One Shot Command or One Shot Logic

showshocka

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showshocka
Join Date
Mar 2011
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USA
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510
I show this Screen shot of pretty much a duplicated rung of logic in a project in a packing machine that is here. It's pulses an output to a counter device. Rungs 2 and 3 does not necessarily makes a lot of since to me. Why couldn't they just have used what is in rungs 3 and 4?

Scanspeed.jpg
 
While they do function the same it is nearly impossible to tell what was on the programmer(s) mind when theydid this. Perhaps thinking of the two 'one-shot' type events in different ways? Maybe they didn't know [ONS] existed when they did the other? You might get a little bit of information from the original programmer, but then maybe not.
 
Could they have perhaps did it to get a longer or shorter output pulse time out of the SLC 5/04?
 
Last edited:
I'm wondering if it is a scrap of leftover test code. Maybe the original programmer wasn't confident with one of the two methods and this is a bit of test code so that he could see for himself that they both worked the same by watching the counter devices. Since both worked he may not have bothered to make them the same later.
 
Looks like a test program to me. The ONS instruction, I believe; will not give you an output, if the input is on when the machine first turns on. That should be the only difference.

In any case, if you are having problems, I would add a timer to turn the output on for longer. 1 scan may not be enough for the output card to change states or the input to register on the counter.
 
TConnolly said:
Maybe the original programmer wasn't confident with one of the two methods
Click to expand...
...
I did rungs 3 and 4 to show the comparison between what he did and what I thought it should be. That's way I was asking about the output times, maybe he didn't get what he wanted out of the one shot output time, so he did it that way...
 
It might have been left over from a conversion from an older PLC that didn't have a one-shot.

Even simpler - get rid of the B3/6

xic I:0/0 ons b3:0/5 ote O:0/1
 

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