[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

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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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