SA3 series is three-phase normally open AC solid-state relay, which is a non-contact on-off electronic switch, in which two small terminals are input control terminals, the other large terminal is output controlled terminal, three-phase is six terminal (three in and three out), two-phase is four terminal (two in and two out), photoelectric isolation between input and output. By adding DC signal to the input, the output can change from off state to on state (blocking state when there is no signal), so as to control large load. The whole device has no movable parts and contacts, and can achieve the same function as the common mechanical electromagnetic relay. It is widely used in electric furnace heating constant temperature system, numerical control machinery, plastic machinery, food machinery, packaging machinery, textile machinery, petrochemical equipment, entertainment facilities and other automation control fields, suitable for all kinds of resistive, inductive and capacitive loads