Pulse flow meter

[Fer 1]

Hi, Has anybody has experience on converting the pulse from a flow meter to gallons per second. I try using the pulse to frequency instruction but the output that I get s verr bouncy all over the place. Or do you know of a way to measure the time between two pulses I think this for sure will give me what I'm looking for? Thank you an advance.

[PMCR 66]

Fer There are 2 ways to determine frequency: Count pulses over time, and divide by time, or measure the time between 2 signals. Without averaging, both will show some variation. What is the frequency range of the pulses from the flow meter (your low speed and your high speed), and what resolution are you trying to show. Also, what PLC (and input module if appropriate) are you using?

[Fer 1]

Iam using the high speed input from a CP1L PLC and my flow meter resolution is 132 pulses / gallon my flow range is 2.6 - 26gal/min. I try using the PRV2 instruction to determine the frequency over a second, but the output is all over the place im not sure if this is coming from the signal or that is a scan time error issue...

[PMCR 66]

Fer It should not be a scan time error in the PLC. The high speed counting and frequency measurment functions are both interrupt functions, and are not part of the PLC scan. At a constant flow rate, how much is the measured frequency changing in the PLC?

[Mendon Systems 22]

I suspect your problem is that the PLC is too fast for your data rate. Your pulse rate could be as low as 5 per second. I had a similar problem with an irrigation system control a few years ago. I ended up using the AVG function running in a cyclic task that only ran once per second in order to get enough pulse counts to get a real value. Even then it was a bit erratic. Edited 4 Jun 2012 by Mendon Systems

[Jay Anthony 118]

Good solution, Mendon Systems!

[Fer 1]

Hi Anthony. what is it that you do with the AVG, what are averaging with it?