. Electric railways, theoretically and practically treated . hod employs a potentiometer, consisting primarilyof a standard resistance box containing resistances whosevalues in ohms have been very accurately resistances usually have a negligible temperatureco-efficient. In conjunction with this box a standard cell, asensitive galvanometer having a small period of vibrationand a source of constant form the complete poten-tiometer testing set. ELECTRICAL MEASUREMENTS. 271 A convenient form of potentiometer is that manufac-tured by Hartmann and Braun of Germany and standar
. Electric railways, theoretically and practically treated . hod employs a potentiometer, consisting primarilyof a standard resistance box containing resistances whosevalues in ohms have been very accurately resistances usually have a negligible temperatureco-efficient. In conjunction with this box a standard cell, asensitive galvanometer having a small period of vibrationand a source of constant form the complete poten-tiometer testing set. ELECTRICAL MEASUREMENTS. 271 A convenient form of potentiometer is that manufac-tured by Hartmann and Braun of Germany and standardizedby the German Standardization Bureau, the Reichsanstalt,This box contains single resistances of a range of i ohm to40,000 ohms. With the potentiometer method, the of a standard cell is balanced against an external throughthe medium of a common resistance. Both sources connected to this resistance, Fig. 169, in such amanner that both will produce the same distribution ofvoltage. A galvanometer placed in series with the stand-. ard cell indicates by a zero deflection when a balanceoccurs. A convenient unit of resistance to employ is1,000 ohms per volt, producing a distribution of voltage ofI volt for each 1,000 ohms included. The method of pro-cedure with a potentiometer is as follows: The standard cell is provided with a thermometer, givingthe temperature of its electrolyte and an accompanyingscale indicating the voltage for all reasonable working tem-peratures. Consulting the thermometer and scale, thevoltage of the cell to four decimal places is , as an example, that the voltage is volts. 2/2 ELECTRIC RAILWAYS. By arrangement of the Hartman and Braun potenti-ometer box, the standard cell may be connected m serieswith a galvanometer through a two-point switch. Oneswitch contact point places 100,000 ohms in series withthe galvanometer, and the second contact point eliminatesthis resistance from the circuit. Referring to the
Size: 2034px × 1229px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublishernewyorkvannostrand
