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Strain-Based Measurement Introduction:filtering. It is often used for this purpose although great care must betaken in assessing the effects that the structural-damping materials mayhave on the frequency- and phase-response of the sensor.Applications Note 1-11:The Strain-Gaged Cantilevered BeamThe cantilevered beam is a fundamentally-simple mechanical structure asshown in Figures 1-36 and 1-37. Figure1-36 shows the metal-beam accelerometerstructure and Figure 1-37 shows the all-silicon design configuration.FIGURE 1-36. Cantilevered-Beam Accelerometer (Steel-Spring Member):Strain GagesAccelerationClampBeamMassThe Cantilever-Beam Accelerometer (Steel Beam)Center of Seismic MassCurvilinear Motion of Seismic MassDamping FluidIn the case of the silicon design, location of the strain gages as far as possiblefrom the bending axis of the beam results in significant strain multiplicationCHAPTER 1-66 The Art of Practical and Precise Strain Based Measurement 2nd Edition © 1999
Applications Note 1-11:and correspondingly high output sensitivities at low beam deflections. The highoutput,all-silicon designs are not typically damped as the low beam deflections donot appreciably displace a damping medium. The cantilevered beam, in general, isa high-strain low-force structure where the strain developed at the surface of thebeam is inversely proportional to the square of the beam thickness and is directlyproportional to the beam length. The strain developed in the beam surface is alsoinversely proportional to the beam width and the beam stiffness (YoungÕs Modulus).Most of the beam length serves only to generate moment loads at the straingage locations while significantly adding mass and contributing to beam deflection.The highest moments exist at the clamp, but continuously and linearly varyalong the entire length of the constant cross-section simple beam. Modified beamsections can be used to linearize the strain field at the strain gage locations butsuch modifications will contribute significantly to the cost of machining.FIGURE 1-37. Cantilevered-Beam Accelerometer (All-Silicon Discrete Gages):Strain GagesDisplacement from NeutralAxis Multiplies Strain at theStrain Gage Locations.ClampSeismicMass (Silicon)Acceleration-induced deflectionExtremely-high natural frequencydue to short effective beam lengthsand small deflections due to strainmulitiplication.This style of accelerometer is notnormally damped due to theextremely-small mass deflections.The cantilevered beam allows strain-sensitive elements to be bonded to both surfacesof the beam where the strain elements will be exposed to equal and oppositeThe Art of Practical and Precise Strain Based Measurement 2nd Edition © 1999 CHAPTER 1-67
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The Art of Practical andPrecise Str
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Special Credits:Mrs. Helen Pierson,
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Table of ContentsBy James G. Pierso
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ContentsApplications Note 4-10:Lead
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ContentsCHAPTER 8Electrical Conside
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CHAPTER 1Strain-BasedMeasurementInt
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Applications Note 1-1: Introduction
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Applications Note 1-1: Introduction
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Applications Note 1-2:The Art of Ap
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Applications Note 1-31. The presenc
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Applications Note 1-3result in a pe
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Applications Note 1-4:The measureme
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