POWER PLANTS FOR TELEPHONE OFFICES 



719 



ringing calls which occur when a ringing generator stops during a busy 

 period and which may overload the motor sufficiently to blow the 

 protective fuses and prevent restarting. 



The battery motor is equipped with an automatic speed regulator 

 which keeps the generator frequency within two per cent of rated 

 speed throughout the range of the battery motor supply voltage. 



It is obvious that a combination which will do so many things at 

 once costs more than a simpler type of machine. The fact, however, 

 that it will operate several central ofBce units and will replace coin 

 control batteries makes it cheaper than the equipment formerly re- 

 quired to do the work. With fewer machines and no batteries, except 

 those for superimposing, installation is simplified. The closer voltage 

 and speed regulation reduce relay and ringing troubles and, in conjunc- 

 tion with the continuity of operation, improve service from the sub- 

 scribers' viewpoint, as well as reduce the amount of maintenance re- 

 quired of the attendants. 



III. The Future Telephone Power Plant 



It may be of interest to consider the direction toward which de- 

 velopments in prospect are leading, that we may learn what the future 

 telephone power plant may be like. It seems probable that further 

 progress will be made in the application of unit panels and unit 



Fig. 13 — One type of signaling machine — ■20-cycle ringing and direct-current 110- 

 volt coin control machine, with reduction gearing for low-speed signals. Driven by 

 a.-c. line motor with reserve battery motor automatically energized upon power 

 failure. Speed controller on battery motor. 



assembles or combinations of machines and control equipment. With 

 the better characteristics, much of this equipment, including storage 

 batteries, can be mounted with the circuit apparatus on standard racks, 

 making self-contained units. 



