Re: [foxboro] Cascade Master Block Reversing Control

Cascade loops do strange things sometimes.  Is the meas (and therefore the 
BCALCO, and FBK of the primary loop) of the secondary or slave loop changing 
during this behaviour?  If so, the FBK of the primary and therefore its output 
would change.  


> 
> From: James B Koenig <koenigjb@xxxxxxxxxxxxx>
> Date: 2005/05/23 Mon PM 04:05:02 EDT
> To: foxboro@xxxxxxxxxxxxx
> Subject: [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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> 

 
 
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