L12_ECE4001_Fall_2008

L12_ECE4001_Fall_2008 - ECE 4001C Fall 2008 Lecture 12...

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ECE 4001, L12, F08 J. Stevenson Kenney © 2008 1 ECE 4001C Fall 2008 Lecture 12 Engineering Measurements Oct. 2, 2008
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ECE 4001, L12, F08 J. Stevenson Kenney © 2008 2 Outline • Introduction • Elements of a Measurement System • Error and Uncertainty • Instrumentation Errors • Calculating Experimental Errors • Calibration Issues • Experimental Test Plan • Summary
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ECE 4001, L12, F08 J. Stevenson Kenney © 2008 3 Elements of a Measurement System • Sensor/transducer – Detect a signal or stimulus (what we are measuring) and produce a measurable output • Signal conditioning – Convert the sensor output into a more usable form • Display/data recorder – Display and/or record the measurement results
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ECE 4001, L12, F08 J. Stevenson Kenney © 2008 4 Example: Thermometer • Sensor: Liquid in the bulb responds to increase in temperature by expanding • Signal Conditioning: Expanding liquid travels up the small tube so that it can be seen • Display/Recorder: Scale marked on the small tube displays the temperature; manual recording of data
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ECE 4001, L12, F08 J. Stevenson Kenney © 2008 5 Example: Electronic Caliper • Sensor: Mechanical calipers • Signal Conditioning: Encoding device to convert mechanical motion to electronic format • Display/Recorder: Digital readout and manual recording of data
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ECE 4001, L12, F08 J. Stevenson Kenney © 2008 6 Example: Thickness Gage • Sensor: Ultrasonic transducer • Signal Conditioning: Analog signal is digitized and processed to determine the material thickness • Display/Recording: Numerical display and built-in data logger
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ECE 4001, L12, F08 J. Stevenson Kenney © 2008 7 Error and Uncertainty • What is error? • Error vs. uncertainty • Human errors • Systematic errors • Random errors • Accuracy and precision
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ECE 4001, L12, F08 J. Stevenson Kenney © 2008 8 Experimental Error • Experimental error does not imply that there is any mistake in the measurement process (although there may be) • The experimenter never (or rarely) knows the true error of a measurement • Human errors (mistakes) can occur, and can also be fixed if identified error = measured value - true value
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ECE 4001, L12, F08 J. Stevenson Kenney © 2008 9 Error vs. Uncertainty • We don’t know the error (otherwise we could correct for it and it wouldn’t be an error) • However, we can estimate the uncertainty • The uncertainty is an estimate of the limits of the error in the measurement • Example: measurement of 10 volts ± 0.5 volts with 95% confidence • We are 95% sure that the true value is between 9.5 and 10.5 volts • The uncertainty is ± 0.5 volts • The level of confident is 95% error (unknown) uncertainty estimate of error limits e w = = =
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ECE 4001, L12, F08 J. Stevenson Kenney © 2008 10 Human Errors (Mistakes) • Incorrect instrument setting • Mistake in experimental setup • Data recording error • Software bug • Inconsistent technique Carefully examine the setup, procedures and data to identify and correct human errors as early as possible in the measurement process
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ECE 4001, L12, F08 J. Stevenson Kenney © 2008 11 Categories of Errors
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L12_ECE4001_Fall_2008 - ECE 4001C Fall 2008 Lecture 12...

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