1. Displacement, velocity and acceleration
Motion Sensors
Displacement, velocity and acceleration

2. Dimensional measurement
Vernier caliper
Micrometers
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 mm is possible

3. Height & depth measurement
Gauge blocks
Dial gauge: typical resolution 0.01 mm
Height & depth gauges

4. Resistive potentiometer
Rotary potentiometer (a) circular; (b) helical
Linear potentiometer
Types: wire-wound, carbon-film and plastic-film (according to resistance element)

5. Rotary differential transformer
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
Primary
Secondary
Rotary differential transformer

6. 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

7. 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

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

9. Optical encoders (coded-disc)
Output is in the form binary numbers to give absolute measure of shaft position
Float encoder

10. Other rotational motion sensors
Gyroscopes
Tachometers
Mechanical flyball
Gyroscope
Photoelectric tachometer
Mechanical flyball

11. Vibration Measurement

16. Energy Harvesting
Source: J.K. Ward and S. Behrens, “Adaptive learning algorithms for vibration energy harvesting”, Smart Materials & Structures 17 (2008)

17. 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.