voltmeter

An instrument for measuring electric potential differences in units of volts.

An electrometer, or a high-resistance galvanometer, or a galvanometer combined with a resistance calibrated so that its indications show the number of volts E. M. F. in the circuit between its terminals. The cut shows one form of volt-meter, for the construction of which see ampere-meter.

It is a direct-reading instrument for the measurement of difference of potential between two points in an electric circuit, as between the terminals of a generator, battery, or electric lamp, or between the mains of a distributing circuit. Voltmeters for use on direct-current circuits are frequently strong-field galvanometers of high resistance, in which case the difference of potential between their terminals is proportional to the current flowing in the voltmeter circuit and is measured by the deflection of a coil suspended in a fixed magnetic field, or sometimes by the movement of a magnet in the field of a fixed coil. Various special forms of electrodynamometer are also used as voltmeters and such instruments are applicable alike to direct and to alternating-current circuits. In cases where it is preferable to have no flow of current in the voltmeter circuit, electrostatic voltmeters are employed. These are usually modifications of the quadrant electrometer of Lord Kelvin, in which a pointer attached to the needle of the instrument moves over a calibrated, direct-reading scale. Electrostatic voltmeters are equally serviceable on direct-and on alternating-current circuits and are especially adapted to measuring high voltages, from 1,000 to 20,000 volts.

An instrument for measuring in volts the differences of potential between different points of an electrical circuit.

An instrument for measuring electric potential in volts.

meter that measures the potential difference between two points