Re: [foxboro] TRKENL and HOLD on PIDA block
- From: "Rick Rys" <rys@xxxxxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Tue, 16 Feb 2010 13:41:29 -0500
Richard,
A couple of points on your application. Setting CEOPT likely makes no
difference, because if your AIN block has BADOPT = 3 (default), the PIDA
block goes to hold due to the BAD status, adding ERROR is essentially
redundant. Also, TRACK wins over HOLD when TRKENL is set to true so you can
put the controller output where you like this way. When you get a line
plug, you may not get a LOR (BAD) so the controller will wind up to 100%
open valve without going to HOLD. Maybe you need to alarm on high
controller output, but why do control actions here?, as keeping the valve
wide open is more or less what you want and the flow controller will handle
it when the plug breaks free. Not sure if putting the valve at 20% does
anything to remove the plug, although maybe it would reduce the bump when
the plug finally breaks up. If you set TRKENL (with TRACK = 20%) when the
controller output stays high for a sustained time you will get a cyclic
behavior and it may not really help much. Maybe what you want to do is to
set TRKENL true if the controller output is greater than 19% open and the
FLOW is less than 1 or 2% of scale for a sustained 20 seconds, as this would
hold the output at 20% via TRKENL and release when the plug breaks up.
Rick Rys P.E.
www.R2controls.com
1 Cherry Street
Mansfield, MA 02048
508-339-6633 Home Office
508-369-5186 Mobile
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