MACHINE SWITCHING TELEPHONE SYSTEM 71 



conditions as are required in the operation of the system. It is made 

 up of circular disks called cams mounted rigidly on a shaft. The 

 plates of the cams are cut so that brushes come in contact with the 

 plates only when the circuit is to be closed. The sequence switch 

 can be stopped at any one of eighteen different positions as required, 

 by the simple opening of the electromagnetic clutch. 



There are many of these sequence switches used in this system, 

 and the arrangement of cutting the cams varies, depending upon the 

 particular circuit combination* which it is desired to establish. 



Selector Frames. Fig. 13 shows thirty selectors with all of the 

 associated mechanism mounted upon one side of a frame ready for 

 operation in an exchange. Both sides of the frame are alike. Five 

 panels of 100 lines each are mounted in this frame, one above the other 

 giving a total capacity of 500 trunks or lines. Thirty selectors, each 

 capable of making connection with any one of the 500 trunks or lines, 

 are placed adjacent to each other on each side of these panels; the 

 entire frame thereby having a capacity of sixty selectors, each of 

 which has access to 500 trunks or lines. 



Immediately to the right of the selectors are the sequence switches 

 and, under protective covers, such relays as are used in connection 

 with the selectors upon the frame shown. 



Selecting apparatus of this general type, but differing in details of 

 design, is used during the different stages of the call as line finders, 

 district selectors, incoming selectors and final selectors, reference to 

 which has been made before. Fig. 14 shows a section of a machine 

 switching office with some of the typical frames. 



The use of apparatus of the substantial construction just described 

 is made possible only through the use of the sender which receives 

 impulses from the subscriber at the rate they are dialed and receives 

 impulses from the selecting mechanism at the rate it is traveling. 

 This obviates the necessity for restrictions in the design of either 

 the dialing circuit or the selecting circuit, such as would be necessary 

 if they were tied together. 



Power Supply Arrangements. Since most of the operations normally 

 required in handling a call in a machine switching office are carried 

 out mechanically, it is evident that a considerably larger amount of 

 power is required than with the manual system. Selectors and 

 sequence switches are propelled mechanically by rotating shafts 

 driven continuously by small motors mounted on each frame. 



The use of small motors on each frame gives a flexible and reliable 

 source of power particularly since the motors now being used are of 

 the special "duplex" type developed for the purpose. They consist 



