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Posted by Mike McCarty on May 08, 2001 at 18:56:12:
In Reply to: Tuning integrating CVs in DMC+ posted by Keith Landells on May 01, 2001 at 07:35:41:
What Dan is talking about is using duplicate level CV's to accomplish the
two
goals of letting the level ramp up or down when the controller needs this for
economics or stability, and also bringing the level to an operator setpoint
when it can. You can't have a DMC controller accomplish both of these goals
with one CV, but the following are a few more details on how to do it
with duplicate CVs.
What you need are two level CVs, using the exact same response models and
process measurement. One CV will be a Pseudo-type ramp, and the other a
Programmed imbalance-type ramp. Tune the pseudo ramp with high LP rank / EQEs
(could be a rank 1000 CV, but not required). Tune such that the controller
will give up on the RampSP when you want it to - rank 1000 CV to have it give
up for unit economics, some lower rank to have it give up on this level in
preference to other CVs. Then set up the programmed imbalance ramp as you
normally would, with tuning to allow it to prevent the level from exceeding
it's high and low limits.
The result here is with no limitations in the unit, the DMC controller will
control the level to it's RampSP on the pseudo ramp CV. When it needs to,
it will give up on the pseudo ramp CV and allow the level to increase or
decrease until it hits the high or low limit on the programmed imbalance
CV. At that point, the DMC controller will act to maintain the level at
the high or low limits. When the unit limits disappear, the controller stops
giving up on the pseudo-ramp CV and will bring the level back to the
pseudo-ramp RampSP.
Mike