Re: [foxboro] Secured Linkages

Chuck,

Not to nitpick, but the SPT parameter isn't always unsecured even if nothing
is connected to it.  If the block is in remote setpoint mode, the SPT
parameter becomes a secured output.  HLBL writing to the SPT of a block in
remote will generate Op Errors (3, I think).

Also, a related interesting tidbit ... if two stations try to write to the
same unsecured parameter in a third station at the same instant, it is
possible to see a similar Op Error.  Apparently, writes to unsecured
parameters temporarily secure the parameter, write the value, then un-secure
it.  Just FYI in case anyone has experienced intermittent, tough to
reproduce Op Error 3s.

Regards,

Doug Lloyd
DGL Controls

-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]On
Behalf Of Jones, Charles R. (Chuck)
Sent: Saturday, September 13, 2003 11:55 AM
To: 'foxboro@xxxxxxxxxxxxx'
Subject: Re: [foxboro] Secured Linkages

To quote from B0193AW - Rev.F (Integrated Control Software Concepts) page
35:
"If the parameter has an established linkage, it is automatically secured.
If there is no linkage (connection), it is available to all users until
someone secures it."

In the ICC, when a  block input parameter has nothing written in it (no
linkage), the parameter may have values written to it while it is running
(from Display Manager, FoxView, or from custom-made programs). This
condition is "unsecured".  If, in the ICC, there is a linkage (connection)
written into a block input parameter, then the only values that may be
written to that parameter come in via the link (usually to an output
parameter of another block)  This condition is "secured".  HLBL code written
to change a secured parameter will surely fail.  (Trust me, I know. ;)
Typical examples taken from a PID block:
 - A PID.MEAS parameter is linked to an AIN.PNT parameter.  Nothing else may
write a value to PID.MEAS except the AIN block.  This PID.MEAS parameter is
secured.
 - A PID.SPT parameter is left unlinked.  Since there is no linkage, the
operators my change the setpoint via a display that is designed for them to
do so.  (Or, I could write HLBL code in an DEP block that would change this
value.)  This PID.SPT parameter is unsecured.

When you have dbvu report the blocks with secured linkages (Is that the '-l'
option?) I suppose it prints out a list of blocks that are linked to other
blocks.  Does it also show the linkages?  I've never tried it.  I usually
use dbvu to resolve CP overruns using '-s' option (to find heavily used
phases) and '-u' option (to find unresolved linkages that cause linkages to
timeout).


Chuck Jones
Refinery Automation Technologist
Tate & Lyle North America -- Lafayette South Plant
765.477.5324 - Office  | 877.536.9219 - Pager



-----Original Message-----
From: Ajay.Tathgir@xxxxxxx [mailto:Ajay.Tathgir@xxxxxxx]
Sent: Saturday, September 13, 2003 1:34 AM
To: foxboro@xxxxxxxxxxxxx
Subject: [foxboro] Secured Linkages


Hi! All

When we run a dbvu on a checkpoint file, it gives a list of blocks with
secured linkages.

My query - what is secured linkage & what does it mean ?


Thanks & Regards

Ajay Tathgir

Reliance Industries Limited
Mumbai - India





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