The general circuit is often divided into two parts: the main circuit and the control circuit. The relay is mainly used for the control circuit and the contactor is mainly used for the main circuit; The relay can realize the function of using one control signal to control another or several signals, and complete the control of start, stop and linkage. The main control object is the contactor; The contact of the contactor is relatively large and has strong bearing capacity. It can realize the control from weak current to strong current, and the control object is electrical appliances.

1、扩大控制范围：例如，多触点继电器控制信号达到某一定值时，可以按触点组的不同形式，同时换接、开断、接通多路电路。

1. Expand the control range: for example, when the control signal of multi contact relay reaches a certain value, it can change, disconnect and connect multiple circuits at the same time according to different forms of contact groups.

2、放大：例如，灵敏型继电器、中间继电器等，用一个很微小的控制量，可以控制很大功率的电路。

2. Amplification: for example, sensitive relay, intermediate relay, etc. with a very small control quantity, a circuit with large power can be controlled.

3、综合信号：例如，当多个控制信号按规定的形式输入多绕组继电器时，经过比较综合，达到预定的控制效果。

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

4、自动、遥控、监测：例如，自动装置上的继电器与其他电器一起，可以组成程序控制线路，从而实现自动化运行

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 realize automatic operation

不同的继电器接线方法会有些差异。下面介绍的是8个接线端子的接线方法。

Different relay wiring methods will be different. The following describes the wiring method of 8 terminals.

5和6是一对公共端子，1和2是一对常闭触点，3和4是一对常开触点。7、8不通电时，5—6和1—2接通，通电后就会断开1—2，而5—6不断，再和3—4接通.

5 and 6 are a pair of common terminals, 1 and 2 are a pair of normally closed contacts, and 3 and 4 are a pair of normally open contacts. 7. 8 when power is off, 5-6 and 1-2 are connected. After power is on, 1-2 will be disconnected, and 5-6 will continue to be connected with 3-4

一般中间继电器是双刀双掷开关，7—8端子接内部的线圈，使用时会并联一个续流二极管，二极管接入时的极性和继电器端子标注相反（8+接二级管的负极，7-接二级管的正极），达到预定值时，继电器会工作驱动电路断开，那一瞬间会因为自感电压产生很高的的电流，而这个电流会流过续流二级管，而不会经过起到电路，从而保护了电路中的元件。

Generally, the intermediate relay is a double pole double throw switch. Terminals 7-8 are connected to the internal coil. When in use, a freewheeling diode will be connected in parallel. The polarity when the diode is connected is opposite to that marked on the relay terminal (8 + is connected to the negative pole of the secondary tube and 7-is connected to the positive pole of the secondary tube). When the predetermined value is reached, the relay will work and the driving circuit will be disconnected, At that moment, a high current will be generated due to the self induced voltage, and this current will flow through the freewheeling diode without passing through the starting circuit, so as to protect the components in the circuit.