Obafemi Awolowo University, Ile-Ife, Nigeria

Faculty of Technology

Department of Electronic & Electrical Engineering

EEE 521 – Instrumentation Engineering

2010/2011 Harmattan Semester Examination

INSTRUCTIONS:

Answer ANY FOURquestionsTime allowed: 3 Hours

Name: ______

Matric No.: ______

Question 1.

  1. During the calibration of a mercury-in-glass thermometer, the following data was obtained (T is temperature in °C and h is the height of the mercury in the glass in mm):

T (°C) / 0 / 5 / 10 / 15 / 20 / 25 / 30 / 35 / 40 / 45 / 50 / 55 / 60
h (mm) / 2 / 4.24 / 5.16 / 5.87 / 6.47 / 7 / 7.48 / 7.92 / 8.32 / 8.71 / 9.07 / 9.42 / 9.75
  1. Is the thermometer linear? (2 marks)
  2. What is the approximate sensitivity of the thermometer when measuring 10°C? (2 marks)
  3. What is the approximate sensitivity of the thermometer when measuring 50°C? (2 marks)
  4. Does the instrument have any bias? (2 marks)
  1. After the calibration process is complete for a certain thermometer, the transient response analysis of the thermometer shows that it is a single-time-constant instrument. It has a time constant of 5 seconds and a gain 1. If the thermometer is reading 0°C and then it is suddenly thrown into a pot of water which is at a temperature of 50°C,
  2. What will be the error (in °C) in the reading of the thermometer after 5 seconds and 10 seconds respectively? (3 marks)
  3. How long will it take before the reading of the thermometer to have a percentage error less than 1 %? (3 marks)
  4. Draw a Wheatstone bridge circuit which can be used to measure the resistance of a strain gauge. Find the calibration of the system when the bridge circuit is operated in the deflection mode. Find the sensitivity of the instrument with respect to a change in the strain gauge’s resistance. (6 marks)

Question 2.

  1. Suppose that the components of the circuit shown in Figure 1 have the following values:R1 = 400Ω; R2 = 600 Ω; R3 = 1000 Ω; R4 = 500 Ω; R5 = 1000 Ω. The voltage across AB is measured by a voltmeter whose internal resistance is 9500. What is the measurement error (in terms of E0) caused by the resistance of the measuring instrument? (5 marks)

Figure 1

  1. A spring balance is calibrated in an environment at a temperature of 20°C and has thefollowing deflection/load characteristic:

Load (kg) / 0 / 1 / 2 / 3
Deflection (mm) / 0 / 20 / 40 / 60

It is then used in an environment at a temperature of 30°C and the following deflection/load characteristic is measured.

Load (kg) / 0 / 1 / 2 / 3
Deflection (mm) / 5 / 27 / 49 / 71
  1. Determine the sensitivities at 20°C and at 30°C. (2 marks)
  2. Determine the total zero drift and sensitivity drift at 30°C. (2 marks)
  3. Determine the zero drift and sensitivity drift per °C change in ambient temperature. (2 marks)
  4. Determine the total zero drift and sensitivity drift at 10°C. (2 marks)
  1. How can we minimize systematic error in measurement? (3 marks)
  2. Define the following: (4 marks)
  3. Systematic error
  4. Bias
  5. Random error
  6. Precision

Question 3.

  1. Draw three diagrams showing ways in which capacitance can be used to measure displacement. In each case, give the mathematical relationship between the displacement and the capacitance.
    (6 marks)
  2. In the measurement of the levelof a liquid or solid in a container, we may make use of level switches or a continuous level instrument. Explain the difference between these two types of instruments, using examples where possible. (6 marks)
  3. Describe,with the aid of diagrams, two ways in which you can measure the height of rice in a silo.
    (4 marks)
  4. Describe the operation of an optical encoder. (4 marks)

Question 4.

  1. Explain why signal conditioning is necessary.Give three characteristics which we would love our signal variable to have.(5 marks)
  2. What is the opposite of a single-ended signal? Differentiate between a single-ended signal and its opposite. Why do we prefer single-ended signals? (4 marks)
  3. What is the dynamic range of a 12-bit ADC? (2 marks)
  4. Figure 2 shows a temperature measuring instrument. The temperature sensor is linear. It has a resolution of 0.1 °C and measures temperatures from 0 °C to 100 °C. Its sensitivity is 10 mV/°C . The ADC is a 10-bit ADC and it has an input range from 0 to 10 V. The gain of the amplifier is 2.
  5. What is the dynamic range of the sensor? (1 mark)
  6. What is the resolution of the ADC in volts or millivolts? (1 mark)
  7. What is the resolution of the instrument in °C? (2 marks)
  8. Why is there a difference between the resolutions of the sensor and of the instrument?
    (2 marks)
  9. What can be done to give the instrument a maximum resolution? (2 marks)
  10. Why can’t the amplifier have a gain of 20? (1 mark)

Figure 2

Question 5.

  1. What are design specifications? Why are they important? (3 marks)
  2. What are performance specifications? Give three uses of performance specifications. (3 marks)
  3. What are standard specifications? Why are they important? ( 2 marks)
  4. Do I have to use standard specifications in my designs? Explain. (2 marks)
  5. Discuss two approaches to research. (2 marks)
  6. Give four necessary inputs to a design system and discuss how these can be harnessed to ensure creativity in the design process. (8 marks)

Question 6.

  1. Discuss two ways in which nano-instruments can be manufactured. (6 marks)
  2. Why is nanotechnology attractive to instrumentation engineering? (4 marks)
  3. Discuss two ways in which a nanoparticle of gold can differ from a bar of gold giving reasons why these differences exist. (6 marks)
  4. Discuss one application to which nanotechnology and/or nanoscience has already been used.

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