Abstrict
A radiant electric heater comprises a base (2) of thermal and electrical
insulation material, an electrical heating element (3) supported
on or adjacent to the base and having a terminal region (7) at a
location in the heater remote from a periphery of the heater, and
a rod-like temperature-responsive device (9) extending at least
partly across the heater from the periphery thereof at least to
a region proximate the terminal region of the heating element. Electrical
connecting means extends from the terminal region (7) of the heating
element (3) to the periphery of the heater by way of the rod-like
temperature-responsive device (9).
Claims
I claim:
1. A radiant electric heater comprising a base of thermal and electrical
insulation material, an electrical heating element supported relative
to the base and having a terminal region at a location in the heater
remote from a periphery of the heater, a rod-like temperature-responsive
device extending at least partly across the heater from the periphery
thereof at least to a region proximate the terminal region of the
heating element, and electrical connecting means extending from
the terminal region of the heating element to the periphery of the
heater by way of the rod-like temperature-responsive device.
2. A radiant electric heater as claimed in claim 1, wherein the
rod-like temperature-responsive device comprises a differentially-expanding
rod and tube assembly having a rod arranged inside a tube and adapted
to operate switch means at the periphery of the heater.
3. A radiant electric heater as claimed in claim 2, wherein at
least one of the rod and the tube comprises a metal and serves as
the electrical connecting means.
4. A radiant electric heater as claimed in claim 2, wherein the
tube includes an electrical lead passing therethrough and serving
as the electrical connecting means.
5. A radiant electric heater as claimed in claim 4, wherein the
tube is provided with at least two bore-holes passing therethrough,
one containing the rod and the other containing the electrical lead
serving as the electrical connecting means.
6. A radiant electric heater as claimed in claim 3, wherein the
tube comprises an electrical insulating material and the rod comprises
a metal.
7. A radiant electric heater as claimed in claim 6, wherein the
electrical insulating material of the tube is selected from ceramic,
glass, glass-ceramic, quartz and fused vitreous silica.
8. A radiant electric heater as claimed in claim 1, wherein the
rod-like temperature-responsive device comprises a tube in which
is provided an electrical element having an electrical parameter
which changes as a function of temperature.
9. A radiant electric heater as claimed in claim 8, wherein the
electrical resistance of the electrical element changes as a function
of temperature.
10. A radiant electric heater as claimed in claim 8, wherein the
tube in which the electrical element is provided comprises a metal
and serves as the electrical connecting means.
11. A radiant electric heater as claimed in claim 8, wherein the
tube in which the electrical element is provided includes an electrical
lead passing therethrough which is electrically connected to the
terminal region of the heating element and serves as the electrical
connecting means.
12. A radiant electric heater as claimed in claim 11, wherein the
material of the tube is selected from electrically insulating and
electrically conducting material.
13. A radiant electric heater as claimed in claim 12, wherein the
tube comprises a material selected from metal, ceramic, glass, glass-ceramic,
quartz and fused vitreous silica.
14. A radiant electric heater as claimed in claim 1, wherein the
electrical heating element is arranged substantially in the form
of a spiral.
Description [0001] This invention relates to a radiant electric heater particularly,
but not exclusively, for use in cooking appliances, such as glass-ceramic
cooking appliances.
BACKGROUND TO THE INVENTION
[0002] Radiant electric heaters are well known comprising a base
of thermal and electrical insulation material having at least one
electrical heating element supported on or adjacent thereto. The
base may comprise compacted microporous insulation material and
may be provided in a dish-like support, such as of metal.
[0003] The heating element or elements is or are generally of elongate
coiled wire or ribbon form, having electrical terminations at opposite
ends thereof for connection to a power supply.
[0004] A rod-like temperature-responsive device is also generally
provided extending at least partly across the heater and overlying
the heating element or elements.
DESCRIPTION OF PRIOR ART
[0005] In one known arrangement, the heating element is provided
in a pattern incorporating one or more reversals and such that both
ends of the element are situated at the periphery of the heater
and preferably close to each other, where they can be readily provided
with electrically conductive terminations, such as in a terminal
block, to enable the element to be connected to a power supply.
[0006] However another arrangement is known in which the heating
element is arranged in a pattern such that one end is at the periphery
of the heater and the other end is at a location in the heater remote
from the periphery, for example at or near the middle of the heater.
With such an arrangement, which may occur when the heating element
is provided in the form of a simple spiral, it is necessary to provide
a wire link connected to that end termination of the heating element
located remote from the periphery of the heater and extending to
the periphery of the heater. One such wire link is known, provided
externally of the heater and passing through an aperture at the
centre of the base of the heater. However a wire link of this nature,
passing through the base, increases the overall depth of the heater,
which is undesirable.
[0007] Alternatively, a wire link is known which is provided in
or beneath the insulation material of the base. However, the provision
of such a link necessitates additional processing steps in the manufacture
of the heater, thereby adding to the cost of the heater.
OBJECT OF THE INVENTION
[0008] It is an object of the present invention to overcome or
minimise these disadvantages.
SUMMARY OF THE INVENTION
[0009] The present invention provides a radiant electric heater
comprising a base of thermal and electrical insulation material,
an electrical heating element supported relative (on or adjacent)
to the base and having a terminal region at a location in the heater
remote from a periphery of the heater, a rod-like temperature-responsive
device extending at least partly across the heater from the periphery
thereof at least to a region proximate the terminal region of the
heating element, and electrical connecting means extending from
the terminal region of the heating element to the periphery of the
heater by way of the rod-like temperature-responsive device.
[0010] The rod-like temperature-responsive device may comprise
a differentially-expanding rod and tube assembly having a rod arranged
inside a tube and adapted to operate switch means at a periphery
of the heater.
[0011] The rod and/or the tube may comprise a metal and serve as
the electrical connecting means.
[0012] The tube may also include an electrical lead passing therethrough
and serving as the electrical connecting means.
[0013] The tube may be provided with at least two bore-holes passing
therethrough, one containing the rod and the other containing the
electrical lead serving as the electrical connecting means.
[0014] The tube may comprise an electrical insulating material,
such as a material selected from ceramic, glass, glass-ceramic,
quartz and fused vitreous silica, and the rod may comprise a metal.
[0015] Alternatively the rod-like temperature-responsive device
may comprise a tube in which is provided an electrical element having
an electrical parameter which changes as a function of temperature.
Such electrical element may comprise an electrical resistance device
whose electrical resistance changes as a function of temperature.
[0016] The tube in which the electrical element is provided may
comprise a metal and serve as the electrical connecting means.
[0017] Alternatively the tube in which the electrical element is
provided may include an electrical lead passing therethrough which
is electrically connected to the terminal region of the at least
one heating element and serves as the electrical connecting means.
In this case the tube may comprise an electrically insulating or
conducting material, such as a material selected from metal, ceramic,
glass-ceramic, quartz and fused vitreous silica.
[0018] The electrical heating element may be of wire, ribbon, film
or foil form and may be arranged substantially in the form of a
spiral.
[0019] By means of the invention, an electrical connection can
be readily provided from a region of a heating element remote from
the periphery of a heater to a peripheral region of the heater by
way of the rod-like temperature-responsive device, thus eliminating
the need for a lead buried in or beneath an insulation base of the
heater, or for a lead passing through an aperture in the base of
the heater.
[0020] For a better understanding of the 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
[0021] FIG. 1 is a plan view of one embodiment of a radiant electric
heater according to the present invention;
[0022] FIG. 2 is a cross-sectional view of the radiant electric
heater of FIG. 1;
[0023] FIG. 3 is a perspective view of an alternative embodiment
of temperature-responsive device for use in the radiant electric
heater of FIG. 1;
[0024] FIG. 4 is a side view of another alternative embodiment
of temperature-responsive device for use in the radiant electric
heater of FIG. 1; and
[0025] FIG. 5 is a side view of yet another alternative embodiment
of temperature-responsive device for use in the radiant electric
heater of FIG. 1.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0026] Referring to FIGS. 1 and 2, a radiant electric heater, such
as for use in a cooking appliance, comprises a metal dish 1 containing
a base layer 2 of thermal and electrical insulation material, particularly
compacted microporous thermal and electrical insulation material
which is well known to the skilled person.
[0027] An electrical heating element 3 is supported on the base
layer 2. The heating element 3 may be of any of the well known forms,
such as wire, ribbon, film or foil. A particularly well known form
of element 3, as shown in FIGS. 1 and 2, comprises a corrugated
metal ribbon mounted edgewise on the surface of the base layer 2.
[0028] The heating element 3 is arranged in the form of a spiral,
having one end 4 connected to a terminal 5 in a terminal block 6
provided at a peripheral region of the heater.
[0029] The heating element 3 also has an end region 7 at a central
region of the heater remote from the periphery of the heater.
[0030] A well known form of wall 8, of thermal insulation material,
is provided around the periphery of the heater against the side
of the dish 1.
[0031] A rod-like temperature-responsive device 9 extends partly
across the heater from the periphery thereof and is of generally
well known basic construction. The device 9 comprises a differentially-expanding
rod and tube assembly comprising a rod 10 inside a tube 11. The
rod 10 and tube 11 are secured together at one end 12 and operate
switch means of well known form in a switch head 13 arranged outside
the heater at the periphery thereof.
[0032] The temperature-responsive device 9 is secured to the dish
1 of the heater by a bracket 14.
[0033] The device 9 may comprise a relatively high thermal expansion
metal rod 10 inside a relatively low thermal expansion tube 11,
or may comprise a relatively high thermal expansion metal tube 11
containing a relatively low thermal expansion rod 10. Both forms
of construction are well known to the skilled person. The relatively
low thermal expansion rod or tube may, for example, comprise a material
selected from ceramic, glass, glass-ceramic, quartz and fused vitreous
silica. The relatively high thermal expansion metal rod or tube
may comprise a material such as a high temperature withstanding
steel or an iron-chromium-aluminium alloy.
[0034] In accordance with the present invention, the metal component
of the rod and tube assembly, whether the rod 10 or the tube 11,
is used as an electrical connecting means between the end region
7 of the heating element 3 and a terminal region 15 at the periphery
of the heater and such that the heating element 3 is able to be
connected by the terminal regions 5, 15 to a power supply for operation.
[0035] As shown, the end region 7 of the heating element 3 is electrically
connected by a connecting link 16 to the end of metal rod 10 which
extends from insulating tube 11 at the end region 12 of the rod
and tube assembly. The connecting link 16 can be part of the end
region 7 of the heating element 3, or can be a separate conducting
wire or tape welded to the end region 7 of the heating element.
The connecting link 16 is suitably secured and electrically connected
to the end of the metal rod 10 by welding.
[0036] Terminal region 15, provided at the periphery of the heater,
comprises a lead wire electrically connected to an end region 17
of the metal rod 10, suitably inside the switch head 13.
[0037] It is arranged for the metal rod 10 to be electrically isolated
from the switch means inside the switch head 13, for example by
means of an intermediate ceramic member.
[0038] If desired, the terminal region 15 could be connected to,
or integral with, a terminal 18 on the switch head 13. Such connection
could be made either externally or internally on the switch head
13, the latter obviating the need for the terminal region 15 to
extend outside the switch head 13.
[0039] If the outer tube 11 of the temperature-responsive device
9 comprises a metal and the inner rod is of insulating material,
the end region 7 of the heating element 3 is then arranged to be
electrically connected to the tube 11, at the end region 12 of the
rod and tube assembly, instead of to the rod 10. At the other end
of the rod and tube assembly, the lead wire of terminal region 15
is arranged to be connected to the end 19 of the tube 11 instead
of to the end 17 of the rod 10.
[0040] Instead of the end region 7 of the heating element 3 being
electrically connected to the metal tube 11 of the temperature-responsive
device, it could be arranged for a connection 20 to be made between
a tapping point 21 on the heating element 3 and the metal tube 11,
to enable controlled energising of one or more selected regions
of the heating element 3 to be effected.
[0041] An alternative arrangement of the temperature-responsive
device 9 is illustrated in FIG. 3. Here the tube 11, of electrically
insulating material, is provided with two bore-holes running through
it along its length, one of which carries metal rod 10 which is
secured to the tube 11 at end 12 by means of a metal collar arrangement
22. The other end of the metal rod 10 operates one or more switch
means inside switch head 13. The other bore-hole through the tube
11 carries an electrically conducting lead wire 23 which at one
end is electrically connected to the end region 7 of the heating
element 3 and at the other end extends through an aperture 24 in
the tube 11 to form terminal region 15 for the heating element.
[0042] The device 9 is secured to the heater by means of bracket
14 in the same way as the arrangement shown in FIGS. 1 and 2.
[0043] The tube 11 is shown of elliptical cross section. Although
this may be advantageous in order to maintain a low profile for
the device, it is not essential and other cross-sectional shapes,
such as circular or rectangular, could be considered.
[0044] The rod 10 and tube 11 of FIG. 3 are suitably constructed
of the same materials as described for the corresponding rod and
tube in FIGS. 1 and 2.
[0045] Another arrangement of the temperature-responsive device
9 is illustrated in FIG. 4. A metal tube 11A, closed at one end
25, contains an electrical element 26 having an electrical parameter
which changes as a function of temperature. Element 26 is suitably
an electrical resistance element, such as a platinum resistance
element, whose electrical resistance changes as a function of temperature.
[0046] The device 9 is secured to the heater in much the same way
as the corresponding device 9 shown in FIGS. 1 and 2, by means of
a bracket 14.
[0047] Lead wires 27, 28 are connected to the element 26 and extend
outside the heater to appropriate monitoring and control circuitry
(not shown) for the heater.
[0048] The metal tube 11A is used as an electrical connecting means
between the end region 7 of the heating element 3 and a terminal
region 15 at the periphery of the heater. As previously described
with reference to FIGS. 1 and 2, a connecting link 16 is provided
between the end region 7 of the heating element 3 and the end 25
of the metal tube 11A. Link 16 can be part of the end region 7 of
the heating element 3, or can be a separate connecting wire or tape,
and is secured to the end 25 of the metal tube 11A by welding. Terminal
region 15 for the heating element is provided by welding a lead
wire 29 to an opposite end region 30 of the metal tube 11A.
[0049] FIG. 5 shows a variation on the arrangement of FIG. 4 in
which, instead of using tube 11A as the connecting means, a lead
wire 31 is provided, connected to the end region 7 of the heating
element 3 and passing along the interior of the tube 11A to terminal
region 15, a hole 32 being provided in the end of the tube 11A for
entry of the lead wire 31. In this case, the tube 11A can be formed
of a metal, or an insulating material such as ceramic, glass, glass-ceramic,
quartz or fused vitreous silica.
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