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

  • From: "Cossitt, Howard" <howard.cossitt@xxxxxxxxxxxxxxxx>
  • To: <foxboro@xxxxxxxxxxxxx>
  • Date: Tue, 15 May 2007 23:15:16 -0400

Obviously, I won't comment on the pertinence because I would be a tad
biased...

I can however tell you that the Ladder Logic portions represents 1 day
out of the 5 day course schedule. Please find schedule below:
Day 1 AM Ladder Logic Control Solutions Lesson
        PM Ladder Logic Control Solutions Lab
Day 2 AM Sequence Logic Concepts Lesson & Lab
        PM Monitor & Timer Blocks Lesson
Day 3 AM Monitor & Timer Blocks Lab
        Sequence Blocks & HLBL Programming Lesson
        PM Sequence Blocks & HLBL Programming Lab
Day 4 AM Subroutines, SBX's & Operation Lesson
        PM Subroutines, SBX's & Operation Lab
Day 5 AM HLBL Preprocessor lesson
        HLBL Preprocessor lab
        PM Sequential Functional Chart lesson
        Sequential Functional Chart lab

You can check out schedules, detailed course descriptions (including
prerequisites, see note below) and enroll online at:
http://LifetimeLearning.invensys.com

Free advice for Tuesday May 15th 2007: Please remember that if you are
new to the Foxboro I/A Series DCS, you will definitely need at least the
2001 course which is a prerequisite for 2102. It's not a question of
smarts or experience; it's just a matter of mastering the necessary
foundation to profit from the class.

Once you have received the desired feedback, feel free to contact us so
we may help define the learning plan that best meets your performance
requirements. =


Howard C. Cossitt
National Training Coordinator, Lifetime Learning Center
Invensys Systems Canada
Phone: +1-514-421-8095
Fax: +1-514-421-8059
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On Behalf Of Horlacher, Don
Sent: Tuesday, May 15, 2007 6:35 PM
To: 'foxboro@xxxxxxxxxxxxx'
Subject: Re: [foxboro] Sequence code (MON, DEP, IND) opinions

   I am a relatively new Foxboro I/A user, with 10+ years of PLC
programming
experience. I have taken the first main configuration training and am
looking for some feedback on whether the 2102 - Ladder Logic and
Sequence
Control class would be of value to me. We are using PLC's for most of
our
discrete control, so the ladder logic portion is not much use to me. I
would
like to concentrate on the sequence blocks (HLBL).
  Has anyone taken this class? What is the proportion of ladder to HLBL
stuff?

Don Horlacher
Electrical/Control Engineer
ASARCO Hayden
520-356-3500
Email: DHorlacher@xxxxxxxxxx


-----Original Message-----
From: tom.vandewater@xxxxxxxxxxxxxx
[mailto:tom.vandewater@xxxxxxxxxxxxxx]
Sent: Tuesday, May 15, 2007 1:48 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] Sequence code (MON, DEP, IND) opinions


Chuck Jones said:
" When I was first learning this job, I went to an area Users' Group
meeting at the plant where Duc and Tom work.  (At the time, I didn't
know they were world famous...)  What they were doing with sequence
blocks 10 years ago still humbles me when I look at my notes from that
meeting.  (I know, 'cause I just dug them out.)"

Wow Chuck!  Duc and I got a good ribbing from the rest of the guys here
at work because they didn't know that we were "WORLD FAMOUS" either.
I'm impressed that you could still lay hands on that propaganda we put
out at the users group meeting 10 years ago.

We do use a lot of sequence blocks and have developed a modular sequence
strategy that loosely adheres to the S88 standards of UNITS, EQUIPMENT,
OPERATIONS, and PHASES.  It provides a standard HMI interface to allow
operators to transition equipment from one operation to another by
selecting operational targets via the DM based HMI.  We run a
combination of continuous and batch in our processes and I agree that
Foxboro IA provided a lot of ways to accomplish our control goals. =3D20
        Early on we used a lot of ladder logic for discrete device
manipulations and sequence blocks to coordinate the analog and discrete
devices to run our batch and continuous processes.  We have been
replacing a lot of the discrete valve and motor control that used to be
done in ladder logic with CIN/GDEV/COUT blocks that are more easily
documentable/traceable.  We only seldom need the millisecond speed that
the ladder logic provides as Gabriel O'Dwyer mentioned.  All of the
options have value and can be employed if needed.  The sequence blocks
are the only block that allows "connectionless" reads and writes.  That
ability has served us well but not without considerable documentation
pain.  When getting or setting a value from a sequence block, Foxboro
has provided no way to document or search for them. =3D20
        Today, thanks to Duc and Mike Stewart, we have a browser based
queriable database that not only shows the CMPD:BLK.PARAM references
made via direct connections between blocks but also all of the SOFT
"connectionless" gets and sets we make in our sequence code. We always
hoped that FOXCAE, IACC, or IEE would provide that capability because it
is essential for us to know where every control reference originates.
If I want to delete a block from our system I first query the database
to see ALL of the references to it.  If I deleted the block and a
sequence somewhere on our system was trying to write one of its
parameters the sequence could fail/hang-up/or delay based on how much
smarts I included in the code.  I know I will get ripped by many CALC
block / PLB block aficionados for saying it, but I believe the sequence
blocks are the most powerful, understandable, documentable blocks that
Foxboro offers.  There is, however, a lot to know about them.  They
really needed to be optimized on CP-10's and 30's to avoid over running
the CP's.  The optimization on CP40's, 60's, and 270's is still a good
practice but not as critical to the CP if you have two or three poorly
optimized ones.  In situations where high speed batch control is not
required I have used sequence blocks to control an entire process, even
in a CP-10!

Cheers,
Tom VandeWater
Control Systems Developer/Analyst
Dow Corning Corporation
Carrollton, KY   USA



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