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Unformatted text preview: ENGR 202 Midterm Solutions Winter 07-08 Problem 1. You are doing performance testing out in the field on a solar panel that is suspected of malfunctioning. Under strong sunlight the panel output current is expected to be 3 Amps, but this one only measures 2.156 Amps on your HP 34401A multimeter. This meter is 6 months past its last calibration. What instrument error will your meter contribute to the measurement of the 2.156 Amp value? Assume your meter has been warmed up properly for one hour and the temperature is within 23 C 5 C. Solution: Since last calibration is 6 months old, there is no interpolation between 90 days and 1-year values. Use 1-year values. Use range of 3A. Instrument error = (2.156 A)(0.00120) + (3 A)(0.00020) = 0.0025872 A + 0.00060 A = 0.0031872 A Rounding to 3 decimal places = 0.003 A Therefore, 2.156 0.003 A, covering 2.153 A to 2.159 A Problem 3. Ten measurements are made of the thickness (T) of a metal plate, giving 4.82, 4.82, 4.82, 4.83, 4.83, 4.83, 4.83, 4.83, 4.83, 4.83 mm. Determine the mean value and the tolerance limits for a 95% confidence level. Express your answer in the form T = (mean tolerance) with a confidence level of 95%. Solution: Mean = = 4.82+4.82+4.82+4.83+4.83+4.83+4.83+4.83+4.83+4.83 mm = 4.827 mm 10 Std dev (S) = 0.00483 mm using n-1 in denominator (because sample size is <20) = 10 - 1 = 9 For 95% level, t a/2 = 2.262 = 2....
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- Winter '08