AU2007314163B2

AU2007314163B2 - Electric heating appliance with data display

Info

Publication number: AU2007314163B2
Application number: AU2007314163A
Authority: AU
Inventors: Raymond George Corkin
Original assignee: Newell Australia Pty Ltd
Current assignee: Newell Australia Pty Ltd
Priority date: 2006-11-01
Filing date: 2007-11-01
Publication date: 2014-04-03
Anticipated expiration: 2027-11-01
Also published as: WO2008052276A1; AU2007314163A1

Abstract

A method is described for predicting the time required for material held in a heating vessel (10) to reach a temperature threshold. A temperature sensor (28) generates (step 101) a temperature signal related to a temperature of the material. A rate of change of the temperature signal is determined (step 105) with a heating element (22) applying heat to the material. Based on the determined rate of change, a time remaining until the temperature signal reaches the temperature threshold is determined (step 107), and the predicted time is displayed (step 109).

Description

WO 2008/052276 PCT/AU2007/001673 1 Electric heating appliance with data display Field of the invention The present invention relates to heating vessels which include a temperature sensor and a display for displaying information relating to the operation of the heating vessel. 5 Background of the invention Heating vessels (such as kettles, percolators, mocha makers, rice cookers, slow cookers and electric fry ware) are commonly used to prepare food and drinks. These heating vessels often include an electric heating element which heats a contact plate via a heat distribution plate. 10 Normally the heating vessel has a temperature sensor to sense the temperature of the vessel's contents. The temperature detected is used to control the operation of the heating vessel. For instance, a kettle has a temperature sensor to detect when water in the kettle is boiling. In the case of a kettle, the temperature sensor is often a mechanical sensor such as a snap-action bimetallic actuator which turns the kettle off once the 15 water has boiled. Reference to any background art in the specification is not an acknowledgement or any form of suggestion that this background art forms part of the common general knowledge in Australia or any other jurisdiction or that this background art could reasonably be expected to be ascertained, understood and regarded as relevant by a 20 person skilled in the art. Summary of the invention It is an object of the present invention to provide a user of a heating vessel with an estimate of the time remaining for the contents of the vessel to reach a temperature threshold.

2 According to one aspect of the present invention there is provided a heating vessel for heating water located in a heating chamber of the heating vessel comprising: a contact plate having a contact surface configured to be in direct thermal communication with the contents located in the heating chamber of the vessel; 5 means for applying heat to material held in the heating vessel, said means for applying heat comprising: a heat distribution plate in thermal communication with the contact plate, the heat distribution plate defining a void that provides a thermally insulating zone; and a heating element in thermal communication with the heat distribution plate; 10 means for generating a temperature signal related to a temperature of the material, said means comprising: an electronic temperature sensor located in the thermally insulating zone, in thermal communication with the contact plate, the electronic temperature sensor being thermally insulated from the heat distribution plate by the thermally insulating zone; 15 means for determining a rate of change of the temperature signal; means for predicting, based on the rate of change, a time remaining until the temperature signal reaches a temperature threshold; and means for displaying the predicted time. According to a further aspect of the invention there is provided a method of 20 predicting the time required for material held in the heating vessel as described above to reach a temperature threshold, the method comprising: generating a temperature signal related to a temperature of the material; determining a rate of change of the temperature signal with a heating element applying heat to the material; 2A predicting, based on the determined rate of change, a time remaining until the temperature signal reaches the temperature threshold; and displaying the predicted time. Also described herein is a heating vessel comprising 5 means for applying heat to material held in the heating vessel; means for generating a temperature signal related to a temperature of the material; means for determining a rate of change of the temperature signal; means for predicting, based on the rate of change, a time remaining until 10 the temperature signal reaches a temperature threshold; and means for displaying the predicted time. Also described herein is a heating vessel comprising: a heater operable to apply heat to material held in the heating vessel; WO 2008/052276 PCT/AU2007/001673 3 a temperature sensor that generates a temperature signal related to a temperature of the material; a processor arranged to determine a rate of increase in the temperature signal with the heater applying heat and to predict, based on the determined rate, a time 5 remaining until the temperature reaches a threshold; and a display operable to display the predicted time. Brief description of the drawings An embodiment of the invention is now described with reference to the drawings, in which: 10 Figure 1 is a cross-sectional view of an electric kettle; Figure 2 is a partially cut-away view of a heater assembly for the kettle of Figure 1; Figure 3 shows more detail of the heater assembly of Figure 2 including an electronic temperature sensor and heat source controller; Figure 4 shows a cross-sectional view of part of the heater assembly; 15 Figure 5 is a flow diagram of a method for controlling the operation of the kettle, including displaying a predicted time remaining until a temperature threshold is reached; Figure 6 is a flow diagram of a method of generating a load signal and selecting a temperature threshold; Figure 7A illustrates an example of heating element voltage versus time in the method 20 of Figure 5; Figures 7B to 7H illustrate the data displayed on the kettle during the example of Figure 7A; and WO 2008/052276 PCT/AU2007/001673 4 Figure 8 is a plot of temperature versus time illustrating operation of the kettle of Figure 1. Detailed description of the embodiments Heating vessels (such as kettles and percolators) are in common use and are often 5 used to bring liquid contents to the boil or some other desired temperature. The rate of heating depends on factors such as the initial temperature of the liquid contents and the volume of liquid present in the vessel relative to the power available to heat. The arrangements described herein include a data display that provides an estimate of the time required for the contents of the heating vessel to reach a specified temperature, 10 such as the boiling point of water. The described embodiment relates to a kettle, but it will be appreciated that similar arrangements may be used in other heating vessels. Description of kettle with temperature sensor Figure 1 shows a cross-sectional view of an electric kettle 10. The electric kettle has a heating chamber 12, which holds the water to be boiled. The water may be poured into 15 the heating chamber 12 of the kettle through the pouring spout 14. The base wall of the heating chamber 12 is defined by a contact plate 16. Water stored in the heating chamber 12 is in direct contact with one side of the contact plate 16. The contact plate 16 is formed from stainless steel. Other materials which are suitable for contacting water and are resistant to high temperatures and oxidation may be used. 20 The contact plate 16 forms part of a heater assembly 18. The heater assembly is generally located underneath the internal chamber 12 on the opposite side of the contact plate to- the heating chamber 12. One embodiment of the heater assembly 18 is shown in greater detail in Figures 2 to 4. The heater assembly 18 is powered by a power source (not shown) which is external to the kettle 10. The power may be 25 transmitted to the heater assembly 18 using known techniques, for instance through a plug-in electrical lead. The heat used to boil the water is generated by a heating element 20, which terminates in cold tails carrying electrical connections 22. Preferably the heating element 20 is WO 2008/052276 PCT/AU2007/001673 5 powered by electricity. The heating element 22 shown is a resistance element. Other types of heating elements may be used. The heating element 20 is bonded to a heat distribution plate 24. The bonding achieves a good thermal coupling between the heating element 20 and the heat distribution plate 5 24 so that heat generated by the heating element 20 is rapidly and efficiently transferred to the heat distribution plate 24. Many known bonding techniques are suitable including induction welding, flame or oven welding and impact welding. Alternatively the heating element 20 may be mounted to the heat distribution plate 24 using other known techniques, such as mechanical fasteners. 10 The heat distribution plate 24 is induction brazed to the contact plate 16 so there is a good thermal coupling between the heat distribution plate 24 and the contact plate 16. Many other known bonding techniques are suitable, including the bonding techniques mentioned above. Alternatively the heat distribution plate 24 may be mounted to the contact plate 16 using other known techniques, such as mechanical fasteners. 15 The heat distribution plate 24 is formed from aluminium, which is a good thermal conductor, and is of sufficient thickness so that heat is evenly distributed over the contact plate 16. Alternative materials for the heat distribution plate 24 include other metals and metal alloys. The heat distribution plate 24 is generally thicker than the contact plate and formed from a material which is a better thermal conductor than the 20 contact plate 16. The heat distribution plate 24 defines a void 26 in the vicinity of the cold tails 22. The void 26 forms a thermally insulating zone. This is because heat which is transmitted from the heating element 20 to the heat distribution plate 24 is not as readily transmitted across the void 26. The region of the contact plate 16 located in the void 26 does not 25 conduct significant amounts of heat when compared to the aluminium heat distribution plate because the contact plate 16 is thin and formed from stainless steel, which is not as good a thermal conductor.

WO 2008/052276 PCT/AU2007/001673 6 Mounted in the void 26 is an electronic temperature sensor 28. The void 26 provides a thermally insulating zone around the electronic temperature sensor 28. Heat from the heat distribution plate 24 is not readily transmitted to the electronic temperature sensor 28. As a result, the electronic temperature sensor 28 is thermally insulated and is not 5 undesirably influenced by the temperature of the heating element 20 and heat distribution plate 24. Preferably the thermally insulating zone and the temperature sensor 28 are located between the cold tails 22 of the heating element 20. The cold tails do not generate significant amounts of heat, so the electronic temperature sensor 28 is further insulated 10 from the heat generated by the heating element 20. Instead of being empty, the void 26 may be filled, either partially or wholly, with an insulating material, such as silicone or rubber. The temperature sensor 28 is mounted in close proximity to the contact plate 16. Optionally, the temperature sensor 28 may be touching the contact plate 16. This 15 improves the thermal coupling between the electronic temperature sensor 28 and the contact plate 16. The thermal coupling may be further improved using known techniques, such as applying a heat transfer paste. It is an advantage that the temperature sensor 28 is in thermal contact with the contact plate 16 in the region indicated by 29. When water contained in the heating chamber 12 20 of the kettle 10 heats up, the contact plate 16 will heat to a similar temperature. Due to the void 26, the region of the contact plate 16 located within the void is insulated from the heat distribution plate 24 and will more accurately reflect the temperature of the water. Since the temperature sensor 28 is in thermal communication with the contact plate 16, it senses the water temperature with greater accuracy and responsiveness. 25 Thus, the temperature measured by temperature sensor 28 is related to the temperature of the material in the chamber 12. Figures 2 to 4 show the temperature sensor 28 being supported by a sensor support 30. The sensor support 30 is formed from silicone, and is held in place by a bracket 32. Other insulating materials are also suitable. The bracket 32 is mechanically fastened to WO 2008/052276 PCT/AU2007/001673 7 the heat distribution plate 24. The bracket 32 is preferably formed from a relatively rigid material, such as a plastic, metal or metal alloy. The bracket 32 locates the sensor support 30 in the centre of the void 26 so the sensor 28 is insulated and may press the sensor support 30 against the contact plate 16, providing a good thermal connection 5 between the sensor 28 and the contact plate 16. The temperature sensor 28 may be mounted in a number of ways which aim to minimise the influence of heat from the heat distribution plate 24. The temperature sensor 28 is typically a thermistor. NTC thermistors formed from metal oxides are suitable. A thermistor has a number of advantages over other types of 10 temperature sensors. A thermistor senses the temperature of water in the kettle within a continuous range. This provides significantly more information on the temperature of the water than, for example, a bimetallic actuator. A bimetallic actuator is typically activated only when the water reaches a threshold temperature value and is deactivated when the water fall below a threshold temperature value. As a result, a bimetallic actuator only 15 senses whether the water temperature is above or below a threshold value. The thermistor provides responsive and accurate readings because it is mounted in a thermally insulating zone in direct thermal communication with the contact plate16. The heater assembly 18 shown in Figures 2 to 4 has a single void 26 in which the temperature sensor 28 is located. It is also possible to have multiple voids around the 20 temperature sensor. Each void forms a thermally insulating region. By positioning a number of the thermally insulating regions around the sensor 28, a thermally insulating zone is formed. The sensor 28 is still mounted in direct thermal contact with the contact plate 16. The contact plate 16 shown in Figures 2 to 4 is free of indentations, and in one 25 arrangement is uniplanar. This shape improves the accuracy of the temperature sensor 28. Because the contact plate 16 is free of indentations, water contained in the heating chamber 12 of the kettle 10 is able to readily and rapidly mix. This means the temperature of water located immediately above the temperature sensor 28 is more likely to accurately reflect the temperature of the remaining water volume contained in 30 the kettle 10. Consequently the temperature sensor 28 gives more accurate readings of WO 2008/052276 PCT/AU2007/001673 8 the temperature of all of the water in the kettle 10. Other configurations of contact plate 16 may also be used. For example, the contact plate may be concave or convex, or may include a dome-shaped protrusion in the vicinity of the temperature sensor 28. Heat source controller 5 Referring again to Figures 2 to 4, the heater assembly 18 has a heat source controller 34. The heat source controller is electronically connected to the temperature sensor 28 and the heating element 20. The heat source controller 34 controls the operation of the heating element 20 with reference to the temperature sensed by the temperature sensor 28. Preferably, the controller 34 is made up of an electronic circuit or number of 10 electronic circuits including a microprocessor. These circuits may be designed in a number of ways to provide the functionality described below. The heat source controller 34 may have a number of different functions, such as a boil function and a keep warm function, which use feedback from the temperature sensor 28. 15 The functions of the kettle 10 may be operated by a button arrangement, for example one or more momentary push buttons. The one or more buttons are connected to, and provide input to, the controller 34. When a start button is activated, the controller 34 enters a boil mode. The boil mode is graphically displayed in Figure 8. Before activation, the controller 34 is in a standby 20 mode (indicated by "Area 1" in Figure 8). After activation, the controller 34 enters the boiling mode (indicated by "Area 2" in Figure 8). When in the boiling mode, the controller 34 turns on the heating element 20 and begins to heat the water in the kettle. The controller 34 may in addition cause an illuminated ring to produce, for example, red light, to indicate the controller is in the boiling mode and the water is being boiled. 25 The temperature sensor 28 detects when an upper boiling limit has been reached. The upper boiling limit may be 97 0 C, though other limits may be used. At this point the controller enters a boiled mode (indicated by "Area 3" in Figure 8). In the boiled mode, the controller turns off the heating element 20 and the red light in the illuminated ring.

WO 2008/052276 PCT/AU2007/001673 9 The controller may then turn on, for example, a green light to indicate that the water is boiled. In the boiled mode, the temperature sensor 28 continues to sense the temperature of the water. After the heating element 20 is turned off, the water slowly cools. Once the 5 temperature of the water falls to a lower boiling limit, the controller ends the boiled mode and returns to standby mode (indicated by "Area 4" in Figure 8). At this stage, the controller may turn off the green light to indicate the water is no longer at or near boiling temperature. A suitable lower boiling limit is 920C, though other limits may also be used. Display 10 The kettle 10 has a display for presenting data to a user. In one arrangement the display is a liquid crystal screen that may display three or more lines of alphanumeric text. Other types of display may also be used, including a display using light-emitting diodes (LEDs). The display is driven by the controller 34 and may be used to display information relating to the measured temperature and the current state of the kettle 10. 15 As described below, the display may be used to indicate the expected time remaining until the water in the kettle boils. In one arrangement the display has three lines of text. The first line shows the temperature measured by the temperature sensor 28. The second line indicates a state of the kettle, for example "Standby", "Boiling" or "Boiled". The third line shows the 20 estimated time until the water in the kettle boils. Predicting the time to boil Figure 5 illustrates a method 100 for predicting the time required to boil the water in the kettle. The method 100 may be used with the kettle 10, but may also be used with other heating vessels having a temperature measurement and a controller for predicting a 25 time required to reach a temperature threshold. In step 101 the temperature sensor 28 generates an electric signal indicative of an initial temperature of water in the kettle. The signal is provided to the controller 34.

WO 2008/052276 PCT/AU2007/001673 10 In step 103 a user presses the start button of the kettle 10. In response to this action, the controller 34 switches on the heating element 20. In step 105 the controller 34 monitors the output of the temperature sensor 28 and determines the rate at which the measured temperature increases. In one arrangement the rate determination may be 5 performed by code executed by the microprocessor. Alternatively, the rate may be determined by dedicated circuitry in the controller 34 that, for example, generates a derivative of the output of the temperature sensor 28. To improve accuracy, the controller 34 may determine an averaged rate of temperature increase rather than an instantaneous rate. For example, the controller 34 may wait for 10 a preset time after the heating element 20 is switched on before providing a measurement of the rate of increase of temperature. In one arrangement the controller waits for 10 seconds and then emits a rate measurement calculated as: Rate = (T 10 -To)/10 (Equation 1) where T 10 is the measured temperature after 10 seconds and To is the initial 15 temperature. The determined rate is thus the average rise over 10 seconds. If the initial temperature is high, for example over 900C, the controller 34 may wait for a shorter time, for example 5 seconds, before providing the rate measurement. Other techniques of averaging the rate of temperature increase may also be used. Once the controller has started outputting the rate of temperature increase, a rolling average 20 of the rate may be produced. During the initial period after the heating element is switched on, the display may indicate that the controller is busy calculating. For example, the word "Calculating" may appear on the display. Once the measured rate of temperature increase is available, in step 107 the controller 25 uses the measured rate to predict how long it will take the measured temperature to reach a temperature threshold Tthresh. In the preferred embodiment the threshold is a WO 2008/052276 PCT/AU2007/001673 11 temperature value that corresponds to the water boiling. The predicted time may be calculated using a linear extrapolation of the rate determined in equation 1: (Time remaining) = (Tthresh-T)/Rate (Equation 2) where T is the current temperature and Tthresh is the specified threshold temperature. 5 In step 109 the time remaining is displayed. The controller 34 includes a clock, enabling the displayed time to be shown in a count-down manner. The displayed time thus diminishes from the value calculated in equation 2 towards zero. In step 111 the controller 34 checks whether the current temperature has reached Tthresh. If this is the case (the Yes option of step 111) then in step 113 the controller 34 10 switches off the heating element 20 and clears the display of the remaining time. Preferably, the controller 34 continues to monitor the rate of temperature increase, as this enables the time prediction to be updated. For example, if water is added to the kettle 10 the current temperature can change, affecting the time required to reach Tthresh. If the controller 34 determines that the current temperature has not been reached 15 (the No option of step 111), control flow returns to step 105 to obtain an updated value for the rate of temperature increase. The updated rate is then used in step 109 to revise the time prediction using equation 2. The updated value of the rate is preferably an averaged value, for example the average increase in the previous 5 or 10 second interval. 20 If the revised time prediction differs from the currently displayed value of time remaining, the displayed value changes. For example, if water is added to the kettle 10, the displayed 'time until boiling' increases. The method 100 may also include safety checks. For example, if the rate of temperature increase determined in step 105 is greater than or equal to a specified upper value, the 25 controller may act to cut off the heating element. This condition may arise if the kettle is empty or if the contents have boiled away.

WO 2008/052276 PCT/AU2007/001673 12 Reheating In a further arrangement, as illustrated in steps 115 and 117 of Figure 5, the controller 34 determines a pulsed mode of operation for the heating element 20 that would reheat the water in the kettle to the threshold temperature. 5 In step 115 the controller 34 monitors the output of the temperature sensor 28 and determines a rate of temperature decrease after the heat element 20 has been switched off. Then, in step 117 the controller 34 determines a pulsed cycle of operation for the heating element 20 that, if applied, would return the contents of the kettle to the threshold temperature. 10 Setting the threshold temperature based on the load In one arrangement the kettle 10 may have two or more heating modes dependent on the load, i.e. the amount of liquid in the kettle. Low volumes of liquid heat up more rapidly than larger volumes. The rate of change of temperature measured in step 105 thus provides an indication of the load of the kettle. The controller 34 may select a 15 temperature threshold based on the rate of change. If low volumes are deduced (i.e. the rate of change of temperature lies in a specified higher range), then the heating element 20 is switched off at a reduced threshold. In the boiling mode, a reduced threshold for boiling of 930C is suitable, although other values may be used. If the controller 34 deduces that higher volumes of liquid are present (i.e. the rate of 20 change of temperature lies in a specified lower range), the heating element 20 is switched off at a higher threshold, for example 97*C. The controller 34 monitors the rate of change of measured temperature on a regular basis and, if necessary, changes the temperature threshold based on the current rate of change. Thus, for example, if cold water is added to the kettle 10, the controller 34 may 25 need to switch to a heating mode that uses a higher temperature threshold. Two or more heating modes may be established. The controller 34 may have a look-up table that lists suitable thresholds corresponding to different rates of heating.

WO 2008/052276 PCT/AU2007/001673 13 In alternative arrangements the load may be inferred from measurements other than the rate of change of temperature. Such alternative load measurements include the level of liquid in the kettle or the weight of the kettle. For example, a reed switch or capacitive sensor may be used to indicate the level in the kettle. In such an arrangement, the 5 controller 34 may select a higher or lower threshold dependent on whether the level of fluid is above or below a threshold value. Figure 6 illustrates a method 200 of selecting the temperature threshold. In step 201 the temperature sensor 28 generates a temperature signal that is related to the temperature of the water in the kettle 10. In step 203 a load signal is generated that is related to the 10 amount of liquid in the kettle. In the preferred arrangement the load signal corresponds to the rate of temperature change determined by the controller 34 in step 105. Based on the load signal, in step 205 the controller 34 selects a temperature threshold value. The threshold value may be read from a look-up table stored in memory or data storage of the controller 34. The selected value is used in step 107 to predict the time required for 15 the water in the kettle to reach the threshold. Example An example of the method 100 in use is shown in Figures 7A to 7H. Figure 7A is a graph of the heating element voltage versus time. Reference numerals 301-307 indicate points on the graph, and Figures 7B to 7H show the data that is displayed on the kettle 20 display at the respective points. Initially the kettle is in standby mode and at point 301 the display indicates a measured temperature of 22 'C and a state of "Standby". The voltage across the heating element 20 is 0 V. Then the kettle is switched on, for example by a user pressing the "boil" button. At point 302 the heating element 20 is switched on and the display indicates that 25 the kettle is in the "Boiling" state. As displayed, the temperature is still 22 OC. As the controller has not yet predicted a time until boiling, the display shows that the controller 34 is calculating.

WO 2008/052276 PCT/AU2007/001673 14 After a set time (for example 10 seconds or 5 seconds), the voltage across the heating element 20 is switched off. As shown at point 303 the temperature has risen to 25 C, and the display still indicates that the controller 34 is calculating. At point 304 the display shows a predicted time of 4 minutes 7 seconds until the kettle reaches the 5 specified threshold temperature, which in the example is 97 'C. As described above, the controller 34 may select a different threshold temperature if the rate of temperature increase is higher. The time shown on the display decreases and at point 305 the predicted time until boiling is 2 minutes 3 seconds. As seen in Figure 7F, the measured temperature has 10 reached 62 C. At point 306 the measured temperature reaches the designated threshold temperature of 97 'C and, as seen in Figure 7G, the display shows that the kettle 10 is in a "Boiled" state and has returned to standby, with the heating element switched off. The temperature gradually cools and at point 307 the temperature has dropped to 96 C. 15 Once the temperature is below the lower limit (e.g. 92 C), the display no longer shows the "Boiled" indication. Many alternative embodiments of the present invention are possible without departing from the principles of the present invention. For instance, different configurations of kettle and different temperature sensors may be used. Different displays may be used 20 to indicate the predicted time. For example, rather than (or in addition to) using an alphanumeric display, a graphic display may be used. A bar graph may indicate the overall time to reach the threshold, overlaid with a second bar graph indicating what proportion of the total time has elapsed. If the predicted overall time changes, the proportion indicated by the second bar graph is adjusted accordingly. Other graphic 25 objects may also be used, for example a circle indicating the predicted overall time with an incrementing pie-segment showing the proportion of time that has elapsed. The principles of the present invention may be applied to other types of heating vessels, such as percolators, mocha makers, rice cookers, slow cookers and electric fry ware. In each case, the vessel has an electronic sensor that provides an indication of the WO 2008/052276 PCT/AU2007/001673 15 temperature of the vessel contents. The vessel also has a controller for predicting how long it will take for the contents of the vessel to reach a specified temperature and a display for displaying the predicted time. It will be understood that the invention disclosed and defined in this specification 5 extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention. The term "comprises" (or its grammatical variants) is used in this specification as equivalent to the term "includes" and neither term should be taken as excluding the 10 presence of other elements or features.

Claims

1. A heating vessel for heating water located in a heating chamber of the heating vessel comprising: 5 a contact plate having a contact surface configured to be in direct thermal communication with the contents located in the heating chamber of the vessel; means for applying heat to material held in the heating vessel, said means for applying heat comprising: a heat distribution plate in thermal communication with the contact 10 plate, the heat distribution plate defining a void that provides a thermally insulating zone; and a heating element in thermal communication with the heat distribution plate; means for generating a temperature signal related to a temperature of the 15 material, said means comprising: an electronic temperature sensor located in the thermally insulating zone, in thermal communication with the contact plate, the electronic temperature sensor being thermally insulated from the heat distribution plate by the thermally insulating zone; 20 means for determining a rate of change of the temperature signal; means for predicting, based on the rate of change, a time remaining until the temperature signal reaches a temperature threshold; and means for displaying the predicted time. 17

2. A heating vessel as claimed in claim 1, further comprising: means for generating a load signal related to an amount of the material in the heating vessel.

3 A heating vessel as claimed in claim 2 wherein the load signal is 5 dependent on the determined rate of change.

4. A heating vessel as claimed in claim 2 or claim 3 further comprising: means for selecting the threshold temperature based on the load signal.

5. A heating vessel as claimed in claim 4, further comprising: means for storing a predefined set of threshold temperatures, wherein the 10 means for selecting selects the threshold temperature from the predefined set.

6. A method of predicting the time required for material held in the heating vessel according to any one of claims 1-5 to reach a temperature threshold, the method comprising: generating a temperature signal related to a temperature of the material; 15 determining a rate of change of the temperature signal with a heating element applying heat to the material; predicting, based on the determined rate of change, a time remaining until the temperature signal reaches the temperature threshold; and displaying the predicted time. 20

7. A method as claimed in claim 6 wherein the determining, predicting and displaying steps are repeatedly executed. 18

8. A method as claimed in claim 6 or 7 wherein the predicting step uses a linear extrapolation of the determined rate of change to predict the time remaining.

9. A method as claimed in any one claims 6-8 further comprising: generating a load signal related to an amount of the material in the vessel; and 5 selecting the temperature threshold based on the load signal.

10. A method as claimed in claim 9 wherein the load signal is the determined rate of change of the temperature signal.

11. A method as claimed in claim 9 or 10 wherein the selecting step selects the temperature threshold from a predetermined set of thresholds. 10

12. A method as claimed in any one of claims 6-11 wherein the step of determining a rate of change determines an average rate of change of temperature over a predefined period.

13. A method as claimed in any one of claims 6-12 wherein said determining step waits for a specified delay time after the heating element commences applying 15 heat to the material before determining the rate of change.

14. A method as claimed in claim 13 wherein the specified delay is dependent on an initial temperature at or before an initial time the heating element commences applying heat.

15. A method as claimed in any one of claims 6-14 comprising: 20 generating an alarm output if the determined rate of change is greater than or equal to a specified upper threshold.

16. A method as claimed in any one of claims 6-15 wherein said displaying step comprises: 19 displaying a first graphic object representative of a predicted overall time for the material to reach the temperature threshold; and displaying a second graphic object representative of a proportion of the predicted overall time that has elapsed. 5

17. A method as claimed in any one of claims 6-16 wherein said displaying step displays a count-down timer.

18. A method of predicting the time required for material held in a heating vessel to reach a temperature threshold substantially as described herein with reference to Figures 5 to 7H. 10

19. A heating vessel substantially as described herein with reference to the accompanying drawings