120 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



trometer type leak detector. A gas pressure of helium at least 25 per cent 

 greater than the maximum pressure to be encountered at ocean bottom 

 was used. In addition, a radioisotope was used to test the effectiveness 

 of the final tubulation pinch welds and overbrazes which were kept open 

 for the leak tests under high pressure helium. These tests were made 

 with water pressure about 25 per cent greater than the maximum ocean 

 bottom pressure. 



The completed repeater was inserted in a chamber 80 feet long; the 

 chamber was then filled with water and the pressure raised to 7,500 

 pounds per square inch and held at that pressure for at least 15 hours. 

 At the end of this period the closure had to show no sign of crushing or 

 leaking. 



The repeater unit sealed in the closure must be extremely dry to func- 

 tion properly. Any water vapor which might remain after the closure is 

 sealed, or enter during the estimated 20-year minimum life, must be 

 scavenged. A sealed desiccator with a thin diaphragm was, therefore, 

 assembled into the repeater unit sections. After completely drying and 

 sealing the repeater unit except for one tubulation, the diaphragm of 

 the desiccator was ruptured by dry nitrogen pressure and with the en- 

 closure filled with dry nitrogen the final tubulation was immediately 

 sealed off. To insure that the diaphragm was actually broken, a micro- 

 phone was strapped to the outside of the repeater over the location of 

 the desiccator and a second microphone arranged at the end of the 

 closure to pick up background noises. A pen recorder was used to record 

 the sound from the two microphones and also the change in nitrogen 

 pressure. Three simultaneous pips on the chart gave definite indication 

 that the diaphragm had ruptured and that the desiccant had been ex- 

 posed to the internal atmosphere of the repeater. 



QUARTZ CRYSTAL UNITS MANUFACTURED AT KEARNY 



The primary purpose of the crystal unit is to provide the means of 

 identifying and measuring the gain of each repeater in the cable. This 

 basic crystal design is in common usage. The exacting specifications for 

 this application, however, imposed many problems and deviations from 

 normal crystal manufacturing processes. 



Raw Quartz was specially selected for this crystal unit. The manu- 

 facturing process of reducing the quartz to the final plate followed the 

 recognized methods through the roughing operations. Due to the rigid 

 end requirements, the finishing operations were performed under labora- 

 tory conditions. Angular tolerances were one-third of normal limits. No 

 evidence of surface scratches, chipped edges or other surface imper- 



