Analog Voltmeter Design
Given Figure (a) shows a voltmeter circuit consisting of a D'Arsonval meter, two series resistors, and a twoposition selector switch. A current of IFS = 400 μA produces full-scale deflection of the D'Arsonval meter, whose internal resistance is RM = 25 Ω.
(a) Select the series resistance R1 and R2 so that a voltage vx = 100 V produces full-scale deflection when the switch is in position A, and voltage vx = 10 V produces full-scale deflection when the switch is in position B.
(b) What is the voltage across the 20-kΩ resistor in Figure (b)? What is the voltage when the voltmeter in part (a) is set to position A and connected across the 20-kΩ resistor? What is the percentage error introduced connecting the voltmeter?
(c) A different D'Arsonval meter is available with an internal resistance of 100 Ω and a full-scale deflection current of 100 μA. If the voltmeter in part (a) is redesigned using this D'Arsonval meter, would the error found in part (b) be smaller or larger? Explain.