Educational screen & audio-visual guide (c1956-1971])

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Safe Use Of TV Receivers In Schoolrooms JL ELEVISION is coming to be a very common and accepted part of the functioning of modem schools. Indeed, an educational television system designed ultimately to reach schools throughout a state was recently placed in operation in South Carolina. In some states television receivers are used as a means to try out new methods of instruction; in others they are kept available for special programs that have educational interest. While it is true that a television set usually remains in one particular location when it is used in the home, the situation is likely to be very different in the school. The receivers available may be moved frequently from one classroom to another, or they may be put into storage room and brought out into the classroom as the need arises. While most receivers are school property, they may sometimes be brought in from a dealer's shop on loan. It is desirable in all cases that a TV receiver used in a school should be mounted on something that provides a considerable degree of mobility so that it can be moved from room to room with ease and safety and turned into the position most desirable at a given time. In many instances, the receiver will be placed on a relatively tall stand at the front of a classroom in a position where it can easily be viewed by everyone in the class. Because of the conditions of use a television receiver in a schoolroom, and the fact that an accident is more likely to happen than in a home, and with danger to more persons, teachers and supervisors will find it worth while to give special thought to the safety precautions needed to make television viewing safe for students. A television set in which electric potentials as high as 23,000 volts or more may be present, can be a very dangerous appliance under some unusual circumstances, and with any set tliere is the possibility of shock that could cause death to a human being. There are wide differences in design and construction; some receivers are far safer than others, because of the way they are built and protected. No school should have or use or take on loan a television receiver that does not carry the Underwriters' Laboratories' label or emblem, UL. The UL symbol (usually found on the "backboard" of a set) does not guarantee safety I under all circumstances, but it is safe to assume th; a set which carries it has been subjected to th criticism of qualified electiical engineers and has bee manufactured so that it passes certain minimum stanc ards of safety, in respect to accident, shock, and fii hazard. One important requirement established by tt Underwriters' Laboratories is that there be a shiel at the rear of the set. This shield prevents the use' or the exploring fingers of a child, from touching ar i part of the electrical and mechanical parts mounte J inside the cabinet. In addition, there is a requiremei that an interlocking device must be provided that di connects automatically the power connection enterir the set at any time when the shield or backboard the rear is removed. The Underwriters' Laboratori' also include an important requirement that in fro: of the picture tube there must be a protective tran parent plate of such strength as to protect the tul from breakage if it should happen that the front the television set receives a reasonably hard blo' This plate also protects the viewer from the effec of a spontaneous or other type of implosion, a n uncommon occurrence. The Underwriters' Laboratories' requirements wi respect to the possibility of shock hazard is not, the opinion of Consumers' Research, sufficient stringent, for they permit a leakage current (t amount of current which flows through undesir pathways due to deficiencies of insulation, etc.) 5 milliamperes at exposed metal parts. This sm current— only 1/100 of that required to light a 50-w; lamp bulb— is sufficient, if it should pass through t body, to give a severe sensation of shock that can times be the cause of a serious accident because of t sudden uncontrolled or involuntary muscular reactio involved. Typical of exposed metal parts at which sensation of shock may be felt on a defective receiver are exposed parts of the chassis (a parti which is usually not protected by the rear shiek' screws used to fasten the chassis to the cabinet, me control shafts which extend beyond the exterior ' the cabinet and are accessible at the rear and oth which are accessible when control knobs are remov Another potential source of danger exists at poi' Reprinted by special permission from Consumer Bulletin, March 1961 Copyright 1961 by Consumers' Research, Inc., Washington, New Jersey; all rights reserved. 224 Educational Screen and Audiovisual Guide — May, 1!