. The Bell System technical journal . conductor and ground, which was provided by thewater. A capacitance-conductance bridge was used for this purpose. Thecapacitance limits set initially were from to microfaradsper mile at 75°F. Analysis of the core measurements indicates that ateach factory the range of capacitance was held more closely than indi-cated, which illustrates the benefits of servo control to the insulatingprocess. The dc insulation resistance of the core was also measured by applying500 volts for one minute. A minimum insulation resistance requirementof 100,000 mego
. The Bell System technical journal . conductor and ground, which was provided by thewater. A capacitance-conductance bridge was used for this purpose. Thecapacitance limits set initially were from to microfaradsper mile at 75°F. Analysis of the core measurements indicates that ateach factory the range of capacitance was held more closely than indi-cated, which illustrates the benefits of servo control to the insulatingprocess. The dc insulation resistance of the core was also measured by applying500 volts for one minute. A minimum insulation resistance requirementof 100,000 megohm-miles at 75°F was established, but any lengths thathad less than 500,000 megohm-miles were scrutinized for possible sourcesof trouble and were subject to rejection. As a general rule, insulationresistances considerably in excess of 500,000 megohm-miles were ob-tained. The core was tested also at a voltage of 90,000 volts dc for a periodof one minute. This test was designed to catch any gross faults in the SPRING-LOADEDELECTRODES. RECORDER Fig. 9 — SimpUfied block diagram of concentricity gauge for continuous meas-urement of centering of central conductor. CABLE DESIGN AND MANUFACTURE 211 core caused by foreign particles which escaped detection by the othermechanical and electrical tests made on the core. As discussed under the section on jointing, the core lengths were as-sembled and joined together to form a repeater section of cable. Ingeneral, an effort was made to produce the core for a repeater sectionof cable on a particular strander, extruder, and armoring line, and tojoin the lengths together in the order of manufacture. Practical difficul-ties such as the fact that the outputs of two stranders were required tosupply one extruder made it impossible to achieve this objective in allcases. Capacitance deviations from the desired nominal resulted from avariety of causes, such as inaccurate control of the temperature of thewater in the core cooling troughs and imprope
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