Mechanical Engineering Objective Questions { Instrumentation and Control }

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50. Automatic cold junction compensation in thermocouple is provided by :

A. Connecting thermocouple wires, in opposition

B. A nickel wire resistance in series with a manganin resistance

C. Maintaining cold junction temperature constant by a cooling unit

D. Using a photovoltaic cell

51. The material used for resistance temperature sensor is :

D. Any one of above

52. To prevent self-heating errors becoming too great, the current through platinum element (100 ohm) is kept at a very small value :

53. In calibration of temperature sensors by fixed point method, the device is calibrated at :

A. Ice point (0?C)

B. Steam point (100?C)

C. Sulphur point (444.6?C)

D. All of the above

54. Pick up correct statement about calibration of temperature sensors by comparison method using liquid bath :

A. Water is used for temperatures from 0 to 100?C

B. Special grade of paraffin oil is used for temperatures between 100 and 200?C

C. For temperature between 200 and 600?C, a mixture of sodium nitrate and potassium nitrate is used

D. All of above are true

55. Local velocity is measured by a:

B. Venturi tube

C. Orifice plate

D. (a) vena contracta device

56. Flange taps in case of orifice plate are installed:

A. 25 mm from each side of the orfice plate

B. D (pipe diameter) upstream and D/2 downstream

C. Just at surface of orifice plate

D. 2.5 D upstream and 8 D downstream

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