A referenceable source for each type of plc.

Hello all,
I have used the search function to but I can't see to find the information I am looking for. I am currently a student starting to study plcs and have been asked to answer this question.

Describe a genuine real-world application (please provide references) for each type of PLC
(Unitary, Modular and Rack-mounted) and identify why the PLC is selected for the specific[FONT=&quot] application. [/FONT]
You will need to identify the following within your answer:
1. Number of input (I/P) and output (O/P) devices required.
2. Scan Rates.
3. Power Supply.
4. Process speed / memory size.



The thing I am struggling with is just the finding of a website which says x plc is used for x application so I can refrence it. I understand the differences and could come up with ideas of my own for where each one would be used but my teacher wants specific real world uses. Once I have that I wont have any problems finding a datasheet to answer the last part of the question.


Thanks alot for any help you could give me.

Being a student, you should know how to use google..

http://lmgtfy.com/?q=Unitary+Modular+Rack-mounted+PLC

Search, read, learn. Compare what you can find and ask yourself the questions again.

I'm sorry but I have been searching for a a source I can refrence for the last five hours thats why I resorted to asking for some help.

I understand the difference between them all and what they are used for I just need something that says "this specific model of plc is used for this task" for example "this siemens plc is used in controling the water board." or something like that.

but the plcs seem to be so widley used for any application they dont actually specify.

Well, the question you state does not mention a specific brand, just to describe a application for each one.

Just think about it. For example, why would you want to pick a modular PLC?
You can build it to fit your exact specifications, number of inputs/outputs, communication.
You can expand it, so think bigger processes.
You can replace individual modules if something breaks.

I am not trying to be a wise ***, just trying to teach you .

And I am sure you can reference sources like manufacturer websites. A good way to get references is look at the references on the Wikipedia page. No, don't reference Wikipedia, that is a nono. But the sources that are used in the articles can be valuable.

Part of your problem is that your terms, "Unitary" and "Rack-Mounted" aren't used in the real world in the context of PLCs, although you may find some references to "Modular". The terminology seems to be unique to the British HNC exam. If you search this site using those terms as keywords you'll find several references and pretty much universal scorn for the bureaucrats who refuse to adapt the test to current practice.

I just assumed I would need to find the specific brand or make of the plc in use so I can then go on to find the datasheet which would contain the scan rate, memory etc that I have been asked for.

Maybe i'm just reading the question wrong

Thanks for the help boneless.

If you pick one of the larger vendors(eg, Siemans, AB, GE, etc), They will usally have case studies and/or selection criteria for various applications. Now granted these will be inside of their own product lines, but if you research several different venders you should be able to draw conclusions 'across the board'.

you will not find a plc site that says use our brand for this application, but you must use our competitors brand for this application.

search the plc brand websites for overviews.

regards,
james

Thanks guys I have managed to find two of the three so far that gave me general aplication use. Thanks for the help.

I'm going to mention to my tutor that the industry don't actually use the terms that he is teaching us and see what he says.