. Le journal de chemin de fer de rue . de la résistance ohmique totale requise pour une voiture ou le rapport qui devrait exister entre les points différents. Son seul moyen de les traiter est la méthode de coupe et d'essai et cela devrait certainement être éliminé dans les travaux ménagers de voiture chaque fois que possible. Dans la plupart des cas, l'utilisation appropriée d'un instrument de mesure en même temps que la connaissance de la résistance requise permet de gagner beaucoup de temps et d'économiser du temps. Plusieurs instruments sont fournis à cette fin, comme le théohmètre et le pont de Wheatstone bien connu. Les directions d'utilisation sont généralement fixées, de sorte que le
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. The Street railway journal . of the total ohmic resistance requiredfor a car or the ratio that should exist between the differentpoints. His only means of dealing with them is the cut andtry method and this should certainly be eliminated in car housework wherever possible. In most instances much time andvexation could be saved by the proper use of a measuring in-strument along with a knowledge of the required resistance.Several instruments are supplied for this purpose, such as theohmeter and the well known Wheatstone bridge. Explicitdirections for operating are usually attached, so that the work-man of average intelligence can learn to use them in a fewminutes. To obtain an idea of the resistance required and the propor-tioning of the steps, the resistances of an equipment that hasby use on the road proven to be well adjusted should first bemeasured. These resistances can thereafter be taken as astandard for that equipment. The total resistance ordinarilyrequired for a two-motor car with 35-hp or 40-hp motors is. WIRING DIAGRAM OF K-10 CONTROLLER about 6 ohms. A general rule for proportioning would bethat the resistance on each point be half what it is on thepreceding one. With a rheostat resistance of 6 ohms this rulewould give: first point, 6 ohms; second point, 3 ohms; thirdpoint, iy2 ohms, and fourth or last resistance point, ohm.Measuring the resistances down to a point of laboratory accu-racy is not required, as the starting of the car is not affectedappreciably for quite a range of variation. To connect up the most usual form of bridge box it is simplynecessary to join to the terminals of the resistance to be meas-ured the terminals on the box usually marked X. But be-fore connecting the trolley should be removed from the wireto avoid all chance of injury to the instrument. The rheo-stats should be cool, as a high temperature increases thereadings appreciably. The engraving herewith shows a diagram of a K-10 con-troller with resistances and motors in their
