Re: [foxboro] 3 CHARC blocks cascaded

I've just now read this message, so my comments are probably too late,
but...

A CHARC block will not produce a BCALCO value unless PRIBLK is set. And if
PRIBLK is set, you need a control block upstream to terminate the chain. 

For applications where you have a CALC block or something else upstream that
needs the back-calculated CHARC output, eg in a split-range function, you
can drop a BIAS block in between, with a PRIBLK=0, to keep the CHARC block
happy.

eg. 
[CALC]       [BIAS]           [CHARC]        [AOUT]

OUT    -->   RBIAS      -->   MEAS     -->   MEAS
RI01   <--   BCALCO     <--   BCALCO   <--   BCALCO

             PRIBLK=0         PRIBLK=1       PRIBLK=1

Note also that different intialisation contstraints apply to a CHARC when
PRIBLK is set. You can't have a reversal in the characterisation, eg output
rising with input and then falling, because a back-calcuation would not be
possible. But with PRIBLK cleared, this is allowed.

cheers,
Con O'Brien

-----Original Message-----
From: Joerg Wierz [mailto:jwierz@xxxxxxxxxx]
Sent: Thursday, 20 March 2003 2:08 AM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] 3 CHARC blocks cascaded 



Hi, you didn't get any answers because you didn't describe your problem
completely (include top and bottom of your information stream !). What do
you want to do? If you want to maipulate a measurement you don't need any
backcalculation (forget about BCALCI/O, PRIBLK=0). If you want to adapt a
nonlinear valve characteristic in a control loop or somehing like that, then
you should implement back calculation, but you'll also have to take your
AOUT and PID block into the boat.

     PID                       CHARC             AOUT
     OUT   -------> MEAS         OUT   -------> MEAS
     BCALCI<----- BCALCO   BCALCI<-----BCALCO

     PRIBLK=0        PRIBLK=1          PRIBLK=1

Add as many CHARC's inbetween as you like.

J.Wierz
----- Original Message -----
From: "Tamer Ahmed" <tmahmoud1973@xxxxxxxxx>
To: <foxboro@xxxxxxxxxxxxx>
Sent: Sunday, February 09, 2003 10:07 AM
Subject: [foxboro] 3 CHARC blocks cascaded


>
> we have about 56 points and we want to build 3 CHARC
> blocks in cascade
> we are using I/A 6.2.1 and we are trying to build
> these CHARC blocks by connecting the 3 CHARC blocks as
> follows:
>
>    CHARC1           CHARC2             CHARC3
>
>     OUT   -----> MEAS     OUT   -----> MEAS
>     BCALCI<----- BCALCO   BCALCI<-----BCALCO
>
>     PRIBLK=0        PRIBLK=1          PRIBLK=1
>
> but with these connections we the cascade loop are
> open. any one can help
>
>
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your own risks. Read http://www.thecassandraproject.org/disclaimer.html
 
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_______________________________________________________________________
This mailing list is neither sponsored nor endorsed by Invensys Process
Systems (formerly The Foxboro Company). Use the info you obtain here at
your own risks. Read http://www.thecassandraproject.org/disclaimer.html
 
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