Re: [foxboro] 4 to 20 mA output tight closure conditions for valves
- From: <D.Moras@xxxxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Tue, 9 Jul 2013 00:53:53 +0000
Joseph,
I have considered I was hoping there was a simple parameter as I seen in other
systems that could do the trick. Scaling the output 0-20mA would do the job
but it also has other scaling repercussions.
Thank you.
David
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] On
Behalf Of Joseph M. Riccardi
Sent: Monday, 8 July, 2013 8:57 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] 4 to 20 mA output tight closure conditions for valves
Have you considered scaling the 0-20madc scix; I think it is 1?
Joseph M. Riccardi
386-441-0250 Home Office
386-451-7607 Florida Cell
Joe@xxxxxxxxxxxxx
"To give real service you must add something that cannot be bought or measured
with money; and that is sincerity and integrity." - Donald A. Adams
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] On
Behalf Of D.Moras@xxxxxxxxxxxxx
Sent: Sunday, July 7, 2013 11:21 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] 4 to 20 mA output tight closure conditions for valves
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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(formerly The Foxboro Company). Use the info you obtain here at your own risks.
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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
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