Download Electromagnetic Devices

Electromagnetic Devices
ECE 201 Circuit Theory I
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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 Identifications
1 – 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
Armature is held
against the upper
contact by the force of
the spring
Continuity between
terminals 1 and 2
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Energized State
• Normally Closed contact is opened, Normally
Open contact is closed.
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Energized State
Armature is pulled
down by the
electromagnetic field
Continuity between
terminals 1 and 3
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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)
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