Curve, Life.
A characteristic curve showing the relations between the durability and
conditions affecting the same in any appliance. It is used most for
incandescent lamps. The hours of burning before failure give ordinates,
and the rates of burning, expressed indirectly in volts or in
candle-power, give abscissas. For each voltage or for each candle-power
an average duration is deducible from experience, so that two dependent
sets of data are obtained for the construction of the curve.
Curve, Load.
A characteristic curve of a dynamo, expressing the relation between its
voltage and the amount of excitation under a definite condition of
ampere load, at a constant speed. The ordinates represent voltage, the
abscissas ampere turns in the field, and the curves may be constructed
for a flow of 0, 50, 100, or .. , or any other number of amperes.
Fig. 123. LOAD CURVES.
Curve, Magnetization.
A characteristic curve of an electromagnet, indicating the relation of
magnetization to exciting current. Laying off on the axis of ordinates
the quantities of magnetism evoked, and the corresponding strengths of
the exciting current on the axis of abscissas, the curve can be plotted.
It first rises rapidly, indicating a rapid increase of magnetization,
but grows nearly horizontal as the iron becomes more saturated. The
effect due to the coils alone, or the effect produced in the absence of
iron is a straight line, because air does not change in permeability.
Curve of Distribution of Potential in Armature.
A characteristic curve indicating the distribution of potential
difference between adjoining sections of the commutator of an armature
in different positions all around it. The potential differences are
taken by a volt-meter or potential galvanometer, connection with the
armature being made by two small metal brushes, held at a distance apart
equal to the distance from centre to centre of two adjoining commutator
bars. The curve is laid out as if by polar co-ordinates extending around
the cross-section of the commutator, with the distances from the
commutator surface to the curve proportional to the potential
differences as determined by shifting the pair of brushes all around the
commutator.
The above is S. P. Thompson's method. Another method of W. M. Mordey
involves the use of a pilot brush. (See Brush, Pilot.) Otherwise the
method is in general terms identical with the above.