What is a relay? What are the classifications of relay?

Relay is an electrical control device. It 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 the interaction between the control system (also called the input loop) and the controlled system (also called the output loop). Usually used in automatic control circuit, it is actually an "automatic switch" that uses small current to control large current operation. Therefore, it plays the role of automatic adjustment, safety protection and conversion circuit in the circuit.

Relay is an automatic switching element with isolation function, which is widely used in remote control, telemetry, communication, automatic control, electromechanical integration and power electronic equipment. It is one of the most important control elements.

The relay generally has 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 control the controlled circuit "on" and "off"; Between the input part and the output part of the relay, there is an intermediate mechanism (drive part) that can couple and isolate the input, perform functional processing and drive the output part.

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

(1) Enlarge the control range: For example, when the control signal of the multi contact relay reaches a certain value, the multi circuit can be switched, disconnected and connected at the same time according to different forms of contact groups.

(2) Amplification: For example, sensitive relays, intermediate relays, etc. can control circuits with high power with a very small control quantity.

(3) Integrated signal: For example, when multiple control signals are input into the multi winding relay in the specified form, the predetermined control effect can be achieved through comparison and integration.

(4) Automatic, remote control and monitoring: for example, the relay on the automatic device and other electrical appliances can form a program control circuit to achieve automatic operation.

Classification of relays

1. Classification according to operating principle or structural characteristics of relay:

(1) Electromagnetic relay: an electrical relay that works by using the suction force generated by the current in the input circuit between the electromagnet core and the armature.

(2) Solid state relay: refers to a relay with isolated input and output, in which electronic components perform their functions without mechanical moving components.

(3) Temperature relay: a relay that acts when the external temperature reaches a given value.

(4) Reed relay: It is a relay that opens, closes or transfers the circuit by using the reed which is sealed in the tube and has the double functions of electric shock reed and armature magnetic circuit.

(5) Time relay: when the input signal is added or removed, the output part needs to delay or time limit to reach the specified time before closing or disconnecting its controlled line relay.

(6) High frequency relay: It is used to switch high frequency and RF lines with minimum loss.

(7) Polarization relay: a relay that acts under the combined action of a polarized magnetic field and the magnetic field generated by the control current through the control coil. The action direction of the relay depends on the direction of the current flowing through the control coil.

(8) Other types of relays: such as optical relay, acoustic relay, thermal relay, instrument relay, Hall effect relay, differential relay, etc.

2. Classification according to the overall dimensions of relays:

(1) Miniature relay: relay with the longest side size no more than 10mm.

(2) Subminiature miniature relay: relay with the longest side size greater than 10mm but not greater than 25mm.

(3) Miniature relay: relay with the longest side size greater than 25mm but not greater than 50mm.

Note: For sealed or enclosed relays, the overall dimension is the maximum dimension of the three mutually perpendicular directions of the relay body, excluding the dimensions of the mounting piece, the leading out end, the pressing rib, the pressing edge, the flanging and the sealing welding point.

3. It is divided into:

(1) Micro power relay: when the contact open circuit voltage is DC 28V, the (resistance) is 0.1A and 0.2A.

(2) Weak power relay: when the contact open circuit voltage is DC 28V, the (resistance) is 0.5A, 1A relay.

(3) Medium power relay: when the contact open circuit voltage is DC 28V, the (resistance) is 2A, 5A relay.

(4) High power relay: when the contact open circuit voltage is DC 28V, the (resistance) is 10A, 15A, 20A, 25A, 40A.

4. Classification according to protection characteristics of relay:

(1) Sealed relay: relay with low leakage rate, which uses welding or other methods to seal contacts, coils, etc. in the enclosure and isolate them from the surrounding medium.

(2) Enclosed relay: a relay protected by sealed (unsealed) contacts, coils, etc. with a housing.

(3) Open relay: relay without protective cover to protect electric shock and coil.

The above relays are most commonly used in electronic production, which are electromagnetic relay and reed relay.