Abstrict
A radiant electric heater comprises concentrically-arranged heating
elements separated by a dividing wall to form inner and outer heating
zones, the heater having a peripheral wall. A tunnel extends between
the peripheral wall and the dividing wall. A rod-like temperature-responsive
device extends through the tunnel and across the inner heating zone.
An end portion of the inner element extends along the tunnel. A
terminal block is located at the periphery of the heater, end portions
of the inner and outer elements being electrically connected to
terminals provided in the terminal block. An elongate electrically
conductive link is provided having a first end electrically connected
to one terminal and bridging an end portion of the outer element
connected to another terminal, the link being profiled such that
a second end thereof is located within the tunnel and connected
to an end portion of the inner element.
Claims
I claim:
1. A radiant electric heater comprising:
a base of thermal insulation material having supported relative
thereto at least two concentrically-arranged heating elements separated
by a dividing wall of thermal insulation material to form an outer
heating zone and an inner heating zone, the heater having a peripheral
wall of thermal insulation material;
a tunnel formed of thermal insulation material extending between
the peripheral wall and the dividing wall across the outer heating
zone;
a rod-like temperature-responsive device extending from a periphery
of the heater through the tunnel and at least partly across the
inner heating zone, through an aperture provided in the dividing
wall;
at least one end portion of at least one heating element of the
inner heating zone extending along the tunnel;
a terminal block located at the periphery of the heater, the at
least one end portion of the at least one heating element of the
inner heating zone and at least one end portion of at least one
heating element of the outer heating zone being electrically connected
to terminals provided in the terminal block; and
an elongate electrically conductive link having a first end electrically
connected to, or comprising, one of the terminals and extending
to bridge, whilst being electrically insulated from, an end portion
of the at least one heating element of the outer heating zone electrically
connected to another terminal, the link being profiled such that
a second end thereof is located within the tunnel and electrically
connected to an end portion of the at least one heating element
of the inner heating zone.
2. A heater according to claim 1, wherein the at least one heating
element of the outer heating zone is substantially absent from an
area occupied by the tunnel.
3. A heater according to claim 1, wherein the electrically conductive
link is of substantially rigid form.
4. A heater according to claim 3, wherein the link is arranged
to bridge, in spaced relationship with, the end portion of the at
least one heating element of the outer heating zone.
5. A heater according to claim 1, wherein the tunnel has a lower
side edge profiled to accommodate entry of the link into the tunnel.
6. A heater according to claim 5, wherein the profiled lower side
edge of the tunnel additionally provides secure location for the
link.
7. A heater according to claim 5, wherein the lower side edge of
the tunnel is profiled in a manner selected from notches, apertures,
rebates and grooves.
8. A heater according to claim 5, wherein the link is substantially
secured in at least one of the longitudinal and lateral directions
of the tunnel by the lower side edge of the tunnel.
9. A heater according to claim 1, wherein the second end of the
link is provided with means for securing the link to the base of
thermal insulation material.
10. A heater according to claim 9, wherein the means for securing
the second end of the link to the base is selected from a spike
and a pin.
11. A heater according to claim 10, wherein the securing means
is integral with the second end of the link.
12. A heater according to claim 10, wherein the securing means
is separate from the second end of the link.
13. A heater according to claim 1, wherein the link is profiled
such that it has a first upwardly-directed portion in the region
of the first end thereof, a second laterally-directed portion crossing
over the end portion of the at least one heating element of the
outer heating zone, a third portion downwardly directed towards
the base and a fourth portion laterally directed into the tunnel
at the second end of the link.
14. A heater according to claim 1, wherein the second end of the
link is welded to the end portion of the at least one heating element
of the inner heating zone.
15. A heater according to claim 1, wherein the link comprises metal.
16. A heater according to claim 15, wherein the link is of strip
form.
17. A heater according to claim 1, wherein another end portion
of the at least one heating element of the inner heating zone is
electrically connected to a different terminal in the terminal block
from that terminal electrically connected to, or comprising, the
link.
18. A heater according to claim 17, wherein the tunnel is provided
with a laterally-extending portion proximate the peripheral wall
and adapted to shield such other end portion of the at least one
heating element of the inner heating zone.
19. A heater according to claim 17, wherein such other end portion
of the at least one heating element of the inner heating zone is
electrically connected to the same terminal in the terminal block
as the bridged end portion of the at least one heating element of
the outer heating zone.
20. A heater according to claim 1, wherein at least one of the
tunnel, the peripheral wall and the dividing wall comprises bound
vermiculite.
21. A heater according to claim 1, wherein the tunnel is integral
with at least one of the dividing wall and the peripheral wall.
22. A heater according to claim 1, wherein the base comprises microporous
thermal and electrical insulation material.
23. A heater according to claim 1, wherein the heating elements
are of ribbon form.
24. A heater according to claim 23, wherein the heating elements
are supported edgewise on the base.
Description RADIANT ELECTRIC HEATER
The present invention relates to radiant electric heaters, such
as for use in cooking appliances and more especially for use in
cooking appliances having glass-ceramic cooking surfaces.
DESCRIPTION OF PRIOR ART
It is well known to provide a radiant electric heater for use in
a cooking appliance beneath a glass-ceramic cooking surface and
in which at least two concentrically-arranged heating elements,
separated by a dividing wall of thermal insulation material, are
supported on or adjacent to a base of thermal insulation material,
such as microporous thermal and electrical insulation material.
An outer heating zone and an inner heating zone are thereby provided,
the inner heating zone having one or more heating elements which
are generally arranged to be energisable independently of the heating
element or elements of the outer heating zone.
A peripheral wall of thermal insulation material is generally arranged
around the edge of the heater and a rod-like temperature-responsive
device extends from a periphery of the heater across the heater
to a position at least partly across the inner heating zone.
In order to meet a requirement that the temperature-responsive
device should be responsive substantially only to heat from the
inner heating zone, even when both inner and outer heating zones
are energised, it is known to provide a tunnel of thermal insulation
material supported on the base and covering the rod-like temperature-responsive
device between the peripheral wall and the dividing wall in the
outer heating zone. The heating element in the outer heating zone
is arranged to stop short of the tunnel at either side thereof and
hence does not intrude into the tunnel. The temperature-responsive
device is thus thermally isolated from the heating element in the
outer heating zone.
It is further known to provide one or more end portions of the
heating element of the inner heating zone extending into the tunnel
through an aperture in the dividing wall. Such one or more end portions
of the heating element are led through the tunnel and out to terminals
of a terminal block, located at the edge of the heater, for electrically
connecting the element of the inner heating zone to a power supply.
The terminal block is generally located near the end of the temperature-responsive
device at the edge of the heater.
The heating element of the outer heating zone also has end portions
which are electrically connected to terminals in the terminal block
and it is usual to provide a common terminal to which is electrically
connected an end portion of the heating element of the outer heating
zone and also an end portion of the heating element of the inner
heating zone. Two further terminals are usually provided, one connected
to another end portion of the heating element of the inner heating
zone and the other connected to another end portion of the heating
element of the outer heating zone.
Such an arrangement has hitherto placed a restriction on the possible
permutations available for making external connections to the terminal
block. The common terminal was generally restricted to a position
intermediate the other two terminals because if it was required,
for example, to provide the common terminal as one of the other
terminals, particularly a terminal nearer the temperature-responsive
device, the other end portion of the heating element of the outer
heating zone leading thereto would provide a barrier against connection
of the other end portion of the heating element of the inner heating
zone to one of the remaining terminals.
OBJECT OF THE INVENTION
It is an object of the present invention to overcome or minimise
this problem.
SUMMARY OF THE INVENTION
According to the present invention there is provided a radiant
electric heater comprising: a base of thermal insulation material
having supported relative (thereon or adjacent) thereto at least
two concentrically-arranged heating elements separated by a dividing
wall of thermal insulation material to form an outer heating zone
and an inner heating zone, the heater having a peripheral wall of
thermal insulation material; a tunnel formed of thermal insulation
material extending between the peripheral wall and the dividing
wall across the outer heating zone; a rod-like temperature-responsive
device extending from a periphery of the heater through the tunnel
and at least partly across the inner heating zone, through an aperture
provided in the dividing wall; one or more end portions of one or
more heating elements of the inner heating zone extending along
the tunnel; a terminal block located at the periphery of the heater,
the one or more end portions of the one or more heating elements
of the inner heating zone and one or more end portions of one or
more heating elements of the outer heating zone being electrically
connected to terminals provided in the terminal block; an elongate
electrically conductive link being provided having a first end electrically
connected to, or comprising, one of the terminals and extending
to bridge, whilst being electrically insulated from, an end portion
of the one or more heating elements of the outer heating zone electrically
connected to another terminal, the link being profiled such that
a second end thereof is located within the tunnel and electrically
connected to an end portion of the one or more heating elements
of the inner heating zone.
The heating element or elements of the outer heating zone may be
substantially absent from an area occupied by the tunnel.
The electrically conductive link may be of substantially rigid
form and may be arranged to bridge, in spaced relationship with,
the end portion of the one or more heating elements of the outer
heating zone.
The tunnel may have a lower side edge profiled to accommodate entry
of the link into the tunnel and also may provide secure location
for the link. For this purpose the lower side edge of the tunnel
may be notched, apertured, rebated or grooved.
The link may be substantially secured in the longitudinal and/or
lateral direction of the tunnel by the profiled lower side edge
of the tunnel.
The second end of the link may be provided with means for securing
it to the base of thermal insulation material, which means may comprise
a spike or pin. Such spike or pin may be integral with, or separate
from, the second end of the link.
The link may be profiled such that it has a first upwardly-directed
portion in the region of (at or near) the first end thereof, a second
laterally-directed portion crossing over the end portion of the
one or more heating elements of the outer heating zone, a third
portion downwardly directed towards the base and a fourth portion
laterally directed into the tunnel at the second end of the link.
Additionally, the second end of the link may be directed downwardly
towards the base.
The second end of the link may be welded to the end portion of
the one or more heating elements of the inner heating zone.
The link may comprise metal and may be of strip form.
Another end portion of the one or more heating elements of the
inner heating zone may be electrically connected to a different
terminal in the terminal block from that terminal electrically connected
to, or comprising, the link.
The tunnel may be provided with a laterally-extending portion proximate
the peripheral wall and adapted to shield such other end portion
of the one or more heating elements of the inner heating zone. Such
other end portion of the one or more heating elements of the inner
heating zone may be electrically connected to the same terminal
in the terminal block as the bridged end portion of the one or more
heating elements of the outer heating zone.
The tunnel and/or the peripheral wall and/or the dividing wall
may comprise bound vermiculite.
The tunnel may be integral with the dividing wall and/or the peripheral
wall.
The base may comprise microporous thermal and electrical insulation
material.
The heating elements may be of ribbon form and may be supported
edgewise on the base.
The electrically conductive link in the present invention which
is, in effect, mechanically coupled to the tunnel, provides reliable
crossing of a heating element without risk of contact therewith.
Risk of movement of the link in service is minimised as a result
of its securing at the tunnel at one end and at the terminal block
at the other end.
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
FIG. 1 is a plan view of one embodiment of a radiant electric heater
according to the present invention;
FIG. 2 is a cross-sectional view of the heater of FIG. 1;
FIG. 3 is a perspective view of the heater of FIG. 1;
FIG. 4 is a detailed perspective view of part of the heater of
FIG. 1;
FIG. 5 is an underside view of a tunnel region of the heater of
FIG. 1;
FIG. 6 is a top view of part of the heater of FIG. 1 with the tunnel
thereof removed; and
FIG. 7 is a modification of part of FIG. 5, showing a spike or
pin securing the electrically conductive link inside the tunnel
of the heater.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to FIGS. 1, 2 and 3, a radiant electric heater 1, for
use under a glass-ceramic surface (not shown) of a cooking appliance,
has a metal support dish 2 containing a base 3 of microporous thermal
and electrical insulation material. A peripheral wall 4 of thermal
insulation material, such as bound vermiculite, is provided around
the outside edge of the heater. Such vermiculite suitably comprises
exfoliated particles of vermiculite bound with potassium silicate.
Two heating zones are provided, separated by a dividing wall 5
of thermal insulation material, such as bound vermiculite. An inner
heating zone 6 contains at least one heating element 7, supported
on the base 3 and suitably comprising one or more edgewise-mounted
corrugated ribbons. An outer heating zone 8 contains at least one
heating element 9, of similar form to the heating element 7.
A rod-like temperature-responsive device 10 of well-known form
extends across the heater from the periphery thereof and partly
across the inner heating zone 6, through an aperture provided in
the dividing wall 5.
In order that the temperature-responsive device 10 can be made
responsive to heat generated only by the one or more heating elements
7 in the inner heating zone 6, even when the one or more heating
elements 9 in the outer heating zone 8 is or are energised, a tunnel
11 of thermal insulation material, such as bound vermiculite, is
provided. The tunnel 11 is of substantially inverted U-shaped cross-section
and extends between the peripheral wall 4 and the dividing wall
5, covering the rod-like temperature-responsive device 10 in this
region. The one or more heating elements 9 in the outer heating
zone 8 is or are arranged to stop short of the tunnel 11. The temperature-responsive
device 10 is therefore thermally isolated by the tunnel 11 from
the heating element or elements 9 of the outer heating zone 8.
End portions 7A and 7B of the one or more heating elements 7 of
the inner heating zone 6 are arranged to pass directly or indirectly
through the tunnel 11, for electrical connection to terminals 12
and 13 of a terminal block 14 provided at a peripheral edge of the
heater.
The end portion 7A is electrically connected to terminal 12 and
an end portion 9A of the one or more heating elements 9 of the outer
heating zone 8 is also electrically connected to terminal 12. The
terminal 12 therefore serves as a common terminal for the heating
elements 7 and 9.
The one or more heating elements 9 of the outer heating zone 8
also have another end portion 9B electrically connected to a terminal
15 of the terminal block 14.
For the end portion 7B of the one or more heating elements 7 of
the inner heating zone 6 to be electrically connected to the terminal
13 of the terminal block 14, it is necessary to cross the end portion
9A of the one or more heating elements 9 of the outer heating zone
8. Such crossing must be without risk of electrical contact between
the two end portions and be reliable under high temperature conditions
prevailing in the heater and also when subjected to mechanical shock.
As will now be described in detail with particular reference to
FIGS. 4 to 7, an elongate electrically conductive link 16 is provided
which has one end connected to, or forming part of, terminal 13
of the terminal block 14. The link 16 bridges the end portion 9A
of the one or more heating elements 9 and enters the tunnel 11 where
it is connected at its other end to the end portion 7B of the one
or more heating elements 7.
The electrically conductive link 16 is suitably formed of substantially
rigid metal strip material. It is profiled such that it has a first
end 17 connected, such as by welding, or forming part of, to the
terminal 13 of the terminal block 14. The link 16 has an upwardly-directed
portion 18, at or near the first end 17, and a laterally-directed
portion 19 crossing over, while being spaced from, the end portion
9A of the one or more heating elements 9 of the outer heating zone.
A further portion 20 of the link 16 is downwardly-directed towards
the base 3 of the heater, followed by a still further portion 21
of the link which is laterally-directed into the tunnel 11. The
link 16 therefore forms a bridge over the end portion 9A of the
heating element or elements 9.
As shown particularly in FIGS. 4 and 5, the tunnel has profiled
regions 22, 23, suitably in the form of one or more notches, apertures,
rebates or grooves, at its lower side edge to securely locate the
link and allow it to enter the tunnel 11 between the lower edge
of the tunnel and the base 3.
A second end 24 of the link 16 is secured, for example by welding,
to the end portion 7B of the one or more heating elements 7 inside
the tunnel 11.
FIG. 7 is a modification of FIG. 5, in which a spike or pin 27
is provided on the link 16 at or near the second end 24 thereof.
Such spike or pin 27 is inserted into the base 3 to provide additional
securing of the link 16. The spike or pin 27 can be integral with,
or separate from, the end of the link 16.
A lateral extension 25 can be provided on the tunnel 11 in the
vicinity of the peripheral wall 4 to form a cover for the end portion
7A of the element or elements 7 where it approaches the terminal
block 14. This eliminates light from the end portion 7A of the element
or elements 7 being observable by a user and hence improves the
aesthetic appearance of the heater in use.
The arrangement of the link 16, particularly the portion 21, provides
secure location thereof in the longitudinal and lateral directions
of the tunnel 11 and minimises risk of displacement of the link
and contact with the portion 9A of the heating element or elements
9 which it bridges.
For operation of the heater 1, the common terminal 12 is connected
to a power supply by way of a switch head 26 of the temperature-responsive
device 10. The other terminals 13 and 15 are also connectable to
the power supply to enable the one or more heating elements 7 of
the inner heating zone 6 to be energised alone or together with
the one or more heating elements 9 of the outer heating zone 8.
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