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.

Types of EnergyMechanical 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.

A good sensor obeys the following rules:Is sensitive to the measured propertyIs insensitive to any other property likely to be

encountered in its applicationDoes not influence the measured propertyIdeal sensors are designed to be linear or linear to some

simple mathematical function of the measurement.

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

Energy SensorsAn 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.

Need for SensorsSensors are pervasive. They are embedded

in our bodies, automobiles, airplanes, cellular telephones, radios, chemical plants, industrial plants and countless other applications.

Commonly Measured QuantitiesStimulus 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,

Pressure, Torque

Choosing a Sensor

Mechanical Energy SensorsMechanical 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.

Acceleration SensingAcceleration Sensing

Capacitive accelerometerGood performance over low frequency range, can

measure gravity!Heavier (~ 100 g) and bigger size than piezoelectric

accelerometerMeasurement range up to +/- 200 gMore expensive than piezoelectric accelerometerSensitivity typically from 10 – 1000 mV/gFrequency bandwidth typically from 0 to 800 HzOperating temperature: -65 – 120 C

Acceleration SensingAcceleration SensingPiezoelectric 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 gLess expensive than capacitive accelerometerSensitivity typically from 5 – 100 mv/gBroad frequency bandwidth (typically 0.2 – 5 kHz)Operating temperature: -70 – 150 C

Force SensingForce Sensing

Metal foil strain-gage based (load cell)Good in low frequency responseHigh load ratingResolution lower than piezoelectricity-basedRugged, typically big size, heavy weight

Force SensingForce Sensing

Piezoelectricity based (force sensor)lower cutoff frequency at 0.01 Hz

can NOT be used for static load measurementGood in high frequencyHigh resolutionLimited operating temperature (can not be used

for high temperature applications)Compact size, light

Displacement SensingDisplacement Sensing

LVDT (Linear Variable Differential Transformer): Inductance-based electromechanical

sensor“Infinite” resolution

limited by external electronicsLimited 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 lifetimeAccuracy limited mostly by linearity

0.1%-1% typicalModels with strokes from mm’s to 1

m available

Velocity SensingVelocity 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)

Heat Energy SensorHeat 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.

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

p n

I

+ V -

Photoresistors• Light sensitive variable resistors. • Its resistance depends on the intensity of light incident upon it.

– Under dark condition, resistance is quite high (M: called dark resistance).– Under bright condition, resistance is lowered (few hundred ).

• 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.

Symbol

10 10log logR P

R

101 103102

101

104

102

103

104

Relative illumination (P)

                                                                                               

                     

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Hybrid Engine TestingMaterials and Component TestingHydraulic Systems TestingTesting and Fabrication of Thin Film Solar CellsPollutant Remediation SystemsDirect Energy Conversion ProcessesOTEC (Ocean Thermal Energy Conversion)Plants—(Pressure and Force Measurement for Pumps and Mooring Systems)Fuel AnalyzersHandling Systems for Nuclear Fuel Rods

Applications Fuel Cell Research and Development

Fuel Cell Production

Hydro-Current Framing Fluid Control Systems

Large-scale Hydrogen Production

Wind Turbine Transmission Monitoring

Wind Turbine Lubrication Systems

Geothermal Pumping Systems

Proof-Of-Concept Testing and Validation

Hybrid Battery Testing

SWAC (Salt Water Air Conditioning) 

Pumping Systems

• 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