Student Name: Student ID: CHEMICAL ENGINEERING 2I03 DAY CLASS Duration 2 hours McMaster University Practice Exam Dr. M. Thompson The final test includes 60 questions on 12 pages. This test paper must be returned with the answers written on the pages. You are responsible for ensuring that your copy of the paper is complete. Bring any discrepancy to the attention of your invigilator. SPECIAL INSTRUCTIONS 1. McMaster standard calculator (Casio FX-991) ONLY is permitted. 2. Marks for the problems are given (Total of 70 marks) 3. Ensure name and ID number are included above. 4. All work must be done in the provided area for each question. Work done on the back of blank pages in this test or on scrap paper will not be marked. 5. Answers with more than one circled answer will be graded as incorrect. Group One - TRUE / FALSE Questions (1 Mark per question) Circle only the correct response 1. T F A manometer s static sensitivity is proportional to the specific gravity of the manometer fluid 2. T F The LVDT has better position resolution but a smaller range than the linear potentiometer. 3. T F A large thermocouple will reach a steady state value sooner if subjected to a small step input than a large step input. 4. T F A strain gage does not require material deformation to sense force. 5. T F The linear potentiometer is a resistance potentiometer (a rheostat or variable resistor). The voltage output of the potentiometer is proportional to the extension length? Continued on Page 2
6. T F Thermistors are normally not as sensitive as RTDs, but are much less expensive to manufacture. 7. T F Quantization error can be reduced by signal amplification. 8. T F FSO stands for fixed standardized output. 9. T F The linear potentiometer is a resistance potentiometer (a rheostat or variable resistor). Is the voltage output of the potentiometer proportional to the extension length? 10. T F A proving ring is used to calibrate load cells. Group Two Multiple Choice Questions (1 Mark per question) Circle the letter corresponding to the most appropriate answer 16. A thermistor: a) requires a constant cold junction to remain calibrated. b) changes resistance in proportion to changes in temperature. c) outputs a small voltage which is proportional to the temperature. d) requires a voltage source to function. e) both b) and d) are correct 17. The quantization size of an ADC is related to: a) the speed of the A/D conversion. b) the number of bits of the A/D converter. c) the amplitude of the input signal relative to the full range of the A/D converter. d) all of the above are correct. e) only B and C are correct. 18. Which of the following properties are generally desirable in a transducer? a) Large time constant b) Low natural frequency c) Linearity d) A, B & C are all desirable e) B & C are both desirable
19. Which of the following temperature sensors is the least expensive to purchase and implement? a) Thermocouple b) Thermistor c) Infra Red Detector d) RTD 20. If the Nyquist sampling criteria was satisfied for an input signal with a frequency of 1kHz, what was the sampling rate? a) 1 khz b) 200 khz c) 2 khz d) None of the above 21. What kind of elastic element was used in a pressure transducer? a) a foil bonded to the diaphragm b) a stretched wire c) a piezoresistive semiconductor d) none of the above 22. The number of different values that can be discretized by a 12 bit ADC is: a) 4096 b) 2048 c) 1024 d) 256 e) 512 23. If a 30 Hz signal for the measurement is being deteriorated by the noise of nearby electrical devices, these errors can be reduced by: a) shielding the cables b) using a notch filter c) Using a band pass filter d) both a) and c) are correct 24. Aliasing describes the phenomena: a) in which signal frequency appears higher than the actual value due to inadequate sampling rate.
b) in which signal frequency appears lower than the actual value due to inadequate sampling rate. c) in which signal waveform appears distorted. 25. Which of the following never depends on the sampling rate? a) Frequency of the sampled signal b) Magnitude of the sampled signal c) Nyquist frequency of the input signal d) Shape of the sampled signal 26. The plot of magnitude ratio vs frequency at right is typical of a: a) low pass filter b) high pass filter c) band pass filter d) notch filter 27. A transducer being used to measure vibrations with a frequency range of 10-500 Hz is very sensitive to noise from electrical motors running at 500-1000 RPM. The effect of the noise can be minimized by passing the output through a: a) Low pass filter b) high pass filter c) notch filter d) bandpass filter 28. The quantization error in a data set could be reduced by first a) increasing the speed of the electronics. b) increasing the number of bits in the ADC
c) amplifying the input signal d) both B and C are correct. e) A, B and C are all correct. 29. If the 60 Hz signal from nearby electrical devices is creating measurement system interference errors these errors can be reduced by: a) shielding the cables b) using a notch filter c) Using a band pass filter d) Both a & b e) Both a & c 30. The aliasing frequency that results from sampling a signal of 60 Hz at a sample rate of 90 Hz is: (use the folding diagram at the end of this test to help) a) 30 Hz b) 59.9 Hz c) 60.3 Hz d) 79.8 Hz e) 90 Hz (more to come...31 50) Group Three Short Answer Questions [Any sentences follow the number indicated by the question will NOT be considered in the grading for that question] 51. List four reference pressure instruments useful in the calibration of pressure sensors. Explain in one sentence. (2 Marks) McLeod Barometer Manometer Deadweight tester 52. In one sentence, define resolution of quantization. (2 Marks) Q = E FSR / (A/D bits) 53. In one sentence, state four categories of chemical sensors (2 Marks)
Electrochemical Calorimeter Thermometric Optical biological 54. Explain in one sentence the operational principle of sample and hold. (2 Marks) Capacitor holds the voltage signal till its value is manipulated for less sophisticated ADC systems, like a handheld unit. 55. Name the two disadvantages of using flow meters based on moving mechanical parts like a paddle or gear. Two sentences maximum. (2 Marks) impairs flow area, directly in contact with fluid THE END