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Applications Note 1-1: IntroductionEvery effort has been made in this work to avoid math-intensive models of sensorperformance. When possible, simpler and more understandable mathematicalmodels have been used rather than the more rigorous models in the interest of clarity.The focus of this work is the thermomechanical behavior of the generalizedsensor. The material discussed in the following pages is an ÒApplications CompendiumÓdetailing many of the very simple phenomena that have frustrated many anengineer. To an instrument engineer, the embarrassment of not having consideredthis or that phenomenon in a particular measurement environment, is a familiarfeeling. We are spared this embarrassment when the ÒtruthÓ remains unknown.Indeed, in the mind of the purist measurement statistician, the ÒtruthÓ remains foreverunknowable as even national reference standards possess finite uncertaintylimitations.Much of the information contained in this work will appear to be of the simple ÒIknew thatÓ kind. It is written to be so. After having been frustrated by poor dataquality in the past, how many times have you slapped your forehead and exclaimedÒI should have known better!Ó? The parameter that very likely was the source offrustration, was either not properly specified, absent altogether, or specified in anambiguous way. In many cases, the manufacturers themselves truly have no ideahow their devices will or wonÕt function in specialized environments or in uniquecombinations of environments. In the end, as engineers, it is our responsibility todefine to the sensor manufacturer, our assessment of the measurement environment,and to work with the manufacturer to achieve mutual success.Much of the information contained in these pages has not previously been in printor has been buried within written works intended more to impress colleagues thanto instruct others. The material contained herein is common-sense physics. Youwill also note that some repetition of material exists within these pages. This repetitionis necessary to link associated concepts together and to provide a writtenwork that, in the end, can be used as a quick, stand alone reference manual.The two primary strain gage types discussed are the piezoresistive and metallicfoil-basedstrain gage. The very high intrinsic strain sensitivity of the piezoresistivedevice makes visible phenomena that are typically low-level error sources forthe metallic-foil-gaged sensor but are, none-the-less, sources of error that mayThe Art of Practical and Precise Strain Based Measurement 2nd Edition © 1999 CHAPTER 1-3