Re: [foxboro] foxboro Digest V8 #251

In a message dated 7/26/2008 01:04:00 Central Daylight Time,  
foxboro@xxxxxxxxxxxxx writes:
How  about adding an Integral deadband to PIDA blocks, so that when the
process  is within the deadband, the Integral action is turned  off


I do this regularly with my advanced level control application  (ALC).  It is 
pretty easy to use a calculator to flop your connected INT  parameter between 
9999 (inside deadband) to whatever you want when outside the  deadband.  The 
nonlinear controller, by the way, works great (unlike the  one Honeywell put 
in and didn't support in Plantscape), but I usually only  double the gain 
outside the deadband, and have gone as high a tripling it for  special 
circumstances.  Remember, you don't want the CV to come barreling  in and out 
the other 
side of the deadband because of how severely you turned it  around when 
outside. 
 So the original tuning has to be able to take back  over once the deadband 
is entered, and you need to be somewhat judicious in  choosing the width of the 
deadband, which in the nonlin controller, does not  have to be symmetric 
about the setpoint.
 
RGC
12803 Josey Creek Ct.
Cypress, TX 77433
713-805-8742  cell
281-256-1111 home office/FAX
281-256-1333  home



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