Date:
09/12/2013 (Monday)
Title:
Research and Findings (Solenoid)
The Function of Solenoid
A locking solenoid is a conventional solenoid, a wire
coil that is magnetized when paired with an electrical current, that is made
to lock a door or device. The locking solenoid is small enough to fit into a
lock, where it keeps the locking mechanism from moving unless an
electromagnetic force is used to gain access. When the door is locked, no power
is used, so the solenoid has a long duty cycle and tends to run off batteries.
While most lock solenoids are very small, there are some large ones made for
heavy-duty equipment and safety devices. The most common places a locking
solenoid is used are in doors, vending machines and turnstiles.
When a door or device locks via a locking solenoid, it
is using basic electromagnetic forces to control the lock. The solenoid fits in
the locking mechanism and, when locked, will expand so the device cannot unlock
by sheer force. An electromagnetic force is needed to tell the solenoid to
move, thus allowing the device to unlock and open.
While the locking solenoid will keep the device
locked, it is not technically on when in locking mode, because no power is
being used. The solenoid only needs power when unlocking and, because most
devices are consistently locked, very little energy is ever required by the
solenoid. For this reason, most solenoids run on battery power, and the battery
rarely needs to be changed.
The majority of locking solenoids are made to be
small, because they fit in small devices, but there are some that are large and
exhibit powerful electromagnetic forces. Heavy-duty solenoids are used in
construction equipment such as forklifts to lock the mast when the machine is
off or not operating. Unlike smaller solenoids that exhibit the force of about
45 Newtons, these larger solenoids use about 1,000 Newtons to lock the
equipment in place.
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| Solenoid |
Current Applications
The most common devices that use a locking solenoid
are usually small, around the size of a human adult or less, and do not need
much locking force. Hotels, offices and other secure areas use these solenoids
to lock doors, because picking a solenoid lock is very difficult. Instead of
the easily broken padlocks long used on vending machines, solenoid locks are
modern alternatives. Turnstiles at parks, subways and entertainment events use
solenoids to stop people unless they are authorized to pass through.
How Do Push &
Pull Action Solenoids Work?
Solenoids are made up
of a coil of wire and a plunger or actuator. The coil of wire is wound many
times around a plastic spool. The copper wire is lightly coated with a varnish
to electrically insulate the wire from conducting power to each strand, since
the wires are lay next to each other and touching. This allows the coil of wire
to have a long length for creating a magnetic field.
The generation of the magnetic field is
dependent upon the way the coil is wound. The magnetic field can either be a
push or pull type of field. Since the coil is wound around the plastic spool,
the plunger or actuator fits inside of the spool. Attached to the plunger is a
mechanical lever that can increase the movement of the "in" or
"out" action of the electric solenoid.
As other linear
solenoids push/pull solenoids are on/off type actuators and develop force in
one direction when energised. The return force must be provided externally,
e.g. by a return spring.
"Push-Pull"
solenoids are the most robust series of linear solenoids and are therefore the
best option for heavy duty applications. They offer a very high holding force
at a comparably low power input. This makes them ideally suited for
applications asking for low power consumption or low heat dissipation.
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| Operation of Solenoid |
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