EP0244242A2

EP0244242A2 - Safety means for use with a heating or cooking appliance

Info

Publication number: EP0244242A2
Application number: EP87303860A
Authority: EP
Inventors: Kulwant Mandir
Original assignee: Valor Heating Ltd
Current assignee: Valor Heating Ltd
Priority date: 1986-05-02
Filing date: 1987-04-30
Publication date: 1987-11-04
Also published as: EP0244242A3; GB8610789D0; GB8710271D0; GB2192505A

Abstract

Safety means for a heating or cooking appliance having a frangible screen (11) wherein said screen is provided with at least one electrically conductive track (12) which is connected to energy supply control means (18) which is capable of assuming either an operative mode which will permit the supply of a fuel or electrical energy to the appliance or an inoperative mode in which the supply of such fuel or electrical energy will be interrupted, said energy supply control means (18) being arranged so that it cannot be maintained in its operative mode unless said electrically conductive track (12) remains unbroken.

Description

This invention relates to safety means for a heating or cooking appliance which may be energised by a gaseous fuel, or by a liquid fuel or by electrical energy.
A heating or cooking appliance may be provided with a screen that may be formed of a transparent or translucent material such as glass or any other frangible material. It is possible because of the frangible nature of such screens, that they can, by accident, be broken whilst the associated appliance is in use, thus leading to the danger of a person or persons near to the appliance coming into contact with the heating element or elements of the appliance and/or with undesirable products of combustion. The invention can be applied to microwave ovens as well as to other forms of heating or cooking appliances.
It is an object of the present invention to provide in an effective way safety means for use with an applicance as above-described and which is operable to terminate or prevent operation of the appliance if the associated screen is broken.
In accordance with the invention there is provided safety means for a heating or cooking applicance having a frangible screen wherein said screen is provided with at least one electrically conductive track which is connected to energy supply control means which is capable of assuming either an operative mode which will permit the supply of a fuel or electrical energy to the applicance or an inoperative mode in which the supply of such fuel or electrical energy will be interrupted, said energy supply control means being arranged so that it cannot be maintained in its operative mode unless said electrically conductive track remains unbroken.
The or each electrically conductive track may be formed by an electrically conductive liquid which is applied (and subsequently baked or otherwise hardened) in a predetermined pattern to a face or edge of the screen, or alternatively the or each track may be formed of a metallic strip or foil which is laid on the face or edge of the screen. Alternatively where the screen is of laminated construction the or each track may be disposed within the interior of the screen.
Where the appliance is provided with burners arranged to consume gaseous or liquid fuel, the electrically conductive track or tracks may be electrically connected to a thermo-couple and an electro-magnetically operated valve, the thermo-couple being arranged to be heated by the burners so that when the latter are alight a current flow will be generated to set said valve in an open position provided also that the or each of said track remains unbroken, the arrangement being such that breakage of said track or tracks will result in the interruption of the circuit to the valve and consequent closing of the valve and the shutting off of the fuel supply.
Alternatively if the appliance is electrically energised, the electrically conductive track or tracks may be connected to a relay or switch so that electrical energy can only be supplied to the heating element or elements of the appliance whilst said track or tracks remain unbroken.
The invention will now be more particularly described with reference to the accompanying drawings in which Figure 1 is an elevation of a screen forming part of one example of safety means in accordance with the invention, and Figure 2 is a circuit diagram.
As shown in Figure 1 the screen 10 is of rectangular form and is made of glass or other frangible material, said screen being disposed at the front of a heating or cooking applicance and serving, inter alia, to prevent direct contact between a person standing near to the applicance and the burners or heating elements of the applicance and/or undesirable products of combustion.
The screen may be mounted in a suitable frame 11 and it is provided with at least one electrically conductive track which is indicated by reference numeral 12. Said track or tracks may be formed by an electrically conductive liquid such as an electrically conductive ink which is printed by means of a silk screening process onto one face of the screen and adjacent to the edge thereof (as shown in the drawing) so that it follows the periphery of the screen substantially all the way round. Typically said track may be of the order of 0.2 inches in width although of course any other convenient width may be used if desired and furthermore, as indicated above, more than one track can be used if desired. After printing of the track or tracks onto the screen the screen is baked to fuse the material of the track to the screen. It will be understood that other hardening procedures may be used depending upon the nature of the track material.
The or each track 12 has two separated ends 13 and 14 but 15 otherwise continuous around the screen and said ends 13 and 14 may be connected, in the case where the heating or cooking appliance is fired by gaseous or liquid fuel, in an electrical circuit which includes a thermo-couple and an electro-magnetically operated valve. The thermo-couple and associated valve are known per se and the arrangement is such that the sensing element of the thermo-couple is in use heated by the burner or burners of the appliance and whilst so heated the thermo-couple will generate a current sufficient to open the electro-magnetically operated valve. On the other hand if the burner or burners should be extinguished for any reason then current will not be generated to hold open the valve so that it will close to cut off the supply of fuel to the burner or burners.
The safety means in accordance with the present invention however includes also the provision of the aforementioned screen and electrically conductive track and the arrangement is such that if the screen is broken to an extent which involves also breakage of the conductive track then the above-mentioned connection to the electro-magnetically actuated valve will also be broken or short circuited by breakage of the track, and again the valve will close to shut off the supply of fuel to the appliance. In other words the valve will only remain open provided that the sensing element of the thermo-couple is sufficiently heated and provided also that the screen and its track remain unbroken. Naturally there will be provided a manually operable override arrangement whereby during a start-up routine fuel can be supplied to the burner or burners in order that the thermo-couple can be heated to its operating temperature. If desired the operation of the manual override can be dependent upon the track 12 being unbroken.
The power source for the electro-magnetically operated valve need not be a thermo-couple and for example a battery or a connection to a domestic electricity supply via a transformer could provide power for the valve dependent upon the integrity of the track or tracks of the screen.
The invention can also be applied to an electrically energised heating or cooking appliance in which case the two ends 13 and 14 of said track 12 may be connected through a relay or switch which is used to control the supply of electrical energy to the appliance. The supply of such energy will only be maintained if the aforesaid track on the screen remains unbroken. If however the screen and the associated track are broken then the arrangement is such that the aforesaid relay or switch will be set in a position in which the supply of energy to the heating elements is interrupted.
As above described the electrically conductive track on the screen is applied to one face of the screen. Alternatively however tracks could be applied if desired to both faces of the screen and/or to one or more edges of the screen. Also where the screen is of laminated construction the track or tracks can be provided within the interior of the screen.
As an alternative to printing or otherwise depositing the track on the screen, the or each track could be defined by metallic strip or foil laid on and adhesively secured to the screen.
Figure 2 illustrates a simple control circuit, it being understood that other circuit configurations are possible. The track 12 is electrically connected at one end 13, by means of a lead 15 to one pole of a power supply 16 which may be a replaceable or rechargeable battery, a thermo-couple powered by heat generated by the appliance with which is safety means is being used, a transformer reducing the voltage of the domestic electricity supply to an acceptable safe voltage, or of any other convenient form. The other end 14 of the track 12 is electrically connected through a lead 17 to the operating coil of an electro-magnetic control device 18 which may, in the case of a gas or liquid fuel burning appliance, be an electro- magentic valve controlling the flow of fuel to the burner or burners of the appliance. Where the appliance is electrically powered then the device 18 may be a relay or other electrically operated switch and although electro-magnetic operation is referred to above it is to be understood that an electrically operated solid state switching device could be used. In each case power from the supply 16 is required to maintain the device 18 operative, that is to say to maintain the device 18 in a state such that it permits the flow of fuel or electricity to the appliance. The return path of the circuit is provided by lead 19 connecting the device 18 to the other pole of the supply 16. An on/off switch may be provided in the circuit for example as shown at 21. Assuming the switch 21 to be closed and the track 12 to be intact then the device 18 will be operative and the appliance can be energised. However, if the track 12 is broken, for example by breakage of the screen 11 then the circuit between the supply 16 and the device 18 cannot be completed and the appliance is rendered inoperative.

Claims

1. Safety means for a heating or cooking appliance having a frangible screen charactorized in that said screen (11) is provided with at least one electrically conductive track (12) which is connected to energy supply control means (18) which is capable of assuming either an operative mode which will permit the supply of a fuel or electrical energy to the appliance or an inoperative mode in which the supply of such fuel or electrical energy will be interrupted, said energy supply control means (18) being arranged so that it cannot be maintained in its operative mode unless said electrically conductive track (12) remains unbroken.

2. Safety means as claimed in claim 1 charactorized in that said track (12) is applied to said screen (11) in a liquid form.

3. Safety means as claimed in claim 1 charactorized in that said track (12) is applied to said screen (11) in the form of a metallic strip or foil.

4. Safety means as claimed in anyone of claims 1 to 3 charactorized in that the track (12) is provided on a face of the screen (11).

5. Safety means as claimed in anyone of claims 1 to 3 charactorized in that the track (12) is provided on the edge of the screen (11).

6. Safety means as claimed in anyone of claims 1 to 3 charactorized in that said screen (12) is of laminated construction and said track (12) is within the screen.

7. Safety means as claimed in anyone of the preceding claims charactorized in that the appliance has burners arranged to consume gaseous or liquid fuel, said electrically conductive track (12) being electrically connected to a thermo-couple (16) and an electro-magnetically operated valve (15), the thermo-couple (16) being arranged to be heated by the burners so that when the latter are alight a current flow will be generated to set said valve (16) in an open position provided also that said track (12) remains unbroken, the arrangement being such that breakage of said track will result in the interruption of the circuit to the valve (18) and consequent closing of the valve (18) and the shutting off of the fuel supply.

8. Safety means as claimed in anyone of claims 1 to 6 charactorized in that the appliance is electrically energised, the electrically conductive track (12) being connected to an electrically operated switch means (18) controlling the supply of electrical energy to the appliance whereby electrical energy can only be supplied to the heating element or elements of the appliance whilst said track (12) remains unbroken.

9. Safety means as claimed in anyone of claims 1 to 8 charctorized in that the screen (11) carries at least one further electrically conductive track.