Re: [foxboro] 4 to 20 mA output tight closure conditions for valves
- From: <D.Moras@xxxxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Tue, 9 Jul 2013 01:01:10 +0000
Terry,
Yes valve / positioner adjustments can be made but this was a general question
and not specific to one valve in particular. If there was a simple soft
parameter option this could provide operational gain in the interim of valve
repairs or as the positioned cal / seat condition changes.
Thank you.
David
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] On
Behalf Of Terry Doucet
Sent: Monday, 8 July, 2013 10:41 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] 4 to 20 mA output tight closure conditions for valves
Can the application handle a valve positioner? Calibrate the positioner to
ensure closed and this should give full spring or full air to get the valve
closed.
> From: D.Moras@xxxxxxxxxxxxx
> To: foxboro@xxxxxxxxxxxxx
> Subject: Re: [foxboro] 4 to 20 mA output tight closure conditions for
> valves
> Date: Mon, 8 Jul 2013 03:21:18 +0000
>
> Hi,
> Does anyone know if there is a Foxboro 4 to 20mA output option that
> causes the mA value to be forced below 4mA (simulated tight shut off
> condition) when the output of a controller is at 0%. I have seen this as a
> standard option in other systems for some valves that don't tend to pinch off
> the best when at zero command (4mA), instead they stay partially open. I'm
> wondering if something can be done in FOX to compensate Setting the LSCO1
> parameter of the AOUT block to force the DCS output to drive below 4mA when
> the output command is at 0%, may do it but I looks messy. It looks like
> changing the LSCO1 parameter to a positive value will cause the RAWC value to
> drive the A/D converter safely below 4mA. See example below. Has anyone
> actually tried this.
>
> SCO = 3: Inverse Linear (12800 to 64000) Analogue Output 4 to 20 mA
> RAWC = ((OUT - LSCO1) * 51200/(HSCO1 - LSCO1)) + 12800
>
> Signal conditioning setting (SCO) = 3, = 4 to 20mA
>
>
> LSCO1
>
> 5.5
>
> LSCO1
>
> 5.5
>
> HSCO1
>
> 100
>
> HSCO1
>
> 100
>
> 51200
>
> Range of integer count
>
> 51200
>
> Range of integer count
>
> 12800
>
> Offset bias for integer count
>
> 12800
>
> Offset bias for integer count
>
> OUT
>
> 0
>
> OUT
>
> 100
>
> RAWC
>
> 9820.10582
>
> RAWC
>
> 64000
>
> RAWC@4mA<mailto:RAWC@4mA>
>
> 12800
>
> RAWC@4mA<mailto:RAWC@4mA>
>
> 12800
>
>
> 0% output mA
>
> 3.068783069
>
> 100% output mA
>
> 20
>
>
>
> Any views or a neater way to engineer this functionality?
>
> Regards,
>
> David
>
>
>
>
> ______________________________________________________________________
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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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_______________________________________________________________________
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
foxboro mailing list: //www.freelists.org/list/foxboro
to subscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=join
to unsubscribe: mailto:foxboro-request@xxxxxxxxxxxxx?subject=leave
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