Re: [foxboro] Daily Totalizer Question

How does the operator enter the value?  Is it directly into the detail
display or through a graphic display?  If you use a graphic, you can have
the operator enter the value into a real input of a CALCA block; then pulse
a Boolean input to accept the value and store it in memory.  The memory
location would be read to the accumulator and output on a real out that is
connected to the MATH block.  However, I would do all the math functions in
the CALCA block and eliminate the MATH block.

Max Brent
Process Control Associates, Ltd.
max.brent@xxxxxxxxx

-----Original Message-----
From: Angela Gruber [mailto:aag43220@xxxxxxxxxxx] 
Sent: Tuesday, July 16, 2002 12:21 PM
To: foxboro@xxxxxxxxxxxxx
Subject: [foxboro] Daily Totalizer Question


Hi list:

This is my first posting so bear with me.

I figured out a simple way to do this temporarily but I am looking for some 
thoughts to see if there is something.  BTW - we recently upgraded to 
version 6.3

-----

We had/have a need to calculate a month-to-date production number utilizing 
weigh tickets from railcars.  Currently, the operator enters in the daily 
railcar loading amount before midnight into a AIN block.  Whatever number is

in the system before midnight is considered to be the final number for the 
day.

To get the month-to-date number, I made a simple MATH block that checks to 
see if the daily railcar amount (the AIN block pnt value) has changed.  If 
it hasn't changed, it does nothing (assumes the number is the previous 
amount).  If it has changed (assumes its a new amount for the current day), 
it adds it to the current accumulated value and stores the new number for 
the next comparison.  I currently have the block set to a period of 8 (60 
minutes) to give it the longest time between scans.  I have also edited 
mastercron to reset the accumulated value at the beginning of the month back

to 0.

It seems to be working (I have only been running it for 3 weeks now).  I 
think it could be better.  The problem I could run into (but haven't yet) is

if an operator incorrectly enters in the wrong number before one of the 
hourly scans, the MATH calculates (it sees a change), the operator enters in

the correct number after the scan time.  The block would then recalculate 
again, only it would be too high - I don't know of a simple way to get it to

subtract out the error other than having us DCS-folk manually fix it.

But ideally, I would like for the period to be every 24 hours -this would 
minimize the error mentioned above because it wouldn't matter much if data 
was entered in prior to the scan.  At the same time, though, I would like to

keep it as simple as possible.  Perhaps some sort of script that would 
toggle the MATH block from MANUAL to AUTO just before midnight, the block 
would calculate (put it on a faster period when its configured so it will 
scan while in AUTO), then toggle back to MANUAL just after midnight?  Or 
maye something totally different?

Your feedback is much appreciated

Angie Gruber
OxyVinyls, La Porte, TX











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