Electrical Instrumentation interview questions


1.  Explain the working principle of the variable inductance type transducer?

A. The working principle of the variable inductance type transducer is based on the variation of self-inductance, variation of the mutual inductance, and also due to the production of the eddy currents.

2. What is an active and passive transducer?

A. The active transducer is a self-generating type of transducer that doesn’t need external power, and it would create an analog voltage or current if it is simulated by some physical form of energy an example for this type of transducers are thermocouple, photovoltaic cell, or a moving coil generator. A passive transducer needs an external power

3. What is a transducer?

A. Transducer is an electronic device that is capable to convert one form of energy into electrical energy. The input energy could be chemical, mechanical, thermal, optical, or electrical.

4. What are the types of electrochemical transducer?

* PH probes

* Electro-galvanic fuel cell

* Hydrogen sensor

5. What changes does a mechanical transducer sense, is it electrical, physical, chemical, or biological?

A. A mechanical transducer would sense physical changes only

6. Explain electrical transducer?

A. The electrical transducer would respond to physical quantities that are non-electrical like pressure, temperature, etc, and then it would create an equivalent electrical signal as output. There are two parts in an electrical transducer the first part is the sensing element and the second part is the transduction element.

7. Is it possible to amplify an electrical signal?

A. Yes electrical signal can be amplified or attenuated with the help of static devices

8. What are the advantages and disadvantages of an electrical transducer?

A. The power requirements of an electrical transducer are very less, these transducers are small, and they can be easily ported as well. These transducers are really costly

9. What is a digital transducer?

A. A digital transducer is a transducer that converts the input signal into the output signal and this would be a discrete function of time

10. Explain a mechanical transducer?

A. A mechanical transducer would create physical or mechanical signals as the output as a response to the physical changes in a system. A mechanical transducer generates physical signals according to the changes in the system’s physical conditions.

11. What are the types of thermoelectric transducers?

A. RTD, thermocouple, peltier cooler, and thermistor

12. How should we select a transducer?

A. It must be selected according to the

  • Operation principle
  • Sensitivity
  • Operating range
  • Accuracy.

13. What are the test inputs of a transducer?

A. Impulse input, step input, ramp input, parabolic input, and sinusoidal input.

14. How can we classify the transducer?

A. It can be classified as

* Active or passive

* Resistive, capacitive, inductive

* Analog and digital

* Primary and secondary

* Transducers and inverse transducers

15. What are the types of resistance thermometers?

A. Resistance temperature detectors and thermistors

16. What is a resistance thermometer?

A. This is a resistive type of transducer

17. What are the types of strain gauge?

A. There are four types of strain gauge and they are

  • Wire strain gauge
  • Foil strain gauge
  • Film strain gauge
  • Semiconductor strain gauge

18. What is a displacement transducer?

A. This type of transducer would convert the applied force to a displacement and these transducers would use a mechanical device to do this process and they are called force summing devices.

19. Name some of the force summing devices which is used by the pressure transducers?

A. Bellows, straight tube, bourdon tube, and diaphragm

20. Explain strain gauge?

A. Strain gauge is a type of passive transducer and it operates by using the electrical resistance variation properties in the wires, by using this property the transducer would determine the strain.

21. What are the different types of measurements that we can do by using a strain gauge?

A. We can use a strain gauge to measure weight, pressure, mechanical force, and displacement.

22. What is an input and output transducer?

A. The input transducer is mostly used as a measurement device and they are also called an instrument transducer, while the output transducer does the delivery of the output signals like pressure, force, torque, etc.

23. Give some examples for the active transducer?

A. Thermocouple, photovoltaic cell, photoelectric cell, piezoelectric transducer etc.

24. Give some examples for passive transducer?

A. Strain gauge, thermistor, LVDT, resistance thermometer

25. How is a sensor different from a transducer?

A. A transducer is a device that would convert one form of signal to another form like mechanical energy to electrical energy. The sensor would convert any form of energy into electrical energy. A sensor is the sensing element in a system and it won’t be directly coupled to the system under examination. The transducer operates by using a small amount of energy from the system, while a sensor does this without any physical connection to the system.

26. What are the advantages of LVDT?

A. Good displacement range, high sensitivity, output linearity, they are insensitive to temperature changes, and there is no physical contact during the operation so frictionless operation

27. For what types of measurement do we use an LVDT?

A. It can be used to measure the displacement ranging from millimeter to centimeter. These transducers are also used to measure the force, weight, pressure, etc.

28. Explain see-beck effect?

A. If we join different metal wires together to create two junctions and if these two junctions are held at different temperatures then there will an electric current flow in the circuit.

29. What is a Thompson effect?

A.  In case if there is a temperature difference exists in a wire of the same metal, then a see beck effect can be seen in that circuit and this contribution is called the Thomson effect.

30. What are the required characteristics for a transducer?

A. Accuracy, linearity, reliability, repeatability, good stability, quick response, compact and high sensitivity.

31. What is the operating principle of an electromagnetic transducer?

A. In this type of transducer the measurand will be converted to the voltage induced in a conductor by the change in magnetic flux in the absence of excitation. This is a type of active transducer

32. Explain the operating principle of an inductive transducer?

A. In this type the measurand will be converted into a change in self-inductance of a single-coil, this is done by displacing the core of the coil which is connected to the mechanical sensing element.

33. What is an inverse transducer?

A. It can be considered as the opposite of a transducer, this device would convert the electrical signal to a non-electric quantity.

34. What are the types of a resistive transducer?

A. Strain gauge, thermistors, potentiometers, and resistance thermometer

35. For what purpose do we use an ultrasonic transducer?

A. This type of transducer uses ultrasound to measure certain parameters such as fluid level, flow rate, etc.

36. Why does a transducer require minimum loading?

A. A transducer needs a minimum amount of load, the minimum loading effect of the transducer ensures the minimum error.

37. What is the need for temperature compensation in a transducer?

A. By the temperature compensation we can minimize some errors in the transducer, in some transducer error could occur because of the change in temperature so with the help of temperature compensation we can minimize these errors.

38. Is it possible to use a transducer in an environment with vibrations?

A. We can use transducer in a vibrating environment by using dampers

39. What are the commonly used elements in a wire strain gauge?

A. In a strain gauge nickel and copper are the most used element because they exhibit a high value of specific resistance

40. How does the resistance change in a wire wound strain gauge?

A. The resistance change in this type of strain gauge is because of change in length and diameter

41. For what purpose do we use a bonded wire strain gauge?

A. This type of strain gauge is mostly used for stress analysis and also for the construction of the transducer

42. Explain why a transducer should be rugged?

A. A transducer should be rugged because it must be capable to withstand overload and it would require some safety arrangements in order to withstand the overload

43. What do you need a transducer to be linear?

A. The output and input characteristics of a transducer should be linear and the transducer should have these characteristics in a controlled manner

44. What are the required factors for a transducer output?

A. The output signal quality of the transducer must be good the signal to noise ratio must be good and the output signal should have good amplitude

45. Explain the difference between inverse transducer and transducers?

A. Transducers are devices that are connected to a circuit that has no electrical input and output an example of this will be pressure gauge and strain gauge. The inverse transducer would convert the electrical signals to non-electrical signals.

46. What is a resistance strain gauge?

A. This type of transducer is used for measuring displacement, this type of strain gauge is composed of a grid of wire and it has a protective covering too.

47. What is a semiconductor strain gauge?

A. The semiconductor strain gauge has a semiconductor material and mostly it is silicon the resistivity of the semiconductor is higher than a conductor.

48. What are the required properties of thermocouple metals?

A. The thermocouple materials must not melt within the range of temperature requirements and they should not corrode at their higher temperature. The EMF which is created by the couple must be constant for a given temperature throughout its life.

49. Name the type of scale which is used in a thermocouple meter?

A. Square law scale is used in a thermocouple meter

50. For what purpose do we use a thermocouple meter?

A. Mostly it is used to measure the radio frequency currents which have a frequency range of thousand megahertz.

51. Is it possible to measure AC by using a thermocouple?

A. Yes we can use a thermocouple to measure AC of high frequency very accurately, the operation of this device is based on the principle of heat generation due to current.

52. Explain a hall-effect transducer and for what purpose do we use it?

A. We can use a hall-effect transducer for the displacement measurement, the working principle of this device is based on the effect of magnetic fields on moving charges. This transducer will be located in a gap, so if there is any displacement in the ferromagnetic structure would change the magnetic field and thus the output voltage will be changed by this.

53. What are the applications of a hall effect transducer

A. Current can be measured by this device without any electrical connections between the meter and the circuit. This transducer can be used as an analog multiplier, it can also measure the strength of the magnetic field according to the electric voltage.

54. What are pyrometers?

A. The pyrometers are devices which is used to do the high temperature measurements.

55. Name the types of pyrometer?

A. Resistance pyrometers, thermocouple pyrometers, radiation pyrometers, and optical pyrometers.

56. What are the non-electric quantities that can be measured by using a strain gauge?

A. This transducer is used in load cells and also in load rings to measure the force-producing strain. The resistance wire type strain gauges can be used to measure stress, force, and torque in a structure. Complex structures such as roads, bridges would have dynamic strains and this can be measured by using a strain gauge.

57.  For what purpose do we use a synchro-transducer?

A. This transducer is mostly used to measure the position

58. What are optical pyrometers?

A. Optical pyrometers can be used for high-temperature measurements, such as the temperature of the furnace.

59. What are the advantages of radiation pyrometers?

A. It can measure high temperatures, and also they can measure the temperature of a moving object.

60. Name the two light sensitive transducers?

A. Photoconductive cell and photovoltaic cell

61. For what purpose do we use an eddy current tachometer and tacho-generator?

A. The rotational speed of the shaft can be measured by using an eddy current tachometer and it works on the principle of eddy current. By using a tacho-generator we can measure the rotational speed from distance.

62. Explain stroboscope?

A. This device can produce light at a controlled frequency and it can be used to measure the rotational speed of the shaft accurately.

63. What are the applications of LVDT’s?

A. It can be used to do the direct displacement measurement, thickness measurement, surface roughness, etc.

64. What is V R I T?

A. VRIT stands for variable reluctance inductive transducer and it can be used to measure displacement.

65. Name the transducer which can convert the ground movement or velocity to voltage?

A. Geophone can convert the ground movement to voltage and they are used in remote ground sensors.

66. Explain the relation between scale factor and sensitivity of a transducer?

A. The scale factor of the transducer is inverse of sensitivity, the major required factor for a transducer is a sensitivity in order to provide better output good sensitivity is required.

67. What is the difference analog and digital transducers?

A. The analog transducer would convert the physical quantity to analog signals while the digital transducer would convert the physical quantity to digital signals.

68. Which transducer can be used to measure force?

A. Piezoelectric transducer can be used to measure force, electric signals will be created by piezoelectric crystals if pressure is applied to it.

69. For what purpose should we use a capacitive transducer?

A. We can use a capacitive transducer to do the dynamic measurement, this transducer would convert the measurements to the changes in capacitance. The change in capacitance takes place if there is a change in dielectric or if there is a change in distance between the plates.

70. Why selenium is used in photoconductive cell?

A. If the selenium is exposed to light it shows photoconductive action, the reduction of the resistance during a light exposure is the photoconductive action.

71. For what purpose do we use a bimetallic element?

A. This device can be used to measure the temperature, it converts the input temperature to displacement.

72. Which liquid is used in a liquid steel bulb thermometer for the temperature measurement upto 60000C?

A. Mercury is used in this thermometer because it can provide a temperature range of -4000C – 65000C.

73. Why bourdon tube is used in liquid expansion system?

A. The bourdon tubes are capable to convert the pressure into displacement and in liquid expansion systems, output expansion pressure is applied to the bourdon tube for indication.

74. What would happen if a bimetallic type thermometer is heated?

A. If a bimetallic type thermometer is heated then curling would take place to the side of the metal that has the least temperature coefficient. The number of curls will be proportional to the applied temperature.

75. Explain thermal storage capacity?

A. It is the ratio of the net amount of heat received and stored in the body for certain time interval.

76. For what purpose do we use a load cell?

A. Load cells are used to measure the slowly moving weights

77. What are the required characteristics of a strain gauge?

A. It should have a good frequency response and also it should have a high value of the gauge factor. It should not have a creep effect.

78. Give some examples for electromagnetic transducer?

A. Magnetic cartridge, hall effect transducer, antenna (converts electromagnetic wave to electric current), cathode ray tube, tape head, etc.

79. Give some examples for electromechanical transducer?

A. Tactile sensor, airflow sensor, string potentiometer, strain gauge, accelerometer, rotary and linear motor, galvanometer, etc.

80. Is it possible to use diaphragm elements to do the force measurement?

A. Yes it is possible, the diaphragm elements would act like flat springs in case of force measurement and it can be used for both the force and pressure measurement.

81. Is load cell a primary transducer?

A. Yes load cell is a primary transducer, primary transducers are devices that would convert the measurand into mechanical quantities. The load cell does the conversion of the measurand into strain or displacement which is mechanical quantities.

82. Does thermistors have good stability?

A. The stability of the thermistors are not satisfactory, it can be improved by using high temperature.

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