THE TYPE PI CARRIER SYSTEM 375 



of the PI carrier, however, the heat dissipation during the idle period is 

 less than 1 watt for the entire terminal. To prevent condensation, the 

 housing or apparatus case is sealed by means of a neoprene gasket. To 

 further reduce the moisture content of the trapped air, the use of a desic- 

 cant is specified. The apparatus case is made of die-cast aluminum with 

 the outside walls finished in white enamel to keep heat absorption to a 

 minimum. The system was designed to operate between temperature 

 extremes of — 40°F and +140°F. This limitation might necessitate the 

 additional installation of sun shields in a few cases where extreme temper- 

 atures prevail. 



The terminal equipment at the central office makes use of the same 

 type of printed wiring boards plugged into a connector as used at the 

 remote location. In the central office, however, the outer housing is dis- 

 pensed with and the connector is mounted on mounting brackets 

 on standard relay racks. The relay rack layouts can be arranged in a 

 number of ways to suit the particular installation, since no shop wired 

 bays are used. A tj^pical 11'6" relay rack layout will provide for 10 ter- 

 minals. No line jacks or alarm features are provided and fusing may be 

 obtained from existing fuse boards in the office. The equipment also 

 lends itself to wall mounting in locations where relay rack space is not 

 available. 



5.4 Testing and Maintenance Features 



One great advantage of the equipment design used in the PI carrier 

 system is the ease with which an entire terminal or repeater can be trans- 

 ported to, and installed at, a remote location. In case of trouble, the 

 entire equipment unit, be it a terminal or a repeater, can be readily re- 

 placed. It is not expected that the maintenance man will attempt to 

 replace an individual printed board at a remote location; however, this 

 procedure is perfectly feasible in a central office. To facilitate the loca- 

 tion of trouble in a unit, the various boards are provided with test points 

 located at the outer end of the boards so as to be easily accessible to the 

 maintenance man. 



Certain precautions will have to be taken at central repair centers in 

 replacing defective individual components in order not to damage the 

 printed wiring. Too much heat applied by a large soldering iron will de- 

 stroy the adhesive bond between the copper conductor and the phenolic 

 board, but repair can be made under certain controlled conditions. A 

 limited amount of wiring modifications can also be made to the printed 

 wiring by inserting strap wires in place of components. 



