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Tel: (815) 753-9975                                                                                                         Department of Mechanical Engineering

E-mail: kostic@niu.edu                                                                                                                             DeKalb, IL 60115-2854

Web: www.kostic.niu.edu                                                                                                                                                        USA

September 26, 2001;  Group:            

MEE 390 Midterm Exam

Open Textbook exam ONLY. Put your zipped bags and other things away of your reach. If not obvious or defined, the notation is as in Textbook. There may be more or less given data than necessary. Make reasonable assumptions only if necessary. Show all your work or give specific reference. Write distinctly, be very specific/quantitative and use units throughout. If possible always support your answer with a sketch, and be straightforward and concise.

NO COMMUNICATIONS WITH OTHER STUDENTS FOR ANY REASON. KEEP YOUR DONE WORK STRICTLY IN FRONT OF YOU. BOX ALL REQUESTED FINAL RESULTS WITH UNITS. Confirm your agreement to comply with your Signature:

                                                                          ________________________________________________          

Problem 1:

A periodic input is measured using a first-order instrument with time constant t=0.2 sec. Calculate (also sketch and verify on the corresponding diagram) measurement frequency range in Hz, so that the corresponding magnitude ratio will be within ± 3 decibel (dB) range.

Problem 2:

Mean value and its standard deviation of a sample data set of 90 pressure measurements are 400 psi and 3 psi, respectively. (a) Determine the sample standard deviation. (b) What is the 95% probable precision interval for the mean value, based on the above measurements? (c) Estimate the probability for a measurement’s precision interval of ± 10 psi.

Problem 3:

A resistance-type temperature sensor is calibrated and its output in ohms against standard temperature input in ⁰F is recorded as:

     R, Sensor resistance (Ω)         T, Standard temperature (⁰F)

                        4.4                                                        20

                        6.6                                                        40

                        7.7                                                        60

Using the least square method fit the above data with the equation R = a Ö(T). (a)Calculate the coefficient "a" and (b) the static sensitivity at 25 ⁰F.

Box all REQUESTED FINAL RESULTS with their UNITS.