# Measurement and Instrumentation

Measurement and Instrumentation
Question:-
Option (A)
Ohmmeter
Option (B)
A series type ohmmeter
Option (C)
A shunt type ohmmeter
Option (D)
A voltmeter and an ammeter
Correct Option:
D
Question:-
Option (A)
1, 2, 3 and 4
Option (B)
2, 3 and 4
Option (C)
1 and 2
Option (D)
1, 3 and 4
Correct Option:
A
Question Solution:
The resistance of earth electrode should be low to give good protection. An earth electrode will only be effective so long it has low resistance to the earth and can carry large currents without deteriorating
Question:-
Option (A)
1 and 2
Option (B)
2 and 3
Option (C)
3 and 4
Option (D)
1 and 3
Correct Option:
D
Question Solution:
. Thermo-couple instrument has a “square-law response” so it does not have a linear scale
. Their accuracy can be as high as 1% for frequency up to 50 MHz and can be classified as RF instruments. Above this frequency the effective resistance of heater wire is increased on account of skin effect thereby reducing the accuracy. Tubular designs are used for heater wire above 3A to reduce errors on account of skin effect produced by high frequencies. For small currents up to 3A, the heater wire is solid and very thin.
. At normal rated current, the heater attains a temperature of 300°C. if we pass twice the rated current, the heater would give a temperature of nearly 4 times the normal temperature i.e. 1200°C. it is obvious that square law rate will bring the heater to nearly its burn out temperature thus it is imperative that the heater be protected against damaging over loads. The fuses do not provide any protection as due to overload the heater wire may burn out before fuse blows out. Thus the overload capacity of thermocouple instruments is small as compared with other instruments and is about 150 percent of the full scale current
Question:-
Option (A)
It provides deflection of the beam
Option (B)
It increases the brightness of the trace if the signal frequency is higher than 10 MHz
Option (C)
It accelerate the beam before deflection
Option (D)
It increases the brightness of the trace of low frequency signal
Correct Option:
B
Question Solution:
In an electrostatic system of deflection a low value of accelerating voltage (Ea) should be used to give high deflection sensitivity [Sa(1/Ea)}.
This voltage is usually kept below 4kV. Although this voltage gives god senility but reduces brightness, which can be seriously impaired at high frequencies If signals of frequencies higher than 10 MHz are to be displayed , post deflection acceleration is necessary to increase the brightness of the trace which otherwise would be dim