Simulating non-ideal multimeters: revisiting the ammeter–voltmeter method

Abstract

The ammeter–voltmeter method is a classic approach for determining electrical resistance, widely used in educational and laboratory contexts. However, it may be presented under idealized assumptions that disregard the internal resistance of measuring instruments. This simplification, frequently found in both textbooks and circuit simulators, can lead to inaccurate measurements and overlook important experimental considerations. To address this gap, this study investigates how the internal resistance of voltmeters and ammeters affects resistance measurement accuracy and how virtual instruments can be adapted to more realistically emulate physical laboratory conditions. Using Tinkercad, we characterized the internal resistance of the simulator’s default virtual multimeters and implemented modifications to simulate quasi-real multimeters with internal resistance. These modified instruments were applied in several configurations of the ammeter–voltmeter method to evaluate their influence on the measurement of resistors of varying magnitudes. Results show that measurement accuracy is highly sensitive to the configuration used and to the relationship between the internal resistances of the instruments and the unknown resistor. Conditions were identified under which each setup provides accurate or distorted results, including cases where either current division or additional voltage drops lead to systematic errors. This work indicates the importance of modeling instrument limitations, even in virtual environments, to better represent the complexity of real-world measurements. The proposed simulation approach may be particularly useful in scenarios with limited laboratory access or as a tool to prepare for or reflect upon physical experiments.