Pulse Control System

in engineering, an automatic control system in which control is achieved by signals of short duration (pulses) generated at predetermined times.

The pulse nature of the control system results mainly from the principle of operation of the system. For example, a radar station transmits short electromagnetic pulses, which are reflected by the target and are then used in a ground control system. The pulse mode of control is convenient in multichannel systems, in cases where the control signal sequences for different channels are separated in time or phase. In communications engineering the use of pulse signals improves the protection of messages against interferences and facilitates message coding. Sometimes the train of control signals is interrupted periodically, with the special purpose of improving the quality of system operation (in the so-called discontinuous control systems).

A pulse control system consists of a pulse-modulating element and a continuous part, which is acted on by a modulated pulse train. It may be assumed that in a pulse control system the train of control pulses is being modulated by a continuous signal, which acts upon amplitude, duration, position (phase), or quantity of pulses per unit time. Consequently, pulse control systems can be classified as having amplitude, width, phase, or frequency modulation. Artificial interruption of the signal is a special kind of modulation (“key-operated control systems”). If the continuous part of the system is linear, the pulse control system is also linear in the case of amplitude modulation and approximately linear in the case of shallow width modulation. Attainment of the finite time of transient processes is feasible in pulse control systems.

Mathematically, a pulse control system is described as a system of equations for finite differences. The z-transform (“discrete Laplace transform”) is most convenient for analytic study of linear pulse control systems. The characteristics of the pulse system may be corrected not only by means of corrective devices but also by changing the repetition rate or shape of the pulses. If the pulse repetition period is short (as compared to the basic time constants of the system), the properties of a pulse control system approach those of a continuous control system.