1-29
meters indicate smaller amounts of voltage. Since most voltage measurements involve voltage larger than
.1 volt, a method must be used to extend the voltage reading.
Figure 1-28 illustrates the method of increasing the voltage range of a voltmeter.
Figure 1-28.—A voltmeter and a range resistor.
In figure 1-28(A), a voltmeter with a range of 10 volts and a resistance of 1 kilohm (R2) is connected
in parallel to resistor R1. The meter has .01 ampere of current (full-scale deflection) and indicates 10
volts. In figure 1-28(B), the voltage has been increased to 100 volts. This is more than the meter can
measure. A 9 kilohm resistor (R3) is connected in series with the meter (R2). The meter (R
2) now has .01
ampere of current (full-scale deflection). But since R3 has increased the voltage capability of the meter,
the meter indicates 100 volts. R3 has changed the range of the meter.
Voltmeters can be constructed with several ranges by the use of a switch and internal resistors.
Figure 1-29 shows a voltmeter with a meter movement of 100 ohms and 1 milliampere full-scale
deflection with 5 ranges of voltage through the use of a switch. In this way a voltmeter can be used to
measure several different ranges of voltage.
