GB317642A - Improvements in apparatus for the measurement of the capacitance and power factor of electrical condensers - Google Patents

Abstract

317,642. Campbell, A. Aug. 23, 1928. Capacities and power-factors, measuring; sets of resistances and inductances.-Capacitance and condenser power factor are measured by means of a modified Care Foster bridge in which no external resistance is added in the arm containing the condenser under test. As shown in Fig. 2, the four arms of the bridge include resistances P, Q, R, s, self-inductances L, l, a mutual inductance M, and the condenser C to be tested, of which s represents the internal losses. For small power-factors balance is obtained by adjusting the resistances P, Q, R. For large power-factors the inductances L, l may be adjusted. The resistance Q may be calibrated to read the power-factor directly. If the resistance P is kept constant, the capacitance C is proportional to the reciprocal of the resistance R, which may be arranged as a conductance box so as to be direct reading. In the modification shown in Fig. 3 the resistance Q is formed as a slide wire with its zero at E, the portion H corresponding to negative values. A small variable resistance JX may be included to compensate for the variation of the arm R. In a further modification the arm Q is dispensed with and balance is obtained by 'varying one or both of the resistances P, R and also one or both of the inductances L, l, In order to permit continuous variation of the inductance l from negative values through zero to its maximum positive value a variable self-inductance of constant resistance X, Fig. 2, is included in the arm R and is shown in Fig. 6. Two inductances a, b are arranged at right angles so as to have no mutual inductance, or they may consist of toroidal windings or by winding each set of sections on a pair of equal bobbins in opposite directions so as to be astatic. The inductances a, b have tappings brought to stud switches A, B through sets of resistances p, q of such values that the resistance of the whole circuit is constant for all positions of the switch arms. Alternatively the sections a, b may consist of sets of independent coils connected together at one end and having their other ends connected to the studs. A fixed inductance and a slide wire r are arranged in series with the coils a, b, a variable portion of the slide wire r being shunted by a condenser k. The slide wire r may be calibrated to read self-inductance directly. For high sensitivity the detecting instrument may be connected to the bridge through a thermionic valve amplifier. The positions of the detecting instrument and the source may be interchanged.