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Strain-Based Measurement Introduction:the stops effectively forms a damping gap or squeeze film that alsocontributes to the damping factor that results as shown in Figure 1-29.FIGURE 1-29. Fluidic Damping:BeamStrain Gages MassAccelerationFoundationFilm Damping ContributionBulk DampingCurvilinear Motion of Seismic MassDamping FluidThe damping factor ultimately achieved is highly controllable by precisionmixing of the damping fluids, in some cases even while the sensoris being dynamically excited. Usually a known high-viscosity value issolvent-diluted down to the desired damping factor. Due to the highvariation in damping fluid viscosity with changing temperature, theresulting sensor will show a strong damping-factor dependency withrespect to temperature. Typically the second-order response willchange by +5dB/100 degrees F due to this damping factor variation.Another implication of the damping-factor variation with temperatureis that the input and output phase response becomes a strong functionof temperature as well. Both effects are as shown in Figure 1-30.CHAPTER 1-58 The Art of Practical and Precise Strain Based Measurement 2nd Edition © 1999
Applications Note 1-10:FIGURE 1-30. Fluidic Damping, Thermal Effects:Magnitude ofResponse21.5.125DecreasingTemperaturez = 1z = .3z = .5z = .7Increasing Temperature.2 .5 1 2 3w/w 0The Second-Order Magnitude Response(Effect of Temperature on Fluidic Damping)logPhaseAngle0-30-60-90-120DecreasingTemperaturez = 5-150-180IncreasingTemperaturez = .1z = .7z = 2logIn fluid-damped systems, the presence of entrained air bubbles within theaccelerometer would cause large variations in damping factor as the bubblesmigrate around inside the accelerometer. The objective of fluidicdampingprocesses is to eliminate all internal air bubbles. These devicesare normally vacuum-filled by immersing the device to be damped in a volumeof silicone oil, pulling a vacuum over the oil and holding the vacuumuntil all of the air entrained within the device is removed and replaced bythe fill fluid. The vacuum-filling method also serves to effectively degasThe Art of Practical and Precise Strain Based Measurement 2nd Edition © 1999 CHAPTER 1-59
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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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