Re: [foxboro] Calculations
- From: "Roger Smith" <arbysmith@xxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Tue, 14 Jun 2011 13:50:34 -0700
You can use the ACCUM block's MTRFAC so the block gives you the correct
average at the end of 3 minutes. Then use a CALCA to grab that value and
hold it, and also reset the ACCUM for the next 3 minutes period. You could
also just do the whole thing in the CALCA.
Roger Smith
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] On
Behalf Of Jones, Charles R. (Chuck)
Sent: Tuesday, June 14, 2011 11:38 AM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] Calculations
"I understand this as "break the hour into 20 three minute segments
(blocks of time--not rolling average) and calculate the average value in
each"......No it would actually be not breaking the hour but just
average a 3 minute block in time and output it, then another 3 minute
block and output and so forth."
To me, these are two ways of saying the same thing. Meaning, I was
trying to say what you said. I just used too many words. >smile<
You could feed the values of the opacity into an accumulator. Every 3
minutes, divide the total by the number of half seconds in 3 minutes
(360) to get the average. Then reset the accumulator.
"Should have read create an alarm if opacity is 20% or above for more
than 3 minutes in any 30 minute period."
This, to me, is the harder of the two problems. I would set up a REALM
block with an alarm set for 20%. Send the Boolean value of the HAIND to
an accumulator to count the number of half seconds the opacity is in
violation. Then you would need an IND sequence block to harvest this
data and reset the accumulator as often as is expedient. (I would
suggest every 30s.) Divide by two to get the number of seconds in
violation and store them into a rolling array that keeps enough samples
to account for 30 minutes. Whenever the sum value of the accumulated
seconds of violation exceed 180, send the alarm.
You could probably get the same IND block to harvest data from both
blocks.
Do you reckon that would work?
Chuck Jones
Automation Technologist
Tate & Lyle Lafayette Plant
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