in control, an automatic control system in which at least one component has a relay characteristic. A relay system is one type of nonlinear sampled-data automatic-control system.
A distinction is made between two-step and multistep relay systems. The fundamental characteristic of two-step relay systems is the presence of self-maintained oscillations in the output (controlled) parameter of the system when the system is in a steady-state condition—that is, after transient processes have ended. The amplitude and period of the self-maintained oscillations are determined by the relay characteristic of the relay element used, the dynamic characteristics of the controlled system, the actuating mechanisms, and the measuring and converting devices in the automatic control system.
Relay systems are relatively simple to manufacture and operate, and their cost is low. The use of contactless relay elements improves the reliability of the system. Relay systems are extensively used in the control of various production processes.