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Strain-Based Measurement Introduction:the fill fluid. Gases dissolved within the fill fluid can result in cavitationunder certain operating conditions. The implication of having acompletely oil-filled rigidly-confined volume is that the oil, whenheated, will tend to expand, but cannot. The internal pressure will risedramatically with increasing temperature producing large case strain,as shown in Figure 1-31.FIGURE 1-31. Fluidic Damping, Thermal Implications:Housing Distortion created by internal pressure risewith increasing temperature MassAcceleration FoundationSeals:Highly-Stressed atHigh TemperaureDamping FluidThe inclusion of an internal gas-filled expansion-absorbing bladder toaccommodate the fluid volumetric expansion is workable in the largeraccelerometer designs but is difficult to implement with the more miniaturizeddesigns. In completely fluid-filled designs, the pressure mayrise by as much as 2,000 psi per 100 degrees F. As a consequence, thisinternal pressure will act upon the available internal area producingforces that will stress the integrity of the sensor seals and will mechanicallystress the structure of the accelerometer. The loss of dampingfluid cannot be confirmed by visual inspection due to the small volumeof fluid present internally and the high possibility of the fluid beingexternally sourced. To detect the loss of damping fluid, an initial fre-CHAPTER 1-60 The Art of Practical and Precise Strain Based Measurement 2nd Edition © 1999