Definition
Performances d’un système asservi

A servo system is designed to perform a certain task: deliver an output signal that is a known function of the input signal. Its performance is therefore judged by comparing the actual output with the desired output. Symbolically, this leads to the diagram in figure 1, in which the dashed chain is fictitious.

Most often, we want to obtain a physical quantity at the output that is ideally a copy of the input, to within a constant factor α, α having a dimension since the physical natures of the input and output are generally different. By explaining the loop structure of the servo system, we obtain the diagram shown in figure 2.

If the sensor is chosen so that its transfer function (transmittance) is equal to β = 1/ α, and if the...