EP3736500B1

EP3736500B1 - Panel for a cooking hob

Info

Publication number: EP3736500B1
Application number: EP19173111.6A
Authority: EP
Inventors: Nevzat YALIN; Erol Özen
Original assignee: Vestel Elektronik Sanayi ve Ticaret AS
Current assignee: Vestel Elektronik Sanayi ve Ticaret AS
Priority date: 2019-05-07
Filing date: 2019-05-07
Publication date: 2022-07-06
Anticipated expiration: 2039-05-07
Also published as: EP3736500A1

Description

Technical Field

The present disclosure relates to a panel for a cooking hob.

Background

When using a cooking appliance, such as a cooker or hob or the like, to heat items in a pan or the like, it can happen that the contents of the pan overflow onto the cooking surface. It is desirable to detect such overflow events for safety reasons, so that for example a user can be warned and/or corrective action can be taken (such as the cooking appliance turning itself off automatically). A number of arrangements for detecting overflow of a cooking appliance are known, but they typically have one or more limitations.
US2012160820A1 discloses a cooking device which is capable of accurately detecting a liquid boiled over from a container in various directions and which is easy to use.
US2013008891A1 discloses an induction heating cooker that is capable of preventing a phenomenon that a drive circuit is stopped or a high-frequency current is reduced because boiling over is erroneously determined due to a fluctuation in electrostatic capacitance during cooking.

Summary

According to a first aspect disclosed herein, there is provided a panel for a cooking hob, the panel being formed of an electrically and thermally insulative material, the panel comprising:

an upper surface which provides a cooking surface in use;
a lower surface which is opposed to the upper surface;
the upper surface having a plurality of rows of plural resistors arrayed across the upper surface;
the lower surface having a plurality of rows of plural resistors arrayed across the lower surface corresponding to the rows of plural resistors arrayed across the upper surface; and
plural electrically conductive pins extending from the upper surface into the body of the panel towards the lower surface, each pin being electrically connected at a first end to a junction between a respective pair of serially connected resistors of the upper surface;
wherein the resistors in each row of the upper surface are normally electrically connected in series with each other and the resistors in each row of the lower surface are normally not electrically connected with each other;
each pin being arranged such that when heat is applied to a region of the upper surface corresponding to the first end of the pin, the pin expands such that the second end of the pin makes an electrical connection to the corresponding pair of resistors of the lower surface, thereby electrically connecting said pair of resistors of the lower surface in series with each other and with the corresponding pair of resistors of the upper surface.

When heat is applied to a region of the upper surface, such as when for example a hot liquid overflows from a pan that is being heated on the hob in use, corresponding resistors in the upper and/or lower surface and in the neighbourhood of that heated region are electrically connected with each other. The resistance through the rows of resistors changes in dependence on which resistors are electrically connected to each other. The electrical resistance through the rows can be measured which therefore gives an indication of where heat is being applied to the upper surface. This in turn gives an indication of how much liquid has overflowed and exactly where. Appropriate measures can then be taken.
The hob may for example be a stand-alone hob or may be part of a cooker which also includes an oven.
When heat is applied to a region of the upper surface, the resistors in the one of the upper surface and the lower surface that underlie said region of the upper surface where heat is applied may be electrically connected in parallel with the resistors in the one of the upper surface and the lower surface that underlie said region of the upper surface where heat is applied.
In an example, the panel comprises plural thermally conductive pads on the upper surface, the thermally conductive pads being located at the junctions between respective pairs of serially connected resistors of the upper surface to transfer heat to the first ends of the pins when heat is applied to the thermally conductive pad.
According to a second aspect disclosed herein, there is provided a panel for a cooking hob, the panel being formed of an electrically and thermally insulative material, the panel comprising:

an upper surface which provides a cooking surface in use;
a lower surface which is opposed to the upper surface;
the upper surface having a plurality of rows of plural resistors arrayed across the upper surface;
the lower surface having a plurality of rows of plural resistors arrayed across the lower surface corresponding to the rows of plural resistors arrayed across the upper surface;
wherein the resistors in each row of the upper surface are normally not electrically connected in series with each other and the resistors in each row of the lower surface are normally electrically connected with each other;
the panel comprising plural electrically conductive pads on the upper surface, the electrically conductive pads being located between respective pairs of resistors of the upper surface,
the panel comprising plural electrically conductive pins extending from the lower surface into the body of the panel towards the upper surface;
each pin being electrically connected at a first end to a junction between a respective pair of serially connected resistors of the lower surface;
each electrically conductive pad being arranged such that when heat is applied to a region of the upper surface corresponding to the pad, the pad expands to make an electrical connection between the corresponding pair of resistors of the upper surface, thereby electrically connecting said pair of resistors of the upper surface in series with each other and with the corresponding pair of resistors of the lower surface via the pin.

In one example, the second end of the pin may normally be electrically connected with the pad. In another example, the second end of the pin may not be normally be electrically connected with the pad and makes an electrical connection with the pad when the pad expands.
In an example, the rows of resistors of the upper surface are parallel to each other.
In an example, the rows of resistors of the lower surface are parallel to each other.
In an example, each of the resistors of the rows of the upper surface has the same resistance.
In an example, each of the resistors of the rows of the lower surface has the same resistance.
In an example, each of the resistors of the rows of the upper surface and the rows of the lower surface has the same resistance.
In an example, the resistance of at least some of the resistors is different.
There may also be provided a cooking appliance comprising a hob having a panel as described above, a controller in communication with the rows of resistors of the upper surface and the lower surface, the controller being arranged to obtain a measure of the electrical resistance of the rows of resistors of the upper surface and the lower surface and to determine therefrom the location of said region or regions where heat is applied to the upper surface.

Brief Description of the Drawings

To assist understanding of the present disclosure and to show how embodiments may be put into effect, reference is made by way of example to the accompanying drawings in which:

Figure 1 shows schematically a perspective view of a first example of a panel for a cooking hob connected to a controller;
Figure 2 shows schematically a detailed perspective view of a portion of the panel of Figure 1;
Figures 3A and 3B show schematically different examples of electrical connection of resistors in the panel of Figures 1 and 2 according to where heat is applied to the panel; and
Figure 4 shows schematically a detailed perspective view of a portion of a second example of a panel.

Detailed Description

Examples of embodiments of the present invention will now be described with reference to the accompanying drawings. The drawings show examples of panels for a cooking appliance. The cooking appliance may be for example a stand-alone hob (having one or more heater "rings") or may be for example a cooker having a hob and one or more ovens, a grill, etc. The cooking appliance may for example use inductive heating of the pans or other cooking vessels placed on the hob, or may be an electric cooking appliance which has electrical resistive heating elements, a gas cooking appliance, a heat exchanger cooking appliance, etc. The panel may therefore be or be part of an inductive hob. In such a case, and in some other types of hob, the panel may be electrically insulative and may be formed of for example glass or ceramics or the like. In other examples, the panel may surround and/or underlie the heating rings of an electric or a gas or a heat exchanger hob.
As mentioned, when using a cooking appliance, such as a hob or cooker or having a hob or the like, to heat items in a pan or other cooking vessel, it can happen that the contents of the pan overflow onto the upper, cooking surface of the panel. It is desirable to detect such overflow events to prevent overheating for safety reasons and to prevent or minimise spoilage or messing of the cooking surface. For example, a user can be warned and/or corrective action can be taken, such as the cooking appliance turning itself off automatically.
Examples described herein use rows of resistors in the upper and lower surfaces of the panel. The resistors in each row of the upper surface or the lower surface are normally electrically connected in series with each other and the resistors in each row of the other surface are normally not electrically connected with each other. The panel is arranged such that when heat is applied to a region of the upper (cooking) surface, the not-normally-connected resistors that underlie the region of the upper surface where heat is applied are electrically connected in series with each other and are electrically connected with the resistors in the other surface that underlie the region of the upper surface where heat is applied. This affects the electrical resistance that is effectively provided by the various rows of resistors. The resistances of the rows of resistors can be measured so as to enable the location of the region or regions where heat is being applied to be identified. This in turn gives an indication of how much liquid or other material has overflowed onto the cooking surface and exactly where. The user can then be warned and/or corrective action taken automatically (such as switching off the cooking appliance or turning down the heat being provided by the whole cooking appliance or at least locally in the region where an overspill has been detected). A number of different ways of arranging the resistors in the upper and lower surfaces are possible.
Referring now to Figure 1, this shows schematically a perspective view of a first example of a panel 10 for a cooking hob (not shown). The cooking hob may be a stand-alone hob or may be provided as part of a cooker. The hob may be for example an inductive heating hob or may be an electric or gas hob or use a heat exchange method. The panel 10 provides a cooking surface, which is susceptible to spilling or overflow of liquids or the like from cooking vessels being heated on the hob in use. In some examples, the panel 10 is formed principally of an electrically insulative material, such as for example glass or ceramics or the like.
The panel 10 has an upper surface 12, which provides the cooking surface in use, and an opposed lower surface 14. The panel 10 is solid throughout substantially the whole of its volume other than having through holes 16 which pass between the uppers and lower surfaces 12, 14, as will be discussed further below.
The panel 10 has a number of rows 18 of resistors 20 across the upper surface 12 or at least close to the upper surface 12, each upper row 18 having plural resistors 20. Likewise, the panel 10 has a number of rows 22 of resistors 24 across the lower surface 14 or at least close to the lower surface 14, each lower row 22 having plural resistors 24.
In the example shown, the rows 18, 22 are parallel to each other. In the example shown, the rows 18, 22 of resistors 20, 24 are arrayed across the panel 10 so as to provide coverage across substantially the whole of the upper and lower surfaces 12, 14. In the example shown, the spacing between the upper rows 18 and the lower rows 22 is the same, and the size of and distance between the resistors 20, 24 within the rows 18, 22 are the same. As a result, in this example, there is effectively a one-to-one correspondence between resistors 20 in the upper rows 18 and resistors 24 in the lower rows 22. This simplifies the measuring and control aspects, which will be discussed further below. There may nevertheless be examples where it may be useful to have different distances between some of the resistors 20, 24 and/or different size of resistors 20, 24. It will be understood from the following that having a greater number of resistors 20, 24 in the upper and lower surfaces 12, 14 will improve the resolution of the system (in the sense that localised heating of small regions of the upper surface 12 can be detected more readily and accurately), though the manufacturing cost and complexity rises with the number of resistors 20, 24.
Furthermore, in an example, the electrical resistance of the resistors 20 in the upper rows 18 is the same. In an example, the electrical resistance of the resistors 24 in the lower rows 22 is the same. In an example, the electrical resistance of the resistors 20, 24 in the upper and lower rows 18, 24 is the same. This again simplifies the measuring and control aspects, which will be discussed further below. There may nevertheless be examples where it may be useful to have different resistances for some of the resistors 20, 24. For example, as will be appreciated from the following, having different resistances for at least some of the resistors 20, 24 can help to identify the region where spillage has occurred more accurately.
In this example, the resistors 20 in each of the upper rows 18 are normally electrically connected in series with each other within the row 18. That is, in each of the upper rows 18, adjacent resistors 20 are electrically connected to each other at all times. On the other hand, the resistors 24 in each of the lower rows 22 are normally not electrically connected with each other within the row 22. That is, in each of the lower rows 22, adjacent resistors 24 are not electrically connected with each other within the row 22 as a default, in particular when heat is not being applied to the panel 10 (which may occur when for example hot liquid or other material spills onto the upper surface 12). Instead, the resistors 24 in each of the lower rows 22 are electrically connected with an adjacent resistor 24 in the row 22 only when (sufficient) heat is applied to the region of the upper surface 12 of the panel 10 that overlies the relevant resistor 24. In the present example, this is achieved as follows.
Referring additionally to Figure 2, which shows schematically a detailed perspective view of a portion of the panel 10 of Figure 1, adjacent resistors 20 in the uppers rows 18 may be directly electrically connected to each other or may be electrically connected to each other via a pad 30 located at the junction between adjacent pairs of resistors 20. In the case that the pads 30 provide the electrical connection between the adjacent pairs of resistors 20 in the upper rows 18, the pads 30 are formed of or include an electrically conductive material. The pads 30 are also thermally conductive. The pads 30 may conveniently be made of or include a metal.
On the other hand, in this example adjacent resistors 24 in the lower rows 22 are separated from each other by respective small holes ( "pin holes") 32 in the material of the panel 10 located at the junctions between adjacent pairs of resistors 24. The pin holes 32 represent the end of the cylindrical through holes 16 which extend through the panel 10 from the upper surface 12 to the lower surface 14. One end of the cylindrical through holes 16 are centred between pairs of resistors 20 in the upper surface 12. The second end of the cylindrical through holes 16 are centred between pairs of resistors 24 in the lower surface 14.
Each through hole 16 contains a length of material in the form of a thin and elongate shaft or pin 34. The upper end of each pin 34 is in thermal contact with the respective pad 30 that is provided between the corresponding pair of resistors 20 in the upper row 18. The length of the pin 34 when the pin 34 is cold (for example, at say room temperature and not at some elevated temperature) is just less than the thickness of the panel 10 between the upper and lower surfaces 12, 14. As such, the lower end of each pin 34 does not normally extend to the lower surface 14. The material of the pin 34 is such that the pin 34 extends or lengthens when heated and also so that the pin 34 is electrically conductive. The pins 34 may conveniently be made of metal for example. As a result, if a pad 30 is heated by for example hot liquid or other material spilling onto the upper surface 12 on or in the region of the pad 30, heat is transferred to the corresponding pin 34. This causes the pin 34 to expand and so increase in length such that the lower end of the pin 34 extends into and fills the pin hole 32 in the lower surface 14. The pin 34 therefore makes the electrical contact between the adjacent pair of resistors 24 in the lower surface 14. It will be understood that a spillage of hot liquid or other material onto the upper surface 12 will typically cause heating of a number of pads 30 and therefore will typically make the connection between a number of corresponding pairs of adjacent resistors 24 in the lower surface 14, depending on for example how much liquid or other material is spilt and the spacing between rows 18 and the size of the resistors 20.
The effect of this can be seen in Figures 3A and 3B. These figures show schematically different examples of electrical connection of resistors 20, 24 in the panel of Figures 1 and 2 according to where heat is applied to the panel 10. In each case, a pan 40 is indicated schematically, with hot liquid or other material 42 overflowing the edges of the pan 40.
In Figure 3A, the spillage of material 42 is relatively small and therefore only extends over a relatively small region near the pan 40. As such, only a relatively small number of adjacent pairs of resistors 24 in a relatively small number of rows 22 in the lower surface 14 are electrically connected to each other by expansion of the corresponding pins 34 into the pin holes 32. In the portion of the row 22 of the lower surface 14 that can be seen in Figure 3A, only the three leftmost pins 34 have expanded to fill the corresponding pin holes 32 between adjacent pairs of resistors 24 in the lower surface 14. In contrast, the other pins 34 have not extended to fill pin holes 32 between other pairs of resistors 24 in the lower surface 14 as those other pins 34 have not been heated or heated sufficiently. As can be seen in Figure 3A, which is effectively a circuit diagram for this part of the panel 10, the pins 34 that have expanded to fill pin holes 32 between adjacent pairs of resistors 24 in the lower surface 14 also make an electrical connection to the junction between corresponding pairs of resistors 20 in the upper surface 12. In this example, the electrical connection of a pin 34 to the junction between a pair of resistors 20 in the upper surface 12 is via the pin 34 being in contact with the pad 30 between the pair of resistors 20.
In Figure 3B, the spillage of material 42 is relatively large and therefore extends to a relatively large region near the pan 40. As such, a relatively large number of adjacent pairs of resistors 24 in a relatively large number of rows 22 in the lower surface 14 are electrically connected to each other by expansion of the corresponding pins 34 into the pin holes 32. In the portion of the row 22 of the lower surface 14 that can be seen in Figure 3B, all of the pins 34 have expanded to fill the corresponding pin holes 32 between adjacent pairs of resistors 24 in the lower surface 14. Again, it is noted that the pins 34 that have expanded to fill pin holes 32 between adjacent pairs of resistors 24 in the lower surface 14 also make an electrical connection to the junction between corresponding pairs of resistors 20 in the upper surface 12.
Knowing the resistance of the various resistors 20, 24 in the upper and lower rows 18, 22, a calculation can be made in advance of the overall electrical resistance for each combination when different pairs of adjacent resistors 24 in each lower row 22 are connected to each other and to the corresponding resistors 20 in the corresponding upper row 18. This may be carried out during for example manufacture of the panel 10 or the appliance in which the panel 10 is installed. It may be noted that the overall resistance for each combination when different pairs of adjacent resistors 24 in each lower row 22 are connected to each other and to the corresponding resistors 20 in the corresponding upper row 18 will (at least in general) be different and unique. This data can be stored in some permanent, non-volatile memory or data storage area of the panel 10 or appliance, and may be stored in the form of for example a look-up table. This enables the resistance to be measured and then looked up so as to be able to identify which resistors 24 in the lower rows 22 have been electrically connected to each other and to which resistors 20 in the upper rows 18. This enables the extent of the region of the upper surface 12 that has been subject to a (hot) spillage to be identified.
For example, Figure 1 shows schematically a controller 50 having separate electrical connections 52 to one end of each upper row 18 and each lower row 22 of resistors 20, 24. (In Figure 1, the electrical connections to the lower rows 22 is indicated for only one of the lower rows 22 for reasons of clarity.) The controller 50 may be a processor, a microcontroller, etc. The controller 50 can continuously or periodically measure the resistance of each circuit formed by an upper row 18 and lower row 22 of resistors 20, 24. From the measured resistance, the controller 50 can identify which resistors 24 in the lower rows 22 have been electrically connected to each other and to which resistors 20 in the upper rows 18 and thereby identify the extent of the region of the upper surface 12 that has been subject to a (hot) spillage. It may be noted that, for a particular circuit formed by an upper row 18 and lower row 22 of resistors 20, 24, if there is no localised heating affecting that upper row 18 and lower 22 of resistors 20, 24, then the electrical resistance is effectively infinite as the circuit is "open".
Having identified the extent of the region of the upper surface 12 that has been subject to a (hot) spillage, the controller 50 can cause some appropriate action to be taken. For example, the controller 50 can cause an appropriate warning to be triggered for the user, such as for example sounding an alarm and/or causing warning lights on the appliance to be flashed, etc. The controller 50 may for example shut down the heating supplied by the cooking appliance, at least for heating rings or the like near the region that has been subject to a (hot) spillage. This may be particularly appropriate in the case that the controller 50 determines that the region is relatively large. In the case that the region 50 is identified as being close to an edge of the panel 10, the controller 50 may cause anti-leakage measures to be implemented, such as causing retaining flaps or the like to be operated to be positioned around the edges so as to retain liquid on the upper surface 12.
Referring now to Figure 4, this shows schematically a detailed perspective view of a portion of a second example of a panel 410. In this second example, components and features that correspond to components and features of the first example have their reference numerals increased by 400.
In this second example, the arrangement of which resistors are normally connected and not connected (when there is no hot spillage on the panel 410) is reversed compared to the first example. In particular in the second example, the resistors 424 in each of the lower rows 422 are normally electrically connected with each other within the row 22. That is, in each of the lower rows 422, adjacent resistors 424 are electrically connected to each other at all times. On the other hand, in the second example, the resistors 420 in each of the upper rows 418 are normally not electrically connected in series with each other within the row 418. That is, in each of the upper rows 418, adjacent resistors 420 are not electrically connected with each other within the row 418 as a default, in particular when heat is not being applied to the panel 410 (by for example hot liquid or other material spilling onto the upper surface 412). Instead, the resistors 420 in each of the upper rows 418 are electrically connected with an adjacent resistor 420 in the row 418 only when (sufficient) heat is applied to the region of the upper surface 42 of the panel 410 that overlies the relevant resistor 420. In the present example, this is achieved as follows.
In this second example, electrically conductive pads 460 are provided at the locations between adjacent pairs of resistors 420 in each of the upper rows 418. Each pad 460 is sized so that normally it does not extend far enough laterally to contact the adjacent resistors 420 (as shown by hatching in Figure 4). On the other hand, when (sufficient) heat is applied to the pad 460, the pad 460 expands so as to make an electrical contact with the adjacent resistors 420 (as shown by shading in Figure 4), thereby electrically connecting the pair of adjacent resistors 420. The pads 460 may be located in respective blind holes or recesses 470 in the upper surface 412 of the panel 410 which allow the pads 460 to expand and contract when heat is applied or removed. In addition, each pad 460 is respectively electrically connected to the junction between the corresponding adjacent pairs of resistors 424 in the lower surface 414 by pins 480 which extend through through holes 416 in the panel 410.
It may be noted that in this second example, the pins 480 always connect the pads 460 at the upper surface 412 to the junctions between the corresponding adjacent pairs of resistors 424 in the lower surface 414, and it is expansion of the pads 460 at the upper surface 412 that makes the connection between adjacent pairs of resistors 420 in the upper surface 412. This contrasts with the first example where expansion of the pin 480 makes the connection between adjacent pairs of resistors 24 in the lower surface 14.
Operation of the second example is in substance the same as for the first example and will not be repeated here.
In summary, in accordance with the examples described herein, a panel for a cooking hob has rows of resistors that are normally electrically connected in series with each other and rows of resistors that are normally not electrically connected with each other. When heat is applied to the panel, such as when a hot liquid or the like spills or overflows onto an upper, cooking surface of the panel, the not-normally-connected resistors that underlie the region of the upper surface where heat is applied are electrically connected in series with each other and with resistors in the other rows. The electrical resistance through the rows can be measured. This gives an indication of where heat is being applied to the upper surface. This in turn gives an indication of how much liquid has overflowed and exactly where.
It will be understood that the processor or processing system or circuitry referred to herein may in practice be provided by a single chip or integrated circuit or plural chips or integrated circuits, optionally provided as a chipset, an application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), digital signal processor (DSP), graphics processing units (GPUs), etc. The chip or chips may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry, which are configurable so as to operate in accordance with the exemplary embodiments. In this regard, the exemplary embodiments may be implemented at least in part by computer software stored in (non-transitory) memory and executable by the processor, or by hardware, or by a combination of tangibly stored software and hardware (and tangibly stored firmware).
Reference is made herein to data storage for storing data. This may be provided by a single device or by plural devices. Suitable devices include for example a hard disk and non-volatile semiconductor memory (including for example a solid-state drive or SSD).

Claims

A panel (10) for a cooking hob, the panel (10) being formed of an electrically and thermally insulative material, the panel (10) comprising:
an upper surface (12) which provides a cooking surface in use;

a lower surface (14) which is opposed to the upper surface (12);

the upper surface (12) having a plurality of rows (18) of plural resistors (20) arrayed across the upper surface (12);

the lower surface (14) having a plurality of rows (22) of plural resistors (24) arrayed across the lower surface (14) corresponding to the rows (18) of plural resistors (20) arrayed across the upper surface (12); and

plural electrically conductive pins (34) extending from the upper surface (12) into the body of the panel (10) towards the lower surface (14), each pin (34) being electrically connected at a first end to a junction between a respective pair of serially connected resistors (20) of the upper surface (12);

wherein the resistors (20) in each row (18) of the upper surface (12) are normally electrically connected in series with each other and the resistors (24) in each row (22) of the lower surface (14) are normally not electrically connected with each other;

each pin (34) being arranged such that when heat is applied to a region of the upper surface (12) corresponding to the first end of the pin (34), the pin (34) expands such that the second end of the pin (34) makes an electrical connection to the corresponding pair of resistors (24) of the lower surface (14), thereby electrically connecting said pair of resistors (24) of the lower surface (14) in series with each other and with the corresponding pair of resistors (20) of the upper surface (12).
A panel (10) according to claim 1, wherein the panel comprises plural thermally conductive pads (30) on the upper surface (12), the thermally conductive pads (30) being located at the junctions between respective pairs of serially connected resistors (20) of the upper surface (12) to transfer heat to the first ends of the pins (34) when heat is applied to the thermally conductive pad (30).
A panel (410) for a cooking hob, the panel (410) being formed of an electrically and thermally insulative material, the panel (410) comprising:
an upper surface (412) which provides a cooking surface in use;

a lower surface (414) which is opposed to the upper surface (412);

the upper surface (412) having a plurality of rows (418) of plural resistors (420) arrayed across the upper surface (412);

the lower surface (414) having a plurality of rows (422) of plural resistors (424) arrayed across the lower surface (414) corresponding to the rows (418) of plural resistors (420) arrayed across the upper surface (412);

wherein the resistors (420) in each row (418) of the upper surface (412) are normally not electrically connected in series with each other and the resistors (424) in each row (422) of the lower surface (414) are normally electrically connected with each other;

the panel (410) comprising plural electrically conductive pads (460) on the upper surface (412), the electrically conductive pads (460) being located between respective pairs of resistors (420) of the upper surface (412),

the panel (410) comprising plural electrically conductive pins (480) extending from the lower surface (414) into the body of the panel (410) towards the upper surface (412);

each pin (480) being electrically connected at a first end to a junction between a respective pair of serially connected resistors (424) of the lower surface (414);

each electrically conductive pad (460) being arranged such that when heat is applied to a region of the upper surface (412) corresponding to the pad (460), the pad (460) expands to make an electrical connection between the corresponding pair of resistors (420) of the upper surface (412), thereby electrically connecting said pair of resistors (420) of the upper surface (412) in series with each other and with the corresponding pair of resistors (424) of the lower surface (414) via the pin (480).
A panel (10, 410) according to any of claims 1 to 3, wherein the rows (18, 418) of resistors (20, 420) of the upper surface (12, 412) are parallel to each other.
A panel (10, 410) according to any of claims 1 to 4, wherein the rows (22, 422) of resistors (24, 424) of the lower surface (14, 414) are parallel to each other.
A panel (10, 410) according to any of claims 1 to 5, wherein each of the resistors (20, 420) of the rows (18, 418) of the upper surface (12, 412) has the same resistance.
A panel (10, 410) according to any of claims 1 to 6, wherein each of the resistors (24, 424) of the rows (22, 422) of the lower surface (14, 414) has the same resistance.
A panel (10, 410) according to claim 6 and claim 7, wherein each of the resistors (20, 24, 420, 424) of the rows (18, 418) of the upper surface (12, 412) and the rows (22, 422) of the lower surface (14, 414) has the same resistance.
A panel (10, 410) according to any of claims 1 to 7, wherein the resistance of at least some of the resistors (20, 24, 420, 424) is different.
A cooking appliance comprising a hob having a panel (10, 410) according to any of claims 1 to 9, a controller in communication with the rows (18, 22, 418, 422) of resistors (20, 24, 420, 424) of the upper surface (12, 412) and the lower surface (14, 414), the controller being arranged to obtain a measure of the electrical resistance of the rows (18, 22, 418, 422) of resistors (20, 24, 420, 424) of the upper surface (12, 412) and the lower surface (14, 414) and to determine therefrom the location of said region or regions where heat is applied to the upper surface (12, 412).