Electromagnetic Relay Basics: Components and Advantages

An electromagnetic relay is an electrical control device used to control the flow of current, voltage, and power. Electromagnetic relays control the on/off operation of a circuit through the principle of electromagnetic induction, allowing a low-power control signal to control the on/off operation of a high-power circuit. Electromagnetic relays play a vital role in a variety of applications, ranging from home appliances to industrial automation systems. ATO.com will cover the basics of electromagnetic relays, including types and benefits.

How Electromagnetic Relays Work

Electromagnetic relays operate based on the principle of electromagnetic induction, in which an electromagnetic coil surrounds a removable iron core. When current is passed through the coil, the resulting magnetic field attracts the iron core, causing it to move inside the electromagnetic relay. When the excitation coil is energized, it produces a magnetic field that affects the movable contacts, causing them to attract or repel. This process can be used to control the on/off operation of a circuit. Electromagnetic relays are commonly used to control a variety of electrical equipment such as electric motors, lights, heating elements, fans, and air conditioning systems, and for signal transmission and control tasks in automation systems.

Components of Main Parts

Excitation Coil: This is the core part of an electromagnetic relay, which is a coil wound on an iron core, usually made of insulated wire. When a current is passed through the excitation coil, it generates a magnetic field.

Core: The core is a movable iron part, usually located inside the coil. It is attracted by the magnetic field generated by the coil, which changes the state of the electromagnetic relay.

Electrical Contacts: Electrical contacts are mechanical parts connected to the iron core to open or close a circuit. There are usually fixed and moving contacts, and the state of contact between them is controlled by the position of the iron core. Next to the excitation coil of an electromagnetic relay, there are usually one or more movable contacts. These contacts are switches connected to a high-power circuit, and the movable contacts can be opened or closed by the action of the electromagnetic relay, thus controlling the on-off of the circuit. Opposed to the movable contacts are fixed contacts. These contacts are in contact with the movable contacts and the fixed contacts open or close the connection when the movable contacts are actuated.

Springs: Electromagnetic relays are usually equipped with springs that are used to hold the movable contacts in a specific position. The spring is usually used to restore the initial state of the electrical contacts to ensure reliable circuit switching. When the excitation coil is energized, the magnetic field attracts the movable contacts, causing them to overcome the spring force and change position, thus opening and closing the circuit.

Advantages of Electromagnetic Relays

• Electrical Isolation: Electromagnetic relays provide electrical isolation, thereby separating the control circuit from the controlled circuit to ensure safety and prevent circuit interference.
• Reliability: Electromagnetic relays offer high reliability, long life, and little need for maintenance for applications that require long-term operation.
• Adaptability: Electromagnetic relays can be used in circuits of various voltages and current levels, thus providing greater adaptability.
• High current tolerance: Some electromagnetic relays can withstand high currents, making them suitable for applications that require switching of high-power devices.
• Control of Multiple Circuits: Electromagnetic relays can be used to control multiple circuits, including single-pole single-throw, single-pole double-throw, and double-pole single-throw configurations, making them adaptable to different applications.
• Instantaneous Action: Electromagnetic relays can switch circuit states in an instant, making them suitable for applications that require a quick response.
• Simple to Operate: Electromagnetic relays are usually easy to install and operate and do not require complex control systems.
• Economical: Electromagnetic relays are usually relatively inexpensive, making them competitive in cost-sensitive applications.

Despite their many advantages, electromagnetic relays have some limitations, such as the potential for wear and tear on mechanical parts, the need for more frequent maintenance, and the potential for electromagnetic interference in high-frequency AC applications. Electromagnetic relays are an important component in the field of electrical control, their basic principles, different types, and advantages make them suitable for a wide range of applications, from low-voltage household appliances to high-voltage industrial equipment, and an understanding of how they work and the different types of electromagnetic relays is essential for their correct selection and use.