Improvements in Electric Arc Lamps.
Year: 1894

page_text: Date of Application, 19th Sept., 1894-Accepted, 5th Jan., 1895
COMPLETE SPECIFICATION.
Improvements in Electric Arc Lamps.
I, JAMES DEVONSHIRE Secretary of The British Thomson-Houston, Limited,
of 38 Parliament Street, Westminster, in the County of Middlesex, (a com-
munication from Elihu Thomson, of Swampscott, County of Essex, State of
Massachusetts, U.S.A.) 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 relates to electric arc lamps, and has for its object the production
of a cheap and effective are lamp adapted for use on continuous current circuits,
although with suitable modifications to be described, it may be operated on
alternating current circuits. By the improved construction a simple arc lamp is
obtained which, when desired, can be adjusted so that at a certain strength of
current its action shall be like that of a differential lamp, wherein one magnet in
the direct circuit acts differentially or pulls against another magnet in the derived
circuit around the lamp although the action is not differential, but reproduces the
effects of differential lamps. With a little higher strength of current, the lamp
regulates its arc entirely by the action of the shunt or derived circuit magnet;
this variation may be accomplished for the normal current by a simple change in
the effect of the main circuit winding, as by shunting it or varying its turns.
The lamp constructed according to this invention is particularly designed for use
on constant potential circuits or "incandescent" circuits as they are called, in
which a potential of 110 volts-or other low voltage, is used to operate two arc
lamps in series, including a damping or choking coil in the series. This invention
however is not limited to such conditions of service, as by modifications to be
pointed out it may be applied on series or alternating current circuits.
In the drawings hereunto annexed and hereby made part of this Specification,
like letters refer to like parts throughout, and therein
Figure is a side elevation, partly in section, of a lamp embodying this
invention,
Figure 2 is a rear elevation of the shunt magnet and feeding mechanism,
Figures 3, 4, 5, 6 and 7 show details of the dash pot or pneumatic check,
Figure 8, 11, 12 and 13 show the detent and detent wheel of the feed mechanism,
Figure 9 shows in diagram the connections of the lamp with a suitable cut-out,
Figure 10 is a similar view of a modified form of a lamp adapted to alternating
current circuits,
Figure 14 shows the connection of the rack rod to the gear,
Figure 15 is a diagrammatic view, partly in section and partly in elevation, of a
lamp provided with the improved impedance or steadying coil,
Figure 16 is a view of the focussing arrangement, and
Figure 17 shows the method of arranging the detent d and the detent wheel D
to prevent arcing between them.
In Figure
the upper carbon electrode E is carried on a rack rod R, the lower
electrode E¹ being stationary, this rack rod engages with a pinion on the shaft,
which bears a large gear G, the teeth of which engage in a pinion, seen in Figure 9,
on a second shaft to the right, which second shaft carries a detent wheel D of
peculiar construction, to be hereinafter described. A lever frame L, pivoted
concentrically with the wheel D, encloses the wheel work, mounts the shaft in
place, and is connected to an iron core I, which, when attracted, raises the rack rod R,

page_text: by raising the gearing G and pinion on the same shaft with G, with which the rack
rod meshes. The core I moves in the axis of a solenoid coil C carrying the main
current of the lamp, which enters at P, passing through the coil C, thence to
the frame work or to the spring bearing on the rack rod as usual, and leaving
the lamp at N, this connection is shown dotted because in ordinary cases it
follows the frame work and goes to the negative binding post of the lamp.
K is a derived circuit magnet, wound with wire and connected by one of its
terminals to the negative side of the lamp as usual and by the other terminal to
an insulated detent d carried on its own armature lever, the detent when down on
the wheel D completes the shunt connection from the frame work of the lamp
through the magnet, K to the terminal N. While the coil C may be an enclosing
solenoid, it is preferable to make the magnet K of two coils as in ordinary electro
magnets. These are indicated at K, K, Figure 2, which is a view at right angles
to Figure 1. The armature N¹ of the magnet K is shown at a little distance
away, the pawl d resting in the fine teeth of the detent wheel D. An adjustable
spring S is arranged to pull the armature N down towards the frame L to the right
of its pivotal point, so that any downward movement of the core I will relax the
spring S, and its upward movement will tighten the spring. Hence when the
core I moves up or down by variations of current in the coil C, the tension of
the retractile spring and the action of the shunt magnet K is varied likewise. Z is
a stop on the armature N' of the shunt magnet K K which when the armature
is down and the frame L, owing to the descent of the core I, has dropped the
gear G causes the end of the lever frame to raise the detent d from the teeth of
the wheel D, and so release the mechanism, whereupon the current is immediately
weakened or taken off the lamp altogether. It will be readily seen that the descent
of the core 1, followed by the descent of the left hand portion of the lever frame L,
causes a rise of its right hand end and the elevation of the stop Z thereon, thus
forcing the armature N¹ towards the magnet K K, positively, and raising the
detent d.
It is preferable to combine the core I or other parts in such a way as to provide
a dash-pot or air cushion, although a separate dash-pot cushion for checking the
movements might be introduced. To this end the coil C is wound upon a brass
tube and the core I, as in Figures 3 to 7, is made up of a piece of iron pipe I, on the
upper part of which is strung a piston of brass or other suitable metal p, mounted
on a cap e which also acts as a stop and prevents the core I being pulled too far into
the coil C, a projection on the cap c being provided, as shown, which abuts on the
head of the cylinder or dash-pot tube above. A bent connecting rod 3 enters the
hollow piston I, and engages near the point 1, Figure 1, with the lever frame L. A
single pint, Figure 3, inserted through openings in the pistor, in the upper end of the
core 1, in depending lugs on the cap c, and in the upper end of the connecting rods,
ties all these parts together before their insertion in the cylinder upon which the
coil C is wound, after which the pin t cannot escape or be disengaged without
withdrawing the parts.
A portion of the rim of the detent wheel D and the insulated detent d, carried
by the armature lever L' of the magnet K is shown separately in Figure 8. The
detent or pawl d is made of silver. The detent wheel D is either silver plated or
a corrugated strip of silver is placed on its periphery. Figure 11 shows a strip
of thin sheet silver which is suitably corrugated and bent around the periphery of
the detent wheel D, as indicated in Figure 12, and secured thereto in any suitable
way, as by soldering. This gives a succession of moderately fine rounded teeth,
and is cheaply produced, while it permits also the use of the preferable metal silver
for the periphery of the wheel.
A skeleton view of the connections and arrangements of the lamp is shown in
Figure 9 and will be understood from what has gone before in the way of descriptive
matter. It should be stated here that it is preferable to surround the core of the
magnet K with a copper tube or good conductor, as indicated at T, Figure 9, so as
to make its action moderately sluggish and also to abolish sparking at the contacts

page_text: by annulling the self-induction of the winding. As indicated in Figure 14, it is
preferable not to fasten the wheel G firmly to its axis, but to arrange a ratchet
connection, as usual, so that the rack rod R may run upward without rotating the
mechanism, but on the downward motion the wheel work will turn. The action of
the lamp may be briefly stated as follows. On the passage of the current through
the lamp with the detent d in an upraised position with the main core I down, the
wheel work is free so that, the carbons are always in contact, the current passes
through the solenoid coil C and then through the carbons E E' and out at
the negative terminal. This causes an attraction and uplifting of the core I,
which raises the frame L, lifting the pinion g, Figure 9, meshing with the rack rod,
hut on the instant of such uplifting the armature lever L' is released and the
detent d falls into place on the edge of the wheel D, stopping the wheel work.
Hence any further motion upward raises the carbon rack-rod and starts an arc.
This are continues until by the increase of the current in the shunt magnet it.
attracts its armature against the action of the spring S, and in so doing opens its
own circuit between the detent d and the wheel rim of D, at the same time releasing
a tooth on the wheel, which slips by the detent. The lifting of the detent d
however so weakens the magnet K that a re-engagement of the detent and wheel
at once takes place, and the feed of the lamp is perfectly positive as well as delicate
and is accomplished with practically little or no spark between the detent d and the
rim of the wheel D. If the force of the current in C is great enough to pull the
core up to its highest point, as limited by the projections on the piston cap c,
Figure 4, then the spring S, Figure 2, becomes set at a given force and the lamp
feeds always when such force is overcome by the pull of the magnet K, a fraction
of a volt being generally sufficient to determine whether or not the lamp shall feed.
If however the force of the current or the turns of the coil C or the weight of the
core and frame work which it lifts, are such that the core floats, as it may be
called, or the projections on the cap c do not strike, then the action of the shunt
magnet is dependent on the position of the core 1 as determined by the current in C
rising or falling, because the retractile force of the spring when the core I is
In such cases
floating is variable according to the position of the lever frame L.
the feeding action of the lamp is dependent upon the current as well as on the
voltage of the are, and may be made closely approximate to the differential action
of a good differential lamp. As described, the lamp is adapted perfectly to operate
on constant potential circuits.
1f a number of lamps are to be operated in series on a circuit, a cut-out is
needed in case of failure to feed, and a suitable cut-out is shown in Figure 9
connected by dotted lines. A small electro-magnet with an armature and contact
making lever is shown at M, L. On the magnet is placed a heavy copper casing
or tube T' to render its action quite sluggish. Wound upon the core is also a
winding K of fine wire and comparatively high resistance, which is placed in
shunt to the detent d and the wheel D, so that when the detent leaves the wheel,
the fine wire is in circuit in series with the wire on the magnet K, or in derived
circuit around the are, but when the detent d touches the wheel rim K' is shunted.
If by failure to feed, the detent d leaves the wheel D frequently, or vibrates
rapidly thereon, it energizes the shunting fine wire coil K' sufficiently to cause the
armature of the magnet M to be attracted and close the contact at A, thereby
causing the current to pass through a second winding J, of coarse wire, which
connects the terminals of the lamp through the contact A and so maintains the
force of the magnet M, keeping the contact A closed until the carbons E, E' are
brought together to again shunt the coil J. While in this arrangement the fine
wire coil K has been placed in shunt around the contact between the detent d and
the wheel D to act as a cut out in case of a failure to feed, it is manifest that a
coil of considerable resistance may be used around the contact irrespectively of its
cut-out function. This however is not desirable in case of lamps working on
constant potential circuits, while it might be desirable on lamps working on
constant current or in series with other lamps.

page_text: To adapt the lamp to work satisfactorily and readily on alternating circuits of
constant potential and not in series with other lamps, the arrangement may be
modified as shown in Figure 10. In this case the core I is of course laminated and
divided so as to cut off eddy-currents in it, while the main current coil C acts to
lift the laminated core and create the arc in the same way as in Figures 1 and 9, but
the feeding is effected by a simple weakening of the current due to the lengthening
of the arc established between the carbons E E'. The core therefore descends
and closes a contact at Q on the end of the lever frame L. The contact Q is in
circuit with a coil C³, around the laminated core I, forming a secondary to the main
coil C, which thus becomes the primary of a transformer or induction coil. The
coil C is in circuit with the coil on the feeding magnet K2, and the detent d and
wheel D also form a contact in this local circuit, which depends for its current on
induction from the main coil C acting on the coil C2 as a secondary. When the
contact Q closes detent d will be down, but will be at once lifted by the energizing
of the magnet K2 by the induced currents from C². The lamp will therefore feed
by the raising of the detent d, but as this detent breaks the local circuit on its rise,
the feeding is interrupted and can only take place by renewed breaks or liftings of the
armature of the magnet K². Hence the feeding is gradual and continuous until
the carbon is fed to a sufficient extent to slightly increase the current in C and open
contact Q. Where the lamps are to be used in series on alternating circuits, the
arrangement of the circuits may be as in Figure 9 with the exception of the damping
tube T on the magnet M which should have a laminated core and be wound so as to
be put into derived circuit around the arc. There is apt to be more spark at the
contacts between d and D in such an arrangement than is desirable, and hence a
"dead
resistance shunt taking the place of K' should in such cases be employed
around said contact.
"
To render the current steady when a lamp is used on alternating current circuits
of constant potential it is preferable to employ an inductive coil which acts to prevent
sudden fluctuations in the strength of the current, as shown in Figure 15, this coil
may conveniently be placed in the top of the lamp box, and may comprise a number
of turns of wire C³ conveying the main current to the lamp surrounded by an iron
core I, of circular form preferably, and arranged so that the heat generated by the
coil passes off freely from the upper part of the lamp. This coil acts by its
impedance, that is, by its resistance and self-induction combined, to steady the
current. Below it is mounted the mechanism, such as has been described in the
preceding figures, or other suitable feeding mechanism. The main line is shown in
heavy dotted lines passing from the insulated binding post through the impedance
coil and thence through the arc producing magnet coil C, and then through the
carbons of the lamp.
It is sometimes desirable to construct the lamp so that both carbons are moved
the lower carbon upward and the upper carbon downward, and if the relative sizes
of the carbon be selected so that the rate of burning is the same for the lower and
upper carbon, a focussing action is easily obtained by the device shown in Figure 16.
Here the rack rod R is carried on the pinion y as in the figures preceding. A cord
or chain attached to the rack-rod at a point adjacent to the wheel passes over the
wheel, which is free to move on its pivots suitably mounted in the lamp case, and the
other end of the cord is carried on a second rod 2 which serves as the means of
sustaining the carrier of the lower carbon. The rack rod R and the rod
may
be
square and pass through suitable openings in the frame, as indicated, such openings
embracing enough of the rod to form efficient guides and allow free vertical movement.
The rod is made tubular and the lower carbon carrier is insulated therefrom, an
insulated conductor passing down through the rod connecting the lower carbon
carrier to the negative terminal of the lamp.
In some cases in which the potential of the circuit on which the lamp is run is
moderately high the dropping of the core 1, owing to the cessation of current on the
burning out of the carbons might cause the detent d to be lifted from the wheel D
when sufficient potential exists across the break or separation to maintain a small

page_text: current in the form of a diminutive arc. This would eventually damage the
structure by burning the insulation and by injuring the metal surfaces. If the
separation at d were increased in range, this difficulty would be obviated, but another
means for obviating it and avoiding the difficulty is to make a second break in the
connection from the shunt magnet K to the detent in series with the break at d.. To
this end an insulated strip V is fixed to the frame of the lamp, having a contact
piece at its upper end, while another piece w is insulated on the armature lever L'.
This last piece w is connected to the detent pawl d and moves with it.
armature lever L' is down, contact will be made between in 1 V. an l als
and the wheel D, both in series with the shunt coil K. When however by the fall
of the core I the arinature lever L' is lifted to open the contact at d, the contact
between w and V is at the same time opened to a considerable extent on account of
the leverage given to them. One or both of the contacts w or V are made flexible,
and the opening of the contact is just after the opening of d, an 1 its closing, like vise,
is just before the closing of d.
When the
between d
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 what
I claim is :-
1. In an electric arc lamp, a series coil, a core reciprocating therein, a frame
pivoted to the frame of the lamp and actuated by such core, gearing carried in the
frame, a rack-rod for the upper carbon meshing with such gearing, a detent
engaging with the gearing and fixed to the armature, a damped shunt magnet
actuating the detent and a stop affixed to the frame and arranged, substantially as
described, to lift the detent when the current ceases.
2. The method of operating an alternating current arc lamp, which consists in
actuating the magnet controlling the feed with current induced from the main or arc
producing current.
3. The method of operating an alternating current arc lamp, which consists in
actuating a magnet controlling the feed with current derived from a secondary coil
in inductive relation to the series coil of the lamp.
4. In an electric arc lamp, the combination of a series coil, a second coil in
inductive relation thereto, a magnet in the circuit of the second coil, a detent
actuated by the magnet, gearing operated by the series coil, and a contact a lapted
to close the circuit through the second coil and the feed magnet.
5. In an electric arc lamp, a series coil, a core for such coil, a second coil in
inductive relation to, the series coil, a magnet in the circuit of such second coil, a
detent actuated by the magnet, a frame connected to the core of the series coil and
containing the gearing, a rack-rod meshing with the gearing, and a contact actuated
by the movement of the core or frame and arranged and adapted, as herein
described, to complete the circuit through the second coil upon the descent of the
core.
6. In an electric arc lamp, a series coil, a core reciprocating in such series coil,
a frame pivotted to the frame of the lamp and connected to such core, gearing in the
frame, a rack-rod for the carbons meshing with such gearing, a detent preventing
the descent of the carbon, a magnet operating such detent, a second coil upon the
same core with the series coil, a circuit including the detent, the magnet, and
the second coil, and a contact adapted to close such circuit upon the descent of the
carbon, whereby the inductive current in the second coil is caused to operate the
detent and release the gearing to feed the lamp by a step-by-step or incremental
motion.
7. An electric are lamp for alternating current circuits provided with an impedance
coil adapted to steady the arc.
8. An electric arc lamp for alternating current circuits provided with a coil having
both resistance and self-induction and arranged in the circuit so that the current
passes through such coil before passing through the series coil of the lamp, whereby

page_text: the current in the lamp is steadied and the arc and illumination made more
uniform.
9. In an electric arc lamp, a detent wheel for the gearing comprising a corrugated
strip of silver secured to the rim of the wheel.
10. In an electric are lamp, a dash-pot for the core of the series coil comprising
a tube provided with a cap adapted to register with the shell of the solenoid, a
smaller tube comprising the iron of the core, and a rod arranged to connect with
the moving part of the lamp, the parts being secured together by a single pin, as
herein set out.
11. In an electric are lamp, a cut-out comprising the following elements, a contact
closing a circuit around the lamp, a magnet adapted to actuate the contact and
having two windings, one in shunt to the feeding contacts of the lamp and the other
included in the circuit around the lamp closed by the contact.
12. In an electric lamp, a series coil, the gearing actuated thereby and adapted
to separate the carbons to establish an arc, a shunt feeding coil arranged to release
the gearing and feeding the carbons together, and a cut-out comprising an electro-
magnet having thereon a closed conductor and two energizing windings, one a shunt
around contacts in the circuit of the shunt feeding magnet of the lamp and the other
a coarser winding for conveying the main current, and contacts completing the
circuit through said coarse winding and adapted to be closed by the armature of
said magnet.
13. In an electric are lamp, the combination of a series magnet for establishing
the arc, a shunt magnet adapted to feed the carbons towards each other by the
separation of contacts in its own circuit, a circuit in shunt to said contacts, and a
cut-out adapted to be actuated by the current flowing in said shunt circuit.
14. In an electric arc lamp, operated by gearing and provided with a detent for
such gearing embraced in the circuit of the shunt feeding magnet, a second or
auxiliary break in such shunt circuit adapted to prevent the formation of an are
between the detent and the wheel with which it engages.
15. In an electric are lamp, operated by gearing and provided with a gear detent
wheel D and a detent d actuated by the shunt magnet of the lamp and included in
its circuit, a second or auxiliary break having flexible contacts and included in the
shunt circuit of the lamp, all arranged as herein described, to prevent the formation
* of an arc between the detent and the detent wheel.
Dated this 18th day of September 1894.
JAMES DEVONSHIRE.