TC emf outputName:______________________ Person Number:____________________ Department of Mechanical and Aerospace Engineering MAE334 - Introduction to Instrumentation and Computers Midterm Examination October 18, 2001 Closed Book and Notes For each question, choose the best answer and place a mark corresponding to that answer on the machine scoring form. Be sure you put your name and 8-digit person number on both the questionnaire and the scoring sheet. Failure to turn in this questionnaire with your name and student number on it along with the answer sheet will result in a grade of ZERO.0. Fill in circle 1 under GRADE OR EDUCATION on side two of your answer sheet (and fill in your name, person number). 1. Waveforms can be broadly classified into these 3 types: a. Periodic, aperiodic and static b. Stationary, ergodic and nondeterministic c. Static, dynamic and nondeterministic d. None of the above 2. The slope of the static calibration curve is known as the: a. Response function b. Time constant c. Static sensitivity d. None of the above 3. The degree of conformity of a measure to a standard is know as the: a. Precision b. Accuracy c. Sensitivity d. Resolution 4. The average error in a series of repeated measurements of the same static input will quantify the: a. Sensitivity error. b. Resolution error. c. Bias error. d. Standard deviation. 5. When sampling a complex periodic signal, the length of the data record should be an integral multiple of the period: a. to be able to Fourier transform and inverse transform the signal. b. to be able to determine the exact period of the signal. c. to avoid leakage in the Fourier transform. d. to avoid signal aliasing.6. The Fourier transform of a continuous signal: a. Maps the time domain to the frequency domain. b. Provides frequency amplitude and phase angle information. c. Is a continuous function. d. All of the above. 7. A discrete digital representation of a signal is always less precise than the original input signal. a. True b. False 8. Quantization refers to a. the fact that A/D conversion process requires a finite amount of time. b. the fact that the number representing an analog signal has a finite precision. c. Both (a) and (b) are correct. d. Neither (a) or (b) are correct. 9. The Nyquist or (folding) frequency is: a. twice the highest frequency in the signal b. half the highest frequency in the signal c. half the sampling frequency of the signal d. none of the above 10. When frequencies in a signal are aliased, the sampled signal will appear to have a frequency content which is greater than that of the input signal. (a) true (b) false11. The minimum sampling frequency necessary to avoid aliasing a waveform containing frequencies of 25, 75, 100 and 200 Hz is a. 200 samples/sec. b. 400 samples/sec. c. 1000 samples/sec. d. 2000 samples/sec. 12. The National Instruments LAB PC-1200/AI hardware used in the laboratory has a pre-amplification gain setting of 1: a. when the input range is 0.2 Volts total. b. when the input range is 10 Volts total. c. which is independent of the input range. d. none of the above. 13. The best signal to noise ratio one can expect from a 12 bit analog to digital converter is: a. 24 dB. b. 48 dB. c. 72 dB. d. 96 dB. 14. Linear response instruments: a. Have a better dynamic response than nonlinear instruments. b. Are easier to calibrate. c. Have a constant static sensitivity over their range. d. All of the above are correct. e. Only (b) and (c) are correct. 15. The first moment is also know as a. The variance b. The mean c. The time constant d. The standard deviation16. A precision error a. introduces scatter into a series of measurements of the same input. b. can be minimized by careful static calibration. c. can be minimized by repeating the measurement of the same input many times and averaging the results. d. Both (a) and (c) are correct. 17. The time constant of a first order system a. is independent of the input signal waveform. b. is a measure of the speed of response to a change in input. c. is inversely related to the size of an applied step input. d. All of the above are correct. e. both (a) and (b) are correct. 18. The dynamic response of a first order sensor will tend to: a. attenuate higher frequencies more than lower ones. b. overshoot the actual signal in response to a step input. c. be linear. d. none of the above. 19. The thermocouple is considered a first order instrument because a. it has only one sensing element. b. its static behavior is described by a first order differential equation. c. its dynamic behavior is described by a first order differential equation. d. both (a) and (c) are correct. e. both (b) and (c) are correct.20. A reference junction for the thermocouple used in Experiment 2: a. Is not needed for the type of thermocouple used. b. Is a solid-state temperature sensor on the ADC input board. c. Is a solid-state temperature sensor in the probe itself. d. Is the room temperature junction where the thermocouple is connected to the ADC. e. (a), (b) & (d) are correct. 21. It is important that the leads of a thermocouple between the measurement junction and the reference junction be held at a constant temperature. a. True b. False Sample of Random Variable x i xii xi1 0.98000 11 1.0200 2 1.0700 12 1.2600 3 0.86000 13 1.0800 4 1.1600 14 1.0200 5 0.96000 15 0.94000 6 0.68000 16 1.1100 7 1.3400 17 0.99000 8 1.0400 18 0.78000 9 1.2100 19 1.0600 10 0.86000 20 0.96000 Table 1. Sample data set with a Gaussian distribution, a mean value of 1.0190 and a standard deviation of 0.15768.22. Given the data set in table 1, the number of degrees of freedom, ν, of the standard deviation, Sx, is: a. ν = 17 b. ν = 18 c. ν = 19 d. ν = 20 23. Given the data set in table 1, estimate the interval of values over which 95% of the measurements of x should be expected to lie. a. 1.0190 +/- 0.14979 b. 1.0190 +/- 0.32891 c. 1.0190 +/- 0.15768 d. 1.0190 +/- 0.33002 (1.0190 +/- t19,95Sx) 24. Given the data set in table 1, the uncertainty in the mean value could be reduced by: a. decreasing the sensitivity of the measuring instrument. b. increasing the total number of measurements. c. improving the precision of the measuring instrument. d. both (a) and (b) are correct. e. both (b) and (c) are correct. 25. Estimate the true mean value of the measurand to within 95% probability based on this finite data set. a. 1.0190 +/- 0.073795