Additionally contact terminals and pressure

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Additionally, contact terminals and pressure regulators are used throughout the plant. The most common causes of leaks in cable plants are corrosion (particularly in coastal areas), electrolysis, squirrels, boring beetles, abrasion from wind and weather, hunters and outside workmen. Abrasion during installation and corrosion are the most frequent causes of cable sheath trouble in underground ducted passages. Principles of Ultrasound Tests for Leaks in Telephone Cable Sheaths The technique of ultrasound leak testing and location in telephone cables involves scanning the pressure system with the directional airborne signal probe and coordinating the direction of the characteristic hissing sound with its intensity (Fig. 20a). The aerial and underground pressurized cable plant of the modern telephone system is a large, low pressure system that lends itself to ultrasound leak testing during maintenance. All cable pressurization has resulted in overall reduction in outlay for cable plant maintenance. This is particularly true in the reduction of emergency repair time formerly encountered when rain entering the cable sheath resulted in widespread service disruption. Although highly portable ultrasonic translator leak detectors have permitted technicians to locate sheath damage in pressurized telephone cable from the ground, prudent supervisory management has established preinspection procedures to speed the operation further. It is typical practice, for example, for a splicer to perform the following preliminary steps on a cable failing to maintain the gas at nominal 70 kPa (10 lb f ·in. –2 gage) pressure. 218 Acoustic Emission Testing P ART 7. Ultrasound Leak Testing of Pressurized Telephone Cables F IGURE 20. Detection of leakage from telephone cable sheaths: (a) pressurized cable; (b) overhead cable. (a) (b)
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1. Connect nitrogen cylinders set to give a gage pressure of 70 kPa (10 lb f ·in. –2 ) at strategic locations along the cable. Such cylinders often are allowed to remain connected for 24 h or longer to build up sufficient pressure. 2. Take cable pressure readings at selected points. This practice is particularly important on such cables as cross country toll lines that often traverse a line-of-sight right of way across precipitous terrain. 3. The readings taken at each pressure point are then plotted on graph paper. Each grid on the paper is selected by the inspector to represent a known distance as determined from the mechanic’s cable plant maps. 4. An alternative means of narrowing down the point of the leak is with the cable pressurization computer. Procedure for Ultrasonic Leak Testing of Overhead Telephone Cable After the technician has determined the general location of the leakage to within the length of three sections or less, the technician would normally walk the route, using either a hand held probe or with a parabolic microphone hand held probe (Fig. 20b).
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  • Fall '19
  • Acoustic Emission

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