Improvements in Aro Lamps.
Year: 1889

page_text: Date of Application, 17th Apr., 1889
Complete Specification Left, 17th Feb., 1890-Accepted, 22nd Mar., 1890
PROVISIONAL SPECIFICATION.
Improvements in Aro Lamps.
I, GEORGE HOOKнAм of Nos. 7 & 8 New Bartholomew Street Birmingham, Mann-
facturer do hereby declare the nature of this invention to be as follows :-
-
In the simplest form of arc lamp constructed according to my invention the feed
mechanism is actuated by the weight of the upper carbon & the carbon-holder. The
descent of this weight is retarded by the eddy-currents generated in a Foucault disc,
similar to that described in the Complete Specification of Letters Patent granted to me
and numbered 4225/87 with which disc the weight is connected by multiplying gear.
It is so arranged that when the current & the E. M. F. are normal the rate of approach
between the carbons is approximately that required to maintain the current & the
E. M. F. at their normal values. If C represents a circuit carrying the main current,
& E a circuit formed by a shunt between the terminals of the lamp, then the said
Foucault disc may be retarded (more or less) by two magnets, one whose magnetising
force is proportional to C E, the other to C + E.
-
The C+E magnet may clamp the disc (& stop the feed) when E C exceeds a
certain value. For alternating currents the disc must be retarded by a permanent
magnet,, & the strength of the motive force may be increased or diminished by a
solenoid or solenoids, or equivalent devices, so as to obtain the same result. And both
with direct & alternating currents the + E magnetising effect may be applied
directly, to one of the carbons, so as to diminish the energy consumed in the arc when
it tends to exceed a given value. Instead of utilizing the weight of the carbon & its
holder, I may employ a spring motor as in clockwork, or an electro-motor, especially
when used as described in my meter patent above referred to. In the latter case I
may differentially wind the magnets of the motor so as to assist in regulating the rate
of feed. In both cases the motor works against Foucault currents, which increase or
diminish in intensity (the rate varying as the square of such intensity) according to
the requirements of the arc.
I may feed the carbon (or carbons) down tubes or guides accurately in line with
one another it being so arranged that when no current is passing the carbons may
come together, & one of them be clipped (& in some cases withdrawn to the required
distance) on the passage of sufficient current.
To this 16th d
A: 1000
COMPLETE SPECIFICATION.
Improvements in Arc Lamps.
I GEORGE HOOKHAM of Nos. 7 & 8 New Bartholomew Street, Birmingham, Manu-
facturer do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by the
following statement :-
In the simplest form of arc-lamp constructed according to my invention the feed
mechanism is actuated by the weight of the upper carbon-holder & carbon. The
descent of this weight is retarded by the eddy-currents generated in a Foucault dise
similar to that described in the Complete Specification of Letters Patent granted to
me and numbered 4225/87, with which disc the weight is connected by a multiplying
gear. It is so arranged that when the current and the E. M. F. are normal, the rate
of approach between the carbons is approximately that required to keep them normal.
If C represents a circuit carrying the main current, & E a circuit formed by a shunt
between the terminals of the lamp, then the said Foucault disc may be retarded (more
גנ..מ

page_text: or less) by two magnets, one whose magnetising force is proportional to C-E, the
other to C+E. The C+E magnet may clamp the disc (& stop the feed) when EC
exceeds a certain value. Instead of utilizing the weight of the
upper
carbon and its
holder as a motive force, I may use a spring motor, consisting of a spring like the
main-spring of a clock driving a train of wheels, wh. in conjunction with the Foucault
disc will, when the current & E. M. F. are normal, give approximately the proper rate
of feed. In any case the motor works against Foucault currents wh. increase or
decrease in intensity according to the requirements of the arc.
By the method above described I can, by the use of two separate magnets pro-
ducing Foucault currents in the copper disc, construct a lamp in which the energy
expended in the arc shall, within narrow limits, remain constant, even though both
current and E. M. F. be subject to variation. In practice, however, the current
supplied to arc-lamps is approximately constant either in quantity or pressure: i.e.
either the current or the E. M. F. may be assumed invariable. In these cases a
single magnet producing currents in the disc will suffice; & I will first describe
with reference to the accompanying drawing the construction of a lamp according to
my invention, suitable for running in parallel on a circuit in which the E. M. F. is
assumed constant.
In Fig. 1, wh. represents an arc-lamp constructed according to my invention, A'is
the upper carbon-holder. This, in a lamp of ordinary dimensions (consuming, say,
50 watts.) should weigh not less than about 4 lbs. A is connected by a cord, pulleys,
and multiplying gear, not requiring special description, with a copper disc B. The
dise B, would, if left uncontrolled, rotate at great speed under the influence of the
weight of A. Ü is an electro-magnet (shown also in side elevation in Fig. 2) through
whose coils the main current passes; its poles N, S, generating powerful currents in
the disc B. These currents retard the rotation of the disc, & consequently the descent
of the upper carbon. D is a clamp which arrests the motion of the disc when no
current is passing in the high-resistance shunt-magnet, E. The terminals of this
shunt are so connected with the lamp-switch that current passes through the shunt-
coils as soon as the lamp is switched on, & continues so to pass, causing the magnet to
attract the clamp D, till the lamp is switched-off; the object being to prevent the
racing of the disc when the lamp is cut out. F is an electro-magnet made by the
main current. While this current is passing through the arc, F attracts & holds
down the lower carbon-holder, G, against the action of a spring: its function is to
strike the arc as soon as current passes across the carbons. The operation of the lamp
is as follows:-
The weight of the upper carbon-holder, and the brake-strength of the magnet C
(which brake-strength may be increased by splitting-up the poles as described in
iny before-mentioned Specification viz. that numbered 4225/87) are adjusted by trial,
till with normal current the rate of descent of A approximately compensates for
the waste of the carbons; the retarding action of C being in all cases very great
as compared with the friction to be overcome by the weight of A in its descent.
Suppose that the carbons are not in contact when the lamp is switched-on. The
clamp D is raised, no current is passing in C, and the disc B races till the carbons
touch. Current now passes; G is attracted, and the arc is struck.
The rapid
rotation of B is immediately arrested by the action of the magnet, C, and the
rate of descent of A tends to be normal. If the rate exceeds the normal, & the
carbon points approach too closely, the current in C increases and the disc is
retarded; if on the other hand the carbons recede too far the one from the other,
the current in C diminishes and the feed is accelerated. Thus the action of the
magnet on the disc brings about a rate of feed, which is normal within narrow
limits. When the lamp is switched-off, the carbons are left touching, or almost
touching each other, & the lamp is ready for use when again required. The iron
in the magnet C should be far removed from saturation under the influence of the
main current.
For use in series with other lamps, on a constant-current circuit, the magnet C
must be wound differentially with coils carrying the main and shunt currents. The

page_text: main current preponderates, and the strength of the magnet is proportional to the
difference between the two magnetizing effects. If, now, the arc becomes too long,
the E. M. F. rises, this difference becomes smaller, & the feed is accelerated. On the
contrary if the arc becomes too short, the feed is retarded. An automatic cut-out of
a common type is provided, which breaks the shunt current round this magnet, when
the main current is broken.
Lastly, suppose both the current & E. M. F. to be variable. A single magnet
differentially wound as above is now insufficient, since the difference may remain
constant even though both terms vary. This magnet must, therefore, be supplemented
by another (applied to another part of the disc) which should be magnetized in the
same sense by the main & shunt currents acting in conjunction. The action of the
two magnets combined will tend to keep the energy expended in the arc constant.
For instance, suppose both current & E. M. F. to fall off. The action of the first
magnet may remain unchanged; but the second will cause the carbons to approach
and increase the energy consumed in the arc. The function of the differential magnet
is to tend to keep the relation between current & E. M. F. fairly constant: which
relation might vary to any extent under the action of the other magnet alone. On
any circuit this arrangement is the best, unless either the current or E. M. F. is main-
tained absolutely constant; but in practice it is not generally necessary.
I do not confine myself to the use of a disc of metal for the brake: I may use
any other figure of revolution.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
:-
In an arc-lamp the construction and arrangement of parts whereby the feed of the
carbons is regulated by the increase or decrease of electrical currents generated in
a metal disc substantially as described & illustrated in the accompanying drawing.
Dated this 15th day of February 1890.
GEORGE HUUKHAM.