12.7 PRACTICAL APPLICATION: A CASE STUDY 541- Basic principles of electromechanical energy conversion, including induction, interaction,
alignment, and torque production. - Simplified analysis of electromechanical transducers, such as electromagnets, position and
velocity sensors, relays, solenoids, and loudspeakers, which convert electric signals to
mechanical forces, or mechanical motion to electric signals. - Calculating the emf produced in ac and dc machines.
- Generation of rotating magnetic fields.
- Evaluating forces and torques in magnetic-field systems, from the coupled-circuit viewpoint
and the magnetic-field viewpoint. - Basic aspects of motors and generators.
12.7 PRACTICAL APPLICATION: A CASE STUDY
Sensors or Transducers
In almost all engineering applications there arises a need to measure some physical quantities, such
as positions, displacements, speeds, forces, torques, temperatures, pressures, or flows. Devices
known assensorsortransducersconvert a physical quantity to a more readily manipulated
electrical quantity (such as voltage or current), such that changes in physical quantity usually
produce proportional changes in electrical quantity. The direct output of the sensor may often
need additional manipulation, known assignal conditioning, for the output to be in a useful
form free from noise and intereference. The conditioned sensor signal may then besampledand
converted todigitalform and stored in acomputerfor additional manipulation or display. A
typical computer-basedmeasurement systemusing a sensor is represented in block diagram form
in Figure 12.7.1. Table 12.7.1 lists various sensors and their uses.
TABLE 12.7.1Sensors classified according to variable sensed
Variable Sensed Sensor or TransducerVariations in dimensions due to motion Strain gauge
Resistive potentiometer
Variable reluctance sensor
Moving-coil transducer
Seismic sensor
Temperature Thermocouple
Resistance temperature detector
Radiation detector
Force, torque, and pressure Capacitive sensor
Piezoelectric transducer
Flow Magnetic flow meter
Turbine flow meter
Hot-wire anemometer
Ultrasonic sensor
Light intensity Photoelectric sensor
Humidity Semiconductor transducer
Chemical composition Solid-state gas sensor
Liquid level Differential-pressure transducer