solid state relay (SSR) is an electronic switching device in which a small control signal controls a larger load current or

voltage.

It comprises a voltage or current sensor which responds to an appropriate input (control signal), a solid-state electronic switching

device of some kind which switches power to the load circuitry either on or off, and some coupling mechanism to enable the

control signal to activate this switch without mechanical parts.

The relay may be designed to switch either AC or DC to the load. It is functionally equivalent to an electromechanical relay, but

has no moving parts.