Calculating Flow with Pulse Input

[Sebu 0]

Hi All, I am working with Micrologix controllers. I would like to know how can we calculate Flow (example: interms of GPM) based on the pulse inputs. In my case I am using paddel wheel. If anybody have the logic can you share with me? Regards Sebu

[sthompson 3]

Use a Counter and a Timer, then mathematically calculate your flow. The longer your time snapshot, the more accurate, but with a slower update time. The shorter your time snapshot the faster your update, but the more error introduced for +/- one count etc. Stu......

[TConnolly 13]

Unless you are using the bottom dwelling Micrologix 1000, consider using the Micrologix HSC function file (look under +Controller -Function files in the project tree in Logix500). Use the HSC to count pulses and an STI to compute flow rate. Your flowmeter will have a gallons/pulse specification. Multiply that by the number of pulses to find how much fluid has passed. Example: My flow meter is 1 cu. in/pulse. Since there are 231 cu. inches in a gallon then each pulse = 1/231 of a gallon. So by multiplying the number of pulses in one second by 1/231 I can get my flow in gallons per second. To convert to gallons per minute I then multiply by 60. By combining terms 1/231 and 60 I get 60/231. If I configure a 1 second STI then in the STI subroutine I multiply the HSC accumulator by .25974 to get GPM and then reset the HSC accumulator. If your pulses are coming at the PLC faster than two times the PLC scan time then the HSC, which is a hardware counter instead of a software counter, has the advantage that you don't have to worry about missed pulses. The STI will run at exactly the interval you specify so you don't have to worry about the scan time considerations of a software timer. Edited 2 Aug 2011 by Alaric

[sthompson 3]

Aleric's solution is much better for this PLC. Stu....

[TimWilborne 108]

Or use an EII and time the spacing between each pulse. It makes your flow display look a little more "real time" and what I like is it leave the second high speed input of the pair available. So many ways to skin a cat...

[mhowasso 5]

What is an EII..???

[Mickey 71]

"Event Input Interrupt" See pdf below. EII.pdf