Re: [foxboro] Foxboro Control Philosophy 101

If it is of any help, the Foxboro IDP10 and earlier 863DP and a low-flow
cutoff available as part of the transmitter setup, so long as the
transmitter was in square root mode (output linear with flow) On IDP10,
there are two mode: soft cutoff and clamp. Might be easier to do it there
(assuming you have this kind of transmitter) than in the I/A system.

Charlie Doran
Invensys Systems (Foxboro)
----- Original Message -----
From: "Corey R Clingo" <clingoc@xxxxxxxxxxxxx>
To: <foxboro@xxxxxxxxxxxxx>
Sent: October 26, 2001 10:19 AM
Subject: Re: [foxboro] Foxboro Control Philosophy 101


>
> We've used SCI 7 on square-rooted inputs, as they tend to be noisy down
low, but
> 3/4% is not always enough to silence the spurious readings.  And this
isn't
> available on linear inputs, unless you use a 0-64000 SCI and adjust your
ranges
> accordingly, which then would make the bad-loop detection too sensitive on
the
> low end (and talk about troubleshooting confusion!).
>
> On the other system I've used (starts with an "H" ;-), there is a low
cutoff
> parameter, which causes the displayed input to got to zero if the actual
input
> was between (low range - OSV) and that parameter.  Worked great.  But the
KSCALE
> thing here looks good, too, except that you have to use another block.
>
> Corey
>
>
>
>
>
> William C Ricker <wcricker@xxxxxxxxxxxxxxx> on 10/25/2001 05:24:12 PM
>
> Please respond to foxboro@xxxxxxxxxxxxx
> To:   foxboro <foxboro
> cc:
> Subject:  Re: [foxboro] Foxboro Control Philosophy 101
>
>
>
>
> Low Cutoff SCI's are:
> SCI =  6: Square root, low cutoff (0 to 64000), clamp < 3/4% ("0 to 100%")
> SCI =  7: Square root, low cutoff (12800 to 64000), clamp < 3/4% ("20 to
> 100%")
>
> SCI =  9: Linear, low cutoff (1600 to 64000) ("0 to 100%, Elevated Zero")
> SCI = 10: Linear, low cutoff (12800 to 64000)("20 to 100%")
>
> SCI = 13: Square root, low cutoff (14080 to 64000),("20 to 100%, Elevated
> Zero")
>
> HOWEVER,
> I have thought (but never tried) to bring a boolean value into the KSCALE
of
> the
> AIN.
> When its set, you would get VALUE * 1 or VALUE
> When its not, you would get VALUE * 0 or 0
>
> The theory sounds good, no?
>
> W C Ricker
>
>
>
>
>
>
>
>
>
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