Re: [foxboro] foxboro Digest V3 #273

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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