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MANAGERS AND PROJECTIONISTS 519
OPERATING INSTRUCTIONS.— Before starting motor, have lamp carbons separated and projector table switches open. Close motor starting switch. Close short circuiting switch which controls lamp you do NOT wish to use. Allow sufficient time for generator voltage to build up before attempting to strike an arc, say 15 seconds from time of starting motor, then bring carbons together, instantly, slightly separating them again. As the carbons heat up, gradually separate them until the proper arc length is had, whereupon the voltmeter will show 55 volts, provided the carbons be of correct size and correctly set. Any desired change in amperage, within the range of the machine, may be made by changing the position of the field rheostat regulator, but it must be remembered that the regulator provides means for obtaining amperage in excess of the rated capacity of the machine, which excess should not be used continuously. It is intended only to provide excess current for use where a temporary excess of light is desired by reason of a very dense film, or by reason of heavy tinting. The regulator also provides means for obtaining a less amperage than the rated capacity of the machine. If the projectionist will take advantage of this provision he will not only improve his work, but will also effect a considerable saving in light bills.
TO STRIKE A SECOND ARC— Assuming one projector to be already in operation, adjust its arc to a 55-volt length, then bring the carbons of the idle lamp into contact, and, still holding carbons of idle lamp in contact, open panel board short circuiting switch controlling that lamp. When switch is open, instantly but slowly separate carbons, in the manner already directed for a single arc. When both lamps are in use the voltmeter on panel board will indicate the combined voltage of both arcs, which should read between 105 and 120 volts, probably about 110.
To "kill" either arc it is only necessary to close the panel board switch controlling that lamp. This in no way affects the remaining arc.
The multiple type is best suited to houses where spotlights, double dissolvers and other apparatus of widely different current requirements are used intermittently with the projectors. This is particularly true today when many houses operate at from 15 to 25 amperes on the projector, using a reflecting arc and require 50 amperes for the spot. With this low projector current the superior efficiency of the series system becomes of less moment and the flexibility of the multiple unit makes its advantage felt.