Voltmeter

Test Instruments & Measuring Devices VOLTMETERS The accuracy of a voltmeter (K_v) is defined as the ratio of measured voltage when the meter is in the circuit (V_w) to the voltage measured with the meter out of the circuit. Equation (14-2) is a mathematical representation of the accuracy of a voltmeter, or true voltage (V_o). (14-2) K_v V_w V_o Meter accuracy can also be determined by comparing the relationship between the input and circuit resistances using Ohm’s Law as described below. K_v V_w V_o V_w I_mR_in I_mR_in V_o I_m V_o R_o R_in � � � � � � � � V_o R_in R_o R_in V_o K_v R_in R_o R_in where I_m = meter current V_o = true voltage R_o = circuit resistance R_in = input resistance of the voltmeter K_w = indicated voltage K_v = meter accuracy Rev. 0 Page 7 ES-14