Comparative tests of carbon, metallized carbon and tantalum filament lamps . omes incandes-cent, especially in the carbon lamp. O 380360340320300280260240 220200IHO160110 120 AN! me TAl :ed ? CA .RB( 1300 1400 1500 1600 1700 1800 1900Fig. 2 Filament Temperature, Degrees Cent. As a result of the positive coefficients of the metallized andtantalum filaments, the lamps flash up to full incandescence much AMRINE—COMPARATIVE TESTS OF LAMPS 5 more quickly than the carbon lamp. When the current is turnedon, the filament, being cold, has a low resistance and there is arush of current considerably abov
Comparative tests of carbon, metallized carbon and tantalum filament lamps . omes incandes-cent, especially in the carbon lamp. O 380360340320300280260240 220200IHO160110 120 AN! me TAl :ed ? CA .RB( 1300 1400 1500 1600 1700 1800 1900Fig. 2 Filament Temperature, Degrees Cent. As a result of the positive coefficients of the metallized andtantalum filaments, the lamps flash up to full incandescence much AMRINE—COMPARATIVE TESTS OF LAMPS 5 more quickly than the carbon lamp. When the current is turnedon, the filament, being cold, has a low resistance and there is arush of current considerably above normal. This excessive cur-rent is rapidly cut down as the lamp reaches incandescence onaccount of the increase in resistance. The carbon lamp, havingthe greatest resistance when cold, allows but a comparativelysmall current to pass at first, but gradually allows it to increaseas the resistance becomes less. This is beautifully shown by theoscillograms of the rise in current in the three lamps shown inFig. 3. With the carbon lamp it is seen that the current almost s. 04 .06 .08 .10 .12 .14 .16 Time in Seconds .20 .26 .9 /1E1 ED - r ?)Rf c ?CA r— 1 ,02 . 04 . 06 . 08 .10 12 .14 .16 Time in Seconds 26 TAr LU M OR, c : N T - .0 .02 .18 20 22 04 .06 .08 ,1(1 .12 .14 .16 Time in SecondsFig. .3 Oscillograms op Initial Currents instantly rises to about .35 ampere, and then rises in almost astraight line to the full steady value of current in about .26 sec- I « I 6 ILLINOIS ENGINEERING EXPERIMENT STATION ond. With the metallized lamp the current rises at once to ampere, almost the full steady current, then increases to a max-imum value of .55 ampere in approximately .05 second, indicatinga negative temperatui-e coefficient at the lower temperatures. Itthen decreases gradually to the normal steady value in about .16second. The curve for the tantalum lamp indicates that a rushof current takes place as soon as the circuit is closed, reachinga maximum of about .93
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