Note: Descriptions are shown in the official language in which they were submitted.
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This applicati~n is a divisional of applicatiom No.
481 412 filed May 13, 1985.
This invention relates to improvements in heating apparat~e
and in particular though not exclusively, to heating apparatus
of the type disclosed in our co-pending U.~. Patent Application
No.8320717 (Publication No. 2132060A~ ? incorporating one or more
sources of in~ra~red radiation.
The heating apparatus disclosed in U~K. Patent Application
No. 8320717 consists of, in one example, a shallow tray member
- containing a layer of thermally-insulative material 9 above which
four infra-red-emitting, tungsten-halogen la~ps are supported.
The tray member, usually along with a number of similar members
maj be mounted beneath a layer of glass ceramic to form a
cooking hob.
A thermal limiter is preferably provided in the heating
apparatus to ensure that the maximum operating temperature Or
the glass ceramic is not exceeded. A number of discrete
temperature settings are also provided by swltching the lamps
into series and/or parallel configurations, ~herein one or more
diodes are usually required to achieve one or more of the lower
settings.
However, some problems may be ~ound to occur under
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particular circum~tances of operat~on of the apparatu3 7 such as
operation o~ th~ limiter cawing it to trip and di3connect the
powPr ~upply ~o the lamps 9 ~hich may be a source of annoyance
for a user of the apparatus, or lt may not be de3irable to use
the diodes in the s~ltching arrangement, as they tend to
interfere ~ith the harmonics of the main ~upply.
It is therefore an object of the present invention to
provide heating apparatus which alleviates at least the
above-mentioned potential problems, as well as bein~
cost-effective.
According to the present invention, there i~ provided a
heating unit suitable for mounting in a cooking hob9 said unit
comprisinS a base layer of thermally-insulative material, a
peripheral thermally-insulative wall to define a first hotplate
region, an inner t~ermally-insulati~e wall to define a second
hotplate region located within said first region, at least one
infra-red lamp each including a fllament emissive of in~ra-red
radiation and commensurate with said second hotplate region,
further heating means commensurate with said first hotplate
region, further heating means commensurate with ~aid fir~t
hotplate region 9 and means for energising ~aid filament and said
further heating mean~ independently and concurrently,
selectively.
The invention will be de~cribed by way of example only with
reference to the accompanying drawings 9 wherein:-
Figure 1 sho~s a schematic plan view of one embodiment of
the invention,
~igure 2 Qhows an alternative embodiment to that ~hown in
Figure 1~
30Figure~ 3a and 3b show ~witching arrangements to provide
discrete power outputs in accordance with the invention,
Figures ll and 5 show two further embodiments of the
inveDtior., and
Figure 6 shows a ~chematic sectional view through I-I in
Figure 1 of the embodiment 3hown, mounted in a cooking hob.
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Referring to Figure 1, there is shown a heating unit
cor.3isting of a circular tray 1 having a layer 2 of
thermally-ir,sulative material~ such as microporous material,
disposed therein and a peripheral thermally-in~ulative wall 3,
within which rour infra-red lamps, one shown at 4, are
supported. Each lamp 4 consists of tungsten filament 5
supported within a tubular quartz envelope 6, ~nd each end of
each lamp 4 i~ formed ~ith a pinch seal (not shown), having a
conrection between the respective end of the filament 5 and ar
electrical connector sealed therein, each pinch ~eal being
hou3ed within a ceramic end cap, such as at 7.
The tray 1 also include3 an inner thermally-insulative wall
89 uhich is concentric ~ith the peripheral wall 3 and of such a
diameter as to enclose the entire length of all o~ the filaments
5 within the lamps 4.
BetwePn the peripheral wall 3 and the inner wall 8, two
conventional, electrical, wire-wound heating elements 9 and 10
are disposed.
As shown in Figure 6, the heating unit is preferahly
mour~ted beneath, and urged up towards, a glass ceramic plate l9,
by a suitable mounting arrangement 20, to form a hotplate of a
cooking hob. The mounting arrangement 2G is fixed to a base 21
of a housing for the coo~ing hob.
The four la~p filament3 5 and the two elements 9 and 10 may
be energised independently and/or concurrently, 90 that only the
central hotplate region ~ithin the inner wall or alternatively
the whole region may be heated. Furthermore, any combination
of one or more lamps and one or both elements may be energised
to provide various discrete power outputs, and thus temperature
settings, whilst maintaining an aesthetically pleasing balanced
effect of the lamps, as seen through the glass ceramic plate.
Preferably, a thermal limiter (not shown) either mechanical
or electror,ic, is also employed within the heating apparatus to
limit the operating temperature of the apparatus to prevent
damage to the glass cçramic by overheating. It may be
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preferabl~ for the limiter to control the heating el~ments 9 and
1O only? 30 that tripping of the limiter would not be ~o
con3picuous, as only the elements, and not the lamps, ~ould be
de-energised if overheating occurred.
It may be preferable to arra~ge that switching of the lamp
filaments into variou series and~or parallel configurations
provides relatively hi8h power outputs and that energisation of
ore or both o~ the heating elements 9 and 10 provides lower
power outputs.
tO Figure 2, ~herein like parts are labelled with like
reference numerals uith respect to Figure 1, ~hows an
alternative embodiment to that shown in Figure 1, wherein only
three 'amps, such as at 4, are provided in combination with only
one heating element 9.
Such an arrangement~ as shown in Figure 2, may be
advantageous in that one lamp ha been replaced by a
conventional heating element, thereby providing a cost saving in
manufacture of the apparatus.
Figures 3a and 3b show the configurations of four lamp
filaments 11 ko 14 requlred to generate the third lowest and the
lowest po~er ou~puts Or the apparatus. The remainin8
configurations ~or the power outputs provided are shown in our
abo~e-mentioned co-pendir~ ~.R. Patent Application No~8320717,
~herein the config~rations giving the sa~e power outputs as
tho~e ~ho~D in Figures 3a and 3b also include one or more diodes
to generate the required power output.
~cwever, the use of these diodes may be disadvantageous, as
they tend to cause harmonics disturbances in the mains power
~upply.
The present configurations shown in Figures 3a and 3b
overcome this disadvantage by including an additional element 15
in series with the configuration formed by lamp filaments 11 to
14, which, uhen switched into the two configurations generates
the ~ame respective power outputs as ~hen diodes are used. The
element 15 may be either a fifth lamp filament or a conventional
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heating element as ~o~n in Figures 1 and 2.
A further use o~ the additional element 15 may be as a
pre-heating device to produce ~aster warm~up periods of the
apparatus. The use Or the element 15 would provide a high
power output ~or an initial warm-up period, the length of which
could be controlled by a timer and/or a thermal 3en~0r device.
The element 15 could also be used at various times during
- enersisation of the lamp ~ilaments 11 to 14, but pre~erably not
continuously. Subse~uent use Or the element 15 after the
initial ~arm-up period could be controlled manually.
The initial warm-up period could be controlled by any
suitable type of timing device J SO that the element 15 is
de-energised at the end of a predetermined time, such as 6 mins.
~or example.
Alternatively or additionally, the initial warm-up period
could be controlled by any suitable thermal dev.ce, including a
pre-set thermostat dispo~ed at any suitable location within the
apparatus to cause de-energi~ation of element 15 when a certain
operatin3 temperature is attained. Possible advanta~es of
using a pre-heating element 15 may be that power outputs
exceeding the limit that the glass ceramic is ~apable o~
withstanding may be utilised, because it is only ener~ised until
the required operatir~ temperature is attained, and additionally
at lowPr outputs, a thermal lim ter to protect the glass ceramic
may not be required, as the glass ceramic should not exceed it~
limit at these lo~er outputs. This therefore ~ay provide an
additional cost saving.
However, if a limiter to protect the glass ceramic is
employed, it may be necessary to cause the timer and/or thermal
device controlling the pre-heating element 15 to by-pass the
limiter, at least while the element 15 is initially energised,
to prevent nui3ance trlpping o~ the limiter.
Figures 4 and 5, wherein like parts are also labelled with
like re~erence numerals with respect to Figures 1 and 2, show
two alternative embodiment~ w~ch include an additional filament
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accommodated wlthin each lamp, instead of a conYentional heating
element.
Each lamp, as at 4 shown in Figure 4 accommodate~ a
filamert 5, the ~ength Or ~hich is commensurate ~ith the area of
tbe inDer hotplate region within t~e wall 8, and a 3econd
filament 16, the len3th of which is commen~urate with the area
of the ~hole hotplate region within the outer wall 3. The two
filaments may be energised independently and~or concurrently as
required.
The embodiment s~o~n in Figure 5 i5 provided with a
non-central inner hotplate region within the inner wall ~9 which
is integral around part of its circumference with the outer ~all
3. A iamp filament 18 is acco~modated within each lamp 4,
ha~i~g a length commensurate with the area of the whole hotplate
re~ion. However, each filament 18 is tapped at a point 19
along it~ length, so that, if required only the filament length
coiDciding with the area of the inner hotplate region may be
energised. Filament 18 thus ef~ectively con3ists of a filament
~2 co~men~urate the inner hotplate region and an extended
~0 portion 23 thereof commensurate with the whole hotplate region.
The embodiments ~hown in Figure~ 4 and 5 may be
adv2ntageous in providing an increased number of switching
co~binatios of the ~ilament3~ especially if they are maintained
at 2 100~ output, as well as being cost-effective, because t~o
~il2ments are accommodated within only one l~mp.
In the preferred embodiment of the heating apparatus
disclosed in U.K. Patent Appli~ation No.8320717, each lamp is
provided with an infra-red-reflective coating applied to the
lcwer half of the quartz envelope~ to reflect radiation emitted
do~ardly from the filaments back in an upwards direction
to~ards the glas9 ceramic plate.
It m~y ho~ever be preferable to provide a suitable
infra-red reflector between the lamps ard the layer 2 of
thermally-insulative ~aterial, which may be cost-effective and
easier to manufacture.
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It ~an o~ cour~P be enYisaged that some Or the dirferent
embodiments ~hown in the Figures could be used in co~binatlon
with each other, as well as each embodiment being u3ed in
i301ation.
