Automatic Manufacturing Testing of Relay Switching Circuits

Early telephone central office installations were of the manual switchboard type which were relatively simple and required few relay circuits other than those located in switchboards themselves. Installation effort, in addition to actual erection of the switchboards, equipment frames, fuse boards and the like consisted largely of running and terminating the central office cabling. As the telephone art grew, both with the introduction of the dial telephones, and carrier and repeater equipments for long distance calls and the consequent need for interconnection of these various types of systems, a considerable variety of relay switching circuits was required. To reduce the installation time and effort the practice of doing as much circuit wiring in the factory as possible was introduced. Relay switching units are now completely assembled, wired to terminal strips and tested in the shop. Since these are in effect working circuits the installation testing effort, after the connection of office cabling, consists largely of overall tests required to insure the proper functioning of the entire office. Due to the wide variety and complexity of these units, many of which have optional circuit conditions t h a t can be supplied on order and few of which have sufficient demand to justify specially designed high pro1155