Abstrict
An electric heater (10) incorporates at least one heating element
(20), at least one wall member (16) upstanding in the heater, and
a device (42) is provided for detecting a cooking utensil (6) supported
on an upper surface (4) of a cooking plate (2) overlying the heater.
The device (42) comprises at least one inductively-operating loop
(44) of electrically conductive material having a plurality of portions
(50, 52, 54) adapted to extend over and spaced from the at least
one electric heating element (20) between fixed supporting regions
(56, 58, 60, 62) on the at least one wall member (16). The at least
one loop (44) of electrically conductive material is such that the
plurality of portions (50, 52, 54) are substantially incapable of
self-support as such at normal operating temperatures of the electric
heater. The plurality of portions (50, 52, 54) are supported by
elongate members (64, 66, 68) of heat-withstanding material.
Claims
I claim:
1. An electric heater incorporating at least one heating element,
at least one wall member upstanding in the heater, and a device
for detecting a cooking utensil supported on an upper surface of
a cooking plate overlying the heater, the device comprising at least
one inductively operating loop of electrically conductive material
having a plurality of portions thereof adapted to extend over and
spaced from the at least one electric heating element between fixed
supporting regions on the at least one wall member, the at least
one loop of electrically conductive material being such that the
plurality of portions are substantially incapable of self-support
as such at normal operating temperatures of the electric heater,
the plurality of portions being supported by elongate members of
heat-withstanding material.
2. A heater as claimed in claim 1, wherein the at least one wall
member is adapted to contact the lower surface of the cooking plate.
3. A heater as claimed in claim 1, wherein the at least one wall
member comprises thermal and electrical insulation material.
4. A heater as claimed in claim 1, wherein the fixed supporting
regions are provided at upper regions of the at least one wall member.
5. A heater as claimed in claim 4, wherein the fixed supporting
regions are provided in the form of recesses or channels for receiving
at least one of: at least one of intermediate portions and end portions
of the at least one loop of electrically conductive material; and
at least one of the ends of the elongate members.
6. A heater as claimed in claim 4, wherein the fixed supporting
regions are provided in the form of regions of the at least one
wall member into which at least one of: at least one of the intermediate
portions and end portions of the at least one loop of electrically
conductive material are embedded or moulded; and at least one of
the ends of the elongate members are embedded or moulded.
7. A heater as claimed in claim 1, wherein the elongate members
of heat-withstanding material are selected from beams and tubes.
8. A heater as claimed in claim 7, wherein the beams comprise channels
for receiving the portions of the at least one loop of electrically
conductive material.
9. A heater as claimed in claim 8, wherein the beams are arranged
such that the channels are open towards the lower surface of the
cooking plate.
10. A heater as claimed in claim 7, wherein the tubes are selected
from circular, oval and rectangular cross-section tubes.
11. A heater as claimed in claim 1, wherein the elongate members
of heat-withstanding material comprise ceramic material.
12. A heater as claimed in claim 11, wherein the ceramic material
is selected from steatite, cordierite, alumina and a glass material
such as quartz.
13. A heater as claimed in claim 1, wherein the elongate members
are each substantially linear.
14. A heater as claimed in claim 13, wherein the elongate members
are arranged in a configuration selected from a substantially rectangular,
a substantially triangular, a substantially trapezoidal and a substantially
V-shaped array.
15. A heater as claimed in claim 1, wherein the elongate members
are interconnected or united at ends thereof to form a frame.
16. A heater as claimed in claim 1, wherein the at least one loop
of electrically conductive material comprises a material in a form
selected from thin wire and ribbon having a composition selected
from metal and metal alloy.
17. A heater as claimed in claim 16, wherein the at least one loop
of electrically conductive material comprises a single turn of the
thin wire or ribbon.
18. A heater as claimed in claim 1, wherein the at least one loop
of electrically conductive material comprises a material which is
susceptible to damage by direct thermal radiation from the at least
one electric heating element, the plurality of portions of the at
least one loop being substantially protected from such damage by
being shielded by the elongate members from the direct thermal radiation.
19. A heater as claimed in claim 18, wherein the electrically conductive
material comprises a material selected from ferritic stainless steel,
austenitic stainless steel and a copper alloy.
20. A heater as claimed in claim 1 and including at least two heating
zones, each incorporating at least one heating element and each
being surrounded by one of the wall members, at least two of the
loops of the electrically conductive material being provided, the
loops being associated with the at least two heating zones to detect
different sizes of the cooking utensil supported on the upper surface
of the cooking plate.
21. A heater as claimed in claim 1, wherein the at least one loop
of electrically conductive material has open ends thereof adapted
to be electrically connected to circuit means for detecting a change
in electrical inductance in the at least one loop associated with
placement and/or removal of the cooking utensil relative to the
upper surface of the cooking plate and for effecting an appropriate
one of energising and de-energising the at least one electric heating
element.
22. A heater as claimed in claim 21, wherein the open ends of the
at least one loop of electrically conductive material are electrically
connected to electrical terminal means provided at a peripheral
region of the electric heater.
23. A heater as claimed in claim 22, wherein the electrical terminal
means are provided on a terminal block.
24. A heater as claimed in claim 23, wherein the terminal block
comprises or forms part of a housing associated with a temperature-responsive
device provided on the electric heater.
25. A heater as claimed in claim 1, wherein the at least one wall
member comprises bound vermiculite.
26. A heater as claimed in claim 1, wherein the cooking plate comprises
glass-ceramic material.
27. A heater as claimed in claim 1 and including a base layer of
thermal and electrical insulation material relative to which is
supported the at least one electric heating element.
28. A heater as claimed in claim 1 and including a dish-like support.
29. A heater as claimed in claim 28, wherein the dish-like support
comprises metal.
Description [0001] This invention relates to an electric heater incorporating
a device for detecting a cooking utensil, such as a pan, supported
on an upper surface of a cooking plate, such as of glass-ceramic
material, overlying the heater, the electric heater incorporating
at least one electric heating element. Such a device comprises at
least one inductively-operating loop of electrically conductive
material which is provided in the heater and is electrically connected
to an electrical circuit, such as an oscillatory circuit, which
operates to detect changes in electrical inductance in the loop
of electrically conductive material resulting from placement and/or
removal of the cooking utensil on and/or from the upper surface
of the cooking plate, and to effect appropriate energising and/or
de-energising of the at least one electric heating element.
DESCRIPTION OF PRIOR ART
[0002] For efficient operation of the detecting device, it has
been found necessary to provide the inductively-operating loop as
close as possible to the lower surface of the cooking plate and
also such that it extends spaced from and at least partly overlying
the electric heating element. This has hitherto been accomplished
by providing the loop of a relatively thick rigid wire material
so as to be self-supporting where it overhangs the heating element,
and particularly to avoid deformation and sagging when subjected
to normal operating temperatures in the heater. Furthermore, because
such a loop is exposed to direct thermal radiation from the underlying
heating element or elements and subjected to temperatures of the
order of 750 degrees Celsius, it has been found necessary to provide
the loop of a relatively expensive material which is not susceptible
to thermal damage by the direct thermal radiation from the heating
element or elements.
[0003] It has also been proposed to provide a wire-form inductively-operating
loop stretched across the top of a heater between supports at the
periphery of the heater, the wire-form loop being suitably arranged
in the form of an open triangle. However, in order to avoid deformation
and sagging of the loop during operation of the heater, it has been
found necessary to provide one or more elastically-resilient supports
for the loop, to maintain a suitable mechanical tension in the loop.
Such an arrangement is inconvenient to implement.
OBJECT OF THE INVENTION
[0004] It is an object of the present invention to overcome or
minimise the aforementioned problems.
SUMMARY OF THE INVENTION
[0005] According to the present invention there is provided an
electric heater incorporating at least one heating element, at least
one wall member upstanding in the heater, and a device for detecting
a cooking utensil supported on an upper surface of a cooking plate
overlying the heater, the device comprising at least one inductively-operating
loop of electrically conductive material having a plurality of portions
thereof adapted to extend over and spaced from the at least one
electric heating element between fixed supporting regions on the
least one wall member, the at least one loop of electrically conductive
material being such that the plurality of portions are substantially
incapable of self-support as such at normal operating temperatures
of the electric heater, the plurality of portions being supported
by elongate members of heat-withstanding material.
[0006] For the avoidance of doubt, it is to be understood that
by the plurality of portions of the at least one loop of electrically
conductive material being substantially incapable of self-support
at normal operating temperatures of the electric heater, it is meant
that the plurality of portions would undergo deformation, such as
sagging, at normal operating temperatures of the electric heater,
if not supported.
[0007] The at least one wall member may be adapted to contact the
lower surface of the cooking plate and may comprise thermal and
electrical insulation material. The fixed supporting regions may
be provided at upper regions of the at least one wall member, such
as in the form of recesses or channels for receiving intermediate
and/or end portions of the at least one loop of electrically conductive
material or ends of the elongate members, or in the form of regions
of the at least one wall member into which the intermediate and/or
end portions of the at least one loop of electrically conductive
material, or the ends of the elongate members, are embedded or moulded.
[0008] The elongate members of heat-withstanding material may comprise
beams or tubes. Such beams may comprise channels for receiving the
portions of the at least one loop of electrically conductive material,
and the beams may be arranged such that the channels are open towards
the lower surface of the cooking plate. Such tubes may be of circular,
oval or rectangular cross-section.
[0009] The elongate members of heat-withstanding material may comprise
ceramic material, such as steatite, cordierite, alumina or a glass
material such as quartz.
[0010] The elongate members may each be substantially linear and
may be arranged in a substantially rectangular, triangular, trapezoidal
or V-shaped array.
[0011] The elongate members may be interconnected or united at
ends thereof to form a frame.
[0012] The at least one loop of electrically conductive material
may comprise a thin wire or ribbon of metal or metal alloy and may
comprise a single turn thereof.
[0013] The at least one loop of electrically conductive material
may comprise a material which is susceptible to damage by direct
thermal radiation from the at least one electric heating element,
the plurality of portions of the at least one loop being substantially
protected from such damage by being shielded by the elongate members
from the direct thermal radiation. The electrically conductive material
may comprise a ferritic or austenitic stainless steel or a copper
alloy.
[0014] The electric heater may comprise at least two heating zones,
each incorporating at least one heating element and each being surrounded
by one of the wall members, at least two of the loops of the electrically
conductive material being provided, the loops being associated with
the at least two heating zones to detect different sizes of the
cooking utensil supported on the upper surface of the cooking plate.
[0015] The at least one loop of electrically conductive material
may have open ends thereof adapted to be electrically connected
to circuit means for detecting a change in electrical inductance
in the at least one loop associated with placement and/or removal
of the cooking utensil on and/or from the upper surface of the cooking
plate and for effecting appropriate energising and/or de-energising
of the at least one electric heating element.
[0016] The open ends of the at least one loop of electrically conductive
material may be electrically connected to the circuit means by way
of electrical terminal means provided at a peripheral region of
the electric heater. Such electrical terminal means may be provided
on a terminal block, which may comprise or form part of a housing
associated with a temperature-responsive device provided on the
electric heater.
[0017] The device may be provided as a modular assembly for attaching
to the electric heater. Such modular assembly may include the at
least one wall member.
[0018] The at least one wall member may comprise bound vermiculite.
[0019] The cooking plate may comprise glass-ceramic material.
[0020] The electric heater may comprise a base layer of thermal
and electrical insulation material relative to which is supported
the at least one electric heating element.
[0021] The electric heater may comprise a dish-like support, such
as of metal.
[0022] By means of the present invention an inductively-operating
loop of electrically conductive material may be provided of relatively
thin wire or ribbon material, which has portions thereof supported
by elongate members overlying one or more heating elements in a
heater, the loop also being protected by the elongate members against
thermal radiation damage from the heating element or elements, thereby
avoiding a requirement for very high temperature-withstanding material
to be used for the loop.
[0023] For a better understanding of the present invention and
to show more clearly how it may be carried into effect, reference
will now be made by way of example to the accompanying drawings
in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is an exploded perspective view of an assembly of
a cooking utensil supported on an upper surface of a cooking plate
overlying an electric heater arranged in contact with a lower surface
of the cooking plate, the electric heater being provided with an
embodiment of a cooking utensil detection device according to the
present invention;
[0025] FIGS. 2A, 2B and 2C are cross-sectional views of alternative
constructions of elongate members supporting portions of an inductively-operating
loop of electrically conductive material in the detection device
of FIG. 1;
[0026] FIGS. 3A to 3D are detailed perspective views of alternative
arrangements of fixed supporting regions on a wall member, for the
inductively-operating loop in the cooking utensil detection device
of FIG. 1;
[0027] FIG. 4 is a plan view of an integral arrangement of the
elongate members supporting the portions of the inductively-operating
loop, for use as an alternative arrangement in the detection device
of FIG. 1;
[0028] FIG. 5 is a perspective view of an alternative embodiment
of cooking utensil detection device according to the present invention;
and
[0029] FIG. 6 is an exploded perspective view of a further assembly
of a cooking utensil supported on an upper surface of a cooking
plate overlying an electric heater arranged in contact with a lower
surface of the cooking plate, the electric heater having two heating
zones and being provided with a further embodiment of cooking utensil
detection device according to the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0030] Referring to FIG. 1, a glass-ceramic cooking plate 2 has
an upper surface 4 for receiving a cooking utensil 6, such as a
pan. A lower surface 8 of the cooking plate 2 has an electric heater
10 supported in contact therewith.
[0031] The electric heater 10 comprises a dish-like support 12,
such as of metal, in which is a base layer 14 of thermal and electrical
insulation material, such as microporous thermal and electrical
insulation material. A peripheral wall member 16 of thermal and
electrical insulation material, such as bound vermiculite, is arranged
upstanding in the dish-like support 12 and has an upper surface
18 contacting the lower surface 8 of the cooking plate 2.
[0032] At least one radiant electrical resistance heating element
20 is supported relative to the base layer 14. The heating element
or elements 20 can comprise any of the well-known forms of heating
element, such as wire, ribbon, foil or lamp forms, or combinations
thereof. In particular, the heating element or elements 20 can be
of corrugated ribbon form, supported edgewise on the base layer
14 of insulation material.
[0033] A terminal block 22 is provided at the edge of the dish-like
support 12 and electrically connected to one end of the heating
element or elements 20.
[0034] A temperature-responsive device 24, of known basic construction,
has an elongate probe portion 26 extending at least partly across
the heater and overlying the heating element or elements 20. The
temperature-responsive device 24 also has a housing portion 28 of
electrically insulating material arranged externally of the heater
and suitably containing one or more switch components of known form.
The housing portion 28 supports electrical terminals, two of which
are visible in FIG. 1 and denoted by reference numerals 30 and 32.
[0035] The heating element or elements 20 is or are electrically
connected to a power supply 34 by way of leads 36 and 38 and a control
system 40, which may include microprocessor-based circuitry. The
lead 36 is connected to one end of the heating element or elements
20 by way of the terminal block 22. The lead 38 is connected to
the other end of the heating element or elements 20 by way of the
terminal 30 on one side of the housing portion 28 of the temperature-responsive
device 24, a switch means (not shown) inside the housing portion
28, and a further terminal (not shown) on the opposite side of the
housing portion 28.
[0036] A device 42 is provided for detecting the cooking utensil
6 when placed on and removed from the cooking plate 2 and operating
to automatically energise and de-energise the heater 10 by way of
the control system 40. The device 42 comprises an inductively-operating
loop 44 of electrically conductive material, in the form of thin
wire or ribbon, having open end or terminal portions 46, 48. The
loop 44 of wire or ribbon suitably comprises a ferritic or austenitic
stainless steel or a copper alloy.
[0037] The loop 44 has three portions 50, 52, 54 arranged in triangular
form and extending over and spaced from the heating element or elements
20, between fixed supporting regions 56, 58, 60 and 62 provided
at upper regions of the wall member 16.
[0038] The wire or ribbon material of the loop 44 is such that
the wire or ribbon portions 50, 52, 54 of the loop are substantially
incapable of self-support per se and if used alone would deform
and sag, particularly under the high temperature operating conditions
of the heater, which involves temperatures of up to about 750 degrees
Celsius. Furthermore, the material of the loop 44 would be susceptible
to harmful damage and degradation if subjected to direct thermal
radiation from the heating element or elements 20. These problems
are overcome in the present invention by providing elongate members
64, 66, 68 of heat-withstanding material to support and shield the
portions 50, 52, 54 of the loop 44. The elongate members 64, 66,
68 suitably comprise ceramic material, such as steatite, cordierite,
alumina or a glass material such as quartz. The elongate members
64, 66, 68, are substantially linear and may be in the form of tubes,
such as of circular or oval cross-section, as shown in FIGS. 2A
and 2B, or may be in the form of channels, as shown in FIG. 2C.
Such channels are suitably arranged to be open towards the lower
surface 8 of the cooking plate 2.
[0039] The fixed supporting regions 56, 58, 60 and 62 are suitably
provided at upper regions of the wall member 16 and may be in the
form of recesses or channels for receiving intermediate 70 and/or
end 46, 48 portions of the loop 44, for example as illustrated in
FIG. 3A, or for receiving ends 72, 74 of the elongate members 64,
66, 68, such as illustrated in FIG. 3B.
[0040] Alternatively, the fixed supporting regions 56, 58, 60 and
62 may comprise upper regions of the wall member 16 into which the
intermediate 70 and/or end portions 46, 48 of the loop 44 are embedded
or moulded, as illustrated in FIG. 3C, or into which the ends 72,
74 of the elongate members 64, 66, 68 are embedded or moulded, as
illustrated in FIG. 3D.
[0041] As illustrated in FIG. 4, the elongate members 64, 66, 68
may be interconnected or united at ends thereof to form an integral
frame 76, particularly of channel form, in which the loop 44 is
supported, the frame 76 being supported at fixed supporting regions
on the wall member 16, in similar manner as previously described
with reference to the supporting regions 56, 58, 60 and 62.
[0042] The terminal or end portions 46 and 48 of the loop 44 are
arranged to exit the heater 10, through appropriate apertures in
the dish-like support 12, and are conveniently connected to terminals
provided on either side of the housing portion 28 of the temperature-responsive
device 24, although a separate terminal block could be provided
if desired. Only one such terminal, denoted by reference numeral
32, is visible in FIG. 1. These terminals have no electrical connection
to the temperature-responsive device 24 and leads 78, 80 are provided
therefrom to the control system 40.
[0043] The control system 40 is adapted to operate in known manner
to detect a change in electrical inductance in the loop 44 associated
with placement and/or removal of the cooking utensil 6 on and/or
from the upper surface 4 of the cooking plate 2 and for effecting
appropriate energising and/or de-energising of the heating element
or elements 20. Such control system 40 may, for example, include
an electrical oscillatory or resonant circuit.
[0044] Although a triangular arrangement of the loop 44 is shown
in FIG. 1, other arrangements are possible. For example, one of
the three portions 50, 52, 54 of the loop could be dispensed with
and a simple V-shaped arrangement of the loop 44 provided. Alternatively,
an arrangement of four or more portions of the loop could be provided,
such as to provide a rectangular or trapezoidal arrangement of the
loop portions. This is illustrated in FIG. 5, in which, in addition
to the three portions 50, 52 and 54 of the loop, a further portion
82 is included, to provide the rectangular or trapezoidal arrangement.
[0045] The construction, including the support of the loop on the
wall member 16, the mounting on the associated heater 10, and the
electrical connections and control system, are substantially as
previously described with reference to FIG. 1.
[0046] FIG. 5 also illustrates a further feature of the present
invention. The detection device 42 can be provided in modular form
for easy fitting to an electric heater. The loop 44, with whatever
selected number of portions, is pre-assembled on the wall member
16 and may also be pre-assembled with its end terminal regions 46,
48 connected to electrical terminals 32 and 84 provided on the housing
portion 28 of the temperature-responsive device 24, or on a separate
terminal block if desired.
[0047] The device of the present invention can also be applied
to heaters having more than one heating zone, such as two or more
concentrically-arranged heating zones, and used to energise one
or more heating zones according to the size of cooking utensil 6
detected on the cooking plate 2. This is illustrated in FIG. 6.
Here an electric heater 10, with a metal dish-like support 12 and
a base layer 14 of insulation material is provided with two concentric
heating elements 20A and 20B, which are arranged such that inner
element 20A can be either energised alone or together with outer
element 20B. The detection device 42 comprises an inner wall member
16A concentrically arranged with an outer wall member 16B. The inner
wall member 16A provides the heater with two separated heating zones
86 and 88, the outer wall member 16B serving as a peripheral wall
on the heater 10. A tunnel 90 of thermal insulation material extends
across the outer heating zone 88. Terminal portions 92, 94 of the
inner heating element 20A pass through the tunnel 90 for connection
to a terminal block 22 and/or terminals on a housing portion 28
of a temperature-responsive device 24. An elongate probe portion
26 of the temperature-responsive device 24 also passes through the
tunnel 90. Two inductively-operating loops 44A and 44B are provided,
each constructed in substantially the same manner as previously
described with reference to FIGS. 1 to 5.
[0048] Loop 44A has its portions 50A, 52A, 54A and 82A supported
and shielded by their associated elongate tubular or channel-form
members and extending in the inner heating zone 86 between the fixed
supporting regions on the wall member 16A. Loop 44B has its portions
50B, 52B, 54B and 82B supported and shielded by their associated
elongate tubular or channel-form members and extending in the outer
heating zone 88 between the fixed supporting regions on the wall
member 16B.
[0049] The two loops 44A and 44B have a common end terminal region
96 extending outside of the heater 10 and connected to a terminal
84 provided on the housing 28 of the temperature-responsive device
24. The other end terminal regions 98, 100 of the loops 44A and
44B respectively, also extend outside of the heater 10 and are connected
to further separate terminals, only one of which 32 is shown, provided
on the housing portion 28 of the temperature-responsive device 24.
In substantially the same way as previously described with reference
to FIG. 1, leads are provided, extending from the terminals on the
housing portion 28 and the terminal block 22, to a control system
(such as the control system 40 of FIG. 1), to enable the electrical
inductance in the loops 44A and 44B to be monitored.
[0050] The control system monitors the electrical inductance of
the loops 44A and 44B, the inductance values varying according to
whether a large cooking utensil 6 is located on the cooking plate
2 and covering both heating zones 86, 88 of the heater 10, or whether
a small cooking utensil 6 is located on the cooking plate 2 and
covering substantially only the inner heating zone 86. When a small
cooking utensil 6 is located, the control system operates to automatically
energise only the heating element 20A in the inner heating zone
86. When a larger cooking utensil 6 is located, the control system
operates to automatically energise the heating elements 20A and
20B in the inner and outer heating zones 86 and 88. |