one shots

Hi, I am having problems with oneshots. I understand basically what they do, but I do not understand the animation. After the button has been allowed to go fully off, the button is then pushed in, why does this not result in the difu being true? It does when the switch is initially pushed at the start of the animation.

cheers, Robbie

robbie said:

It does when the switch is initially pushed at the start of the animation.

Click to expand...

Sorry to ask robbie but what are you talking about. Is this something on you PC where you simulate or on the WEB or realtime monitoring. What's the software your using?

robbie

I guess you useing Omron.You cant see the DIFU animation it too fast

if you want to make sure it work.use internal bit like that.[/ladder]

           PB

-----------{0.0}-----------{DIFU 200.00)----



                           Stop PB

-----------{200.00}--I-----{  }----{200.01}----

                     I

-----------{200.01}--I

When the PB pushed 200.00 go on for one cycle and hold 200.01.

that the only way you can see if it work or not.

If it is Omron, CX-Programmer v3.2 has a differential monitor. Use it and it will count the triggers for use. Great little tool.
beerchug

Sorry for not making myslef clear! I am talking about using the animationion, which is part of the explanation on one shots on this website.

I understand all the logic on the second rung, and I think, or maybe thought, I understood how the one shot works. But when watching the animation I don't follow one part.

The guys finger pushes the button and the difu goes on. Then the guy pushes the button further and the difu goes off( fair enough ). Then the guy releases the button twice untill it is completely off. Then he presses it half in, but the difu does not become true. I thought the difu went on when the logic changed from false to true for one scan. However, it is only when the button is pushed in completely that the difu comes on.

Am I missing something here, am I seeing the animation incorrectly? Could you please run me through each of the scans on that the animation shows, and relate it to the button being pushed.

Sorry for being dense!

Bob
As you know I new to CX how I use it?
My next project going to be with CX. after that It will be more clear for me.
Thanks

Hi Robbie,

I really hope I don't end up sticking my foot in it with this, but I believe the animation itself is a bit confusing with the two different "pushed" positions you see. I believe the one-shot works the way you think - its logic state is only true for one scan regardless of the condition driving it.

This means that your driving condition (the finger) can remain true (pushed in) for however long but the one-shot (difu) will only be true for the one-scan. That is the simple gist of it.

The rising-edge, falling-edge thing just tells specifically "when" the one-shot triggers.

Hope I am right and I hope that helps.

Steve

ArikBY, when in monitor mode, right click on the bit and then click on differential monitor. You can select rising or falling edge.
beerchug

Robbie-
I looked at the animation and I can see where your confusion comes from. Steve's answer is the correct one. The thing that is probably throwing you is that the button is in two different physical locations when the DIFU triggers. This is just an animation artifact. It's a little tough to envision because the button presses appear to be happening as fast as the plc is scanning, which usually can't happen.
When you think about this animation, try to separate the two button presses and picture a pause between them. Consider the intermediate states of the button as shown in the animation as a single button press. The way the bit sequence is shown on the first button press is more correct IMHO. The input and the DIFU come on together and the DIFU turns off on the next scan.

I hope this helps some.
Keith