. Effective resistance and inductance of iron and bimetallic wires . quencies of50 or 100 cycles per second or alow resistance telephone for thehigher frequencies. The cur-rent for the bridge was sup-plied by two generators, one for50 and I GO cycles and the otherfor frequencies from 500 to3000 cycles. These machineswere run by storage 12 to I or 24 to I step-downtransformer of 600 watts ca-pacity was used to reduce thevoltage on the bridge and toincrease the available current. The current in the bridge was readby Hartmann and Braun hot-wire ammeters of i, 5, and 10 amperesrange. A
. Effective resistance and inductance of iron and bimetallic wires . quencies of50 or 100 cycles per second or alow resistance telephone for thehigher frequencies. The cur-rent for the bridge was sup-plied by two generators, one for50 and I GO cycles and the otherfor frequencies from 500 to3000 cycles. These machineswere run by storage 12 to I or 24 to I step-downtransformer of 600 watts ca-pacity was used to reduce thevoltage on the bridge and toincrease the available current. The current in the bridge was readby Hartmann and Braun hot-wire ammeters of i, 5, and 10 amperesrange. A variable resistance p was introduced into the bridge inseries with the condenser C for the following purpose: The balance ofan ideal Anderson bridge—that is, a bridge made up of completelynoninductive resistances, perfect condenser, etc.—is independent ofthe frequency and the equations for balance when P=--R, are L=CS (R + 2r)S-Q = o In an actual bridge, however, the resistance coils have residualinductance and the condenser is absorbing. On this account, the. Transformer ?^ Fig. 12,—Anderson bridge 238 Bulletin of the Bureau of Standards [ bridge balance at high frequencies and especially the resistancebalance, will change considerably with the frequency. In a bridgesuch as that used in this work where the range of balance is some-what limited, even though no error may be introduced, consider-able changes in balance with the frequency are inconvenient. If we assume the residual inductance I3 in P and in i^, I4 in 5and I5 in r and a resistance p in series with a perfect condenser C,the equation^^ which gives the condition for a resistance balancemay be brought into the form S-Q=pC[{R^-2r)\,-\-S\,-\-2S\,-Lp\ neglecting smaller terms. In a low-resistance bridge the residual inductances are positiveand the factor within the brackets can be reduced to zero by aproper choice of p. The resistance balance of the bridge thenbecomes independent of the frequency. However, th
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