Question Bank SENSORS AND INSTRUMENTATION [EE-305/405]

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1 UNIT-1 1. Discuss liquid in glass thermometers? 2. Write a short note on strain gauges. 3. Mention the various temperature scales and relation between them. 4. An experiment is conducted to calibrate a copper constantan thermocouple. With cold junction at 0 C, emf obtained at boiling point of water (100 C) and boiling point of sulphur (445 C) are 5 mv and 25 mv, respectively. If the relation is given by e = a(t1-t2)+b(t1 2 -t2 2 ) Determine constants a and b. The above thermocouple indicates 2 mv with cold junction at 40 C. Determine the unknown hot junction temperature. If the cold junction is maintained at 40 C, what would be the emf when hot junction temperature is at 500 C? 5. Explain, with a neat sketch, the construction and working of a RTD. 6. Mention the guidelines in selection of a flow meter for a particular application. 7. What is Reynolds number? On what factor does it depend? 8. What is Pressure? What are different types of pressure scales? Write at least 5 units of pressure. 9. What are Elastic type pressure transducers? What are different types of primary sensing elements used in them? Explain their construction with a neat and clean diagram. 10. Explain the construction and working of LVDT along with its characteristics. 11. Sketch a thermocouple circuit showing the important details and discuss in brief about the method used to measure output obtained from a thermocouple. 12. What are thermocouples? Explain their working principle with a neat diagram? What are the materials normally used in making thermocouples? What are their major advantages? Give their range. 13. What is RTD? Explain its principle and working? What are its advantages and disadvantages? 14. Convert the temperature -40 C in to K, F and R scales. 15. Why are compensating lead wires used in thermocouples? 16. Describe the material used for RTDs and its salient features. 17. Give the salient features of liquid in glass thermometers. 1 Neema Verma, Asstt. Professor, EC Department,HITM

2 18. Discuss the loading effects and find error in measurement of output voltage in potentiometer. 19. Write a short note on optical encoders. 20. Explain Seismic transducers? 21. With the help of neat labeled diagram briefly discuss spring-mass type accelerometers? 22. Describe the criteria for selection of transducers for a particular application? 23. Give the various characteristics of a transducer? 24. Explain various errors with respect to a transducer? 25. Give the constructional details of a resistance potential divider and derive the expression for its output voltage when connected across a meter of finite impedance. 26. Explain the construction of wire wound strain gauges and derive the expression for the gauge factor. 27. Give an overview of inductive transducers? Explain the construction and principle of working of a LVDT. 28. Discuss LVDT based pressure sensor? 29. Write a brief note on ultrasonic type flow sensor? 30. Write a short note on various level sensors used in industrial applications. 31. Give the concept of smart sensors? 32. Define the following terms: Error, Transducer, Sensors, Resolution, Threshold, Deviation, Range, Span, Gauge factor UNIT-II 33. Discuss any one type of DVM? 34. Mention the advantages of digital instruments over analog instruments? 35. Explain how an electronic analog voltmeter can be used to measure alternating current. 36. Sketch the circuit of a half wave rectifier with amplification of an AC electronic VM. 37. Sketch the circuit of a full wave rectifier with amplification of an AC electronic VM. 38. What are the major sources of errors? Explain the following terms- Systematic Error, Relative Error, Limiting errors 39. Explain the following terms, 2 Neema Verma, Asstt. Professor, EC Department,HITM

3 Accuracy, Precision, Resolution, Sensitivity, Fidelity, Threshold, Resolution 40. An 820 Ω resistance with an accuracy of ±10% carries a current of 10 ma. The current was measured by an analog meter on 25 ma range with an accuracy of ±2% of full scale. Calculate the power dissipated P in the resistor and % error in P. 41. Explain the working of DC voltmeter with neat diagram and also write about Swamping resistance and Multi range voltmeters. 42. A moving coil voltmeter has a uniform scale with 100 divisions, the full scale reading is 200 V and 1/10 of a scale division can be estimated with a fair degree of certainty. Find resolution of the instrument. [Ans: 0.2 V] 43. Two resistances are specified are specified as, R 1 = 36Ω ± 5% R 2 = 75Ω ± 5% Calculate the magnitude of limiting error in ohms and in percent if two resistances are connected in parallel. [Ans: ±3.65Ω] 44. A particular bridge gives the value of unknown resistance as: R x = R 2 R 3 R 1 R 1 = 120 Ω ± 0.1%, The values of known resistances are: R 2 = 2700 Ω ± 0.5% R 3 = 470 Ω ± 0.5% Find unknown resistance and limiting error in percent and ohms. [Ans: KΩ, ± 1.1%] 45. Differentiate clearly between systematic and random errors. 46. List various sources of errors in measurement. 47. Distinguish between Intelligent instrumentation system and Dumb instrumentation system. 48. A 600V voltmeter is specified to be accurate within ±2.5% at FSD. Calculate the limiting error when the instrument is used to measure a voltage of 400V. [Ans: 3.75%] [UPTU ] 49. A 3mA meter movement with an internal resistance of 100Ω is to be converted into 0-150mA ammeter. Calculate the value of shunt resistor. [Ans: 2.04Ω] 3 Neema Verma, Asstt. Professor, EC Department,HITM

4 50. Design a universal shunt to provide ammeter with the current ranges 2A, 10A and 15 A. The basic meter has internal resistance R m = 50Ω and full scale deflection current of 2 ma. [Ans: Ω, Ω, Ω] 51. Write a note on wheat stone bridge. 52. Discuss the limitations of wheat stone bridge. 53. Mention the basic two conditions which must be met in order to have a balanced bridge. 54. The values of resistances are R1=1000 Ω, R2= 100 Ω, R3=2005 Ω, Rx =200 Ω. The battery is 5V. The galvanometer has current sensitivity of 10mm/µA and internal resistance of 100. Calculate deflection of galvanometer and sensitivity of bridge in terms of deflection per unit change in resistance. [Ans: Ig=2.77µA, deflection= 27.7mm, sensitivity = 5.54mm/Ω] 55. Explain Kelvin s double bridge with its working and advantages. 56. Discuss substitution method of resistance measurement. 57. Find the unknown resistance X, Standard resistance =100.03µΩ, inner ratio arms = Ω and 200 Ω, Outer ratio arms = Ω and 200Ω, Connecting resistance = 700 µω, find unknown resistance. [Ans: µω] 4 Neema Verma, Asstt. Professor, EC Department,HITM

5 58. For a bridge, the ratio arms are each 100 Ω and bridge is balanced with standard arm adjusted to 230 Ω. If each of the ratio arms has accuracy of ±0.02% and standard has ±0.01% accuracy guaranteed, what are the limiting values of unknown resistance? [Ans: 230 Ω, Ω and Ω] 59. Explain the principle of Kelvin s double bridge and its importance in measuring low resistance values. 60. Explain Schering Bridge with the help of phasor diagram. Also find its dissipation factor. 61. Name few methods of measuring inductance. Explain any one in detail. 62. Explain the measurement of quality factor of a coil. Also mention its advantages and disadvantages. 63. Explain Anderson s bridge along with its phasor diagram. 64. Mention the types of detectors used in bridge measurement. 65. What do you understand by Q-meter? 66. Give the various methods for connecting the unknown components to Q-meter? 67. A coil of resistance 10 Ω is connected in the Q meter circuit. Resonance occurs at a frequency of 1MHz with the tuning capacitor set at 65pF. Calculate the percentage error introduced in the calculated value of Q if a resistance of 0.02 Ω is used across the oscillator circuit. [Ans: Qact = 245, Qmeas =244.5, %error =0.2%] 68. Mention few applications of Q-meter? 69. Describe the working of De-Sauty Bridge. 5 Neema Verma, Asstt. Professor, EC Department,HITM

6 70. Find the value of unknown resistance using Hay s bridge. 71. Find equivalent parallel resistance and capacitance that causes Wein Bridge to null with following component values. R3 =3.1KΩ, R2 = 25KΩ, R1 = 100KΩ, C1 =5.2 µf, f= 2.5 KHz. [Ans: 12.4 KΩ, 20.3 pf] 72. How can the frequency be determined using a bridge? Draw this bridge and derive condition for balance. 73. Define Q-factor of a coil. Explain with a circuit diagram the construction and principle of operation of a basic Q-meter. 74. What is meant by dissipation factor of a leakage capacitor? 75. What is meant by time constant of a coil? 76. Derive the balanced conditions of Owens s bridge. Draw the vector diagram of currents and voltages of the bridge arms at the balance condition. 77. Why actual Q-factor of a coil is larger than the calculated Q-factor? 78. What is dielectric loss in a dielectric? 79. Name commonly used detectors for ac bridges. 80. Discuss harmonic distortion analyzer. 81. Give a brief note of wave analyzer. 82. With suitable block diagram explain spectrum analyzer. 6 Neema Verma, Asstt. Professor, EC Department,HITM

Electronic Measurements & Instrumentation. 1. Draw the Maxwell s Bridge Circuit and derives the expression for the unknown element at balance?

Electronic Measurements & Instrumentation. 1. Draw the Maxwell s Bridge Circuit and derives the expression for the unknown element at balance? UNIT -6 1. Draw the Maxwell s Bridge Circuit and derives the expression for the unknown element at balance? Ans: Maxwell's bridge, shown in Fig. 1.1, measures an unknown inductance in of standard arm offers