[foxboro] Sequence code (MON, DEP, IND) opinions

  • From: Corey R Clingo <corey.clingo@xxxxxxxx>
  • To: foxboro@xxxxxxxxxxxxx
  • Date: Mon, 14 May 2007 13:39:56 -0500

I see a significant amount of discussion on here regarding use of these 
blocks and sequence code.  Not wanting to ignore a potential tool in my 
toolbox....OK, really I'm just lazy* and do not want to pass up an 
opportunity to get a computer to do something instead of me.

Some background: my plants are continuous processes.  I inherited systems 
in both plants.  Neither system had any sequence code in it - nada.  I had 
heard all the horror stories about sequence code loading CPs, issues with 
memory fragmentation, etc. etc., so I never took a big interest in 
learning it.


I then had an application, non-control, where a large number of complex 
calculations were being performed.  I felt it was a good application for 
sequence code, so I built an IND block and got after it.  It worked fine, 
but at the default BPCSTM of 100, it caused a CP30A's idle time to drop by 
over 30% (it was about 50 lines of code, with a WAIT loop back to the 
beginning).  I set BPCSTM to about 10, and the idle time problem went 
away, but I only got away with it because this application did not need 
anywhere near real-time performance.  I sgain shied away for using it do 
do anything that did have such requirements.


Which is a shame, really.  I used the sequence equivalent fairly 
frequently in my Brand H days, partly because they did not really have a 
CALC* equivalent (you had logic, or math, but not both in one block), 
partly because some flavors of their sequence-equivalent had wide system 
access that I needed.  I don't think I'd go crazy with it on I/A, but 
there are 2 or 3 applications where it would be nice to have if it didn't 
have the issues I saw.


So how do others use sequence on I/A?  Batch only?  How do you get around 
the CP loading issues?  What other issues do you have?  How do you get 
good performance and reesponsive interaction with a human operator?  Vi or 
emacs? :)


Thanks,
Corey Clingo
BASF Corporation




 
 
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