Electromagnetic Devices

ECE 201 Circuit Theory I 1

Electromagnetic Devices

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Solenoid

• Has a movable iron core called a plunger

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Unenergized state

• Plunger is extended

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Plunger is extended by the force of the spring

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Energized State

• Plunger is retracted

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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.

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Uses of Solenoids

• Provide movement– Door locks– Valves

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Relays

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

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

4 and 5 – Coil

This is a single – pole double – throw relay

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Unenergized State

• Normally Closed

Continuity between terminals 1 and 2

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

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Energized State

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

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Energized State

Continuity between terminals 1 and 3

Armature is pulled down by the electromagnetic field

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Typical Construction and Circuit Symbol

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Loudspeaker

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

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South pole of permanent magnet is positioned within the coil

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

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

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For a time – Varying Signal

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Coil motion in both directions

Time – Varying signal (voltage or current)