An Improved Apparatus for Maintaining a Constant Temperature of Metallic Wires Heated by an Electric Current.
Year: 1897

page_text: Date of Application, 14th May, 1897 Accepted, 17th July, 1897
COMPLETE SPECIFICATION.
An Improved Apparatus for Maintaining a Constant Temperature of
Metallic Wires Heated by an Electric Current.
We, ROBERT BERGLUND and BARON RICHARD DE WENDEL, both of 4 Lasa-
rettsgatan, Göteborg, in the County of Westergotland, Kingdom of Sweden
Mechanical 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 relates to an apparatus for maintaining constant the temperature
of an electric circuit, more especially of one used for heating purposes.
'T'he
apparatus is so arranged as to stop the flow of the current, used for developing
the heat through the circuit, when the temperature of the latter commences to rise.
above that required and again switch on the current as soon as the temperature of
the circuit has dropped to the required degree.
In the accompanying drawing we have shown such an apparatus in plan.
The apparatus consists of a two-armed pivoted lever a made of metal and acted
upon by a spring i, one arm of said lever being connected with a fine metallic
wire (of platinum, for instance) which at its other end is provided with a tension-
adjusting arrangement as for instance a screw, by means of which the lever is
acted upon in a direction opposite to that in which the spring i tends to move it.
Adjoining the end of the other arm of the lever is an adjustable contact-piece d
which is electrically connected with one extremity of the coil of an electromagnete
while the other extremity of said coil is connected to one of the terminals of a
source of electricity such as a battery f, the other terminal of which is connected
with the lever a. The armature of the electromagnet e consists of a two-armed
lever which is in electric connection with the lever a. Opposite that end of the
armature, which is farthest away from the electromagnet, there is a contact piece h
which is connected to one of the terminals of the current source m such as a storage
battery, used for heating the circuit. The other terminal of the latter source of
electric current is connected with the wire to be heated, said wire being in metallic
connection with the wire b.
The current required for heating .the wire normally passes from the source of
electricity m through the wire k to the wire b and continues through the latter to
the lever and the armature 9 which, as a rule, is held pulled away from the
electromagnet and resting against the contact piece h, so that the current will flow
from the armature through said contact piece and back to the source m.
Assuming now that the temperature, of the wire rises above that required,
then the current flowing through the wire b will heat this wire more than ordinarily,
causing it to expand more than would normally be the case, and, as a result the
other end of the lever a which is normally held away from the contact piece d by
the tight wire b will under the influence of the spring be brought into contact
with the said contact piece d. The circuit from the battery / consequently being
complete through the lever a, the contact piece d and the electromagnet e, the
latter will attract its armature 9 and interrupt the contact of said armature with
the piece h, thus discontinuing the heating current and causing the temperature

page_text: of the wire k to fall. When the wire k has recovered its original temperature, the
wire will contract and deflect the lever a out of contact with the piece d, thus
stopping the flow of current from the battery f. The armature 9 being con-
sequently reversed, the circuit of the wire k will again be closed. By suitable
adjustment of the contact piece d it will evidently be possible to close the battery
circuit at a smaller or greater deflection of the lever a, or elongation of the wire b,
the elongation being dependent on the quantity of electricity flowing through the
wire in a given time.
The adjustment of the contact piece may be accomplished by turning an
eccentric or cam 7 which is in contact with one end of the piece d, which is held
against the eccentric by a spring. It is evident that the armature may equally
well be made as a simple lever, the contact piece in this case being located at
the opposite side of the armature with reference to the electromagnet.
It is also evident that the independent source of electricity f may be dispensed
with, if the electromagnet instead is arranged to be actuated by the current of the
wire by connecting the said electromagnet e with a branch circuit from the said
wire k.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is:-
'
An apparatus, termed an electrothermostat, for maintaining constant the
temperature of metallic wires heated by an electric current, consisting of a tightly
stretched metal wire bone end of which is permanently connected with the wire k
to be heated, which wire is also connected with one of the terminals of a source
of electricity m, while the other end of the aforesaid metal wire b is joined to one
arm of a pivoted lever a which is connected both with the armature g of an
electromagnete and with one terminal of the source of electricity m mentioned,
cr of an independent source of electricity f, a contact piece h which is connected
to the other terminal of the first mentioned source of electricity and against which
the armature g is normally pressed, and a contact piece d connected through the
coil of the electromagnet with the second terminal of the source of electricity m
or f and arranged in the path of the other arm of the pivoted lever a, though
normally not in contact with it, for the purpose, by virtue of the elongation of
the tight metal wire b due to any increase in the temperature of
the wire to be heated, to cause a discontinuance of the flow of current
through the latter wire at the instant an increase of its temperature occurs, and to
bring about a renewed flow of current from the source of electricity when the said
wire has recovered its original temperature.
Doted th
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HASELTINE, LAKE & Co.,
45 Southampton Buildings, W.C., Agents for the Applicants.