NUMERICAL SHEET 1

ANALOG INSTRUMENTS: MEASUREMENTS

1. A moving coil instrument has the following data: No. of turns = 100, width of coil = 20mm, depth

of coil = 30mm, flux density in the gap = 0.1Wb/m². Calculate the deflecting torque while

carrying a current of 10mA. Also calculate the deflection of the control spring constant is

2x10^-6Nm/degree. (60x10^-6Nm, 30°)

2. The following data refers to a moving coil voltmeter.

Resistance, 10000Ω ; Dimensions of coil, 30mmx30mm; No. of turns on coil, 100; flux density in

gap, 0.08Wb/m²; spring constant, 3x10^-6Nm/degree. Find the deflection produced by a voltage

of 200V. (48°)

3. The wire of a moving coil voltmeter is 40mm long and 30mm wide and has 100 turns on it. The

control spring exerts a torque of 240x10^-6 Nm when the deflection is 100 divisions on full

scale. If the flux density of the magnetic field in the air gap is 1.0 Wb/m². Estimate the resistance

that must be put in series with the coil to give 1 v/div. The resistance of the voltmeter coil may

be neglected. (50kΩ)

4. Find the multiplying power of a shunt of 200Ω resistance used with a galvanometer of 1000Ω

resistance. Determine the value of shunt resistance to give a multiplying factor of 50.

(20.4Ω)

5. A moving coil ammeter has a fixed shunt of 0.02Ω. With a coil resistance of R = 1000Ω and a

potential difference of 500mV across it, full scale deflection is obtained.

A. To what shunted current does this correspond?

B. Calculate the value of R to give full scale deflection when shunted current I is 10A, 75A.

C. With what value of R is 40% deflection obtained with I = 100A.

( <A>0.5mA, <B>400Ω,3000Ω, <C>10000Ω).

6. The coil of a measuring instrument has a resistance of 1Ω, and the instrument has a full scale

deflection of 250 V when a resistance of 4999Ω is connected in series with it. Find

A. The current range of the instrument when used as an ammeter with the coil connected across

a shunt of 1/499Ω. (25A)

B. The value of the shunt resistance for the instrument to give a FSD of 50A. (0.001001Ω)

7. Design a multi-range ammeter with ranges of 1A, 5A, 25A and 125A employing individual shunts

in each case. A d’Arsonval movement with an internal resistance of 730Ω and a full scale current

of 5mA is available. (3.67Ω, 0.73Ω, 0.146Ω, 0.0292Ω)

8. In the circuit, it is desired to measure the voltage across 10kΩ resistance. If a multimeter of

sensitivity 4kΩ/volt and range 0-10V is used for the purpose, what will be the reading?

(8.88V)

9. In the circuit shown in fig2, find the voltage at points A, B,C and D.

A. before the meter is connected and

B. after the meter is connected.

Explain why the meter readings differ from those without the meter connected.

(100V, 80V, 60V, 30V; 100V, 63V,42.8V, 22.2V)