Omron Differentiate

Lemming · Apr 11, 2019

Howdy

Having a poke at some Omron code, and run into a scenario I didn't think should work. A TIMX on the end of a rung with preceding contacts. The thing I dont understand is the contacts are differentiated, so would have expected the timer not to run other than a single scan ? I put the ladder in simulate mode, and seems to work as if not differentiation ?

Haven't seen the ladder running in the PLC, so not certain isn't a simulate issue ? Any info useful..

Cheers Chris

gtsuport · Apr 12, 2019

Can you re-post the image.
It did not get uploaded.
gtsuport

Lemming · Apr 14, 2019

With pic, hopefully..

BITS N BYTES · Apr 15, 2019

Downward Differentiated Instruction

Lemming · Apr 15, 2019

Yep, that's how understood they work. So given the TIMX needs an input on to decrement, cant work ??

Prob safest to wander off to site and plug in to confirm

sbaum · Apr 15, 2019

Your rung is always true, so the downward differentiate will reset the timer if any of those conditions transition from 1 to 0.
Better take a closer look at the timing chart Bits N Bytes posted.

Those differentiate are very handy but it can take a bit (no pun intended) to wrap your mind around them.

Lemming · Apr 15, 2019

Yeah, just looked at the instruction help posted by BITS N BYTES again, and can see now thanks.. Not how I expected it to work.. (my preconceived idea got in the way of the help file

I thought any diff contact was true for a single scan only, but makes sense that can also be not true for a single scan as well.

Thanks for the replies

Lemming · Apr 15, 2019

Out of interest, where did you find the timing chart ?

I looked at the help file baked in to CX, and it stated the output ON for one scan on either LD or NOT_LD depending on the transition and diff applied. Couldn't find any reference to how it actually works..

So if using a NOT_LD with a diff up, is OFF for 1 scan on the bit rising edge ? I'm assuming the rung in the image resets the timer on any transition of the 4 bits ?

BITS N BYTES · Apr 15, 2019

http://www.plctalk.net/qanda/showthread.php?p=620324#post620324

Lemming · Apr 15, 2019

Thanks heaps

BITS N BYTES · Apr 16, 2019

Lemming said:
Out of interest, where did you find the timing chart ?

/quote]

It,s in the programming manual for each PLC. Just search for "differentiate".

Omron Differentiate

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