Emergency Stop!?

[WaterSparky]

What are the regulations that apply to EM stops & PLCs

Would I be able to incorporate the circuit within the PLC or does it have to be hardwired?
If so could someone point me towards some regulations and or some litrature?

Thanks!

 

[telectrix]

i would say that the e stop should be wired directly in the control circuit of whatever machinery it's meant to stop in an emergency.

 

[Darkwood]

What safety Cat is your E-stop requirements?
Your question comes with many more questions about risk assessment and the safety system required ... as a rule of thumb your E-stop will be a primary isolation system upstream and sparate of your PLC etc and normally a safety relay is used now you can have a channel from the safety relay telling thePLC to display a message or sound a buzzer etc but using a PLC to control the E-Stops requires indepth knowledge.... some PLC's meet the standards to function E-stop and usually use communication rails and addressable devices but i suspect you are not on about these advanced control management systems.

BS 60204-1 is one of the main regulations that cover this area ... if you are asking the question i hope you are not already doing the work but preparing as altering and designing machinery control systems comes with a high level of responsibility and a need for understanding of the above BS-EN 60204-1..

Note different machinery may have its own specific BS-EN standards to follow ...its a mine field of regulations out there but a good place to start and you thought the BS7671 was expensive think again!!!

Check the link out too..

http://www.cechina.cn/ELetter/Standard/safety/EN954-1.pdf

 

[WaterSparky]

I work in the Water and Sewage treatment industry all of our PLCs are addressed of course and without going into detail are networked on site to one another and then via our own private network to our head office. Our communications is by Mod-bus over Ethernet or Profi-bus. So these maybe suitable but, I dont think we use them for this anyway. This was generalized question as the PLC in question i`m working on is a micro-PLC (zelio) like Mitsubishi alphas etc. But I would also like to know of the this affected me whilst at work, working with the more complex systems.

It would seem my system would come under B. If i read that correctly. I understand that an risk assessment on guarding, powered guarding etc should be done to the situation in question.

Oh I`m not doing the work at the moment merely coding the PLC and came to E stop portion and the thought brought me to here!

Cheers.

 

[Darkwood]

I build design smaller control systems and as it goes use various PLC's including Zelio 2 and Siemens Logo etc i don't really get involved with the more advanced set-ups so will avoid advising on such but noting the particular PLC and seeing if it complies to fail safe E-stop use is your best bet although i don't know of any micro- plc that does.... but i'll stand corrected if others comment to the contruary.

As each system and risk assessment can be different and is subject to sometimes differing opinions unless clearly obvious its a hard iitial question to answer.... i would say in your case on the micro PLC's a separate E-stop system is required if the safety assessment calls for one.

Consider what a program crash or corruption might do to using plc for E-STOP function.

 

[WaterSparky]

Like I say what I am doing now involves an Zelio, so your help would be muchly appreciated. I was just asking if you had more advice or the more complex side.

All the Zelio will be controlling is a PH correction system.

Throw a bag of sodium bi-carbonate in then set the system going, the mixer runs for x H:M then after that the dosing pump kicks in which then after High PH has subsided I will be using a relay off the inlet PH meter to shut it down. Pretty much it. I'm putting an E-stop outside on the tank just in case the operator needs to shut the system down outside, as the panel is inside 15M away? Views on the system? Any ideas?

Also opinions on the Logo Vs Zelio? I cant see much difference but, I just wondered as we only ever use Schneider gear.

Cheers.

 

[Darkwood]

I prefer Zelio due to the boolean function that lets you have several inputs that you can customize for an output so several arrangements of high and low inputs can be tailored to give a high or low output of your choice...

Logo has a limited version in that you can double click over a logic input and inverse it but this limits the output to only one input arrangement.

I also like the CAM block function of zelio which if put with pulse input will sequence up to 50 arrangements good to learn by creating a xmas light display pattern.

Without knowing your exact needs within the program its hard to advice but spend time use each function in a small program and learn them as i said my fav' is the boolean function since using it my programming has been made alot easier.

Im off out now ill reply later any queries ..

 

[Paultrim123321]

As has been posted above, there are many different standards to refer to, for example BS EN13850 Safety of Machinery;Emergency Stop,
BS EN13849-1/BS EN61508/BS EN62061. All of these standards relate to safety related parts of control systems and are implemented in different ways depending on the design principles. What is common to all is the need to carry out a risk assesment/risk reduction or quantitive risk assessment if your using 61508.
If I where you I would firstly decide which standard is relevant to your needs then produce a risk assessment on your design principles. From this it will guide you to the PL/Category of safety circuit you require. The components you use will have a critical result in your safety circuit meeting its designed performance level so take when selecting your hardware. As regard to interfacing your E-Stop safety circuit with PLC, as has been mentioned above you can interface your ESR with your PLC as long as it doesn't have a detrimental effect on your safety circuit. No good good having a dual channel PILZ safety relay with your E-Stops if they're interfaced incorrectly with your PLC which could result in a PLC output failure overriding the safety circuit.

 

[Paultrim123321]

In basic terms, If its not a Safety PLC then I would suggest that all PLC outputs for motor control etc are wired through the auxiliaries of your ESR. In the event of a PLC output failure, your ESR will still have overall control of all circuits which you need to isolate under E-Stop conditions.

 

[WaterSparky]

Cheers for all the replies guys, Ive taken all you guys have said and the boys at work!