High speed counter software/hardware filtering?

[bbird]

I have an application using the low end of the highspeed counter scale on a flow switch. The flow switch counts give a pretty accurate indication of volume when counted correctly. The flow switch uses a reed relay at 50pps. (customer supplied and working with competitors plc) The reed generates some contact bounce at a much higher frequency that the HS counter picks up. This gives some issues with volume dispensed. I'd like to filter it without adding external components/signal conditioners. It would be nice in the config of the HS counter to set a minimum pulse width to ignore. Is there a way to do this either in the module config or via software?

I realize i may have to do to some signal conditioning external to the plc but thought I would throw it out in case there is something I am not aware of.

- Brian

[Joe Tauser]

At that speed you really don't need to use the HSC. If you set up an 2.5 ms interrupt subroutine it will inherently filter the input to 200 Hz. Put an Immediate input in it along with a positive transitional contact that increments a register. Let me know if you need an example.

Joe T.

[bbird]

Thanks, I hadn't considered the interupt subroutine which is exactly why I posted it.

[Joe Tauser]

Let me know if it works. Worst case is you'll have to hang a 0.1 uF cap across the input and 0V to filter out the bounce.

I had to use the interrupt trick on an -E1B module reading 10 "low-speed" pulsing flow meters. For anyone else looking at this post, note that the Immediate Input function is only valid for inputs on the main board of the controller. It doesn't work on expansion modules.

Joe T.

[bbird]

Everything went as planned and no more phantom counts.  thanks!