As it touches one wheel it turns it in one direction. This moves a
sliding contact in one direction so as to increase a resistance. This
corresponds to a motion of the plunger in one direction. As the driving
wheel moves in the opposite direction by a reverse action it diminishes
the resistance. Thus the increase and decrease of resistance correspond
to opposite movements of the solenoid plunger, and consequently to
opposite variations in the current. The whole is so adjusted that the
variations in resistance maintain a constant amperage. The resistance is
in the exciting circuit of the dynamo.
In Brush's regulator, which is purely mechanical, a series dynamo is
made to give a constant current by introducing across the field magnets
a shunt of variable resistance, whose resistance is changed by an
electro-magnet, whose coils are in circuit with the main current. Carbon
resistance discs are used which the electro-magnet by its attraction for
its armature, presses with varying intensity. This alters the
resistance, decreasing it as the current increases and the reverse. As
the connection is in shunt this action goes to maintain a constant
current.
Regulation, Constant Potential.
The regulation of constant potential dynamos is executed on the same
lines as that of constant current dynamos. If done by a controlling
coil, it must for constant potential regulation be wound with fine wire
and connected as a shunt for some part of the machine.
Regulation of Dynamos.
The regulation of dynamos so that they shall maintain a constant
potential difference in the leads of their circuit for multiple arc
systems or shall deliver a constant current in series systems. Hence two
different systems of regulation are required, (a) constant potential
regulation--(b) constant current regulation. The first named is by far
the more important, as it concerns multiple arc lighting, which is the
system universally used for incandescent lighting.
S. P. Thompson thus summarizes the methods of governing or regulating
dynamos. Premising that alteration of the magnetic flux is the almost
universal way of control, it can be done in two ways; first, by varying
the excitation or ampere turns of the field, and second by varying the
reluctance of the magnetic circuit. The excitation or magnetic flux may
be varied
(a) by hand, with the aid of rheostats and commutators in the exciting
circuit;
(b) automatically, by governors, taking the place of the hand;
(c) by compound windings. The magnetic circuit may have its reluctance
caused to vary in several ways;
(d) by moving the pole pieces nearer to or further from the armature;
(e) by opening or closing some gap in the magnetic circuit (field-magnet
core);
(f) by drawing the armature endways from between the pole pieces;
(g) by shunting some of the magnetic lines away from the armature by a
magnetic shunt.
The latter magnetic circuit methods d, e, f, and g, have never met with
much success except on small machines or motors. Method e is adopted in
the Edison motor, the yoke being withdrawn or brought nearer the cores
of the coils. (See Regulation, Constant Current-Regulation, constant
Potential.)