what is PID controller and what are its applications?

Answer 1

It's a proportional integral controller. It a controller that uses more tha simple feedback to adjust parameters in a control loop. It can look at the history of a process and rates of change and adjust its outputs. Here's an intro write up...

http://en.wikipedia.org/wiki/PID_controller

Answer 2

Programmable integrated device, it can be used for different application like temperature, pressure etc., in process application.

Answer 3

an elecric device to read the values an elemenate the error