[foxboro] global variable setpoint limiting
- From: "Lowell, Tim:" <Tim.C.Lowell@xxxxxxxxxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Thu, 31 Mar 2005 11:49:19 -0500
Has anybody out there devised a way to implement variable setpoint
limiting on every PIDA block in the system? We're talking about it
here, but we don't see any way to do it without building a companion
CALC block for every PIDA block, which isn't going to happen.
What we envision is a custom PIDA faceplate where you can enter in a
percentage from the current setpoint that you want the setpoint limited
(could be zero). If the console guy mistypes the setpoint so that it
goes outside the limits, a faceplate pops up and says "Are you sure?"
which he can acknowledge or hit "cancel".
From what I can see about the SPHLIM and SPLLIM, there isn't any way to
calculate a percentage of the current setpoint aside from a CALC block,
or maybe a sequence block. I suppose you could pass the selected
COMPOUND and BLOCK name to a shell script as arguments, do an omgetimp
to get the current SPT value, calculate the limits and do an omsetimp to
set them back into the SPHLIM and SPLLIM, but that seems like pretty
shaky programming. Has anybody ever tried anything like this?
Tim Lowell
Control Systems Engineer
ConocoPhillips Trainer Refinery
(610) 364-8362
tim.c.lowell@xxxxxxxxxxxxxxxxxx
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