1) An ammeter as in Figure 1 has a PMMC instrument with a coil resistance of Rm = 99Ω and f.s.d current of 0.1mA. Shunt resistance Rs = 1Ω. Determine the total current passing through the ammeter at a) f.s.d, b) 0.5 f.s.d, c) 0.25 f.s.d

Ans: [10mA, 5mA, 2.5mA]

3) An ammeter is connected to measure the current in a 10Ω load supplied from a 10V source as in Figure 2. Calculate the circuit current if the ammeter resistance Rs is :

a) 0.1Ω

b) 1.0Ω

Also in each case, calculate the effect of the ammeter on the current level.

Ans: [0.99A, 1.0%, 0.909A, 9.1%]

4) A PMMC instrument with a f.s.d of 100μA and a coil resistance of 1kΩ in Figure 3 to be converted into a voltmeter. Determine the required multiplier resistance if the voltmeter is to measure 100V at full scale. Also calculate the applied voltage when the instrument indicates 0.75, 0.5 and 0.25 f.s.d.

Ans: [999kΩ, 75V, 25V]

5) A PMMC instrument with a f.s.d of 50μA and Rm = 1700Ω to be employed as a voltmeter with range of 10V, 50V and 100V. Calculate the required values of multiplier resistors for the circuits of Figure 4(a) and Figure 4(b).

Ans: [a)198.3kΩ, 998.3kΩ, 1.9983MΩ, b)198.3kΩ, 800kΩ, 1MΩ]

6) A voltmeter on a 5V range is connected to measure the voltage across R2 = 50kΩ in the circuit shown in Figure 5 given R1 = 70kΩ. Calculate VR2

a) without the meter connected

b) with a voltmeter having a sensitivity of 20kΩ/V

c) with a voltmeter having a sensitivity of 200kΩ/V

Ans: [5V, 3.87V, 4.86V]