. The Bell System technical journal . the wire is tied, thedirection of winding reversed, and an exactly equal number of turnswound over the first 14, but in an opposite direction. This brings thewire to the beginning. It is again tied, carried parallel to the axisof the spool over this first section and a second section wound. Thisis continued until ten sections have been applied. A thin sheet ofmica is tied in place around the winding and the projecting ends of thewire bared of insulation. The whole is then baked to anneal the wireand dry the insulation. While hot, it is dipped several times
. The Bell System technical journal . the wire is tied, thedirection of winding reversed, and an exactly equal number of turnswound over the first 14, but in an opposite direction. This brings thewire to the beginning. It is again tied, carried parallel to the axisof the spool over this first section and a second section wound. Thisis continued until ten sections have been applied. A thin sheet ofmica is tied in place around the winding and the projecting ends of thewire bared of insulation. The whole is then baked to anneal the wireand dry the insulation. While hot, it is dipped several times in moltenasphalt compound until a continuous coating of this moisture-proofmaterial has been formed over the winding and surrounding micawrapping. Adjustment for resistance balance is made by varying thelength of the two wire ends. The effective reactances of coils made as above are positive beforeassembly in their shields. The effect of the shield is to increase thecapacitance. Table II gives data obtained on the two coils made for. Fig. 12—Ratio arms the bridge and shows the uniformity of phase-angle difference main-tained by these coils over the operating frequency range. Finaladjustment for reactance balance is made with the coils in the bridgecircuit, a small amount of inductive coiling of the terminal leadssufficing for this purpose. In establishing this balance, use is madeof the reversing switch described in the following section. Fig. 12shows these coils assembled in their shields. 160 BELL SYSTEM TECHNICAL JOURNAL TABLE IIEffective Inductance of Ratio Arm Coils Microhenrys Test Frequency Before Coating After Coating Assembled in Shield Coil A Coil B Coil .4 Coil B Coil A Coil B 1,000 cycles 50,000 cycles - - - - Resistance of each coil = ohms Reversing Switches. As will be noted from the diagram showingthe circuit arrangement of the reversing switches, these are requiredto be completely enclosed in a shield which
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
