GB641498A - Improvements relating to electrical bridge networks - Google Patents

Abstract

641,498. Bridge circuits for measuring. COSSOR, Ltd., A. C., and WHITELEY, J. W. Oct. 31, 1947, No. 29126. [Class 37] A bridge has two arms 1, 2, Fig. 2, consisting of coupled coils, the third and fourth arms Z1, Z2 being connected between the ends of the arms 1, 2, as shown ; the stray capacitance between A and earth is in shunt with the input across Z4 and so introduces no error, while at balance, the point B is at earth potential and again stray capacitance between B and earth produces no error. The unknown impedance Z1, Fig. 3, may be connected to the bridge by screened leads 15, 16 ; the supply to the bridge is applied at terminals 6, 7; the bridge may be enclosed in an earthed screen; it is shown that variations in impedances Z3, Z4 have no effect at balance. Where the reactance of conductor 15 and the resistance of the screens 17, 18 are not low enough to render the variations of Z3, Z4 of no significance, condensers 20, 21 are inserted as shown in Fig. 4. As shown in Fig. 5, a capacitance 38 mounted on a rotating shaft (not shown) is coupled by slip-rings to a screened cable to the bridge comprising coupled coils 1, 2 and balancing capacitance 22 in shunt with any one of fixed capacitances 23 ... 25 ; the input is applied at 6, 7 and the output is taken from 50, 51 ; a resistance 42 balances quadrature voltage across 12, 13 due to the resistance of the screens 17, 18; condenser 44 is adjusted to compensate for any difference between the power-factor of 38 and 22 (with 23 ... 25) ; calibration is performed with variable condenser 29.