GB2148678A - Heating apparatus - Google Patents

Abstract

Heating apparatus consists of a tray 1, which has a layer 2 of thermally insulative material disposed therewithin, above which four infra-red-emitting, tungsten-halogen lamps 3 to 6 are supported. The apparatus is urged upwardly towards a disc 8 of a glass ceramic material, which is set in a surround 9 forming the upper surface of a cooking hob. The apparatus includes a switching arrangement for interconnecting the lamps 3 to 6 in various combinations to provide a range of power outputs, and two oppositely-directed diodes (20, 21), Fig. 3 (not shown), are connected in a parallel arrangement into at least one of the combinations to suppress substantially one or more harmonics of the mains power supply, which may otherwise cause a disturbance during operation of lamps 3 to 6. <IMAGE>

Description

SPECIFICATION Heating apparatus This invention relates to heating apparatus and in particular,though not exclusively, to such apparatus ofthe kind described in our copending Application No.

8320717, incorporating one or more sources of infra-red radiation.

Heating apparatus ofthis kind consists of, in one example, a shallow, circulartray member containing thermally insulative material and supporting four tubular, infra-red-emitting,tungsten-halogen lamps.

Preferably, the tray member, togetherwith three similar members, is mounted beneath a continuous layer ofglass ceramic, so as to form a cooking hob.

In Application No. 8320717, temperature control of the heating apparatus is implemented buy a switching arrangement, which provides a number of switching combinationsofthe respectivefilamentsofthefour lamps, so asto produce a number of discrete control settings, which correspond to different power outputs to produce an optimised heat output curve. To achieve two ofthe lower power outputs, a diode is connected in series with the combination.

It has been found howeverthat harmonic disturbances tend to be carried on the main supply, during operation oftheswitching arrangement in at least one of the combinations in which a diode is utilised.

Furthermore, it may be desirable to incorporate heating apparatus of this kind into a conventional cooking hob,wherein a number of electrical heating elements or gas burners are usually mounted and which is generally provided with an upper surface of enamelled steel, stainless steel or other such mate rials,which may not be transmissive to infra-red radiation.

It is an object ofthe invention to provide heating apparatus including an improved switching arrangement to control the power outputs therefrom.

It is another object ofthe present invention to incorporate heating apparatus ofthe above-mentioned kind which emits infra-red radiation into a conventional cooking hob, which generally incorporates electrical heating elements or gas burners.

According to the present invention there is provided a heating apparatus including a number of sources of infra-red radiation, said apparatus being mounted beneath a layer of infra-red-transmissive material extending over at least an area directly above said apparatus, said apparatus also including a switching arrangementfor interconnecting said sources of infra-red radiation in various combinations, said combinations being connected to a mains power supply so as to provide a range of power outputs from said sources, said switching arrangement including a diode arrangement connected into one or more of said combinations to suppress substantially one or more harmonics of the mains power supply.

The diode arrangement preferably comprises two oppositely-directed diodes, which are connected in a parallel arrangement into one ofthe combinations providing a relatively low power setting, so as to suppress at leastthe second and fourth mains harmonics.

The layerofinfra-redtransmissive material is preferably substantially confined to said area and preferably comprises a glass ceramic disc, which is set into a surround of enamelled steel, stainless steel or other suitable material of a conventional cooking hob.

The peripheral edge of the glass ceramic disc may be provided with a trimming ring of stainless steel or other material, which extends over the join between the edge ofthe disc and the edge ofthe surround.

The invention will now befurther described by way of example onlywith reference to the accompanying drawings, wherein: Figure 1 shows a sectional view of heating apparatus, in accordance with one example of the present invention, Figure 2 shows a plan view of a cooking hob incorporating four of such heating apparatus, and, Figure 3 shows a switching arrangement therefor, in accordance with one example of the invention.

Referring to Figure 1, heating apparatus consists of a generallycirculartray 1, preferablyformedfrom metal, which has a layer 2 of thermally insulative material disposed therewithin, on the base thereof. A number, preferably four, sources of infra-red radiation, shown at 3 to 6, which preferably each consist of atubularinfra-red-emitting,tungsten-halogen lamp, are supported above the layer 2, so thattheyare arranged across the circular area ofthe tray 1. A moulding 7 of ceramic fibre material is arranged around the peripheryofthetray 1,to act as packing material therefor, and the tray is urged upwardly, by a resiliently-mounted support plate (not shown).

The heating apparatus so far described is the subject of Application No. 8320717. The present heating apparatus shown in Figure 1 is urged upwardly towards a disc 8 of an infra-red transmissive material, which is preferably glass ceramic and the extent of which is preferably substantially confined to the circular area directly above the tray 1, within which the infra-red lamps 3 two 6aresupported.

The disc8 is set in a surround 9 of enamelled steel, stainless steel, or any other suitable material, which forms the upper surface of a conventional cooking hob.

It can be seen from Figure 1 that the disc8 is raised above the surface level of the surround 9 and, extending around the periphery of the disc 8, is a trim ring 10, made of stainless steel or another suitable material, which coversthejoinwherethe respective edges ofthe disc8 and the surround 9 meet.

A saucepan, or other cooking utensil, containing food to be cooked maythus be placed upon the circular area ofthe glass ceramic dise so that it may be heated by infra-red radiation emitted from the lamps 3 to 6, which is transmitted through the glass ceramic.

Figure 2 shows a plan view of cooking hob of a conventional cooker, having an enamelled or stainless steel uppersurface 9, which surrounds four glass ceramic discs, 11 to 14, each having a trim ring 15 to 18 respectively provided therearound.

The heating apparatus disclosed in Application No.

8320717 is provided with a switching arrangement which produces six switching combinations offour 500Wfilaments of the infra-red lamps 3 to 6 respectively, arranged across the tray 1,thereby providing six discrete control settings which correspond to six different power outputs to give an optimised heat output curve. To achieve the power outputs required forthefirstand third control settings, as shown in Figure 3, a diode, such as at 19, is required in series with thefilamentcombination.

However, in accordance with the present invention, it has been found advantageous to include a diode arrangement consisting of two oppositely-directed diodes 20 and 21 which are connected in a parallel arrangement as shown, into the combination providingthethird control setting,therebysuppressing the second and fourth mains harmonics, which tended to cause harmonic disturbances to be carried on the mains supply, when utilising only one diode.

The diodes 20, 21 may of course be connected into one or more ofthe otherfilament combinations, should harmonic disturbances be found to be carried on the mains supply during operation ofthat particular combination.

It can therefore be envisagedthatthe present heating apparatus which emits infra-red radiation, may be incorporated into a conventional cooking hob and includes an improved switching arrangementto control the poweroutputtherefrom.

Claims (8)

1. Heating apparatus including a numberof sources of infra-red radiation, said apparatus being mounted beneath a layer of infra-red-transmissive material extending over at least an area directly above said apparatus, said apparatus also including a switching arrangement for interconnecting said sources of infra-red radiation in various combinations, said combinations being connected to a mains power supply so as to provide a range of power outputs from said sources, said switching arrangement including a diode arrangement connected into one or more of said combinations to suppress substantially one or more harmonics of the mains power supply.

2. Heating apparatus as claimed in Claim 1 wherein said diode arrangement includes two diodes, said diodes being oppositely-directed and connected in a parallel arrangementto suppress a numberof said mains harmonics.

3. Heating apparatus as claimed in Claim 1 or 2 wherein said layer of infra-red transmissive material is substantially confined to said area directly above said apparatus and set in a surround of a material which is substantially non-transmissive to infra-red radiation.

4. Heating apparatus as claimed in Claim 3 wherein said material which is substantially non-transmissiveto infra-red radiation is enamelled or stainless steel.

5. Heating apparatus as claimed in any preceding claim wherein said infra-red-transmissive material is a glass ceramic.

6. A cooking hob incorporating one or more of said heating apparatus as claimed in any preceding claim.

7. Heating apparatus substantially as herein described with reference to the accompanying drawings.

8. Acooking hob substantially as herein described with reference to the accompanying drawings.