Multiple Range Voltmeters

The simplified voltmeter in Figure 145 has only one range (1 volt), which means that it can measure voltages from 0 volts to 1 volt. In order for the meter to be more useful, additional multiplier resistors must be used. One resistor must be used for each desired range.

For a 50μA movement, the total resistance required is 20 k Ω for each volt of full scale reading. In other words, the sensitivity for a 50μA movement is always 20 k Ωr egardless of the selected range. The full-scale meter current is 50μA at any range selection. To find the total meter resistance, multiply the sensitivity by the full scale voltage for that particular range. For example for a 10 volt range, RT = (20k Ω/V)/(10 V) = 200k Ω.T he total resistance for the 1 volt range is 20k Ω,s o RM for a 10 V range will be 200k Ω− 20k Ω = 180k Ω. This two-range voltmeter is illustrated in Figure 146.