Volt

VOLT, the practical unit used for measuring potential differences (electrical). 1 V is equal to 10⁸ absolute electromagnetic units (CGSM) of potential, or 1/300 of an absolute electrostatic unit (CGSE). Such is, approximately, the potential difference between the electrodes of a copper-zinc cell. Voltammeter, an instrument that served to determine the quantity of electricity passed when modern instruments allowing the measurement of current strength and the quantity of electricity were not yet known. The voltammeter consists of a vessel with two electrodes immersed in a solution of silver or copper salts. The current to be measured is passed through this solution. Voltmeter, an instrument for measuring electrical voltage between two points of an electrical circuit. It is mostly a recalibrated ammeter (see), with a winding having as large a resistance as possible and therefore made of significantly thinner wire. The following types of voltmeters are distinguished: 1) a moving-coil voltmeter with a permanent magnet (suitable only for direct current); 2) a moving-iron (electromagnetic) voltmeter with a flat or round coil (suitable for direct and alternating currents); 3) an electrodynamic voltmeter (suitable for direct and alternating currents); 4) a thermal voltmeter (suitable for...

high frequencies); 5) an induction voltmeter with an electromagnetic shield and a rotating field (suitable only for alternating current of a certain frequency). - The connection of a voltmeter into a circuit is fundamentally different from the connection of an ammeter. The figure shows the connection diagram for both instruments, where the letter V designates the voltmeter, the letter A the ammeter, and the letter r the electrical energy receiver. As can be seen, the voltmeter is connected in parallel with the receiver r, and the ammeter in series with it. - In addition to the instruments listed above, which are essentially recalibrated ammeters, the following are also used: 6) an electrostatic voltmeter, based on the attraction between the movable and fixed plates of a capacitor, between which the measured voltage or a part of it is established (suitable for direct and alternating current and are the sole type of instrument used in the direct measurement of high voltages - up to 300 kV); 7) a thermoelectric voltmeter, used for very low alternating current voltages. - A voltmeter is usually built for small voltage ranges (from 30 to 120 V), with the exception of electrostatic voltmeters; to increase the measurement range, 1) additional resistances and 2) voltage instrument transformers are used.