An electromagnetic relay is a type of relay that uses an electromagnet to control the switching action. It consists of a coil, an armature, and a set of contacts. When a current flows through the coil, it creates a magnetic field that attracts the armature, causing it to move and make or break the contacts.
Here’s how an electromagnetic relay typically operates:
- Coil: The relay coil is an insulated wire wound around a core. When a voltage is applied across the coil, a current flows through it, generating a magnetic field.
- Armature: The armature is a movable component within the relay. It usually consists of a ferromagnetic material, such as iron, and is attracted to the magnetic field generated by the coil.
- Contacts: The relay contacts are metal plates or strips that make or break the electrical connection when the relay is activated. There are typically two sets of contacts—normally open (NO) and normally closed (NC)—which change their state depending on the position of the armature.
- Normally Open (NO) Contacts: In the resting state, when the relay coil is not energized, the NO contacts are open, interrupting the circuit.
- Normally Closed (NC) Contacts: In the resting state, when the relay coil is not energized, the NC contacts are closed, providing a continuous electrical connection in the circuit.
- Switching Action: When the current flows through the coil, the magnetic field attracts the armature towards it. This movement of the armature causes the contacts to change state.
- Energized State: When the coil is energized, the armature is attracted, and the NO contacts close, establishing an electrical connection. Simultaneously, the NC contacts open, interrupting the circuit.
- De-energized State: When the coil is de-energized, the magnetic field dissipates, and the armature returns to its resting position under spring tension. The NO contacts open, breaking the electrical connection, while the NC contacts close, providing a continuous connection.
Electromagnetic relays are widely used in various applications, including industrial control systems, power distribution, automotive systems, telecommunications, and more. They provide galvanic isolation between the control circuit and the switched circuit, allowing control of high voltages or currents using low-voltage control signals. Their reliability, versatility, and ability to handle both AC and DC currents make them popular in many electrical and electronic systems.