NTPC Placement Paper Technical - Other Govt. Cotton Hill Girls HSS, Trivandrum-16 Apr 2011

Posted by FreshersWorld

7 Jan, 2012

The question paper had a total of 120 questions in which 70 questions were from technical and 50 from aptitude. Duration- 2 hours. A candidate should clear cut-offs for both the sections to get shortlisted. NTPC will decide the cut off after reviewing the questions for errors, receiving feedback from candidates and finally, after evaluating the OMR sheets. The cut off will be such that around four times the number of vacancies will be called. So altogether 2000 people will be shortlisted for the GD/PI process.

Below are some of the questions that I could recollect from Control and Instrumentation paper. Post your feedback and queries, if any.

1. Technique used in telegraphy- On/off keying, fsk etc. 2. TF=10/(s+5)^3. Gain margin in dB. 3. If the point -1 +j0 is encircled, then gain margin=? 0, less than 0, infinity etc. 4. Given a transfer function. Identify zeroes and poles. 5. Response of an RLC circuit to impulse signal is: decaying exponential, parabola etc. 6. LASCR can be turned on by: light only, gate pulse only, either, neither. 7. Transistor SOA is a plot of: Vce vs Ice. 8. Proportional band and proportional gain relation: PB=100/gain, 200/gain, gain/100 etc. 9. Advantage of PI controller- eliminates offset error. 10. A TF= 10sin6t*e^-10t. Find natural frequency. 11. A TF= 10sin6t*e^-10t. (same TF in both questions) Find damping ratio. 12. A simple question based on Routh Array. 13. AM band=300kHz to 3 Mhz. A signal of 20KHz is modulated by AM. Number of channels=? 4,8,16 etc. 14.Higher fan out of MOS is due to- its high output impedance. 15. The radix point in number system- binary point, decimal point, octal point etc (ambiguous question?_ 16. Logic swing is- 0.2 V, 0.4, 0.6V etc. 17. The clamping diode in TTL gate is ? to reduce negative overshoot, reduce current etc. 18. Advantages of DTL over RTL- 19. Which among the following logic families is more complex? DTL, RTL, I2L etc 20. Voltage and current rating of static thyristor- voltages ranging from 5V to 500V and current from 30A to 1000A. Not sure. 21. Dark current in a photodiode- exponential, linear, etc. 22. Dark current in a photodiode in darkness- doubles every 10C rise in temp, doubles every 1C, etc. 23. Laplace transform of e^-at u(t). 24. F(t)= Cos(100pi*t)+ cos(200pi*t). Required sampling rate? 25. A thyristor is in parallel with a snubber circuit(RC in series). Why is the voltage across the thyristor zero? The options were confusing- one was that snubber prevents dv/dt triggering(which is true, but not the answer to the question). Another option was that the snubber acts as a short circuit. 26. Match the following for generation, detection methods for FM, AM etc. Eg- FM, DSBSC on one side and balanced modulator, reactance modulator, Weaver circuit etc on the other. 27. Unit of admittance. 28. Match the following for units of capacitance, magnetic flux etc. 29. Current gain for a transistor where Ic<IE is given by- Ic/Ie, Ic/Ib, Ie/Ic etc. 30. Reciprocal of ?osculator? circuit is- cloverleaf, and some other weird choices. 31. Phase lag compensator is used to- increase relative stability, increase bandwidth etc. 32. Kirchoffs law is based on ? current density is same in a circuit, current density changes with space etc. 33. Which of the following sensors cannot be used for static measurements?- resistive, capacitive, inductive and piezo sensors. 34. Potentiometers are used for- position measurement. 35. The basic apparatus for measuring pH consists of- reference electrode+battery+ something. 36. Range of non-contact ultrasonic sensor- very close options- .3-180m, .31-18m, .18-30m etc. 37. Arrange the following in increasing order of frequency- visible light, IR, UV 38. Capacitive sensors- miller effect based question. 39. Input impedance of CRO is- M? range 40. Desired characteristics of LASER- monochromatic+ coherent+ high radiant energy 41. Noise is inherently absent in- PAM,PPM,PWM,PCM 42. A galvanometer can be made to read high currents by- connecting a shunt resistance of low value in parallel. 43. Q meter question- whether some parameters? measured value is equal to/ less than/ greater than its true value. 44. A thyristor is used in a boost circuit. Vcc=220A. Vo=660V. Thyristor currents Isc=80A. On time duration = 1.5?s, off time=4 ?s. The power dissipated during this process- options were 3300W,3300W; 800W,800W; 4000W,4000W etc. Unit of Vcc was ?A? itself. Wrong question, i guess. 45. Transistor operating at 25 degree C, forward biased. Which of the following depicts its operation? PBSOA, and three other five letter words, each ending with SOB, SOC and SOD. 46. Peak to peak voltage across a 5.6k,1/4W resistor is displayed on a CRO in 10 divisions where 1 div=50mV. The current across the resistor = ___? 47. Combing current is two nodes is ___? wrong question. Options were ?, 0, ?, v1+v2 48. Sensitivity of an AC voltmeter to an AC voltage is ___ fraction of DC sensitivity. Options- 0.707, 1.414, 0.9 etc 49. The most important parameter in a displacement sensor is- area of the sensing area, area of the sensing probe, strength of magnetic field etc. 50. Given a TF and was asked to find the centroid of root locus plot. 51. Expansion of LASER

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The question paper had a total of 120 questions in which 70 questions were from technical and 50 from aptitude. Duration- 2 hours. A candidate should clear cut-offs for both the sections to get shortlisted. NTPC will decide the cut off after reviewing the questions for errors, receiving feedback from candidates and finally, after evaluating the OMR sheets. The cut off will be such that around four times the number of vacancies will be called. So altogether 2000 people will be shortlisted for the GD/PI process.

Below are some of the questions that I could recollect from Control and Instrumentation paper. Post your feedback and queries, if any.

1. Technique used in telegraphy- On/off keying, fsk etc.

2. TF=10/(s+5)^3. Gain margin in dB.

3. If the point -1 +j0 is encircled, then gain margin=? 0, less than 0, infinity etc.

4. Given a transfer function. Identify zeroes and poles.

5. Response of an RLC circuit to impulse signal is: decaying exponential, parabola etc.

6. LASCR can be turned on by: light only, gate pulse only, either, neither.

7. Transistor SOA is a plot of: Vce vs Ice.

8. Proportional band and proportional gain relation: PB=100/gain, 200/gain, gain/100 etc.

9. Advantage of PI controller- eliminates offset error.

10. A TF= 10sin6t*e^-10t. Find natural frequency.

11. A TF= 10sin6t*e^-10t. (same TF in both questions) Find damping ratio.

12. A simple question based on Routh Array.

13. AM band=300kHz to 3 Mhz. A signal of 20KHz is modulated by AM. Number of channels=? 4,8,16 etc.

14.Higher fan out of MOS is due to- its high output impedance.

15. The radix point in number system- binary point, decimal point, octal point etc (ambiguous question?_

16. Logic swing is- 0.2 V, 0.4, 0.6V etc.

17. The clamping diode in TTL gate is ? to reduce negative overshoot, reduce current etc.

18. Advantages of DTL over RTL-

19. Which among the following logic families is more complex? DTL, RTL, I2L etc

20. Voltage and current rating of static thyristor- voltages ranging from 5V to 500V and current from 30A to 1000A. Not sure.

21. Dark current in a photodiode- exponential, linear, etc.

22. Dark current in a photodiode in darkness- doubles every 10C rise in temp, doubles every 1C, etc.

23. Laplace transform of e^-at u(t).

24. F(t)= Cos(100pi*t)+ cos(200pi*t). Required sampling rate?

25. A thyristor is in parallel with a snubber circuit(RC in series). Why is the voltage across the thyristor zero? The options were confusing- one was that snubber prevents dv/dt triggering(which is true, but not the answer to the question). Another option was that the snubber acts as a short circuit.

26. Match the following for generation, detection methods for FM, AM etc. Eg- FM, DSBSC on one side and balanced modulator, reactance modulator, Weaver circuit etc on the other.

27. Unit of admittance.

28. Match the following for units of capacitance, magnetic flux etc.

29. Current gain for a transistor where Ic<IE is given by- Ic/Ie, Ic/Ib, Ie/Ic etc.

30. Reciprocal of ?osculator? circuit is- cloverleaf, and some other weird choices.

31. Phase lag compensator is used to- increase relative stability, increase bandwidth etc.

32. Kirchoffs law is based on ? current density is same in a circuit, current density changes with space etc.

33. Which of the following sensors cannot be used for static measurements?- resistive, capacitive, inductive and piezo sensors.

34. Potentiometers are used for- position measurement.

35. The basic apparatus for measuring pH consists of- reference electrode+battery+ something.

36. Range of non-contact ultrasonic sensor- very close options- .3-180m, .31-18m, .18-30m etc.

37. Arrange the following in increasing order of frequency- visible light, IR, UV

38. Capacitive sensors- miller effect based question.

39. Input impedance of CRO is- M? range

40. Desired characteristics of LASER- monochromatic+ coherent+ high radiant energy

41. Noise is inherently absent in- PAM,PPM,PWM,PCM

42. A galvanometer can be made to read high currents by- connecting a shunt resistance of low value in parallel.

43. Q meter question- whether some parameters? measured value is equal to/ less than/ greater than its true value.

44. A thyristor is used in a boost circuit. Vcc=220A. Vo=660V. Thyristor currents Isc=80A. On time duration = 1.5?s, off time=4 ?s. The power dissipated during this process- options were 3300W,3300W; 800W,800W; 4000W,4000W etc. Unit of Vcc was ?A? itself. Wrong question, i guess.

45. Transistor operating at 25 degree C, forward biased. Which of the following depicts its operation? PBSOA, and three other five letter words, each ending with SOB, SOC and SOD.

46. Peak to peak voltage across a 5.6k,1/4W resistor is displayed on a CRO in 10 divisions where 1 div=50mV. The current across the resistor = ___?

47. Combing current is two nodes is ___? wrong question. Options were ?, 0, ?, v1+v2

48. Sensitivity of an AC voltmeter to an AC voltage is ___ fraction of DC sensitivity. Options- 0.707, 1.414, 0.9 etc

49. The most important parameter in a displacement sensor is- area of the sensing area, area of the sensing probe, strength of magnetic field etc.

50. Given a TF and was asked to find the centroid of root locus plot.

51. Expansion of LASER