What are the differences between several common relays

Update:23-11-2021
The relay is an automatic control device. When the input (electricity, magnetism, sound, light, heat) reaches a certain value, its output will undergo a jump change. We often use electromagnetic relays, single-phase relay, thermal relays and time relays. The principle and characteristics of the relay: When the input (such as voltage, current, temperature, etc.) reaches the specified value, the electrical device of the controlled output circuit is turned on or off. It can be divided into two categories of electrical relays (such as current, voltage, frequency, power, etc.) and non-electrical relays (such as temperature, pressure, speed, etc.). It has the advantages of fast action, stable operation, long service life, small size, etc. It is widely used in power protection, automation, sports, remote control, measurement and communication equipment. A relay is an electronic control device with a control system (also called an input circuit) and a controlled system (also called an output circuit). Usually used in automatic control circuits. In fact, it plays the role of automatic adjustment, safety protection and switching circuit.

Electromagnetic relay
Electromagnetic relays are generally composed of iron cores, coils, armatures, contact reeds, etc. When a certain voltage is applied to both ends of the coil, a certain current will be generated in the coil, thereby generating electromagnetic effects. The armature will overcome the pulling force of the return spring to attract the iron core under the action of electromagnetic force, so that the moving contact and the static contact (normally open contact) of the armature are closed. When the coil is de-energized, the electromagnetic attraction disappears, and the armature returns to its original position under the action of the spring's reaction force, so that the moving contact and the original static contact (normally closed contact) are closed. In addition, the "normally open and normally closed" contacts of the relay can be distinguished as follows: the static contact that is in the off state when the relay coil is not energized is called the "normally open contact (NO contact)"; the static contact that is in the conducting state The contact is called "normally closed contact (NC contact)".Electromagnetic relays include voltage relays, current relays, and magnetic latching relays.

Voltage relay
Our most commonly used intermediate relay is a voltage relay. The structure and principle of the intermediate relay are basically the same as that of the AC contactor. The main difference between the intermediate relay and the contactor is that the main contact of the contactor can pass a large current, while the contact of the intermediate relay can only pass a small current, and the overload capacity is small. Therefore, the intermediate relay can only be used in the control circuit, generally without the main contact, with a large number of auxiliary contacts.

According to the different input circuits, intermediate relays can be divided into DC relays and AC relays, which are generally composed of base and contacts. In actual work, the circuit with current less than 5A can also be directly completed with an intermediate relay, not just as a control circuit. Because the intermediate relay has a wide range of voltage requirements, it has been widely used in practice. For example, a 12V DC intermediate relay can work normally from 9V to 15V.

Overvoltage protection relay is also a kind of voltage relay. The self-combining over-voltage and under-voltage protection relays can play a protective role when the voltage is abnormal. For example, when the mains voltage exceeds or falls below the operating voltage of the protector, the protector can quickly and reliably cut off the load power to protect electrical appliances and personal safety. When the mains voltage returns to normal, the protector automatically turns on the power supply and restores the power supply. Now it is becoming more and more popular in the family.

Current relay
Current relay is the most commonly used component in power system relay protection. Current relay has the advantages of simple wiring, fast and reliable operation, convenient maintenance and long service life. As a protection component, current relay is widely used in overload and short circuit protection circuits of motors, transformers and transmission lines.

The detection object of the current relay is the current change of the circuit or the main electrical components. When the current exceeds (or falls below) a certain setting value, the relay will act to complete the relay's control and protection functions. Current relays can be divided into electromagnetic current relays and static current relays according to their structure types.

Magnetic latching relay
Magnetic latching relay is a new type of relay developed in recent years. It is also an automatic switch. Like other electromagnetic relays, it can automatically turn on and off the circuit. The difference is that the normally closed or normally open state of the magnetic latching relay completely depends on the action of the permanent magnet, and the switching state of the magnetic latching relay is triggered by a pulsed electrical signal of a certain width.
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