Pulses to PLC - GPM

Anyone had success with convering pulses into the HSC of a PLC and generating a GPM reading? Here's the set up:

PLC (Idec in this case) with HSC inputs up to 10K

Signet Scientific (+GF) #515 paddle wheel pulse generator where the paddle wheel component of the generator resides inside a pipe.

A 'K' factor is applied to the formula depending on pipe size, schedule and saddle fitting (adaptor for connecting the generator to the pipe). Pipe sizes range from 4" to 12".

I can't get a stable reading on the counter. Has anyone had experience with the Signet unit? Or any similar unit for that matter.

Any help or suggestions are greatly appreciated.

How does the IDEC high speed counter calculate frequency? There are two methods typically used, counts per unit time and time per X pulses.

If your system uses counts per unit time, you need to set a time unit that strikes the best balance between stability and update speed. For example, if you use a fast time unit (say 100 msec) and the output from your flowmeter is nominally 5 pulses per time unit, you might reasonably expect to see either 4, 5, or 6 pulses in any given time unit. That's a +/- 20 percent variation. If you lengthened the time unit to 1 second, you'd have a nominal frequency of 50 pulses per time unit and you might see 49, 50, or 51 pulses in any given sample. Now the variation is +/- 2 percent.

If your system keeps track of time to accumulate some number of pulses, then you probably have control over the number of pulses. As before, you select a number of pulses that balances stability with update frequency.

Thanks, Steve ...

The IDEC doesn't have a frequency instruction so I'll have to do something similar to your suggestion. But I can establish a set point for a specific count.

I think what I'm trying to do with this post is troll the waters and see what suggestions that may come up. I haven't done this kinda thing in the past, so I want to see if there're any ideas that will lead me to the epiphany that I'm hoping to experience in writing this part of my system code.

Once I get this going, I have to do something similar for another customer to establish an FPM readout on an OIT. Slow, slow speed. Maybe a max of 2 FPS, i.e.120 FPM.

... rab