Re: [foxboro] HLBL question
- From: "Mike" <precision1@xxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Tue, 26 Jan 2010 18:09:42 -0600
Pat / Jerry,
We have had issues with the following code:
::PIDA.MA := FALSE ;
::PIDA.OUT := 0.0 ;
It may not happen every time the code executes; however, we found that if MA
is True then the object manager may not be able to set the PIDA mode to
False before executing the write to the OUT parameter. The example coding
below may not work in all cases; however, it works without any issues for
us.
::PIDA.MA := FALSE ;
WAIT UNTIL ::PIDA.MA = FALSE;
::PIDA.OUT := 0.0 ;
This method will insure that the controller is in the correct mode before
executing the next line of code. For us, it was more important to insure
that the controller is always in the correct mode before executing a write
to either a SP or OUT.
Mike Bardwell
DCS Analyst
Rubicon / Huntsman
Geismar, La.
FCP270, InFusion 1.2.1, IA 8.4.2
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] On
Behalf Of foxpat
Sent: Wednesday, January 20, 2010 10:18 AM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] HLBL question
Jerry,
Are you sure about this?
I never had any problems with, for example, following code without wait:
::PIDA.MA := FALSE ;
::PIDA.OUT := 0.0 ;
It is my understanding that the PIDA will be 'forced' executed as soon as
the .MA parameter changes, regardless the PERIOD/PHASE of the PIDA. I do
recall that this has not always worked like this (version 3.x ?).
If you were to set a PIDA.PERIOD of say 4 (10 sec.) and you would change the
.MA just after it executed, it will execute again and not wait 10 seconds to
reflect the .MA change.
Also the PIDA most likely first checks the .MA status, detects it's in
manual and therefore will accept the output change.
Try it and let us know!
Pat
-----Oorspronkelijk bericht-----
Van: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
Namens Jerry Hidahl
Verzonden: woensdag 20 januari 2010 14:56
Aan: foxboro@xxxxxxxxxxxxx
Onderwerp: Re: [foxboro] HLBL question
Tim,
Presumably, you're setting these controllers to manual in order to set the
outputs to a safe value. Here's a tip. Wait one BPC (WAIT 0.5; works)
before attempting to change the output, or else you may have a run time
error for attempting to change a secured parameter (error -3, if I remember
right). The PIDA blocks have to process, even if they are in the same
compound, before you can change the output. You can change all the modes in
one cycle, then all the outputs in the next to save time.
Jerry Hidahl
Process Control Engineer
Port Neches Performance Products
Huntsman Corporation
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