A device that measures voltage. Voltmeters in common use include digital voltmeters, cathode-ray oscilloscopes, and d.c. instruments (such as permanent-magnet moving-coil instruments).
In order to provide the minimum disturbance in the circuit containing the voltage to be measured, voltmeters are required to pass very little current and therefore require a very high input impedance. Digital voltmeters, cathode-ray oscilloscopes, and the now little used valve voltmeter comply with this requirement. A large series resistance however is required in the case of the moving-coil voltmeter and the electrostatic voltmeter in order to increase their input impedances. The electrostatic voltmeter is a voltmeter based upon the principle of operation of a quadrant electrometer or other type of electrometer.