Characteristic Curve.
A curve indicating the variations in electro-motive force developed
during the rotations of the armature of a dynamo or other generator of
E. M. F. The term as used in the electrical sense is thus applied,
although the indicator diagram of a steam engine may be termed its
characteristic curve, and so in many other cases. As the amperes taken
from a series generator are increased in number, the E. M. F. rises, it
may be very rapidly up to a certain point, and thereafter more slowly.
To construct the curve coordinates, q. v., are employed. The resistance
of the dynamo and of the outer circuit being known, the current
intensity is measured. To obtain variations in electro-motive force the
external resistance is changed. Thus a number of ampere readings with
varying known resistance are obtained, and for each one an
electro-motive force is calculated by Ohm's law. From these data a curve
is plotted, usually with volts laid off on the ordinate and amperes on
the abscissa.
By other methods other characteristic curves may be obtained, for which
the titles under Curve may be consulted.