The Moving picture world (November 1922-December 1922)

December 16, 1922 MOVING PICTURE WORLD 679 Thanksgiving Eve of Fifteen Years Ago Recalled by Hallberg {Continued from last issue) WITHIN about ten days after the conception of the idea of using a special transformer for the control of projector arc lamps, a complete model was finished and tested and the result was an efficient and reliable device which came up to my expectations, and of which the following is a brief description: "An iron core was provided built up from thin sheets of high grade transformer steel approximately as illustrated in Figure 1. Several hundred of these sheets were stacked on top of each other in order to form the magnetic core for the economizer and Figure 2 gives an end view. "In ordinary step-up or step-down transformers which are of the constant potential type the primary and secondary windings are equally divided so that part of each primary and part of each secondary will be on each one of the two iron core legs as illustrated in Figure 3. The characteristics of this kind of a transformer, therefore, are not at all suited for the control of a carbon arc because at the instant the carbons are put together the transformer will be under a practical short circuit on account of the fact that the magnetic lines of force set up in the core bv the primary winding would also be included within the secondary coils or turns of wire. Different Arrangement Necessary "An entirely difTerent arrangement had to be used in order to allow leakage of the magnetic lines of force so that all the magnetic lines set up by the primary winding would not have to pass through the secondary coil. In consequence thereof a new design was developed as illustrated m Figure 4 in which the primary was put on one leg and the secondary on the other leg of the transformer core, said coils being separated by several inches. The result of this arrangement would be that the lines of force set up by the primary would pass through both legs of the core as illustrated by the arrows in Figure 4 as long as the secondary winding was open or not loaded and under this condition a very small amperage would be taken from the line through the primary because of the great self-induction of the device. "When load is put on the secondary, such for instance, as an arc between two carbon points the magnetic lines of force no longer flow entirely through both core legs but some are shunted through the air space between the two coils and only the necessary amount of magnetism passes through the second core leg of which th^ secondary is placed, as illustrated in a general way in Figure 5. "If we stop for a moment and analyze what happens in Figure 5 we will find that when the carbons are separated and no current flows in the secondary then when the primary is connected to the line, practically all of the magnetic lines of force will pass back and forth through both core legs, when the carbons are put together practically all of the lines of force which start in that part of the core surrounded by the primary winding pass through the air around the primary coil and if the short circuit is maintained this condition will continue, at which time a properly designed transformer of this type will allow slightly more normal full load current in amperes to flow through the primary winding. Counter Effect Lessened "If the carbons should be separated, which increases the resistance of the arc circuit, then the counter effect on the secondary core is lessened and some of the lines of force instead of passing on the outside of the primary coil begin to crowd through the second leg of the core generating voltage and current in the arc circuit, which phenomena increases only when the arc has been established at the proper length with the proper number of amperes flowing at which time the transformer and the arc are in balance. If an impurity passes tiirough the arc lowering its resistance the current does not go up materially but a less number of lines of force pass through the secondary coil, therefore, reducing the voltage for that instant and thus maintaining a practically constant current at the arc. "This is a very desirable feature because it not only makes the device perfectly safe but on account of the entire principle of operation being electro magnetic with a very low resistance in the coils there is comparatively little heat generated and it is impossible to blow fuses and during operation the automatic feature of shunting the magnetic lines of force through or away from the secondary coil stabilizes the arc and permits the carbon points to be held quite close together so that both rratcrs may be focused upon the aperture in one spot of practically double the intensity through no other means with A. C. at the arc. The First Model "On the first model made the primary coil was provided with one leading-in wire connected to the line and on the end of the coil three leads or taps were brought out so that the second line wire could be attached to a lesser number of turns for low line voltage or for high amperage at the arc, and likewise a greater number of turns could be included by moving the line wire to the last tap so as to include maximum number of turns in the primary coil for high line voltage or for low amperage at the arc. "The first Hallberg Economizer was placed, in a wooden cabinet with the primary and secondary terminals coming out through insulating porcelain bushings in the top and with ventilating openings in the bottom and on the sides. It seems strange to replace a hot rheostat which would glow red in service with a device in a wooden box but notwithstanding this fact the economizer was approved and the first one was installed in a Jersey City theatre during the Winter of 1907. FIGURE 6 Early Model of Economizer "Well do I remember the afternoon when the try-out was made. An old 25 to 30 ampere rheostat with several coils short circuited on 110 volt 60 cycle alternating current with 40 ampere fuses as regularly installed for service was first used for the test during one reel' of the afternoon show. Then before the second reel, the first Hallberg Economizer was substituted and with an ampere meter in the line and another one in the lamp circuit, the line switch was closed, indicating 2 amperes. When the arc was struck the current taken from the line was about 26 amperes and the current at the arc was 45 amperes and with Ys cored Electra pink labeled carbons the illumination on the screen with the second reel was practically three times as brilliant as with the rheostat taking more amperage from the line during the first reel. The improvement was so marked that when the show was over I stood with the exhibitor in the doorway and many of the patrons stopped to inquire what the new improvement was which made the picture so brilliant after the first reel. "After that, things moved swiftly and before long the economizer was placed in a circular metal case with perforated brass cover. Figure 6, and that type remained the standard for almost five years. "The wider application of the economizer in places where the line voltage varied and where it was desired to change the amperage at the arc during the performance it was found inconvenient to shift the line terminal to the d i ff e r e n t transformer t a p and in c o n s equence thereof a switch with three points was provided so arranged that the second line wire could be disconnected and connected instantaneously for or to any one of the three line taps on the economizer primary. "With this design and construction only two line and two lamp leads were brought out as the connections were made internally and then the control handle for the three point switch was mounted on top of the economizer case for quick adjustment and that is the type now in regular service as illustrated in Figure 7." IXOIWMIJJO-"'ANSfO»Ml" ft FIGURE 7 Present Model of Economizer FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 Principles of Operation of Hallberg Economizer Illustrated by Diagrams FIGURE 5