Displacement sensor LVDT sensor

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Displacement sensorLVDT sensor
LVDT stands for Linear Variable Differential
Transformer

• For operation, the LVDT's primary winding is
  energized by alternating current of appropriate
• amplitude and frequency, known as the primary
  excitation.
• The LVDT's electrical output signal is the
  differential AC voltage between the two secondary
  windings, which varies with the axial position of
  the core within the LVDT coil.
• Usually this AC output voltage is converted by
  suitable electronic circuitry to high level DC
  voltage or current that is more convenient to use.

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Displacement sensorLVDT sensor

• Advantages
• Friction-Free Operation
• One of the most important features of an LVDT is
  its friction-free operation. In normal use, there
  is no mechanical contact between the LVDT's core
  and coil assembly, so there is no rubbing,
  dragging or other source of friction. This
  feature is particularly useful in materials
  testing, vibration displacement measurements, and
  high resolution dimensional gaging systems.
• Infinite Resolution
• Since an LVDT operates on electromagnetic
  coupling principles in a friction-free structure,
  it can measure infinitesimally small changes in
  core position. This infinite resolution
  capability is limited only by the noise in an
  LVDT signal conditioner and the output display's
  resolution.
• Unlimited Mechanical Life
• Because there is normally no contact between the
  LVDT's core and coil structure, no parts can rub
  together or wear out. This means that an LVDT
  features unlimited mechanical life. This factor
  is especially important in high reliability
  applications such as aircraft, satellites and
  space vehicles, and nuclear installations.
• Low output impedance and noise/interference

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Hall Effect sensor Basics Lorentz force and
Hall effect
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Hall Effect sensor Chip and Spec
ANALOG DEVICES - AD22151YRZ - IC, HALL EFFECT
SENSOR, LINEAR, 8-SOIC
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Hall Effect sensor Analog and Digital o/p
Analog Output circuit
Digital Output circuit
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The Schmitt trigger waveforms
A small positive vi would make the o/p voltage
positive (saturated to supply voltage usually),
or a small negative voltage would saturate the
o/p voltage to negative supply voltage.
Suppose Vo 5 V. Then as long as we have Vin gt
-5 V, we have the vi gt 0, and the o/p voltage
remains at 5 V. However, if Vin lt -5 V, then vi
lt 0, and the o/p will switch to -5V. Then vo will
remain at -5 V, unless vin exceeds 5 V.
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Hall Effect sensor Applications II

• To sense displacement or rotation, Hall Effect
  sensors will have to use a magnet mounted to a
  moving part
• The magnet can be brought closer or further, or
  interrupted to produce a square wave signal
• In some applications, 4 Hall Sensors are arranged
  in a quad cell (like a wheatstone bridge) to
  sense rotary signal

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Optical sensors Fiber Optic sensors
Vibration and displacement sensor

• Fiber optic sensors are great because they sense
  by non-contact means, which at the very basic
  level is simply based on the changes in light
  intensity
• A common application is to couple light from one
  fiber to another by means of a movable mirror,
  which based on changes such as pressure, would
  couple different intensity of light to the
  receiving fiber.
• Another applications is in sensing the level of
  liquid as shown in the adjacent figure. When the
  liquid is in touch with the bent section of the
  tube, more light scatter into water, and less
  light is detected at the other end.

Liquid level sensor
Vibration and displacement sensor utilizing FO
cable with microbends
FO strain sensors
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Linear Optical sensors I

• Used for precision position sensing over the
  short and long range
• An IR LED is typically used to send out the
  signal, which is then sensed from a object using
  a position sensitive detector
• The detector consists of p and n doped Si layers
  positioned on opposite side of the bar. Wherever
  the light beam falls, it creates a low resistance
  path connecting the top and the bottom layers
• The movement of the object can be calculated from
  the movement of the spot on the detector

Mathematical Analysis
If the beam hits at a distance x from the
electrode A, and the corresponding resistance is
Rx, then the overall photoelectric current I0
will be split into IA and IB as
RD is the resistance between the terminals A and B
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Linear Optical sensors II
Assuming linear variation of resistance with
distance, IA and IB can be written as
Then the ratio of the current P is given as
or
Applying similar triangle principles from Fig.
7.38 we have
Thus we have