Re: [foxboro] filter 4-20 signal
- From: "Jones, Charles R. (Chuck)" <Chuck.Jones@xxxxxxxxxxxxxxx>
- To: "'foxboro@xxxxxxxxxxxxx'" <foxboro@xxxxxxxxxxxxx>
- Date: Thu, 28 Apr 2005 09:11:21 -0500
A variation of this solution is to use a SIGSEL block instead of a CALC or
CALCA block. Set up the DTIME block to have 8 "buckets" (NUMBKT = 8).
Connect each of the buckets to a different input of a SIGSEL block. Set the
SIGSEL block SELOPT to 3 to have it average the eight inputs. You can
configure the DTIME block to whatever time you wish. I haven't done a block
equivalent estimation, but I believe this will be more efficient than using
a CALC or CALCA. (And, it's a lot easier.)
However, I think that Corey was referring to the DTOPT in the DTIME block.
If this parameter is set, at the end of each time period the current
measurement is passed into the "bucket brigade". If the option is not set,
then the DTIME block calculates the average value over the time period and
puts the average value into the first bucket of the "brigade". If one needs
an averaging algorithm instead of a first-order Butterworth filter, then
this block can be used. It is possible to set up the DTIME to only have one
bucket.
The problem is that Dirk wants to send this signal to a controller. All of
these solutions will create a time lag between the measurement and the
control block. Since he mentions that it will be controlling a temperature,
this may still be acceptable. But then that begs the question, "Why are
temperature readings so erratic that they need to be filtered?" I'm used to
temperature being one of the more slow and stable control measurements. I
could be spoiled...
Chuck Jones
Refinery Automation Technologist
Tate & Lyle -- Lafayette South Plant
765.477.5324 - Office | 877.536.9219 - Pager
"Love making is like UNIX. If you don't know it, you won't miss it."
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] On
Behalf Of Clement, Mark (KIDDMET)
Sent: Thursday, April 28, 2005 8:37 AM
To: 'foxboro@xxxxxxxxxxxxx'
Subject: Re: [foxboro] filter 4-20 signal
The DTIME's buckets are accessible (connectable) - so you could tie the
buckets to a calc block and do moving averages=20
my 2 cents
Mark
-----Original Message-----
From: Corey R Clingo [mailto:clingoc@xxxxxxxxxxxxx]
Sent: Thursday, April 28, 2005 9:27 AM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] filter 4-20 signal
The DTIME block has some options that will do this. I believe it can =
take=20
several samples of an analog value and then spit out an average. =
However,=20
it is not "rolling"; in other words, it gathers, say, 10 samples, and =
on=20
the 10th it outputs an average.
To get a rolling average, we have used CALC/CALCA blocks here. I've =
seen=20
at least two implementations. I can post some CALC code if you like.
And of course the filtering option on the AIN is there...
Corey Clingo
BASF Corp.
"Dirk Pauwels" <dirkpauwels_1@xxxxxxxxxxx>
Sent by: foxboro-bounce@xxxxxxxxxxxxx
04/28/2005 05:15 AM
Please respond to foxboro
To: foxboro=20
cc:=20
Subject: [foxboro] filter 4-20 signal
Does any of you guys know how to "filter" a 4-20 signal? I have a temp
signal that varies a lot from 20=B0c to 40=B0c, we plan to use it in=20
automation,
but I need to get rid of the "peaks", so if the average temp in a =
1minute
time periode is approx 35=B0 but it showed peaks from 22 to 38,I need =
to=20
show
the operator the avgtemp of 35=B0 and use this avg temp in the auto =
control.
I'm using a sequence now, but I'm sure there are far better sollutions.
Thanks & Rgds,
Dirk Pauwels - DCS coordinator
Engineering dept.
Lawter International BVBA
An RSM Company
Ketenislaan 1c ? Haven 1520
B-9130 Kallo, Belgium
T. +32.(0)3.570.95.97/ Mob. +32.(0)497.428.300
F. +32.(0)3.570.16.09
E mail: dirk.pauwels@xxxxxxxxxx
=20
=20
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