Independent Camera Drive for the A-C. Interlock Motor System

The a-c. interlock motor system used to drive cameras, recording, rerecording, and projection machines in synchronism has special advantages in such applications as driving projector and camera for projection background process. The system is generally started from a central point, such as the recording room, and the cameraman does not have means for running his camera independently as is so often required for photographing slates, exposure tests, and silent scenes. — An addition has been made to the system to give it the advantages of the synchronous motor system: namely, the facilities enabling the cameraman to operate his camera at will at regular speed. The addition consists of a set of relays with control circuits, and a frequency-changer and field-exciter set. Normally, the camera motors are connected to the common interlock system through the relays. If, however, the button provided at the camera is depressed, the pilot relay operates the main relays which transfer the camera motor circuit to the bus of the frequency-changer and field-exciter set. One phase of the rotor is short-circuited, and the remainder is excited with direct current and serves as the field. The three-phase stator is supplied with three-phase power of a frequency that will cause the motor to run at the required speed, the same speed as when driven with the interlock system. — The power developed by the a-c. interlock camera motor when operated as a synchronous motor is approximately the same as under normal operating conditions. The acceleration is typical of small synchronous motors when the power supply is suddenly connected. The pull-in torque is superior to the slotted-rotor type of as-synchronous motor. The operation of the system is smooth, simple, and efficient, and has, after several years of use, proved its value.

Print ISSN

0097-5834

Published

1939-04

Content type

Original Research

DOI

10.5594/J16563