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Old April 11th, 2019, 06:37 PM   #1
Lemming
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Omron Differentiate

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
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Last edited by Lemming; April 11th, 2019 at 06:40 PM.
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Old April 12th, 2019, 05:58 AM   #2
gtsuport
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Can you re-post the image.
It did not get uploaded.
gtsuport
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Old April 14th, 2019, 06:44 PM   #3
Lemming
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With pic, hopefully..
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Old April 15th, 2019, 09:57 AM   #4
BITS N BYTES
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Downward Differentiated Instruction
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Old April 15th, 2019, 01:50 PM   #5
Lemming
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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
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Old April 15th, 2019, 02:04 PM   #6
sbaum
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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.
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Old April 15th, 2019, 02:48 PM   #7
Lemming
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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
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Old April 15th, 2019, 03:35 PM   #8
Lemming
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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 ?
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Old April 15th, 2019, 06:58 PM   #9
BITS N BYTES
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http://www.plctalk.net/qanda/showthr...324#post620324
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Old April 15th, 2019, 07:33 PM   #10
Lemming
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Thanks heaps
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Old April 16th, 2019, 07:50 AM   #11
BITS N BYTES
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[quote=Lemming;813191]Out of interest, where did you find the timing chart ?

/quote]


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


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