Re: [foxboro] TRKENL and HOLD on PIDA block
- From: "Targosky, Richard S." <rstargosky@xxxxxxx>
- To: "'foxboro@xxxxxxxxxxxxx'" <foxboro@xxxxxxxxxxxxx>
- Date: Tue, 16 Feb 2010 12:44:45 -0500
Joe-
When the plug breaks free - the xmiter goes off-scale high right now and the
valve has already wound itself wide open.
So - a normal HI / HIHI alarm does not help. One scan we are at a low flow
condition and a second later when the plug breaks free - HIHI - actually
off-scale. I guess we could consider a HI OUTPUT alarm.
Thanks-
Rick T
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] On
Behalf Of Joseph M. Riccardi
Sent: Tuesday, February 16, 2010 12:35 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] TRKENL and HOLD on PIDA block
Rick,
Maybe I am missing something but I would look to prevent the problem. Not
sure what the FT45 range is, or what the alarm settings are, but any chance
you could "tie the TRKENL of the PID block FIC45.TRKENL back to the"
High-High alarm instead (set the High-High alarm just below the HOR but
above the High alarm) and simply prevent the loop from ever reaching the HOR
in this situation? Or if the HOR is inevitable once the plugging starts,
TRACK should 0%; no?
Either way, you could also label the High-High setting "FT45 plugged" to
forewarn the operator?
Joseph M. Riccardi
DCS Services - Industrial Process Control
Joe@xxxxxxxxxxxxx
"To give real service you must add something that cannot be bought or
measured with money; and that is sincerity and integrity." - Donald A. Adams
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] On
Behalf Of Targosky, Richard S.
Sent: Tuesday, February 16, 2010 11:57 AM
To: foxboro@xxxxxxxxxxxxx
Subject: [foxboro] TRKENL and HOLD on PIDA block
Hello List-
We have a PIDA block which is a Flow Control Loop. (FIC45) The MEAS for this
block is FT45.PNT. The CEOPT is set to a 1 to put the PID into HOLD if there
is an IO error.
The problem is this - this flow goes into a heat exch - which can plug-off.
So - the PID block responds by driving the valve open. Eventually - the
plug breaks free - and the FT goes off-scale hi (BAD_IO). This puts the PID
block into HOLD and the valve output stays at its high value - this keeps
the FT off-scale hi - and all is bad!!
Best solution - re-range the xmitter so you do not create the off-scale
condition. But - we cannot do this right now.
Proposed solution - I will tie the TRKENL of the PID block FIC45.TRKENL back
to the High Out-of-Range (HOR) of the flow transmitter FT45.HOL.
I will set the TRACK value to 20 % as was suggested by operations.
The effect of this change (I think) is this --
If the Flow Transmitter goes to an Off-Scale high value - the block will
goto TRACK enable. This will drive the block to the 20% output value.
When the flow comes back into range (which should be rather quickly) - The
HOR bit should go back to 0 and PID action (AUTO) should take over in a
bumpless fashion. If the operator needs to put the loop into MANUAL to move
the valve they can - MAN takes precedence to TRACK.
My question to the list -
HOLD (thru CEOPT) or TRKENL - which one takes precedent?? Looking thru the
Foxboro documentation - I do not see an answer.
My concern is that even if I tie the TRKENL back - that the BAD_IO may still
force the loop into HOLD.
Rick Targosky
PPG Industries
Natrium, WV
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_______________________________________________________________________
This mailing list is neither sponsored nor endorsed by Invensys Process
Systems (formerly The Foxboro Company). Use the info you obtain here at
your own risks. Read http://www.thecassandraproject.org/disclaimer.html
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