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Session Topic: 6B, Voltage-Ratio |
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Paper Title: Practical Strain Gage Device Signal Conditioning Calibration and Application |
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Date & Time: WEDNESDAY, August 7, 2002 |
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8:30 - 10:00am PARALLEL SESSIONS - SESSION 6 |
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Speaker: Timothy W. Kypta |
Email: tkypta@afs.bwauto.com |
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Typically, signal-conditioning applications incorporate a ratio-metric calculation to convert the measurand to an engineering unit. Some techniques are better than others at achieving the desired results. In an ideal ratio-metric measurement, the output of the device is determined by dividing the excitation voltage into the strain gage mV output, or mV/V. The resultant mV/V signal is divided by the full-scale mV/V signal demonstrating the percentage of full-scale output. The percentage value is then multiplied by the full-scale force unit to arrive at an engineering unit equal to the applied force. In our not so perfect world some signal conditioners use an assumed constant voltage regulated power supply and then simply apply a fixed gain amplifier to the signal. These excitation supplies rarely meet their own specification for voltage regulation resulting in significant measurement error. Calibration techniques utilizing Wheatstone bridge simulators and voltage standards are discussed. Focus will be on trending of calibration data for strain gage devices and utilizing a best-fit straight-line method for determining uncertainty. Techniques employed to overcome systematic error incorporated by fixed signal conditioning; the application of slope and intercept calculations for transducers used in data acquisition systems. Shunt calibration versus using applied force, why we should be wary of the results that shunt calibration provides, and some other interesting facts about shunt calibration are discussed. |
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