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MANAGERS AND PROJECTIONISTS 543
The commutator is six inches in diameter, and of varying widths, the latter dependent upon amperage capacity of the individual machine. It is composed of alternate segments which are both mechanically and electrically connected. This means that each alternate commutator bar is thus connected clear around the commutator, thus forming two separate commutator units which are connected to the A. C. supply lines through sliding contacts made between stationary copper rings and rotating carbon discs, both the rings and discs having as their center the axis of rotation, or center of the shaft.
The rectifying action is obtained due to the fact that at the instant of reversal of the alternating current pulse, each succeeding contacting segment of the commutator has come into position which permits or causes current to flow only in one direction through the conductor attached to it.
Direct current is collected from the commutator by means of graphite brushes, which are electrically connected into two separate groups, one of which goes direct to the arc. The other group forms the return circuit from the arc.
The brush holder studs are mounted on a yoke, in the usual manner. This yoke may be rotated through a small angle (rocked back and forth) about the commutator, thus permitting shifting of the commutation point in order to secure the best results in rectification.
TRANSFORMER AN INTEGRAL PART.— The supply line voltage is reduced to arc voltage by means of a transformer, which is embodied in the machine itself and is an integral part thereof. It therefore follows that reduction of line to arc voltage is accomplished at only the usual loss inherent in a transformer, which should be well within 10 per cent, of the total. A well designed transformer is the most economical method used in practice for accomplishing this particular thing. The Syncroverter designed for motion picture projection work is, except for the wall panel used under certain conditions, an entirely self contained machine.
REFLECTOR ARC LAMP WORK.— For supplying current to reflector arc lamps the "Type 25" Syncroverter is especially designed. This unit is illustrated in Fig. 165. Its dimensions are, height 40 inches at back, width 14 inches, length 20 inches. Its weight is 250 pounds. All Syncroverters designed for motion picture work are completely protected by a pressed steel meshed fabric.