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page_28_missing_page_ - R m = internal resistance of...

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b) Loading Errors and Impedance Matching If a measurement system affects the variable being measured or if a sensor changes the physical variable being measured, a loading error (i.e., difference between actual and measured values) results. Good measurement design attempts to minimize these errors. Null balance techniques minimize these errors, while deflection methods require careful consideration to minimize these errors. Consider loading errors for the voltage dividing circuit below (
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Unformatted text preview: R m = internal resistance of measuring volt meter (input impedance), E = measured voltage). Now, the current from the voltage source is = = + + I EiRequiv EiR2 R1RmR1 Rm . As = -E0 Ei IR2 , = + + E0Ei 11 R2R11 R1Rm . For R m = , = + E0Ei R1R1 R2 . The difference between these two values is the loading error due to a finite R m . For R m = , the loading error is 0. Consider an example with a Wheatstone bridge, whose 4 arms correspond to strain gauges. 28...
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This note was uploaded on 05/04/2010 for the course CEE 291 taught by Professor Hoopes during the Spring '10 term at Wisconsin.

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