General Stop - Step7

Hi,

I have some DI on my project which should be somekind of "general stop", when they are 1 I need immediatelly to stop motor. They need to raise an interupt, I suppose.

Can that be done in Step7?

Thanx

Hello Lesa;

You seem to plan to use an external digital signal (through a hardware interrupt, possibly) to stop a running motor. Is that right?
Sounds like an emergency stop program to me. How fast and how safe must this system be?
If you search for other threads on "Emergency Stop" (it has been discussed a few times here) you will see that the concensus is to hardwire e-stop circuits, for safety reasons. PLCs are just not fast enough in most cases to ensure the safety of the operators in a danger situation.
Please review the preceding discussions, if you still want to proceed through programming, come back at us with details.
Hope this helps,
Daniel Chartier

Thank you Daniel for replay,
I have read post you said and I think thay you are rignt, that should be done hw way, BUT now we are comming to part of the story that driving me nuts.

Nothing in this factory is "normal". Bad project, diferent hw state than project documentation says, 2 t/h instead 35 t/h like it should be, SCADA on no-name home comp 3m from 2x400KW motors...
And in that mess I need to write parts of new code.
E-stop (we call it G-stop (t<->p ) isn't hardwired. I need to stop motors for conveyors, mixers, crusthing mills and forming press.
It shoul be pretty fast, people are working near by.

On that mashines are E - stop buttons or ropes. When worker press it or draw it I get 1 on some DI.
What next?

Best regards

Hello lesa;

Boy, I really feel for you, I have worked in similar conditions before (never for long, my peace of mind is more precious to me than a job, under most circumstances.
That being said:
You could use the G-stop signal as a run permissive for the motor. If the signal comes in, it blocks the motor Run signal, stopping the motor. It can come from a hardware interrupt digital input, if you want to make sure the CPU is made aware quickly.
Make sure your field signal is wired Fail-safe, to proptect the workers.

Hope this helps,
Daniel Chartier

Hi Lesa.

It sounds like it is a real mess.
In the EU you and your company can be dragged to court and sentenced if you havent followed the guidelines (*). I dont know if this is the case in your country.

Best is if the conveyors etc. are protected by passive means, which means that there are guards that blocks you from getting parts of you body into the dangerous places.
Let me guess that this is not the case at your place.
As the very least, you should wire the E-stops or Wirestops directly into the start circuit of each conveyor. This is only category 1, which is probably not enough for such a dangerous device as a conveyor, but it is a hell of a lot better than nothing. Do NOT rely on using a standard PLC as a safety device.

*: I have experienced an accidence with one of our machines at a customer in Germany. Someone was hospitalised. I was interviewed by the local police, and had to show how our machine was safe (i.e. could be stopped safely, could be shutdown safely for maintenance etc.), and we had to send them a copy of the socalled "technical file". Because we had done everything to the book we werent blamed. The injured person had shown gross negligence.

Hi guys, tnx for replay and thanks for understanding,
@Daniel
That was my question, how to assign a HW interupt to DI in Step7.
Sorry for my lack of english terminology, what "field signal is wired Fail-safe" means?

@Jasper
on every mashine are guards and that is OK but I don't want to think, count and depent on it. There is always man-factor, I don't know what can go wrong, so I want to what I'm asking. Like you said:"The injured person had shown gross negligence". LOL!

At the very least I'll do what you said.