyone else has experienced this.

We've got some ACCUM blocks that have been accumulating significantly
differently than reports from PI.  We blamed it on PI scan times and
compression until I noticed that the ACCUM blocks are ALWAYS lower that PI,
and for some specific accumulators significantly lower.  We're using these
specific ones for accumulating run-time and utilization.

In a side by side test with a CALC block, the manual CALC block accumulation
matches PI, as does a 1 rate second data collector.

Digging deeper, it appears that all our old ACCUM blocks used "HOLD" to stop
them when the equipment was off.  All our newer ones (last 10-15 years or
so) use MA to stop.  The ones I've noticed the error on all use MA connected
to the equipment run indication or "utilized" bit.  My theory is that during
the Manual-Auto transition I'm not accumulating for one cycle.  As some of
these see thousands of cycles a day that really adds up.  One of our
engineering vendors used the MA connection to stop the accumulator during
several large projects, and all smaller projects since then have followed
that standard.

I'll test comparing HOLD to MA, but if someone can confirm my theory it'll
make things easier.

Cheers,

Kevin


 
 
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[foxboro] ACCUM inaccuracy

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