Voltmeter

A voltmeter is an instrument used to measure the electrical potential difference, or voltage, between two points in an electrical circuit. To avoid altering the circuit, it is connected in parallel with the element under test. An ideal voltmeter has infinite input impedance, meaning no current is drawn from the circuit; real meters have finite but typically high input resistance to minimize loading errors.

There are two main types of voltmeters: analog and digital. Analog voltmeters use a galvanometer with a calibrated series resistor network to extend the range. The current through the galvanometer is proportional to the voltage across the test points, and the pointer deflection is read from a scale. Digital voltmeters convert the input voltage to a digital value using an analog-to-digital converter and display it as a numeric readout. Digital meters generally provide higher accuracy and easier reading, and often offer higher input impedance through buffering.

AC and DC voltmeters differ in handling alternating or direct currents. DC voltmeters display the instantaneous or average voltage, while AC or true-RMS voltmeters measure the effective voltage of an alternating signal. Some meters are true-RMS capable, while others are average-responding and require a conversion.

Applications include testing power supplies, components, and circuits, troubleshooting, and validating implementations in electronics labs and industry. Typical voltage ranges span from millivolts to kilovolts, with appropriate safety and isolation considerations. Calibration and specification adherence are important for accuracy, and meters may include additional features such as auto-range, data logging, and input protections.