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Mechanical Engineering Objective Questions { Instrumentation and Control }

43. Pick up false statement about liquid-inmetal thermometers :
A.Remote indication of temperature can't be given
B.Error is produced if capillary passes through hot zone
C.Error also occurs if instrument base is at high ambient temperature error can also creep in by the head of the liquid if the bulb is installed either above or below the Bourdon
D.(e) these are used for Industrial applications where accuracy is not so important.

44. Twisting the thermocouple wires together and heat welding them :
A.Is the standard practice of making junction
B.Would result in noise generation
C.Cause small errors du-2; to local e.m.f. which may arise if the junction is too long
D.Would slow down the response

45. Which of the following thermocouple generates highest e.m.f. for a given temperature :
D.Platinum-rhodium platinum

46. Protective coating by a suitable cover are applied over strain gauge in order to protect it against
A.Temperature rise
B.Dust and dirt

47. The resistance of strain gauge grid used in pressure transducers is of the order of
A.0.1 to 1 ohm
B.1 to 10 ohm
C.10 to 100 ohm
D.100 to 2000 ohm

48. During temperature changing conditions, quite appreciable difference, occurs between the -true-temperature and the measured temperature because of the time required for the transfer of heat through thermometer pockets (thermowells) to thermometer sensing element. This time lag is of the order of :
A.0.1 to 1 sec
B.1 to 2.5 sec
C.2.5 to 10 or 20 sec
D.25 to 100 sec

49. Pick up false statement :
A.Copper-constantan thermocouple is a stable couple resistant to both oxidising and reducing atmosphere, but needs protection from acidic vapours
B.Copper-constantan thermocouple is used as a reference standard for calibration purposes.
C.Iron-constantant couple can be made stable by using enamelled iron
D.Both wires of chromel-alumel thermocouples are prone to damage by sulphurous gases

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