01․ Which one of the following meters has maximum loading effect on the circuit under measurement ?
Maximum loading effect takes place due to low sensitivity of the instrument.
02․ The inductance of a certain moving iron ammeter is expressed as L = 2+5θ-θ2 µH. The control spring torque is 2 × 10-6 Nm/radian. Find the deflection in radians for a current of 2A.
The deflecting torque of a moving iron instrument (T) = 0.5I2dL/dθ. I = 2A; T = 2 × 10-6 Nm/radian; dL/dθ = 5-2θ µH; So, 5-2θ = 1; θ = 2.
03․ A variable w is related to three other variables x, y and z as w = xy/z. The variables are measured with meters of accuracy ± 0.5% reading, ± 1% of full scale value and ± 1.5% reading. The actual readings of the three meters are 80, 20 and 50 with 100 being the full scale value for all three. The maximum uncertainty in the measurement of w will be
04․ Assertion (A) : It is always desirable to take the reading of an indicating instrument very close to the full scale reading. Reason (R) : Accuracy of an indicating instrument is maximum at the full scale deflection and error increases as reading comes closer to the beginning of the scale.
Accuracy of an indicating instrument is maximum at the full scale deflection and error increases as reading comes closer to the beginning of the scale.