What are the Types of Relays Used in Electronic Products

What are the types of relays? What are the commonly used relays?

There are many kinds of relays. According to the input quantity, they can be divided into voltage relay, current relay, time relay, speed relay, pressure relay, etc.; according to the working principle, they can be divided into electromagnetic relay, induction relay, electric relay, electronic relay, etc.; according to the purpose, they can be divided into control relay, protection relay, etc.; according to the change form of input quantity, they can be divided into whether there is relay and measurement relay.

Whether there is a relay acts according to the presence or absence of input quantity. When there is no input quantity, the relay does not act. When there is an input quantity, the relay acts, such as intermediate relay, general relay, time relay, etc. The measuring relay acts according to the change of input quantity. Its input quantity always exists during operation. The relay acts only when the input quantity reaches a certain value, such as current relay, voltage relay, thermal relay, speed relay, pressure relay, liquid level relay, etc.

01. electromagnetic relay

Most of the relays used in the control circuit are electromagnetic relays. Electromagnetic relay has the characteristics of simple structure, low price, convenient use and maintenance, small contact capacity (generally below SA), large number of contacts without distinction between main and auxiliary, no arc extinguishing device, small volume, rapid and accurate action, sensitive and reliable control, etc., and is widely used in low-voltage control system. Commonly used electromagnetic relays include current relay, voltage relay, intermediate relay and various small general relays.

The structure and working principle of electromagnetic relay are similar to that of contactor, which is mainly composed of electromagnetic mechanism and contact. There are two kinds of electromagnetic relays, DC and AC. Apply voltage or current to both ends of the coil to generate electromagnetic force. When the electromagnetic force is greater than the spring reaction, suck the armature to make the normally open and normally closed contact act; When the voltage or current of the coil drops or disappears, the armature is released and the contact is reset.

02. Thermal relay

Thermal relay is mainly used for overload protection of electrical equipment (mainly motors). Thermal relay is an electrical appliance that uses the principle of current thermal effect. It has inverse time limit action characteristics similar to the allowable Overload Characteristics of the motor. It is mainly used in conjunction with the contactor to protect the overload and open phase of three-phase asynchronous motor. In actual operation, three-phase asynchronous motor often encounters overcurrent (overload and open phase) caused by electrical or mechanical reasons. If the overcurrent is not serious, the duration is short, and the winding does not exceed the allowable temperature rise, this overcurrent is allowed; If the overcurrent condition is serious and lasts for a long time, the insulation aging of the motor will be accelerated, and even the motor will be burned. Therefore, the motor protection device should be set in the motor circuit. There are many kinds of commonly used motor protection devices, and the bimetallic thermal relay is the most widely used. Bimetallic chip thermal relays are three-phase, with and without phase failure protection.

03. time relay

Time relay is used to control time in control circuit. There are many kinds of them, which can be divided into electromagnetic type, air damping type, electric type and electronic type according to the action principle, and can be divided into power on delay type and power off delay type according to the delay mode. The air damping time relay uses the principle of air damping to obtain time delay. It is composed of electromagnetic mechanism, time delay mechanism and contact system. The electromagnetic mechanism is a direct acting double E-core, the contact system uses i-x5 microswitch, and the time-delay mechanism uses an airbag damper.