Safety circuits schematics

Does anyone has an idea of where to get literature about proven safety circuits with all its faulty conditions? ... or maybe a internet link?

thanks a lot for any help.

This site may have some material that could be useful: http://www.sti.com/

Safety schematics to make your own safety module

Thanks for your quick reply.
to get more detailed:
To realize a simple safety circuit for a protected area, I was planning to use two electro mechanical safety relais.
The observation area has two door switches to connect to the circuit. I have realized that not all circuits meet the needs for a category 3 supervisior circuit. Does any one know a source of schematics with the faulty descirptions?

I have added an example of this kind of schematics, hope it works

thanks a lot for any help

Zaurus:

The determination of the proper safety components and circuit depend on a full safety survey of the machine and poenntial hazzards. If anyone does actually suggest a curcuit to you with the limited information given so far, I would not follow it.

Also, at least here in the states, people are absolutely crazy about responsibility regarding safety due to the over zealous use of legal suits if an accident occurs.

I will mention that if you are guarding an area where a person may enter the danger zone then you may be wise to look at trapped key guard doors or a suplimental safety system such as an area scanner or safety matt that ensures there are no personnel within the guarded area.

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There are definately different philosophies regarding all sorts of safety. When I first left school I worked at a company that made door systems for mass transit vehicles. Our doors had what we called a safety edge which sensed when it hit something and reversed the doors to allow the obstruction (usually a person) to move in or out. We ended up doing a project with a European door manufacturer. When I asked their engineers what they used for a safety edge first I had to explain what I was talking about. After I got across the idea of what I meant they promptly said, "Why would anyone stand in the doors when they are closing?"

Thanks Norman,
I do understand your concerns, and of yours the door story does not sound professional at all.

Examples / Descriptions of safety circuits
There are such books on the market that show some explicit circuits with relay techniques and also explain what faults can / cannot be detected. So I was expecting there must be more then this one book, maybe even internet pages, for example of the manufactures of the mechanical relays. Matsushita has such descriptions too of the SFN technologies.
http://www.mew-europe.com/home/www/eu/en/relay/sfn/index_euen.html

The picture of the circuit in my previous message was from HENGSTLER, where they describe how faulty analyses within safety systems can be done.

So here is a very specific design for Category 3, that has some faults that cannot be detected, that for only Category3. Base for the Category is the EN 954-1 / ISO 13849-1.
So what I am looking for is more of this kind of examples that describe safety circuits of category3 / 4.

One nice book that I found already is the BIA-Report, Categories for Safety-related Control Systems in Accordance with EN 954-1, English version.

And here is the example, 2 relays, 2 door switches and the "safe output" for the motors.