. Motion picture electricity. For the highest class of rheostats, a special wire madefrom an alloy composed mainly of nickel and copper issometimes used. The object in using nickel copper wireis to prevent rust, especially where the rheostat is usedoutdoors, or transported from place to place where itwould be likely to be subjected to severe weather condi-tions, and consequent unusual and rapid temperaturechange. MOTION PICTURE ELECTRICITY 145 Non-Adjustable Type.—Fig. 82 illustrates a rheostathaving the resistance unit composed of a resistance wiremounted in zigzag form on small insulating bu
. Motion picture electricity. For the highest class of rheostats, a special wire madefrom an alloy composed mainly of nickel and copper issometimes used. The object in using nickel copper wireis to prevent rust, especially where the rheostat is usedoutdoors, or transported from place to place where itwould be likely to be subjected to severe weather condi-tions, and consequent unusual and rapid temperaturechange. MOTION PICTURE ELECTRICITY 145 Non-Adjustable Type.—Fig. 82 illustrates a rheostathaving the resistance unit composed of a resistance wiremounted in zigzag form on small insulating buttons, sup-ported by a suitable metal frame, enclosed in a ventilatedmetal case. The illustration shows the beginning andend of the resistance wire attached to proper binding postsor terminals supported on an insulating block or metal casing is generally made of perforated sheet-iron, aluminum or brass and this cover or protecting casemust entirely enclose the resistance unit and terminals and. Fig. 83 suitable openings with proper bushings should be pro-vided in the metal case, through which the asbestos cov-ered copper cables may enter for making connection withthe binding posts. It is evident with such a rheostat asdescribed in the illustration, if the proper size wire isused, would be absolutely fireproof and almost indestruct-ible and the great advantage of this particular type of 146 MOTION PICTURE ELECTRICITY rheostat is due to the fact that the resistance wire is con-tinuous from one end to the other without a break. Fig. 83 illustrates a similar type of rheostat, which is,however, somewhat simpler in construction, in that it re-quires a lesser number of insulating supports which is ac-complished by winding the resistance wire on an arbor inthe form of a spiral, so as to make the resistance unitmore compact. This form of resistance unit can, ofcourse, not be operated at as high a temperature as thedesign illustrated in Fig. 82 on account of the possible sag-g
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Keywords: ., bo, bookcentury1900, bookdecade1910, bookidmotionpictureele00hall
