Re: [foxboro] foxboro Digest V3 #273




All,

Thank you for your input.  I understand that we will only receive one kick
per toggle of the Sample Ready Bit.  The problem is, basis our
configuration, the kick seemed to be only proportional to the last change
in measurement as opposed to adding something extra from an integral term
when the measurement continues to deviate from setpoint.  I was just
inquiring to see if anyone had discovered any special hints as to how the
controller mode and other PIDA block parameters might be set differently
when trying to use the PIDA block in Sample Ready mode versus the standard
mode.   There is some evidence that the Integral term is handled
differently in the Sample Ready mode.

Neil Martin
Huntsman Polymers Corporation
2505 South Grandview
Odessa, TX.  79766
ph) 432-640-8436
pager)432-742-4289
email page)9157424289@xxxxxxxxxxxxxxxxxx


                                                                                
                                                 
                      Rguercio@xxxxxxx                                          
                                                 
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                      eelists.org              Subject:  Re: [foxboro] foxboro 
Digest V3 #273                                    
                                                                                
                                                 
                                                                                
                                                 
                      09/16/03 07:53 PM                                         
                                                 
                      Please respond to                                         
                                                 
                      foxboro                                                   
                                                 
                                                                                
                                                 
                                                                                
                                                 




Neil,
If I understand what you are doing, you are only getting feedback once each

32 minutes as your PV.  I believe you should only expect one controller
action
per feedback cycle, as the controller has no better information to act on
in
the meantime - ie, it cannot see any change in the PV by definition for
another
32 minutes, so it doesn't try to make more than the initial move.  I
believe
this is the correct mode of operation for a "Sample Ready" PIDA controller,
as
it is similar to a situation where we want the controller to make moves
sooner than the process deadtime, but realize that is pointless as there
has not
been time to give the controller the results of its last move any sooner.
What
I have done and seen done to deal with this situation is use some kind of
property calculator to interpolate/estimate empirically the property
measurement
based on a simple modelling alogrithm (Aspen does this more or less
rigorously
with their IQ inferential product) which also updates every analyzer
update.
Good luck, and let me know if you need any more help.  Rick Guercio, RG
Consulting  713-805-8742 (former Foxboro APC Manager - Hi, Alex!)




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_______________________________________________________________________
This mailing list is neither sponsored nor endorsed by Invensys Process
Systems (formerly The Foxboro Company). Use the info you obtain here at
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