Workshop and Production Section AIRCRAFT ENGINEERING September, 1942 TABLE I TABLE II H E ever-growing use of fluorescent tubes for DIAGNOSIS FROM THE BEHAVIOUR OF THE TUBE DIAGNOSIS FROM THE PERFORMANCE OF THE GLOW SWITCH lighting in all kinds of industrial premises is Symptom. Possible cause Remedy significant of their efficiency and versatility. Symptom Possible Cause Remedy Althoug h they are only a little over two years old Switch contacts May be due to the short Replace the sup man y thousands are now helping to speed the war lock in the closed ing of the resistance in pressor The tube flickers on 1. Tube has run full life, 1. Replace tube position the radio suppressor unit effort twenty-four hours a day, seven days a week, and off or 2. Faulty glow switch, 2. Replace glow in factories th e country over. Glow persists while Low extinction voltage Replace glow tending to switch on switch Tha t the tubes have withstood such rigorous lamp is burning switch. If glow still and off. persists with new Examination of the conditions of service is, a t least, indicative of their switch, fault is switch in such cases robustness an d reliability. As wit h most othe r things, probably in the usually discloses that however, maintenance of these thousands of tubes tube, which should an excess glow persists be replaced. when the tube is oper is a necessity an d thi s involves rathe r more tha n the ating; replacemen t of a fuse, th e location of a faulty lamp- Switch electrodes This may be caused by or Check wiring and holder connexion or a broken wire, as is th e usual loose in bulb an earth in the switch 3. Faulty tube put in new switch 3, Replace tube lead procedure wit h a tungsten lamp installation. N.B. Low line voltage, low ambient tempera Since th e correct working of a fluorescent tube is Too rapid opera Faulty switch ture, or cold draughts Replace switch only attaine d with th e aid of auxiliary equipment— tion of glow switch. may be contributing This will result in factors choke, power factor correction condenser, starting the lamp switching switch and radio interference suppressor unit—it on and off as the Tube has the ap Switching the tube This usually occurs only filaments have no is likely tha t th e erratic functioning of a tub e or th e pearance of the off and re-starting when the tube is new, time to heat up whole light column after a few seconds failure t o light ma y be due to faults in the circuit and disappears after a moving, usually in is often a cure. If short period of use associated with this equipment. A faulty starting the form of a spiral the effect con connected locally. Otherwise damage t o sound com switch, for example, ma y b e th e sole cause of a tube tinues for a long ponent s may be caused. being intermittently lighted and extinguished, or period, replace tube Th e location of defects can often be expedited by if the tube does not light, though one filament is simply trying th e starting switch and/or the tube glowing, th e fault may lie wit h th e starting switch, Apparent slowing Tube has probably run Replace tube from th e defective circuit in a n adjacen t good circuit. th e radi o suppressor circuit or a n eart h on th e wiring. down of the cycle its full life (see above) Bu t the wise engineer will no t tr y a good tube in a flicker to 25-cycle Th e following notes and tables may facilitate periods circuit tha t is suspected of being faulty. I t is im diagnosis and location of such faults in fluorescent portan t t o check th e supply voltage wit h tha t of the tub e installations. The tube does not Switch contacts have Replace switch. A equipmen t being used and to make sure that the light up when locked in the closed temporary remedy I n the first place it is important to be able to switched on but position may be to give the correct choke tappings are being used. Also ascer recognize a tube that has reached the end of its both filaments are switch a tap, tai n tha t the choke is connected in the phase lead, useful life in the normal way. The most usual alight which may cause a s this tend s to minimize th e effects of an "earth " contacts to open symptom s are: on an y par t of th e circuit. (a) When first switched on ther e is a tendency for Tube does not light, Earth fault on switch or If earth not de I t is wort h noting tha t as soon as a tub e is alight, th e tub e to flicker "on " and "off." and one filament radio suppressor circuit. tectable on the only is glowing May be a short inside wiring, replace th e starting switch associated with it is out of (6) Blackening of th e tub e a t one or bot h ends. the radio suppressor or radio suppressor circuit and can, therefore, be temporarily removed (c) An apparent slowing down of th e periodicity, an earth on the wiring unit an d used for replacement or testing on an adjacent giving cycle flicker comparable with a tube faulty circuit without affecting the operation of the When tube is 1. Broken tube filament, 1. Can be detected on a 25-cycle installation. switched on nothing or by careful exam tub e from which i t ha s been removed. Excessive brightnes s of th e filament at one or both lights up at all ination and if Finall y it should be noted tha t fluorescent tubes, ends of th e tub e may, or ma y not, accompany these discovered, tube must be re like other electric discharge lamps, may continue symptoms . Whenever a tube tha t has burnt for a placed t o give light beyond the period of usefulness, in period approximating to its normal life shows one 2. Glow switch failing 2. Replace switch which event they will soon become so inefficient o r more of thes e symptoms, it is bette r replaced by to close; If new switch that , in the user's own interests, they should be or also fails to a new tube. close, examine replaced. Th e following tables indicate how to diagnose the circuit with T o assist works' engineers in charge of Osram causes of prematur e failure an d appropriat e remedies a test lamp for a fluorescent tube installations further, the G.E.C. break at any t o take. part ha s prepared a card on which much of the above A circui t which is no t functioning correctly should 3. Break in some part of 3. Examine circuit information is given in more concise form and a b e immediately disconnected until such time as the the circuit with test lamp log table is provided so tha t a complete record of and repair any defect can be corrected. If, however, it so happens break each tube and subsequent replacements may be tha t other circuits are operating through the same kep t with a minimum of trouble. Copies of these cards can be supplied, on request *Notes supplied by the General Electric Company, Ltd. See switch the tub e should be removed from the faulty t o the General Electric Co. Ltd., Magnet House, "Tubular Fluorescent Lamps in Industry" and "Fluorescent Lighting", AIRCRAFT ENGINEERING, April, 1942, pp. 111-114. circuit and, if possible, the supply should be dis- Kingsway, London, W.C.2.
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Sep 1, 1942