Introduction - If you have any usage issues, please Google them yourself
In most modern engineering systems, there is a need to control the evolution with
time of one or more of the system variables. Controllers are required to ensure
satisfactory transient and steady-state behavior for these engineering systems. To
guarantee satisfactory performance in the presence of disturbances and model
uncertainty, most controllers in use today employ some form of negative feedback.
A sensor is needed to measure the controlled variable and compare its behavior
to a reference signal. Control action is based on an error signal defined as the
difference between the reference and the actual values.