Wiring a E-Stop

I am nearly finished with my PLC trainer (Micrologix 1000(1761-AWA) and PanelView 300 Micro), and along with the 6 input switches, I would also like to include a 'mushroom' E-Stop button.

What would be the 'Correct' way to wire this? Should it be wired to the input power to the PLC, and if not, what would you recommend? I want it to be as realistic as possible.

I DID do a search for this, but unless I'm blind (at 50 yrs old, the eyesight is going, but ain't that bad yet !!), I can't find a specific answer.

Thank you...

Jim

All inputs MUST get there signals.
ONE input must tell the statue of the E-Stop (En. IF cct is engaged)
All Outputs must be de-energised (hardwired) by the E-Stop.
Program must respect a logic to deal with the E-Stop being disengaged.

Jim,

The purpose of the E-Stop is to stop all activity that might cause harm, especially to people.

In some cases, (relatively small systems) it might be OK to kill everything... including the PLC. All power to the PLC and all output devices is interrupted by the master relay which is controlled by the E-Stop.

In larger systems this issue tends to become a bit more complicated.

If the system is large enough, there might be "Regional" or "Local" E-Stops. In that case, the E-Stop should kill power to the related outputs only; not the PLC. The PLC needs to know that an E-Stop condition exists in the particular area. Meanwhile the PLC handles the remaining areas in light of the E-Stop condition in the particular area.

Then there is a another much more complicated situation.

In some situations, depending on the particular process, it might be more dangerous to simply kill all output power. In those cases, the process needs to follow a particular series of steps in order to not make the situation worse. Think Nuclear Power Plant SCRAM Situation.

There are many processes that use air-valves. Many of those valves are single-coil valves with spring returns. These valves cause a particular motion when they are energized. When the valve is de-energized the motion is reversed. Is this a good idea in an E-Stop situation? It depends.

It's really easy to say that an E-Stop is an E-Stop, no ands, ifs, or buts.

However, E-Stop controls and resulting actions have to be considered very carefully in light of the process and the potential for worsening the situation.

I would say in your case (for training), do this:

1. Install relay (relays?) in between outputs and loads.

2. wire normally closed estop to both PLC input and relay coil (coils?).

3. Now you can leave PLC energized, receive estop signal in PLC which you could program to set off alarm (pilot light, tag at panel view, etc)kill outputs. This will also break outputs to loads which is a common scenario.

You could put the ES back to a safety relay such as PILZ eg http://pilz.com/english/products/safety/safety_relay/default.htm

Then the power flow through the PILZ would kill the power to a coil on an Emergency Stop Relay, which would halt power to necessary stuff like motors. The PILZ would also give an indication back to the PLC for its status. Therefore you can flag up messages etc.

Above is just general stuff, but this subject gets pretty involved depending on the type of machinery and its class rating for safety, and where in the world you are.

An E-Stop is EXACTLY what its said. EMERGENCY STOP.

To often it is used by operators for simple Stops.

An E-Stop should reproduce what happen IF power goes out.

If you want an air valve to act safely with an E-Stop i.e. with a certain logic then your pneumatic system is not design properly.

I have installed a few weeks ago a serie of FAST-STOP Muchrooms PBs.

I was asked for a certain logic when there operators pressed the E-Stop and my answer was No Sir!

They needed to follow a logic when Stopping FAST ... That was not an E-Stop ... it was control. E-Stop is LOSS OF CONTROL. PANIC ... KAPUT ... BOOOMMM!

Under very precise circumstance one can get special treatment from local autority to applie a certain logic to an E-Stop circuits, like with some Inverters which can fail when a load is in movement and the load will Stop slower than if the Inverter is permitted to decelerate it for n-time(s) after the E-Stop circuit is opened.

The one who dare to play with such serious mather are doing it at there own risks.

Again, if a device can arm someone because an E-Stop was pressed, then the problem is not the E-Stop cct, its the device and its failsafe operation.

E-Stop means STOP KNOW! Period.

Easy to say Pierre...

Circumstances sometimes dictate otherwise.

Intelligent planning carries the day.

Don't ever forget... most operators, in most industrial plants are not Nuclear Station Qualified nor Drilled for such.

I have been in situations where "AW-$HIT! STOPS" have caused more problems than they were supposed to prevent.

Pierre, you are talking from a liability point of view... dollar$.
You simply want to be able to say (testify) that your program stopped when the E-Stop was pushed.

In some cases, this might be EXACTLY what should happen.

In other cases, maybe yes, maybe no.

I understand your "Chainsaw Philosophy". However, your "Chainsaw Philosophy" is not necessarily an E-Stop situation.

That is really a matter of having the process following the expected actions and the actual actions and "seeing" when something unexpected happens.

What if your chainsaw only cuts through half of the cable?

Some things are OK or normal. Others, maybe not... maybe.

ICM (Intelligent Crisis Management) is the way.

It takes an awful lot of effort, but... sometimes that is the only way to keep more from being killed.

Say HEY! to Tin-Tin for me.

Terry Woods said:

... you are talking from a liability point of view... dollar$.
You simply want to be able to say (testify) that your program stopped when the E-Stop was pushed.

Click to expand...

I guess your wright. Being a contractor has that tendency.

I recall some years back when I was in charge of Technical Services in a Secondary Lead Smelter, common sense often dictated our ways of doing things over the Code! And every times an inspector would shout and bich about our solutions, after a brief discussion about the whys and the hows, he'd agree with us.

Terry Woods said:

In some cases, this might be EXACTLY what should happen.

In other cases, maybe yes, maybe no.

Click to expand...

The key word is "should". An I fully agree again.

Terry Woods said:

I understand your "Chainsaw Philosophy". However, your "Chainsaw Philosophy" is not necessarily an E-Stop situation.

That is really a matter of having the process following the expected actions and the actual actions and "seeing" when something unexpected happens.

Click to expand...

Terry Woods said:

ICM (Intelligent Crisis Management) is the way.

It takes an awful lot of effort, but... sometimes that is the only way to keep more from being killed.

Click to expand...

Again, being a contractor does not leave me much time to fineesse my way around the loops. Good people in well managed industries have the oportumity to better deal with this. We don't always have time for this common sense thing. We play it safe, not always for the end-user but for our insurance deposit

Terry Woods said:

Say HEY! to Tin-Tin for me.

Click to expand...

Six months ago he did his last trip in my Jeep. The liver so they say. I was holding him in my arms when he got the last shot. My kids where crying at home when I told them.

5 minutes later my beautyfull wife parked her car in the driveway with a cardboard box that was making these funny noises.
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She let me name him. She don't know that Data's cat has the same name. If she only knew !!!

Spot rules

So sorry to hear that about Tin-Tin, Pierre.

Spot looks like a dead-ringer for one of my four cats, Tinkerbell.

We didn't give her the name... she came with a name... Tinkerbell.
She's such a girly-cat. And kinda weird sometimes...

We call her "Stinker" but sometimes we call her "Buck Rogers" or "Jet Jackson". More often than not she appears to be on Space Patrol keeping all of the aliens away from our part of the universe. Apparently, those aliens are popping in and out, from one moment to the next, all over the house. I doesn't pay to get in her way when she's "on-duty". So far we haven't seen any aliens so she must be doing a bang-up job!

We got her, and two others, after we can home one day and found my favorite cat, $hitters, dead in his favorite sleeping spot. We never knew what happened. Anyway, we had $hitter and his brother Mopers. I couldn't bear the idea of Mopers being alone... so we went to get him a little pal... and came back with three little pals. The other two are brother and sister, Tuffy (the little prick) and Gizzy (Gizmo).

It took a while but they all came to terms. Mopers is definitely the boss and the kids know it. Now they all get along great.

It's been a couple of years since my dogs Tucker and Baxter died. We've been thinking yeah, we'll get a couple more puppies... but not yet.

Lately, my wife had been chomping at the bit to get one dog. She wanted a young dog, not quite a puppy.

I insisted that when we get a dog we will get two and that they will be babies... so that they and the cats can come to terms before someone was chewed to death or clawed to death. My insistence of two puppies kinda tempered my wife's urgency for a puppy.

Then my brother, in Florida, sends some pictures of the liter his dogs just had. They are American Eskimos. He said, "I have two brothers left. Do you want them?"

My wife turned into a kid looking through the candy store window. "Can I have one, huh? Can I? Huh? Can I? Pleeeeeaseee?"

Florida seems like it's half-way around the world from Oregon.

I said, "OK... depending on the logistics. BUT, if we take one, we take 'em both!"

So, just before Christmas, it happened. They came in on the Puppy-Line. A cute name that's supposed to make it easier on owners to accept the stressful effects of traveling in the cargo hold with baggage. It was a cross-country flight with connections in St. Louis and Denver. When they finally arrived they looked like they had been dragged all the way on the ground. Not that they looked bad, but they were obviously beaten up by the flight. I'm sure you know what I mean.

So, now we have a pair of American Eskimos, Charlie and Buddy. They know how to get clothes out of the hamper and they think that wall-corners are as tasty as slippers. At the Christmas gift-passing, they would sit on the sidelines, looking like good little angels... waiting for their chance. When something caught the eye, and as soon as we weren't looking, a white dart would fly in, grab a gift package and make a bee-line for the dog-door out to the backyard. Damn! They're almost as fast as the cats... all except for Stinker... I don't think there is a cat on the planet that's as fast as Stinker... well-tuned chasing aliens, don' cha know? Can you say..."Orange Blossom Special?"

They have eaten their way through every appliance cord they can get their little paws on. So far, they've been damned lucky. They've only gotten the ones that were plugged into timers. As luck would have it, the timer outputs were off.

I think maybe I'll plug a couple straight into the wall and leave them laying about. They are really good about going outside to take care of business. However, if they chew through a live-one I might have a puppy-present, or two, to deal with... that would be fine as long as the lesson was learned!

All in all, things are going OK. The cats have established their supremacy and the puppies are coming to terms with their new cat-ruled world. Not that the puppies are intimidated, but they know the line that can't be crossed.

However, when we take Buddy and Charlie out for a walk, that damned Buddy thinks he's 6-foot tall and can kick-a$$ on any four-legged thing in the neighborhood. I can see the Vet-Bills coming in now.

Say "HEY" to Spot for Mopers, Stinker, Tuffy, Gizzy, Charlie, Buddy and me. May he Live Long and Prosper!