Download Position and Motion Sensors

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Potentiometers are a convenient method
of converting the displacement in a
sensor to an electrical variable.
The wiper or slider arm of a linear
potentiometer can be mechanically
connected to the moving section of a
sensor.
Where rotation is involved, a single or
multiturn (up to 10 turns) rotational type
of potentiometer can be used.
For stability, wire-wound devices should
be used, but in environmentallyunfriendly conditions, lifetime of the
potentiometer may be limited by dirt
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Linear variable differential
transformers (LVDT) are devices
that are used for measuring small
distances and are an alternative
to the potentiometer.
These devices are not as costeffective as potentiometers, but
have the advantage of being
noncontact.
The outputs are electrically
isolated, accurate, and have
better longevity than
potentiometers.
A variety of LVDTs is
available, with linear ranges
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Hall effect sensors detect changes
in magnetic field strength and are
used as a close proximity
protector.
The Hall effect occurs in
semiconductor devices.
Without a magnetic field the
current flows directly through the
semiconductor plate and the Hall
voltage is zero.
Under the influence of a magnet
field , the current path in the
semiconductor plate becomes
curved, giving a Hall voltage
between the sides adjacent to the
input/output current.
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There are numerous applications for
ultrasonic distance sensors in
industrial control. Ultrasonic distance
sensors are used in all industries for
measuring the distance to or size of
material objects.
Ultrasonic distance sensors measure
the distance or presence of target
objects by sending a pulsed
ultrasound wave at the object and
then measuring the time for the
sound echo to return. Knowing the
speed of sound, the sensor can
determine the distance of the object.
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The armature of dc
tachogenerators is kept in
permanent magnetic field.
The armature of the
tachometer is coupled to the
machine whose speed is to
be measured.
When the shaft of the
machine revolves, armature
of the tachometer revolves in
the magnetic field producing
an emf proportional to the
speed.
The polarity of the output
voltage indicates the
direction of rotation
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The opt electric tachometer is
a non contact type
tachometer which also called
digital tachometer.
It uses a principal of retro
refractive scanning, in this
scanning the light source and
photo sensor are placed in
common housing.
Light source sends a light
towards a retro refractive
target from which it gets
reflected.
In photo electric tachometers,
the photor detector detects
the reflected ligh and produce
electrical pulse.