Emergency Shut down System

Hi Folks,

How reliable the PLC hander the Emergency shutdown system?

Any Success reference/historical of Project by using PLC?


Regards

The answer to this question is entirely dependent on the result of an serious engineering study to determine the risk "Category" of your application.

The study will consider:

1. What might be the damage or harm caused by a system failure or accident?

2. How often is a failure or accident likely to happen?

3. What is the duration of the risk, and how long are operators exposed to harm?


There is a formal system for analysing these answers and then determining if the application is "Category 1, 2, 3 or 4".


If the answer is Cat. 1 or 2 then a PLC system will be usually acceptable.

If the application is Cat 3 or 4 then usually a specific Safety PLC design will be required.

Cat 1 systems can be handled more or less with normal good PLC system design. As the risk increases then then more redundancy and cross-checking is introduced into the design for Cat 2.

Cat 3 design usually demands (but not always) redundancy and cross-checking within the PLC itself. The best way to do this is to use a specific Safety PLC. The system I am most familiar with is Pilz Safety Automation

Cat 4 systems build on the Safety PLC concept and include fully I/O redundancy, certified components and design at every step.

Rockwell Automation also have a "Guardmaster" Safety PLC. The following is a

GuardMaster Reference

For a CAT 3 or 4, it is common practice to hard wire 2 fail safe circuits into an IEC CAT 4 safety relay. The safety relay then monitors and controls 2 contactors in series with each other.

There are many manufacturers of the safety relay devices. Omron have one that can mount to a CS1 PLC rack and the PLC can monitor the device directly. NOTE: in keeping with IEC standards, the PLC cannot control or reset the safety relay, only monitor the device. A hard reset is required.

Either of these methods are reasonably inexpensive solutions that generally comply with IEC standards.

ADVICE: check with your local authorities (standards, workcover, crane authorities) to find out what is and is not acceptable to them. Standards vary greatly throughout the world, and between different authorities in the same country. For example, some will not allow a PLC to control a lift but a "lift controller" is OK. Guess what the "lift controller" usually is?

Has anyone tried using a safety bus like Asi-safe? Just wondering if people are using these successfully.

Siemens are 'heavy' on that as they have UL/CSA certification for 'E-Stops' on 2-wire bus devices. I think they call it Profibus.

Have only heard of one installation in Southern Ontario. It is very expensive, and from what's been said on this board, don't go there.

Give it a few years.

Running 'Self Repairing' Profibus is a nice idea of course, but what if you clamp an E-Stop Module onto a 12/2 NMD-90 that some bone head has run in a plant. Imagine it is a steel plant with lots of welding. It is dark, and full of soot. ElevMike knows what I mean.

Or run conduit for this Profibus cable. Put Junction boxes everywhere, with lots of slack as you install. If you don't need the cable at that junction box, wrap it around the pipe, 20 times, if you do need it, hope that you can 'cable tie' (not ty-wrap) the length out to where you thought that you needed it. Enjoy.

Give it time.

Hard Wire your E-Stops period. Make all of your PLC outputs depend on the load side of this E-Stop Circuit. Use an E-Stop Relay as needed, but leave provisions for a positive force safety relay.

Don't certify this yourself and allow people to run this equipment.

Johnny

Hi there,

Telemecanique has a new system for safety by ASI.

http://www.telemecanique.com/WEBKITS/MachineSafety/PREVENTA/ENUS/offre/index_secuasi.htm

I have used the Pilz Safety System and can recommend it

see

http://www.pilz.com/english/products/safety/pss/default.htm

Jokab Vital System works well

I have used the Jokab Vital system a couple of times and it is easy to wire and troubleshoot. Every device has diagnostic LEDS. There are even adapters to integrate existing devices into a Vital system. Visit www.jokabsafety.com for more.

I used Siemens ASI-safe a couple of years ago and found it to be really easy to set up, and as yet have had no problems with it. Very few customers are willing to accept this bus style safety so I haven't used it since, so can't comment for recent equipment.

Cheers

It all depends on what you are shutting down and what kind of regulations you have to meet.
I have several ESD systems that are required to be a TMR / SIS system.
(triple modular redundant)(Safety Instrumented System)
That means triplicated I/O and triplicated processors and redundant power supplies with lots of diagnostics that must alarm when there are problems.
I have both Triplex And Triconex systems.
I prefer Triplex. And these systems can be quite expensive