Digital systems
Stability and transient response analysis

The obvious requirement is a stability of control system. Roughly speaking, the controlled output will settle at desired value, in its close neighborhood (tolerance limits), or it will oscillate or fluctuate randomly within tolerance limits. Unstable system exhibits unlimited growth of the error or oscillations with increasing amplitude.

The source of transient response in the control system is a control system dynamics. It manifests itself as inertia, delay, oscillation. It is implied by system ability to accumulate energy or mass (e.g. heat, water, electric charge) or to perform energy transformation from one form to another one (e.g. to exchange static and kinetic energy of a pendulum, electric and magnetic field in circuits with inductors and capacitors).

System dynamics also include a transport delay – e.g. during transport of mass (coal on a belt, water or air in a pipe) or a delay during data transmission and processing (e.g. sound propagation, slow data link communication, computation or slow sampling).