. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . it will readily be seen that if ourchart has a certain fixed line, called thebase line, already ruled upon it, the dis-tance of any point on this base line fromthe line- drawn by the pen will be a meas-ure of the draw-bar pull, and if we havethe paper suitably graduated we can atonce read off the pull in pounds. Sucha chart is shown in Fig. 3, and is a fairexample of all the charts made by dyna-mometer cars. It will be obvious that the spool Mcould just as well be driven by some other
. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . it will readily be seen that if ourchart has a certain fixed line, called thebase line, already ruled upon it, the dis-tance of any point on this base line fromthe line- drawn by the pen will be a meas-ure of the draw-bar pull, and if we havethe paper suitably graduated we can atonce read off the pull in pounds. Sucha chart is shown in Fig. 3, and is a fairexample of all the charts made by dyna-mometer cars. It will be obvious that the spool Mcould just as well be driven by some othersource of power than the car wheels, andthis is frequently the case. The usualarrangement then is to drive the papermechanism by a constant speed electricmotor. Where the paper is operated bythe car wheels the machine is said tohave a distance base and where it isdriven by a motor it has a time is, in the first case the paper movesa distance proportional to the distancecovered by the car, say one inch per 1,000feet, while in the second case the papermoves equal distances in equal periods. FIG. 2. THE MECHANISM OF A DYNAMOMETER CAR. traces a line on the chart K, which isrolled from the spool L onto the spool Mby means of motion transmitted from thewheel of the car through the pulleys Nand O and the belt P. Now if we imagine a locomotive to becoupled to the car, as soon as it starts topull on the coupler D, the lever E willtransmit this force to the piston rod Fand produce a pressure in the cylinder pressure is very high at the coupler,but it is quite small in the cylinder,owing to the proportions of the lever, andthe comparatively large diameter of the of time. On some cars, notably two re-cently constructed by the Southern Rail-way, the paper may be driven either wayby the manipulation of a lever. This is all the mechanism there wouldhave to be on a simple dynamometer carfor measuring and recording the draw-bar pull, but there is one other elementof the greates
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