WO2010129715A1

WO2010129715A1 - Spill-over detection method and system

Info

Publication number: WO2010129715A1
Application number: PCT/US2010/033786
Authority: WO
Inventors: Jianming Huang; Xiaolin Chen
Original assignee: Cypress Semiconductor Corporation
Priority date: 2009-05-05
Filing date: 2010-05-05
Publication date: 2010-11-11
Also published as: CN102461330A

Abstract

A method of detecting overflow of a substance onto a heating appliance may include detecting a change in a capacitance of a capacitive sensor element resulting from proximity of the substance to the capacitive sensor element, determining whether the change in capacitance exceeds a predetermined threshold, and indicating an overflow condition in response to determining that the change in capacitance exceeds the predetermined threshold.

Description

SPILL-OVER DETECTION METHOD AND SYSTEM

RELATED APPLICATIONS

100011 This application claims the benefit of U.S. Provisional Application No. 51/175,700, filed on May 5, 2009.

TECHNICAL FIELD

[0002] This disclosure relates to the field ol user interface devices and, in particular, to the detection of spill-over in cooking appliances and other suitable types ot devices, such as, tor example, induction cookers and the like.

BACKGROUND

[0003] An induction cooker is an electric cooker thai uses principles at electromagnetic induction to heat. During use of an induction cooker, the water or food in the cooking container can spill over to the cooker cover as a result of some accident or from boiling. This may result in some risk of damage to the appliance/devi ce or injury to the users.

[0004] For example, when a substance, such as a liquid, in the induction cooker boils o\ er, buttons or other electronics outside the cooking container mav be damaged or inadvertently acth a ted. [0005] One method for detecting spill-over is ultrasonic detection; however, the

cott of ultrasonic detectors tor this purpose is relatively high.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings.

[0007] Figure t illustrates a cross section of a cooker cover including a capacitivL' sensor clement for detecting a spill-over condition, according to an embodiment.

[0008] Figure 2A illustrates a bottom view of an embodiment ot ύ capacHU e sensor element for detecting a spill-over condition.

[0009] Figure 2B illustrates a side view ot an embodiment ot a capacitive sensor element for detecting a spill-over condition.

[ 0010 ] Figure 3 illustrates a bottom view of a cooker cover including eapacitive sensor elements for detecting a spill-over condition, according to an embodiment.

[0011] Figure A is α circuit diagram illustrating an embodiment of a capacitance defection circuit.

[ 0012 ] Figure 5A is a circuit diagram illustrating an embodiment of a capacitance detection circuit.

[0013] Figure 5B is a circuit diagram illustrating an embodiment ol a capacitance detection circuit [0014] Figure b is a circuit diagram illustrating an embodiment of a capacitance detection circuit.

[ 0015 ] Figure 7 is graph illustrating changes in count values corresponding to change in capacitance of a capacitive sensor element according to an embodiment

[0016] Figure 8 is a flow diagram illustrating one embodiment ot a spill-over detection process.

DETAILED DESCRIPTION

[0017] The following description sets forth numerous specific details such as examples of specific systems, components,, methods, and so forth, in order to provide a good understanding of several embodiments of the present invention. It will be apparent to one skilled in the art however, that at least some embodiments of the present invention may be practiced without these specific details. In other instances, well-known components or methods are not described in detail or are presented in a simple block diagram format in order to avoid unnecessarily obscuring the present invention. Thus, the specific details set forth are merely exemplary. Particular implementations may vary from these exemplary details and still be contemplated to be within the spirit and scope of the present invention.

[0018] One embodiment of an appliance, such as an induction cooker, may- include a spill-over or overflow detection mechanism that detects an overflow of a substance in the appliance. A spill-over or overflow condition may occur, tor example, when a substance or liquid being heated boils over or otherwise escapes a heating container. In one embodiment, a spiil-over or overflow condition may also occur when a liquid or other substance is present on anv surface of the heating appliance outside of the heating container. For example, spilling or dripping liquid or another substance on a surface of the heating appliance may result in an overflow condition being triggered. To prevent damage to the appliance or injury to a user, such an appliance may further perform some action, such as turning off or reducing cooking heat in response to detecting the overflow condition.

[0019] In one embodiment, the spill-over detection mechanism can include a controller and one or several capacitance sensors that are assembled around the cooking container. The capacitance sensors can be connected to the controller. The controller is configured to detect capacitance changes on the sensors to determine if the spill-over condition is occurring. It such a condition occurs, the controller can automatically stop or reduce the heating power of the appliance. [0020] In one embodiment, the controller may be a stand-alone controller, or can be integrated into the system controller, as a partial function of the system controller. In one embodiment, the controller uses one additional pin for detecting the spill-over condition.

[0021] Merely for purposes of illustration and not for limitation, the systems and methods according to the present invention will be discussed below with respect to an induction cooker. However, those of ordinary skill in the art will recognize that the present invention can be used with any suitable type of appliance or device in hich overflow detection is needed. For example, an overflow detection mechanism may be used in a ceramic eooktop, a rice cooker, or other appliance.

[0022] Figure 1 illustrates a cross-section of a cover for an inductive cooker that includes a capacin^'ve sensor element for detecting a spill-over condition, in one embodiment, a capacitive senior element 102 made from metal or another conductive material is attached under the cooker cover KU and is connected or otherwise coupled to a controller (not shown).

[0023] in one embodiment, the capacitive sensor element 102 substantially siu rounds a perimeter of a heating container, such as a cooking container used to contain iood or other substance that is being cooked by an induction cooker. For example, the capacitive sensor element 102 may be positioned around the edges of the cooking cover 101 so that when a cooking container is placed on the cooking cover 101, the capacitive sensor element 102 surrounds the base of the cooking container, in an embodiment, the capacitive sensor element 102 may be situated such that any liquid or other substance spilling over from the heating container will land on or near the capacitive sensor element 102 For example, the capacitive sensor element 102 may surround the opening of the cooking container.

[0024] For example, in an inductive cooker appliance, a metal ring can be adhered, coupled, or otherwise connected under the edge of a cooker cov er, or a metal film can be plated under the cover 101. The shape of the eapacitive sensor element 102 may be a circle, rectangle, bar, or some other arbitrary shape. [0025] In one embodiment where an overflow detection mechanism is implemented in a heating appliance such as a rice cooker, one or more capadtive sensor elements may be positioned around an inside surface of a lid of the heating appliance, In one embodiment the position of the sensor element inside the lid allows the sensor element to detect a liquid or other substance that is nearly overflowing,, before the liquid or other substance overflows from the heating container,

[0026] Figure 2A illustrates an embodiment in which the capadtive sensor element 102 comprises a metal ring that is attached near the edge of cooker cover 101, then connected to a controller 203 as an input. Cooker cover 101 may be part of an outer housing of an inductive cooker, for example, that covers the heating element of the inductive cooker. Figure 2B illustrates a side view of the cooker cover assembly including the cooker cover 101, capadtive sensor element 102, and controller 203. In one embodiment, the controller 203 includes a processing element such as a state machine or a processor coupled with memory tor performing operations related to measuring and recording capacitances or controlling an amount of heat generated. [0027] With reference to Figure 1, an equivalent capacitance CP exists between ground 105 and capacitive sensor element 102. When a substance in the inductive cooker, such as food, water, or some other liquid spills over the cooker cover, the proximity of the overflowing substance to the eapacitive sensor element 102 introduces an equivalent capacitance Cr between the substance, such as water 104, and the capacitance sensor element 102. The equivalent capacitances O and Gp can modeled as capacitances connected in parallel The capacitances G and Ci¹ may be represented by the equivalent capacitance Cx between the eapacitive sensor element 102 and ground.

[0028] In. one embodiment, when other factors are substantially constant, the capacitance CF remains the same regardless of a spill-over condition. Capacitance O changes according to the amount of water 104, or other substance over the eapacitive sensor element 102. The equivalent capacitance Cx will reflect the changes in Ck The detection of changes in G may be performed in many different ways. In one embodiment the changes in G^: may be detected through the charging and discharging of the capacitance Cx. [0029] In one embodiment, the spill-over detection functionality may he combined with other system function controls such as, for example, capacitance- based touch buttons for controls ing the induction cooker. The capacitance sensor can be, for example, a touch button input for the controller, although any suitable capacitance sensor can be used for spill -over detection For example, an Induction cooker may have a number of capacitive touch buttons used to control functions such as the power state or temperature or the cooker. In such an induction cooker, the cαpαcitive sensor clement 102 used for spill-over detection may be connected to the controller 203 and operated tn a similar fas-hton at> the capacity e touch buttons.

[0030] In one embodiment the capacitance of the capacitive sensor element may also be affected by external laetors such as AC interference from, power supply switching. In one embodiment, because such changes in the capacitance of the sensor may attect the spill-over detection function, the controller may periodically update a baseline value of Cx, then compare a measured value of Cx to the updated baseline value of Cx to determine a change m Cx. In one embodiment, a predetermined threshold may be selected such that when the change in Cx exceeds the predetermined threshold, the controller detects the spill-ovei or overflow condition. For example, a capacitance sensor installed under the cooker cover may be connected or otherwise coupled with the controller. During operation oi: the inductive cooker, the controller periodically measures the capacitance Cx. When the controller detects ά change in the equivalent capacitance Cx and the detected change is greater than the predetermined threshold, then a spill-over or overflow c ondition is detected [0031] In one embodiment, in response to detecting the spill -over or overflow condition, the controller indicates that the condition has occurred. I he indication may be, for example, a control signal that is sent to a switch for turning off a heating element of the appliance or tor reducing the amount oi heat supplied by the heating element.

[0032] In one embodiment, the capadtive sensor element 102 rnay be one of sev eral capacitive sensor elements together substantia!!} surround the perimeter of the heating container, such as the base or an opening o! the heating container. Figure 3 illustrates an embodiment in which a spill-over condition may be detected by more than one capacitive senior element. As illustrated in Figure 3, the capacitive sensor elements 301 and 302 are positioned at the edges of the cooker cover 101. liach of the sensor elements 301 and 302 is connected to controller 203.

[0033] The controller can detect the capacitance changes on each of the sensor elements 301 and 302 to determine if the spill-over condition has occurred. In one embodiment, the spill-over condition is triggered when a capacitance change for any of the sensor elements 301 and 302 is greater than a predetermined threshold.

100341 In one embodiment, the controller can detect the changes in capacitance tor the capacitive sensor element 102, 301, or 302 using any one of several methods for detecting capacitances. Merely for purposes of illustration and not limitation,, the following three examples show different implementation circuits for detecting changes in the capacitance of the capadtive sensor elements 102, 301, and 302.

[0035] Figure 4 illustrates one embodiment of a circuit for detecting changes in capacitance of a capadtive sensor element, such as capacitive sensor element 102, 301, or 302, using a relaxation oscillation method. The detection circuit 400 measures a capacitance of a sensor element by generating a periodic signal based on the capacitance of the sensor element, and detecting a change in the period of the oscillating signal, where the change in period results from a change in the capacitance of the sensor element.

[0036] The detection circuit 400 includes comparators 407 and 408 with reference voltages 402 and 403 applied to the inputs of comparators 407 and 408, respectively. Comparator 407 is coupled through a buffer to the S input of the RS latch 409, and comparator 408 is coupled to the R input of the latch 409. Latch 409 has an output Q_BAR that is coupled to a counter 404. Counter 404 is coupled to a controller 405, which is further coupled with a timer 406. The Q_{B AR} output of latch 409 is also coupled with a resistor 401. Resistor 401 is coupled to ground through a capacitance Cx, representing the capacitance between a capacitive sensing element and ground. [0037] When the Q_{B AR} output of the RS latch 409 is high, the capacitance Cx is charges through resistor 401. Consequently, the voltage on Cx w ill rise. When the voltage is higher than the reference voltage 402, the Q_{B AR} output will be Sow, When the Q_{B AR} output is low , then capacitance Cx will discharge through resibtor 401. Accordingly, the voltage on Cx will decrease. When the voltage is lower than reference, voltage 403, the Q_{B AR} output of latch 409 will he high. ') his process continues to generate an oscillating signal with a period depending on the capacitance Cx. At the output of latch 409, counter 404 measures the number of times the Q_{B AR} output transitions during a predefined time inten aS. When the capacitance Cx changes, the number of transitions of Q_{B AR} detected b) the counter 404 during the predefined time period w ill also change, [0038] In one embodiment, a predetermined threshold for detecting a spili-over condition may be defined as a threshold number of: transitions of Q_{B AR} detected by counter 404.

[0039] Figure 5 A illustrates a circuit tor performing a sigma-delta method to detect changes in capacitance, according to an embodiment Detection circuit 501 is configured to detect changes in the capacitance Cx 514. Cx 514 is coupled with switches 512 and 513, which are controlled by a timer 5Ϊ t. Switch 513 is connected to ground, and switch 512 is coupled with a πegath e input of a comparator 509 A reierenee voltage V_{REF 501} is coupled to the positive input ol comparator 509, The output of comparator 509 is coupled with a latch 502, and the output of latch 502 controls a switch 506, which connects the latch 502 output through a resistor R_B 507 to a modu lation capacitor Cvon 508. I atch 502 and counter 503 are clocked by clock 505. Counter 503 is coupled with controller 504. [0040] In one embodiment, switches 512 and 513 are complementary switches lhat operate m a non-overiapping manner, such that the sw itches 512 and 513 are not simultaneously closed at any time during the switching cycle. Tinier 51 1 controls the switching of the switches 512 ami 513. With the switches ^12 and ^13 in operation, the capacitance 514 is repeated. K charged and discharged to ground.

[0041 ] The switches 512 and 513, when operating m this manner, m combination w ith the capacitance Cx 514 may be represented as on equivalent resistance Rx 521 connected between ground and a negative input of comparator 509, as illustrated in Figure 5B. When Cx 514 increases, the equivalent Rx 521 decreases. When Cx 514 decreases, the equivalent Rx 521 increases.

[0041 ] When the output ot RS-iatch 502 is high, the switch 506 will turn on, &o that the latch 502 output charges C_MOD 508 through resistor 507, causing the voltage on C_MOD 508 to increase. When the voltage on CMOO 508 is greater than the reference voltage V_{RE P} 501, the comparator outputs a low signal, causing the latch 502 output to transition low, turning oil switch 506. With switch 30f» oil, C_MOD will discharge to ground through the equivalent resistance Rx 521 until the voltage at the negative input of comparator 50*3 decreases below V^ t 501. When the voltage decreases below VWE, the comparator outputs a high signal and the latch 302 outputs high, continuing the cycle. 1 he comparator 509 and the latch 502 thus cause the voltage on C_MOD to fluctuate around Vm s, w hue the equivalent resistance Rx determines the duly cycle of each latch 502 output. [00431 The output of latch 502 is used to control the enable pin of the cascaded counter 503, so that the counter value reSlecfs the duty cycle of the latch 502 output. Changes in Cx 514 will thus correspond to changes in the counter value detected hy controller 504.

[0044] Figure 8 illustrates a circuit for measuring capacitance of a eapacitive sensor element using a successive approximation method, according to an embodiment. The detection circuit 600 includes a current source 601 that is used to charge the capacitance Cx 603, which is an equivalent capacitance of a capacttive sensor element, such as eapacitivo sensor element !02. During the charging process, the capacitance Cx 603 is connected with a negative input pin of a comparator 607 through a Sow pass filter 602. When the voltage on Cx 603 is lower than the reference voltage Vw i applied to the positive input oi comparator 607, the comparator outputs a high signal to the enable pin of counter 604 to enable counting. The voltage on Cx 603 increase as Cx 603 is charged. [0045] When the voltage on Cx 603 is higher than Vra J, the comparator 607 outputs a low signal and the counter 604 slops counting. The final count value of the counter reflects the charge time for charging Cx 603, which is in turn affected by the capacitance of Cx 603. The controller 605 can detect changes in capacitance from the count value.

[0046] Figure 7 illustrates changes in count value 700 resulting from changes in capacitance of a capacitive sensor element, such as capadtive sensor element 102. In Figure 7, the X axis represents time 701 and the Y axis represents count values 702.

[0047] In one embodiment, the duration before time 710 is the time when an appliance, such as an induction cooker, implement ing the spill-over detection mechanism is powered off. At time 710, the power is turned on and AC noise from the power supply of the appliance begins affecting the capacitance of the capacitive sensor element 102. This causes an increase in the count values detected betweenm time 710 and 711. in one embodiment, the count value during this time may be stored as a measure of the baseline capacitance. This baseline count value may then he compared with future count values to determine whether the capacitance of the sensor element has changed by more than a predetermined threshold . 100481 At time 711, a substance such as water 104 is on or near the capacitive sensor element 102, causing the count value 700 to increase, in one embodiment, tills increase in count value corresponds to a spiil-over or overflow condition. 100491 In addition to the ahove-described methods, there are many other suitable ways for detecting the change in capacitance associated will a spill-over or overt Io vv.

[0050] Figure 7 is α flow diagram illustrating a spill-over or overflow detection process 800, according to one embodiment. The process 800 may be implemented in a controller such as controller 203 connected to a capacitive sensor element 102, tor example. The controller may be implemented in an appliance such as an inductive cooker.

[0051] Process 800 begins at block 802. At block 802, the controller records a baseline capacitance with the appliance powered on. With reference to Figure 7, for example, the controller may record a count value measured at a time between times 710 and 71 1, when the appliance is powered on and nothing is on or near the eapaάtive sensor element. From block 802, the process 800 continues at block 804.

[0052] At block 804, the controller detects a change in a capacitance of the capacitive sensor element. 1-or example, the controller may detect the change in capacitance through the operation of a detection circuit such as circuit 400, 510, or 600. hi one embodiment, the detection circuit returns a measured count value that may be compared with the base! me count value recorded at block 802. From block 804, the process 800 continues at block 806.

[0053] At block 806, the controller determines whether the change in capacitance of the capacitive sensor element exceeds a predetermined threshold. In one embodiment, the controller calculates a difference between the baseline count value and the measured count value, then compares this difference (representing the change in capacitance) to the predetermined threshold. If the capacitance change does not exceed the predetermined threshold, the process 800 continues back to block 804, such that the controller continues to monitor the capacitive sensor element for changes in capacitance.

[0054] It, at block 806, the capacitance change exceeds the predetermined threshold, the process 800 continues at block 808. At block 808,, the controller indicates that a spill-over or overflow condition has occurred. In one embodiment, the indication may be an electronic signal that is transmitted by the controller. From block 808, the process 800 continues at block 810. [0055] At block 8Ϊ0, the controller reduces the amount of heat supplied by a heating element of the appliance. For example, the indication of the spill-over condition sent by the controller may be a control signal that reduces or disconnects power to the heating element. In one embodiment, once the spill- over or overflow condition has been detected, the condition remains asserted until it is reset.

[0056] Thus, bv the above process, a controller implemented in an appliance such as an inductive cooker may detect a spill-over condition and reduce the heat when such a spill-over condition is detected.

[0057] Embodiments of the present invention, described herein, include various operations. These operations may be performed by hardware components, software, firmware, or a combination thereof. As used herein, the terms "coupled to" or "coupled with" may mean coupled directly or indirectly through one or more intervening components. Any of the signals provided over various buses described herein may be time multiplexed with other signals and provided over one or more common buses. Additionally,, the interconnection between circuit components or blocks may be shown as buses or as single signal lines. Each of the buses may alternatively be one or more single signal lines and each of the single signal lines may alternatively be buses.

100581 Certain embodiments may be implemented as a computer program product that may include instructions stored on a computer-readable medium. These instructions may be used to program a general-purpose or special-purpose processor to perform the described operations. A computer-readable medium includes any mechanism for storing or transmitting information in a form (e.g., software, processing application) readable by a machine (e g , a computer). The computer-readable storage medium mav include, but is not limited to, magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto-optical storage medium; read-only memory (ROM); random-access memory (RAM); erasable programmable memory (e.g., FFROM and KKPROM); flash memory, or another type of medium suitable for storing electronic instructions. The computer-readable transmission medium includes, but is not limited to. electrical, optical acoustical, or other form of propagated signal (e.g., carrier waves, infrared signals, digital signals, or the like), or another type oϊ medium suitable for transmitting electronic instructions. [0059] Additionally, some embodiments may be practiced in distributed computing environments where the computer readable medium is stored on and/or executed by more than one computer system. In addition, the information transferred betw een computer systems may either be pulled or pushed across the transmission medium connecting the computer systems. [0060] Although the operations_* of the meϊhod(s) herein <ιw shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may he performed in an inverse order or so that certain operation may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub-operations of distinct operations may be in an intermittent and/or alternating manner. [0061 ] In the foresoine specification, the invention has been described with reference to specific exemplary embodiments thereof, it will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.

Claims

CLAIMSWhat is claimed is:

1. A method of detecting a substance on a heating appliance, comprising: detecting a change in a capacitance of a cαpodtive sensor element, wherein the change in capacitance results from proximity of the substance to the capaeitive sensor element, wherein the capacitive sensor element is coupled with the heating appliance; determining whether the change in capacitance exceeds a predetermined threshold; and indicating an overflow condition in response to determining that the change in capacitance exceeds the predetermined threshold.

2. The method of claim 1, wherein the capacitive sensor element substantially surrounds a perimeter or a heating container on the heating appliance.

3. The method of claim 2, wherein the perimeter of the heating container is around a base of the heating container.

4, The method of claim I, further comprising recording a baseline capacitance, wherein determining whether the change in capacitance exceeds the predetermined threshold comprises comparing a measured capacitance with the baseline capacitance.

5 The method of claim 1, further comprising, in response to determining that the change in capacitance exceeds the predetermined threshold, reducing an amount of heat generated.

6 The method ol claim 5, wherein reducing the amount ol heat generated comprises turning otf the heating appliance

7. The method of claim i, wherein the heating appliance is an induction cooker

8 The method ol claim 1, wherein detecting the change in the capacitance of the capacitive sensor comprises: generating an oscillating signal based on the capacitance or the capacitance sensor element; and delecting α change in a count value associated with the oscillating signal.

9. An apparatus for defecting a substance on a heating appliance, comprising: one or more eapacitive sensor elements configured to substantially surround a perimeter of α heating container; and a controller coupled with the one or more capncitive senbor elements, wherein the controller comprises a processing element configured to: detect a change in a capacitance of the one or more capaύtive sensor elements, wherein the change in capacitance results from proximity oi the substance to the one or more eaparitive sensor elements; determine whether the change in capacitance exceeds a predetermined threshold; and indicate an overflow condition in response to determining that the change in capacitance exceeds the predetermined threshold.

10. The apparatus of claim 9, wherein each of the one or more eapacitive sensor elements is coupled with the controller.

11. The apparatus of claim 10, wherein the perimeter of the heating container is around a base of the heating container

12. The apparatus of claim 10, wherein the processing element is further configured to record a baseline capacitance, and wherein the processing element is configured to determine whether the change in capacitance exceeds the predetermined threshold bv comparing a measured capacitance with the bascϋne capacitance.

13. The apparatus of claim 9, wherein the processing element is configured to reduce an amount ot heat generated in response to determining that the change in capacitance exceeds the predetermined threshold.

14. T he apparatus of claim 13, wherein the processing element is configured to turn off the heating appliance to reduce the amount ot heat generated.

15. The apparatus of claim 9, wherein the heating appliance is an induction cooker,

16. The apparatus of claim 9, wherein detecting the change in the capacitance of the capaesϋve sensor comprises: generating an oscillating signal based on the capacitance of the capacitance sensor element; and detecting a change in a count value associated u ith the oscillating signal.

17. A heating appliance, comprising: a cover configured to support a heating container, wherein the heating container is configured to contain a substance; one or more capacitive sensor elements coupled with the cover, wherein the capacitive sensor element substantially surrounds a perimeter of the heating container; a controller coupled, with the one or more capacitive sensor elements, wherein the controller is configured to adjust an amount of heat generated based on a capacitance of the one or more capacitive sensor elements.

18. The heating appliance of claim 17, wherein adjusting the amount of heat generated comprises turning off the heating appliance.

19. The heating appliance of claim 17, wherein the controller is further configured to: detect a change in the capacitance of the one or more capacitive sensor elements resulting from proximity of the substance to the one or more capacitive sensor elements; determine whether the change in capacitance exceeds a predetermined threshold; and indicate an overflow condition In response to determining that the change In. capacitance exceeds the predetermined threshold.

20. The heating appliance of claim 17, wherein the controller is configured to detect the change in the capacitance of the capadtlve sensor element by: generating an oscillating signal based, on the capacitance of the capacitance sensor element; and detecting a change in count value associated with the osculating signal.