Transcript Micrometers Vernier caliper

Motion Sensors
Displacement, velocity and acceleration
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Dimensional measurement
Micrometers
Vernier caliper
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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
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Height & depth measurement
Gauge blocks
Dial gauge: typical resolution 0.01 mm
Height & depth gauges
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Resistive potentiometer
Linear potentiometer
Rotary potentiometer (a) circular; (b) helical
Types: wire-wound, carbon-film and plastic-film (according to resistance element)
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Linear Variable Differential Transformer (LVDT)
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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
Primary
Secondary
Rotary differential transformer
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Eddy current sensor
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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
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Mechanical flyball
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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