ME 370 Spring 2015

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Name_____________________

NetID_____________________

Lab Section________________

ME 370 Midterm Practice Exam

Wednesday March 4, 2015

NOTE: This is a close book and close notes exam. You are allowed to take a letter-sized, double-sided, and hand-written reference sheet with you. Please hand in your reference sheet together with your exam paper. Do your work on the page of the problem and if necessary on the following blank page. It is mandatory that proper units be included explicitly along with the numerical value for each term in a quantitative calculation, showing how the units of the final answers are derived. Failure to do this will result in no credit. Circle your answer. Be neat!

For each problem, you must show complete work, related equations, and indicate your reasoning. No credit will be given if you do not show the complete work and describe your procedure, even if the answer is correct. Write your name, NetID, and Lab Section. If you cannot remember your lab section number, please provide the time of your lab section.

ME 370 Spring 2015

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Problem 1: A multimeter is used to measure the voltage across resistances shown in circuit diagram below. We know that the driving voltage Ei = 5 V, R1 = 10 MΩ, R2 = 15 MΩ, R3 = 25 MΩ. The measurement voltage between A and B is 2 V.

a) What is the loading impedance of the voltage meter used? b) If we use the meter to measure voltage across B and C, what is the measurement voltage? and what is

error percentage over the true value? c) What is the minimum loading impedance of the multimeter if we want to measure the voltage across

B and C with a maximum error of 1%?

ME 370 Spring 2015

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Problem 2: Consider the signal y(t) = 5+10cos(30t) +15cos(90t) . Determine

a) The frequencies (in Hz) contained in the signal.

b) The minimum sampling rate (in Hz) to avoid aliasing.

c) The frequency resolution of the frequency spectrum if the signal is sampled at that rate for 2 seconds.

d) Sketch the amplitude-frequency spectrum of y(t).

e) Sketch the amplitude-frequency spectrum if the signal is sampled at 20 samples/s.

ME 370 Spring 2015

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Problem 3: If the output signal from a transducer is Ei = 0.1 sin(500) Ei = 0.1sin(500π t )V. This signal is passed to a signal conditioning device, which is shown in figure below. Finally, the output signal is measured by a 12-bit data acquisition card, with a sampling rate of 10 kHz, the range of the data acquisition card is -12 V to +12 V. Here R = 100 kΩ, Rgain = 50 kΩ

a) Determine the error percentage if the device is to sample the original signal Ei. b) Determine the output signal Eo. c) Determine the error percentage if the device is to sample the output signal Eo. d) Assume the input signal is sin(2 )iE ftπ= V, and the Op-Amps with a slew rate of 0.01 V/ms, are

driven with a power supply of 15± V. Determine the maximum frequency that the system can handle properly.

R

R

Rgain

RR R

R3

1

2

4

1 kΩ

0.1 mF

Ei

Eo