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Different kinds of control systems

In order to define more precisely control systems, one can separate them into two different categories:

In fact, feedback can be seen as a link between the output and the input of the system; it is used to obtain a more accurate control by being compared to the input, in order to correct an error.
However, beside this purpose, feedback has numerous other effects, among which stability, bandwith, overall gain, impedance, and sensitivity can be noticed, effects which have their importance in any control application.
Dealing with the properties of control systems, a reader familiar with Digital Signal Processing business will easily recognize numerous properties among which linearity and time-invariance of systems are used to describe the behavior of control systems.`

We have been, so far, describing control systems regardless of them being continuous- or discrete-data systems. The fundamental difference between those two is that a discrete-data system has, at one or more points in it, a signal which is either a pulse train or a digital code. 

Digital control systems are commonly separated into two classes:

The signal in a sampled-data control system is in the form of pulse data. On the other hand, when a digital computer or controller is used in a control system, it is referred to as a Digital Control System. 

Generally, a sampled-data system receives data or information only at specific instants of time, intermittently, since the signal we are dealing with in this case is digital. 

Incorporating sampling into a control system presents numerous advantages among which 2 main can be noticed: