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Instrumentation

Instrumentation. Dr. Xiaofeng Wu. 1. Introduction. Power Supply. Signal Conditioning Circuits. Amplifier. Transducer. Command. Recorder. Data Processor. Controller. Resistive Potentiometer. 3. Strain Gage. 4.

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Instrumentation

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  1. Instrumentation Dr. Xiaofeng Wu 1

  2. Introduction Power Supply Signal Conditioning Circuits Amplifier Transducer Command Recorder Data Processor Controller

  3. Resistive Potentiometer 3

  4. Strain Gage 4 A strain gauge (also strain gage) is a device used to measure the strain of an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive. As the object is deformed, the foil is deformed, causing its electrical resistance to change.

  5. Piezoelectric Sensors A piezoelectric material produces an electric charge when it is subjected to a force or pressure.

  6. Wheatstone Bridge 6

  7. Second-Order RLC Filters

  8. Laplace Transfer Function

  9. Laplace Transform Pairs

  10. Amplifier An amplifier is used to increase low-level signals from a transducer to a level sufficiently high. vi vo vs

  11. Inverting Amplifier 11

  12. Noninverting Amplifier 12

  13. Active Filters 13

  14. Resolution and Quantization Error

  15. Measurement Errors and Uncertainties Errors are a property of the measurement. Measurement is the process of assigning a value to a physical variable based on a sampling from the population of that variable. Uncertainty is a property of the result. The outcome of a measurement is a result, and the uncertainty quantifies the quality of that result. Errors are effects, and uncertainties are numbers. While errors are the effects that cause a measured value to differ from the true value, the uncertainty is an assigned numerical value that quantifies the probable range of these errors.

  16. Propagation of Uncertainty A general relationship between some dependent variable y and a measured variable x

  17. Design Stage Uncertainty The zero-order uncertainty, u0, assumes that the variation expected in the measured values will be only that amount due to instrument resolution and that all other aspects of the measurement are perfectly controlled.

  18. Example 1 x h b A strain gauge is mounted on a steel cantilever beam of rectangular cross section. The gauge is connected in a Wheatstone bridge; initially Rgauge=R2=R3=R4=120 Ω. A gauge resistance change of 0.1 Ω is measured for the loading condition and gauge orientation shown in the following figure. If the gauge factor is 2±0.02 (95%) estimate the strain; Suppose the uncertainty of the resistance change the strain gauge, is ±0.002 Ω (95%). Estimate the uncertainty in the measured strain due to the uncertainties in the bridge resistances and gauge factor. Assume that the bridge is balanced when there is no external force; 18

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