input devices

wanted to know about input devices such as mechanical swithces,photoelectric switches,encodeers,temperature swithes, pressure switches, potentiometers,strain gauges and thermocouple. pls tell me all about it including the symbol, advantages and disadvantages.
since i'm new in plc i really need help on these thing

Its little hard to teach you somthing which took us maney years to learn and we still learning.
Go to manufactures books like A-B Omron and read. if you take book
for particular product like sensors you will find a lot of explanation.
If you have any question we will be happy to help.but you need to focus your question.
Good luck.

Here is a place to start: http://claymore.engineer.gvsu.edu/~jackh/books/plcs/