====== PID Controller ======
A proportional–integral–derivative controller (PID controller) is a generic control loop feedback mechanism (controller) widely used in industrial control systems. A PID controller attempts to correct the error between a measured process variable and a desired setpoint by calculating and then outputting a corrective action that can adjust the process accordingly and rapidly, to keep the error minimal.

===== 참고 =====
  * [[http://en.wikipedia.org/wiki/PID_controller|위키피디아]]