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

  • From: "Michael Kessler" <mkessler@xxxxxxxxxxxx>
  • To: <foxboro@xxxxxxxxxxxxx>
  • Date: Tue, 15 May 2007 11:29:03 -0400

I work in the corn Wet/Dry Milling industry which is mostly a continuous
process with a number of batch operations.

I like CALC/LOGIC for their low overhead, deterministic behaviour, and
traceability of connections for troubleshooting. I always try these first to
solve a control problem. They can be tricky to set up, and it can be a
struggle to document them so operators can understand them but they are
reliable and cheap on resources, and once they're running they never stop.

I like IND sequence blocks for Operator Assist Sequential Start-Up/Shutdown
programs. They are also good at starting/stopping TIMERS, and
Setting/Resetting totalizers. The ability to set as opposed to connect is
useful when a controller can have many remote setpoints depending on what
step a program is on. I'm not sure how object manager loading affects the
ability to SET variables from an IND block. I suspect the IND block uses the
object manager which could cause problems if there are a large number of OM
Overruns in the CP.

Setting up complex systems using MON, IND, DEP, and EXC blocks requires a
thorough understanding of how the blocks interact with each other, and a
good amount of time for design and testing. However the end result is a very
powerful program.

Recently I discovered the STATE block, which when used in conjunction with
CALCA's,LOGIC's and an IND can provide the backbone for a quick, robust, and
easy to modify solution for some of the smaller batch type operations in the
plant such as chemical make-up and transfer, regeneration of ion exchange
beds, changing/coating check filters. I expect Foxboro stopped developing
the STATE block and put their energies into developing the HLBL progamming
language which is a shame because with a few improvements the STATE block
would be an excellent block.


Michael Kessler
KIC Systems

> -----Original Message-----
> From: foxboro-bounce@xxxxxxxxxxxxx
> [mailto:foxboro-bounce@xxxxxxxxxxxxx]On Behalf Of Corey R Clingo
> Sent: Monday, May 14, 2007 2:40 PM
> To: foxboro@xxxxxxxxxxxxx
> Subject: [foxboro] Sequence code (MON, DEP, IND) opinions
>
>
> 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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