Re: [foxboro] One IND block per compound -- still true?

I thought this would be a good time to review my implementation guidelines:
There are a few rules that one should follow when designing a control system:

• Do it in regulatory control blocks. (most efficient; least prone to
  problems)
• If the regulatory control blocks can’t do it, use a CALC block.
  (efficient, but must deal with BAD and coding errors; debugging is a pain) • 
If the CALC block can’t do it, use a Sequence Block (pretty inefficient,
  but in the CP. Code/compilation relatively complex. Debugging is a pain.) • 
If you can’t do it in a sequence block, reconsider if you need to do it.
• If you must do it, see if you can do it in a shell (sh, ksh, csh, perl,
  etc.) script (easier to debug, easy to schedule, remember to use omgetimp
  and omsetimp to avoid broadcasts, remember to use show_params to check the
  IMPORT table)
• If you can’t do it in a script, reconsider doing it.
• If you must do it, see if there is a 3rd party or Foxboro package that
  will do it. (Ask on the mailing list.) • If you must do it and can’t find
  a package, write a program.

If you are going to use HLBL, keep the following in mind:

• 1 line of HLBL code is roughly the same load as an AIN block.

• External OM variable references, e.g., :C:B.P when the compound is in a
  different CP, suspend the block for one full block period. Thus, 20 
  lines setting values will take 10s to execute if the PERIOD is 0.5s.

• Internal block references don't suspend the block, but they are slower
  than you might expect and will have an impact on your loading if you
  have enough of them.

• Remember that code runs until it hits a WAIT, WAITUNTIL, External
  Reference, or BPCSTM is reached.

• Remember that if you don't loop you code back to the top (yes, 
  with a GOTO), it will reach the end of the block and stop.

• Remember that ACTIVE and MA must both be set to true for the block to run.




-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx on behalf of Duc M Do
Sent: Thu 9/25/2008 7:12 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] One IND block per compound -- still true?
 
On Thu, September 25, 2008 7:29 pm, Corey R Clingo wrote:

> OK, I might be turning into an HLBL crackhead :)

He's done step over to the dark side!

> I never saw any mention of the 1-IND-per-compound restriction I've
> heard for all these years, and so I wonder if that limit is still
> real?

I've never heard of that limit. And we have many, many instances of
multiple IND blocks in a compound. Code away!

One thing I'd caution you, be it that you are a neophyte at HLBL. The
default BPCSTM is (IIRC) 100. If you don't change that default to
something reasonable *and* if your codes loop infinitely without a WAIT
statement, you'll drag your CP to its knee in no time flat.

It's good to learn from your mistake; it's better to learn from others'.

Duc




 
 
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entity to whom they are addressed. Please do not copy it or use it for any 
purposes, or disclose its contents to any other person. Further, this e-mail 
and any associated files may be confidential and further may be legally 
privileged. This email is from the Invensys Process Systems business unit of 
Invensys plc which is a company registered in England and Wales with its 
registered office at Portland House, Bressenden Place, London, SW1E 5BF 
(Registered number 166023).  For a list of European legal entities within the 
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