GB2163004A - Control device for contacts in the energisation circuit of a hot plate - Google Patents

Abstract

A control device for controlling energisation of a hot plate (10) is energised through regulator contacts (14, 15) controlled by a sealed temperature sensing system comprising a phial (17), conduit (19) and bellows (18), the last mentioned also operating contacts (32, 33) controlling operation of an indicator (30) providing indication to the user when the temperature of the hot plate is at a dangerously high value, The temperature at which the bellows (18) opens the contacts (14, 15) can be adjusted by mechanism 23. <IMAGE>

Description

SPECIFICATION Control device for controlling the energisation of electrical hot plate type appliances This invention relates to a control device for controlling the electrical energisation of an electrical appliance of the hot plate type (hereinafter referred to as being of the kind specified) in which a hot plate for supporting a vessel (such as a cooking vessel containing a foodstuff) or other article to be heated is presented by a non-metallic member, usually formed of a combined ceramic and vitreous material to and/or through which heat is supplied from an underlying electrical heating element.

The hot plate member, especially when formed of the combined ceramic and vitreous material, known generally as Ceramglass, can reach extremely high temperatures, for example in the region of 650"C and such temperatures may persist for an appreciable time after the heating element has been deenergised when the user switches off the appliance. Injury may be caused to the user if he or she thereafter inadvertently touches the hot plate and it is therefore important to provide in association with appliances of the kind specified a residual heat indicator to warn the user of the temperature condition of the hot plate.

The object of the present invention is to enable such indication to be provided in a simple and economical manner.

According to the invention, there is provided in association with or for an electrical appliance of the kind specified, a control device for controlling the energisation of the appliance comprising a temperature sensing means mounted or adapted for mounting in proximity to the non-metallic hot plate member and which provides an output by way of pressure changes in a working fluid, and which is connected by a conduit to an output element expansible and contractable in response to such pressure changes to cause opening and closing of current regulating contacts connected or adapted for connection in a supply circuit containing the heating element, an indicator means for furnishing an indication to the user of the temperature state of the non-metallic hot plate member, and means operatively connecting the indicator means with the output element to cause the indicator means to present a high temperature indication when the hot plate member is above a predetermined temperature, irrespective of the energisation of the heating element.

By the use of such a device in accordance with the invention, it is unnecessary to employ a sensing means with output element separately from that which must in any case be provided to operate the regulator contacts for the heating element, whilst due to the use of pressure changes in a working fluid transmitted through a conduit, it becomes practicable to site the output element in proximity to both the indicating means and the regulator contacts at a position remote from the hot plate itself, e.g. behind or adjacent to a control panel on which the normal operator controls of the appliance would be situated.

An embodiment of the invention is illustrated by way of example in the accompanying drawing showing diagrammatically the arrangement of hot plate and controlling device in accordance with the invention.

The hot plate may comprise a plate member 10 formed of a known material or ceramicvitreous composition, such as that known generally as Ceramglass, the upwardly presented surface of which is utilised for supporting articles to be heated such as cooking vessels containing foodstuffs.

Beneath the member 10 there is disposed an electrical heating element which may be a helically wound coil in the form of a flat spiral or other suitable shape adjacent to the undersurface of the member 10 so that it can transmit heat thereto by radiation and convection. The member 10 is often of translucent form and the heating element is visible therethrough thus enabling the user to place the article to be heated immediately above the heating element concerned.

The heating element R, is connected in a supply circuit connected to mains terminals t1, t2 by conductors 11, 1 2 and 13, and contains fixed regulator contacts 14 which can be bridged by a movable regulator contact 1 5 to control the supply of current to the heating resistor R1.

The contacts 14 and 1 5 would normally be provided in a regulator unit mounted behind or otherwise in proximity to a control panel 1 6 positioned at a suitable place on the appliance above the hot plate 10, conveniently and safely accessible to the user.

Operation of the movable contacts 1 5 is effected by a temperature sensing means such as a phial 1 7 disposed beneath and in proximity to the hot plate 10 so as to partake of the temperature thereof and connected to an expansible output element such as a bellows 1 8 by way of a conduit 1 9. The phial 1 7 and element R1 may be enclosed in a chamber 20 beneath the hot plate incorporating heat insulating material in its wall.

When the temperature of the hot plate rises, the vapour pressure of the working fluid in the sealed or closed system 17, 18, 1 9 rises, the bellows expands, and provides a mechanical output as indicated by arrow 21 to a movable member 22 carrying the movable contact 1 5 to cause this to separate from contact 1 4 when the temperature of the hot plate is above a predetermined value. The member 22 shown diagrammatically would preferably operate with a snap action.

The operating point, i.e. the temperature at which opening of the contact 1 5 with respect to the contacts 14 takes place, is adjustable by means of an, adjustment device 23 operable by a user accessible knob or control member (not shown) and imposing variable loading on the member 22 as indicated diagrammatically by spring 24.

Also connected to the user control 23 is a further movable contact 25 co-operating with fixed contacts 26 in a circuit containing conductors 27 and a working indicator such as a lamp 28, conveniently situated on or adjacent to the control panel 16, and providing an indication to the user that the appliance is switched on or as the case may be switched off.

The temperature of the hot plate 10 may be very high, for example up to 650"C and due to its thermal capacity, it may be maintained near this temperature and certainly in a range which would be dangerous to the user to touch for a considerable period after the user control has been moved to the off position, and the element R1 de-energised.

To warn the user of this temperature condition of the hot plate 10, an indicator means 29 is provided comprising an indicator lamp 30, conductors 31 and fixed contacts 32 which can be bridged by a movable contact 33 intended to be closed with respect to the fixed contacts when the temperature of the hot plate is at a dangerously high value.

To operate the contacts 33, a mechanical connection, indicated diagrammatically at 34, is made between the bellows 1 8 and the contact 33 so that the latter are maintained closed when the temperature of the hot plate is at a dangerously high value, irrespective of whether the contacts 1 5 are opened or closed, irrespective of the setting of the user control 23.

The working fluid in the sealed system 1 7, 1 8, 1 9 is selected to be capable of withstanding the operating temperature may comprise an amalgamous sodium and potassium.

The features disclosed in the foregoing description, or the accompanying drawing, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, separately or any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims (4)

1. In association with or for an electrical appliance of the kind specified, a control device for controlling the energisation of the appliance comprising a temperature sensing means mounted or adapted for mounting in proximity to the non-metallic hot plate member and which provides an output by way of pressure changes in a working fluid, and which is connected by a conduit to an output element expansible and contractable in response to such pressure changes to cause opening and closing of current regulating contacts connected or adapted for connection in a supply circuit containing the heating element, an indicator means for furnishing an indication to the user of the temperature state of the non-metallic hot plate member, and means operatively connecting the indicator means with the output element to cause the indicator means to present a high temperature indication when the hot plate member is above a predetermined temperature, irrespective of the energisation of the heating element.

2. A device as claimed in Claim 1 wherein the indicator means comprises a visual and/or audible electrically energised device and a circuit containing contacts operable to cause said device to be energised, mounted or adapted for mounting in proximity to the current regulating contacts for the heating element and wherein the output element is mounted or adapted for mounting in proximity to both the indicator contacts and the regulating contacts for the heating element and operates both the sets of contacts mechanically.

3. In association with or for an electrical applicance of the kind specified a control device substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

4. Any novel feature or novel combination of features disclosed herein and/or shown in the accompanying drawing.