pls help me

Hi i am very new to plcs, infact i am just starting out, can anyone please help with the following?

1.) How does the cpu work in general plcs, diagram/s would help.
2.) What type of communication links and networks can be connected?
and how do they work?
3.) and does anyone know anything about health and safety while working with plcs?
Thanx for any help in advance
(I am trying to do some research before i start the class)

Try this link for most of those answers: http://www.plcs.net/contents.shtml

Take a look at the tutorial on this site for an overview of how the typical PLC's operating system works. At the beginner level, you don't need to know any more detail than that.

Just about any network capable of surviving in the environment where PLCs are typically used, has been implemented in some brand of PLC, somewhere.

The health and safety of the people who have to work around the machinery is one of the primary considerations when you're designing a control system. The PLC and its program is just one part of the control system.

I have had a look around the site for the last few days but carnt seem to find anything in any detail on cpus or health and safety

clio2k3 said:

(I am trying to do some research before i start the class)

Click to expand...

That's very commendable.

Give Give this link a try

Paul

Always start with a qoute... intresting style Paul.

That's very commendable.

Click to expand...

Well, the CPU of a PLC works the exact same way as any other CPU, including the one in your PC. The only difference, if any, is that a PLC always (almost) uses a microcontroller and not a microprocessor. For more on microcontrollers or processors, visit www.howstuffworks.com.
As for safety considerations, well, PLCs are definately not a hazard to your health, but you can make it do dangerous things. In an industry (and outside)safety is the responsiblity of every single individual. You need to know as much about safety as you possibly can. Most importantly, you need to know- 'No matter what it's never 100% safe' (remember the Titanic?).
As a PLC programmer what safety measures you should keep in mind depends on the control process that your PLC is a part of. The most basic model of a safety system would be like- Sensors detect any abnormal conidition... informs PLC (or may be something else) of the same... depending on the nature of abnormality the process is stoped and audio-visual warnings are flagged or some pre-defined (by the programmer) routine is followed (by the PLC).
Alternatively, the operator notice something wierd, ponders over it for some time, scratches his head, freak out and hit the STOP button.
Elementary, is it not?

Try the Siemens Energy and Automation site,there is four PLC courses on it which might prove to be useful.