Emergency Stop

When Emergency Stop is pressed on a machine, by code what must we do to the prevent motions from moving (i.e. releasing energy)?

Two problems here:

1) The minor one:
you provide no information. The possibliites are as varied as are all the machines in the world.

2) The big one:
You don't do emergency stops in software. The Estop should always be hardwired. Its not a soft stop. Its an EMERGENCY stop. The industry practice is to use redundant contactors and a hardwired contactor monitor circuit. However, I recommend you monitor your EEstop devices with the PLC so that the program knows to go ahead and shut off the outputs to everything that was shut down by the hardwiring. Its also usefull to annunciate which estop device was actuated.

I typically wire all devices needing inclusion in the estop system to the same output Card(s). Then the output power for those cards is supplied from a source that is switched off when and Estop device is tripped. You will need to do a thorough evaluatin of your system to determine what should be on the estop system and what should not be. If you don't know how or are not sure, then you need to get some help. Somebody's finger, hand, or life could be at stake. Don't take it lightly.

Other sources of stored energy besides electrical must be accounted for: mechanical, springs, gravitational potential energy, compressed air, hydraulic, water pressure, steam, momentum (braking may be required), latent heat, chemical energy, etc. Whether these are hazards or not is entierly dependant on the nature of the equipment.

Also, you probably want to do a search for "emergency" for some of the previous threads talking about this subject... I'm too tired(lazy) to look for it, but there was a pretty extensive thread talking about different philosophies of e-stop circuits around 6 months or so ago....

Another point to note is that generally the e-stop should be wired 'normally closed' and therefore used as a normally open contact in the software. Then if the cable was ever to get damaged it would 'mimic' the stop being pushed.

As Alaric pointed out, safeties should ALWAYS be hardwired. I think that regs now mean you have to use a three channel system with two channels going back to a Pilz relay (or some other type of safety relay - Guardmaster etc) and one channel going back to the PLC for feedback.

Could do with more info on the application though...

Have a look a this thread http://www.plctalk.net/qanda/showthread.php?t=9174

e- stop problem

As the guys said previously e-stops are never wired through your plc always use some hard wiring configuration "pilz" relay. there are different ways to do it. i normally suply the common to the output card from this safety relay as was mentioned above.

"BUT THERE ARE EXCEPTIONS" depending on the plc type i know that telemecanique do a purpose built fale safe card to fit into your rack for this purpose.
to connect all e stops back to this card.
telemecanique are the only ones i have heard of that do this but maybe there are others.

Have a look at the Pilz web site; they have a Safety PLC system.
PSS = Programmable Safety System where the Emergency Stop Buttons; Gate Interlock switches etc can be connected to Inputs on their Safety PLC.

www.pilzsupport.co.uk

moggie said:

Have a look at the Pilz web site; they have a Safety PLC system.
PSS = Programmable Safety System where the Emergency Stop Buttons; Gate Interlock switches etc can be connected to Inputs on their Safety PLC.

www.pilzsupport.co.uk

Click to expand...

A cheaper option is the Pilz Multi.

moggie said:

Have a look at the Pilz web site; they have a Safety PLC system.
PSS = Programmable Safety System where the Emergency Stop Buttons; Gate Interlock switches etc can be connected to Inputs on their Safety PLC.

www.pilzsupport.co.uk

Click to expand...

AB has their line of GuardPLCs too. I'll be using one for the first time on a small 10 ton press application in a couple of months.

Pilz multi is really inexpencive and powerfull enough to replace safety plc in many cases.

panic mode said:

Pilz multi is really inexpencive and powerfull enough to replace safety plc in many cases.

Click to expand...

Sounds good. Now if it only showed up in this customer's approved materials list I could try it out.

Unregistered said:

When Emergency Stop is pressed on a machine, by code what must we do to the prevent motions from moving (i.e. releasing energy)?

Click to expand...

I have been reading the responses given and was hoping the unregistered poster would return and give more information.

He stated " by code what must we do"...Does that mean safety code or programming code? I wasnt sure so did not respond.

I believe these days you should do a "Risk Analysis or Risk Assessment" to determine what regulations are involved. In the US OSHA 29 CFR 1910 Occupational Safety and Healt Standard governs alot of what we do BUT there could be other governing authorities.

Internationally I "think" IEC EN 61508 is a safety standard and some of the guidelines used may be

• EN 292: "Safety of machinery. General principles for design"
• EN 1050: "Principles for risk assessment"
• EN 954-1: "Safety-related parts of control systems"

I say this alot but will say it again....IT DEPENDS. The original question was too ambiguous to offer a qualitative answer.