THE TYPE PI CARRIER SYSTEM 371 



manufacture of electronic equipment has also influenced the design to a 

 great extent. 



5.1 Printed Wiring Boards 



To best meet these objectives, use has been made of plug-in units which 

 have proved successful in other carrier systems, such as the Nl and 0. 

 The assembly technique used here, however, is an entirely new approach 

 for carrier equipment in that the plug-in unit consists of a printed wiring 

 board on which all components are mounted. Printed wiring, which is a 

 comparatively new engineering technique, was selected because of its 

 applicability to automatic assembly, including mass soldering of con- 

 nections. In addition, the use of printed wiring greatly simplifies testing 

 and inspection and assures a more uniform product. The two sides of a 

 typical printed wiring board are shown in Fig. 15. 



5.2 Interconnection of Boards 



The interconnection of the various plug-in units or printed wiring 

 boards, required to make up a complete PI terminal or repeater, is ac- 

 complished by means of a wire connector specifically developed for this 

 project. Basically, the connector consists of a number of accu- 

 rately spaced bare wires running parallel to each other and imbedded 

 in cross member strips of insulating plastic material. At fixed intervals 

 the wires are exposed, and this is where contact is made to terminal con- 

 nectors mounted on the printed wiring boards. These terminal connec- 

 tors, shown in Fig. 16, are made of spring tempered phosphor bronze 



Fig. 16. — Closeup of terminal connectors. 



