Patent Description:
There are two general arrangements of induction cooktops or cookers, which are distinguished by the number and placement of the induction coils. A cooking surface (e.g. a glass surface) is located above the induction coils. Cooking vessels may be placed on the cooking surface where they can be heated by one or more (depending on the arrangement) of the induction coils using electromagnetic induction, as known in the art. Cooking vessels suitable for inductive heating include, e.g., cooking vessels made from or containing ferromagnetic material.

In one arrangement, commonly referred to as a fixed-zone induction cooker, a small number (e.g. four) of induction coils are provided. Each induction coil defines a specific "hob area". A cooking vessel can only be heated if it is placed substantially in one of these hob areas. This requires a user to be careful with the cooking vessel placement and also limits the number of cooking vessels which can be placed on the cooker.

In another arrangement, commonly referred to as a zone-free induction cooker, many smaller induction coils (e.g. twenty, forty, or more) are provided. The induction coils typically cover the entire cooking surface, meaning that a cooking vessel can be placed practically anywhere on the cooking surface, without restriction to specific hob areas. The cooking vessel will then be heated inductively by whichever one or more (typically more) induction coils above which it is located. Sensing devices, such as optical, capacitive, and ultrasonic sensors, are typically provided for detecting the position of the cooking vessel(s) so that the corresponding induction coils can be powered accordingly. <CIT> discloses a method of controlling an induction cooker according to the preamble of claim <NUM> and a controller for an induction cooker according to the preamble of claim <NUM>.

According to a first aspect disclosed herein, there is provided a method of controlling an induction cooker comprising at least two induction coils for inductively heating cooking vessels, the method comprising: providing a detection signal to a first of said induction coils; providing a detection signal to a second of said induction coils; and measuring a response signal from the first induction coil; and identifying that the response signal from the first induction coil includes an indication of a response signal generated at the second induction coil in response to the detection signal provided to the second induction coil, thereby to determine that a same cooking vessel occupies both the first induction coil and the second induction coil.

This avoids having to provide separate sensing devices, such as discrete sensors and the disadvantages associated therewith, as discussed further below.

In an example, the detection signal provided to the second induction coil is provided at a later time than the detection signal is provided to the first induction coil, and the indication of the response signal generated at the second induction coil is an increase in the amplitude of the response signal from the first induction coil at a point in time corresponding to the time at which the detection signal was provided to the second induction coil.

In an example, the detection signal provided to the second induction coil has a frequency different from that of the detection signal provided to the first induction coil, and the indication of the response signal generated at the second induction coil is a sum of the response signal from the first induction coil and the response signal from the second induction coil.

In an example, the method comprises measuring the response signal from the second induction coil; and wherein said identifying is performed in response to both the response signals being damped. In general, a response signal from an induction coil will be damped due to the presence of (at least part of) a cooking vessel occupying the induction coil.

In an example, the method comprises, in response to determining that a same cooking vessel occupies both the first and second induction coils, assigning the first and second induction coils to the same control zone so that the first and second induction coils are controlled by a single control setting.

In an example, the method comprises: measuring the response signal from the second induction coil; identifying that both the response signals are damped but there is no indication of a response signal generated at the second induction coil in response to the second detection signal, to thereby determine that two separate cooking vessels occupy the first and second induction coils respectively; and, in response to determining that two separate vessels occupy the first and second induction coils respectively, assigning each of the first and second induction coils to separate control zones so that the first and second induction coils are controlled by different respective control settings.

In an example, the induction cooker comprises at least three induction coils, and the method comprises: providing a detection signal to a third of said induction coils to cause the third induction coil to generate a response signal; and identifying that the response signal from the first induction coil includes an indication of a response signal generated at the third induction coil in response to the detection signal provided to the third induction coil, thereby to determine that a same cooking vessel occupies both the first induction coil and the third induction coil.

In an example, the detection signal provided to the third induction coil is provided at a later time than the detection signals are provided to the first and second induction coils, and the indication of the response signal generated at the third induction coil is an increase in the amplitude of the response signal from the first induction coil at a point in time corresponding to the time at which the detection signal was provided to the third induction coil.

According to a second aspect disclosed herein, there is provided a controller for an induction cooker comprising at least two induction coils for inductively heating cooking vessels, the controller being configured so as when installed at an induction cooker to: provide a detection signal to a first of said induction coils; provide a detection signal to a second of said induction coils; measure a response signal from the first induction coil; and identify whether the response signal from the first induction coil includes an indication of a response signal generated at the second induction coil in response to the second detection signal, thereby to determine that a same cooking vessel occupies both the first induction coil and the second induction coil.

In an example, the controller is configured to provide the detection signal to the second induction coil at a later time than the detection signal to the first induction coil, and the indication of the response signal generated at the second induction coil is an increase in the amplitude of the response signal from the first induction coil at a point in time corresponding to the time at which the detection signal was provided to the second induction coil.

In an example, the controller is configured to measure the response signal from the second induction coil; and wherein the controller is configured to perform said identifying in response to both the response signals being damped.

In an example, the controller is configured to, in response to determining that a same cooking vessel occupies both the first and second induction coils, assign the first and second induction coils to the same control zone so that the first and second induction coils are controlled by a single control setting.

In an example, the induction cooker comprises at least three induction coils, and the controller is configured to: provide a detection signal to a third of said induction coils to cause the third induction coil to generate a response signal; and identify that the response signal from the first induction coil includes an indication of a response signal generated at the third induction coil in response to the detection signal provided to the third induction coil, thereby to determine that a same cooking vessel occupies both the first induction coil and the third induction coil.

According to a third aspect disclosed herein, there is provided an induction cooker comprising the controller according to the second aspect and a plurality of induction coils.

<FIG> shows an example of an induction cooker <NUM> in accordance with the present disclosure. For reasons that will become clear, the induction cooker <NUM> may be referred to as a "zone-free" or "free-zone" induction cooker.

The induction cooker <NUM> comprises a plurality of induction coils <NUM> and a controller <NUM>. A cooking surface (e.g. a glass surface) is located above the induction coils <NUM>. Vessels (i.e. cooking vessels) made from or containing ferromagnetic material may be placed on the cooking surface where they can be heated by one or more of the induction coils <NUM> using electromagnetic induction. An example of a cooking vessel <NUM> is shown in <FIG> located at the top-right of the cooking surface. The cooking vessel <NUM> may be, for example, a pot, pan, etc., made from or containing ferromagnetic material.

The induction coils <NUM> of the so-called "free-zone" induction cooker <NUM> are smaller than that of a "fixed-zone" induction cooker. For example, each induction coil <NUM> may be (much) smaller than a typical cooking vessel. This means that there is no particular or definite hob area and the user is able to freely position each cooking vessel on the cooking surface. The cooking vessel can then be heated by whichever induction coil(s) <NUM> happen(s) to be located below that position. In the example of <FIG>, the illustrative cooking vessel <NUM> is located above four induction coils <NUM>.

In the example of <FIG>, the induction cooker <NUM> comprises forty-two induction coils <NUM> arranged in a 6x7 rectangular grid. In other examples, there may be more or fewer induction coils <NUM>. In other examples, the induction coils <NUM> may be arranged in a non-rectangular regular (e.g. a hexagonal grid) or an irregular pattern.

The controller <NUM> is operatively coupled to the plurality of induction coils <NUM>. In operation, the controller <NUM> controls the power supplied to each of the plurality of induction coils <NUM> as necessary and thereby controls the amount of inductive heating applied to whatever cooking vessel(s) are present. The controller <NUM> may be implemented, for example, using one or more processors.

The controller <NUM> is able to determine, for a given induction coil <NUM>, whether or not there is currently a cooking vessel present on that induction coil <NUM>, as will now be discussed with reference to <FIG> and <FIG>. This information can be used by the controller <NUM>, for example such that only any induction coil(s) <NUM> that need to be used (as they do have a cooking vessel placed over them) are powered and such that any induction coils <NUM> that are not currently being used (as they do not have a cooking vessel placed over them) are not powered.

To determine whether a given induction coil <NUM> is currently occupied (has a cooking vessel <NUM> located over it), the controller <NUM> probes the induction coil <NUM> by applying a detection signal <NUM> to the induction coil <NUM> and measuring a response signal <NUM> from that induction coil <NUM>. For example, the controller <NUM> may drive the induction coil <NUM> with a known voltage (e.g. a sinusoidal AC voltage) and then observing the resulting current.

<FIG> shows an example in which a detection signal <NUM> is applied to an induction coil <NUM> which is not currently occupied by a cooking vessel <NUM>. In this case, the resulting response signal 501a is substantially undamped and only fades slowly.

<FIG> shows an example in which a detection signal <NUM> is applied to an induction coil <NUM> which is currently occupied by a cooking vessel. In this case, the resulting response signal 501b is (heavily) damped and fades quickly. This is due to eddy currents generated in the cooking vessel drawing power from the detection signal <NUM>.

<FIG> shows an example in which three cooking vessels 400a, 400b, 400c are placed on the induction cooker <NUM>. The first cooking vessel 400a is located in the top-right of the cooking surface. The second cooking vessel 400b is adjacent the first cooking vessel 400a and share a border <NUM>. The third cooking vessel 400c is not adjacent either of the first cooking vessel 400a or second cooking vessel 400b.

A user interface <NUM> is provided via which a user can provide user input to the controller <NUM>. The user interface <NUM> may be, for example, a touchscreen or have operable buttons, etc. Compared to a fixed-zone induction cooker, more sophisticated control is required because the vessels may be placed anywhere on the cooking surface, rather than in predefined "hobs".

To allow the user to vary the heating applied to each cooking vessel <NUM> separately, the induction coils <NUM> may be divided into "control zones". Each control zone is a set of one or more induction coils <NUM> sharing a common control setting (e.g. a power setting). Ideally, each control zone corresponds to (the base area of) a single cooking vessel <NUM>. The controller <NUM> may provide an indication of the current control zones to the user (e.g. on a graphical user interface) so that the user can specify a control setting for each control zone. In other words, each control zone is individually controllable by a user.

The control zones may be defined on an ad-hoc basis depending on the location and position of the cooking vessels. In this example, a first control zone A is defined for the first cooking vessel 400a, a second control zone B for the second cooking vessel 400b, and a third control zone C for the third cooking vessel 400c. The first control zone A comprises the induction coils <NUM> over which the first cooking vessel 400a is located, the second control zone B comprises the induction coils <NUM> over which the second cooking vessel 400b is located, and the third control zone C comprises the induction coils <NUM> over which the third cooking vessel 400c is located.

Detection signals <NUM>, as described above in relation to <FIG> and <FIG>, can be used to determine which induction coils <NUM> are currently occupied by (at least part of) a cooking vessel <NUM>. If the controller <NUM> cannot distinguish between a single cooking vessel and two adjacent or closely located cooking vessels, the controller <NUM> will assign a single control zone for what is in reality two separate cooking vessels. This prevents the user from specifying separate control settings for each cooking vessel, which is undesirable.

To avoid this, the controller <NUM> needs to be able to distinguish between the two scenarios shown in <FIG> with respect to a first induction coil 200a and a second induction coil 200b which are adjacent one another.

In <FIG>, a first cooking vessel 400a occupies the first induction coil 200a and a second cooking vessel 400b occupies the second induction coil 200b. In this case, separate control settings may be desired for each of the first cooking vessel 400a and second cooking vessel 400b. Therefore, the controller <NUM> should assign separate controls zones - a first control zone for the first cooking vessel 400a comprising the first induction coil 200a only, and a second control zone for the second cooking vessel 400b comprising the second induction coil 200b only - so that the user may specify different control settings, using different power settings if desired for example, for each cooking vessel.

In <FIG>, a single cooking vessel 400c occupies both the first induction coil 200a and the second induction coil 200b. In this case, only a single control setting is required for the single cooking vessel 400c. The controller <NUM> should therefore assign a single control zone for the single cooking vessel 400a consisting of both the first induction coil 200a and the second induction coil 200b. The user may then specify a single control setting for the single cooking vessel 400a, which is used by the controller <NUM> to control both the first induction coil 200a and the second induction 200b with the same power setting, etc..

A naive application of detection signals to the induction coils 200a, 200b can allow the controller <NUM> to identify that induction coils are occupied. However, the response signals from the coils will be damped in both scenarios because there is (part of) a cooking vessel located above both coils. That is, unless other measures are taken, there is no way for a controller to distinguish between the scenario in <FIG> and the scenario in <FIG> in order to provide appropriate control options to the user.

Prior art solutions use one or more additional sensing devices for detecting the position of the cooking vessel(s). Examples of such additional sensing devices include optical, capacitive, and ultrasonic sensors. Disadvantages of this include that it creates an additional hardware cost and manufacturing assembly cost. The additional components also increase hardware complexity which may increase the likelihood of failure. Another disadvantage of using such sensing devices is that the determination success rate can be low. This is because both the cooking surface can be thick which reduces the sensor sensitivity and also because the sensing devices are liable to becoming dirty over time as the cooker is used, also reducing the sensor sensitivity.

In examples described herein, a solution is provided which does not require any additional discrete sensing devices (such as optical, capacitive, and ultrasonic sensors as used in the prior art). Instead, the controller <NUM> provides detection signals to each induction coil <NUM> which can be distinguished from each other (either because they are supplied at different times or because the detection signals themselves differ from each other in some detectable way) and observes the response signals to identify whether there is an indication of the response signal provided by one induction coil <NUM> in the response signal received from the other coil <NUM>. Such an indication will be seen only in the case that the same cooking vessel <NUM> occupies both induction coils <NUM>. This is because, in that case, both detection signals are acting on the same cooking vessel and therefore effectively interfere with each other. When there are separate cooking vessels <NUM> on each induction coil <NUM>, no such interference occurs and therefore no indication of one detection signal is identifiable in the other response signal.

There are several ways in which the detection signals provided to each inductive coil <NUM> may be distinguishable or "different". For the purposes of explanation, an example will first be described in which the detection signals are provided to each inductive coil <NUM> at different times (i.e. offset from one another in time). Other examples are described later below.

<FIG> shows a first detection signal 500a and a second detection signal 500b in accordance with an example described herein. Each detection signal comprises a sinusoidal voltage.

The first detection signal 500a is provided to the first induction coil 200a at time t=<NUM>. The second detection signal 500b is provided to the second induction coil 200b at a later time. That is, the second detection signal 500b is offset in time from the first detection signal 500a by a time delay Δt.

<FIG> shows the response signals as received from the first induction coil 200a and second induction coil 200b in response to the detection signals 500a, 500b in accordance with the scenario of <FIG> (separate cooking vessels <NUM>).

In this case, the first response signal 501a and second response signal 501b are each damped sinusoids, indicating that both induction coils 200a, 200b are occupied by a cooking vessel <NUM>. The second response signal 501b is delayed in time relative to the first response signal 501a by Δt.

<FIG> shows the response signals as received from the first induction coil 200a and the second induction coil 200b in response to the detection signals 500a, 500b in accordance with the scenario of <FIG> (single cooking vessel <NUM>).

In this case, the first response signal 501a and second response signal 501b are damped sinusoids as before. However, there is also an indication <NUM> of the second detection signal 500b in the first response signal 501a. This indication <NUM> arises because the detection signal 500b provided to the second induction coil 200b acts on the same cooking vessel <NUM> (i.e. the same piece of material) and therefore changes the response signal 501a as observed at the first induction coil 200a.

This indication may manifest as an additional increase in the amplitude of the response signal 501a. That is, the first response signal <NUM> is not a simple damped signal, but comprises an additional component corresponding to the second detection signal 500b. That is, the first response signal 501a shows an artefact of the second response signal 501b. This means that the second detection signal 500b applied to the second induction coil 200b has had some effect at the first induction coil 200a. As mentioned above, this is only the case when the same cooking vessel occupies both induction coils 200a, 200b. Hence, the presence of such an indication <NUM> can be used to determine that the same cooking vessel <NUM> occupies both the first induction coil 200a and the second induction coil 200b (i.e. to distinguish between a single cooking vessel and separate cooking vessels).

Note that the time delay Δt of the indication <NUM> relative to the start of the first response signal 501a corresponds to the time delay Δt between the second detection signal 500b and the first detection signal 500a. This is returned to below.

<FIG> shows an example method performed by the controller <NUM>.

At S900, the controller <NUM> provides the first detection signal 500a to the first induction coil 200a. This causes the first induction coil 200a to generate a first response signal 501a.

At S901, the controller <NUM> provides the second detection signal 500b to the second induction coil 200b. This causes the second induction coil 200b to generate a second response signal 501b.

At S902, the controller <NUM> measures the first response signal 501a from the first induction coil 200a.

At S903, the controller <NUM> identifies whether there is an indication <NUM> of the second detection signal in the first response signal 501a.

If there is an indication <NUM> of the second detection signal 500b in the first response signal 501a, the controller <NUM> proceeds to S904 in which the controller <NUM> determines that the same vessel <NUM> occupies both the first induction coil 200a and the second induction coil 200b.

On the other hand, if there is no indication <NUM> of the second detection signal 500b in the first response signal 501a, the controller proceeds to S905, where it is determined that it is not the case that the same cooking vessel <NUM> occupies both the first induction coil 200a and second induction coil 200b.

It is appreciated that the method of <FIG> is exemplary and that in other examples the controller <NUM> may perform additional operations, perform the operations in a different order, etc..

For example, the controller <NUM> may additionally measure the second response signal 501b and only perform the identifying at S903 if both the first response signal 501a and second response signal 501b are damped. This is advantageous because if one (or both) of the response signals 501a, 501b are not damped, then there is no cooking vessel <NUM> present on the respective induction coil(s) and therefore the controller <NUM> can rule out the possibility that a single cooking vessel <NUM> occupies both induction coils 200a, 200b without needing to identify presence or absence of the indication <NUM> as described above.

In general, the controller <NUM> may provide a respective detection signal <NUM> and measure a respective response signal <NUM> from any induction coils <NUM> present. Any induction coils <NUM> that provide a damped response signal <NUM> can be determined to by occupied by (part of) a cooking vessel <NUM>. The controller <NUM> can additionally analyse the response signal(s) <NUM> to identify which induction coil(s) <NUM> interfere with which other induction coil(s) <NUM> and use this to determine the location of the cooking vessel(s) <NUM> on the cooking surface, as described above. In particular, the controller <NUM> can identify a border between two adjacent cooking vessels <NUM> if two adjacent induction coils <NUM> provide damped response signals <NUM> but there is no indication <NUM> of another response signal <NUM> being present in either response signal <NUM>.

Once the controller <NUM> has determined the location of the cooking vessel(s) <NUM>, it can provide appropriate control options to the user. To continue the example above, the controller may automatically provide a single control setting for both the first induction coil 200a and second induction coil 200b in response to determining that a same vessel <NUM> occupies both the induction coils 200a, 200b, and automatically provide separate control settings for the first induction coil 200a and the second induction coil 200b in response to determining that two separate cooking vessels <NUM> occupy the induction coils 200a, 200b.

A real-world induction cooker <NUM> may comprise many induction coils <NUM> rather than the two in the simplified example described above. In such cases, there is the possibility of ambiguity between precisely which two (or more) induction coils <NUM> a single cooking vessel <NUM> is occupying. In examples, the controller <NUM> can also identify which adjacent induction coil <NUM> this is by leveraging a property (such as the time delay) of the detection signals <NUM> provided to each induction coil <NUM>.

Consider an induction cooker <NUM> comprising three induction coils 200a, 200b, 200c, for example, where: the first induction coil 200a is adjacent the second induction coil 200b and the third induction coil 200c; and the second induction coil 200b and third induction coil 200c are not adjacent one another.

In this arrangement, the controller <NUM> may provide a respective detection signal <NUM> to each induction coil <NUM> with a different time delay. For example, the controller <NUM> may provide a first detection signal to the first induction coil 200a at time t=<NUM>, a second detection signal to the second induction coil 200b at time t=<NUM>, and a third detection signal to the third induction coil 200c at time t=<NUM>.

Then, when the controller <NUM> measures the response signal from the first induction coil 200a, it can determine the delay between the start of the response signal and the indication <NUM>. If the delay is around <NUM>, then the controller <NUM> determines that the cooking vessel <NUM> occupying the first induction coil 200a is also occupying the second induction coil 200b. If instead the delay is around <NUM>, then the controller <NUM> determines that the cooking vessel <NUM> occupying the first induction coil 200a is also occupying the third induction coil 200c. If there are two indications, at <NUM> and <NUM> respectively, then then the controller <NUM> determines that the cooking vessel <NUM> occupying the first induction coil 200a is also occupying both the second induction coil 200b and the third induction coil 200c.

Similar principles hold for induction cookers <NUM> comprising any number of induction coils <NUM>. In a naive example, each induction coil <NUM> may be driven with its own unique time delay. This is certainly sufficient to allow the controller <NUM> to distinguish between indications <NUM> of each detection signal <NUM>. However, fewer different time delays can be used, depending on the layout of the induction coils <NUM>. This is because, in particular, if the controller <NUM> detects cooking vessels <NUM> which are located on induction coils <NUM> which are non-adjacent (e.g. far apart), then it can be assumed that these are not the same cooking vessel <NUM>. This means that the same detection signal (having the same property, e.g. time delay, frequency (see further below), etc.) can be used for both these induction coils <NUM>. In general, only different detection signals <NUM> are required for the nearest neighbours to a given induction coil <NUM>.

<FIG> shows an example for a regular rectangular array of induction coils <NUM>. In this case, nine different time delays can be used while still achieving the condition that no two adjacent coils have the same time delay. That is, the induction coils <NUM> can be grouped into nine sets, the induction coils <NUM> within each set having the same time delay. For the sake of simplicity, the time delays are labelled simply <NUM>-<NUM>. It is appreciated that the actual time delays may be any time delay that can be accurately resolved by the controller <NUM>. For example, the time delays may be <NUM>, <NUM>, <NUM>,. This can then repeat, meaning that the controller <NUM> can perform the cooking vessel layout determination in less than a second for an induction cooker <NUM> of any size.

As shown in <FIG>, only six different time delays are required if diagonals are excluded.

<FIG> shows an example for a regular hexagonal array of induction coils <NUM>. In this case, seven different time delays can be used while still achieving the condition that no two adjacent coils have the same time delay.

As mentioned earlier above, there are other ways in which the detection signals provided to each inductive coil <NUM> may be "different" or otherwise distinguishable. In general, any property of the detection signal which is detectable in the response from an adjacent induction coil <NUM> when the same cooking vessel <NUM> is present may be used. For example, the detection signals may have different frequencies, and/or may be modulated in some manner (e.g. amplitude modulation, frequency modulation, pulse width modulation), e.g. to embed a different code into each detection signal <NUM>. In such cases, the first response signal 501a is modulated by the second response signal 501b (if the cooking vessel <NUM> is over both induction coils <NUM>, and not otherwise). That is, the first response signal 501a shows an artefact of the second response signal 501b.

Similar considerations to those described above in relation to <FIG> also apply in cases where the detection signals have different frequencies, are modulated in different manners, etc..

As a specific example, with reference to <FIG>, the numbers <NUM>-<NUM> may represent detection signals <NUM> having different frequencies. In this case, the detection signals <NUM> do not need to be delayed relative to one another. Rather, they can all be applied by the controller <NUM> at the same time (though in some examples detection signals <NUM> having different frequencies may be applied at different times, which may assist further in resolving the detected response signals <NUM>). The controller <NUM> may apply a variety of techniques to identify an indication <NUM> in a given response signal <NUM> and, in particular, to identify which other induction coil <NUM> was the cause of the indication <NUM>.

For example, when two different but similar frequencies are used for different detection signals <NUM>, the controller <NUM> may identify a beat frequency in the response signal <NUM> and then determine that the cooking vessel <NUM> overlaps with the other induction coil <NUM> which was provided with the detection signal <NUM> having the specific frequency required to produce that beat frequency.

In another example, the controller <NUM> may apply a Fourier transform (e.g. an FFT) to identify the frequency components of the response signal <NUM>. The controller <NUM> can then assign a single control zone for all the induction coils <NUM> which were provided with those frequencies, as a single cooking vessel <NUM> must be occupying all those induction coils <NUM>.

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).

Claim 1:
A method of controlling an induction cooker (<NUM>) comprising at least two induction coils (<NUM>) for inductively heating cooking vessels (<NUM>), the method comprising:
providing a detection signal (500a) to a first of said induction coils (200a);
providing a detection signal (500b) to a second of said induction coils (200b); and
measuring a response signal (501a) from the first induction coil (200a); and
characterised by
identifying that the response signal (501a) from the first induction coil (200a) includes an indication (<NUM>) of a response signal (501b) generated at the second induction coil (200b) in response to the detection signal (500b) provided to the second induction coil (200b), thereby to determine that a same cooking vessel (<NUM>) occupies both the first induction coil (200a) and the second induction coil (200b).