Help debouncing discrete inputs

[ganutenator]

I'm probably really showing my ignorance this morning...

I need to filter some proximity input sensors.

If I put a timer on & a timer off in series it seems to work but oh no.

If the tmr on is first in the logic, then an ON blip is ignored, but an off blip is seen.

If the tmr off is first in the logic, then an on blip of the input is seen.

What am I missing?

p.s. the plc is a schneider m340 & I am using the function block diagram.

 

[ganutenator]

Ok, if I run the timers individually...

If both timers are done then set the output.
If both timers are not done then reset the output.

It looks messy though using the set & reset instructions. Plus I don't like using latches on inputs.

 

[TurpoUrpo]

Why you dont want to user sr?

You could use two TON's one with if input is true and other with if input is false, first sets bit and second resets bit.

 

[ganutenator]

I guess this will work. It just doesn't look clean.

Anybody have a better idea?

 

[OkiePC]

I typically use two TON timers, one fed by XIC and one fed by XIO instructions on the address to be de-bounced.

I didn't write this but it is a good illustration:

 

[ganutenator]

boy do I miss rslogix. just hated having to address everything.

 

[JerryH]

Another way to do it.