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

  • From: Corey R Clingo <corey.clingo@xxxxxxxx>
  • To: foxboro@xxxxxxxxxxxxx
  • Date: Wed, 16 May 2007 10:58:24 -0500

Many thanks to all who replied.  What got me thinking about this is a 
relatively simple (or so I thought) filter application -- filter for 
awhile, then go through a backflush sequence when the differential 
pressure gets high, fail to offline if one of the valves did not move 
properly, etc..  There are 3 filters, and features such as being able to 
take one offline and being able to manually step through the backflush 
sequence were desired.  It ended up being quite a few CALCA blocks, and 
it's still missing one attribute that will take another CALCA block to 
properly implement (longest-running filter first to backflush when 2 have 
high dP).

I did end up using STATE blocks for the first time to drive all the 
valves, but was somewhat nonplussed with their (lack of) functionality.  I 
expected something like the sequencer/"drum timer" blocks I've used in 
PLCs, but was disappointed.  (I guess riding in the front of the bus 
sometimes is better than riding in the back.)  I ended up using the STATE 
blocks as demultiplexers only, but they did that job well enough.


I guess I'll play with some HLBL more when I get a chance.  I didn't take 
any Foxboro classes until about 5 years after I had been using the system, 
and have found that trial and error on an offline system is the best 
training for me.  And this list is like the professor's office :)


Corey Clingo
BASF Corporation


 
 
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