Educational film magazine; (January-December 1920)

Edited by JAMES R. CAMERON, Projection Engineer THREE WIRE WIRING SYSTEM SYSTEM of wiring where three instead of two sets of two wires are used, generally obtained by connecting two dynamos in series and connecting the third or neutral wire to a point common to both dynamos. The wires are positive, negative and neutral. The advantage of the system is the saving of copper. The disad- vantages are that switches, cut-outs, etc., are more expensive, and unless the system is kept i^k. - t balanced (the same amount of amperage being ^^^^ ^^ drawn off either side of the system) you are ^^^^^^^ liable to damage the lamps on the line. JAMES R. CAMERON The lamps are connected between either of the outside wires and the enutral, and if an equal number of lamps are connected on each side (that is. if the system is balanced) there will be no flow of current in the neutral wire. In any case the amount of amperage in the neutral is the difference between the amount of amperage drawn from either side. This difference should be kept as small as possible. Figure 1 shows a three-wire system, D and E being two 110 volt dynamos connected in series, A is the positive wire, B the neutral wire. The ten amperes being drawn from the positive wire A and re- turning to the dynamo over the negative wire c. Figure 2 shows an unbalanced three-wire 5MH FKJ. . system. Taking it for granted that each of the lamps is drawing one ampere, we have four amperes on one side and six amperes on the other, so our system is unbalanced to the extent of two amperes, this repre- sents the flow of current in the neutral wire. Connected between wires A and C we would have 220 volts (the added voltage of the dynamos). Connected between A and B or between B and C we would have a pressure of 110 volts. Great care should be taken to see that lamps rated for 110 volts are never connected between the two outside wires. Care of the Motor The motor must be kept clean and free from dust and grit; if the commutator becomes rough, smooth it up with No. 00 sandpaper moistened with a little oil. When fitting new brushes, always sand- paper them down to fit the commutator perfectly by passing to and fro beneath the brushes a strip of sandpaper, having the rough side toward the brushes. Be careful to renew the brushes before they get too short, as should the brush holders come in contact with the commutator great damage may be done. Brushes should cover at least two commutator segments and •► ^ — 4- 35 should have just enough tension to hold them securely in place and make good contact. If the tension is too great, it will cause excessive wear on the commuta- tor and sparking. If the tension is not enough, the motor will lose cover. Keep the oil cups well filled with some non-fluid oil and see that the wick in the cups feeds the oil to the motor shafts. Sparking of motors may be laid to several causes: overload, dirt, uneven brushes, improper setting of brushes, high mica, broken segment in commutation, etc. Should the motor become excessively hot after running a while, shut off the current and locate the trouble, which may be due to one or more of the following causes: Improper lubrication of bear- ings, excessive sparking, short circuited field or armature coils, or maybe the driving belt is too tight. Inspect motor prior to show. Keep motor clean and well lubricated. Do not connect a D. C. motor to an A. C. source of supply, or vice versa. See that the voltage marked on motor comes within 10 per cent, of the line voltage. See tliat the brushes are making proper contact and have the rigbt tension. Keep all electrical connections tight. Remember dampness greatly impairs the life of the motor. ISfUSHES FlElM CoilS SKefCH OF THE \NreR\op, of a xi-C. jiym\no o« Moron, QUESTIONS AND ANSWERS I find it impossible to get a clear white li^zht on the screen. There is a brownisb diecoloration that I cannot get rid of; have tried chanfing the make of carbon. The screen seems to be O. K. and my condensers and lens are perfectly clean.— Operator, Trenton, N. J. Your optical train is not set right. To obtain maximum results your arc must be set a given distance from the back of your condensers, your condentert sboald be of a given focal length, and your objective lens of a given diameter. If yoa will write me again and give me the following information I shall be pleased to work the ihing out for you: Amperage drawn at arc, A. C. or D. C.; size of carbons used, focal length of condensers, focal length and diameter of objective lens, distance from front of objective lens to light shutter, and length of throw. I AM THE MOTION PICTURE By Arthur James I am the Motion Picture. I am tlie child of man's genius, the triumph of man over space and time. I am a mute, but I am eloquent to millions. I travel desert sands, I climb the tallest mountain peaks, I traverse prairie, gla- cier, jungle, forest and sea and air and bring the vision of my journeys to the eyes of common men. I am the pleasant hour of prince and child, of master mind and little boy. I instruct, I delight, I thrill, I entertain, I please, I shock, I cheer, I move the world to laughter and to tears. I am the sublime story teller of all the ages. I am the dramas greater brother. I have more friends than all the friendly men of earth. I stir the blood. I quicken the pulses. I pir'^nr- age the imagination. I stimulate the young, I comfort and solace the old and sorrowing. I bring priceless gifts and make them yours. 1 show inore of travel thati all the books penned l>v all the writers of the world. I preach sermons to congregations greater than the combined flocks of the pulpits of all lands, I make for happiness, I make for kindliness, I am the one great international friend. I am history, written for generations to come in a tongue that every race and sect and creed can under- stand. I preserve heroes for posterity. I give cen- turies more of life to the arts and sciences. I am man's greatest and noblest invention. I am the Motion Picture. 20 1