Falling Edge Solution For S5

This is my first, and I hope my last, S5 project. I'm not sure, but I think I have died and went to PLC hell.

I am trying to count the falling edge of an input.

I am working on a cut to length project with 3 different lengths cut from long to short, 1 of each and then starting over.

The material advances on a belt through 3 sets of fiber optic eyes, 1 for each length.

I need to count the part entering the eye on the rising edge with 1 counter and count the part as it exits the same eye on the falling edge with another counter, so I can use the math comparisons to determine which set of eyes makes the cut and which sets are ignored. This is probably more info than needed.

I have submitted my question to Siemens Tech Support several times with pretty much a good luck with that.

I have found in the manual an example of a rising edge detection example, but no mention of the falling edge.

Is there any old schoolers out there that can give me a ladder example of a way to accomplish a falling edge detection with a plc that doesn't offer one. I have tried a few things with a normally closed contact, but I get a count on start up, and I don’t want that, I need a count only after the part has entered and exited, not ant time the eye is empty.

I enjoy your forum and thank you for any help.

Seg 1

AN I 1.0 Input
A F 10.0 Input was on last scan
= F 10.1 Falling Edge - True for 1 scan only.

Seg 2

A I 1.0 Input
= F 10.0 Remember Input was on last scan

This method relies on the segment 2 being executed after segment 1.

Segment 2 sets F 10.0 when the input is on and it will remain true until the next time segment 2 is executed with the input off.

Segment 1 Looks for the input to be off and that it was on last scan i.e. falling edge. F10.1 could then be used to drive your counter.

Nick

Amazingly simple

That is amazingly simple.

These new rising and falling edge functions found in the new platforms have put my brain in the sleep mode.

I have found the first good thing about the S5 platform, it makes my think harder.

I thank you Sir for your help.
Anthony

awrobinson said:

I have found the first good thing about the S5 platform, it makes my think harder.

Click to expand...

The first and the only!

Paul