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Control Systems!

History:

Control systems of one sort or another have been around for a long time...from the days of the ancient Greeks.

In the 1900's and onwards most of the foundation work was laid for Classical Control Theory. With the advent of computers Modern Control Theory and Digital Control Systems came to the fore.

Where are Control Systems?:

They are all around us in:

bulletAeroplanes
bulletCars (ABS)
bulletLifts
bulletKettles
bulletRobots
bulletShips
bulletTrains
bulletWashing machines
bullet...

So here are some questions and tentative answers:

bulletWhat is a control system?
bulletA "device" added to some system that makes the system behave the way we want it to behave.
bulletWhat is an open loop control system?
bulletA system where no system output parameter is used to modify the system behaviour.
bulletWhat is an closed loop control system?
bulletA system where a system output parameter is used to modify the system behaviour.
bulletWhat is feedback?
bulletA system output parameter used to modify the system behaviour.
bulletWhat is an unstable control system?
bulletA system where the output changes in an uncontrolled manner, until it reaches some limit (physical, energy, ...) with or without an input to the system.
bulletWhat is a conditionally stable control system?
bulletA system where the output oscillates indefinitely between some limits after some input to the system.
bulletWhat is a stable control system?
bulletA system where the output reaches some steady state value, ideally equal to the system input, after some desired time interval.

Pictures tell the tale better:

Open Loop:

Closed Loop:

Feedback:

Unstable system:

Conditionally stable system:

Stable system: