Abstrict
A radiant electric heater includes at least first (7) and second
(11) adjacent heating zones. The first heating zone (7) includes
a first heating element portion (5) and the second heating zone
includes a second heating element portion (9). An electrical terminal
(19) is provided at a periphery of the heater for connecting the
first and second heating element portions to a source of electrical
energy. The heating element portions (5, 9) are integral with conjoined
ends connected to a first electrical connector (21), with one free
end connected to a second electrical (23) connector, and with another
free end connected to a third electrical connector (25). The first,
second and third electrical connectors include means for connecting
to the heating element portions in such a way that the heating element
portions are not deflected from their intended path to any substantial
extent.
Claims
We claim:
1. A radiant electric heater comprising at least first and second
adjacent heating zones, the first heating zone including a first
heating element portion and the second heating zone including a
second heating element portion, and terminal means provided at a
periphery of the heater for connecting the first and second heating
element portions to a source of electrical energy, wherein the heating
element portions are integral with conjoined ends. connected to
a first electrical connector, with one free end connected to a second
electrical connector, and with another free end connected to a third
electrical connector, the first, second and third electrical connectors
including means for connecting to the heating element portions in
such a way that the heating element portions are not deflected from
their intended path to any substantial extent.
2. A heater as claimed in claim 1, wherein the heating element
portions are in the form of a ribbon inserted upright into a base
of thermal and electrical insulating material.
3. A heater as claimed in claim 1, wherein the heating element
portions form a heating element in the form of a double spiral,
a first strand of the double spiral extending from a peripheral
region of the heater to a central region thereof and a second strand
of the double spiral extending from the central region to the peripheral
region thereof.
4. A heater as claimed in claim 1, wherein the third electrical
connector is positioned intermediate the first and second electrical
connectors.
5. A heater as claimed in claim 4, wherein a radially inner region
of each of the first and second electrical connectors extends generally
circumferentially of the heater in a direction away from the terminal
block.
6. A heater as claimed in claim 5, wherein the radially inner region
of the first electrical connector extends substantially at 80 degrees
to a portion thereof passing through the terminal block.
7. A heater as claimed in claim 4, wherein the radially inner portion
of the second electrical connector extends substantially at 45 degrees
to a portion thereof passing through the terminal block.
8. A heater as claimed in claim 4, wherein a radially inner region
of the third electrical connector extends generally circumferentially
of the heater in a direction towards one of the first and second
electrical connectors.
9. A heater as claimed in claim 8, wherein the radially inner portion
of the third electrical connector includes a link element which
passes across the region of the conjoined ends of the first and
second heating element portions.
10. A heater as claimed in claim 9, wherein the link element passes
over the region of the conjoined ends of the first and second heating
element portions.
11. A heater as claimed in claim 10, wherein the link element passes
under the region of the conjoined ends of the first and second heating
element portions.
12. A heater as claimed in claim 8, wherein the radially inner
portion of the second electrical connector extends substantially
at 45 degrees to a portion thereof passing through the terminal
block.
13. A heater as claimed in claim 4, wherein a radially inner region
of the second electrical connector extends generally circumferentially
of the heater in a direction away from the terminal block.
14. A heater as claimed in claim 13, wherein the radially inner
portion of the second electrical connector extends substantially
at 45 degrees to a portion thereof passing through the terminal
block.
15. A heater as claimed in claim 13, wherein the radially inner
portion of the third electrical connector includes a link element
which passes across the second heating element portion.
16. A heater as claimed in claim 13, wherein the radially inner
portion of the first electrical connector includes a link element
which passes across the second heating element portion.
17. A heater as claimed in claim 3, wherein two second heating
element portions are provided, the two portions being electrically
connected in parallel.
18. A heater as claimed in claim 17, wherein a conducting link
is provided between the first electrical connector and the first
and second strands of the double spiral in the region of the junction
between the first and second heating zones.
19. A heater as claimed in claim 18, wherein a further conducting
link is provided between the third electrical connector and the
first strand of the double spiral in the region of the junction
between the first and second heating zones.
20. A heater as claimed in claim 19, wherein the first strand is
severed between the first-mentioned and further conducting links.
21. A heater as claimed in claim 1, wherein the first electrical
connector is positioned intermediate the second and third electrical
connectors.
22. A heater as claimed in claim 21, wherein a radially inner region
of each of the second and third electrical connectors extends generally
circumferentially of the heater in a direction away from the terminal
block.
23. A heater as claimed in claim 22, wherein the radially inner
portion of the second electrical connector extends substantially
at 45 degrees to a portion thereof passing through the terminal
block.
24. A heater as claimed in claim 22, wherein the radially inner
portion of the third electrical connector extends substantially
at 45 degrees to a portion thereof passing through the terminal
block.
25. A heater as claimed in claims 22, wherein a radially inner
region of the first electrical connector extends generally circumferentially
of the heater in a direction towards one of the second and third
electrical connectors.
26. A heater as claimed in claim 25, wherein the radially inner
region of the first electrical connector extends substantially at
80 degrees to a portion thereof passing through the terminal block.
Description [0001] This invention relates to a radiant electric heater and
in particular relates to a radiant electric heater, for example
for a glass ceramic cooking appliance, comprising at least first
and second adjacent heating zones.
DESCRIPTION OF PRIOR ART
[0002] It is known to manufacture radiant electric heaters for
glass ceramic top cooking appliances which are provided with two
heating zones in the form of an inner, circular, heating zone and
an outer, annular, heating zone extending around the inner zone.
The inner and outer heating zones may, or may not, be separated
by a dividing wall of thermal insulating material so as to define
if desired separate and distinct heating zones on the glass ceramic
cooking surface. The inner and outer heating zones are each constituted
by a heating element in the form of a ribbon or coil material which
is configured to occupy the space allotted to the heating zone concerned
and which is supported on a base of thermal insulating material
provided in a supporting dish. Thus, a first heating element is
provided in the inner heating zone and a second heating element
is provided in the outer heating zone. A probe-type temperature
sensor or other suitable type of temperature sensor extends over
the outer and inner heating zones and is adapted to be responsive
in particular to the temperature of the glass ceramic cooking surface
in the region of the inner heating zone. The heating elements are
connected to the temperature sensor and to a source of electrical
power by way of a terminal block provided in a peripheral wall of
the supporting dish. The terminal block is provided adjacent to
the temperature sensor and is formed with three electrical connectors
which extend substantially radially relative to the supporting dish,
a first connector adjacent to the temperature sensor, a second connector
remote from the temperature sensor and a third connector intermediate
the first and second connectors. It is common practice in such known
heaters to connect the first connector externally of the supporting
dish directly to an electrical connector of the temperature sensor,
for example by means of welding, and internally of the dish to one
end of each of the first and second heating elements. It is also
common practice to connect the other end of the second heating element
to the second connector within the dish and to connect the other
end of the first heating element to the third connector within the
dish, the connection between the end of the first heating element
and the third connector being by way of a link which is secured
at one end to the end of the first heating element, passes over
the end of the second heating element, and is connected to, or integral
with, the third connector.
[0003] Disadvantages of such known radiant electric heaters are
that the presence of two separate heating elements and the manner
in which the heating elements are secured to the electrical connectors
render the insertion of the heating elements unsuitable for automatic
production methods.
[0004] Similar problems can arise with oval radiant electric heaters
in which a second heating element is provided adjacent to a first
heating element, the first heating element being provided in a circular
heating zone and the second heating element being provided in a
part-circular, substantially arcuate (or crescent shaped) heating
zone.
OBJECT OF THE INVENTION
[0005] It is therefore an object of the present invention to provide
a radiant electric heater which overcomes or at least ameliorates
the above disadvantages.
SUMMARY OF THE INVENTION
[0006] According to the present invention there is provided a radiant
electric heater comprising at least first and second adjacent heating
zones, the first heating zone including a first heating element
portion and the second heating zone including a second heating element
portion, and terminal means provided at a periphery of the heater
for connecting the first and second heating element portions to
a source of electrical energy, wherein the heating element portions
are integral with conjoined ends connected to a first electrical
connector, with one free end connected to a second electrical connector,
and with another free end connected to a third electrical connector,
the first, second and third electrical connectors including means
for connecting to the heating element portions in such a way that
the heating element portions are not deflected from their intended
path to any substantial extent.
[0007] The heating element portions may be in the form of a ribbon
inserted upright into a base of thermal and electrical insulating
material.
[0008] The heating element portions may form a heating element
in the form of a double spiral, a first strand of the double spiral
extending from a peripheral region of the heater to a central region
thereof and a second strand of the double spiral extending from
the central region to the peripheral region thereof.
[0009] The first heating zone may be circular. In such a case,
the second heating zone may be annular and may surround the first
heating zone or the second heating zone may be part-circular and
may partially surround the first heating zone.
[0010] A peripheral wall may be provided around the external periphery
of the heater.
[0011] A dividing wall may be provided between the adjacent heating
zones.
[0012] A temperature limiter may be provided for sensing the temperature
in the region of at least the first heating zone.
[0013] The third electrical connector may be positioned intermediate
the first and second electrical connectors.
[0014] In such a case, a radially inner region of each of the first
and second electrical connectors may extend generally circumferentially
of the heater in a direction away from the terminal block. The radially
inner region of the first electrical connector may extend at an
angle in a range from 70 degrees to 90 degrees, for example substantially
at 80 degrees, to a portion thereof passing through the terminal
block. The radially inner portion of the second electrical connector
may extend at an angle in a range from 30 degrees to 60 degrees,
for example substantially at 45 degrees, to a portion thereof passing
through the terminal block.
[0015] A radially inner region of the third electrical connector
may extend generally circumferentially of the heater in a direction
towards one of the first and second electrical connectors. The radially
inner portion of the third electrical connector may include a link
element which passes across the region of the conjoined ends of
the first and second heating element portions. The link element
may pass over the region of the conjoined ends of the first and
second heating element portions. Alternatively, the link element
may pass under the region of the conjoined ends of the first and
second heating element portions. The radially inner portion of the
second electrical connector may extend at an angle in a range from
30 degrees to 60 degrees, for example substantially at 45 degrees,
to a portion thereof passing through the terminal block.
[0016] Two second heating element portions may be provided, the
two portions being electrically connected in parallel. A conducting
link may be provided between the first electrical connector and
the first and second strands of the double spiral in the region
of the junction between the first and second heating zones. A further
conducting link may be provided between the third electrical connector
and the first strand of the double spiral in the region of the junction
between the first and second heating zones. The first strand may
be severed between the first-mentioned and further conducting links.
[0017] Alternatively, a radially inner region of the second electrical
connector may extend generally circumferentially of the heater in
a direction away from the terminal block. The radially inner portion
of the second electrical connector may extend at an angle in a range
from 30 degrees to 60 degrees, for example substantially at 45 degrees,
to a portion thereof passing through the terminal block. The radially
inner portion of the third electrical connector may include a link
element which passes across the second heating element portion.
The radially inner portion of the first electrical connector may
include a link element which passes across the second heating element
portion.
[0018] In an alternative embodiment, the first electrical connector
is positioned intermediate the second and third electrical connectors.
A radially inner region of each of the second and third electrical
connectors may extend generally circumferentially of the heater
in a direction away from the terminal block. The radially inner
portion of the second electrical connector may extend at an angle
in a range from 30 degrees to 60 degrees, for example substantially
at 45 degrees, to a portion thereof passing through the terminal
block. The radially inner portion of the third electrical connector
may extend at an angle in a range from 30 degrees to 60 degrees,
for example substantially at 45 degrees, to a portion thereof passing
through the terminal block. A radially inner region of the first
electrical connector may extend generally circumferentially of the
heater in a direction towards one of the second and third electrical
connectors. The radially inner region of the first electrical connector
may extend at an angle in a range from 70 degrees to 90 degrees,
for example substantially at 80 degrees, to a portion thereof passing
through the terminal block.
[0019] 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
[0020] FIG. 1 is a perspective view, from above, of one embodiment
of a radiant electric heater according to the present invention;
[0021] FIG. 2 is a view similar to that of FIG. 1 with a peripheral
wall of the radiant electric heater removed;
[0022] FIG. 3 is a view, on a larger scale, of part of the radiant
electric heater shown in FIG. 2, but with a temperature limiter
of the radiant electric heater additionally removed;
[0023] FIG. 4 is a plan view of another embodiment of a radiant
electric heater according to the present invention;
[0024] FIG. 5 is a plan view of a further embodiment of a radiant
electric heater according to the present invention;
[0025] FIG. 6 is a partial perspective view of the radiant electric
heater shown in FIG. 5; and
[0026] FIG. 7 is a perspective view of a conducting link forming
part of the radiant electric heater shown in FIGS. 5 and 6.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0027] The radiant electric heater shown in. FIGS. 1 to 3 comprises
a supporting dish 1, for example of metal, containing a base 3 of
thermal and electrical insulating material, for example compressed
microporous thermal and electrical insulating material. Secured
to the base 3 is a first heating element portion 5 of ribbon form
material inserted upright into the base, the first heating element
portion 5 occupying a substantially circular inner heating zone
7 in the central region of the heater. Also secured to the base
3 is a second heating element portion 9 of ribbon form material
inserted upright into the base, the second heating element portion
9 occupying a substantially annular outer heating zone 11 around
the peripheral region of the heater. The first and second heating
element portions are each part of an integral heating element and
each portion has a free end and a conjoined end integral with a
conjoined end of the other heating element portion.
[0028] In practice, the first heating element portion 5 is arranged
to be energised whenever the heater is energised irrespective of
the size of the cooking utensil placed on a glass ceramic cooking
surface (not shown) below which the heater is arranged, while the
second heating element portion 9 is only energised (in conjunction
with the first heating element portion) when a relatively large
cooking utensil is used such that the cooking utensil overlies both
the first and second heating element portions.
[0029] A peripheral wall 13 of thermal insulating material extends
around the periphery of the heater between the outer heating zone
11 and an upstanding wall of the supporting dish 1.
[0030] A probe-type temperature limiter 15 extends from a periphery
of the heater, a temperature sensor 17 of the limiter 15 extending
substantially over the first heating element portion 5 in the inner
heating zone 7. As shown in FIGS. 1 to 3, the end regions 5A and
5B of the first heating element portion 5 extend beneath the temperature
sensor 17 where the temperature sensor crosses the outer heating
zone 11 in order to reduce as far as practicable the effect of the
second heating element portion on the temperature sensed by the
temperature sensor 17 and to minimise as far as practicable the
change in the temperature of the glass ceramic cooking surface resulting
from when only the first heating element portion or both the first
and second heating element portions are energised.
[0031] A terminal block 19 is mounted on the upstanding wall of
the supporting dish 1 adjacent to the temperature limiter 15 and
is provided with a first electrical connector 21 adjacent to the
temperature limiter, a second electrical connector 23 remote from
the temperature limiter and with a third electrical connector 25
intermediate the first and second electrical connectors.
[0032] Externally of the supporting dish 1, the first electrical
connector 21 is connected directly, for example by welding, to an
electrical connector of the temperature limiter 15.
[0033] Internally of the supporting dish 1 and the peripheral wall
13, the first electrical connector 21 is bent so as to extend substantially
parallel to the circumference of the heater in a direction towards
the temperature limiter 15, that is in a direction away from the
terminal block 19. For example, the internal portion 21A of the
first electrical connector 21 may be bent at an angle of substantially
80 degrees to that part of the connector which passes through the
terminal block. Such a substantially circumferential arrangement
of the internal portion 21A of the first electrical connector 21
allows the conjoined ends of the first heating element portion 5
and the second heating element portion 9 to be arranged adjacent
and substantially parallel to a radially inner face of the portion
21A. Such an arrangement allows the end portions of the first and
second heating element portions to be integral as described above
and to be secured to the portion 21A of the first electrical connector
21, for example by means of welding, so as to form a common connection
for the conjoined ends of the first and second heating element portions.
Thus, as indicated above, the first and second heating element portions
may be integral and may be a single heating element. Thus, only
a single heating element needs to be inserted into the base 3 thereby
facilitating automatic insertion of the heating element portions
by "winding in" the heating element portions from the
free end of the first heating element portion remote from the conjoined
ends of the first and second heating element portions to the free
end of the second heating element portion also remote from the conjoined
ends. Further, in the region where the conjoined ends of the first
and second heating element portions are secured to the portion 21A
of the first electrical connector 21, the conjoined ends are able
to extend substantially circumferentially and do not need to be
deflected to any substantial extent from their intended path, thereby
avoiding small radius bends and further facilitating automatic insertion
of the integral first and second heating element portions.
[0034] Internally of the supporting dish 1 and the peripheral wall
13, the second electrical connector 23 is bent so as to be angled
generally circumferentially of the heater in a direction away from
the temperature limiter 15, that is in a direction away from the
terminal block 19. For example, the internal portion 23A of the
second electrical connector may be bent at an angle of substantially
45 degrees to that part of the connector which passes through the
terminal block 19. Such an angled arrangement of the internal portion
23A of the second electrical connector 23 allows the free end of
the second heating element portion 9 to be arranged adjacent and
substantially parallel to a radially inner face of the portion 23A.
Such an arrangement allows the free end portion of the second heating
element portion 9 to be secured to the portion 23A of the second
electrical connector 23, for example by means of welding, so as
to form a second connection for the second heating element portion
9 without the need for the heating element to be deflected to any
substantial extent from its intended path.
[0035] Internally of the supporting dish 1 and the peripheral wall
13, the third electrical connector 25 is bent so as to be angled
generally circumferentially of the heater in a direction away from
the temperature limiter 15, that is in a direction towards the second
electrical connector 23. For example, the internal portion 25A of
the third electrical connector may be bent at an angle of substantially
45 degrees to that part of the connector which passes through the
terminal block 19. Such an angled arrangement of the internal portion
25A of the third electrical connector 25 allows the third electrical
connector to include a link element 27 to be secured to, or formed
integral with, the remainder of the internal portion 25A of the
third electrical connector 25, the link element extending substantially
at right angles to the remainder of the portion 25A and having a
generally U-shaped configuration so as to extend over (or under)
the conjoined ends of the first and second heating element portions
and to allow the free end of the first heating element portion 5
to be arranged adjacent and substantially parallel to a radially
inner substantially upright face of the link element 27 which extends
generally circumferentially of the heater. Such an arrangement allows
the free end portion of the first heating element portion 5 to be
secured to the link element 27, for example by means of welding,
and thus to the remainder of the portion 25A of the third electrical
connector 25 so as to form a second connection for the first heating
element portion 5 without the need for the heating element to be
deflected to any substantial extent from its intended path.
[0036] As can be seen from FIGS. 1 to 3, the internal portions
of the electrical connectors at each circumferential end of the
terminal block 19 extend generally circumferentially away from the
terminal block, while the internal portion of the intermediate electrical
connector may extend generally circumferentially towards whichever
of the other two electrical connectors is most convenient. Such
an arrangement allows the integral first and second heating element
portions to be inserted into the base while providing gentle bends
with relatively large radii in the regions of the electrical connectors
such that the heating elements do not need to be deflected to any
substantial extent from their intended path.
[0037] Thus, the heating element portions may be inserted into
the base 3 of the radiant electric heater shown in FIGS. 1 to 3
by starting at a free end of one of the heating element portions
and continuing until the free end of the other heating element portion
is reached. In this way, both heating element portions can be inserted
into the base in a single operation, the gentle bends, particularly
in the regions of the internal portions of the connectors, facilitating
automatic insertion and the arrangements of the internal portions
facilitating securement of the heating element portions to the internal
portions of the connectors.
[0038] In use of the radiant electric-heater shown in FIGS. 1 to
3, either the first heating element portion 5 can be energised alone,
or the first and second heating element portions 5 and 9 can be
energised in parallel.
[0039] The radiant electric heater shown in FIGS. 1 to 3 can be
modified in a number of respects. For example, the radiant electric
heater need not be circular, but could be, for example, oval in
configuration with the first heating element portion 5 occupying
a substantially circular heating zone 7 and the second heating element
portion 9 occupying a part-circular (or crescent shaped) heating
zone 11 adjacent to the circular heating zone 7.
[0040] Moreover, although the two heating zones are shown in FIGS.
1 to 3 as being undivided, if desired a dividing wall may be provided
in a manner well known to the skilled person between the two heating
zones so as to define on the glass ceramic cooking surface separate
and distinct heating areas corresponding to the two heating zones.
[0041] Should it not be necessary to provide the first electrical
connector at one end of the terminal block 19 for direct connection
to the temperature limiter 15, and providing there is adequate space
along the circumferential length of the terminal block, the first
electrical connector for the conjoined ends of the integral first
and second heating element portions may be provided intermediate
the second and third electrical connectors, with the internal portion
of the first electrical connector extending in a generally circumferential
direction towards whichever of the other two electrical connectors
is most convenient. Such an arrangement has the advantage that the
link 27 is no longer required and the free end of the first heating
element portion can be secured directly to the internal portion
of the third electrical connector, such internal portion being bent
in a direction generally circumferentially of the heater away from
the terminal block 19, for example at an angle of about 45 degrees
to that part of the third electrical connector which passes through
the terminal block, to allow the free end of the first heating element
portion 5 to be arranged adjacent and substantially parallel to
a radially inner face of the portion 25A. Such an arrangement allows
the free end portion of the first heating element portion to be
secured to the portion 25A of the third electrical connector 25,
for example by means of welding, so as to form a second connection
for the first heating element portion 5.
[0042] Thus, the internal portions of the electrical connectors
at each circumferential end of the terminal block 19 extend generally
circumferentially away from the terminal block, while the internal
portion of the intermediate electrical connector may extend generally
circumferentially towards whichever of the other two electrical
connectors is most convenient.
[0043] Where the radiant electric heater in FIGS. 1 to 3 shows
the internal portion 21A of the first electrical connector 21 angled
in a direction opposite to the internal portion 23A of the second
electrical connector 23 it should be appreciated that all the internal
portions 21A, 23A and 25A could be angled in the same direction
relative to the terminal block 19. In which case the internal portion
21A of the first electrical connector 21 would be bent at an angle
in the range from 30 degrees to 60 degrees, for example substantially
at 45 degrees, to that part of the connector which passes through
the terminal block.
[0044] The radiant electric heater shown in FIG. 4 is similar to
that shown in FIGS. 1 to 3 and the same reference numerals are used
to denote the same or similar components. The radiant electric heater
of FIG. 4 is shown with the peripheral wall 13 omitted, but with
the temperature limiter 15 present.
[0045] As can be seen from FIG. 4, the second heating element portion
9 is wound in from the periphery of the outer heating zone 11 to
the junction between the outer and inner heating zones. The integral
first heating element portion 5 is then wound in from the periphery
of the inner heating zone 7 to the region of the centre of the heater
and is then wound in from the region of the centre of the heater
back to the periphery of the inner heating zone 7.
[0046] The free end of the second heating element portion 9 is
connected to the internal portion 23A of the second electrical terminal
23 of the terminal block 19, the internal portion 23A being bent
so as to be angled in a direction generally circumferentially of
the heater away from the temperature limiter 15, that is in a direction
away from the terminal block 19. For example, the internal portion
23A of the second electrical connector may be bent at an angle of
substantially 45 degrees to that part of the connector which passes
through the terminal block. Such an angled arrangement of the internal
portion 23A of the second electrical connector 23 allows the free
end of the second heating element portion 9 to be arranged adjacent
and substantially parallel to a radially inner face of the portion
23A. Such an arrangement allows the end portion of the second heating
element portion to be secured to the portion 23A of the second electrical
connector 23, for example by means of welding, so as to form a connection
for the second heating element portion 9 without the need for the
heating element to be deflected to any substantial extent from its
intended path.
[0047] The third electrical connector 25 includes link element
27 between the free end of the first heating element portion 5 and
the remainder of the internal portion 25A of the third electrical
connector 25 and extending over (or under) the second heating element
portion 9. In the embodiment of FIG. 4 it is not necessary for the
internal portion of the third electrical connector to be bent relative
to that part which passes through the terminal block. However, the
radially inner end of the link element 27 is formed with a generally
circumferential upright face to allow the free end portion of the
first heating element portion 5 to be secured to the link element
27, for example by means of welding, and thus to the remainder of
the portion 25A of the third electrical connector 25 so as to form
a connection for the first heating element portion 5 without the
need for the free end of the first heating element portion to be
deflected to any substantial extent from its intended path.
[0048] The first electrical connector 21 includes a further link
element 29 provided between the conjoined ends of the integral first
and second heating element portions and the remainder of the internal
portion 21A of the first electrical connector 21 and extending over
(or under) the second heating element portion 9. As with the third
electrical connector 25, it is not necessary for the internal portion
of the electrical connector to be bent relative to that part which
passes through the terminal block 19. However, the radially inner
end of the further link element 29 is formed with a generally circumferential
upright face to allow the conjoined end portions of the first and
second heating element portions to be secured to the further link
element 29, for example by means of welding, and thus to the remainder
of the portion 21A of the first electrical connector 21 so as to
form a connection for the conjoined ends of the first and second
heating element portions 5 and 9 without the need for the conjoined
ends of the first and second heating element portions to be deflected
to any substantial extent from their intended path.
[0049] If desired, the temperature sensor 17 of the temperature
limiter 15 can be rendered insensitive to heat emitted by the second
heating element in any one of a number of ways well known to the
skilled person.
[0050] If desired, the radiant electric heater of FIG. 4 may be
modified to provide more than two heating zones, each heating zone
having a heating element portion. In such a case, the terminal block
requires an electrical connector for each of the two free ends and
an electrical connector for each of the conjoined ends between successive
heating element portions. Thus, a radiant electric heater with three
heating zones will require a terminal block with four electrical
connectors, one for each of the free ends, one for a connection
between the first and second zones and one for a connection between
the second and third zones.
[0051] The radiant electric heater shown in FIGS. 5 to 7 is similar
to that shown in FIG. 4 and the same reference numerals are used
to denote the same or similar components.
[0052] In the embodiment of FIGS. 5 to 7 a single heating element
31 of ribbon form is inserted into the base 3 in a double spiral
pattern beginning from a first end in the peripheral region of the
heater and reversing in the region of the centre of the heater and
returning to the peripheral region of the heater where the heating
element terminates in a second end. Thus, the single heating element
has both incoming and outgoing strands. The first and second ends
are both secured to the first electrical connector 21.
[0053] A dividing wall 33 of thermal and electrical insulating
material is positioned within the heater 1 to divide the heated
area into a central, substantially circular zone 7 and an outer,
substantially annular zone 11.
[0054] A conducting link 35 extends between the first electrical
conductor 21 and both the incoming and outgoing strands of the heating
element 31 in the region of the junction between the first and second
heating zones.
[0055] A conducting link 37 extends between the third electrical
conductor 25 and the incoming strand of the heating element 31 in
the region of the junction between the first and second heating
zones, while the incoming strand is severed between the conducting
links 35 and 37 so as to electrically isolate the portions of the
incoming strand at the conducting links 35 and 37. There is therefore
a single first heating element portion 5 within the central zone
7 formed by the incoming strand extending from the conducting link
37 extending from the third electrical conductor 25 and by the outgoing
strand extending to the conducting link 35 extending from the first
electrical conductor 21.
[0056] In this way, the incoming and outgoing strands in the outer
substantially annular zone are electrically connected in parallel
to form two second heating element portions 9A and 9B, while conjoined
ends of the first and second heating element portions are locate
at the radially inner end of the conducting link 35.
[0057] Thus, the conducting link 35 forms a connection for the
conjoined ends of the first and second heating element portions
without the need for the conjoined ends to be deflected to any substantial
extent from their intended path.
[0058] Using the parallel electrical connection in the outer zone,
it is possible to generate a higher power density in the outer zone
than in the central zone, which is considered desirable in such
radiant electrical heaters.
[0059] FIG. 6 shows the arrangement of the conducting links 35
and 37 in more detail. As can be seen from FIG. 6, the conducting
links may be supported on one or more raised regions of the base
3, one raised region 39 being provided approximately mid-way between
the peripheral wall 13 and the dividing wall 33 and another raised
region 41 being provided substantially coincident with the dividing
wall 33, for example in a cut out region of the dividing wall.
[0060] FIG. 7 shows the conducting link 35 as being of arched configuration
(as is the conducting link 37) and having a substantially U-shaped
portion 43 at its radially inner end in order that the incoming
and outgoing strands of the heating element 31 can be electrically
connected to separate legs of the U-shaped portion. For strength,
the surface of the arched region of the conducting link may be formed
with a reinforcing rib 45.
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