All the observations,
electrical and mechanical, are made simultaneously. The electrical horse
power put into the motor is found by the well known formula C x E / 746;
this simple multiplication and division becomes very tedious and even
laborious if many tests have to be made in quick succession, and to
obviate this trouble, and prevent errors, I have constructed a horse
power diagram, the principle of which is shown in the diagram (Fig. 1).
Graphic representations are of the greatest value in all comparative
tests. Mr. Gisbert Kapp has recently published a useful curve in the
_Electrician_, by means of which one can easily compare the power and
efficiency at a glance (Fig. 2).
The speeds are plotted as abscissae, and the electrical work absorbed
in watts divided by 746 as ordinates; then with a series-wound motor we
obtain the curve, EE. The shape of this curve depends on the type of
the motor. Variation of speed is obtained by loading the brake with
different weights.
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