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Relay (English name: relay) is an electrical control device, which is an electrical appliance that makes a predetermined step change of the controlled quantity in the
electrical output circuit when the change of the input quantity (excitation quantity) meets the specified requirements. It has an interactive relationship between the
control system (also known as the input loop) and the controlled system (also known as the output loop). Usually used in automated control circuits, it is actually an
"automatic switch" that uses a small current to control the operation of a large current. Therefore, it plays the role of automatic regulation, safety protection
and conversion circuit in the circuit.

Functional role

Relay is an automatic switch element with isolation function, which is widely used in remote control, telemetry, communication, automatic control,
mechatronics and power electronic equipment, and is one of the most important control components.

Relays generally have an induction mechanism (input part) that can reflect certain input variables (such as current, voltage, power, impedance, frequency,
temperature, pressure, speed, light, etc.); There is an actuator (output part) that can realize "on" and "off" control of the controlled circuit; Between the input
part and the output part of the relay, there is an intermediate mechanism (drive part) for coupling and isolating the input, functional processing and driving
the output part.

As a control element, in summary, the relay has the following functions:

(1) Expand the control range: For example, when the control signal of the multi-contact relay reaches a certain value, it can be changed, broken, and connected
to the multi-circuit at the same time according to different forms of the contact group.

(2) Amplification: For example, sensitive relays, intermediate relays, etc., can control a large power circuit with a very small control amount.

(3) Integrated signal: For example, when multiple control signals are input into multi-winding relays in the specified form, the predetermined control effect is
achieved through comparative integration.

(4) Automatic, remote control, monitoring: for example, the relay on the automatic device, together with other electrical appliances, can form a program
control line, so as to achieve automatic operation.