Transcript 01_300

Residential Security, Access Control,
and Surveillance
Presentation 1 –
Magnetism and Work
Copyright © 2005 Heathkit Company, Inc. All Rights Reserved
Objectives
At the end of this presentation,
you will be able to:
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
Describe how a magnetic field forms around a
permanent magnet.

Describe the effect of a magnetic field on a reed
switch.

Explain why it doesn’t take the same amount of
magnetic force to hold a reed switch closed as it
does to close the switch.

Describe how a relay works.

Describe how a solenoid works.
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Magnetic Fields
 All
atoms are surrounded by lines of
force called electrical fields.
 In
a similar manner, all magnets are
surrounded by a magnetic field.

The Magnetic Field which surrounds a
magnet is made up of magnetic lines of
force.
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
Magnets have a North and South pole.

Magnetic Lines of Force surround the entire
magnet and are called Flux lines.
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 There
are a number of basic rules and
characteristics that govern flux lines:
 Flux
lines have direction (polarity).
 Flux
lines always form a complete loop.
 Flux
lines cannot cross one another.
 Flux
lines tend to form the smallest possible
loops.
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
Like poles repel because the flux lines repel.

Unlike poles attract because the flux lines
link and shorten.
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
There are several characteristics that apply
to magnets:

Flux refers to the complete magnetic field that
surrounds the magnet.

Flux density refers to the number of flux lines per a unit
of area.

Induction is the creation of a magnetic field in other
materials by passing them through a magnetic flux.

Permeability refers to the way a material accepts
magnetic flux.

Reluctance is an opposition to flux within a material.
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
Magnetic Induction occurs when a magnet causes a
magnetic field to form in another object, like this
piece of iron.

This can also occur if an object with a high
permeability remains in close proximity to the
magnet.
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Reed Switch
A reed switch is a good example of
a mechanism that uses magnetic
induction to perform a task.
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Electricity and Magnetism

You don’t need a magnet to have a magnetic field.

Electrical current can create a magnetic field.

Motion is the link between electricity and
magnetism.





Moving charged particles create a magnetic field.
A large number of moving particles creates a larger field.
Current flow is the movement of negatively charged electrons.
Increasing current flow increases the magnetic field.
Single-conductor magnetic field has no practical value.
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 Coiling
a conductor improves the
magnetic characteristics because this:
 Brings
the flux lines into closer proximity
 Concentrates
the flux lines into the center of the
coil
 Creates
a North and South pole.
 Therefore,
a coiled conductor exhibits
the properties of a magnet.
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(Current)
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Relay
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Relay Uses

Relays allow you to control an electrical circuit from a
distance.

Relays allow you to control a circuit carrying a large
current with a small current.

Relays allow you to control one power source with a
second power source that is completely isolated from
the first power source.

Relays with multiple contacts allow you to control
several different current paths with a single current.
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Solenoid
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Solenoid Construction
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Solenoid Magnetic Fields
Strong Field
Weak Field
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Creating a Third Field
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Fully Active Solenoid
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Solenoid Uses

Solenoids allow you to control mechanical
devices.

Open and close valves to regulate fluid control in a mixing
process.

Latch and unlatch a door locking mechanism.

Automate device selection in a storage system.

Open and close high-current contacts such as those used to
run an automobile starter motor, while at the same time,
engaging the starter drive gear with the flywheel ring gear.
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Residential Security, Access Control,
and Surveillance
End
Copyright © 2005 Heathkit Company, Inc. All Rights Reserved