Need help selecting an Emergency Stop

[dssteven]

Hey everyone,

First post here, hopefully somebody can help me out! I'm an intern at a company that builds large scale concrete screeding equipment and on all of their machines there is an emergency stop button.

We found out shortly after I arrived here that the current emergency stop is freezing when washed and left in the cold. When this happens it won't allow anybody to use the machine if it was pushed down before washed off... We found another Emergency stop that does not freeze and I'm supposed to determine if it will work for the circuit.

All I really need to know is what electronic specifications matter in deciding what emergency stop to use. I have datasheets and more information than I can handle but I am unsure what is relevant and what is pish posh. The circuitry is correct and will kill the circuit where the e-stop is placed but I just want to be sure the e-stop will be able to handle the voltages (12VDC for our small line, 24VDC [I believe] for large line machines)

Please let me know if you have anything to say about this!

Thanks!

 

[gto_ron]

kill switch

Does the full operating current of the machine go through the kill switch? If so check current capacity and voltage rating. If you're stopping a fairly high inductance system you may get some arcing at the contacts.


Ron

 

[CDRIVE]

You haven't provided nearly enough information for an intelligent reply. Is the main ON/OFF control a magnetic contactor? Is the Kill switch a NC or NO model? What's the expected max current through the switch, etc.?

 

[CocaCola]

We found out shortly after I arrived here that the current emergency stop is freezing when washed and left in the cold.

May I suggest the obvious? Stop soaking the electronics with water? Even if it's something as simple as tying a plastic bag around the area when washing...

 

[dssteven]

I apologize, I'm fairly new to industrial style circuits so I apologize for not providing more information.

@CDRIVE: The E-stop is connected as a NC path to ground. When the E-stop is pushed it breaks that path to ground and does not allow current to flow through the rest of the machine. The E-stop we're looking at is mechanical, not magnetic. Is this enough for an intelligent response?

@CocaCola: I told them the same thing but they're large concrete screeding machines. This means they get pretty dirty, often caked with dust and cement. They need to power wash them to keep the contacts from being cemented (At least the water can be thawed out as where the concrete...well...you know...)

Thanks for the replies guys

 

[dssteven]

Oh and gto_ron, there is a negligeable amount of induction (if any) present in the circuitry. In this instance, the NC E-stop simply provides a path to ground and breaks that path when pushed as I understand it. As I said to CDRIVE, the expected current through the E-stop is around 1.2A. I'm just unsure what, on the datasheet, would relate to this.

 

[CDRIVE]

I apologize, I'm fairly new to industrial style circuits so I apologize for not providing more information.

@CDRIVE: The E-stop is connected as a NC path to ground. When the E-stop is pushed it breaks that path to ground and does not allow current to flow through the rest of the machine. The E-stop we're looking at is mechanical, not magnetic. Is this enough for an intelligent response?

I'm not sure if this clears things up or not. Are the Start Stop & E Stop momentary push button switches? Posting a photo of your current power panel might help.

Most industrial machines are controlled with magnetic contactors. They are much safer than common switches becuause a breif power failure will shut the machine down. Imagine ripping a 2 x 8 of southern pine and having a power glitch without one. Ya better duck and do it real fast!!

 

[CDRIVE]

Oh and gto_ron, there is a negligeable amount of induction (if any) present in the circuitry. In this instance, the NC E-stop simply provides a path to ground and breaks that path when pushed as I understand it. As I said to CDRIVE, the expected current through the E-stop is around 1.2A. I'm just unsure what, on the datasheet, would relate to this.

This statement further reinforces my belief that the E Stop controls a contactor. That is.. unless this machine is powered by an internal combustion engine. Please tell me it isn't.

 

[dssteven]

Okay after further review of the circuit layout I've noticed the emergency stop provides a ground for not the entire circuit but just the main power relay. I guess I misunderstood this when I looked at it earlier this week. Essentially it creates a ground at the exit point so no current travels to the circuit and all electronics are killed. The ABB (E-stop) guy helped me out as well and this problem has been resolved.... Thanks for all the input guys I'll do my best to post here and there. I've been looking for a good electronics forum and this seems to fit fine!

Regards

 

[CDRIVE]

Okay after further review of the circuit layout I've noticed the emergency stop provides a ground for not the entire circuit but just the main power relay.

Regards

Thanks for confirming it's a magnetic contactor (Relay). It's always good to be correct.

 

[donkey]

with coca colas idea.... why can't you ziptie a plastic bag over the machine ALL the time? this will prever everything (or alot of stuff) getting in there as well as allowing the button to still be pushed.
the added bonus is for oh&s you can simply remove the ziptie and bag whenever you want to replace it due to poor visibilty

 

[CDRIVE]

Just a thought.. If the staff is going to keep hosing this equipment you may want to find a good Mil Spec or Marine switch. The ones with boots on them.