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Understand common electronic components-digital time relays, small to large "automatic switch"

Relay (Relay)

Relay (English name: Relay) is an electrical control device, which is based on the principle of electromagnetic induction. It is an "automatic switch" that uses a small current to control a large current. It is widely used in remote control, telemetry, communication, automatic control, mechatronics and power electronic equipment. It is one of the important control components.

The core of the relay is an electromagnet. Under the action of current, the electromagnet attracts the armature to drive the switch connected to it to open or close, thereby controlling the on-off of another circuit.

Classification of relays

There are several classification methods for relays:

1. Classified according to the working principle or structural characteristics of relays, they can be divided into: electromagnetic relays, solid state relays, temperature relays, reed relays, time relays, high-frequency relays, polarization relays, etc.

2. According to the size of the relay, it can be divided into: miniature relay, ultra-small miniature relay, small miniature relay.

3. According to the relay load classification, it can be divided into: micro power relay, weak power relay, middle power relay, high power relay.

4. Classified according to the protective features of relays, it can be divided into: sealed relays, closed relays, open relays.

5, according to the relay can be classified according to the principle of action, can be divided into: electromagnetic, induction, rectifier, electronic, digital and so on.

6. According to the physical quantity of the reaction, it can be classified into: current relay, voltage relay, power direction relay, impedance relay, frequency relay, gas (gas) relay.

7. According to the role of the relay in the protection circuit, it can be classified into: start relay, measuring relay, time relay, intermediate relay, signal relay, outlet relay, etc.

The role of the relay

As a control element, the relay plays the role of automatic adjustment, safety protection, and switching circuit in the circuit.

Relay symbol

Because the relay is composed of a coil and a contact group, the graphic symbol of the relay in the circuit diagram also includes two parts: a long box represents the coil; a group of contact symbols represents the contact combination.

▲ Intermediate relay structure and symbol

The new electrical graphic symbol means: relay (collectively), single letter means: K.

Two-letter representation when subdividing:

Voltage relay: KV

Current relay: KA

Time relay: KT

Frequency relay: KF

Pressure relay: KP

Control relay: KC

Signal relay: KS

Grounding relay: KE

▲ Time relay coil symbol

▲ Time relay symbol