USU ECE 5320 - Electrical Resistance Strain Gauges

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ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: Electrical Resistance Strain GaugesOutlineReference listTo Explore FurtherMajor ApplicationsWhy Use Strain Gauges?Stress and Strain TheorySlide 8Slide 9Metallic Strain GaugesSlide 11Slide 12Slide 13Slide 14Gauge FactorSlide 16Grid PatternsSlide 18Strain Gauge MeasurementsSlide 20Slide 21Apparent StrainsSlide 23Slide 24Sources and PricesECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Assignment#01: Literature Survey on Sensors and Actuators Topic: Electrical Resistance Strain GaugesPrepared by:Antoine RousseauDept. of Electrical and Computer Engineering Utah State UniversityE: [email protected]; T: (435)797-2840; F: (435)797-3054W: http://www.engineering.usu.edu/eceMarch 11, 200501/13/19 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-2Outline •Reference List•To Explore Further•Major Applications•Why Use Strain Gauges?•Stress and Strain Theory•Metallic Strain Gauges•Gauge Factor•Grid Patterns•Strain Gauge Measurements•Apparent Strains•Sources and Prices“www.vishay.com”01/13/19 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-3Reference list•John G. Webster, “The Measurement, Instrumentation, and Sensors Handbook”•Richard S. Figliola, Donald E. Beasley, “Theory and Design of Mechanical Measurements”•Robert H. Bishop, “The Mechatronics Handbook”•Warren C. Young, Richard G. Budynas, “Roark’s Formulas for Stress and Strain”01/13/19 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-4To Explore Further •Strain gauge manufacturers:–Vishay–Omega–SMD Sensors–HBM•Strain gauge tutorials:–Measuring Strain With Strain Gauges–The Strain Gauge–Strain Gauges01/13/19 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-5Major Applications •Used to measure the deflection or strain of mechanical components for stress analysis–Static or dynamic analysis possible•Can be used as a component in other sensors–Load cells for measuring large forces–Transducers for measuring pressure, force, or torque01/13/19 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-6Why Use Strain Gauges?•Design of critical load-bearing members–information is needed about distribution of forces, stresses, and strains within the member•Theoretical analysis is usually not sufficient –experimental measurements of physical displacements are required to validate theoretical models and to achieve final design•Strain gauges are used to measure the deformation of a member under load–stresses can then be calculated from the measured deformation01/13/19 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-7Stress and Strain TheoryELinear-elastic region•Stress is defined as a force per area:•Strain is defined as the ratio of the change in length to the original length:AFLL•The relationship between uniaxial stress and strain in the linear-elastic region of the stress-strain curve is given by Hooke’s Law:where E is the modulus of elasticity of the material.E“Theory and Design for Mechanical Measurements”01/13/19 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-8Stress and Strain Theory•In a two-dimensional stress field, a ratio exists between axial strain and lateral strain.•This ratio is calledPoison’s ratio andis defined as:“The Measurement, Instrumentation, and Sensor Handbook”lateral strainaxial strainLa01/13/19 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-9Stress and Strain Theory•For a two-dimensional member loaded in both the x and y directions, a biaxial state of stress exists. The strains and stresses are given as follows:“Theory and Design for Mechanical Measurements”yyExExxEyExExy 1 2yEy x 1201/13/19 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-10Metallic Strain Gauges•Ideal sensor for the measurement of strains would–have good spatial resolution, stress would be measured at a point–be unaffected by changes in ambient conditions–have a high-frequency response for dynamic strain measurements•Bonded resistance strain gauge closely meets these characteristics–resistance of strain gauge changes when it is deformed–change in resistance is easily related to the local strain•History–1856—Lord Kelvin lays the foundation for understanding the changes in the electrical resistance of metals subjected to loads–Late 1930s—Edward Simmons and Arthur Ruge develop bonded metallic wire strain gauges01/13/19 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-11Metallic Strain Gauges•Construction and terminology of typical bonded metallic wire strain gauge:“Theory and Design for Mechanical Measurements”01/13/19 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-12Metallic Strain Gauges•For a metallic conductor of uniform cross-sectional area A, resistivity ρe, and length L, the resistance is given by:•Change in resistance of strain gauges is caused by two effects:–change in value of resistivity, ρe, under strain•dependence of resistivity on mechanical strain is called piezoresistance–change in geometry as length and area change under strain•normal stress along the axis of the conductor will cause a reduction in cross-sectional area and an increase in length, producing a corresponding increase in resistanceALRe01/13/19 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-13Metallic Strain Gauges•A typical strain gauge uses Constantan (45% nickel, 55% copper) which has a resistivity of 49x10-8 Wm“The Measurement, Instrumentation, and Sensor Handbook”01/13/19 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-14Metallic Strain Gauges•Change in resistance can be expressed in terms of Poisson’s ratioeedLdLRdR )21(eedfractional change in resistanceLdLfractional change in lengthRdRfractional change in resistancePoisson’s ratiowhere:01/13/19 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-15Gauge Factor•The change in resistance of a strain gauge is usually


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USU ECE 5320 - Electrical Resistance Strain Gauges

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