Voltmeter:

A simple DC voltmeter could be constructed through placing a resistor (RS), known as a multiplier, within series with the ammeter meter movement, and marking the meter face to read voltage display in the figure. Voltmeters are linked in parallel along with the load (RL) being measured.

Figure: Simple DC Voltmeter

Whenever constructing a voltmeter, the resistance of the multiplier has to be determined to measure the desired voltage. By the Equation(14-1)   is a mathematical representation of the voltmeter's multiplier resistance.

 V    =   I_mR_s + I_mR_m

I_mR_s =V - I_mR_m

R_s = V/I_m -R_m                                                                                 (14-1)

where

V      =   voltage range desired

I_m    =   meter current

R_m   =   meter resistance

R_s    =   multiplier resistance or series resistance