Energy is the ability to do work and can exist in various forms. Sensors are devices that measure a physical quantity and convert it into a signal. Energy sensors specifically respond to an input quantity by generating an output signal, often electrical or optical. Common energy sensors measure mechanical energy through quantities like acceleration, force, displacement; heat/thermal energy through temperature; and light through photoresistors, photodiodes or phototransistors. Energy sensors have applications in areas like fuel cells, wind and solar energy, and nuclear systems.

2. What is Energy?
In Physics, energy is an indirectly observed quantity. It is
often understood as the ability a Physical System has to
do work on other physical systems.
Energy is the capacity of a system to do work.
The total energy contained in an object cannot be created
nor be destroyed in accordance with the law
of conservation of energy.

3. Types of Energy
 Mechanical Energy: is the energy of motion that does the work like the
wind turns a windmill.
 Heat Energy/Thermal Energy: where motion or rise in temperature is
caused by heat like a fire in your fireplace.
 Chemical Energy: is the chemical reaction causing changes; food and fuel
both store chemical energy.
 Seismic Energy: Seismic waves are waves of energy that travel through
the earth, for example as a result of an earthquake, explosion, or some
other process that imparts low-frequency acoustic energy.
 Nuclear Energy: Nuclear potential energy is the potential energy of
the particles inside an atomic nucleus. The nuclear particles are
bound together by the strong nuclear force.
 Solar Energy: Solar energy is the heat and light energy available from the
sun.

4. A good sensor obeys the following
rules:
Is sensitive to the measured property
Is insensitive to any other property likely to be
encountered in its application
Does not influence the measured property
Ideal sensors are designed to be linear or linear to some
simple mathematical function of the measurement.

5. What are Sensors?
A sensor is a device that measures a physical quantity and
converts it into a signal which can be read by an observer
or by an instrument.
 For accuracy, most sensors are calibrated against known
standards.
Left: Thermocouple used as Temperature Sensor

6. Energy Sensors
An Energy Sensor is a device, which responds to an input
quantity by generating a functionally related output
usually in the form of an electrical or optical signal.
The Following Slide shows some energy sensors.

8. Need for Sensors
Sensors are pervasive. They are embedded in our bodies,
automobiles, airplanes, cellular telephones, radios, chemical
plants, industrial plants and countless other applications.

9. Commonly Measured Quantities
Stimulus Quantity
Acoustic Wave (amplitude, phase, polarization),
Spectrum, Wave
Velocity
Biological & Chemical Fluid Concentrations (Gas or Liquid)
Electric Charge, Voltage, Current, Electric Field
(amplitude, phase,
polarization), Conductivity, Permittivity
Magnetic Magnetic Field (amplitude, phase, polarization),
Flux,
Permeability
Optical Refractive Index, Reflectivity, Absorption
Thermal Temperature, Flux, Specific Heat, Thermal
Conductivity
Mechanical Position, Velocity, Acceleration, Force, Strain,
Stress,

10. Choosing a Sensor

11. Mechanical Energy Sensors
Mechanical quantities: displacement, Strain, rotation
velocity, acceleration, pressure, force/torque,
twisting, weight, flow
Here we will consider sensors for displacement,
velocity, acceleration, pressure, force/torque,
twisting, weight and flow.

12. Acceleration Sensing
Capacitive accelerometer
Good performance over low frequency range, can measure
gravity!
Heavier (~ 100 g) and bigger size than piezoelectric
accelerometer
Measurement range up to +/- 200 g
More expensive than piezoelectric accelerometer
Sensitivity typically from 10 – 1000 mV/g
Frequency bandwidth typically from 0 to 800 Hz
Operating temperature: -65 – 120 C

13. Acceleration Sensing
Piezoelectric accelerometer
Nonzero lower cutoff frequency (0.1 – 1 Hz for 5%)
Light, compact size (miniature accelerometer weighing
0.7 g is available)
Measurement range up to +/- 500 g
Less expensive than capacitive accelerometer
Sensitivity typically from 5 – 100 mv/g
Broad frequency bandwidth (typically 0.2 – 5 kHz)
Operating temperature: -70 – 150 C

14. Force Sensing
Metal foil strain-gage based (load cell)
Good in low frequency response
High load rating
Resolution lower than piezoelectricity-based
Rugged, typically big size, heavy weight

15. Force Sensing
Piezoelectricity based (force sensor)
lower cutoff frequency at 0.01 Hz
 can
NOT be used for static load measurement
Good in high frequency
High resolution
Limited operating temperature (can not be used for high
temperature applications)
Compact size, light

16. Displacement Sensing
 LVDT (Linear Variable Differential
Transformer):
 Inductance-based electromechanical sensor
 “Infinite” resolution
 limited by external electronics
 Limited frequency bandwidth (250 Hz
typical for DC-LVDT, 500 Hz for AC-LVDT)
 No contact between the moving core and
coil structure
 no friction, no wear, very long operating
lifetime
 Accuracy limited mostly by linearity
 0.1%-1% typical
 Models with strokes from mm’s to 1 m
available

17. Velocity Sensing
 Scanning Laser Vibrometry
 No physical contact with the test object; facilitate remote, mass-
loading-free vibration measurements on targets
 measuring velocity (translational or angular)
 automated scanning measurements with fast scanning speed
 However, very expensive (> $120K)

18. Heat Energy Sensor
Heat energy (or just heat) is a form of energy which
transfers among particles in a substance (or system) by
means of kinetic energy of those particle. In other words,
under kinetic theory, the heat is transferred by particles
bouncing into each other.
The Sensor used to detect heat energy is known as Heat
Energy Sensor.
The simplest example of a heat energy sensor is a
thermocouple. It provides a voltage proportional to the
temperature across its junctions.

19. Light Sensor
 Light sensors are used in cameras,
infrared detectors, and ambient
lighting applications
 Sensor is composed of
photoconductor such as a
photoresistor, photodiode, or
phototransistor

20. Photoresistors
• Light sensitive variable resistors.
• Its resistance depends on the intensity of light incident upon it.
– Under dark condition, resistance is quite high (MΩ: called dark resistance).
– Under bright condition, resistance is lowered (few hundred Ω).
• Response time:
– When a photoresistor is exposed to light, it takes a few milliseconds, before it
lowers its resistance.
– When a photoresistor experiences removal of light, it may take a few seconds
to return to its dark resistance.
• Photoresisotrs exhibit a nonlinear characteristics for incident optical illumination
versus the resulting resistance. log R = α − β log P
10 10
104
R 103
102
101
101 102 103 104 Symbol
Relative illumination (P)

21. • Hybrid Engine Testing
Materials and Component
• Testing
Hydraulic Systems Testing
• Testing and Fabrication of
Thin Film Solar Cells
• Pollutant Remediation
Systems
• Direct Energy Conversion
Processes
•
OTEC (Ocean Thermal
Energy Conversion)
Plants—(Pressure and
•
Force Measurement for
Pumps and Mooring
Systems)
• Fuel Analyzers
Handling Systems for
• Nuclear Fuel Rods

22. Applications
 Fuel Cell Research and Development • Hybrid Engine Testing
 Fuel Cell Production • Materials and Component Testing
• Hydraulic Systems Testing
 Hydro-Current Framing Fluid Control
Systems • Testing and Fabrication of Thin Film Solar
 Large-scale Hydrogen Production Cells
 Wind Turbine Transmission Monitoring • Pollutant Remediation Systems
• Direct Energy Conversion Processes
 Wind Turbine Lubrication Systems
• OTEC (Ocean Thermal Energy
 Geothermal Pumping Systems Conversion)
 Proof-Of-Concept Testing and Validation • Plants—(Pressure and Force
Measurement for
 Hybrid Battery Testing Pumps and Mooring Systems)
• Fuel Analyzers
 SWAC (Salt Water Air Conditioning)
• Handling Systems for Nuclear Fuel Rods
 Pumping Systems