Digital systems
System identification

System identification is usually done by actuation of the system by shaped input signal, and evaluation of its response at the output. Then, a structure (type, order) of the system and parameters (coefficients) are determined. Often, a step input is considered, the output is then a transient response, discussed earlier. Sometimes, a very short pulse is introduced, then the response is called impulse response. Both signals (and responses) mentioned have a significant theoretical meaning. However, such sudden changes can be impossible or dangerous to use in certain systems, in practice (e.g. the sudden opening or closing of a valve at a long pipe can cause dangerous blasts, also a very fast acceleration of vehicle, elevator or a cableway can be unwanted). Sudden changes are often impossible, due to slow action, e.g. of motor, valve or a heating. So called ramp or trapezoidal signals are then used instead of step and impulse at the input. For their theoretical significance, also a sinusoidal or random (continuous or pulse) signals are used.

Fig. 8.15: Typical input signal types for system