Electric heater incorporating a device for detecting a cooking utensil

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.