Question on emergency stop circuit

Not only that, but always use lighted E-stops so you can tell just by looking! (I know lights fail, but LEDs are pretty robust)


That would be a great idea if you're environment allows it. Our environment gets washed every night by people with corrosive chemicals, then high pressure rinsed with 150 degree hot water at 700Psi, and then gets sanitized. Condensation is also a problem because it gets hot during sanitation and then gets cooled down to 40 degrees during production.



This makes for a lot of corroded/rusted switch contacts and terminals so lighted E-STOPS are just another point of failure, shorts, and bad connections.



We are in the process of testing some banner sealed E-STOPS and they look like they will hold up great but only time will tell.
 
I had the same problem... On the regular. I switched to using the Banner sealed E-Stop, its like IP67, I think. It is amazing. I have 12 or so getting pressure washed every night and not 1 failed yet after a couple years of service. Ill never use anything else in a wash down environment.


We are in the process of testing some of those. They look pretty bombproof, i hope they work as good as they look.
 
Question on emergency stop circuit
________________________________________
Hello everyone. This is my first time designing a system from scratch. The system is for a rubber injection molding press. I have the PLC all put together, wired most of the programming done, and I am working on figuring out the emergency stop circuit now. My understanding is that when you hit the emergency stop button all functions of the machine will cease and cuts all power to everything except the controller and HMIs. I have 2 voltages, 24vDC which powers all inputs, and 110VAC which powers my outputs coming from the PLC.

My main question is, how are you able to have any sort of indicator telling the operator that the emergency stop has been pressed (such as stack light, alarm siren etc.) with out having some sort of output voltage going somewhere? Is it acceptable or common practice for this to be allowed? Our current machines were built with not much thought into these things and dont have any sort of indications that it has been pressed.

I currently have a pop up window on the hmi but thats it so far.
Thanks for your input and comments!

Talldude42,

I have an assumption that you are NOT designing a control system for a new rubber injection molding machine, but instead, are designing a new control system for an existing rubber injection molding machine. (Machinery modifier)

As we did in the past, we merely looked at the existing control system, and replicated it with newer components. The blind replacement with newer components, and replicating the electrical / hydraulic / mechanical design, while which achieves manufacturing requirements, leaves the end users at risk of injury.

You, and your employer, are MODIFIYING a Vertical Clamp Injection Molding Machine. Your company will be held responsible to make sure that the controls retrofit satisfies all applicable CODES and CONSENSUS STANDARDS applicable at the time of remanufacture.

Your original question was related to Emergency Stop terminating power to output devices. This comment indicates that current RISK ASSESMENT strategies are not being considered.

I am not trying to intimidate, conversely, I am trying to awaken, or heighten your awareness that this task is more than your responsibility, as a single individual, merely specifying electrical safety parts and deploying them. The entire machine control system electrical/hydraulic/mechanical, using TEAM based RISK assessment, and TEAM BASED risk abatement strategies.

There is an ANSI Document for Vertical Clamp Injection Molding Machines ANSI/SPI B151.29

There probably are numerous more ANSI / NEC / NFPA / OSHA / Etc… consensus standards applicable to your employers retrofit controls upgrade plans, your employer as owner of the machinery will be held responsible if the retrofit is not deployed to the industry consensus standards of the time of remanufacture.

Not trying to scare you off, actually, the opposite… all injection machines are aged, and the control systems are dying and obsolete. This is an opportunity to put new controls on, with an INCREASED and UP-TO-DATE SAFETY system.

Best regards,

Plastic

Thanks Plastic. I believe you hit the nail on the head, and that is exactly what i am trying to do. I have already made changes to the original plan using a few that have been stated here, added a few safety components and changed some programming around. Although with working 16 hr days for the past couple months has pretty much fried my brain i think but luckily we have a four day weekend coming up which will be much needed.
 
The comments in this thread make me extremely paranoid about any safety circuit ever installed by anyone alive.

On a more serious note, I would consult Rockwell documentation on how a proper safety circuit needs to be implemented, how to properly implement dual redundancy, how to properly de-energize proper circuits (and pneumatics if any?) when an E-Stop condition is detected, etc.

We owe it to ourselves as well as those working in these machines to build robust systems and shouldn't spare a 3rd terminal (2 for redundancy and 1 for PLC indication) due to budgetary constraints. Furthermore, proper safety rated relays must be used to make sure that the response time is respected and the relay always fail-safe. Some of the newer AB safety relays even implement their own voltage comm systems to make sure that a mechanic can't bypass an E-Stop by simply landing wires across.

Just as Plastic mentioned, a lot of considerations need to go into designing a proper safety circuit. I personally never touch them unless absolutely necessary. You will be liable if anything happens.

Cheers,
Vlad
 
The comments in this thread make me extremely paranoid about any safety circuit ever installed by anyone alive.

I think that's the correct reaction.

On a more serious note, I would consult Rockwell documentation on how a proper safety circuit needs to be implemented, how to properly implement dual redundancy, how to properly de-energize proper circuits (and pneumatics if any?) when an E-Stop condition is detected, etc.

This is an important point. Any time I've done a safety system, I've gone to the manufacturers website and downloaded manuals and app examples for exactly how to wire this module up. I know actually RTFM isn't a ***y use of time, but it's important.

Rockwell/Siemens/Pilz/whoever won't tell you whether or not you need a door switch, but they'll sure tell you how to wire one up to their controller.
 
I think that's the correct reaction.



This is an important point. Any time I've done a safety system, I've gone to the manufacturers website and downloaded manuals and app examples for exactly how to wire this module up. I know actually RTFM isn't a ***y use of time, but it's important.

Rockwell/Siemens/Pilz/whoever won't tell you whether or not you need a door switch, but they'll sure tell you how to wire one up to their controller.

Hey, there are engineers who have done safety circuits their entire career. To think that any of us (including myself) can do it better is just a lie. I'd always leverage such contacts when possible and verify twice. Especially when it comes to safety.
 

Similar Topics

Hello, I have plc Schneider TM241CE40T with the hmi HMIS5T. Do you have idea how to disable a button after an emergency stop to vijeo designer ...
Replies
5
Views
1,380
I'm been deciphering a program for a press here. I've gotten most of it deciphered using the manual to understand the instructions (first mitsu...
Replies
8
Views
58
OK. You guys helped me out a bunch with my first Siemens question. I found a bunch of issues with integrity checking the PLC programs I was...
Replies
3
Views
125
Hi all, Writng a FB in ST on Beckhoff TC for a pulser which turns on and off on a cycle, is paused by turning bControlInput to FALSE, but resumes...
Replies
6
Views
129
Hello folks! Never been here before but I have a question that's been bugging me for a while. I recently got a job at a chemical plant that's...
Replies
8
Views
290
Back
Top Bottom