Relays are key components in electrical control systems and are widely used in automation, home appliances, industrial equipment and other fields. Whether it is a simple switch control or a complex logic circuit, relays play an irreplaceable role. This article will introduce the working principle, classification, selection and practical application of relays in detail to help you better understand and use relays.
I. Basic knowledge of relays
1. What is a relay?
A relay is an electrically controlled switch that controls the on and off of a large current through a small current. Its core principle is to use the electromagnetic effect. When the coil is energized, the magnetic field generated will attract the armature, thereby connecting or disconnecting the contacts.
Relays are mainly composed of the following parts:
① Electromagnet: Low-voltage power passes through the electromagnet to generate a magnetic field.
②* Contact: Switch part, used to control high-voltage power.
③ Armature: Attracted by the magnetic field, it drives the movement of the contacts.
④ Spring: Reset the contacts when the power is off.
II. Classification of relays
1. According to the working principle
Electromagnetic relays control contacts through electromagnetic effects.
Solid-state relay: no mechanical contacts, using semiconductor devices to achieve switching functions.
2. Classification by contact type
Normally open (NO): disconnected when the relay is not powered.
Normally closed (NC): closed when the relay is not powered.
Conversion (COM): has both normally open and normally closed functions.
3. Classification by application field
General relay: suitable for general circuit control.
Time relay: has delay function, used for timing control.
Thermal relay: used for motor overload protection.