Page 334 - The Mechatronics Handbook

TABLE 16.1 Type of Sensors for Various Measurement Objectives
Sensor Features
Linear/Rotational sensors
Linear/Rotational variable differential High resolution with wide range capability
transducer (LVDT/RVDT) Very stable in static and quasi-static applications
Optical encoder Simple, reliable, and low-cost solution
Good for both absolute and incremental measurements
Electrical tachometer Resolution depends on type such as generator or magnetic pickups
Hall effect sensor High accuracy over a small to medium range
Capacitive transducer Very high resolution with high sensitivity
Low power requirements
Good for high frequency dynamic measurements
Strain gauge elements Very high accuracy in small ranges
Provides high resolution at low noise levels
Interferometer Laser systems provide extremely high resolution in large ranges
Very reliable and expensive
Magnetic pickup Output is sinusoidal
Gyroscope
Inductosyn Very high resolution over small ranges

Acceleration sensors
Seismic accelerometer Good for measuring frequencies up to 40% of its natural frequency
Piezoelectric accelerometer High sensitivity, compact, and rugged
Very high natural frequency (100 kHz typical)
Force, torque, and pressure sensor
Strain gauge Good for both static and dynamic measurements
Dynamometers/load cells They are also available as micro- and nanosensors
Piezoelectric load cells Good for high precision dynamic force measurements
Tactile sensor Compact, has wide dynamic range, and high
Ultrasonic stress sensor Good for small force measurements

Flow sensors
Pitot tube Widely used as a flow rate sensor to determine speed in aircrafts
Orifice plate Least expensive with limited range
Flow nozzle, venturi tubes Accurate on wide range of flow
More complex and expensive
Rotameter Good for upstream flow measurements
Used in conjunction with variable inductance sensor
Ultrasonic type Good for very high flow rates
Can be used for both upstream and downstream flow measurements
Turbine flow meter Not suited for fluids containing abrasive particles
Relationship between flow rate and angular velocity is linear
Electromagnetic flow meter Least intrusive as it is noncontact type
Can be used with fluids that are corrosive, contaminated, etc.
The fluid has to be electrically conductive

Temperature sensors
Thermocouples This is the cheapest and the most versatile sensor
Applicable over wide temperature ranges (-200∞C to 1200∞C typical)
Thermistors Very high sensitivity in medium ranges (up to 100∞C typical)
Compact but nonlinear in nature
Thermodiodes, thermo transistors Ideally suited for chip temperature measurements
Minimized self heating
RTD—resistance temperature detector More stable over a long period of time compared to thermocouple
Linear over a wide range
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