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Strain-Based Measurement Introduction:sure will increase by the ratio of P 1 /T 1 = P 2 /T 2 , assuming that the internalvolume is fixed, the gas density remains largely unchanged. Therelatively small changes in gas density with temperature change contributeto the small changes observed in damping factor with respect totemperature. The damping factor is predetermined to a large extent bythe dimensions of the gap between the seismic assembly and the outerhousing and is, therefore, a strong function of the fabrication tolerancesand is not easily modified as in the case of the fluid-damped devices.FIGURE 1-34. Gas Damping (Micro-machined Silicon):Piezo resistors (8)Bonding PadsSilicon Cap / Acceleration StopSilicon Seismic MassSilicon Base /Acceleration StopMallory BondsTop view of Seismic Element:Gaseous DampingPiezo ResistorsSeismic MassTabsCHAPTER 1-64 The Art of Practical and Precise Strain Based Measurement 2nd Edition © 1999
Applications Note 1-10:Structural or Solid Damping:It has been established that cyclically-stressed materials dissipate energywithin the material itself. This is the reason that the response of a cantileverbeam accelerometer or piezoelectric accelerometer is not infinite at the resonancefrequency due to the internal damping of the beam material itself.It has also been found that most structural materials such as steel and aluminumwill dissipate energy per stress cycle that is predominantly independentof frequency and is proportional to the square of the amplitude ofvibration. With the energy dissipated per cycle proportional to the square ofthe vibration amplitude, the loss coefficient is constant and the shape of thehysteresis curve remains independent of amplitude and strain rate. In concertwith the intrinsic structural damping afforded by the materials thatcomprise the sensor structure, external or extrinsic materials can be used tofurther aid in the structural damping of the sensor.FIGURE 1-35. Structural-Damping Model:AccelerationAccelerometerFoundationDamping MaterialKRFoundationSolid materials used for structural damping are generally mounted underthe accelerometer structure as shown in Figure 1-35 and therefore presentan additional spring and damper suspension which must be considered inthe determination of the total transfer function of the accelerometer. Soliddamping is not generally useful at low frequencies but can be of use in theexplosives and ordinance testing fields to mitigate the high-frequency componentsthat are induced in explosively-driven structures such as armorplating. It should be realized that structural damping is a form of frequencyThe Art of Practical and Precise Strain Based Measurement 2nd Edition © 1999 CHAPTER 1-65
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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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