Improvements in Means or Apparatus for Regulating the Temperature of Electrical Heating, Cooking, or like Apparatus.
Year: 1893

page_text: Date of Application, 30th May, 1893
Complete Specification Left, 23rd Feb., 1894-Accepted, 25th May, 1894
PROVISIONAL SPECIFICATION.
Improvements in Means or Apparatus for Regulating
the
Temperature of Electrical Heating, Cooking, or like
Apparatus.
We ROOKES EVELYN BELL CROMPTON, Engineer, and HERBERT JOHN
DOWSING, Engineer, both of Mansion House Buildings in the City of London do
hereby declare the nature of this invention to be as follows:-
Our invention relates to Improvements in Means or Apparatus for Regulating
the Temperature of Electrical Heating Cooking or like Apparatus. In some
forms of electrical heating and cooking apparatus where it is desired to obtain
the required temperature as rapidly as possible it is provided with one or more
than one electrical circuit arranged with cut off switches or other devices so that
when the apparatus is first set to work several such circuits are switched into
parallel with one another and the rate at which the apparatus is heated up as
well as the consumption of energy is thereby increased. As soon as the desired
temperature is obtained in most cases it is necessary to cut off several of these
auxiliary circuits, leaving one or more circuits only in action which are sufficient
to maintain the temperature at the desired point. Hitherto the switch arrangements
to cut off the auxiliary circuits have been actuated by hand but by our improve-
ments we substitute for hand switches a series of automatic switches operated in
one or other of the following manners. We here use the word switch to denote
any apparatus for interrupting the circuits so as to prevent the flow of electricity
continuing longer in that circuit. The simplest form of apparatus for this
purpose is an adaptation of the fuse device well known to electricians which fuses
and cuts off the current of electricity if too great a current passes through that
circuit. In this particular instance we employ various alloys of lead, tin and
bismuth so proportioned that they fuse at varying temperatures ranging from
205 deg. of the Fahr. thermometer upwards. We place a properly proportioned
fuse made of a strip of this metal so that it forms part of one of the auxiliary
circuits but we make its cross section such that it will not fuse and interrupt the
circuit by the action of the current itself; but we so place and arrange it that it
fuses and interrupts the circuit from the rise in temperature of the apparatus itself.
In case we have several auxiliary circuits we may arrange them with fuses having
a varying degree of fusibility i.e. so that the first one fuses and cuts off one auxiliary
circuit as soon as the temperature reaches 250 deg. the second one fuses and cuts off
a second circuit as soon as the temperature reaches 280 deg. and the 3rd one fuses
and cuts off a circuit as soon as the temperature reaches 300 leaving a single circuit
alone to maintain the desired temperature. Such an arrangement is particularly
useful and simple and easily managed as in the case of an electric oven. Although
placing the fuse which is melted at the desired temperature so that it forms part
of the electrical circuit is the simplest manner of effecting one object, in some
cases we prefer to arrange that the fuse acts mechanically on a cut off switch by
holding the switch against the action of a spring which comes into action as soon
as the fuse melts and allows the spring to pull the switch off.
Another method which we can use for switching off the circuits in rotation in
order to keep the temperature to the desired point may consist of various devices
of releasing a detent or catch and thus allowing a spring or weighted switch to
come into action. Among other devices we propose the use of a compound bar
formed of dissimilar metals the end of which can be displaced to a sufficient extent
to release the catch. The bar may be variously formed or prolonged and bent so

page_text: as to take the form of a spiral in order that the movement of the end which
actuates the catch or detent may pass through a large space although the range in
temperature is small.
Another method which we can use for accurately regulating the temperature of
an electrical oven is to employ electrical relays to obtain sufficient power to switch
off the circuits and to actuate these relays by thermo electric couples or by the
varying expansion of two dissimilar metals forming a vibrating tongue or lever or
by the expansion of mercury in a properly arranged thermometer tube, or by the
expansion of air in a properly arranged chamber fitted with levers &c. similar to
those well known to makers of the aneroid barometer. These relay arrangements
can all of them be contrived so as not only to cut off the current but also to
switch it on again and renew the supply and hence maintain the temperature
constant.
Dated the 29th day of May 1893.
WM. BROOKES & SON,
55 & 56, Chancery Lane, London, Agents for the Applicants.
Improvements in Means or Apparatus for Regulating the
Temperature of Electrical Heating, Cooking, or like
Apparatus.
We ROOKES EVELYN BELL CROMPTON Engineer and HERBERT JOHN
DOWSING Engineer both of Mansion House Buildings, in the City of London,
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 :-
Our invention relates to Improvements in Means or Apparatus for Regulating
the Temperature of Electrical Heating, Cooking or like Apparatus. In some
forms of electrical heating and cooking apparatus where it is desired to obtain the
required temperature as rapidly as possible it is provided with one or more than
one electrical circuit arranged with cut off switches or other devices so that when
the apparatus is first set to work several such circuits are switched into parallel
with one another and the rate at which the apparatus is heated up as well as the
consumption of energy is thereby increased.
As soon as the desired temperature is obtained in most cases it is necessary to cut
off several of these auxiliary circuits leaving one or more circuits only in action
which are sufficient to maintain the temperature at the desired point.
Hitherto the switch arrangements to cut off the auxiliary circuits have been
actuated by hand but by our improvements we substitute for hand switches a series
of automatic switches operated in one or other of the following manners.
We here use the word switch to denote any apparatus for interrupting the
circuits so as to prevent the flow of electricity continuing longer in that circuit.
The simplest form of apparatus for this purpose is an adaptation of the fuse device
well known to electricians which fuses and cuts off the current of electricity if
too great a current passes through that circuit. In this particular instance we
employ various alloys of lead, tin and bismuth so proportioned that they fuse at
varying temperatures ranging from 205 deg. of the Fahr. thermometer upwards.
We place a properly proportioned fuse made of a strip of this metal so that it
forms part of one of the auxiliary circuits but we make it cross section such that
it will not fuse and interrupt the circuit by the action of the current itself; but we
so place and arrange it that it fuses and interrupts the circuit from the rise in
temperature of the apparatus itself. In case we have several auxiliary circuits we
may arrange them with fuses having a varying degree of fusibility i.e. so that the

page_text: first one fuses and cuts off one auxiliary circuit as soon as the temperature reaches
250 deg. the second one fuses and cuts off a second circuit as soon as the tempera-
ture reaches 280 deg. and the third one fuses and cuts off a circuit as soon as the
temperature reaches 300 leaving a single circuit alone to maintain the desired
temperature. Such an arrangement is particularly useful and simple and easily
managed as in the case of an electric oven. Although placing the fuse which is
melted at the desired temperature so that it forms part of the electrical circuit is
the simplest manner of effecting one object, in some cases we prefer to arrange that
the fuse acts mechanically on a cut off switch by holding the switch against the
action of a spring which conies into action as soon as the fuse melts and allows the
spring to pull the switch off.
Another method which we can use for switching off the circuits in rotation in
order to keep the temperature to the desired point may consist of various devices
of releasing a detent or catch and thus allowing a spring or weighted switch to come
into action.
Among other devices we propose the use of a compound bar formed of dissimilar
metals the end of which can be displaced to a sufficient extent to release the catch.
The bar may be variously formed or prolonged and bent so as to take the form of
a spiral in order that the movement of the end which actuates the catch or detent
may pass through a large space although the range in temperature is small.
Fig. 1 shews an embodiment of this latter method, r being the compound ring of
metals of dissimilar expansions, s the catch, s the spring actuating said catch with
a constant tendency to release itself from the sharp tooth of the ring, is a
button on the spindle 83 and serving to replace the catch s in engagement with the
tooth r¹.
Another method which we can use for accurately regulating the temperature of
an electrical oven is to employ electrical relays to obtain sufficient power to switch
off the circuits and to actuate these relays by thermoelectric couples or by the
varying expansion of two dissimilar metals forming a vibrating tongue or lever or
by the expansion of mercury in a properly arranged thermometer tube, or by the
expansion of air in a properly arranged chamber fitted with levers etcetera similar
to those well known to makers of the aneroid barometer these relay arrangements
can all of them be contrived so as not only to cut off the current but also to switch
it on again and renew the supply and hence maintain the temperature constant.
Figures 5, 6 and 7 shew the various methods mentioned of actuating the
mechanism which switches the current off and on by means of a relay. In all
these figures the external circuit S C represents an electric circuit actuated by any
of the well known electro-magnet or solenoid devices for moving the switching
apparatus, and in every case the vibrating lever L of the relay makes and breaks
contact in this circuit at the contact point P. This lever is actuated and its
position controlled by the current passing through the relay circuit RC. The
wire from point P passes to the oven and the wire leading to the pivot at end of
lever L is from the supply.
In Figure 5 the relay circuit includes a thermo electric couple T the alternate
joints of which, namely those shewn on the left hand in the drawing, are placed so
as to be maintained at the same temperature as the body which is to be electrically
heated; the other alternate junctions being maintained at the temperature of the
surrounding air. In this way a current of electricity is generated by the thermo
electric couple, the E.M.F. of which depends on the difference in temperature
between the junctions at the right hand and those at the left hand of the thermo
electric couple. The spring S is so adjusted that when the temperature conditions
in the body to be heated are those desired, then the corresponding E. M. F. and
consequent current in the relay circuit is not quite sufficient to attract the lever and
so open the circuit S. C. When however the temperature of the left hand junctions
increases to an undesirable degree the vibrating lever L is attracted, the circuit is
open and a switching apparatus which switches off the current is called into
action.

page_text: In Figure 6 the relay mechanism is the same but the current in the relay circuit
is varied by means of the vibrating tongue V, which is so constructed of two
metals, having different coefficients of expansion, that when it is heated beyond
any desired point the relay circuit is closed as above and with similar effects.
In this and in the succeeding case a special source of electric current must be
provided in the relay circuit shewn by the battery B.
In Figure 7 in place of the vibrating tongue, a thermometer tube is shewn, by
the expansion of the mercury in which the relay circuit R C is closed by the
mercury making contact at the point K. In all other respects the arrangement is
the same.
Figures 8 and 9 show two positions of an air chamber device for opening the
external circuit S C. Here G is a closed chamber the cover of which is formed of
thin corrugated metal similar to that of the exhausted chamber of an aneroid. As
soon as the body to which this is attached is to an undesirable extent, the expansion
of the air causes the cover to lift and this movement being multiplied by the lever
arrangement shewn, opens the external circuit S. C. as before.
Fig. 2 shews an arrangement of parts adapted for carrying into effect the
regulation of an electrically heated oven, which may be used instead of the
foregoing. is a rod of (say) zinc resting in a loop or frame secured to
the framing, on which are mounted the supports 1³, 1³, for the table which
carries the bearing for the vertical pin or axis extending upward from the rod 7.
Into a conical recess in the head of this axis & enters the conical end of a screw
pin which engages a correspondingly threaded seat formed in the plate spring
table and mounted on the pin , is the button by which said pin may be
turned, and by such turning, said pin caused to project more or less into the head
of the axis and thereby vary the extent of expansion of the rod which can take
place before the plate or table * is lifted. m is a fixed pin forming a centre or
pivot for an inclined or cam piece m¹ and m³ is a spring box within which is a
coiled spring m³ shewn by dotted lines, connected to the said box and cam so as to
give a constant tendency to said cam to fly away from between the plate and the
shorter support 13 between which it is at normal temperatures securely gripped but
when the temperature attained is sufficiently high to expand the zinc rod enough to
lift plate against the resistance to flexure afforded by its connection rigidly to
the longer support ³, modified by the point at which the lift is regulated by the
screw, then the grip on the cam m¹ being relaxed it is moved away and the
electrical continuity of the circuit is broken until said cam is replaced. 18 is a
pointer on the button which as it rotates traverses over a scale 1 marked on the
plate, and by its aid the regulation may be better adjusted.
Fig. 3 shews a modification of the foregoing the main feature of which consists
in the employment of a divided rod and the intervention of a lever 110 rocking on
a pivot carried by the support whereby the range of expausion in a circum-
scribed space may be increased and the delicacy of the instrument improved.
Fig. 4 is an enlarged sectional detail of the screw pin and its seating.
By the intervention of this arrangement the injury of the circuits or of the parts
of the enamelled plates in which they are embedded may be avoided.
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 :-
In means or apparatus for regulating the temperature of heating, cooking or
other like apparatus in which the heating is effected by electrical energy.
1. The construction and use of switch arrangements whereby the expansion of a
metal body or piece (composed either of one uniform or of dissimilar metals) under
the influence of an accession of heat in excess of that for which adjustment has
been made, shall cause a catch or trigger to be released and the electrical circuit
to be broken, substantially as herein before set forth and illustrated with reference
to Figs. 1, 6, 7, 8 and 9.

page_text: 2. The construction and use of a switch device wherein the expansion of a body
or bodies of metal under the influence of an excessive degree of temperature is
caused, upon a regulated point being passed, to move a spring pressure plate or
part and release a cam or incline so as to break the electrical circuit and cause
diminution of electrical energy and consequently of the heat developed, substantially
as set forth and illustrated with reference to Figs. 2 and 3.
3. The hereinbefore described method of arranging fusible bodies in a series of
circuits the individual fuses being graduated in the degree of fusibility at which
they respectively melt and break continuity of one or more of the series of circuits
from an increase in temperature in the heating, cooking or like apparatus itself,
substantially as set forth and for the purpose specified.
4. The intervention of a fusible body in a heating apparatus of the kind described,
so that a cut off switch is held out of action until by undesirable accession of heat
in that apparatus itself said fusible body is caused to melt and release the cut off
device which causes diminution of the electric energy supplied and of the heat
evolved, as and for the purpose set forth.
5. The arrangement and combination of parts of apparatus for regulating the
temperature of electrical heating cooking or like apparatus substantially as set
forth and illustrated with reference to Fig. 5.
Dated the 22nd day of February 1894
WM. BROOKES & SON,
55 & 56, Chancery Lane, London, Agents for the Applicants.