Re: [foxboro] filter 4-20 signal

Thanks for the tip Chuck,

Regarding the time delay for controlling purposes: the delay is no problem, 
we're using 2 flaking belts each 60m long, the product enters the belt at 
250°c and is cooled by means of water nozzles on the bottom of the belt. We 
have 3 IR temp sensors at the end of each belt. This would enable us to 
measure the way the product is spread on the belt. Depending on the temp we 
would control beltspeed. So if the temp varies a lot this control is 
useless, we had to find a way to filter out the high and low peaks. For the 
moment the option of an AIN with FLOp and FTIME works fine. I'll also test 
the other suggestions.

Thanks to everyone for your suggestions, it's been a great help.

Dirk

>From: "Jones, Charles R. (Chuck)" <Chuck.Jones@xxxxxxxxxxxxxxx>
>Reply-To: foxboro@xxxxxxxxxxxxx
>To: "'foxboro@xxxxxxxxxxxxx'" <foxboro@xxxxxxxxxxxxx>
>Subject: Re: [foxboro] filter 4-20 signal
>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
>
>
>
>
>
>
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