Electromagnetic Devices

ECE 201 Circuit Theory I 1

Electromagnetic Devices


Solenoid

• Has a movable iron core called a plunger



Unenergized state

• Plunger is extended


Plunger is extended by the force of the spring


Energized State

• Plunger is retracted


Both iron cores become magnetized, and the South pole of the stationary core attracts the North pole of the movable core, causing it to slide inward, retracting the plunger and compressing the spring.

This happens as long as there is sufficient current. When the current is turned off, the magnetic fields collapse and the force of the spring pushes the plunger out.


Uses of Solenoids

• Provide movement– Door locks– Valves


Relays

• Used to open or close contacts (switches)• Mechanical Relay



Terminal Identifications1 – Common (COM) 2 – Normally Closed (NC) 3 – Normally Open (NO)

4 and 5 – Coil

This is a single – pole double – throw relay


Unenergized State

• Normally Closed

Continuity between terminals 1 and 2

Armature is held against the upper contact by the force of the spring


Energized State

• Normally Closed contact is opened, Normally Open contact is closed.



Energized State

Continuity between terminals 1 and 3

Armature is pulled down by the electromagnetic field


Typical Construction and Circuit Symbol


Loudspeaker

• Interaction between the fields of a coil and a permanent magnet


South pole of permanent magnet is positioned within the coil


Magnetic field produced by the current interacts with the permanent magnet field, causing the coil to move right


When the current in the coil reverses, its field is in the opposite direction, causing the coil to move left.


For a time – Varying Signal


Coil motion in both directions

Time – Varying signal (voltage or current)

Documents

Electromagnetic Devices