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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 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.
A good sensor obeys the followingrules: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 Quantities Stimulus Quantity Acoustic Wave (amplitude, phase, polarization), Spectrum, Wave VelocityBiological & 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,
Mechanical Energy SensorsMechanical quantities: displacement, Strain, rotation velocity, acceleration, pressure, force/torque, twisting, weight, flowHere we will consider sensors for displacement, velocity, acceleration, pressure, force/torque, twisting, weight and flow.
Acceleration SensingCapacitive 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
Acceleration 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 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
Force SensingMetal 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
Force SensingPiezoelectricity 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
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
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)
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
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 104R 103 102 101 101 102 103 104 Symbol Relative illumination (P)
• 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
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