Re: [foxboro] CALC vs. IND question
- From: dirk.pauwels@xxxxxxxxxx
- To: foxboro@xxxxxxxxxxxxx
- Date: Thu, 27 Mar 2008 09:36:57 +0100
Allthough sequence is easy to configure and it's tempting to use IND over
Calc , we try to use calc or logic where possible. (Along with PLB's for
interlocking) If we do use sequences these remain inactive until we
actually need them. They're triggered by MON blocks or other conditions.
For stuff that has to run 24/7 we use calc/logic when possible. We have a
lot of sequences doing pressure/heating cycles, loading raw materials,
controlling utilities etc.. and with the CP60's we experienced in some
cases, when 2 sequences had to swap data, (seq waiting for input from
another sequence), that they "missed" the input's so we had to build in
wait's, repeats, for's and counters. Changing BPCSTM helped also.
I would suggest reviewing your calc logic, if it has to run 24/7 keep it in
calc's otherwise use mon block's to activate the seq when needed.
Rgds,
Dirk Pauwels - DCS/MOC coordinator
Engineering dept.
Hexion Specialty Chemicals
E mail: dirk.pauwels@xxxxxxxxxx
T. +32.(0)3.570.95.97
F. +32.(0)3.570.16.09
Mob. +32.(0)497.428.300
Mike_Adams@m-petf
ilm.com
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Subject
26/03/2008 21:45 [foxboro] CALC vs. IND question
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Hello list,
I have some existing compounds in 4 I/A nodes that each have about 20 CALC
blocks running at a 2 sec period with pretty good phasing. These blocks
are running somewhat arcane mathematical calculations with 15 to 25 steps
each but only 2 or 3 real outputs are generated per CALC block.
The CALC steps are not commented at all. We are running into problems
where it is becoming harder to keep up with what is going on in these CALCs
and it is very hard to edit them efficiently. I am interested in replacing
these CALCs with IND blocks that would do the same work but be much easier
to troubleshoot, document & edit.
I know that INDs load the system more than CALCs but I'm not sure by what
degree. All 4 control processors involved are CP30s. Two of these CPs are
lightly loaded but the other 2 are heavily loaded.
If I configured an IND to run at the same period as a CALC and do the same
calculations, what would a reasonable guesstimate of the increase in load
be? I just want to get a rough idea on a 1:1 comparison for starters.
I realize I can probably do the following to ease the load increase
incurred by going to INDs:
- lengthen the period to 5 sec & phase them well
- put 2 or 3 CALC blocks worth of steps into 1 IND
- place strategic WAIT statements in the IND code
Thanks in advance,
Mike Adams
Mitsubishi Polyester Film, LLC
Greer, SC USA
864-879-5231
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