Year: 1885

page_text: I, EDGAR ARTHUR ASHCROFT, of N° 14 Finsbury Oircus in the City of London,
Electric Engineer do hereby declare the nature of this invention to be as follows:-
This invention is intended to secure a steady and continuous regulation of the
distance between the two carbons generally used in electric arc lamps.
This is effected by the employment of an electro motor, having. a continuous
revolving armature of annular or drum form (such as those of Gramme, Siemens,
Schuckert, Edison &c) placed in a shunt circuit from the two terminals of the
lamp, for the purpose of bringing the carbons together.
The carbons are separated by means of a weight, and an incandescent carbon
lamp is placed in the same shunt circuit as the above mentioned motor for the
purpose of counteracting (by its decreased resistance at high temperature) the
increased resistance of the wire of the motor, due to the heating effect of the
electric current. The arrangement of the lamp which I prefer to employ for
carrying out my said invention is as follows:-
The upper carbon is carried by a toothed rack with which gears a pinion on the
motor spindle, or driven thereby by intermediate gearing, which rack is suspended
by a weighted cord passing over a pulley, the weight being greater than that of
the rack rod and carbon, so as to draw the carbons apart. Or the weight may be
replaced by a spring for the same purpose. The motor being placed on a shunt,
receives but a small portion of the current by reason of its high resistance and that
of the incandescent carbon lamp in circuit.
As the carbons are apart on closing the circuit, the only path for the current is
through the coils of the electro motor; this is consequently set in motion and
thereby effects the contact of the carbons.
When this takes place, the difference of potentials between the lamp terminal is
decreased owing to the decreased total resistance of the lamp, and the weight raises
the rack until the arc attains the normal length to which the lamp is adjusted (on
account of the decreased power of the motor to overcome the action of the said
weight). As the carbons consume away, the increased. resistance of the arc causes
an increased difference of potentials between the lamp terminals, causing more
current to flow through the motor, enduing it with power to readjust the arc by
driving the rack down until the carbons attain the normal distance. The increased
difference of potentials also causes more current to flow through the incandescent
DO71

page_text: lamp which is in the same circuit as the motor, and by heating it to higher
incandesence, reducing its resistance, thus further adding to the sensitive action of
the motor. This goes on until the carbons are consumed, when the motion of the
rack is arrested by a small stop pin.
The rack and positive terminal are insulated from the remaining portions of the
lamp, as is also the motor. The negative terminal is in contact with the frame of
the lamp and receives the return current from the lower carbon through supporting
rods.
“ABEL & IMRAY,
Agents for the Applicant.
I, EDGAR ARTHUR ASHCROFT, of N° 14 Finsbury Circus in the City of London,
Electric Engineer, 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 :—
This invention is intended to secure a steady and continuous regulation of the
distance between the two carbons generally used in electric arc lamps.
This is effected by the employment of an electro motor, having a continuous
revolving armature of annular or drum form (such as those of Gramme, Siemens,
Schuckert, Edison &c) placed in a shunt circuit from the two terminals of the
lamp for the purpose of bringing the carbons together.
The carbons are separated by means of a weight, and an incandescent carbon
lamp is placed in the same shunt circuit as the above mentioned motor for the
purpose of counteracting (by its decreased resistance at high temperature) the
increased resistance of the wire of the motor, due to the heating effect of the
electric current. One arrangement of the lamp which I employ for carrying out
my said invention is as follows:-
The upper carbon is carried by a toothed rack with which gears a pinion on the
motor spindle, or driven thereby by intermediate gearing, which rack is suspended
by a weighted cord passing over a pulley, the weight being greater than the rack
rod and carbon, so as to draw the carbons apart. Or the weight may be replaced
by a spring for the same purpose. The motor being placed on a shunt, receives
but a small portion of the current by reason of its high resistance and that of the
incandescent carbon lamp in circuit with it,

page_text: As the carbons are apart on closing the circuit, the only path for the current is
through the coils of the electro motor; this is consequently set in motion and
thereby effects the contact of the carbons.
When this takes place, the difference of potentials between the lamp terminals
is decreased owing to the decreased proportional resistance to the lamp relatively
to the total resistance of the circuit in which it is placed, and the weight raises
the rack until the arc attains the normal, length to which the lamp is adjusted
(on account of the decreased power of the motor to overcome the action of the said
weight). As the carbons consume away the increased resistance of the arc causes
an increased difference of potentials between the lamp terminals, causing more
current to flow through the motor, endowing it with power to readjust the arc by
driving the rack down until the carbons attain the normal distance. The increased
difference of potentials also causes more current to flow through the incandescent
lamp which is in the same circuit as the motor, and by heating it to higher
incandescence, reduces its resistance, thus further adding to the sensitive action of
the motor. This goes on until the carbons are consumed, when the motion of the
rack is arrested by a small stop pin.
The rack and positive terminal are insulated from the remaining portions of the
lamp, as is also the motor. The negative terminal is in contact with the frame of
the lamp and receives the return current from the lower carbon through supporting
rods.
Figs. 1 to 3 of the accompanying drawings shew an electric are lamp con-
structed according to my above described invention. Fig. 1 shews a front elevation,
Fig. 2 shews a side elevation, Fig. 3 shews an enlarged detail.
The framing A of the lamp carries at bottom the fixed lower carbon holder B,
while at top it carries a pulley C over which passes a cord D having a toothed
rack E attached to its one end that carries the upper carbon holder B¹, while its
other end carries a weight F that overbalances the weight of the rack and its
carbon, so that the weight always has a tendency to draw the upper carbon away
from the lower carbon. G is an electric motor, the axis of whose revolving
armature G' has a pinion in gear with a rack E.
The current of the lamp passes from screw H through wire I to the bracket J
that carries the motor and which is insulated from the framing A of the lamp;
from this bracket it is conveyed by a contact brush at K to the rack E, whence it
passes through the holder B¹ and upper carbon, to the lower carbon holder B and
framing A to the screw L. From the point M a shunt current passes through the
incandescent lamp N, insulated from the framing A, and thence through the coils
of the electro motor to the framing A. and screw L. Thus assuming the carbons
to be at the normal distance apart, only so much of the current will pass through
the shunt circuit as will enable the armature G¹ in tending to move the rack E
and upper carbon downwards, to hold in balance the opposite tendency of the
weight F to move the carbon upwards, but as soon as by the burning away of the
carbons or from some other cause the resistance of the lamp circuit is increased,
the resulting increase of the current in the shunt circuit will cause the armature to
move the upper carbon downwards until the normal resistance of the lamp is again
established, when in consequence of the corresponding decrease of current in the
shunt circuit the above described equilibrium between the action of the armature
and the weight will be re-established.
On the cessation of the current, the weight, meeting with no resistance from the
motor, will draw the carbons apart and on again starting the current, as the whole
of this will in the first instance pass through the shunt circuit, the motor will
move the upper carbon downwards until the lamp circuit is closed, after which
the adjustment of the carbon to the normal distance will be effected in the above
described manner. By introducing an incandescent lamp N into the shunt circuit,
the decreased resistance of this due to an increase in the shunt current will com-
pensate for the increased resistance of the motor's coils due to the heating effect
of such increase of current.

page_text: Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that I am
aware that it has been proposed before to include one or more electro-motors in the
circuit of a lamp, these being so arranged as, by its or their rotation in contrary
directions, according as the lamp circuits' resistance is increased or diminished, to
move the carbons either nearer together or farther apart, and I therefore do not
claim such an arrangement but what I claim is:-
1. In an arc electric lamp, regulating the distance of the carbons by means of an
electro-motor included in a shunt circuit of the lamp, operating in combination
with a weight in such manner that while the electro motor always tends to bring
the carbons together, the weight always tends to separate them, substantially as
berein described.
2. In combination with a shunt circuit of an arc lamp, the use of a carbon
conductor or glow lamp forming part of such circuit and which, when raised to
incandescence, reduces the resistance of the shunt circuit and thus compensates for 1
the increase of resistance due to the heating of the metallic part of the conductor
of the shunt circuit, substantially as herein described.