AU2012265567A1 - Temperature sensing for an electric heating device - Google Patents

Abstract

An electric heating device (1) comprising: a substrate (3) having a first area (15) and a second area (17); an electrically resistive heating layer (19) disposed at the first area (15) for heating the substrate (3), wherein the electrically resistive heating layer (19) is not disposed at the second area (17); and an electronic temperature sensor (20) located to measure temperature at the second area (17), and distanced from the electrically resistive heating layer (19) to limit thermal communication between the electronic temperature sensor (21) and the electrically resistive heating layer (19). 2q Figure 1

Description

P/00/0 I Regulation 3. AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Temperature sensing for an electric heating device The following statement is a full description of this invention, including the best method of performing it known to us: 2 Temperature sensing for an electric heating device Field of the invention The present disclosure relates to electric heating devices that include temperature sensors for accurately detecting the temperature of particular areas of the electric heating device. 5 Background of the invention Electric heating devices (such as heating vessels, kettles, toasters, grills and hotplates) are commonly used for food and drink preparation. In addition, other electric heating devices, such as clothes irons and clothes presses are used in domestic and commercial settings. Known electric heating devices may include a heat source such as an electric heating 10 element which, being electrically resistive, heats up when an electrical current is passed through the electric heating element. In practical applications, the electric heating element may heat a heat distribution plate, which in turn heats a contact plate. The heat distribution plate, as the name implies, distributes heat substantially evenly across a thermal junction between the heat distribution plate and the contact plate. The heated contact plate provides heat for the relevant 15 application. For example, in a heating vessel such as a kettle, the contact plate may be in direct contact with water in a heating chamber of the kettle. For a contact grill, the contact plate may be the cooking surface. For an iron, the contact plate may be the hot plate of the iron. In a heating vessel, there may be a temperature sensor to sense the temperature of the vessel's contents. The temperature detected is used to control the operation of the heating vessel. 20 For instance, a kettle has a temperature sensor to detect when water in the kettle is boiling. In the case of a kettle, the temperature sensor is often a mechanical sensor such as a snap-action bi metallic actuator which turns the kettle off once the water has reached a specified temperature. In some kettles, steam from boiling water may be directed to the bi-metallic sensor to turn off the kettle. 25 It is known to secure the temperature sensor to the heat distribution plate. This arrangement may greatly reduce the accuracy of the temperature sensor. The temperature sensor senses the temperature of the heat distribution plate and does not directly sense the temperature of the vessel's contents. Because of this, discrepancies may arise between the measured 3 temperature and the actual temperature of the contents. For a kettle, this may result in the kettle switching off before the water is actually boiling. An inaccurate temperature sensor limits the potential functionality of the heating vessel. Since the temperature of the vessel's contents is not accurately sensed, only a limited range of functions controlled with reference to an approximate 5 temperature reading is possible. For example, in the case of a kettle, it is only possible to stop the kettle boiling based on an approximate boiling point. Similarly, other heating devices may have corresponding problems with accurately measuring the temperature of the contact plate, or other associated surfaces. This may affect accurate temperature control of the heating devices, leading to undesired variations in 10 temperature to areas of the heating device or thermally associated objects. Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art. 15 Summary of the invention In a first aspect, there is provided an electric heating device comprising: a substrate having a first area and a second area; an electrically resistive heating layer disposed at the first area for heating the substrate, wherein the electrically resistive heating layer is not disposed at the second area; and an electronic temperature sensor located to measure temperature at the 20 second area, and distanced from the electrically resistive heating layer to limit thermal communication between the electronic temperature sensor and the electrically resistive heating layer. In one form, the electric heating device further comprises; a controller for controlling the electrically resistive heating layer; and a user interface to select between different heating modes 25 of the controller, wherein the controller controls the electrically resistive heating layer responsive to the temperature sensed by the electronic temperature sensor and dependent on a selection made with the user interface.

4 In one form, the heating modes include a specified temperature mode in which the controller acts to maintain the temperature sensed by the electronic temperature sensor substantially at a specified temperature. In one form of the electric heating device, the first area and second area are disposed on a 5 first surface of the substrate. In a further form, the second area is surrounded by the first area. In yet another form, the second area is adjacent the first area. In one form of the electric heating device, the substrate comprises a material with low thermal expansion properties. In one form, the substrate is made of ceramic or a glass-ceramic. A glass-ceramic that may be suitable is SCHOTT CERANTM, offered by SCHOTT AG, 10 10 Hattenbergstrasse, 55122 Mainz, Germany. This material, in a panel form, has low thermal conductivity. Furthermore, this material has high temperature and mechanical stability, and resistance to thermal shock. The material may also assist in heat transfer by allowing transmittance of infrared radiation. In one form of the electric heating device, the electrically resistive heating layer 15 comprises a printed heating element. In a further form, the printed heating element comprises a printed track with a tortuous path or labyrinth like path. In another form of the electric heating device, the electrically resistive heating layer comprises a film heating element. In another form of the electric heating device, there is provided one or more further 20 electronic temperature sensors located to measure temperature at the second area, and distanced from the electrically resistive heating layer to limit thermal communication between the further electronic temperature sensors and the electrically resistive heating layer. In another form of the electric heating device, the substrate has one or more further areas, wherein the electrically resistive layer is not disposed at the further areas, and wherein one or 25 more additional electronic temperature sensors are located to measure temperature at the further areas, the additional electronic temperature sensors distanced from the electrically resistive heating layer to limit thermal communication between the additional electronic temperature sensors and the electrically resistive heating layer.

5 The electric heating device may be in the form of a heating vessel, kettle, deep fryer, slow cooker, room heater, toaster, flat grill, contact grill, hot plate, or clothes iron. In another aspect, there is provided a kettle for heating water located in a heating chamber of the kettle, the kettle comprising: a substrate in thermal communication with the 5 heating chamber, the substrate having a first surface outside the heating chamber, and the first surface having a first area and a second area; an electrically resistive heating layer disposed at the first area for heating the substrate, wherein the electrically resistive heating layer is not disposed at the second area; and an electronic temperature sensor located to measure temperature at the second area, and distanced from the electrically resistive heating layer to limit thermal 10 communication between the electronic temperature sensor and the electrically resistive heating layer. In one form, the kettle further comprises: a controller for controlling the electrically resistive heating layer; and a user interface to select between different heating modes of the controller, wherein the controller controls the electrically resistive heating layer responsive to the 15 temperature sensed by the electronic temperature sensor and dependent on a selection made with the user interface. In another aspect, there is provided a toaster for heating foodstuff located in a cavity of the toaster, the toaster comprising: a substrate in thermal communication with the cavity, the substrate having a first surface outside the cavity, and the first surface having a first area and a 20 second area; an electrically resistive heating layer disposed at the first area for heating the substrate, wherein the electrically resistive heating layer is not disposed at the second area; and an electronic temperature sensor located to measure temperature at the second area, and distanced from the electrically resistive heating layer to limit thermal communication between the electronic temperature sensor and the electrically resistive heating layer. 25 In one form, the toaster, further comprises: a controller for controlling the electrically resistive heating layer; and a user interface to select between different heating modes of the controller, wherein the controller controls the electrically resistive heating layer responsive to the temperature sensed by the electronic temperature sensor and dependent on a selection made with the user interface.

6 In another aspect, there is provided a contact grill for heating foodstuff located on the grilling surface, the contact grill comprising: a substrate in thermal communication with the grilling surface, the substrate having a first surface separate to the grilling surface, the first surface having a first area and a second area; an electrically resistive heating layer disposed at 5 the first area for heating the substrate, wherein the electrically resistive heating layer is not disposed at the second area; and an electronic temperature sensor located to measure temperature at the second area, and distanced from the electrically resistive heating layer to limit thermal communication between the electronic temperature sensor and the electrically resistive heating layer. 10 In one form, the contact grill further comprises a controller for controlling the electrically resistive heating layer; and a user interface to select between different heating modes of the controller, wherein the controller controls the electrically resistive heating layer responsive to the temperature sensed by the electronic temperature sensor and dependent on a selection made with the user interface. 15 In another aspect, there is provided a clothes iron for ironing clothes in contact with an ironing surface of the clothes iron, the clothes iron comprising: a substrate in thermal communication with the ironing surface, the substrate having a first surface separate to the ironing surface, the first surface having a first area and a second area; an electrically resistive heating layer disposed at the first area for heating the substrate, wherein the electrically resistive 20 heating layer is not disposed at the second area; and an electronic temperature sensor located to measure temperature at the second area, and distanced from the electrically resistive heating layer to limit thermal communication between the electronic temperature sensor and the electrically resistive heating layer. In one form, the clothes iron further comprises: a controller for controlling the electrically 25 resistive heating layer; and a user interface to select between different heating modes of the controller, wherein the controller controls the electrically resistive heating layer responsive to the temperature sensed by the electronic temperature sensor and dependent on a selection made with the user interface.

7 As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives, components, integers or steps. Further aspects of the present invention and further embodiments of the aspects described 5 in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings. Brief description of the drawings Fig. 1 is a partially sectioned bottom perspective view of an electric heating device in the form of a kettle; 10 Fig. 2 is a bottom perspective view of a substrate with an electrically resistive heating layer for the kettle in Fig. 1; Fig. 3 is a partially sectioned bottom perspective view of a side wall of the kettle in Fig. 1; Fig. 4 is a close up view of a portion of the partially sectioned bottom perspective view in 15 Fig. 3; Fig. 5 is a partially sectioned bottom perspective view of a side wall and substrate of the kettle in Fig. 1; Fig. 6 is a close up view of a portion of the partially sectioned bottom perspective view in Fig. 5; 20 Fig. 7 is a partially sectioned top perspective view of a support assembly for the kettle in Fig. 1; Fig. 8 is a top perspective view of the support assembly of Fig. 7 and a control unit; Fig. 9 is a top perspective view of the support assembly of Fig. 7 with the control unit secured to the support assembly; 25 Fig. 10 is an alternative perspective view of the support assembly and control unit in Fig. 9; 8 Fig. 1I is a perspective view of the substrate for an embodiment of the kettle; Fig. 12 is a perspective view of the substrate with the electrically resistive heating layer according to one embodiment; Fig. 13 is a perspective view of the substrate with the electrically resistive heating layer 5 according to another embodiment; Fig. 14 is a perspective view of the substrate with the electrically resistive heating layer according to yet another embodiment; Fig. 15 is a close up perspective view of the electronic temperature sensor located with the substrate of Fig. 12; 10 Fig. 16 is a close up perspective view of the electronic temperature sensor located with the substrate of Fig. 13; Fig. 17. is a close up perspective view of the electronic temperature sensor located with the substrate of Fig. 14; Fig. 18 is a bottom perspective view of the substrate with the electrically resistive heating 15 layer having a labyrinth form in accordance with another embodiment; Fig. 19 is a bottom perspective view of the substrate of Fig. 18 with an electronic temperature sensor located to measure temperature of the substrate; Fig. 20 is a bottom perspective view of the substrate of Fig. 19 with the control unit located with the substrate; 20 Fig. 21 is a bottom perspective view of the substrate with the electrically resistive heating layer in another form in accordance with another embodiment; Fig. 22 is a top perspective view of a substrate for a heating device in accordance with another embodiment; Fig. 23 is a top perspective view of a substrate for a heating device in accordance with yet 25 another embodiment; 9 Fig. 24 is a top perspective view of a substrate for a clothes iron in accordance with one embodiment; Fig. 25 is a top perspective view of the substrate of Fig 24, with the electronic temperature sensors located to measure temperature of the substrate; 5 Fig. 26 is a top perspective view of a substrate for a clothes iron in accordance with another embodiment; and Fig. 27 is a top perspective view of the substrate of Fig. 26, with the electronic temperature sensors located to measure temperature of the substrate. Detailed description of the embodiments 10 Fig. 1 shows a partially sectioned view of a heating appliance I that is part of an electric kettle 3. The kettle 3 has a side wall 5, and a base wall to define a heating chamber 7 where a volume of water can be heated. The base wall is defined by a substrate 9, having two substantial surfaces, a first surface 11 facing away from the heating chamber 7, and a second surface 13 facing the heating chamber 7 and opposite the first surface 11. The substantially planar first 15 surface 11 has a first area 15, and a second area 17. An electrically resistive heating layer 19 is disposed at a first area 15 for heating the substrate 9, which in turn heats the volume of water in the heating chamber 7. An electronic temperature sensor 20 is located to measure temperature at the second area 17. The electronic temperature sensor 20 is distanced from the electrically resistive heating layer 19 to limit thermal communication between the electronic temperature 20 sensor 20 and the electrically resistive heating layer 19. In Fig. 1, the electronic temperature sensor 20 and sensor support 21 are in direct contact with the second area 17, although it can be appreciated the electronic temperature sensor 20 may measure temperature without direct contact, such as being in thermal communication with one another by conduction through an intermediate element, or by measuring radiation emitted or 25 reflected from the second area 17 to the electronic temperature sensor 20. Below the side wall 5 and the base wall is a support assembly 23. In addition to supporting the side wall 5 and base wall of the kettle 3, the support assembly 23 bolsters brackets 25 for the sensor support 21.

10 In the illustrated embodiment, a control unit 27 is secured to the support assembly 23. The control unit 27 has a power connector 29 for connecting to, and receiving electrical power from a power base (not shown). The control unit 27 may communicate with a controller (not shown) for controlling electrical current to the electrically resistive heating layer 19. The 5 controller may be located within, or be part of the control unit 27. Alternatively, the controller may be located external to the control unit 27, such as in the support assembly 23, or in a power base. The controller may include a printed circuit board with a microprocessor or microcontroller. In some arrangements the printed circuit board and microprocessor may be located in the 10 power base. In such an arrangement, it may be desirable to use a multi pin power connector (such as a 5 pin power connector), to provide power and electronic communication between the power base and the control unit 27. A user interface (not shown) is provided to select between different heating modes of the controller, whereby the controller controlling the electrically resistive heating layer 19 is 15 responsive to the temperature sensed by the electronic temperature sensor 20 and dependent on a selection made with the user interface. The components of the kettle 3 will now be described in detail. Fig. 2 illustrates the substrate 9 with the electrically resistive heating layer 19. The substrate 9 is substantially disc shaped, with the first and second surfaces 11, 13 on opposing 20 sides. In one form, the substrate 9 is made of a material having low thermal expansion properties. This may include SCHOTT CERANTM. The first area 15 of the first surface 11, on which the electrically resistive heating layer 19 is disposed, is substantially annular with the exception of the interruption of the second area 17. Thus an opening 18 is provided through the electrically resistive heating layer 19 at the region of the second area 17. The opening 18 25 permits the electronic temperature sensor 20 to measure the temperature of the substrate 9 at the second area 17. A further opening 32 through the centre of the annular electrically resistive heating layer 19 defines a central area 31 of the first surface 11. This further opening allows direct contact and thermal conduction to bi-metallic snap actuators 33 that will be discussed below.

11 The electrically resistive heating layer 19 includes a material having an electrical resistance, whereby current passed through the heating layer 19 causes the heating layer 19 to heat up. The heating layer 19 transfers heat to the first area 15 of the substrate 9 including by conduction and/or radiation. 5 The electrically resistive heating layer 19 may be in the form of a film applied to substrate 9. The application of the heating layer 19 may include printing, spraying, gluing, moulding, vulcanizing and other means. In one form, the electrically resistive heating layer 19 may be a track applied to the substrate 9. To optimize heat transfer to the substrate 9, the track may be applied in a labyrinth form. This provides an increased track length, and may assist in 10 evenly distributing heat to the substrate 9. It may also optimise a contact surface area between the heating layer 19 and the first surface 11. Figs. 3 and 4 illustrate the side wall 5 of the kettle 3. The side wall 5 is in the form of a continuous side wall, forming a substantially cylindrical heating chamber 7. An annular flange 35 extends perpendicular to the side wall 5, in a direction radially inwards to the heating 15 chamber 7. Bosses 37 with internal threading extend downwardly from the annular flange 35. The bosses 37 provide fastening points to secure the side wall 5 to the support assembly 23, which in turn allows the substrate 9 to be sealingly clamped in position. Figs. 5 and 6 illustrate the substrate 9 located with the side wall 5. A seal 39, which may be in the form of a gasket or glue, provides a sealed arrangement between the substrate 9 and the 20 flange 35. In the illustrated embodiment, the seal 39 is in the form of an annular band with an inwardly facing C-shaped cross-section that wraps over the edge surfaces of the disc-shaped substrate 9. Referring to Fig. 1, the seal 39 is clamped in between the flange 35 and a surface 45 of the support assembly 23, which in turn clamps against the edge of the substrate 9. This provides a sealed arrangement between the substrate 9 and the side wall 5 to define the heating 25 chamber 7. Figs. 7 to 10 illustrates the support assembly 23 with and without the control unit 27. The support assembly 23, has fastening protrusions 41, each having apertures 43 for allowing a fastener (not shown) to secure the support assembly 23 to the bosses 37 of the side wall 5. The top surface 45 of the fastening protrusion, as discussed above, provides one half of the clamp 30 against the seal 39, although in other embodiments, the top surface 45 can clamp directly against 12 the substrate 9, or alternatively not at all. Alternatively, the substrate 9 may be glued or otherwise sealed to the side wall 5, and it may not be necessary to clamp the substrate 9. The sensor support 21 is attached to bracket 25, which in turn is secured to the support assembly 23. The bracket 25 may be made of steel, stainless steel or any other suitable material. 5 The sensor support 21, that holds the temperature sensor 20, may be made of a resilient material, such as silicone. The resilience of the sensor support 21 allows the temperature sensor 20 of the assembled kettle 3, to be biased against the second area 17. This maintains good physical contact and thermal communication between the temperature sensor 20 and the exposed area 17 of the substrate 9, even if the assembled components of the kettle 3 are manufactured 10 with loose tolerances, or the assembly becomes loose over time. Furthermore, the silicone material may act as thermal insulation between the temperature sensor 20 and the support assembly 23. The electronic temperature sensor 20 may include a thermocouple to produce a measureable voltage having a known relationship with the temperature of the thermocouple. In 15 another form, the electronic temperature sensor 20 includes a resistance temperature detector (RTD), such as a thermistor, which contains a material with a known electrical resistance at various temperatures, and whereby the resistance is measured to determine the temperature at the measured location. However, it is to be appreciated that any other suitable electronic temperature sensor may be used. 20 The control unit 27 is secured to the support assembly 23, via fasteners (not shown) passing through apertures 47. The apertures 47 may seat a resilient element, such as a silicone washer to bias the control unit 27 towards the substrate 9 when the kettle 3 is assembled. This ensures good contact between the sensor 20 and bi-metallic snap actuators 33 with the substrate 9. Alternatively, springs may be located to bias the control unit 27 to the substrate 9. 25 As best illustrated in Fig. 10, the control unit 27 is secured such that the connector 29 is accessible from the bottom of the support assembly 23. This allows the kettle 3 to be placed onto a power base (not shown) to provide power to heat the water, whilst allowing the user to remove the kettle 3 to dispense water from the kettle 3 at another location.

13 Fig. 10 shows a (stylised) 5 pin connector 29, although other configurations such as a 3 pin connection may be used. The bi-metallic snap actuators 33 secured to the control unit 27, and in contact with the central area 31 of the substrate 9, provide a safety shut-off of the power to the electrically 5 resistive heating layer 19. These snap actuators 33 may operate as part of a thermal fuse to prevent over heating of the heating device 1. As with the temperature sensors 20 and sensor supports 21, the bi-metallic snap actuators and/or the associated components of the thermal fuse, when the kettle is assembled, may be biased towards the central area 31 to maintain contact with the substrate 9. This bias may be due to securing the snap actuators with a resilient material, 10 such as silicone, to ensure the bi-metallic snap actuators 33 are in physical contact and thermal communication with the central area 31. This may also provide thermal insulation between the bi-metallic snap actuators 33/thermal fuse, and the control unit 27/support assembly 23. In one embodiment, the bi-metallic snap actuators in a normal state allow electrical current to pass through an electric circuit. This electric circuit is part of an electric circuit that 15 directly or indirectly provides power, or is an electric circuit that controls power to the electrically resistive heating layer 19. When the bi-metallic snap actuators 33 reach a high temperature threshold (such as when the kettle is switched on without water in the heating chamber 7, or a logic or electronic failure of the controller), the snap actuators distort in shape, thereby breaking the electric circuit. In turn, this stops power to the electrically resistive heating 20 layer 19. Operation The operation of the electronic temperature sensor 20 to measure the temperature of the substrate 9 will now be described with reference to Fig. 1. The electronic temperature sensor 20 measures temperature from the second area 17 of the substrate 9. In the illustrated embodiment, 25 the temperature sensor 20 is in direct contact with the second area 17, thereby allowing measurement of the temperature by conduction from the substrate 9. As shown in Fig. 1, the electronic temperature sensor 20 does not contact the electrically resistive heating layer 19 that is disposed at the first area 15. The electronic temperature sensor 20 is thus distanced from the electrically resistive heating layer to limit thermal communication, 30 in particular conduction of heat, directly between the electronic temperature sensor 20 and the 14 electrically resistive heating layer 19. It is to be appreciated some indirect conduction from the electrically resistive heating layer 19 to the electronic temperature sensor 20 may occur via the substrate 9. Furthermore, some thermal communication between the electronic temperature sensor 20 and the electrically resistive heating layer 19 may occur through radiation and 5 convection. To minimize this, the electronic temperature sensor support 21 may be provided with a shield (not shown) to limit thermal communication by radiation and convection. To obtain an indication of the heating temperature of the water in the heating chamber 7 (or any other area thermally associated with the substrate 9), the temperature of the substrate 9 is measured at the second area 17. As the substrate 9 is in thermal communication with the heating 10 chamber 7, the temperature at the second area 17 provides a suitable measurement to determine the temperature of the water contained in the heating chamber 7. The temperature at the second area 17 may be taken as being approximately the same as the temperature of the water in the heating chamber 7. Alternatively, the temperature of the second area 17 may be used as an input value in a mathematical function to determine the approximate value of the water temperature in 15 the heating chamber 7. Alternatively, the temperature of the second area 17 may be cross referenced with, or interpolated with known data. This allows approximation of the water temperature by matching the known correlation between the temperature of the second area 17 and the water temperature in the heating chamber 7. The modes of operation of the kettle will now be described. The user, using the user 20 interface, may select a heating mode as well as optionally providing operating parameters to the controller. In a "boil" mode, the electrically resistive heating layer 19 is heated by providing electrical current via the control unit 27 until the water contained in the heating chamber 7 reaches a boiling temperature of approximately 100'C. When the temperature of the water 25 reaches boiling point as detected by the electronic temperature sensor 20, the controller stops the electrical current to the electrically resistive heating layer 19 that is heating the chamber 7, either immediately or with a time delay. In a "heat to specified temperature" mode, the electrically resistive heating layer 19 is heated until the water contained in the heating chamber 7 reaches the specified temperature. The 30 specified temperature may be a parameter entered by the user through the user interface. In a 15 similar operation to the boil mode, once the specified temperature is reached, the controller stops the electrical current to the electrically resistive heating layer 9, either immediately or with a time delay. In a "keep warm" mode, the controller maintains the temperature of the water contained 5 in the heating chamber 7 approximately at a specified temperature or in a temperature range around the specified temperature. The specified temperature may be a parameter specified by the user through the user interface, or in another form, the temperature at which the water in the kettle 3 is at the time the keep warm mode is initiated. In this mode, the controller may provide electrical current to the electrically resistive heating layer when the temperature of the water is 10 below a lower threshold, and conversely, stop supply of electrical current to the heating layer when the temperature of the water is above an upper threshold. Typically, the specified temperature would be in a range of temperatures between the lower and upper threshold, with the thresholds calculated from the specified temperature. In one form the controller may act to vary electrical current depending on the deviation of the temperature of the water from the specified 15 temperature. A "sleep mode" or "auto-shutoff mode" may be provided to pause or stop the keep warm mode after a time period has elapsed to save power. In a "boil and keep warm" mode, the electrically resistive layer 19 is initially heated by providing electrical current via the control unit 27 until the water in the heating chamber 7 reaches a boiling temperature. The water in the vessel is then allowed to cool to a specified 20 temperature, or temperature range, whereby the controller enters a "keep warm" phase, where the controller maintains the temperature of the water in the heating chamber 7 in a similar manner to the "keep warm" mode described above. In the "boil and keep warm" mode, the specified temperature may be a parameter specified by the user through the user interface. It is to be appreciated other modes of operation of the kettle 3, and more generally, the 25 electric heating device 1 may be implemented. The modes may include input from the temperature sensor and also other parameters, including those set by the user or from the context or environment. Fabrication Fabrication of embodiments of the substrate 9 with the electrically resistive heating layer 30 19 will now be described with reference to Figs. 11 to 17. Fig. I1 illustrates a substrate 9 16 without the heating layer 19. The substrate 9 may be made of SCHOTT CERAN

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, having low thermal expansion properties which is advantageous as it will lower the risk of expanding and cracking the heating layer 19. The electrically resistive heating layer 19 is applied to the first surface 11 of the substrate 5 9. As described above, this application may include printing, spraying, gluing, moulding, electroplating, vacuum lamination, bonding, vulcanizing and other means. In one particular form, the electrically resistive heating layer is bonded with adhesives using a high-temperature vacuum lamination process. The second area 17 of the first surface 11 may be masked (i.e. covered) during application of the heating layer to provide the opening 18 through the heating 10 layer 19 to the surface 11. Alternatively, the mask may allow the heating layer 19 to be formed with other configurations, including a labyrinth form. In the embodiments illustrated in Figs 12 to 14, electrical contacts 49 in electrical conduction with the heating layer 19, may be applied, either before, concurrently or after the application of the heating layer 19 to the substrate 9. The electrical contacts 49 provide an 15 interface to electrical connections to the control unit 27 to provide electrical current to the heating layer. The electrical contacts 49 may be constructed of copper, gold or any other electrically conductive material suitable for connection with electrical circuits. In one form, electrical connections (not shown) from the control unit 27 or controller to the electrical contacts 49 may be soldered to the electrical contacts 49. In another form, the electrical connections may 20 be clamped or physically abutted to the electrical contacts 49. It should be appreciated any suitable electrical connecting means may be used. The embodiment in Figs. 12 and 15 illustrates a small opening 18 and corresponding second area 17 relative to the size of the sensor support 21. In this embodiment, the heating layer 19 is maximized, however the heating layer 19 is located relatively close to the electronic 25 temperature sensor 20. The embodiment in Figs. 13 and 16 illustrates a larger opening 18 and corresponding second area 17 when compared to the embodiment in Figs. 12 and 15. Advantageously, a greater distance is provided between the heating layer 19 and the electronic temperature sensor 20 when compared to the above embodiment. This may assist in further limiting thermal communication 30 between the heating layer 19 and the electronic temperature sensor 20.

17 The embodiment in Figs. 14 and 17 illustrates yet an even larger opening 18 and corresponding second area 17. In this embodiment, the opening 18 extends to the outer edge of the heating layer 19. Advantageously, the large exposed second area 17 of the first surface II of the substrate 9, allows room to directly mount various components, including the electronic 5 temperature sensor 20 and sensor support 21. This arrangement in mounting components to the substrate 9 may be advantageous as the substrate 9 may be made of a stronger material than the heating layer 19. Furthermore, the heating element 19 may operate at a temperature much greater than the second area 17 of the substrate 9 may reach during normal use. Thereby mounting components to the second area 17 may be more practical than securing to the heating 10 element 19, or the first area 15. Advantages In addition to any other advantages disclosed in this description, embodiments of the present disclosure may have the following advantages. By distancing the electronic temperature sensor from the electrically resistive heating 15 layer, thermal communication between the electronic temperature sensor and the electrically resistive heating layer may be limited. Advantageously, this may allow the electronic temperature sensor to obtain a more accurate reading of the second area of the substrate, with limited or without direct interference from the electrically resistive heating layer. In one embodiment, this arrangement is particularly useful in limiting heat from the electrically resistive 20 layer from being thermally communicated to the electronic temperature sensor by radiation or convection. Furthermore, by sensing the temperature of the substrate at the second area, it may be possible to determine the approximate temperature of another area that is thermally associated with the substrate, such as water in the heating cavity of a kettle defined in part by the substrate. 25 The use of a substrate, heated by an electrically resistive heating layer may provide a smaller and simpler construction of components of an electric heating device. As discussed above, prior art heating devices may include the use of a heating element, a heat distribution plate and a contact plate. These components are generally stacked one on top of each other, which may increase the size and complexity of the heating device. In contrast, embodiments of 30 the disclosure may require fewer components or layers. In one embodiment, the electrically 18 resistive heating layer is a film, thereby reducing the overall thickness compared to prior art devices. Variations Although the above embodiments are described in the context of a kettle, it is to be 5 appreciated the same concept and principles apply to other electric heating devices. Figs. 18 to 20 illustrates one variation of the electrically resistive heating layer 19 on the substrate 9. In this embodiment, the electrically resistive heating layer 19 is in the form of a printed track on the first surface 11 of the substrate 9. The track is in a labyrinth form, providing a tortuous path of the heating layer across the first surface 11. This track arrangement provides 10 an increased electrical path on the heating layer 19, which may be advantageous in providing increased resistance of the heating layer 19. Such an arrangement may also provide improved and/or consistent heat generation of the heating layer 19 across the entire length of the track of the heating layer 19. This arrangement may also provide a more consistent and/or predictable heat generation and transfer to the substrate 9. 15 As illustrated in Figs. 18 to 20, the second area 17 is surrounded by the heating layer 19 on the first surface 11, the second area 17 allowing the electronic temperature sensor 20 to measure the temperature of the substrate 9. Furthermore, the central area 31 is also surrounded by the heating layer 19, to provide a thermal junction on the substrate 9 to contact with the bi metallic snap actuators 33. 20 Another embodiment of the substrate 9 and electrically resistive heating layer 19 for a kettle 3 is illustrated in Fig. 21. In this embodiment, two electronic temperature sensors 20 and respective sensor supports 21 are provided for measuring the temperature of the substrate 9. This may be advantageous as a contingency in case of failure of one of the electronic temperature sensors 20. Alternatively, the temperature of different areas of the substrate 9 may 25 be measured. Having more than one temperatures sensor also allows averaging of the temperature readings to provide a better temperature determination of the substrate 9 and other thermally associated areas. Note in the illustrated embodiment, the second areas 17 associated with the electronic temperature sensors 20 are on the side edges of the electrically resistive heating layer 19. Thus in this embodiment there is no clear "opening 18" through the heating 30 layer 19 as apparent in the above described embodiments.

19 Toaster or grill variation Figs. 22 and 23 illustrate part of a heating device 1 in the form of a grill or toaster. The heating device includes a flat substrate 63, that has a first surface 11 on which is disposed a heating layer 19, and an opposing second surface 13 that may form part of the cooking surface 5 for a contact grill or a cavity wall of the toaster/grill. Fig. 22 illustrates a substrate 63 with the electrically resistive heating layer 19 substantially across the first surface 11. Four second areas 17, accessible through openings 18, are provided on the first surface to allow the electronic temperature sensors 20 to measure the temperature of the substrate 63 at the respective second areas 17. 10 Fig. 23 illustrates another embodiment, with the electrically resistive heating layer 19 covering the first area 15 part of the first surface 11. Two second areas 17 of the first surface 11 are provided on side edges of the heating layer 19 covering the first area 15. The second areas 17 each have electronic temperature sensors 20 with sensor supports 21 to measure the temperature of the substrate 63 at the respective second areas 17. 15 In use, the heating layer 19 is heated by providing electrical current through the heating layer 19 to heat the substrate 63. The heated substrate 63 may radiate, conduct or with the assistance of convection, transfer heat to foodstuff or other items that face the second surface 13. Clothes iron variation. Figs. 24 to 27 illustrates part of a heating device I in the form of a clothes iron. The 20 substrate 73 in one embodiment may be the hot plate of the iron. Typically, the hot plate has two opposite flat surfaces, and in the shape of a shield. A heating layer 19 is disposed on the first surface 11. The opposite second surface 13 may be the ironing surface with which the clothes are ironed. Figs. 24 and 25 illustrate one embodiment where the substrate 73 has the electrically 25 resistive heating layer 19 substantially across the first surface 11. Two second areas 17, accessible through openings 18, allow the electronic temperature sensors 20 to measure the temperature of the substrate 73 at the second areas 17.

20 Figs. 26 and 27 illustrates another embodiment, with the electrically resistive heating layer 19 covering part of the first area 15 of the first surface 11. Two second areas 17 of the first surface 11 are located on side edges of the heating layer 19. The second areas 17 have respective electronic temperature sensors 20 with sensor supports 21 to measure the temperature of the 5 substrate 63 at the respective second areas 17. In use, the heating layer 19 is heated by providing electrical current through the heating layer 19 to heat the hot plate, in the form of substrate 73. The heated substrate 73, via the face of the second surface 13, transfers heat to the clothes by direct contact. It will be understood that the invention disclosed and defined in this specification extends 10 to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Claims (22)

1. An electric heating device comprising: - a substrate having a first area and a second area; 5 - an electrically resistive heating layer disposed at the first area for heating the substrate, wherein the electrically resistive heating layer is not disposed at the second area; and - an electronic temperature sensor located to measure temperature at the second area, and distanced from the electrically resistive heating layer to limit thermal communication between the electronic temperature sensor and the electrically resistive heating layer. 10

2. An electric heating device according to claim 1, further comprising; - a controller for controlling the electrically resistive heating layer; and - a user interface to select between different heating modes of the controller, wherein the controller controls the electrically resistive heating layer responsive to the temperature sensed by the electronic temperature sensor and dependent on a selection made with 15 the user interface.

3. An electric heating device according to claim 2, wherein the heating modes include a specified temperature mode in which the controller acts to maintain the temperature sensed by the electronic temperature sensor substantially at a specified temperature.

4. An electric heating device according to any one of the preceding claims, wherein 20 the first area and second area are disposed on a first surface of the substrate.

5. An electric heating device according to claim 4, wherein the second area is surrounded by the first area.

6. An electric heating device according to claim 4, wherein the second area is adjacent the first area. 22

7. An electric heating device according to any preceding claim, wherein the substrate comprises a material with low thermal expansion properties.

8. An electric heating device according to claim 7, wherein the substrate comprises SCHOTT CERAN TM glass-ceramic. 5

9. An electric heating device according to any one of the preceding claims wherein the electrically resistive heating layer comprises a printed heating element.

10. An electric heating device according to claim 9 wherein the printed heating element comprises a printed track with a tortuous (labyrinth) path.

11. An electric heating device according to any one of claims 1 to 8, wherein the 10 electrically resistive heating layer comprises a film heating element.

12. An electric heating device according to any one of the preceding claims, further comprising one or more further electronic temperature sensors located to measure temperature at the second area, and distanced from the electrically resistive heating layer to limit thermal communication between the further electronic temperature sensors and the electrically resistive 15 heating layer.

13. An electric heating device according to any one of the preceding claims, wherein the substrate has one or more further areas, wherein the electrically resistive layer is not disposed at the further areas, and wherein one or more additional electronic temperature sensors are located to measure temperature at the further areas, the electronic temperature sensors distanced 20 from the electrically resistive heating layer to limit thermal communication between the additional electronic temperature sensors and the electrically resistive heating layer.

14. An electric heating device according to any one of the preceding claims wherein the heating device is a kettle, toaster, flat grill, contact grill, hot plate, or clothes iron.

15. A kettle for heating water located in a heating chamber of the kettle, the kettle 25 comprising: - a substrate in thermal communication with the heating chamber, the substrate having a first surface outside the heating chamber, and the first surface having a first area and a second area; 23 - an electrically resistive heating layer disposed at the first area for heating the substrate, wherein the electrically resistive heating layer is not disposed at the second area; and - an electronic temperature sensor located to measure temperature at the second area, and distanced from the electrically resistive heating layer to limit thermal communication 5 between the electronic temperature sensor and the electrically resistive heating layer.

16. A kettle according to claim 15, further comprising - a controller for controlling the electrically resistive heating layer; and - a user interface to select between different heating modes of the controller, wherein the controller controls the electrically resistive heating layer responsive to the 10 temperature sensed by the electronic temperature sensor and dependent on a selection made with the user interface.

17. A toaster for heating foodstuff located in a cavity of the toaster, the toaster comprising: - a substrate in thermal communication with the cavity, the substrate having a first 15 surface outside the cavity, and the first surface having a first area and a second area; - an electrically resistive heating layer disposed at the first area for heating the substrate, wherein the electrically resistive heating layer is not disposed at the second area; and - an electronic temperature sensor located to measure temperature at the second area, and distanced from the electrically resistive heating layer to limit thermal communication 20 between the electronic temperature sensor and the electrically resistive heating layer.

18. A toaster according to claim 17, further comprising - a controller for controlling the electrically resistive heating layer; and - a user interface to select between different heating modes of the controller, wherein the controller controls the electrically resistive heating layer responsive to the 25 temperature sensed by the electronic temperature sensor and dependent on a selection made with the user interface. 24

19. A contact grill for heating foodstuff located on the grilling surface, the contact grill comprising: - a substrate in thermal communication with the grilling surface, the substrate having a first surface separate to the grilling surface, the first surface having a first area and a 5 second area; - an electrically resistive heating layer disposed at the first area for heating the substrate, wherein the electrically resistive heating layer is not disposed at the second area; and - an electronic temperature sensor located to measure temperature at the second area, and distanced from the electrically resistive heating layer to limit thermal communication 10 between the electronic temperature sensor and the electrically resistive heating layer.

20. A contact grill according to claim 19, further comprising: - a controller for controlling the electrically resistive heating layer; and - a user interface to select between different heating modes of the controller, wherein the controller controls the electrically resistive heating layer responsive to the 15 temperature sensed by the electronic temperature sensor and dependent on a selection made with the user interface.

21. A clothes iron for ironing clothes in contact with an ironing surface of the clothes iron, the clothes iron comprising: - a substrate in thermal communication with the ironing surface, the substrate 20 having a first surface separate to the ironing surface, the first surface having a first area and a second area; - an electrically resistive heating layer disposed at the first area for heating the substrate, wherein the electrically resistive heating layer is not disposed at the second area; and - an electronic temperature sensor located to measure temperature at the second 25 area, and distanced from the electrically resistive heating layer to limit thermal communication between the electronic temperature sensor and the electrically resistive heating layer. 25

22. A clothes iron according to claim 20, further comprising: - a controller for controlling the electrically resistive heating layer; and - a user interface to select between different heating modes of the controller, wherein the controller controls the electrically resistive heating layer responsive to the 5 temperature sensed by the electronic temperature sensor and dependent on a selection made with the user interface.