SYNCHRONIZED SOUND PICTURES 



195 



When starting up for the first time it is necessary that the various 

 units should Hne up properly as to phase otherwise there will be a 

 local flow of current in the rotor circuits, which will cause the motors 

 to operate as induction motors and run away. Under running con- 

 ditions the system is very stable showing no tendency to hunt or surge 

 between units, for the reason that being polyphase each phase as it 

 becomes inactive (when the induced e.m.f. passes through zero) acts 

 as a damping winding for the other two active phases. 



3 PHRASE o 

 60 CYCLE o 

 POWER 



ROTOR 

 BUSES 



CAMERAS, RECORDING MACHINES OR PROJECTORS 



Fig. 1 1 — Diagram of synchronizing system for recording. 



If the load on a particular unit of this system is varied there will 

 be a variation in the phase angle between this unit and other parts 

 of the system in the same manner as in the case of a synchronous 

 motor of the ordinary type. The magnitude of this phase angle, 

 however, does not vary more than 30 electrical degrees or 15 mechanical 

 degrees and is sufficiently small so that it produces an inappreciable 

 effect on the synchronization. 



Discussion 



The above described motor equipment with its associated control 

 circuits has been in practical use for over a year both in recording 

 and reproducing work and there have been practically no troubles in 

 service. 



In the design of this equipment, first consideration has been given 

 to its precision and reliability in operation and the provision of 

 adequate margins to care for all variations in service conditions. As a 

 result it has been possible to maintain a high standard of quality in 

 music and speech reproduction. 



