Total with var. flow meter, say what!

My boss bought and old piece of equipment, does not want to spend any money (sound familiar)anyways, I have to fill a tank with water. The tank holds 220 gallons, but they want to be able to call for as little as 5 gallons. All I have is a flow meter that gives me a 4- 20 ma signal. I have used a SCP to get my GPM which is 45.3 but, it varies about 6 gallons time to time. The operator will enter how many gallons with a key pad on the HMI Panel View. I need a way to get a total that is accurate even though the flow varies. I did a DIV by 60 to get my GPS but having trouble getting around the variances. Any suggestion

What PLC are we talking about? For example AB ControlLogix/CompactLogix have Totalizing functions built in.

Also some flowmeters have totalizing functionality too.

If you are reasonably certain that your 4 20 mA is accurate then use a smaller time span. Stick to 3 or more times greater than PLC scan as your time span and then work out your flow rate. In theory the smaller the time period the more accurate you will become , but if your boss needs better accuracy tell him to put his hand in wallet..

Micrologix 1400 expan. slot Ang IF4 mod. and yes the 4-20 is good checked it, double checked it, then checked it again. The water psi changes and thus the flow rate, tried to div by 60 and then sample for 10 sec to cal and this is off.

oldnerd said:

tried to div by 60 and then sample for 10 sec to cal and this is off.

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It should have been: _____ (value and eng units)
The calculated result was: ______ (value and eng units)

Thanks

your right just was in a hurry when posted.
Did get it worked out thanks for the help.
With in .75 to 1 gallons at 110 gallon setting, not bad.