GB2584184A

GB2584184A - Liquid level sensor apparatus and methods for use in cooking appliances

Info

Publication number: GB2584184A
Application number: GB2002725.6A
Authority: GB
Inventors: Maclachlan Douglas; Reid Steven
Original assignee: AFE Group Ltd
Current assignee: AFE Group Ltd
Priority date: 2019-02-26
Filing date: 2020-02-26
Publication date: 2020-11-25
Anticipated expiration: 2040-02-26
Also published as: WO2020174241A1; GB201902592D0; GB202002725D0; GB2584184B

Abstract

A deep fat fryer 1 comprises a tank 2, a heater 17 and a control module 50 for controlling the heater. Disposed in the tank is a sensor module 18 having at least one capacitive sensing element 40, 42 that detects a level of liquid in the tank. An evaluation module 46 evaluates a signal from the capacitive sensing element(s), determines the presence of liquid at the level of the capacitive sensing element(s) and sends an alarm condition signal to the control module if liquid is not present. A guard compartment 58 is either: fixedly mounted within an internal volume of the tank; or mounted with the sensor module to a moveable sensor module mount, such that the guard compartment can be deployed into and out of the tank. In both instances the guard compartment is in fluid communication with a remaining volume of the tank. The sensor module is housed within the guard compartment such that it is spaced from internal surfaces of the compartment so as to be electrically isolated therefrom. The guard compartment can be opened to access the sensor module without removing the compartment and sensor module from the tank. Also disclosed is a kit of parts for fitting to an apparatus for heating liquid.

Description

1 LIQUID LEVEL SENSOR APPARATUS AND METHODS FOR USE IN COOKING 2 APPLIANCES

4 Field of the invention

6 The invention relates to the field of cooking appliances and more specifically to appliances for 7 cooking liquids such as deep fat fryers. The invention provides apparatus for heating liquids, 8 especially oil for cooking, and method(s) of using the apparatus.

Background to the invention

12 It is known to provide deep fat fryers with sensors to monitor oil within the fryer. Typically, such 13 sensors are provided in the form of temperature sensors such as thermocouples and the 14 temperature of the oil is monitored. Such temperature sensors may alert a user when the temperature of the oil within the fryer is not within a predetermined acceptable range (e.g. 16 between 150 °C and 190 °C), said range being determined in accordance with safety 17 regulations. Such sensors may also operate to prevent heating if the temperature of the oil 18 exceeds a predetermined upper temperature (e.g. 230 °C).

In both cases, the temperature of the oil is monitored. The presence and/or volume and/or level 21 of oil within the fryer is typically not monitored or is not monitored directly.

23 Deep fat fryers may use temperature sensors positioned at two different heights within the fryer 24 in use to indicate when a top up is needed (i.e. to indicate when the fryer should be filled with additional oil). When both temperature sensors are submerged within the oil, both will detect 26 substantially the same temperature and, when the oil level is reduced such that one (first) 27 temperature sensor is not submerged in the oil while one (second) temperature sensor is 1 submerged in the oil, these will detect two different temperatures. When two different 2 temperatures are detected this can be used as a prompt to alert a user to the fact that the oil 3 level has reduced. In response a user may add more oil to the fryer.

The disadvantage of such temperature sensors as described above is that if the oil level is 6 reduced sufficiently that neither of the two temperature sensors are submerged in oil (i.e. if both 7 are in air) these two temperature sensors will detect substantially the same temperature, with 8 the result that no difference in temperature will be detected and the user will not then be alerted 9 to a temperature difference (and so will not be aware of the reduced oil level).

11 JP2004016798 YOSHIO describes evaluating the quality of frying oil. US9927415 BAUMANN 12 describes an oil quality sensor. US8497691 BEHLE describes an oil quality sensor. US5197376 13 BIRD describes a horizontal capacitor electrode in a tank. JP2004008253 RYOICHI discloses 14 a fryer which may detect an oil level within a tank. CN206390810 TINGYOU discloses a fryer having an automatic liquid level detector. EP 0095063 discloses a control system for an 16 immersion heater. JP 2004/016789 discloses a device for monitoring oil quality.

18 Reliable oil level detection in the extremely violent and challenging environment of deep fat 19 fryers during use is not straightforward. As well as liquid oil at very high temperature, gaseous oil bubbles and food debris may be present. It is for this reason that level measurements have 21 typically been provided by temperature sensors, and indeed, attempts to measure oil levels in 22 this environment are therefore rare.

24 In the changeable and violent environment of a deep fat fryer, use of existing sensors is often not sufficiently reliable to allow automatic operation. In commercial fryers, oil is cooled and 26 drained from a cooking tank and filtered at the end of a shift for recycling and reuse, ready for 27 reintroduction back into a cooking tank ready for next day. Human error can result in this last 28 job of re-introduction of oil being forgotten. Without visual inspection, the absence of oil in the 29 tank may not be noticed until after the burners and/or heaters are switched on and/or fired up and this can be dangerous.

32 Accordingly, the invention seeks to reduce or alleviate the problems and disadvantages of the 33 prior art and in particular of deep fat fryers and oil monitors of deep fat fryers.

Summary of the invention

37 According to a first aspect of the invention there is provided an apparatus for heating liquid, 38 typically cooking liquid, e.g. oil, in a tank, comprising: 39 - a tank having an internal volume for retaining a liquid; - a heater; 1 a control module for controlling the heater; 2 a sensor module disposed (or optionally disposable) in the tank comprising at least one 3 sensing element (e.g. a capacitive sensing element) (e.g. a capacitive sensing element 4 disposed at a first predetermined level in the tank) operative to detect a level of liquid in the tank (e.g. in use); 6 an evaluation module for evaluating a signal from the at least one sensing element (e.g. a 7 capacitive sensing element) to determine the presence (or not) of liquid at the level of the 8 at least one sensing element (e.g. a capacitive sensing element) in the tank and configured 9 to send an alarm condition signal to the control module if liquid is not present (e.g. in use); the apparatus further comprising an (e.g. openable) guard compartment fixedly mounted 11 within the internal volume of the tank (or optionally mounted to a moveable (e.g. tiltable, 12 optionally rotatably tiltable) sensor module mount, preferably such that the guard 13 compartment can be deployed (e.g. by tilting and/or rotating) into and/or out of the tank, 14 e.g. without detaching the guard compartment from the apparatus) and (e.g. in use the guard compartment is) in fluid communication with a remaining volume of the tank (e.g. 16 the remaining volume within the internal volume external to the compartment), the sensor 17 module housed within the (e.g. openable) guard compartment in a spaced apart manner 18 from internal surfaces of the guard compartment so as to be electrically isolated therefrom; 19 whereby the (e.g. openable) guard compartment can be opened (e.g. is configured to be opened) (or optionally slid relative to the sensor module) without detaching the guard 21 compartment and/or sensor module from the tank (optionally without removing the guard 22 compartment and/or sensor module from the tank but preferably without removing the 23 guard compartment and/or sensor module from the apparatus) (e.g. to facilitate access to 24 and cleaning of the sensor module and/or guard compartment).

26 Although typically the sensor module is disposed (and preferably fixedly disposed) within the 27 tank, in some embodiments the sensor module is mounted (preferably with the (e.g. openable) 28 guard compartment) to a moveable sensor module mount, optionally such that the sensor 29 module may be deployed (e.g. by tilting and/or rotating (via the moveable sensor mount)) into or out of the tank, in which case the at least one sensing element (e.g. a capacitive sensing 31 element) is operative to detect a level of liquid in the tank in use (i.e. when the sensor module 32 is in the tank). Although typically the (e.g. openable) guard compartment is fixedly mounted 33 within the tank, in some embodiments the (e.g. openable) guard compartment is fixedly 34 mounted (preferably with the sensor module) to a moveable sensor module mount, optionally such that the (e.g. openable) guard compartment may be deployed (e.g. by tilting and/or rotating 36 (via the moveable sensor mount)) into or out of the tank, in which case the (e.g. openable) 37 guard compartment is in fluid communication with the remaining volume of the tank (e.g. the 38 remaining volume within the internal volume external to the compartment in use, (i.e. when the 39 (e.g. openable) guard compartment is in the tank). Typically, the (e.g. openable) guard compartment is formed around and attached to the sensor module.

2 A control unit comprising the control module may be provided. Typically, the evaluation module 3 is connected to the control unit but is physically separate from the control unit however, in some 4 embodiments, the evaluation module may be an integral part of the control unit. The control unit may comprise one or more relays. One relay may control an audible and/or visual alarm 6 e.g. "FILL UP REQUIRED". Once the tank is refilled, the relay may cut power to the "FILL UP 7 REQUIRED" alarm, causing it to cease. Another relay may control an emergency switch-off 8 circuit which is powered when the relay is switched, causing the emergency switch-off circuit to 9 issue an audible and/or visual alarm and to switch off power to the heater (which may cause various safety switches to trip e.g. a pilot light).

12 The cooking liquid may be water but is more usually oil (or optionally may be another cooking 13 fat in liquid form). As an example of the type of capacitive sensing measurements which may 14 be used, liquid, e.g. oil, is detectable by operation of the first capacitive sensing element if the oil is present in a volume adjacent to the capacitive sensing element, the volume extending 16 typically horizontally in use to the side walls of the surroundings of the capacitive sensing 17 element, e.g. to the side walls of the guard compartment. The one or more side walls of the 18 guard compartment may be made up of the (inner) walls of the tank. As described elsewhere, 19 it is helpful if the walls of the guard compartment are generally or substantially perpendicular to the orientation of the sensed volume (i.e. to the shallow, typically horizontal, volume of oil 21 sensed by the capacitive sensing element), e.g. in use.

23 The advantage of using a sensor module as described above is that the sensor module detects 24 the presence of liquid (typically oil, for example cooking oil, optionally cooking fat) and not the temperature of liquid. Accordingly, if the liquid level is low this can be detected, and a user can 26 be alerted and/or the fryer can be switched off. This is in contrast to existing temperature-based 27 monitors in that existing monitors fail where the liquid level drops below the level of the 28 temperature sensor and the temperature sensor measures the temperature of air instead of the 29 temperature of oil in the fryer. When oil levels in fryers are very low or fryers are empty, there is a significant risk of fires, therefore apparatus comprising a sensor module according to the 31 present invention helps to mitigate fire risk.

33 Each capacitive sensing element may comprise one or more, and typically two capacitive 34 sensing electrodes (one a measurement electrode and one a screening electrode which may be in two parts). Each capacitive sensing element may be used to determine if oil is present in 36 a respective volume extending to the side walls of the guard compartment. The sensor module 37 may comprise two capacitive sensing elements for sensing different levels (here for example in 38 a vertical direction) of liquid, each of which may comprise one or more, typically two, capacitive 39 sensing electrodes. The capacitive sensing electrode(s) may (each) form one electrode of a capacitor, the other being part of the sensor module surroundings e.g. wall(s) of the tank or 1 wall(s) of the guard compartment or a separate electrode. This is known as a three-electrode 2 measurement and sensor modules using such measurement regimes are available from 3 Rechner Sensors (Rechner (UK) Ltd, Pangbourne, Berkshire, UK).

By 'capacitive' is meant forming a part of a capacitor and/or a part of a capacitive measurement 6 regime, in use, as would be understood by one skilled in the art.

8 The sensing capacitive element(s) (and in particular one or more electrode(s) within these) may 9 form one side of a capacitor, the other side being formed by (e.g. at least part of) the tank or (e.g. openable) guard compartment (or guard, or part of the (e.g. openable) guard 11 compartment) when present. Accordingly, (in use) a capacitive sensing electrode of the or each 12 capacitive sensing element and the wall(s) of the tank or wall(s) of the guard compartment may 13 form a measurement capacitor, wherein the dielectric of the capacitor will be made up of the 14 contents of the tank. For example, the dielectric would be cooking oil when the tank is filled with cooking oil. Preferably, at least part (and preferably most), of the or each side wall of the guard 16 compartment is generally or substantially vertical in use.

18 The guard compartment generally physically isolates the sensor module from a main cooking 19 portion of the internal volume of the tank whilst remaining in fluid communication, so that liquid can freely circulate (around both the internal volume of the tank and the internal volume of the 21 guard compartment).

23 The (e.g. openable) guard compartment may comprise a first part having an opening in a side 24 wall to access the sensor module for cleaning, the first part being fixedly mounted to a wall of the tank, and a retractable second part, movable in at least a vertical direction with respect to 26 the first part to uncover the opening in the first part, allowing access to the sensor module for 27 cleaning.

29 The retractable second part may be movable in at least a horizontal direction with respect to the first part to partially block access to a main portion of the intemal volume of the tank. The 31 retractable second part may be configured to be temporarily locked in a retracted (e.g. cleaning) 32 position such that at least a portion of the second part is above (e.g. vertically above, i.e. in 33 use) the first part, or at least a portion of the second part may be above and to one side of the 34 first part to partially block access to a main portion of the internal volume of the tank.

36 In an example embodiment, at least one of the fixed first part and the retractable second part 37 may comprise at least one track and the other of the fixed first part and retractable second part 38 may comprise at least one pin configured to inter-engage with and travel in the at least one 39 track, wherein the retractable second part can travel (e.g. reciprocally to and fro and/or may pivot) with respect to the first part as the pin travels in at least one track. Typically, the at least 1 one pin may be associated with, e.g. integrally formed in the first part, however in some 2 embodiments the first part further comprises at least one hole in which the at least one pin may 3 be retained. The pin may be a shank extending between two opposing side walls of the first 4 part, and the track may be two shaped elongate apertures in the two corresponding opposing side walls of the second part. Typically, the at least one track comprises a bend, the bend being 6 at a lower end of the at least one track when the track is in the retractable second part, and the 7 bend being at an upper end of the at least one track when the track is in the fixed first part.

9 The or each track may be at a front end of a side wall of the retractable second part and may have a bend or corner in it of angle 60° to 120°, or 75° to 115°, or more usually generally or 11 substantially equal to 90° at a lower end of the track, extending rearwardly, facilitating the 12 movement of the retractable second part laterally forward away from the fixed first part.

13 Conversely, the or each track may be at a rear end of a side wall of the fixed first part and may 14 have a bend or corner in it of 60° to 120°, or 75° to 115°, or more usually generally or substantially equal to 90°, at an upper end of the track extending forwardly, facilitating the 16 movement of the retractable second part laterally forward away from the fixed first part. Other 17 arrangements can be envisaged in which the retractable second part can be re-positioned on 18 and with respect to the fixed first part to partially or wholly block access to the internal volume 19 (e.g. for cooking baskets) when the sensor module is exposed for cleaning.

21 The advantage of providing a guard compartment comprising a retractable second part and a 22 fixed first part according to example embodiments of the invention is that the retractable second 23 part can be moved e.g. slidably, (e.g. substantially) vertically, from a first (e.g. cooking) position 24 into a second (e.g. cleaning) position, to thereby open the guard compartment and allow for cleaning of the guard compartment. The first fixed part is intended to remain fixed to the tank, 26 except when under repair (when it may be disassembled and removed).

28 In some embodiments, the first part may comprise the at least one pin and the second fixed 29 part may comprise at least two tracks arranged opposite one another in respective opposing side walls of the retractable second part.

32 The advantage of providing the or each track within the retractable second part is that the or 33 each track can also then be more easily cleaned, when it is retracted into a cleaning position.

Preferably, the or each track will be closed-ended, i.e. it will be closed at each end. The 36 provision of a pin and closed-ended tracks prevents the retractable second part from being 37 (easily) completely removed from the fixed first part. Accordingly, when the guard compartment 38 is in a cleaning position ready to be cleaned it is not completely dismantled or removed from 39 the fryer. As such, a user is less likely to forget to reassemble the guard, and less likely to forget 1 to return it to the fryer, and a user therefore is less likely to attempt to use the fryer without the 2 guard compartment, which may be unsafe.

4 In addition, when the retractable second part is in the cleaning position, it provides a clear visual signal to a user that the guard compartment is not currently in the first (e.g. cooking) position 6 and that the apparatus should therefore not be used until the retractable second part is returned 7 to the first (e.g. cooking) position. Further, when the retractable second part is in the second 8 (e.g. cleaning) position it provides a physical barrier, in that it is difficult and may not be possible 9 for a user to place a fryer basket (e.g. to hold food) into the tank when the retractable second part is in the second (e.g. cleaning) position. This provides the advantage that the apparatus 11 cannot (easily) be used without the guard compartment, thus providing for more safe usage of 12 the apparatus.

14 Preferably, the retractable second part is tiltable with respect to the first part and comprises a stop member for engaging with the first part (or vice versa) to prevent tilting beyond a limited 16 angle, which may be less than 90° to the vertical. The first and second parts may be elongate 17 and have a central longitudinal axis and it is the angle of this axis in the second part with respect 18 to the axis in the first part which is typically generally or substantially vertical in use that may be 19 considered when determining tilt. The presence of the retractable second part above and to one side of the fixed first part and preferably also above the rim of the tank prevents normal 21 use of the tank when the sensor module is exposed.

23 Thus, the retractable second part can travel upwards and downwards and may pivot forwards 24 (or backwards) (e.g. slightly), as the at least one pin travels in the bend, and can be held tilted away from the vertical when the pin reaches the end of the track, in a locked position above 26 and (e.g. slightly) tilted with respect to the first part. The now retracted second part partially 27 blocks the access to the internal volume of the tank, providing both a visual indicator and 28 physical preventer, limiting access to the tank e.g. to prevent the introduction of cooking 29 baskets. Typically, the retractable second part may further comprise a rebate and a stop member.

32 Typically, the first part is U-shaped in cross-section when viewed from above, having an 33 opening on at least one side. Typically, the guard compartment (e.g. the retractable second 34 part and the fixed first part) has a substantially square cross-section (i.e. when viewed from above, in use) however, one skilled in the art will appreciate that other cross-sectional shapes 36 (e.g. circular, rectangular, 5-sided, 6-sided etc.) may also be suitable.

38 Typically, the second part is sized and shaped to close the opening when the second part is in 39 its lowered position with respect to the first part so that the guide compartment is generally 1 physically isolated from the remainder of an internal volume of the tank but is in fluid 2 communication with it.

4 Preferably, the guard compartment is (i.e. in use) within and in liquid communication with the remaining internal volume of the tank. Preferably, the sensor module is (i.e. in use) within the 6 guard compartment and is in liquid communication with the tank and the guard compartment.

8 The second part may be positioned about the first part, or vice versa. The heater may be a gas 9 heater comprising a manifold of gas nozzles underneath the tank or it may be an electric heater with electric heating elements below, or more usually, within the tank.

12 The apparatus may be a gas-powered deep fat fryer. The heater may comprise one or more 13 gas burners. The apparatus may be an electrically-powered deep fat fryer. The heater may 14 comprise one or more electrical heating elements.

16 The sensor module may comprise a sensing portion and a mounting block, and further the 17 mounting block and at least part of (and typically the first part of) the guard compartment may 18 be correspondingly sized and shaped to fit together with limited relative movement. For 19 example, the mounting block may have at least one face which is (e.g. at least partially) conformal with at least one internal surface of the first part of the guard compartment. The 21 mounting block may aid in the alignment of the sensor module within the guard compartment.

23 In some embodiments, the (e.g. openable) guard compartment may comprise, or may further 24 comprise, an array of spaced apart elongate guard elements and/or a guard e.g. a wall (e.g. a perforated plate or grid or net, optionally a foraminous plate) arranged within the tank, the array 26 of guard elements and/or guard wall (e.g. a plate) separating a section of the tank, within which 27 the sensor module is mounted, from a main volume of the tank. In some embodiments the wall 28 may comprise a fish plate, as is known in the art.

The (e.g. perforated) guard wall or plate may separate the guard elements from the remainder 31 of the tank internal volume, and the guard elements and guard plate may together provide a 32 guard compartment (or further guard compartment) for generally physically isolating the sensor 33 module from the main cooking portion of the internal volume of the tank whilst remaining in fluid 34 communication so fluid (e.g. liquid) can freely circulate.

36 The array of guard elements and/or (e.g. perforated) guard wall (e.g. a plate, optionally a 37 foraminous plate) may be pivotable about a horizontal axis to a retracted position vertically 38 above and at least partially over the tank (i.e. in use), opening the compartment (for example, 39 to thereby allow a user to clean the sensor module), in this way, the rotatable guard elements 1 provide a visual indicator and physical preventer which (e.g. at least partially) blocks access to 2 the cooking portion of the internal volume of the tank.

4 In some embodiments, the array of guard elements may be an array of heating elements. For example, this may be the case where the apparatus is an electrically-powered deep fat fryer, 6 which is heated by electrical heating elements.

8 Typically, the control module is configured to shut-off the heater e.g. by operating a relay to 9 activate an emergency switch off circuit upon receipt of the alarm condition signal associated with the capacitive sensing element, which may be the lowest capacitive sensing element where 11 more than one capacitive sensing element is provided in the sensor module. For example, the 12 alarm condition signal (e.g. a change in voltage or digital logic level) is typically provided when 13 oil drops below the sensor. This may be the result of a change in dielectric constant and, as a 14 result, the power to a low oil level relay may be removed, which may allow power through a contact to a flashing LED and buzzer. At the same time a contact may open, and the heater 16 may thus be shut off (i.e. the power supply to the heater may thus be stopped and the heater 17 therefore switches off and no longer outputs heat).

19 Thus, the apparatus may further comprise one or more lights e.g. light emitting diodes (LEDs) and/or one or more sounders (e.g. buzzers).

22 Thus, the control module may comprise one or more relays which may control alarm(s) and/or 23 emergency circuits which may in turn switch off the heater and trip any associated safety alarms 24 which may continue to sound (and/or illuminate) until the safety circuit is reset.

26 Typically, the control module is configured to provide an alarm (for example, the alarm may 27 comprise illuminating or flashing a light or LED, and/or making a noise, for example causing a 28 buzzer to sound etc.) upon receipt of the alarm condition signal associated with the capacitive 29 sensing element. The alarm may be a light indicating that the tank requires manual refilling.

The alarm may cease once oil is added and the capacitive sensing element senses oil. The 31 evaluation module may control two power relays which cause the different LEDs and buzzer to 32 operate depending on the oil level.

34 The main controller for the apparatus (e.g. fryer) may not interact directly with the oil level sensor circuitry (within the evaluation module). The controller and the oil level sensor circuitry 36 (in the evaluation module) typically both interact with an electronic spark igniter (burner 37 controller). Electromechanical thermostats may be used with the oil level sensor and the 38 evaluation module.

1 In some embodiments the control unit may provide an alarm and/or signal to an (e.g. external) 2 automated system and the automated system may re-fill the tank. This may require the fryer to 3 be switched off and cooled prior to refilling.

The sensor module typically comprises an elongate sensing portion, and the sensing portion 6 may comprise a first capacitive sensing element at a first height, in use, (e.g. relative to the 7 internal volume/height of the tank) and a second capacitive sensing element at a second height 8 below the first height (e.g. relative to the internal volume/height of the tank), the first and second 9 capacitive sensing elements being operative independently.

11 The elongate sensing portion of the sensor module may comprise at least two capacitive 12 sensing elements, however in some embodiments the elongate sensing portion comprises one 13 capacitive sensing element, or at least three capacitive sensing elements, or an array of (e.g. 14 spaced apart) capacitive sensing elements. Preferably, each capacitive sensing element is independently operative from the or each other capacitive sensing element, where present.

17 Typically, the first capacitive sensing element is operative to detect a first low level of liquid and 18 trigger the evaluation module to send a first alarm condition signal to the control module in 19 response and the control module illuminating and/or sounding an alarm indicating the tank requires refilling. Thus, if liquid is not present at the higher level of the first capacitive sensing 21 element, then a refill alarm and/or refilling can be triggered by the control unit upon receipt of 22 the first alarm condition signal indicating that the tank requires refilling. To 'non-manually' top 23 up or replace oil, the fryer has to be switched off so that a pump switch can be operated.

24 Automatic refilling is more complex, but may be carried out with appropriate safeguards associated with refilling, as understood in the art.

27 Typically, the second capacitive sensing element is operative to detect a second low level of 28 liquid (which is typically a very low level and is a lower level than the first low level) and trigger 29 the evaluation unit to send a second alarm condition signal to the control module indicating or operative to switch off the heater. For example, the control module may comprise a relay which 31 triggers an emergency switch-off circuit upon receipt of a second alarm condition signal. Thus, 32 if liquid is not present at the lower level of the second capacitive sensing element, then a shut 33 off alarm can be triggered by the control module upon receipt of the second alarm condition 34 signal indicating that the liquid level in the tank is at a very low level and heating should be stopped.

37 In some embodiments the apparatus is a deep fat fryer. In some embodiments the apparatus 38 is a cooking appliance. Typically, the deep fat fryer is a gas-powered deep fat fryer however, in 39 some embodiments the deep fat fryer may be an electrically-powered deep fat fryer. Typically, the apparatus is a deep fat fryer suitable for commercial use, for example use in a commercial 1 catering kitchen, however one skilled in the art will appreciate that the apparatus may be a deep 2 fat fryer suitable for domestic use.

4 Typically, the guard compartment (e.g. the openable compartment and/or the retractable second part) comprises a sloping roof, for example a roof which is sloped in one or more 6 directions with respect to the horizontal during normal use. Advantageously, a sloping roof 7 allows a fryer basket, any debris and/orfood pieces that land on the guard compartment to slide 8 off of the guard compartment.

The apparatus may further comprise at least one temperature sensor. The apparatus may 11 further comprise one or more thermostats. For example, the apparatus may comprise an 12 operational thermostat to maintain and control the normal operating temperature of the oil 13 and/or a safety thermostat to switch off the heater when a (e.g. regulated, optionally 14 predetermined or preselected) temperature is reached (e.g. by triggering the emergency switch-off circuit).

17 Typically, the operating thermostat will be operable to monitor the temperature of the tank (e.g. 18 the contents of the tank) and to switch on or off a heat supply (e.g. the gas supply, optionally 19 the electricity supply to one or more electrical elements) in order to cause the temperature of the tank (e.g. the contents of the tank) to approach a preselected temperature which may be 21 selected by the user. For example, the operating thermostat may cause the temperature of the 22 tank vary between 20 °C below the preselected temperature and 20 °C above the preselected 23 temperature, or between 10 °C below and 10 °C above the preselected temperature, or 24 preferably between 5 °C below and 5 °C above the preselected temperature, or more preferably within (e.g. up to) 1 °C of the preselected temperature. Typically, the preselected temperature 26 will be between 130 °C and 190 °C, or between 130 °C and 200 °C, or preferably between 150 27 °C and 190 °C.

29 Typically, the safety thermostat will turn the apparatus off (e.g. it may turn the heat supply off) if the tank (e.g. the contents of the tank) has a temperature above 215°C to 224°C to prevent 31 the temperature of the oil in the tank from going above 230 °C (which is a requirement of safety 32 regulations). Preferably, if the safety thermostat (or an alarm condition signal from a capacitive 33 sensing element) turns the apparatus off (e.g. if it turns the heat supply off) it will be necessary 34 to wait for the apparatus to cool down (e.g. to ambient temperature and/or to room temperature, e.g. to 20 °C, or optionally to below 40 °C) before the apparatus can be turned back on.

36 Preferably, if the safety thermostat turns the apparatus off it will not be possible to turn the 37 apparatus on unless a user does so manually.

39 In some embodiments, the one or more lights (e.g. one or more lamps or LEDs) may comprise a first, red light (and/or lamp and/or LED) which is switched on when the apparatus is in use to 1 indicate that the apparatus has a power supply, and one or more further lights (e.g. one or more 2 lamps or LEDs). Typically, the one or more further lights (e.g. one or more lamps or LEDs) 3 includes a first low oil indicator light which is typically off (i.e. in use during normal operation) 4 and which is switched on when the evaluation module determines that the first (upper) capacitive sensing element is not submerged (e.g. in cooking oil or in cooking fat) and sends a 6 first alarm condition signal. It may be that the first low oil indicator light is an LED (e.g. a red 7 LED). The one or more lights (e.g. one or more LEDs) may further comprise a second, 8 (optionally red) light (and/or lamp or LED) which is switched on (and may be flashing and/or 9 accompanied by a buzzer and/or other visual and/or or audible alarms) when the apparatus (e.g. the fryer) is in use and when the evaluation module determines that the second (lower) 11 capacitive sensing element is not submerged (e.g. in cooking oil or in cooking fat). Typically, 12 these will continue to show or sound until the second alarm condition signal is no longer 13 received (e.g. either the second (lower) and optionally first (upper) capacitive sensor is 14 submerged, typically in oil, and thus indicates that oil is present, or the power is off which would also shut off the heater). One skilled in the art will appreciate that other combinations and/or 16 configurations of lights (e.g. lamps and/or LEDs), as well as other combinations and/or 17 configurations of sounders, may be used. For example, a first low oil indicator light may be lit 18 at all times when the apparatus is in use, and may be (e.g. may display) green when the 19 evaluation module determines that the first (upper) capacitive sensing element is submerged (e.g. in cooking oil or in cooking fat) and may be (e.g. may display) red when the control module 21 has determined that the first (upper) capacitive sensing element is not submerged (e.g. in 22 cooking oil or in cooking fat).

24 Typically, when upper and lower capacitive sensing elements are provided, when a first alarm condition signal from the upper sensing element is received, this may trigger a first 'refilling 26 needed' alarm and particular light and/or sound and, indeed, a refilling action by an operator 27 and when a second alarm condition signal from the lower sensing element is received, a more 28 serious 'unsafe' alarm and particular light and/or sound is raised and typically the heater is 29 switched off (e.g. an emergency switch-off circuit is activated). Indeed, the control unit may be connected to the internet or other communication (Bluetooth, GSM, LORA network etc.) means 31 to facilitate a remote alarm, for example in a kitchen or office, or for monitoring and/or inspection 32 and/or re-filling etc. 34 The sensor module typically comprises a mounting boss. Typically, the mounting boss comprises stainless steel. Preferably, the mounting boss comprises food-safe material(s).

37 The sensor module may comprise an elongate sensor portion and the or each capacitive 38 sensing element may be within the elongate sensor portion. Typically, at least one capacitive 39 sensing element is (i.e. in use) within 30 mm of the floor of the tank, or within 20 mm of the floor of the tank, or preferably within 10 mm of the floor of the tank. Where a second capacitive 1 sensing element is provided, it is typically positioned within (i.e. in use) 50 mm of the floor of 2 the tank, or within 70 mm of the floor of the tank, or preferably within 90 mm of the floor of the 3 tank. One or more capacitive sensing element(s) may be positioned such that, in use, it is 4 generally within the lower 10% of the full height of the tank, or within the lower 5% of the full height of the tank. One or more capacitive sensing element(s) may be positioned such that, in 6 use, it is generally within the upper 10% of the full height of the tank, or within the upper 30% 7 of the full height of the tank, or preferably within the upper 50% of the full height of the tank.

9 The guard compartment may have a cross-sectional area of at least 1 cm2. Preferably the guard compartment has a cross-sectional area of at least 1.5 cm2. The guard compartment typically 11 has a cross-sectional area of less than 5 cm2. The guard compartment may have a width of at 12 least 0.5 cm, or at least 0.7 cm, or preferably at least 1 cm. The guard compartment may have 13 a height of at least 0.5 cm, or at least 0.7 cm, or preferably at least 1 cm. The guard 14 compartment may have a diameter of at least 0.25 cm, or at least 0.35 cm, or preferably at least 0.5 cm.

17 The or each of the walls of the guard compartment may be at least 0.5 mm thick, preferably at 18 least 1 mm thick, optionally 2 mm thick.

Typically, the capacitive sensing elements comprise polyether ketone (PEEK). Preferably, the 21 sensor module is made of food-safe materials and/or is coated with a food-safe coating. The 22 advantage of using stainless steel and/or PEEK and/or other food-safe materials and/or 23 coatings is that the sensor module can be used in existing fryers. Preferably, the sensor module 24 has an operating temperature of at least 250 °C, or at least 280 °C, or at least 350 °C. The advantage of using a sensor module having an operating temperature of at least 250 °C is that 26 the sensor module can be used in existing fryers.

28 The guard compartment typically comprises a scratch-resistant material. The guard 29 compartment may comprise a scratch-resistant coating. The guard compartment may comprise Scotch-Brite (TM). The guard compartment may comprise stainless steel. The advantage of 31 providing a guard compartment comprising a scratch-resistant material (preferably a scratch- 32 resistant coating) is that this makes it less likely that food matter (e.g. batter) will stick to the 33 guard compartment which could otherwise limit the circulation of oil throughout the tank 34 including within the guard compartment.

36 In some embodiments the apparatus (e.g. the fryer) may further comprise a fry plate, the fry 37 plate may typically comprise a metal, (typically stainless steel) planar plate which is retained 38 within the tank at its base. The fry plate typically comprises a series of drainage holes which 39 may be in the form of perforations, slits, gratings, cavities, etc. The fry plate prevents larger pieces of food or other solids from falling to the base of the tank where they are difficult to 1 remove, while the holes in the fry plate allow oil to circulate more or less freely throughout the 2 tank. Typically, the holes extend across substantially the majority of the fry plate. In one 3 embodiment, the fry plate extends beneath the guard compartment, but the holes do not extend, 4 in that part of the fry plate, beneath the guard compartment.

6 In each embodiment of the invention, it is not possible to operate the apparatus (e.g. the gas- 7 powered fryer or the electrically-powered fryer) without the (e.g. openable) guard compartment 8 in place. In the instance of a gas-powered fryer, when the guard compartment is open it is not 9 possible to place a fryer basket into the tank. In the case of an electrically-powered fryer, the guard compartment (and the sensor module which is retained by the guard compartment) can 11 only be removed from the tank by moving (optionally rotating and/or tilting) the guard 12 compartment with the sensor module via the moveable sensor module mount (which typically 13 comprises (e.g. is) the heating element head), and thus also the heating elements, out of the 14 tank; in which instance it is not possible either to place a fryer basket into the tank, nor is it possible for the heating elements to heat the liquid within the tank. This provides the advantage 16 that an operator cannot forget to return the guard compartment to the tank, for example 17 following cleaning or maintenance.

19 A further aspect of the invention provides a method of operating an apparatus comprising one or more of the following steps: 21 a) heating liquid (e.g. oil) in the tank; and/or 22 b) cooking food in the liquid (e.g. oil) in the tank; and/or 23 c) opening the openable guard compartment to clean the sensor module (or optionally 24 sliding the guard compartment up and/or down in parallel to and with respect to the sensor module to thereby allow access to the sensor module); and/or 26 d) temporarily locking the openable guard compartment above and at least partially 27 over a cooking portion of the internal volume of the tank and/or temporarily locking the 28 reciprocating upper part of the guard compartment (where present) in a fixed position 29 above the first part exposing the opening and providing access to the sensor module located within the first part.

32 Preferably, the method may further comprise one or more of the following steps: 33 t) operating a sensing element (e.g. a capacitive sensing element) to detect a level of 34 liquid and triggering the evaluation module to send an alarm condition signal to the control unit to illuminate and/or sound an alarm, and/or to shut off the heater e.g. by a 36 relay in the control module activating an emergency switch-off circuit; and/or 37 h) operating a sensing element (e.g. a capacitive sensing element) to detect a level of 38 liquid and triggering the evaluation module to send an alarm condition signal to the 39 control unit to illuminate and/or sound an alarm, and/or to re-fill the tank; and/or 1 i) providing a sensing portion comprising a first sensing element (e.g. a capacitive 2 sensing element) at a first height, in use, (e.g. relative to the internal height of the tank) 3 and a second sensing element (e.g. a capacitive sensing element) at a second height 4 below the first height, the first and second sensing element(s) (e.g. capacitive sensing elements) being operative independently and operating the first sensing element (e.g. 6 a capacitive sensing element) to detect a first low level of liquid and (e.g. trigger the 7 evaluation module to) send a first alarm condition signal to the control unit (this may be 8 a change in voltage level e.g. LOW to HIGH or HIGH to LOW, to operate a relay in the 9 control module to switch on an alarm) indicating the tank requires refilling, and operating the second sensing element (e.g. a capacitive sensing element) to detect a 11 second low level of liquid (which is typically a very low level) and (e.g. to trigger the 12 evaluation unit to) send a second alarm condition signal to the control unit (this may be 13 a change in voltage level e.g. LOW to HIGH or HIGH to LOW, to operate a relay in the 14 control module to switch on an alarm) to shut off the heater.

16 In some embodiments, steps (f) and/or (h) may comprise the sensing element (e.g. capacitive 17 sensing element(s)) providing measurements to the evaluation unit which evaluates the 18 measurements and sends a signal representing an alarm condition to the control module which 19 may be operative to shut off the heater and may flash an LED and/or may sound a buzzer when a very low level of oil is detected, and/or may be operative to indicate the tank requires refilling 21 and/or may light an LED when a low level of oil is detected.

23 The invention thus provides in one or more examples, an apparatus for heating cooking liquid 24 in tank wherein the tank has a sensor module disposed in the tank comprising at least one capacitive sensing element operative to detect a level of liquid in the tank and an evaluation 26 module for evaluating a signal from the capacitive sensing element (or elements) to determine 27 the presence of liquid at the level of the capacitive sensing element (or elements), wherein the 28 evaluation module is configured to send an alarm condition signal to a control module if liquid 29 is not present. The apparatus also has a guard compartment in which the sensor module is housed; whereby the guard compartment can be opened to clean the sensor module without 31 removing the compartment and sensor module from the tank.

33 Although the invention is discussed in relation to capacitive sensing elements and capacitive 34 sensing elements are preferred, it will be understood that other sensing elements may be used e.g. inductive, proximity, temperature, optical etc. as understood by those skilled in the art.

37 In a further example embodiment, where the (e.g. openable) guard compartment is fixedly 38 mounted to a movable (e.g. tiltable and/or rotatable) mount, the moveable (e.g. tiltable and/or 39 rotatable) mount comprises (typically is) a (e.g. tiltable, preferably rotatably tiltable) heating element head. Optionally, the (e.g. openable) guard compartment may be fixedly mounted to 1 the (e.g. tillable, preferably rotatably tiltable) heating element head via a (e.g. rotatable, 2 threaded) connector. Preferably, the guard compartment is retractable (and may be cylindrical), 3 and moveable in at least a vertical direction with respect to the sensor module (e.g. it may be 4 slidably moveable in respect to the sensor module). The (e.g. cylindrical) guard compartment is typically moveable in an upwards and/or downward direction to allow direct access to the 6 sensor module, e.g. to allow cleaning and/or maintenance of the sensor module. In some 7 embodiments, the guard compartment may be mechanically connected to the moveable mount 8 (e.g. the heating element head) via a mounting boss. The guard compartment is shaped and 9 sized to slide over and retain the sensor module and/or the mounting boss. The guard compartment typically further comprises a collar section which is typically at the upper end of 11 the guard compartment (i.e. the end positioned between the moveable mount and the sensor 12 module (e.g. the between the moveable mount and the first (upper) capacitive sensing 13 element)). The collar section is typically wide enough to prevent food matter (e.g. batter) from 14 entering the guard compartment (e.g. from above). This is advantageous because if food matter enters the guard compartment this can lead to false readings from the sensor module, for 16 example to indicate that oil is present when it is not, which would be unsafe. In addition, the 17 collar section provides additional weight to the guard compartment, which helps to encourage 18 the guard compartment to (slidingly) move downwards over the sensor module under gravity, 19 in use.

21 In some embodiments the guard compartment may be fixed in place in a desired position (e.g. 22 at a desired height) however it typically is not (i.e. it is typically free to sliding move in a direction 23 parallel to the length of the sensor module). In some embodiments the guard compartment may 24 mechanically connected to the moveable mount (e.g. the heating element head) via a (e.g. rotatable, optionally threated) connector. Where present, the connector is mechanically 26 connected to the guard compartment and the moveable mount (e.g. the heating element head) 27 by rotating the (e.g. rotatable, optionally threaded) connector, optionally to thereby engage or 28 disengage a screw thread.

In some embodiments, the method may (e.g. alternatively or additionally) comprise deploying 31 (e.g. by tilting and/or rotating, e.g. via the moveable mount (which may be the heating element 32 head) the sensor module (and typically the guard compartment) out of the tank and sliding the 33 guard compartment laterally with respect to the sensor module to thereby allow access to the 34 sensor module. The method may (e.g. alternatively or additionally) comprise deploying (e.g. by tilting and/or rotating, e.g. via the moveable mount (which may be the heating element head) 36 the sensor module (and typically the guard compartment) in to the tank and sliding the guard 37 compartment laterally with respect to the sensor module to thereby prevent access to the 38 sensor module, for example following cleaning and/or maintenance of the sensor module, 39 and/or guard compartment, and/or tank, an/or apparatus etc. 1 The guard compartment (and preferably the sensor module) is typically positioned between 2 electric heating elements. The (e.g. cylindrical) guard compartment typically comprises at least 3 one guard wall, the guard wall comprising at least one perforated section (e.g. a perforated 4 section comprising a series of perforations, or a grid or a net). The guard compartment may comprise a threaded connector, connecting the guard compartment to the mounting boss.

6 Where the guard compartment is positioned between electrical heating elements, the apparatus 7 may further comprise an optional further guard wall (e.g. a perforated plate or grid) arranged 8 within the tank (but typically not connected to the (e.g. cylindrical) guard compartment). The 9 guard wall may be a fish plate (as is known in the art). It will be understood that, in such embodiments, the further guard wall may be removed, and the apparatus may be operated 11 either with or without the further guard wall.

13 The moveable (e.g. tiltable and/or rotatable) mount is typically attached (e.g. mechanically 14 connected) to the tank. The moveable (e.g. tiltable and/or rotatable) mount may be attached (e.g. mechanically connected) to a heating element head. In some embodiments, the moveable 16 (e.g. tiltable and/or rotatable) mount may comprise (optionally be) a heating element head. The 17 moveable (e.g. tiltable and/or rotatable) mount may be attached to one or more (electrical) 18 heating element.

The mounting boss is typically mechanically connected to the (e.g. rotatably tiltable) moveable 21 mount (e.g. the heating element head). In use, i.e. when the sensor module is being cleaned, 22 the moveable mount (e.g. the heating element head) may be rotated to thereby tilt the mounting 23 boss, (cylindrical) guard compartment, sensor module (and typically electrical heating 24 elements) out of the tank and where present the (e.g. rotatable, threaded) connector is detached (typically rotated) to allow the guard compartment to be freely moved (e.g. slidingly 26 moved up and and/or down in a parallel direction) in relation to the sensor module. This provides 27 the advantage that the guard compartment may be slidably moved out of the way of the sensor 28 module, allowing an operator access to the sensor module, e.g. for cleaning and/or 29 maintenance. However, the guard compartment cannot be moved past the moveable mount (e.g. the heating element head), thus providing the further advantage that the guard 31 compartment (as well as the sensor module) cannot be removed from the apparatus and thus 32 the apparatus cannot be used without the guard compartment. Such use of the apparatus 33 without the guard compartment would be unsafe.

The advantage of providing a guard compartment which is slidably moveable, (e.g. 36 substantially) vertically (e.g. in parallel to and relative to the sensor module), from a first (e.g. 37 cooking) position into a second (e.g. cleaning) position, is that this thereby allows the guard 38 compartment to be moved relative to the sensor module to allow cleaning (and/or maintenance) 39 of the sensor module and/or of the guard compartment.

1 The guard compartment is more easily moveable (for example, from the first (e.g. cooking) 2 position into the second (e.g. cleaning) position) relative to the sensor module when the guard 3 compartment, sensor module and heating elements are moved (e.g. tilted and/or rotated) out 4 of the tank via the moveable mount (typically the heating element head). When the guard compartment, sensor module and heating elements are moved (e.g. deployed, optionally tilted 6 and/or rotated) (back) into the tank via the moveable mount (typically the heating element head) 7 the guard compartment slides back over the sensor module under gravity and thus 8 automatically to the first (e.g. cooking) position (e.g. if it has not already been moved into this 9 position by an operator). This provides the advantage that if an operator forgets to move the guard compartment into the first (e.g. cooking position), for example, after cleaning, the 11 apparatus is still safe to use because the guard compartment will move into the first (e.g. 12 cooking) position automatically.

14 A further example embodiment of the invention provides a kit of parts comprising an apparatus for heating liquid in a tank, comprising: a tank having an internal volume for retaining a liquid; 16 a heater; and a control module for controlling the heater; 17 the kit of parts comprising: a sensor module comprising at least one (e.g. capacitive) sensing 18 element operative to detect a level of liquid (e.g. in the tank, e.g. in use); an evaluation module 19 for evaluating a signal from the at least one (e.g. capacitive) sensing element to determine the presence (or not) of liquid and configured to send an alarm condition signal to the control 21 module if liquid is not present (e.g. in use); and an (e.g. openable) guard compartment 22 mountable within the internal volume of the tank or mountable (preferably with the sensor 23 module) to a moveable (e.g. rotatable and/or tiltable) mount, preferably such that when 24 mounted to the moveable (e.g. rotatable and/or tiltable) mount, the guard compartment (and preferably also the sensor module) can be deployed (e.g. by rotating and/or tilting) into and/or 26 out of the tank (e.g. without detaching it from the apparatus), wherein when the sensor module 27 and guard compartment are in the tank they are in fluid communication with a remaining volume 28 of the tank.

In a further example embodiment, the invention comprises a kit of parts for fitting (e.g. 31 retrofitting) to an (e.g. existing) apparatus for heating liquid (typically cooking liquid, e.g. oil), in 32 a tank, the apparatus comprising: 33 a tank having an internal volume for retaining a liquid; 34 a heater; a control module (e.g. for controlling the heater) 36 and the kit of parts comprising: 37 a sensor module; 38 at least one (e.g. capacitive) sensing element operative to detect a level of liquid (e.g. in 39 the tank, e.g. in use); 1 an evaluation module for evaluating a signal from the at least one (e.g. capacitive) sensing 2 element to determine the presence (or not) of liquid and configured to generate an alarm 3 condition signal to the control module if liquid is not present (e.g. in use); 4 a (e.g. openable) guard compartment mountable within the internal volume of the tank, or mountable (preferably with the sensor module) to a moveable (e.g. tiltable and/or rotatably 6 tiltable) mount, preferably such that when mounted to the moveable (e.g. rotatable and/or 7 tiltable) mount, the guard compartment (and preferably also the sensor module) can be 8 deployed (e.g. by tilting and/or rotating) into and/or out of the tank, (e.g. without detaching 9 it from the apparatus) and wherein, when the sensor module and guard compartment are in the tank they are in fluid communication with a remaining volume of the tank (i.e. when 11 installed or retrofitted).

12 The (e.g. capacitive) sensing module may be configured to send the alarm condition to the 13 control module. However, the kit of parts may further comprise an alarm module, the alarm 14 module being configured to receive an alarm condition and issue an (e.g. visual and/or audible) alarm, in which case the (e.g. capacitive) sensing module may altematively or additionally be 16 configured to send the alarm condition to the alarm module. The (e.g. capacitive) sensing 17 module may be configured to send the alarm condition to a control unit, where provided (e.g. 18 a control unit as described above).

19 Typically, the apparatus is an apparatus for cooking food. Typically, the apparatus is a fryer, optionally a deep fat fryer, for example a gas-powered deep fat fryer or an electrically-powered 21 deep fat fryer. Typically, the liquid is cooking fat, for example cooking oil. The heater may 22 comprise one or more gas burners. The heater may comprise one or more electrical heating 23 elements. Were the guard compartment is mountable to a moveable (e.g. rotatable and/or 24 tiltable) mount, the apparatus is typically an electrically-powered deep fat fryer and the moveable (e.g. rotatable and/or tiltable) mount typically comprises (e.g. is) a (e.g. rotatable, 26 tiltable) heating element head.

28 It will be understood that any feature of any one or more embodiments of any aspect of the 29 invention may be combined or used with any other feature in any other one or more embodiments of any other aspect of the invention.

32 Description of the Drawings

34 Example embodiments of the present invention will now be described and illustrated, by way of example only, with reference to the following figures in which: 37 Figure 1 is an exploded, perspective view diagram of a gas-powered deep fat fryer according 38 to the invention; 2 Figure 2a is a block diagram of the apparatus in an example embodiment; 4 Figure 2b is a flow chart indicating the main steps carried out by the control unit in an example embodiment; 7 Figures 3a, 3b, 3c and 3d are, respectively, a perspective, side elevation, front elevation and 8 cross-sectional view of a (lower, fixed) first part of a guard compartment according to an 9 embodiment of the invention (typically for use with a gas fryer); 11 Figures 4a, 4b, 4c, and 4d are, respectively, perspective, side elevation, front elevation and 12 cross-section view of an (upper) retractable second part of a guard compartment according to 13 an embodiment of the invention (typically for use with a gas fryer); Figure 5 is a perspective view diagram of the guard compartment in a servicing or cleaning 16 position in an embodiment of the invention (typically for use with a gas fryer); 18 Figure 6a is a perspective view diagram of an electrically-powered deep fat fryer, with an 19 alternative guard wall forming a guard compartment in place in an example embodiment; 21 Figure 6b is a perspective view diagram of the deep fat fryer of Figure 6a, with the alternative 22 guard wall removed; 24 Figure 7 is a perspective view diagram of the deep fat fryer of Figures 6a and 6b, with an array of guard elements (here the heating elements) raised in a further example embodiment; 27 Figure 8 is a diagram of a further example embodiment of a (cylindrical) guard compartment 28 according to a further example embodiment of the invention, in an electric fryer in an engaged 29 position (e.g. for cooking) and Figure 8b is a diagram of the same (cylindrical) guard compartment in an electrically powered deep fat fryer in a servicing or cleaning position; 32 Figures 9a and 9b are, respectively, front elevation and cross-section view of the cylindrical 33 guard compartment according to the embodiment of the invention as shown in Figures 8a and 34 8b (typically for use with an electrically powered deep fat fryer); and 36 Figure 10 is an example control panel for a deep fat fryer according to the invention.

38 Detailed Description of an Example Embodiment

1 It will be understood by those skilled in the art that any dimensions and relative orientations 2 such as lower and higher, above and below, and any directions, such as vertical, horizontal, 3 upper, lower, axial, radial, longitudinal, tangential, etc., referred to in this application are within 4 expected structural tolerances and limits for the technical field (here including heating liquids such as cooking oil) and the apparatus and methods described, and these should be interpreted 6 with this in mind.

8 Figure 1 is an exploded perspective view diagram of an apparatus 1 in the form of a deep fat 9 fryer according to a first example embodiment of the invention. The deep fat fryer has a tank 2 for cooking liquid e.g. cooking fat or cooking oil in a heater module 17 which may be mounted 11 within a hob 30. The tank has a rear wall 4, a front wall 6, a first side wall 8, a second side wall 12 10, and a flat floor 16 having a v-shaped trough 14. In this example embodiment the deep fat 13 fryer is a gas-powered deep fat fryer in that it has a heater 17, which burns gas, beneath the 14 flat floor of the tank, here arranged on either side of the v-shaped trough, to thereby heat (e.g. the contents of) the tank, by burning gas, heating the tank in a direction 12 beneath the tank.

16 In use, debris (e.g. food particles) may fall into the v-shaped trough. The shape of the trough 17 discourages debris (e.g. food particles) from circulating within the cooking fat in the tank and 18 allows such debris to be collected and more easily removed.

The apparatus further has a sensor module in the form of a capacitive sensing module 18 21 configured to detect the presence of liquid (typically oil, e.g. cooking oil, or cooking fat). The 22 capacitive sensing module 18 has a mounting shaft 20 which engages in use with a mounting 23 boss 26 on the outer side of the tank 2 and is connected to the mounting boss 26 via a screw 24 thread 22. It will be understood that any holes through the tank 2 walls must be sealed against liquid loss and rated for cooking liquids and temperatures. The mounting shaft 20 has an 26 electrical connector 24 which electrically connects the capacitive sensing module 18 to a sensor 27 evaluation module 46. The capacitive sensing module 18 also has a mounting block 68 typically 28 having at least one, and here three flat side walls and a sensor portion 41 (here an elongate 29 downwardly projecting sensor portion) comprising capacitive sensing elements 40 and 42. The combination of the mounting shaft 20, mounting boss 26 and mounting block 68 allow the 31 capacitive sensing module 18 to be accurately aligned and rigidly fixed within the tank 2 and, 32 in particular, within a separate compartment within tank 2, here a guard compartment 58 (which 33 may be thought of as a generally box shaped construction) and which provides some protection 34 as a guard from solids approaching sensor module 18. The walls of the guard compartment are preferably generally or substantially vertical in use, as are sensing electrodes within the sensor 36 module. The sensing electrodes may be annular or ring-shaped with a central axis arranged 37 parallel to surrounding walls (e.g. vertically). Although in this example embodiment the 38 mounting block has a square cross-section when viewed from above (i.e. in use) one skilled in 39 the art will appreciate that other cross-sections may also be suitable for locating same within a correspondingly sized and/or shaped guard compartment.

2 The sensing elements may be capacitive sensing elements, and the capacitive sensing 3 elements may be of any suitable kind e.g. capacitive electrodes.

Thus, the capacitive sensing module 18 is housed within a guard compartment 58. In this 6 example embodiment, the guard compartment has a fixed first part 60 (see figures 3a to 3d for 7 more detail) and a retractable second part 62 (see figures 4a to 4d for more detail). The 8 retractable second part 62 has a first track 34 which here is closed-ended in a first side wall 9 and a second track (not shown) also here closed-ended in a second opposing side wall, the first and second tracks being substantially the same size and shape, and parallel to, one 11 another. The (upper) retractable second part 62 also has a sloped roof 32. The sloped roof 32 12 enables a fryer basket, any solid or liquid debris (e.g. food particles) that land on the guard 13 compartment 58 to slide off the sloped roof 32. The (lower) first fixed part 60 has a first hole 14 74a in a first side wall and a second hole 74b in a second side wall which is substantially the same size and shape, and is substantially parallel to, the first hole. A pin 36, or shank or similar, 16 is retained by, and passes substantially through, the first hole 74a, the first track 34, the second 17 hole 74b and the second track to thereby connect the (upper) retractable second part and the 18 (lower) fixed first part moveably theretogether. One skilled in the art will appreciate that in some 19 embodiments the (lower) fixed first part may alternatively have an integrally formed pin, in which case it may not have a first or second hole.

22 The (upper) retractable second part 62 is sized and shaped such that, in use, it may slidably 23 receive (or be received in) and retain (or be retained in or about) the (lower) fixed first part 60 24 travelling with respect to the fixed first point 60. The pin 36 functions as a retainer (and may also function as a pivot) in that, in use, the (e.g. track of the) (upper) retractable second part 62 26 may be moved vertically to and fro (and rotationally) with respect to the (lower) fixed first part 27 60 (and hence the pin) such that the guard compartment 58 may be opened without being 28 dismantled or removed from the tank 2. See Figure 5 for a view of the guard compartment 58 29 when open.

31 The first and second tracks 34 in the first and second side walls of the (upper) retractable 32 second part 62 have an elongate track section which runs parallel an elongate axis (e.g. along 33 the height) of the (upper) retractable second part 62 (i.e. in use) and which runs the majority of 34 the height of the (upper) retractable second part 62. The first and second tracks 34 in the first and second side walls of the (upper) retractable second part 62 have a bend 64 in the track 36 close to the base (i.e. the lower part in use) of the (upper) retractable second part 62. In this 37 example embodiment, the bend 64 has a 90° angle and leads to a short track section which 38 runs substantially perpendicular to the elongate track section (although one skilled in the art will 39 recognise that other angles may alternatively be appropriate). Accordingly, in use, if the (upper) retractable second part 62 is moved vertically with respect to both the (lower) fixed first part 60 1 and the pin 36, then when the pin 36 reaches the bend 64 in the track, the (upper) retractable 2 second part 62 can be moved laterally with respect to the (lower) fixed first part 60. When the 3 pin 36 is at the end of the tracks 34, the (upper) retractable second part 62 may be rotated with 4 respect of the pin 36 such that a base or lower edge 72 of exposed side wall of the (upper) retractable second part 62 contacts the front wall of the (lower) fixed first part 60. In this respect 6 the base of the (upper) retractable second part 62 may be considered as a stop member.

8 The advantage of being able to open the guard compartment 58 in this way is that it allows 9 ease of access to (e.g. the interior of) the guard compartment 58 for cleaning. This allows a user to clean the guard compartment 58 without being able (in normal use) to remove it 11 completely from the tank 2. It is preferable that the guard compartment 58 is not removed from 12 the tank because the guard compartment 58 protects the capacitive sensing module 18 from 13 significant damage and may prevent the capacitive sensing module 18 from becoming coated 14 (e.g. especially in foodstuffs such as batter, which can change phase from liquid to solid when cooked) which could cause the capacitive sensing module 18 to give a false oil level reading.

17 The guard compartment walls are therefore, generally or substantially solid, having few holes, 18 and/or small holes (e.g. holes 78 in Figure 4d), but are not liquid-tight in any sense allowing 19 free flow of liquid, e.g. oil, in and out of the guard compartment.

21 The second part 62 is open at its base to enable it to slide upwards with respect to the first part 22 60. Indeed, the guard compartment 58 may also be open at its base to facilitate liquid flow.

24 The (lower) fixed first part 60 also has a notch 38 at its base which may be configured for engaging with an optional fry plate (not shown). Where used, typically the fry plate is a planar 26 metal (e.g. stainless steel) plate which contains multiple small holes across its surface and 27 which extend through the plate, however the fry plate may not have holes at the position on its 28 surface which would be directly beneath the lower guard compartment 58 in use. It has been 29 surprisingly found that the combination of a fry plate which lacks holes directly beneath the guard compartment 58 reduces the instances of debris (e.g. food particles) entering the guard 31 compartment 58. The notch 38 is also helpful and enables close positioning of the fry plate and 32 the guard compartment 58 together.

34 The apparatus further has a control module 50 within a control unit, an operational thermostat 54, a safety thermostat 56, two light emitting diodes (LEDs) 28a, 28b, a control unit mounting 36 panel 44, two relays 48a, 48b within control module 50, and a power supply 52. In some 37 embodiments of the invention the apparatus also has a sounder (not shown). Relays 48a and 38 48b may each be connected to the evaluation module by one or more wires. The evaluation 39 module typically provides a change in voltage along the wire(s) (e.g. LOW to HIGH or HIGH to LOW) to indicate an alarm condition signal to a respective relay. Upon receipt of a first alarm 1 condition signal, relay 48a is operative to illuminate a refill light 28a. Upon receipt of a second 2 alarm condition signal, relay 48b is operative to trigger an emergency switch-off circuit and to 3 illuminate a flashing LED 28b and to sound a continuous alarm. Power is removed from the 4 heater, as a result of which the heater switches off. Switch on of the heater is prevented until the fryer is reset as understood in the art.

7 In this example embodiment, the capacitive sensing module 18 has a first lower capacitive 8 sensing element 40 and a second upper capacitive sensing element 42. Each capacitive 9 sensing element (known as a 'sensing zone' or 'sensing point') has one or more electrodes, e.g. a measurement electrode and a reference or screening electrode which may be in two 11 parts, one positioned above and one below the measurement electrode. The tank (or guard 12 compartment when present) also forms an electrode and is at the same voltage level as a guard 13 compartment when present -typically ground. Thus, the sensing module comprises one or 14 more sensing zones, each provided by a respective capacitive sensing element 40, 42, located part way along the body (known as a sensor portion) of the sensor module. This first receiving 16 electrode (the measurement electrode) defines a 360-degree cylindrical disc of sensitivity 17 between it and its surroundings (the tank/guard). This could be thought of a disc-shaped region 18 or shallow cylinder, in use extending horizontally i.e. parallel to the surface 80 of the oil -see 19 Figure 5. The two-part second electrode (a screening electrode) may be provided and located with one part above and one part below the first receiving electrode within the sensor module 21 and this prevents field lines from straying above and below the sensing volume of the 22 measurement electrode. Thus, in some embodiments, a three-electrode circuit may be used to 23 monitor capacitance at each sensing zone 40, 42 (in a volume extending horizontally to the 24 surrounding walls). The sensor evaluation module may determine if a control condition is met, indicating in this invention that oil is present (or not), and if not, an alarm condition signal is 26 issued (e.g. a voltage level may change). A particularly suitable type of level sensor, KFS-52 27 and a corresponding evaluation unit is KFA-52 are available from Rechner Sensors (Rechner 28 (UK) Ltd.). Other types of level sensors, particularly capacitive level sensors may be used.

In this example embodiment, the sensor evaluation module 46 is configured to carry out this 31 evaluation for each of the lower capacitive sensing element 40 and the upper capacitive sensing 32 element 42, and issue first and second alarm condition signals as described elsewhere.

34 Turning to figure 2a, the sensor evaluation module 46 is connected to both the lower capacitive sensing element 40 and the upper capacitive sensing element 42 and further with a control unit 36 comprising a control module 50 and relays 48a, 48b. Accordingly, the sensor evaluation module 37 46 determines the status of the lower capacitive sensing element 40, and independently 38 determines the status of the upper capacitive sensing element 42 (assessing if oil is present at 39 the level of each sensing zone (i.e. present in the shallow volume (e.g. the horizontal volume) between each respective sensing element 40, 42 and the surrounding walls of the guard 1 compartment), and provides first and/or second alarm condition signal(s) to the control module 2 50 (e.g. as a change in voltage along independent control wires (not shown)).

4 In more detail, when the oil level sensor signals to the evaluation unit that the oil level is low (top sensing zone 42) the oil lop up' level LED illuminates. This indicator has no effect on the 6 operation of the fryer. A wire from the evaluation unit connects directly into relay 48a which in 7 turn connects directly to the low oil warning lamp. When the oil level sensor signals to the 8 evaluation unit that the oil level is very low (bottom sensing zone 40), the low oil level LED 9 flashes and a sounder alarm comes on. The fryer control system is disabled and the heater (e.g. one or more burners or one or more electrical heating elements) will extinguish or be 11 switched off. A separate wire from the evaluation unit connects to a second relay 48b. This in 12 turn connects to an ignition box which disables the ignition circuit. The output of the relay is 13 also connected to flashing LED and a sounder/buzzer. In order to pump oil back up into the 14 fryer pan, the fryer has to be switched off and the oil pump switched on. Once the pan has been filled, the fryer can be turned on; enabling the ignition circuit and the gas burners will relight (or 16 the electrical elements will be switched back on).

18 Figure 2b is a flow chart of the steps taken by the control module 50. The control module 50 19 receives an alarm condition signal as determined by the sensor evaluation module 46 in step 210. The alarm condition signal(s) are preferably arranged to indicate that one or more e.g. one 21 or both capacitive sensing element(s) 40, 42 is/are not in liquid. Accordingly, as the liquid level 22 falls past first sensing element 42 then the other sensing element 40, first one then the other 23 alarm condition signal(s) are delivered e.g. as a change in voltage along the wire(s).

If an alarm condition signal is received or determined, the tank 2 is low or very low (e.g. empty) 26 on oil and needs to be refilled or shut off. In this latter case, the control module 50 causes heater 27 17 at least to be switched off, typically by switching off the gas burners (although one skilled in 28 this art will recognise that, where the apparatus is an electrically-powered deep fat fryer, the 29 controller may instead switch off the power supply to one or more electrical heating elements).

In this case, in this example embodiment the tank must be re-filled before the heater 17 can be 31 switched back on (for example by switching on the gas bumers). In addition, the tank must 32 typically be allowed to cool before the heater 17 can be switched back on (for example, the tank 33 may be allowed to cool to below 40 °C).

Typically, as the liquid level falls the control module determines the receipt of an alarm condition 36 signal from the evaluation module for the upper capacitive sensing element 42 first (in step 220) 37 and may initiate a refill in step 230, then proceeds to determine receipt of an alarm condition 38 signal from the evaluation module for the lower capacitive sensing element 42 (in step 240) and 39 shuts off the heater 17 in step 250.

1 The control module 50 may repeat these steps and continue to monitor the change in alarm 2 condition signal(s) in step 260.

4 Figures 3a, 3b, 3c and 3d are, respectively, a perspective, side elevation, front elevation and cross-sectional view of a (lower, fixed) first part of a guard compartment according to an 6 embodiment of the invention (typically for use with a gas fryer); 8 Figures 4a, 4b, 4c, and 4d are, respectively, perspective, side elevation, front elevation and 9 cross-section view of an (upper) retractable second part of a guard compartment according to an embodiment of the invention (typically for use with a gas fryer); 12 It will be understood that in some embodiments of the invention the steps described above may 13 be carried out in a different order. For example, rather than relatively direct control via a change 14 in voltage on wires from the evaluation module to relays 48a, 48b in the control module, the control module might first determine whether the lower capacitive sensing element is in oil and 16 subsequently determine whether the upper capacitive sensing element is in oil or vice versa. In 17 some embodiments these steps may be carried out simultaneously (e.g. where wires to relays 18 48a, 48b are used).

Figure 5 shows the guard compartment 58 in a retracted tilted orientation overhanging oil 82 21 and a reflection 84 can be seen in oil surface 80. The shallow (e.g. disc shaped) sensing zone 22 provided by each capacitive sensing element 40, 42 is generally or substantially parallel to the 23 oil surface 80.

Figures 6a and 6b are perspective view diagrams of a second example embodiment of the 26 apparatus 100. In this example embodiment the apparatus is an electrically-powered deep fat 27 fryer, in that electric heating elements 160, 160a are provided which are retained within the tank 28 102 of the apparatus to thereby heat cooking fat (e.g. cooking oil) in use. In this example 29 embodiment, the apparatus further comprises a guard compartment 158 sectioned off from a cooking volume of tank 102. A guard wall or plate (here in the form of a fish plate) 159 forming 31 guard compartment 158 can be removed, for example in order to clean the electric heating 32 elements 160, 160a. In figure 6a the guard wall 159 of guard component 158 is present; in 33 figure 6b it has been removed. In this example embodiment, the capacitive sensor module 34 element 118 is located between an array 160 of guard (heating) elements 160a but may be located behind such an array. The guard elements 160a are here in the form of electric heating 36 elements. The capacitive sensor element 118 may be connected to the apparatus via a 37 rotatable (heating) element head 166 on which heating elements 160a are mounted. As with 38 the first example embodiment, the capacitive sensing module 118 has a first (lower) capacitive 39 sensing element 140 and a second (upper) capacitive sensing element 142. The apparatus 100 also has an LED 128 and a temperature control dial 162, and a vent 164.

2 Figure 7 is a further perspective view diagram of the second example embodiment of figures 3 6a and 6b. Here, an array of guard (e.g. the electrical) elements 160a have been rotated about 4 a hinge 168 out of the tank 102, here along with the capacitive sensing element 118. In this way, the electrical elements 160 and the capacitive sensor module 118 can be cleaned or 6 otherwise maintained. However, the rotated elements 160a (and optionally also sensor module 7 118) provide a visual indicator and physical preventer essentially preventing use when these 8 are not in a cooking position within tank 102.

Figures 8a and 8b are perspective view diagrams of a third example embodiment of the 11 apparatus. In this example embodiment the apparatus is an electrically-powered deep fat fryer, 12 in that electric heating elements 304 are provided which are retained within the tank of the 13 apparatus to thereby heat cooking fat (e.g. cooking oil) in use. In this example embodiment, the 14 apparatus further comprises a cylindrical guard compartment 300 which retains the capacitive sensing module 312. In this example embodiment, the capacitive sensing module 312 is located 16 between an array of electric heating elements 304 but may alternatively be located in front of 17 or behind such an array. The capacitive sensing module 312 may be connected to the 18 apparatus via a rotatable mount in the form of the rotatable (heating) element head (not shown) 19 on which heating elements 304 are mounted.

21 In use, e.g. during cooking, the guard compartment 300 retains the capacitive sensing module 22 312. The guard compartment 300, capacitive sensing module 312, and electrical heating 23 elements 304 are positioned close to the rear of the cooking tank and are substantially parallel 24 to the rear wall of the cooking tank 308. The electrical heating elements extend towards but do not reach the base of the cooking tank 310. The base of the capacitive sensing module 312 is 26 within the lower one-third of the full depth of the cooking tank.

28 The guard compartment 300 further comprises two arrays of perforations 306 which allow liquid 29 (e.g. cooking fat) to freely circulate within the tank and within the guard compartment 300. The guard compartment 300 is open-ended at its base. The guard compartment is mounted to a 31 mounting boss 314 which in turn is connected to the rotatable mount, here in the form of the 32 rotatable (heating) element head (not shown). The guard compartment also has a collar section 33 316.

In figure 8a the cylindrical guard compartment 300 is in the normal, cooking position; in figure 36 8b it has been moved upward (i.e. in a direction substantially perpendicular to the surface of 37 the oil in the tank) over the capacitive sensing module 312 and is thus in a position which may 38 allow cleaning of the capacitive sensing module 312 (although ease of cleaning is typically 39 improved by rotating moveable mount (i.e. the (heating) element head) to thereby also rotate the heating elements 304, mounting boss 314, guard compartment 300 and capacitive sensing 1 module 312, out of the tank). The guard compartment 300 is moved into place such that it 2 retains the capacitive sensing module 312 by sliding it down over the capacitive sensing module 3 312. The guard compartment 300 may be slidingly moved upwards over and out of the way of 4 the capacitive sensing module 312 (e.g. to allow cleaning of the capacitive sensing module 312). However, the guard compartment 300 cannot be moved past the moveable mount (i.e. 6 the (heating) element head) and thus cannot be completely removed from the apparatus.

8 As with the first and second example embodiments, the capacitive sensing module 312 has a 9 first (lower) capacitive sensing element 302 and a second (upper) capacitive sensing element (not shown).

12 Figures 9a and 9b are, respectively, front elevation and cross-section view of a guard 13 compartment according to the third example embodiment of the invention. Although the guard 14 compartment of figures 9a and 9b is typically for use with an electrically powered deep fat fryer it may in some instances also be suitable for gas powered deep fat fryers.

17 Figure 10 is an example embodiment of a control panel 318 of a deep fat fryer according the 18 invention. Such a control panel 318 includes are-fill oil LED 320 which indicates (when lit) when 19 additional oil should be introduced into the tank 2, 102 (i.e. when the oil level has reduced below the second (upper) capacitive sensing element 42 and the second (upper) capacitive sensing 21 element 42 is therefore no longer submerged in oil), a low oil LED 322 which indicates (when 22 lit) when the level of oil has reduced below the first (lower) capacitive sensing element 40 and 23 the first (lower) capacitive sensing element is therefore no longer submerged in oil), a 24 temperature control dial 324, a power indicator LED 326 and a hot LED 328 which indicates that the oil in the tank is heated to above a predetermined temperature. It will be appreciated 26 that other combinations and configurations of LEDS, controls, buzzers, sounders, etc may be 27 used.

29 Different level sensing technologies exist, however a capacitive sensor may be preferred for providing an oil level measurement (or optionally a measurement of oil temperature), because 31 such sensors are little affected by the quality of oil and are without moving parts.

33 The challenge, however, has been to develop specific guard arrangements that protect the 34 sensor but also allow oil to move freely around the tank and the guard, and at the same time which can be raised for cleaning but will not detach from the tank (or apparatus) and will 36 preferably overlay the tank. Thus, the guard cannot (easily) be removed by the operator, thus 37 preventing the sensor from being able to provide a false positive unsafe status. Indeed, it is 38 more obvious to the operator that the guard (compartment) is in the cleaning position not the 39 operational position.

1 Other embodiments can be envisaged by those skilled in the art from this application.

3 List of reference numerals 1. Apparatus 6 2. Tank 7 4. Rear wall 8 6. Front wall 9 8. First side wall 10. Second side wall 11 12. Direction of heat application (e.g. from gas burner) 12 14. V-shaped trough 13 16. Flat floor 14 17. Heater (e.g. array of gas burners) 18. Sensor module 16 20. Mounting shaft 17 22. Screw thread 18 24. Electrical connector 19 26. Mounting boss 28a, 28b. LEDs 21 30. Hob 22 32. Sloped roof 23 34. Track 24 36. Pin (e.g. spigot; may function as pivot) 38. Notch 26 40. First (lower) capacitive sensing element 27 41. Elongate sensor portion 28 42. Second (upper) capacitive sensing element 29 44. Control unit mounting panel 46. Sensor evaluation module 31 48a, 48b. Relays 32 50. Control module 33 52. Power supply 34 54. Operational thermostat 56. Safety thermostat 36 58. Guard compartment 37 60. Fixed first part 38 62. Retractable second part 39 64. Bend in track 66. Opening 1 68. Mounting block 2 70. Rebate 3 72. Stop member 4 74, 74a, 74b. Holes to receive pin 76. Side wall of fixed first part 6 78. Grid of perforations/holes 7 80. Surface level of oil 8 82. Oil 9 84. Reflection 100. Apparatus 11 102. Tank 12 118. Sensor module 13 128. LED/LEDs 14 140. First (lower) capacitive sensing element 142. Second (upper) capacitive sensing element 16 158. Element guard compartment 17 159. Guard plate (e.g. fish plate) 18 160. Array of guard elements (e.g. heating elements) 19 160a. Electric heating element 162. Temperature control dial 21 164. Vents 22 166. Heating element head 23 167. Heater (heating elements) 24 168. Hinge 200. Method of operation of control module 26 210. Receive alarm condition signal from evaluation module 27 220. Determine whether upper capacitive sensing element is in oil 28 230. Trigger top-up alert 29 240. Determine whether lower capacitive sensing element is in oil 250. Switch off fryer 31 260. Request updated capacitance measurements 32 300. Sliding guard compartment 33 302. First (lower) capacitive sensing element 34 304. Electric heating element 306. Grid of perforations 36 308. Rear wall of tank 37 310. Base of tank 38 312. Sensor module 39 314. Mounting boss 316. Collar section 1 318. Control panel 2 320. Re-fill oil LED 3 322. Low oil LED 4 324. Temperature control dial 326. Power indicator LED 6 328. Hot LED

Claims

1 Claims 3 1. An apparatus for heating liquid in a tank, comprising: 4 a tank having an internal volume for retaining a liquid; - a heater; 6 a control module for controlling the heater; 7 a sensor module disposed or disposable in the tank comprising at least one 8 capacitive sensing element operative to detect a level of liquid in the tank; 9 - an evaluation module for evaluating a signal from the at least one capacitive sensing element to determine the presence of liquid at the level of the at least one 11 capacitive sensing element in the tank and configured to send an alarm condition 12 signal to the control module if liquid is not present in use; and 13 - a guard compartment fixedly mounted within the internal volume of the tank or 14 mounted with the sensor module to a moveable sensor module mount, such that the guard compartment can be deployed into and out of the tank, and in use is in 16 fluid communication with a remaining volume of the tank, the sensor module 17 housed within the guard compartment in a spaced apart manner from internal 18 surfaces of the compartment so as to be electrically isolated therefrom; 19 -whereby the guard compartment can be opened, or slid relative to the sensor module, to access the sensor module without detaching the compartment and/or 21 sensor module from the apparatus.23

2. An apparatus according to claim 1, wherein the sensor module is disposed in the tank; 24 and the guard compartment is fixedly mounted within the internal volume of the tank and in fluid communication with a remaining volume of the tank, the sensor module 26 housed within the guard compartment in a spaced apart manner from internal surfaces 27 of the compartment so as to be electrically isolated therefrom; whereby the guard 28 compartment can be opened to access the sensor module without removing the 29 compartment and/or sensor module from the tank.31

3. An apparatus according to claim 1, 32 wherein the sensor module is disposable in the tank, the sensor module comprising at 33 least one capacitive sensing element operative to detect a level of liquid in the tank in 34 use; the guard compartment is fixedly mounted with the sensor module to a moveable 36 mount, such that the guard compartment can be deployed into and out of the tank, and 37 in use is in fluid communication with a remaining volume of the tank; 38 whereby the guard compartment can be slid relative to the sensor module to access 39 the sensor module without detaching the compartment and/or sensor module from the apparatus.2

4. An apparatus according to any one preceding claim, in which the guard compartment 3 is formed around and attached to the sensor module.

5. An apparatus according to any one preceding claim, in which the guard compartment 6 comprises a first part having an opening in a side wall to access the sensor module for 7 cleaning, the first part being fixedly mounted to a wall of the tank and, a retractable 8 second part, movable in at least a vertical direction with respect to the first part to 9 uncover the opening in the first part, allowing access to the sensor module for cleaning.11

6. An apparatus according to claim 5, in which the retractable second part is movable in 12 at least a horizontal direction with respect to the first part to partially block access to a 13 main portion of the intemal volume of the tank.

7. An apparatus according to claim 5 or 6 in which the retractable second part is 16 configured to be temporarily locked in a retracted position such that at least a portion 17 of the second part is above the first part, or at least a portion of the second part is above 18 and to one side of the first part to partially block access to a main portion of the internal 19 volume of the tank.21

8. An apparatus according to any one of claims 5 to 7, in which at least one of the fixed 22 first part and the retractable second part comprises at least one track and the other of 23 the fixed first part and retractable second part comprises at least one pin configured to 24 interengage with and travel in the at least one track, wherein the retractable second part can travel with respect to the first part as the pin travels in at least one track.27

9. An apparatus according to claim 8, in which the at least one track comprises a bend, 28 the bend being at a lower end of the at least one track when the track is in the 29 retractable second part, and the bend is at an upper end of the at least one track when the track is in the fixed first part.32

10. An apparatus according to any of claims 5 to 9 in which the first part comprises at least 33 one pin and the second part comprises at least two tracks arranged opposite one 34 another in respective opposing side walls of the retractable second part.36

11. An apparatus according to any of claims 5 to 10 in which the retractable second part is 37 tiltable with respect to the first part and comprises a stop member for engaging with the 38 first part (or vice versa) to prevent tilting beyond a limited predetermined angle.1

12. An apparatus according to any of claims 5 to 11 in which the first part is U-shaped in 2 cross-section when viewed from above, having an opening on at least one side.4

13. An apparatus according to any of claims 5 to 12 in which the second part is sized and shaped to close the opening when the second part is in its lowered position with respect 6 to the first part so that the guide compartment is generally physically isolated from the 7 remainder of internal volume of the tank but is in fluid communication with it.9

14. An apparatus according to any one of claims 1 3, or 4, in which where the guard compartment is fixedly mounted to a moveable mount, the moveable mount comprising 11 a heating element head, optionally wherein the guard compartment is mounted to the 12 element head via a connector, and wherein the guard compartment is moveable in at 13 least a vertical direction with respect to the sensor module.

15. An apparatus according to any one preceding claim, in which the sensor module 16 comprises a sensing portion and a mounting block, optionally wherein the mounting 17 block and at least part of the guard compartment are correspondingly sized and shaped 18 to fit together with limited relative movement.

16. An apparatus according to any preceding claim, in which the guard compartment 21 comprises, or further comprises, an array of spaced apart elongate guard elements 22 and/or a guard wall arranged within the tank, the array of guard elements and/or guard 23 wall separating a section of the tank, within which the sensor module is mounted, from 24 a main volume of the tank.26

17. An apparatus according to claim 16, in which the array of guard elements and/or guard 27 wall is/are pivotable about a horizontal axis to a retracted position vertically above and 28 at least partially over the tank, opening the compartment.

18. An apparatus according to claim 16 or 17, in which the array of guard elements is an 31 array of heating elements.33

19. An apparatus according to any preceding claim, in which the control module is 34 configured to shut-off the heater upon receipt of the alarm condition signal associated with the capacitive sensing element.37

20. An apparatus according to any preceding claim, in which the control module is 38 configured to provide an alarm upon receipt of the alarm condition signal associated 39 with the capacitive sensor element.1

21. An apparatus according to any preceding claim, in which the sensor module comprises 2 an elongate sensing portion, and the sensing portion comprises a first capacitive 3 sensing element at a first height, in use, and a second capacitive sensing element at a 4 second height below the first height, the first and second capacitive sensing elements being operative independently.7

22. An apparatus according to claim 21, in which the first capacitive sensing element is 8 operative to detect a first low level of liquid and trigger the evaluation module to send 9 a first alarm condition signal to the control module, and upon receipt of which, the control module is operative to indicate the tank requires refilling.12

23. An apparatus according to claim 21 or 22, in which the second capacitive sensing 13 element is operative to detect a second low level of liquid and trigger the evaluation 14 unit to send a second alarm condition signal to the control module, and upon receipt of which, the control module is operative to switch off the heater.17

24. An apparatus according to any preceding claim, in which the apparatus is a deep fat 18 fryer or other cooking appliance.

25. An apparatus according to any preceding claim, in which the guard compartment 21 comprises a sloping roof.23

26. An apparatus according to any one preceding claim, wherein the apparatus is a gas- 24 powered deep fat fryer and the heater comprises one or more gas burners.26

27. An apparatus according to any one of claims 1 to 25 wherein, the apparatus is an 27 electrically-powered deep fat fryer and the heater comprises one or more electrical 28 heating elements.

28. A method of operating an apparatus according to any preceding claim comprising one 31 or more of the following steps: 32 a) heating liquid in the tank; and/or, 33 b) cooking food in the liquid in the tank; and/or, 34 c) opening the guard compartment to clean the sensor module; and/or d) temporarily locking the guard compartment above and at least partially over 36 a cooking portion of the internal volume of the tank and/or temporarily locking 37 the reciprocating upper part of the guard compartment in a fixed position above 38 the first part exposing the opening and providing access to the sensor module 39 located within the first part.41

29. A method according to claim 28, comprising one or more of the following steps: 1 t) operating a capacitive sensing element to detect a level of liquid and 2 triggering the evaluation module to send an alarm condition signal to the control 3 module to illuminate and/or sound an alarm, and/or to shut off the heater; 4 and/or, h) operating a capacitive sensing element to detect a level of liquid and 6 triggering the evaluation module to send an alarm condition signal to the control 7 module to illuminate and/or sound an alarm, and/or to re-fill the tank; and/or, 8 i) providing a sensing portion comprising a first capacitive sensing element at 9 a first height, in use, and a second capacitive sensing element at a second height below the first height, the first and second capacitive sensing elements 11 being operative independently, and operating the first capacitive sensing 12 element to detect a first low level of liquid and to trigger the evaluation module 13 to send a first alarm condition signal to the control module to refill the tank, and 14 operating the second capacitive sensing element to detect a second low level of liquid and trigger the evaluation unit to send a second alarm condition signal 16 to the control module to shut off the heater.18

30. A kit of parts comprising an apparatus for heating liquid in a tank, comprising: 19 a tank having an internal volume for retaining a liquid; a heater; 21 and a control module for controlling the heater; 22 the kit of parts comprising: 23 a sensor module comprising at least one capacitive sensing element operative 24 to detect a level of liquid; an evaluation module for evaluating a signal from the at least one capacitive 26 sensing element to determine the presence of liquid and configured to send an 27 alarm condition signal to the control module if liquid is not present in use; and 28 a guard compartment mountable within the internal volume of the tank or 29 mountable with the sensor module to a moveable mount, such that when mounted to a moveable mount, the guard compartment and sensor module 31 can be deployed into and out of the tank, 32 wherein when the sensor module and guard compartment are in the tank they 33 are in fluid communication with a remaining volume of the tank.

31. A kit of parts for fitting to an apparatus for heating liquid, the apparatus comprising: 36 a tank having an internal volume for retaining a liquid; 37 a heater; and 38 a control module, 39 and the kit of parts comprising a sensor module comprising: at least one capacitive sensing element operative to detect a level of liquid; 1 an evaluation module for evaluating a signal from the at least one capacitive 2 sensing element to determine the presence of liquid and configured to 3 generate an alarm condition signal if liquid is not present; 4 a guard compartment mountable within the internal volume of the tank, or mountable to a moveable mount, such when mounted to the moveable mount, 6 the guard compartment can be deployed into and out of the tank, 7 and wherein, when the sensor module and guard compartment are in the tank they are in 8 fluid communication with a remaining volume of the tank.