[foxboro] Cascade Master Block Reversing Control

Thought I would ask this all knowing - been there - seen that list for
information before I went to TAC.
I have a problem with our cascade loops that only shows up once in awhile.
Lately more often. Every loop I have seen this on is a quiet Master temp
control loop using various temp, press or flow slave controllers.

The Master block will start controlling backwards. Example, when the
measurement rises above setpoint and the output should drive lower, it
actually starts rising instead. If you take the slave block out of remote
and then put it back into remote, the Master block will start acting
correctly again. This only happens on cascaded controls.

This has gone on in several version levels, for many years, but lately I am
told by our Techs that this has been happening once every two to three
weeks now, instead of only happening once every year or so, unless not
being reported.

Almost all of our cascaded controls are configured as shown below. Below is
the configuration of the last one that reversed control.

Currently running v6.5 with AP51B and CP40A's

Master Block (temp)                       Slave Block (press)
AOUT
Period   2                                Period   2
Period   2
Phase    1                                Phase    1
Phase    1
FBK      :SlaveBlock.BCALCO               FBK      :SlaveBlock.OUT
MEAS     :SlaveBlock.OUT
MODOPT   5                                MODOPT   5
PRIBLK   1
INCOPT   0                                INCOPT   1
PRIBLK   0                                PRIBLK   1
INITI    :SlaveBlock.INITO                INITI    :AOUT.INITO
BCALCI   :SlaveBlock.BCALCO               BCALCI   :AOUT.BCALCO
LOCSP    1                                LOCSP    0
                                          RSP      :MasterBlock.OUT
DERIV    0.02                             DERIV    0.0

I have also found several, but not all have had derivative set in the
Master block, the loop that did this a few weeks ago, two weeks in a row
(only known time same control loop this close together), did not have the
derivative set.

No other configuration set other than alarming functions. Since this
appears random , and not sure how to repeat it, I am not sure what my step
might be to stop it form happening.

Has anyone seen anything like this?
Where should I start looking to correct this?

thank you

James B Koenig
Production Data Tech
BASF Corp.

 
 
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