Continuous Incremental Thickness Measurements of Non-Conductive Cable Sheath

1.1 The New Cable A type of telephone cable has been developed in which lead is replaced with a polyethylene sheath extruded over a metal jacket. Since description of various aspects of this development can be found in the technical literature, 1 ' 2 ' 3 ' 4 only some details of the cable construction and production that are pertinent to the understanding of the new measuring system, will be briefly outlined here. The cable core, Fig. 1, is covered with a thin layer of a highly conductive metal, such as aluminum,1 or two layers of different metals, such as aluminum and steel,2, 5 sealed longitudinally. To achieve the desired 353 354 T H E B E L L SYSTEM TECHNICAL J O U R N A L , MARCH 1 9 5 4 mechanical properties, the metal jacket is corrugated circumferentially. Between the metal layer and the plastic sheathing, a bonding viscous thermoplastic compound is applied (Fig. 2). Normally, this compound fills the depressions of the corrugations on the metal surface adjacent to the surrounding polyethylene jacket. The sheathed cable leaves the extruder with an essentially uniform speed, under pulling force of a capstan. For various sizes of cables and production settings, this speed may range from 30 to 80 feet per minute. After leaving the extruder, the cable is cooled in a trough of water and, before reaching the testing position, dried with compressed air.