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Old January 14th, 2014, 03:52 PM   #1
sparkytex
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Need Help making a totalizer for a flow transmitter

Hello all,

I've got to make a totalizer for our digester acid fill using rslogix 5. I have a flow transmitter scaled for 0-16000 LPM using a CPT function. What I need to do is create a totalizer so that when the acid fill valve opens the totalizer begins totalizing the total amount of acid being pumped into the digester. Once the acid fill valve closes the totalizer will stop and the final number will be the total amount of acid that was pumped into our digester during the fill time. I'm not quite sure which way to go on this one for logic wise. I was hoping some one could lend me a hand.

thanks, tex
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Old January 14th, 2014, 04:11 PM   #2
MATT116
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See attached its RSLogix 500 but you should be able to easily adapt it to RSLogix 5
Attached Files
File Type: zip Totalizer.zip (15.8 KB, 100 views)
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Old January 14th, 2014, 04:35 PM   #3
sparkytex
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I'm a little lost in this. What did you mean by the counter counts every time the STI has been enetered? The way I see the counter is counting on scan time which is way to fast to be compared to seconds. Not trying to be rude in any way im just not quite understanding the logic.

edit ** - also this totalizer is being used for all 9 digesters. each digester is tied into the same acid fill line. So the same flow transmitter is used for each digester. What the engineer wants is a total for each acid fill on every digester. So i'll have to reset the totalizer once the next digester is being put into acid fill sequence so every digester has its own acid fill total.
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Last edited by sparkytex; January 14th, 2014 at 04:44 PM.
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Old January 14th, 2014, 04:39 PM   #4
MATT116
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STI = scan time interrupt.
Processor Status > STI tab
Setpoint 100 = 1sec
File number = 3 of course this would be what ever file number your totalizer is
Do not call this program anywhere else in your program

So basically every second the processor will stop what its doing run the totalizer program then return to where it was.
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Old January 14th, 2014, 05:09 PM   #5
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Ok I seem to some what have the STI figured out. Im using a "spare" ladder for testing this, ladder 52. under SP I have 1000 because set at 100 it was counting way to fast. under file name I have 52. The STI doesn't seem to work when I enabled a JSR set to U:52. do I just use the STI as sort of a JSR and it will automatically scan the ladder without a JSR because the STI enables it to do so every 1 second?
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Old January 14th, 2014, 05:20 PM   #6
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Not sure what the time base options are on rslogix 5 but 500 is x10 so 100x10=1000ms or 1 second

Correct the STI is acting like the JSR so DO NOT call LAD 52 with a JSR

Oyea make sure the enable bit is set in STI settings tab
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Old January 14th, 2014, 05:28 PM   #7
Steve Bailey
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I didn't look at the sample, but here's a generic "be careful" if you're using floating-point numbers.

If the size of your incremental volume is small and you will be totalizing over a long time period, you can expect problems when the total gets large. Any floating point number in the 32-bit IEEE representation is only good for about seven significant digits. If your increment size is 0.1 liters, when the total approaches 1 million liters, the totalizer will stop. If you increment size is 0.01 liters, you'll have problems as the total approaches 100,000 liters.

If you need to totalize small increments to large totals it is better to use 32-bit integers. If you do that, and your increment size is 0.01 liters (centiliters), your totalizer is good for plus or minus 2.1 billion centiliters. That's 21 million liters instead of 100,000.
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Old January 14th, 2014, 05:50 PM   #8
sparkytex
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Quote:
Originally Posted by MATT116 View Post
Not sure what the time base options are on rslogix 5 but 500 is x10 so 100x10=1000ms or 1 second

Correct the STI is acting like the JSR so DO NOT call LAD 52 with a JSR

Oyea make sure the enable bit is set in STI settings tab
Yah it must be a bit different in rslogix 5 because there isn't an enable option, as soon as I typed in the setpoint and file number and exited out of the window it began scanning. But its working just fine right now. My biggest headache is going to be figuring out logically how to reset the totalizer with each digester acid fill. As only a 5 out of 9 acid fill valves have position feedback to the PLC. Thanks for the help guys. I may have other questions as I progress with this. I'll just re-post in this thread if I have another question!

TEX
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Old January 15th, 2014, 08:31 AM   #9
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I would suggest from past experience that when you reset the totalizer copy the current total into a "previous total" so the operator can always see what the last run was.
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Old January 15th, 2014, 12:46 PM   #10
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Quote:
Originally Posted by MATT116 View Post
I would suggest from past experience that when you reset the totalizer copy the current total into a "previous total" so the operator can always see what the last run was.
Good idea!!
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