a10 Sensor EXamples for Structural Dynamics Example: fixed-fixed Goal: Explain what they measure and how they work beam with center load laser sensors excitation accelerometers gyroscopes strain gages m load cells inductive sensors shaker EI ground First flexible mode frequency: 0=14 F(m+0.375m) 16.810(16682) assachusetts Institute of Technology
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GG.aln Strain Gages Strain △ Strain gages measure strain differential displacement over a finite area via a change in electrical resistance R=lp[Q2 Current Nominal length io: I( With applied strain: I (+△)p implementation Wheatstone bridge iaY ni balance circuit bond to test article strain gages feature polyimide-encapsulated GND constantan grids with V+ copper-coated solder tabs Mfg Ref:http://www.measurementsgroup.com 16.810(16682) assachusetts Institute of Technology Ui
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IG aln Accelerometers Accelerometers measure linear acceleration in one, two or three ￥()→s2X(s-3 axes. We distinguish (generally neglect initial conditions) single Vs. multi axis accelerometers mag +40db/dec DC versus non-DC accelerometers rolloff Recorded voltage response to base motion 1(t)=K(t)+V out Can measure: linear, centrifugal and gravitational acceleration Use caution when double-integrating acceleration to get position(drift) Single-Axis C1 Accelerometer must be aligned with sensing axis C2 Example: Kistler Piezobeam (not responsive at Dc Example: Summit capacitive Manufacturers: Kistler. Vibrometer Summit accelerometer Dc capable) 16.810(16682) Massachusetts Institute of Technology
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in Laser Displacement sensors sensor Records displacement directly x()→>X(s) via slant range measurement TVDC cal Settings 1: 2um-60 ms II: 15um-2ms target l:50m0.15ms0 Resolution tradeoff patlal vs temporal Distance x is recorded via triangulation . 7 between the laser diode(emitter), the target and the receiver range. (position sensitive device -PSD) Advantages Vibrometers include advanced processing contact-free measurement and scanning capabilities Disadvantages Manufacturers: Keyence, MTI Instruments need reflective, flat target limited resolution 1 g 16.810(16682) Massachusetts Institute of Technology Ui
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IGA10 Force Transducers/ Load cells Force Transducers/Load Cells are capable of measuring Up to 6 dOF of force on three orthogonal axes, and the moment (torque)about each axis, to completely define the loading at the sensor's location The high stiffness also results in a high resonant frequency allowing accurate sensor response to rapid force changes Load cells are electro-mechanical transducers that translate force or weight into voltage Mz My They usually contain strain gages internally F Manufacturers: JR3, Transducer techniques Inc 16.810(16682) Massachusetts Institute of Technology 10
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