Improvements in Electric Arc Lamps.
Year: 1893

page_text: Date of Application, 27th Mar., 1893-Accepted, 13th May. 1893
COMPLETE SPECIFICATION.
Improvements in Electric Arc Lamps.
We, SIEMENS BROTHERS & Co. LIMITED, of 12 Queen Anne's Gate, West-
minster, in the County of London, and JOHN NEBEL, of 74 Woodland Terrace,
Old Charlton, in the County of Kent, all Electrical Engineers, 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 has reference to the construction of electric arc lamps described
in the Specification to Patent No. 366 of 1888, in which the upper carbon of the
lamp was suspended from a spring barrel controlled by an escapement and by a
pivotted frame carrying an armature that was acted upon by an electro magnet in
a shunt of the lamp circuit.
The present invention relates to certain improvements in the construction of the
said lamp, which we will proceed to describe with reference to the accompanying
drawings in which
Fig. 1 shews a front elevation of the lamp with the casing in section, Fig. 2
shews a side elevation and Fig. 3 a plan.
The main features of the lamp are similar to those described in the said
Specification, that is to say, a metal band A from which the upper carbon holder K
is suspended, is coiled round the periphery of a spring barrel B, mounted with its
axis upon a frame C, pivotted on points D, and carrying an armature E, the
frame C being suspended by a spring F from a post G, and having its position
controlled by an electro magnet H. This electro magnet however, instead of
having its pole pieces at top, and being excited by a shunt current only, as in the
original construction, is, according to our present invention, constructed with its
pole pieces H at bottom, and it is provided firstly with windings of thick wire in
series with the lamp circuit and secondly with windings of thin wire which are in
a shunt on the lamp circuit, the last named windings being so arranged that the
current therein acts in opposition to that of the series windings, so that while the
series current by itself produces a strong electro magnet, the shunt current tends
to weaken this magnet.
These windings are so arranged that when the lamp is in normal action, the series
winding produces more ampére-turns than the shunt windings, and the magnetic
force thus produced in attracting the armature E maintains the frame C in the
requisite raised position for maintaining the carbons at the required distance apart
for forming the arc.
The two different windings may either each be situated on a separate limb of the
magnet, or they may both be partly situated on each limb.
The frame C carries clockwork mechanism II controlled by an escapement J so
as to regulate the rotation of the barrel B during the descent of the upper carbon
holder, as in the original arrangement, and, a stop L is provided for arresting the
escapement and consequently the descent of the upper carbon when, in the norma
working of the lamp, the current passing through the series winding is sufficiently
powerful to hold the armature and frame in such a raised position that the
tongue J of the escapement comes in contact with the stop L. The attractive
force of the electro magnet combined with the upward pull of the spring Fare so
proportioned relatively to the downward pull of the frame, barrel, and upper
carbon holder, that under the above mentioned conditions the upper carbon will be
held at the exact distance from the lower carbon to form the required arc, this
distance being capable of regulation by adjustment of the post G that supports the
spring F as in the previous construction.
When the resistance of the arc increases, owing to the burning away of the

page_text: carbons, less current will pass through the series windings and more will pass
through the shunt windings of the magnet. The force of the latter being
proportionately decreased, the frame C will sink by gravity sufficiently to free the
escapement J from the stop L whereupon the clockwork will be set in motion to
allow of the approach of the carbons to the required extent, after which the
frame C will again rise and the clockwork be stopped as before.
When the current ceases, the frame C will descend again, and the clockwork will
be set in motion until the upper carbon has descended and rests upon the lower
carbon.
Thus on the current being again started the full strength passing through the
series windings of the magnet will cause this to raise the frame C and upper carbon
sufficiently to form the arc.
If the carbons have burnt away to such an extent that they cannot come in
contact as described, or if the clockwork should stick so as to prevent this, then
the frame C will descend still farther until a contact plate M carried thereby
touches at its one end the contact pillar N in connection with the lamp frame or
positive terminal O and at its other end the contact pillar N¹ insulated from the
frame and connected with the negative terminal 01. The lamp being thus short
circuited, all the other lamps in series on the same circuit will remain in action.
P is a dash pot, of any suitable construction, connected to the frame C for
steadying its motion; Q is a spring operating as in the original construction
for compensating for the loss of weight due to the burning away of the upper
carbon.
R is a spring also operating as before for winding up the band on the barrel
when the upper carbon holder is raised by hand.
Having now particularly described and ascertained the nature of this inven-
tion and in what manuer the same is to be performed, we declare that what
we claim is :-
1. In an electric are lamp of the kind herein referred to, the combination with
the rocking frame C of an electro magnet H having lower pole pieces H¹ and
having thick wire windings in series with the lamp circuit and thin wire windings in
a shunt on the lamp circuit operating in opposition to the series windings, the
arrangement being such that in the normal working of the lamp the attraction of
the electro magnet excited by the series current will hold the armature and frame
in a raised position so as to form the arc and to stop the descent of the carbon,
while on the resistance of the arc increasing, the consequent increase of the shunt
current will weaken the electro magnet sufficiently to cause the descent of the
frame, and the consequent lowering of the upper carbon by the clockwork, sub-
stantially as described.
2. In combination with the frame C referred to in the preceding claim, the use of
a contact plate M carried by the frame, and of contact posts N N¹ connected
respectively with the positive and negative terminals of the lamp, so that when the
frame C sinks sufficiently for the plate M to make contact with the posts N N' the
lamp will be short circuited, substantially as described.
Dated this 27th day of March 1893.
ABEL & IMRAY,
Agents for the Applicants.