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If PMMC meter have internal resistance of 10Ω and full scale range of 1mA. Assume we wish to increase the meter range to 1A. Calculate internal resistance.
Ans: 0.01001Ω
2. Design an Ayrton shunt by indirect method to provide an ammeter with current ranges 1A, 5A, and 10A, if PMMC meter have internal resistance of 50Ω and full scale current of 1mA.
Ans: 1A Range, R=0.05005Ω
5A Range, R= 0.04004 Ω
10A Range, R= 5.005 x 10^-3 Ω
3. Design a multirange ammeter to provide an ammeter with a current range of 0-5mA, 0-25 mA and 0-50 mA. A D’Arsonval meter movement with an internal resistance of 70Ω and full scale current of 100 uA.
ans: R1 = 1.43Ω, R2 = 0.281Ω, R3 = 0.14Ω
4. A PMMC instrument has a three-resistor Ayrton shunt connected across it to make an ammeter. The resistance values are R1 = 5.0Ω, R2 = 0.50Ω and R3 = 0.1Ω.
The meter has Rm = 1kΩ and I f.s.d = 50μA. Calculate the three ranges of the ammeter.
ans: I1 = 8.99mA, I2 = 83.8mA, I3 = 0.5A
5. As a DC voltmeter, a simple D' Arsonval movement with a full-scale deflection of 26 µA and an internal resistance of 250Ω is utilized.
Calculate the multiplier resistance required to measure a voltage range of 0 to 20V.
(hint: got 2 method of solution)
Ans: 799.75kΩ
6. Transform a basic D’ Arsonval movement with an internal resistance of 100Ω and a full scale deflection current of 1mA into a multirange DC voltmeter with voltage ranges of 015V and 0-50V.
Ans: R1=14.9kΩ, R2=35kΩ
7. Two different voltmeters are used to measure the voltage across R, in the circuit. The meters are as follows:Meter 1: S=1 k/V, Rm = 0.2ks, range 10VMeter 2: S = 20 kV, R = 1.5k, range 10 V
Calculate:
i. Voltage across R, without any meter across it (ans: 5V) ii. Voltage across R, when meter 1 is used (ans: 3.53V)iii. Voltage across R, when meter 2 is used (ans: 4.9V)iv. Error in the voltmeters (ans: 29.4%, 2%)
Calculate:
i. Voltage across R, without any meter across it (ans: 5V) ii. Voltage across R, when meter 1 is used (ans: 3.53V)iii. Voltage across R, when meter 2 is used (ans: 4.9V)iv. Error in the voltmeters (ans: 29.4%, 2%)
8. Figure shows a simple series circuit of R1 and R2 connected to a 100Vdcsource. If the voltage across R2 is to be measured by voltmeters having
a) a sensitivity of 1000 Ω/Vb) a sensitivity of 20000 Ω/V
find which voltmeter will read the accurate value of voltage across R2.Both meters are used on the 50 V range.
a) a sensitivity of 1000 Ω/Vb) a sensitivity of 20000 Ω/V
find which voltmeter will read the accurate value of voltage across R2.Both meters are used on the 50 V range.
9. An an instrument engineer, you are required to design an ohmmeter. Therefore, specify at least 3 scales to be marked on the meter face. Sketch the meter face by marking the scales. The specified specifications are indicated as in Table 1 below:
(answer: Rx=9kΩ, 3kΩ, 1kΩ, 0)
10. In the circuit above, a 2 mA meter movement with an internal resistance, Rm of 100Ω is to be used. The battery voltage is 10V. Its half-scale defelction is 3000Ω.
a) Calculate the values of R1 and R2. (ans: R1= 2940Ω, R2= 150Ω)
b) Find the change in R2 if the battery voltage drops by 15%. (ans: from 150Ω to 171.43Ω)
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