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Motion SensorsDisplacement, velocity and acceleration

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Dimensional measurement

• One complete revolution = 0.5 mm (usually)• With 50 divisions, each division movement

corresponds to 0.01 mm• If user can control every one-fifth of a

division, a resolution of 0.002 mm is possible

MicrometersVernier caliper

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Height & depth measurement

Gauge blocks

Dial gauge: typical resolution 0.01 mm Height & depth gauges

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Types: wire-wound, carbon-film and plastic-film (according to resistance element)

Linear potentiometer Rotary potentiometer (a) circular; (b) helical

Resistive potentiometer

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Primary Secondary

Linear Variable Differential Transformer (LVDT)

• Inductive displacement sensor.• Transformer with 1 primary & 2 secondary coils, connected in series opposition• Output voltage (difference between induced voltages) is proportional to core

displacement• Zero reading when core is centered

Rotary differential transformer

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Eddy current sensor• Inductive displacement sensor.• Coil is excited at high frequency (typically 1 MHz)• This induces eddy current in the target• Eddy current alters the inductance of the probe coil• This change can be translated into a voltage proportional to the air gap

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Piezoelectric transducers

• A piezoelectric material generates charge when deformed• Induced charge leaks away with time• Piezoelectric transducers are not suitable for static or slowly-varying dispalcements

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Optical encoders (incremental)• Measure instantaneous angular position of a shaft• Output is in the form of pulses to be counted

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Optical encoders (coded-disc)

• Output is in the form binary numbers to give absolute measure of shaft position

Float encoder

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Other rotational motion sensors• Gyroscopes• Tachometers • Mechanical flyball

Gyroscope

Photoelectric tachometer

Mechanical flyball

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Vibration Measurement

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Energy Harvesting

Source: J.K. Ward and S. Behrens, “Adaptive learning algorithms for vibration energy harvesting”, Smart Materials & Structures 17 (2008) 035025 1-9.

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Vibration-based Energy Harvesting

Source: B.P. Mann and N.D.Sims, “Energy harvesting from the nonlinear oscillations of magentic levitation”, Journal of Sound and Vibration (2008) in press.

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