Relay is a kind of automatic switching component with isolation function, which is widely used in remote control, remote measuring, telecom, automatic control, integration of machinery and electrification, electric and electronic equipments. It’s one of the most important controlling components.

Generally, relays have the inductive organ (input part) that can reflect the input value (such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light etc.); have the executive organ (output part) that has the capability of switching the controlled circuit “on” or “off”; between the input and output parts, there is the medium organ (actuator) that can make input value coupling-isolation and drive the output part.

As a kind of controlling component, generally, relay mainly has the following functions

1.To enlarge the range of control. E.g., when the controlling signal of a multi-contacts relay reaches a certain value, according to the different forms of the contacts, it can synchronously change over, close or open several circuits.

2.Enlargement. E.g., sensitive relays and medium relays can control a high-power circuit with minute controlling power.

3.To integrate signals. E.g., when several controlling signals are put into a multi-winding relay in the stated form, the relay can realize the expectant controlling function by analyzing the different signals.

4.Automatization, remote control and monitoring. E.g., in automatic equipments, the relays and other electronic components can constitute program-controlled circuit, realizing the automatic operation.