FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
& The Patent Rules, 2003
COMPLETE SPECIFICATION
1. TITLE OF THE INVENTION:
ELECTRICAL APPLIANCES AND COMPONENTS
2. APPLICANT:
Name: Otter Controls Limited
Nationality: UK
Address: Tongue Lane Industrial Estate, Dew Pond Lane, Fairfield BUXTON,
Derbyshire SK17 7LF, United Kingdom.
3. PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the invention and the manner in which it is to be performed:

Field of the Invention
The present invention relates to electrical appliances, particularly domestic appliances such as
liquid heaters and'or stirrers, and components therefor, particularly, although not exclusively,
to healing elements, to a thermal control for controlling the heating element, to a control
method for the control and to a computer program product for implementing the control
method.
Background to the Invention
Thick film heating elements generally comprise one or more heating tracks that are printed as aii ink or paste onto an insulating substrate and fined to.form tracks of high electrical resistivity. Connecting tracks may be printed in a separate layer. and fixed to form connecting tracks of low resistivity. The insulating substrate may be of an electrically insulating material, such as ceramic, or may be metallic with an insulating surface layer. Such thick film elements are typically used in liquid heating vessels, flow-Through healers, electric irons and other domestic appliances. In liquid heating vessels, the substrate is typically a substantially flat steel plate that forms the bottom of a liquid reservoir, with the tracks deposited on the underside, to form an underfloor heating element.
Heating elements usually require some form of clement prelection, arranged to disconnect the heating current when the element begins to overheat, In thick film elements, protection may be provided by a mechanical thermostat such as a bimetal in thermal contact with the element. However,, in many applications it is preferable to integrate the element protection within the thick film element. An example of this approach is the 'E-fusf (RTM) element protection disclosed for example in WO 20Q6/083162 AL in which the thick film element in deposited on a dielectric comprising first and second dielectric layers with an electrically conductive layer in between. When the element overheats, a leakage current Is detected between the thick film element and the electrically conductive layer, in response to which the hearing current is disconnected. The 'E-fast1 clement protection has proved successful, hut for some applications there is a need for a lower-cost solution.
Patent publication EP-A-286 215 discloses a thick film heater for a hob, including a thick film temperature sensor track of high temperature coefficient. The heating track and the sensor track may be manufactured in the same process. To detect local hot spots, the sensor track may be arranged closely to follow the path of the associated heating track so as to cover a

large area of the substrate,
Patent publication EP-A-485 211 discloses a thick film heater comprising a conductive heating track formed of pure nickel and a resistive track formed of standard thick film resistor material, inteidigjtated with the heating track and acting as a thermistor. The thick film heater may be incorporated m a kettle harving a steam sensor in an upper part of the kettle reservoir.
Patent publication GB-A-2269980 discloses a kettle with a thick film heater element and first and second thick film temperature sensing tracks arranged to detect tilting of the kettle by detecting a difference in resistance between the first and second temperature sensors.
The applicant's patent publication WO 08/012:506 Al discloses a cordless electrical connector having current-carrying components scaled therein, and a washable electrical appliance incorporating such a connector. The applicant's patent publication WO 09/103762 discloses further aspects of a washable electrical appliance.
Patent application number WQ 09/020384 discloses a milk iru thing appliance in which the stiirer part, including the motor: for the stirrer, is positioned within the cover assembly of the appliance. The stirrer/cover assembly is electrically detachable from the appliance heating reservoir,
Heating and/or frothing of milk presents particular problems, although these problems may occur with other liquids having similar properties. These problems include: preventing the liquid to be heated sticking to the reservoir during or after the heating cycle; position and speed of a stirrer for optimum performance; position and temperature: setting of the thermostats within the appliance; thermal mass of the heating element; ability to reset the thermostat so that the appliance can be reused immediately after the milk has been poured from Ihe appliance; how to identity build-up of deposits on a heating element such that the appliance needs to be thoroughly cleaned.
Once milk deposits have stuck or burnt onto a heating element, domestic cleaners such as vinegar or baking soda are no logger effective: such deposits tan be removed wirti industrial cleaning fluids, but these are not suitable for domestic uger for example, US 3755184 discloses a cleaning technique for Teflon using solvents that are now banned frcm use.
The applicant's patent publication WO-A-07/09G63G discloses a heated liquid dispenser, improvements to which are disclosed in the present application.

Statements of the Invention
According to one aspect of the present invention, there is provided a thick film heating clement comprising a substrate having a (hick film tearing track and a temperature sensor comprising a thick film temperature sensing track formed thereon, wherein the temperature sensing track comprises ofleor more first sections of a first material having a high resistivity and/or a high temperature coefficient of resistance, and one or more second sections of a second material having a low resistivity andVor a low temperature coefficient of resistance. According to another aspect of the present invention, there is provided a thick film heating element comprising a substrate having a thick film beating Hack and a temperature sensor comprising a thick film temperature sensing track formed thereon, wherein the heating track comprises at least a pair of substantially parallel heating actions connected at one end, wherein the temperature sensing track extends between said pair of substantially parallel sections and comprises substantially parallel seraor sections connected adjacent said one end-According to another aspect of the present invention, there js provided a thick film heating element comprising a substrate having a thick film beating track and a temperature sensor comprising a thick film temperature sensing track formed thereon, wherein the heating track and the temperature sensing track are formed of the same thick film material,
According to another aspect of the present invention, there is provided a thick film heating element comprising a substrate having a thick film heating track and a steam sensor formed integrally thereon,
In an embodiment of the present invention, there is provided a printed or thick film element having ore or more additional tracks. The additional tracks may be of a PTC (positive temperature coefficient) material. The additional track may be used to monitor lemperature of the element, such as during normal use, to detect overheating such as in a dry boil condition, to monitor scale build up or to identify if the healer is being used to heat liquid other than water. The additional (rack may be arranged to act as a steam sensor by monitoring a localised increase in temperature or by monitoring a localised increase in humidity/moistae. A signal from the additional track may be sensed and enhanced by employing a 'dithering' process to improve the useful temperature measurement resolution.
According to anoth&r aspect of the invention, there is provided a heated liquid dispenser comprising a reservoir, heating means operable to heal the contents of the reservoir, dispensing means for dispensing the contents of the reservoir, and means for stirring the

contents of the reservoir.
According to another aspect of the invention, there is provided a heated liquid dispenser comprising a reservoir, heating means operable to heat the contents of the reservoir, and dispensing means foe dispensing the contents of (he reservoir, wherein the hitting means comprises a heater and a liquid chamber for containing liquid heated by the heater, the liquid chamber being in thermal contact with the reservoir.
According to another aspect of the invention, there is provided a liquid heating appliance comprising a first liqued chamber, electrically powered heating means operable to heat a first liquid within the first chamber, and a second chamber in thermal contact with the first chamber such that a second liquid within the second chamber is heated indirectly by the heating of the first liquid, the appliance including means far introducing steam and/or vapour from the heated Grst liquid from the first chamber into the second chamber so that the steam and/or vapour passes through the second liquid. The second chamber may be located substantially within Lhe first chamber, so as lo enhance the thermal contact therebetween. The second chamber may be removable from within the first chamber.
According to another aspect of the invention there is a liquid heating element plate liavitig a localised heating element arranged in thermal contact therewith through a substrate located between the element plate and the heating element, the substrate being thicker in the vicinity of the heating element so as to distribute heal evenly over the element plate. The substrate may further decrease in thickness towards the centre thereof.
According to another aspect of the present invention, there is provided a liquid heater comprising an element plate for contacting the liquid to be heated, and a localised heating clement arranged in thermal contact with the element plate through a substrate located between the element plate and the heating element, the substrate having a void in the vicinity of the heating element, so as to distribute heat evenly over the element plate.
According to another aspect of the present invention there is provided a liquid heating element plate having a localised heating element airinged in thermal contact therewith through a subslrate located between the. element plate and the heating element, the substrate extending outwardly beyond the element plate so as to distribute heat evenly over the element plate. The outward extension of the substrate may be in the plane of the inner part of the substrate, or may extend out of that plane. The element plate may have a thermally conductive sidewall extending therefrom, and the outward extension of the substrate may be in thermal

contact with the side wall.
According to another aspect of (he present invention, there is provided a liquid heating element plate having a localised heating element arranged in thermal contact; therewith, the localised heating element having an elongate convoluted shape so as to distribute heat evenly over the element plate. There may be provided a second localised heating element located outward of the first localised heating element
According to another aspect of the invention there is provided a liquid heating and alining appliance, comprising a liquid reservoir having a healing element plate in the base thereof and a noiatable stirrer for stirring the liquid within the reservoir, the heating element plate having a sheathed heater thermally coupled thereto, the sheathed heater being substantially concentric with the rotatable stirrer. The stirrer is preferably located above the element plate, with a small clearance therebetween. The stirrer preferably extends directly opposite the sheathed heater. The stirrer preferably extends radially proximate a side wall of the reservoir. The stirrer is preferably mounted above the reservoir and extends downwardly .into the reservoir towards the element plate. The stirrer may be artanged to froth the liquid, for example for creating frothed milk for cappuccino, or simply to stir the liquid during healing, for example for heating milk for latte. The stirrer may include a temperahire sensor such as a thermocouple, for sensing the temperature of the liquid directly; the sensor may be connected through the shaft of the stirrer to a control.
According to another aspect of the invention there is provided a liquid heating and stirring appliance, comprising a liquid reservoir having a heater for healing liquid within the reservoir and a stirrer for stirring the liquid within the reservoir the appliance including a control for actuating the stirrer after the heating of the heater is reduced or switched off. Preferably the control includes a timer for determining a period after the heating for which the stirrer is actuated, or a thermostat for determining when the temperature of the liquid has stabilised after heating.
According to another aspect of the present invention, there is provided a method of detecting deposition of solids in a liquid heater for heating milk or similar liquids by means of a detected temperature, comprising comparing the rate of temperature rise with time after an initial hearing period with a first threshold value and, if the rate of temperature rise exceeds the threshold and the absolute temperature exceeds a second threshold, determining a solid deposition condition.

According to another aspect of the present invention, there is provided a method of detecting deposition of solids, in a liquid heater for heating milk or similar liquids by means of a detected temperature, comprising comparing the rate of temperature rise with time after an initiaj healing period vyith a threshold value and,, if the rate of temperature rise exceeds the threshold, determining a dry boil condition.
According to another aspect of the invention there is provided a liquid heating and stirring appliance, comprising a liqud reservoir having an element plate for heating liquid within the reservoir and a stirrer for stirring the liquid within the reservoir, the appliance including a control for detecting the rate of temperature rise of the element plate during heating, determining that the stirrer is absent or inoperative if the rate of rise exceeds a threshold.
According to another aspect oi the invention there is provided a liquid heating and stirring appliance, comprising a liquid reservoir for heating liquid within the reservoir and a stirrer for stilting-the liquid within the reservoir, the stirrer comprising a stirring element within the reservoir, electromagnetically. coupled to a driving means outside the reservoir. The driving means may comprise an electromagnetic coil,
According to another aspect of the invention there is provided a heated liquid dispenser having a liquid reservoir and a detachable assembly, the assembly being electrically powered by attachment lo the reservoir, the assembly comprising a plurality of discrete electrical functions, for example a stirrer and pumped dispenser,
Brief Description of the Drawings
Specific embodiments of the invention will now be described with reference to the
accompanying drawings, a brief synopsis of which is set out below.
Figure I is a schematic diagram of a kettle incorporating a thick film element plate according to the first or second embodiment of the invention.
Figure 2 is a plan view of a thick film element plate incorporating a temperature sensor in a first embodiment of the invention.
Figure 3 is a plan view of a thick film element plate incorporating a temperature sensor in a second embodiment of the invention.
Figure 4 is a schematic diagram of a kettle incorporating the thick film element plate of the third or fourth embodiment of the invention.
Figure 5 is a plan view of a thick film element plate incorporating a stemm

sensor in a third embodiment of the invention,
Figure 6 is a plan view of a thick film element plate incorporating a steam sensor in n fourth embodiment of the invention.
Figure 7 is a plan view of a capacitative steam sensor in an embodiment of the present invention,
Figure 8 is a circuit diagram of a sensor circuit for uae with the first embodiment of the invention.
Figure 9 is a graph showing digital conversion values of an analog signal, such as generated by the temperature sensor or steam sensor in embodiments of the invention.
Figure 10 is a graph showing digital conversion of an analog signal, such as generated by the temperature sensor or steam sensor in embodiments of the invention, with a moving average of the digital conversion values being taken as a digital measurement signal.
Figure 11 is a graph showing digital conversion of an analog signal, such as generated by the temperature sensor or steam sensor in embodiments of the invention, with an dithering signal being applied thereto before digital conversion, and a moving average of the digital conversion values being taken as a digital measurement signal.
Figure 12 shows a diagrammatic representation of a first prior art example of a heated liquid dispenser.
Figure 13 shows a cut-away of the reservoir and the dispensing means of the example of Figure 12.
Figure 14 shows a second prior art example of a heated Jiquid dispenser.
Figure 15 shows a top view of a suitable heating element temperature contra! for use in the first and second prior art examples.
Figures 16 to 18 show different embodiments of a heated liquid dispenser comprising at least three separate portions.
Figure 19 shows an interchangeable dispensing part for connection to a heating portion.

Figures 20 and 21 show alternative dispensing portions.
Figure 22 shows a reservoir for inverted filling.
Figure 23 shows a heated liquid dispenser with an integral powcTcd stirrer,
Figure 24 sltows a heated liquid dispenser with an integral manual stirrer,
Figure 15 shows a heated liquid dispenser with a refill during assembly, and when assembled.
Figure 26 shows a heated liquid dispenser with a reservoir having an inner and outer chamber.
Figure 27 is a cross-sectiou in the plane A-A of Figure 26,
Figure 28 shows the inner chamber removed from the outer chamber.
Figures 29a to 29c show a schemaiic cross section of a heated reservoir complete with interna] paddie, shaft and bearing case, in respective variants,
Figures 29d, 29e and 29f respectively show isometric views of different paddle options in ftothers in embodiments of die invention.
Figures 29g and 29h show isometric views, from above and below respectively, of a frother in a further embodiment.
Figm-e 29i shows an isometric view of a stirrer in a further embodiment of the invention.
Figure 29j shows an isometric view of a frother in a further embodiment of the invention.
Figure 29k shows an isometric view of a frother in a further embodiment of the invention.
Figures 30a, 30b and 30c show a schematic cross section of a heated reservoir in which the substrate is profiled to distribute the heat in a more uniform maimer, in respeccive variants.
Figures 3 la and 31b show an alternative schematic cross section of a heated reservoir in which die substrate is profiled to distribute heat in a more uniform manner. Figure 31 b includes a thermostat.
Figures 32a and 32b respectively show a schematic cross section of a heated

reservoir in which the substrate is extended outside the circumference of The reservoir, in respective variants.
Figures 33a and 33b show a schematic cross section of a heated reservoir with the thermostat positioned cm the outside perimeter of the reservoir, in respective variants.
Figures 34a, 34b and 34c respectively show alternative embodiments of the heating elements.
Figure 35 shows a schematic cross section of a heated liquid dispensing appliance with a removable electrically operated pump and stirring assembly housed within the lid part of the appliance
Figure 36 shows a schematic cross section of a heated liquid container in which steam generated in a first chamber is forced though the liquid to be heated in a second chamber, in a first embodiment.
Figure 37 Shows a schematic cross section of a heated liquid container in which steam generated in the first chamber passes through the liquid to be heated in the second chamber, in a second embodiment.
Figure 38 is a graph showing resistance of a PTC sensor against time for a normal milk heating cycle with a clean element surface.
Figure 39 is a graph showing resistance of a PTC sensor against time for a dry boil test in which a healer is energised without liquid being present in a reservoir.
Figure 40 is a graph showing resistance of a PTC sensor against time in a test situation in which liquid is allowed to boil dry in the reservoir.
Figure 41 is a graph showing resistance of PTC sensor against time for five consecutive heating cycles in which milk deposits accumulate on a heater.
Figure 42 is a graph showing the first 20 seconds of each cycle of the graph of Figure 41.
Figures 43a and 43b show a flowchart of an algorithm for detecting dry boil and milk bum in a milk frother.
Detailed Description of Embodiments

In the description of the embodiments, similar or analogous parts are identified by the same rcference numerals between the different embodiments,
Liquid Heating Vessel with Thermistor
Figure 3 shows schematically a jug kettle with an electronic control, as an example of a liquid heating vessel to which tin; first and second embodiments of the invention may be applied. In this example, the ketde is a cordless kettle comprising a vessel body 1 and a power base 2 having respective body and base cordless connectors 3 and 4, such as 360° cordless connectors of the type described in patent publication WO-A-94/06185 and/or as sold by Otter Controls Ltd. under the CS4/CS7 (power base socket) and CP7 (appliance plug) references. The power base is conncctabte by a power cord 13 to an electrical power outlet (not shown).
The vessel body 1 comprises a reservoir 5 for containing water to be heated, and a base section 6, as well as a spout 7, a lid & and a handle 9. Water is heated by an element plate 12 forming the hase of the reservoir 5, and including a heating element on the underside (i.e. facing toward s the base section 6) The element plate 12 may be fitted into the vessel body using the Easifix (RTM) fitting as described in WO 99/17645. The element comprises a thick film element. Preferably, the element plate 12 is composed of stainless steel. The element plate may be circular, oval, rectangular oi any shape required to fit the vessel body. The element plate 12 is described in more detail below.
The base section contains an electronic control 10 for controlling the operational state of the vessel, as will be described in more detail below, A user interface 11 allows the user to operate the vessel, and may provide a display of the operational state of the vessel. The control electronics may be divided between the user interface 11 and the control 10 as desired.
A thermistor 14 is arranged to sense the temperature of water in the reservoir 5 through the element plate 12, and is preferably thermally isolated from the heating element. In this example, there is no steani tube to carry steam from the top of the reservoir 5 to the control 10, since boiling is detected from the input of the thermistor 14 rather than by sensing steam, as will be described in more detail below. The thermistor 14 may have a negative temperature coefficient (NTC). In some of the embodiments described below, boiling is detected by means other than temperature sensing, so that Lhe thermistor 14 is not required.
The vessel may have one or more additional features, some of which are described in more details below, However, to avoid repetition, some of these features will be outlined here,

Additional heating features of the vessel uiay include a 'keep warm1 feature, in which the liquid is maintained around a predetermined temperature, preferably after boiling; this may be done by intermittent activation of the main heating element, or by intermittent or continuous activation of a secondaiy heating element. The predetennincJ temperature may be jus! below boiling point or a lower temperature such as 80oC, and may be selectable by the user.
Another heating feature is a sub-boil feature, in which tine liquid is heated up to a predetennined temperature below boiling, such as SOX for making coffee, and the heating power is tlien switched off or reduced, for example to activate a keep warm mode- The predetermined temperature may be selectable by the user.
Another heating feature is a prolonged boil feature, whereby the liquid is heated to boiling and then boiled for at least a prcdetcimined time, such as 30 seconds to 2 minutes, to sterilize the liquid,
The user interlace 11 may comprise a remote control, as described for example in
PCT/GB08/002073.
The element plate 12 may comprise one or more elements coruiectable to a plurality of electrical swkeis, for example as described in PCT/OD0S/00280S,
Thick Film Element Hate
Each of the embodiments described below comprises a thick film element plate 12 for a liquid
heating vessel, comprising a substantially circular steel substrate 21, preferably of stainless steel "flie heating elements in these embodiments are rated at 3.1 kW for a 240 VAC power
supply.
A dielectric layer 22 is deposited on the substrate 21.. Thick film heating track portions 23 of high resistivity material are deposited on the dielectric layef 22, and contacts 24a, 24b of low resistivity material are deposited on the dielectric layer 22 and in electrical contact with the ends of the heating track portions 23. Connecting portions 25 are formed from the same low resistivity material, to connect heating track portions 23 together in series. Bridges 26 of the same low conductivity material may be formed over bends in the heating track portions 23, to avoid overheating. Nest, a protective glaze may be deposited over at least some parts of the clement plate 12. to provide electrical insulation and/or to protect parts from corrosion, External contacts, such as contacts 24a, 24bf 31, 32a and 32b are left unglazsd so as to allow electrical connection thereto.

The theunistor 14 may be mounted irt the central area of the element plate, shown as a central blank area in the drawings, and connected to contacts 31 and 32b. The heating track 23 is designed to make as much use of the area around the outside of the element as possible. The central area is kept free or heating track 23 to reduce direct conduction of heat from the Heating track 23 to the thermistor 14, which therefore tracks the water temperature more accurately.
First Embodiment
In the fust embodiment, a sensor track 30 is deposited on the dielectric 22, Advantageously, the sensor track 30 is deposited at the same time as the heating track 23, i& therefore substantially coplanar with, and forms part of the same layer as the healing track 23. The sensor track 30 is preferably formed from the same resistive track material as the heating track 23: which is generally much cheaper than high resistivity/TCR material (63 pence per gram versus 805 pence per gram at 3 rd December 2008). However this material has a relatively low resistivity (e.g. 20-200 mΩ/squane, for example 100mΩ/square) for the purposes of temperature sensing, and a relatively low temperature coefficient of resistance (TOR), which results in a relatively low .signal strength.
The sensor track 30 is designed to be as long and as thin as possible in order to maximise the resistance and hence the strength of the signal derived from the sensor track 30, such as a voltage signal. Moreover, the sensor track 30 is distributed over the majority of the element plate 12 in order to be able to sense overheating in substantially any area of the element plate 12, and therefore be suitable for detection of spots, boil-dry caused by Lilting, and scale build up. To achieve these advantages, the sensor track 30 extends along gaps between the heating track portions 23 and doubles back on itself, such that the sensor track 30 includes substantially parallel sections connected continuously at their ends by narrow bends of substantially 180o. These ends may be located adjacent to bends in the heating track portions 23.
Sensor contacts 32a, 32b are connected to either end of the sensor track 30, to allow electrical connection of the sensor track 30 to a sensor circuit or to the electronic control 10 for detecting a temperature condition of the element plate 12- Specific embodiments of the sensor circuit and the electronic sensor are described in more detail in the separate sections below,
Second Embodiment
The second embodiment, as shown in Figure 3, differs from the first embodiment in that the

sensor tract 30 includes sensing sections 33 of a high resistivity, high TCR materia]. The resistivity may typically be in the range I-100 Ω/square, for example 10 Ω; square. The TCR may typically be in die range ISOCKSOOO ppm, These sections 33 are connected in series by discrete sections of the sensor teack 30, made of the same material au the healer track 23 as in the first embodiment; this is cheaper than connecting the sensing sections 33 with the low resistivity material from which the contacts 24a, 24b, 31, 32a and 32b are made, which typically contains silver. In addition, the material, having a PTC, will contribute to the change in signal with temperature.
The sensing sections 33 are placed in areas that arc likely to experience a high rate of temperature rise in a dry-boil condition. In addition, they are distributed around the element in order to detect a tilted boil-dry regardless of the direction of tilt.
The sensing sections 33 provide higher signal strength, but are more expensive in both material and labour than the first embodiment, because an additional material is required for the sensing sections 33, The lengths of the sensing sections 33 can be selected to provide the desired trade-off of cost against performance.
Liquid Heating Vessel with Steam Sensor
Figure 4 showns schematically a. jug kettle with an electronic control, as an example of a liquid hearing vessel to which the first and second embodiments of the invention may be applied The kettle is similar to that shown in Figure 1; similar parts are indicated by the same reference numerals, and their description is not repeated here. However, instead of using the thermistor 14 for boil detection, there is provided a steam rube 17 that conveys steam from above the water level to a steam chamber 18 beneath me element plate 12 when the liquid boils, as shown by the clashed line in Figure 4. A steam sensor 40 is provided on the underside of the element plate 12 within rhe steam chamber 18, as described in more detail below. The steam chamber may provide a volume for the containment of steam in the space beneath the element plate 12, and may at least partially segregate the staatrt sensor 40 from, other electrical components, such as the electronic control 10. In this way, damage to other electrical components, caused by ingress of steam, may be prevented or mitigated.
Figure 4 shows the steam sensor 40 formed at the centre of the element plate 12 and the steam tube 17 passing through an aperture at an edge of the element plate 12, This arrangement requires a relatively long steam chamber 18 under the element plate 12 to convey steam to the steam sensor 40, Alternatively, the steam tube 17 could pass through an aperture in the central

part of the element plate 13, adjacent the steam sensor 40, so that less space i.s occupied by the steam chamber 18. Alternatively, the steam sensor 40 could be positioned in any suitable area of the element plate 12 and advantageously may be positioned towards the edge of the element plate 12 for easier access to a steam tube 17 positioned to one side of (he reservoir 5, or outside the reservoir 5.
Third Embodiment
The third embodiment differs from the first embodiment in that a steam sensor 40 is formed Oil the element plate using thick film printing. The steam sensor 40 comprises a long, thin track of higher resistive material, typically in the range 1-tOO H/square, for example 10 El/square. The TCR may typically be in the range 1500-3000 ppm. The track is arranged in a labyrinthine or serpentine arrangement so as to be compressed into a small area. The steam sensor 40 is electrically connected between contacts 31 and 32b. When the liquid boils, steam is directed through Ihc steam tube 17 onto the steam sensor 40, which senses a sudden or step change in local humidity, for example by detecting a change in resistance or capacitance In response to this change, the electronic control 10 reduces or switches off heating power in the liquid heating vessel.
An alternative embodiment of the steam sensor 40 is shown in more detail hi Figure 7, Instead of comprising a continuous track, the steam sensor 40 comprises a patr of tnterdigitaled silver electrodes 40a, 40b formed on a barium titanate (BaTiO3) thick film layer 42 deposited on the dielectric layer 22. The capacitance between the electrodes 40a, 40b depends on the humidity and or level of moisture between the electrodes 40a, 40b.
Preferably, the steam sensor 40 is left unglared so as to be more sensitive to humidity. Selection of the material of the steam sensor 40 is very important to prevent silver migration, For example, the silver electrodes may include a highlcvd of palladium.
Preferably, the steam serisor 40 is dried out after sensing a boil condition, A discrete heating track may be provided to dry out the steam sensor 40; or the steam sensor 40 may be dried out by ambient heating or heat conducted through the dement Alternatively, a low current may be provided through the steam sensor 40 for detecting humidity until a boil condition is detected, and a higher current may be passed through Ihc steam sensor 40 after boiling is detected, so as to dry out the steam sensor 40.
Before the steam sensor 40 has dried out, it may be unable to detect whether the liquid in the liquid heading vessel is boiling. Therefore, if a heating current is manually switched on soon

after boiling, the heating element may be re-energised for a predetermined time, such as 15 seconds, and then switched off without determining whether boiling has occurred.
Fourth Embodiment
The fourth embodiment, as shown in Figure 6, differs from the third embodiment in lhat the steam sensor 40 is sensitive to temperature rather than humidity; for example^ the resistivily of steam sensor 40 may be sensitive to temperature. Steam impinging on the steam sensor 40 of this embodiment causes a sudden change in the sensed temperature, in response to which the electronic control 10 reduces or switches off heating power in the liquid heating vessel. The steam sensor 40 may be calibrated so that a change in temperature corresponding to the impingement of steam may be reliably detected,
Sensor Circuit
As shown in Figure 8, the sensor tack 30 may be placed in series with a resistor 16 across a low supply voltage V, and a change in voltage VI across the resistor 16 may be detected by the electronic control 10 as an indication of the change in resistance R2 of the sensor track 30. The heating current may be disconnected or reduced when either a resistance threshold has been reached or a rate of resistance change has been reached for the resistance of the sensor track 30. The sensitivity of the sensor circuit may be improved by using an amplifier.
Digital Con version
For input to the electronic control 10, the voltage Vl will typically be converted to a digital value by an analog-to-digital converter (ADC). This results in a quantised digital measurement value which may have a poor resolution if the signal is small relative to the input range of (he ADC, as shown for example in Figure 9.
The resolution may be enhanced by averaging the digital measurement values. For example, Figure 10 Shows the result of taking a moving average of 10 measurements as the input value, Although the transitions between quantised measurement values are smoother than the result shown in Figure 9, the measurement values are still highly quantised
The resolution of the measurement values may be greatly improved by adding a periodic :dither' signal to the analog signal to be measured, before input to the ADC, and taking a moving average of 10 measurements by the ADC as the measurement values, as shown in Figure 11. The amplitude of the dither signal is preferably at least equal to the resolution of the ADC, and more preferably twice as large, so that the measured analog signal transitions

between at least two digital output values of the ADC, even if the analog signal to be measured is static. As a result, the 'dithered1 average measurement values have a much greater resolution than that shown in Figures y and 10.
Heated Liquid Dispenser
A heated liquid dispenser will now be described, aspects of which may comprise developments of the heated liquid dispenser disclosed in WO-A-07/096630; part of the description is included below as background.
A first example, shown in Figures 12 and 13, comprises an electrically heated spray bottle having a reservoir 110, a nozzle 1 12 and a power base 113. [lie nozzle 112 is connected to a manually actuable trigger 114, a pump mechanism 116 and a lube 118. The trigger 114 actuates the pump mechanism 116. The pump mechanism 1 IS comprises a piston 120 housed within a cylinder 122. A spring 124 is also located in said cylinder 122, When a user pulls the trigger 114, the pislon 120 is pushed into the cylinder 122 and, hence compresses the spring 124. When the trigger 114 is released, the piston is pushed back into the cylinder 122 by action of the spring.
When the piston is pushed within the cylinder, fluid is forced out of the pump mechanism 116, When the trigger 114 is released, the piston 120 moves out of the cylinder 22 (while still being retained within the cylinder housing), thus causing fluid liquid from the reservoir 110 to be drawn up (he tube 118.
The pump mechanism 116 further comprises two one-way valves 124, 126 - one located between the cylinder 122 and the reservoir 110, and one between the cylinder 122 and the nozzle 112. This ensures that the liquied drawn from the reservoir 110 is forced out of die nozzle 112 and cannot flow back into the reservoir 110,
The nozzle 112 is rotatable such that a user may select between a concentrated jet and a dispersed spray. Such nozzles are known on existing spray bottles, and will not be described in depth here.
A heating element such as a thick film element plate 12 is disposed in the base of the reservoir 1107 together with a thermostat 12S to de-cnergise the Element 12 when a predetermined temperature is reached. For example, the predetermined Temperature may be 60nC, which is. a suitable temperature for defrosting windscreens, or for use in. cleaning operations using heated detergents for example. More generally, the predetermined temperature may be in the range 40° C to 70oC.

The heating element 12 may include a keep-warm element that IE energised after the predetermined temperature is reached, so as to keep the liquid warm at a temperature below the predetermined tempera lure. Alternative ly„ the thermostat 123 may switch on the heating element 12 when the temperarure of the liquid falls below it predetermined lower temperature,
There may also be provided an overheat control 130 for protecting the heating element 12 from overheating should the thermostat 128 fail. The overheat control 130 may switch oft power to the heating element 12 when an overheat temperature significantly higher than the predetemiitied temperature is delected. The overheat temperature may be between 70oC and WC, and most preferably 80oC.
A temperature control suitable for use in this embodiment is described in GB-A-0329636, and shown in Figure 15. The control comprises first and second thermal actuators 128, 130. Said thermal actuators 128, 130 comprise bimetal discs that are operable to undergo a snap transformation. When each of the thermal actuators 128, 310, undergoes their snap transformation they are configured lo cause the clement 12 to be de-energised, and hence prevent the liquid within the reservoir 110 from being heated beyond a particular temperature.
in the present example, die first thermal actuator 128 is typically configured to undergo its snap transformation at the predetermined temperature, such as 60aC. The second thermal actuator 130 is; configured to activate at tire overheat temperature, for example 80oC- in other embodiments the first and second actuators jrray be configured as two completely separate components mounted in different positions within the appliance.
The power base 113 is operable to provide power to the heating element 12 to heat (he liquid in the reservoir 110 to a temperature below boiling. In one embodiment, the base 115 comprises a 360° electrical connector of the type described in. for example, EP-A-0 922 426. This arrangement is particularly advantageous in that the user may use the heated spray hottle without having to carry the wejghi of the power base 113.
En an alternative example, the thermostat 128 may be included within the power base 13, find may be corrnectable to a temperature sensor located within the reservoir portion.
A vent 140 is provided in a wad of the reservoir 110 to ensure that the pressure inside the reservoir 110 does not rise significantly due to the increase in the temperature of the contents of said reservoir 1 ] 0. The vent 140 may be of any suitable configuration, such as; an aperture in the wall of the reservoir 110, or a valve such as a slit valve or spring-loaded pressure relief valve.

The wall of the reservoir 110 may comprise a thermally insulated portion 144, so that a user may hold the reservoir 110 without discomfort when the liquid has reached the desired temperature. The Thermally insulated portion 44 need only extend over a portion of the wall arranged for holding hy the user. Alternatively, the entire wall may be thermally insulated, although thi & may add to the weight of the heated spray bottle.
Indication means, such as a light 142 (for example an I,ED), may be provided Lo indicate when the thermostat 128 has heen activated, and hence when the temperature of the liquid contained in the reservoir 110 has been heated to the predetermined temperature limit.
Furthermore, it is preferred that the indiration means 142 is located within the power base 113, as such arrangement allows for the reservoir portion cf the apparatus to be easily washed in,.for example, a dishwasher. Accordingly a washable connector, such as one that is described in GB 23S7523 is preferable over a standard connector used on a typical electric jug,
This example provides advantages in providing more efficient cleaning when using detergents, and in an alternative use, is safer than using, for example, a kettle of boiling water when de-icing a car windscreen. Jt is more convenient and safer than having to heat water in a kettle and then pour the water into a spray bottle. It also uses less power, and does not use the chemicals present in conventional spray de-icers. Another application is the spraying of oils or fats such as soya oil, which is used as an alternative to butter when cooking or for seasoning of, for example, popcorn
A second example comprises a heated sauce dispenser as shown diagrammatical I y in Figure 14. In this embodiment, liquid is dispensed through a tube 112 rather than a spray nozzle. Sauce or condiment may be heated within the reservoir 110 until the predetermined temperature is reached, and the sauce or condiment may then be dispensed at this temperature using the pump L16. The sauce or condiment may be kept warm using a keep warm heater as described above. The present example may be particularly useful in wanning chocolate sauce,
In each embodiment, it would be advantageous if the pump or spray is powered by a power source within the appliance, such as a rechargeable battery or capacitor, so that the pump or spray can be operated when the appliance is disconnected from a cordless power base.
In an alternative embodiment, the power base 113 comprises an induction heater and the heating element 12 comprises a plate that is inductively heated by the induction heater when the reservoir 110 is mounted on the power base 113.

Mnltipart Appliance
The main body of the liquid heating appliance disclosed in WOA-07/096630 composes two separable parts: a heated reservoir 110 and a dispensing part comprising the nozzle 112. The main body may be connected to a power base 1J 3,
In an embodiment of the present invention, the main body of a heated liquid dispenser comprises at least three separable portions: a dispensing portion, a healing portion and an intermediate portion collectable between the heating portion and the dispensing portion, The heating portion contains a heating element 12, and optionally electrical components such as a thermal control and/or a cordless connector, and may or may not include die reservoir 110. The reservoir 110 may be defined by one or more of these portions, and may tor example extend from the healing portion to the intermediate portion. Different sizes of intermediate portion may be used to allow die volume of the reservoir to be varied. A low profi le appljanee may comprise a heating portion not including the reservoir, and a low profile intermediate portion.
In an alternative embodiment, the order of connection of the portions may be different; for example, the healing portion may be connectabte to the dispensing portion, and a reservoir portion may be connected to the dispensing portion or to the heating portion; all three portions may be connected together via a common single connector. All that is required is that the heating portion heat liquid in the reservoir before or during dispensing.
Specific embodiments ore shown in Figures 16 to 18,which relate to improvements on the heated spray bottle of Figures 12 and 13. As shown in Figure 13, a tube 118 may be provided so that liquid is drawn from the bottom of the reservoir 110. The tube 118 may include a filter to prevent particles from entering the dispensing mechanism. The tube 118 may contain a non-return valve.
In the embodiment of Figure 16, the nozzle 112 is arranged on the dispensing portion, the intermediate portion comprises the thermally insulated handle portion 144 and the heating portion comprises the reservoir 110. In the embodimenr of Figure 17, the nozzle 112 is
arranged on the dispensing portion, the intermediate portion comprises die thermally insulated handle portion 144 and the reservoir 110, and the heating portion comprises the heating element 12; in other words, the heating element 12 forms a detachable floor for the reservoir
110,
The embodiment of Figure 18 comprises four separable portions: a dispensing portion

comprising Lhe nozzte 112, a first intermediate portion comprising the thermally insulated handle portion 144, a second intermediate portion comprising the reservoir 110, and a healing portion comprising tbe heating element 12.
The different portions may be separably correctable by means of any suitable coupling, such as a screw or bayonet lining. Where rotational alignment is required between the different portions, this may be facilitated or enforced by the coupling; for example, a bayonet coupling that allows coupling in only one rotational orientation,
An advantage of the division of the appliance into at least three separate portions is that the portions may be more easily cleaned: For example, at least one opening of a portion may he large enough to facilitate internal cleaning.
The heating portion may be washable in a dishwasher, for example using any of the means discussed above for rendering components dishwashahle. Alternatively, the dispensing portion and/or the intermediate portion may be dishwashable, but the heating portion may be cleanable by wiping, to avoid ingress of water into electrical parte; this is particularly suitable for embodiments where the heating portion comprises a detachable flour of Lhe reservoir 110, since (he floor is easily accessible for wiping clean,
The intermediate portion and/or the dispensing portion may be disposable if too difficult to clean. Tn this way, at least part of the appliance, such as the heating portion, may be reused.
Alternatively, any one of the separate components could be fitted with a disposable sleeve, insert or liner containing a substance to be dispensed, so that the sleeve or insert can be disposed without requiring the separate component to be cleaned, The disposable sleeve, insert or liner may be provided pre-filled with the liquid to be dispensed, or as a separate consumable to be filled with the liquid by the user.
Another advantage is that each portion may be constructed so as to optimise the function thereof; for example, the intermediate portion may be constructed from a material that is thermally insulating and/or comfortable to hold, while the heating portion may be constructed of heat-resistant material. The heating portion may also be made of thermally insulating material} to reduce heat Joss. The appliance may be suitable for use at table, for dispensing heated liquids, and may therefore have an insulated base to avoid damaging the table,
The heating portion may be interchangeably connectable to any one of a plurality of different portions, such as Intermediate portions and/or dispensing portions. In the embodiment shown in Figure 19, a dispensing portion comprising a dispensing tube 112 and a pump 116 as in the

example of figure 15 is connectahle to the reservoir portion 110 of the embodiment of Figure 16. The intermediate portion may function as sat adapter to allow connection of a standard dispensing portion to the heating portion, or vice versa.
Alternative dispensing portions may be used, which may be interchangeably coimectablc to the intermediate portion and/or to the heating portion. In one embodiment, Figure 20 shotvs a dispensing portion having a pump 116 for pressurizing the reservoir 110, and a spray nozzle 1J2, connected to the reservoir 110 by a flexible conduit 132. The dispensing portion may include the reservoir 110 and may be removably connectable to a heating portion comprising a heating element 12. Figure 21 shows a variant having an electrically powered pump U6. The pump 116 may be powered by a power supply, such as a battery, enabling the pump to be used when the appliance is disconnected from the cordless power base. .
The intermediate portion nr dispensing portion containing a reservoir may be interchangeable so thai..different liquids may be dispensed in turn. For example, a reservoir 110 containing a first liquid may be detached from the hearing portion and replaced by a reservoir 110 containing a second liquid. This is particularly advantageous for example ^vhen applying liquids of different types, such as different coloured paints or coatings, different colours or consistencies of icing, different cleaning fluids or different oils in aromatherapy.; where contamination between the different liquids should be avoided. The reservoir 110 should be removable from the heating portion without spilling the contents thereof. One or more supports or housings may be provided for storage of interchangeable portions so that the liquid may be kept within those portions when removed from other portions. The supports or housing*, may each include a cover to prevent leakage or drying of the liquid contained within the respective portion.
The reservoir 110 may be tillable in an inverted position. In the embodiment of Figure 22, die reservoir 110 has an internal passage 134 depending downwardly from the upper opening of the reservoir 110, so that the reservoir 110 may be filled in an inverted position without the contents running out through the upper opening. The reservoir 110 may include level marking so that the volume of liquid contained therein in the inverted position may be judged.
Where the reservoir is formed by both the heating portion and intermediate portion, the reservoir 110 may be filled by assembling the heating portion and intermediate portion, filling the reservoir 110, and then attaching the dispensing portion.
Where the liquid comprises a two part mixture, one part of the mixture may be placed in the

healing portion and the intermediate portion may them be connected to the heating portion. The other part of the mixture is then poured into the intermediate portion to the desired level. This allows the proportions of the parts of the midline Do be determined accurately.
'ITie liquid or solid to be heated may be supplied in a pre-packed container thai forms the intermediate portion and is assembled to the heating portion before use- this assembly may pierce the container or otherwise cause it to open so that the contents can be heated by the heating element 115.
Stirring/Agitation
The heated liquid dispenser may include a stirrer 136 or other means for mixing the contents of the reservoir 110, for example to avoid separation or to promote emulsfication of the contents. As shown in figure 23, the stirrer 136 may be powered by a mechanical connection to a motor, or by a magnetic coupling. The magnetic coupling may be provided through the top or bottom part of the appliance or alternatively tlirou&h the perimeter of the appliance, for example by using one or more electromagnetic coils arranged around the periphery of the appliance, as described in more detail below. The motor may be powered by a power source wiiJiin the appliance, such as a rechargeable battery or capacitor, so that the motor can be operated when the appliance is disconnected from a cordless power base. The motor and stirrer 136 may be provided as an integrated assembly,"for example, within the appliance lid .part, removably mountablc on or within the appliance by the end user. Alternatively, the motor and stirrer may be provided as discrete components, one or bodi of which are removably mountablc on or within the appliance by the end user,
In a further embodiment more than one electrical driven function can be included in the removably mountable part. As shown in Figure 35 the lid assembly 221, shown by dotted lines, can be removably connected and disconnected to and from the reservoir 110, with the electrical connections being made via detachable electrical connection means 240, The assembly 221 includes an electrical pump 116, an actuator or trigger 114 Tor Lhe pump 116 and conduits 118, 112 to and from the pump 116 to allow dispensing, together with a motor 241 arranged to drive the stirrer 136. The assembly 221 also includes an. integral cover 220 to seal against the reservoir 110 and a hand It part 222 to support the appliance whilst activating the trigger 114. The heating means for the element plate 12 is a printed element 205 which forms the bottom part of the reservoir 110. Controls (not shown) and electrical connections (not shown) are found within the base component 6 and electrical wiring (not shown) communicates from the base component 6 to the electrical connection means 240 via a cover

230 on the reservoir 110,
Tn further embodiments, additional or alternative electrical functions for example aerators or vibrators can be included within the removable ltd assembly 221.
Alternatively, as show in Figure 24, (he stirrer 136 may he manually driven, for example by a handle 140. The stirrer 136 may be coupled to the manual actuation of the pump 1 ] 6, So that the contents are stirred and dispensed by a single action.
The stirrer 136 may be driven from the bottom, top or side of the appliance, and the dispensing portion may be arranged accordingly. For example, the dispensing portion may be mounted on the side of or below the reservoir 110.
The stirrer 136 may be centrally mounted in the reservoir 110 or offset from the centre of the reservoir 110. The stirrer 136 may take any one of a variety of forms, such as a rotatable inner wall or wall portion of the reservoir HO, optionally with one or more inward projections such as fins, to promote mixing of the contents. Instead of stirring the contents of the reservoir 110, the contents may be aerated, for example, by pumping air into the reservoir 110 via a tube or agitated for example by causing part or all of the reservoir, or a part within the reservoir, to vibrate or oscillate.
Melting/Liquefaction
The substance to be dispensed may be viscous or a solid or gel at room temperature, but may become less viscous,, liquefy or melt when heated by the heating element 12 so that it can be dispensed more easily; examples include butter, cooking fats, glue or silicotic sealant. As shown in Figure 25, the contents, may be supplied as a refill 142 of standard size and/or shape that fits within the reservoir 110 and comes into contact with the heating element 1 \ such as a standard Lube of silicone sealant, in which case a standard silicone gun-type dispense may be used as the dispensing portion. Alternatively, the refill 142 may include a housing forming the intermediate portion conncttable to the heating portion and the dispensing portion, the housing being disposable after use.
The appliance may include means for ensuring that the pump is only enabled to be energised after the substance becomes sufficiently liquid to be dispensed, such as a thermostat or timer to detect or infer that the substance has been heated to the correct temperature. Where the appliance includes the stirrer 136, the appliance may include control means for detecting the viscosity of the substance by actuating the stirrer 136, and inhibiting energising the pump until the viscosity is sufficiently low for dispensing. The control means may comprise a

sensor, such as a motor protector, that detects excess loading on the motor for the stirrer. In this case, the motor protector may switch off the motor under excess loading, and re-energisc the motor when the motor protestor resets itself, until the motor is able to run continuously; the pump is then enabled to be energised. The pump may be energised automatically in response to being enabled, or the pump may be energised manually when enabled.
In an alternative embodiment of The invention, the substance to be dispensed is provided as a gel that liquefies when stirred or agitated. In that case, the appliance need not include aheater, but instead includes a slinxr or agitator as described above.
Thermal Mass
In another embodiment, shown in Figures 26 to 28, the reservoir 110 may comprise a first chamber 110a for containing liquid heated by the heating element 12 and a second chamber 110b for containing the Liquid to be dispensed, healed by the liquid ui the first chamber 110a_ In the specific embodiment, the second chamber 110b is at least partially contained wiihin the first chamber 110a, in the manner of a bain marie7 The first chamber 110a may contain water and Ihc second chamber 110b may contain a liquid (hat is sensitive to overheating, such as Hollandaise sauce. butter., syrup or melted chocolate,
In addition to heating the liqmd in the second chamber 110b, steam and/or vapour from the water heated within the first chamber 110a may be used to agitate, aerate or.froth tlie liquid, for example milk, in the second chamber 110b.
Figure 36 shows an arrangement whereby water 250 is poured into the first chamber 110a via an orifice 252 and then sealed by a cover 220. The liquid 251 to be heated in the second chamber 110b enters through the top of the chamber 110b which may or may not be covered depending on the method of dispensing. A passage 260 communicates between the first and second chamber, The top part of this passage is preferably higher than the orifice 252 and the top of the chamber 110b so that the liquid from both chambers is kept separate. The liquid 250 is heated by a beating element 205, such as a printed (thick film) heating element, and upon boiling steam and/or vapour generated in the first reservoir 110a is then transferred by steam pressure into the liquid 251 via the tube 260 with the result that the liquid 251 is both heated and aerated (or steamed). The tube 260 may include a Venturi or dispensing head SQ that the pressure, direction and amount of steam and vapour entering the second chamber 110b can be varied depending on the liquid contained in the second chamber 110b. It is envisaged for example that this apparatus may froth milk in a similar manner to the milk

farthers found on the outside of the tradilional cappuccino coffee maters. If the second reservoir 110b is covered) then means must be provided to prevent excess pressure caused by the steam, pressure passing through the liquid 251.
The liquid 251 may be dispensed by pouring, oi via a nozzle or pump.
In additional embodiments air can be pumped into the liquid 251 either separately or via die . tube 260 so that the air and steam may combine to enhance the frothing process.
Figure 37 shows an alternative embodiment that utilises steam and/or vapour to heat and aerate the liquid 251 Ly be heated in the second reservoir 110b, In this embodiment the second chamber 110b is removably positioned inside the first chamber 110a and a seal 270 is provided between the two chambers.
The liquid 250 is heated by a heating element 205 and the pressure generated by the steam causes the steam and vapour to pass into the liquid 251 in the second chamber 110b via one or more one-way valves 260 positioned in the base of the second chamber 110b. Once the pressure has subsided, the valves 260 return to a closed position to prevent the liquid 251 passing into the first chamber I1 Oa.
Each ofthc embodiments of Figures 36 and 37 may also include a stirrer 136.
As shown in Figure 25 and Figure 37, the second chamber 110b may be removable from the first chamber 110a for cleaning purposes or for other reasons as discussed below. The second chamber 110b may be separably attached to the dispensing porliun, and may be removable from the first chamber 110a during a dispensing operuuon. In this way, the user need not lift the first chamber 110a and its contents during a dispensing operation, but may return the secorid chamber 11 Ob with the dispensing portion to die first chamber 110a to reheat die contents of (he second chamber 110b. In that case, the heating portion need not be provided widi a cordless connector since the heating portion is not lifted by the user during a. dispensing operation;,
The first chamber 110a need not contain a liquid, but may instead comprise a solid thermal mass that is heated by the beater 12 and releases heat into die liquid to be dispensed. Instead of a thermal mass, a material may be used to exhibits a reversible exothermic reaction that absorbs heat from the heater 34 and releases heat into the liquid to be dispensed,
Pressure Equalisation in Reservoir
The vent 140 in the reservoir MO may be sealed by a ventilated membrane that allows

pressure equalisation when gas within the reservoir 110 is heated. The membrane may be rajade of a fluoropolymer fabric such as Oore-tex™. Alternatively, the membrane may be of a resilient material such as silicone having one or more small apertures such as holes or cioss-cuts. Under normal conditions, the resilient membrane is effectively watertight but the apertures open when expanded under pressure-Alternatively, the reservoir 110 may have a variable volume, such as by means of a piston or expansion chamber, so chat the volume thereof increases as gas within the reservoir 110 is heated.
Further featum
The dispensing portion may be arranged to dispense a predetermined quantity of liquid in response to a single user actuation, for example by the arrangement of the pump 116. The amount of liquid dispensed by a single user actuation, .or the rate oi dispensing, may be adjustable by the user.
The dispensing portion may include an interlock-so that liquid cannot be dispensed unless above a first predetermined temperature and/or below a second predetennined temperature. The appliance may include a temperature indicator to indicate whether the temperature of the liquid contents is above a first predetermined temperature andVor below a second predetermined temperature. The temperature indicator may be thermoehrumic, electronic, electrical or mechanical.
The appliance may include means to show the user how long the liquid has been in the appliance, for example to advise if the constituents need rembting or are no longer fit for use, The means may comprise a timing mechanism, counter or indicator, such as a chemical indicator involving a slow reaction that changes colour or other discernible properties over a length of tune.
The dispensing portion may include a ratchet type dispenser so that liquid is dispensed as the dispenser is progressively actuated, and the dispenser must then be reset.
The appliance may include means for illuminating certain portions for improved operation; for example, the area around or in front of the nozzle or tube 112 may be illuminated. The reservoir 110 may be illuminated internal lyr and/or may have a transparent or translucent wall or wall portion so that the contents cun be easily seen, for example to judge the level or
condition of the contents. The reservoir 110 may have visible level markings so that the volume of liquid present in the reservoir 110 can be easily determined by the user. In the case

of a cordless appliance, the means for illuminating may be powered by a power supply contained within the body of the appliance so that ulurni nation may be provided when the appliance body is disconnected from the cordless base. The power supply may comprise a rechargeable battery or capacitor thar is recharged when, Lhe appliance body is connected to
the power base. Alternatively, the power supply may comprise a non-rechargeable battery.
The appliance may be a cordless appliance connectable to a cordless power base, or may have a permanently connected power cord. The cordless base may be a 360° cordless base.
The reservoir 110 may be made of stainless steel, plastic, glass, or ceramic, The sides of the reservoir 110 may be parallel, concave or convex. The reservoir 110 may be rectangular or oval in horizontal cross-section for easier storage, or may be circular in cross-section. The reservoir may be double walled, with both walls of one material or nrade of two different materials. The double wall assembly could provide thermal insulation or the materials may be selected for a specific property. The thermal insulation may comprise a vacuum or thermally insulating material hetween the walls.
The heating element may be an underfloor element plate, an immersed element, or an element incorporated into or formed on a wall of the reservoir 110. The heating element may be a resistance heater, a self-remulating PTC heater, a trace heater, an ohmic heater, an induction heater, a radiant heater or an ultrasonic heater. The uiiderfloor element plate may have a thick film, dircast or sheathed element. The thick: "fllrci element may include overheat protection, such as the E-fast™ protection disclosed in WO-A-2006083162 or Parallel E-Fast as disclosed in WO-A-2008/150172. The element plate may be laser-welded onto the base of the reservoir 110, for example as disclosed in WO-A-2007/136256.
In an alternative embodiment, the heater may be a flow-through heater arranged to heat liquid as it is dispensed, rather than heating the contents of the reservoir before dispensing,
Heated liquid dispensing applications
Applications of the heated liquid dispenser in embodimcnls of the invention include: dispensing heated fragrances such as perfume or air freshener; dispensing heated detergent solution For improved cleaning, such as for ovens Eind/or barbeques; dispensing heated insecticide for greater efficacy; dispensing Li quids that sue solid or viscous at room temperature but dispensable when heated; applications that require two or more consiiluents to mix or react together before dispensing; dispensing heated glue or sealant such as silicone sealant; dispensing paint; dispensing liquids comprising components, that -tend to separate;

dispensing liquids that require heating, stirring or agitation to cause a reaction required to achieve a desired effect:; for example frothed milk, dispensing liquid shoe polish; dispensing waterproofing treatment; dispensing wax palish for cars and the like; dispensing cleaning fluid for example for alloy wheels; dispensing heated cooking oil for improved coverage; dispensing wann water for bairdressing applications; and dispensing heated massage or aromatherapy oil,
Heating and Control Solutions for Milk and other liquids with similar properties Heating and/or frothing of milk presents particular problems, although these problems may occur with other liquids having similar properties.
Preoblem to be overcome include:
* Preventing the Liquid to be heated sticking to the reservoir during 01 after the heating cycle.
* Position and speed of stirrer within the liquid container.
* Position and temperature setting of the thermostats within the appliance.
* Thermal mass of the heating element
* Non-uniformity of temperature of the liquid.
* Ability to reset the thermostat so that the appliance can be reused immediately after me milk has been poured from the appliance.
* In the case thai deposits are building up on the element - how to identify that the appliance needs to be thoroughly cleaned.
Pre venting milk residue sticking to the reservoir during or after the heating cycle This solution is important to the functioning of any liquid heating vessel in which a part of the liquid solidifies above a certain temperature. An appliance that is required to heat milk would preferably include a non-stick coating; however, this coating will not present deposits being left on the element if the temperature of the appliance in contact with the milk teaches certain temperatures. The inventors have determined that, with milk: little or no solidification takes place if the temperature of the part of the appliance in contact with the milk can be kept below 100 °C; gradual build up of deposits occurs when the part of the appliance in contact wim the milk is around 150oC; and extensive build up of deposits occurs when the part of the appliance in contact with the milk reach 200°C

In a clean appliance, during the heating process, the milk, within the appliance acts as a heat sink and can effectively keep the majority of the wet side of the heating element al around 100CC providing the heating element is configured so that the heat is distributed evenly across the surface it is known that printed elements do distribute the heat evenly so that deposits are less likely with this type of heating source. However many of the appliances on the market include sheathed heating elements where the heat is concentrated immediately above the sheath and it is with these elements that deposits are more likely to occur.
Once a deposit has started to form then this acts to slow down the heat transfer and effectively increases the localised temperature in each subsequent beating process. Very quickly the temperature in the vicinity of the deposit Increases to the point that the deposits become burnt and extremely difficult to remove.
The following embodiments aim 1c- limit the temperatures so any build up of deposits can be easily removed, for example with a damp cloth.
In addition to the element type,, other factors such as the temperature of the milk at which the heater is switched off, die power of die heating element, the distribution of the heat within the heating cliaraber and the time at which the milk is poured from the heating chamber after the heating cycle may each be contributory to the build up of deposits.
Solutions which prevent burning, for example lowering the temperature at which the appliance switches off, may reduce the user satisfaction with the appliance so that each solution must he balanced against lowering of the performance of the appliance.
Sheathed Element Substrate
It is known that adding a highly conductive wafer of material on one or both sides of a stainless steel element plate can even out the heat distribution of a heating element; however, this solution is expensive as it requires an additional step which is not within the accepted technologies in the technical field.
The following embodiments put forward solutions to prevent uneven temperature distribution on the wet side of an element plate, preferably comprising stainless steel, during the heating operation.
Figure 30a shows a cross section of a metal heating chamber 110 for a milk frother. In this case the mechanical sheathed element 202 is attached to an aluminium substrate 201 'which in
turn is attached directly onto the base 12 of die metal chamber 110, so that the base 12 acts as

a heated element plate. It would normally be expected that the aluminium substrate 201 would be uniform iti thickness, but in this embodiment the substrate 201 has been increased in thickness above the element sheath 202 so that there is more mass in this area to dissipate the heat, which will result in a decrease in the temperature of the element plate 12 immediately above this area. Figure 30b shows a simitar configuration to the heating chamber 1L0 of Figure 30a, however in (his embodiment a void or recess 203 is provided in the substrate 201 between the element sheath 202 and the element plate 12, This void 203 pre vents a direct beat path from the element sheath 202 onto the element plate 12. The void 203 may comprise an annular channel in the upper surface of the substrate 201, extending at least over the sheath 202, The annular channel may comprise a complete annulus, or an annular section (i.e. extending over less than 360°). The void 203 may be filled with a material having a thermal conductivity selected so as to even out the temperature distribution across the element plate. This material may be formed as an annular piece for location in the annular channel during assembly. The material may be a metal of low thermal conductivity, such as stainless steel. The material may be integrated within the external surface of the heating chamber 110, for example welded onto the heating chamber prior to mounting of the substrate 20l on the heating chamber 110. This arrangement may facilitate bonding of the substrate 201 onto the heating chamber 110.
In an alternative embodiment shown in Figure 30c, the substrate 201 is increased in thickness radially inwardly and/or outwardly of the element sheath 202; this arrangement still spreads the heat more widely over the element plate 12, but with a reduced height relative to thai of Figure 30a.
Figure 31a shows a similar configuration to Figure 30a, however in this embodiment the substrate 201 has a radially inner or central portion that is thinner than a radially outer portion of the substrate 201, so that die heat distribution across the element plate 12 is more even. In other words, diere are at least three different thicknesses of the substrate 201: a thick portion in an outer radial position on which the sheath 202 is mounted; a radially intermediate portion of intermediate thickness; and a thin, radially inner portion, The gradation in thickness may be continuous rather than stepped as shown in Figures 30 and 31. This configuration has the further advantage of reducing the thermal mass of the substrate, which may help reduce the overheating of the element plate 12 when the milk is poured out of the appliance.
Figures 32a and 32b are. similar to Figure 30a, however in these embodiments the substrate 201 extends beyond "the edge of the circumference of the healing chamber 110. In the

embodiment of Figure 32a the substrate 201 extends radially outwardly in the same plane as the inner portion of the substrate 201. In the embodiment of Figure 32b. the substrate extends out of the plane of the inner portion, towards the heating chamber 110, and extends around and in thermal contact with the outside surface of the side wall of the chamher 110.
In either embodiment, the additional mass of tlie extruded tiuter portion of the substrate 201 acts to lower the average temperature of the element substrate 201 and in the embodiment of Figure 32b, the form of the substrate 201 acts to increase the area of thermal contact between the substrate 201 and the beating chamber 110.
The embodiments of Figures 32a and 32b have been illustrated with a uniform thickness substrate 301 but the thickness may vary as illustrated in Figures 30a5 30b or 31a.
As detailed above, the propensity for milk to burn on the element plate during normal use is reduced because the milk acts as a heat sink; however, (he propensity increases dramatically when the frothed milk is poured from the appliance immediately after the (heimostat switches . off, In that case, as the bulk Of the milk has been removed, lhc residual heat in die element can increase the temperature on the wet side to around 200°C, a temperature at which the residue of the milk will bum almost-immediatety.
Adding additional mass at the periphery of the element plate 12 in these embodiments increases the area over which the heat from Lhc substrate 201 can dissipate and effectively reduces the overshoot temperature in these areas when the milk has been poured off
Figures 34a, 34b and 34c show embodiments with alternative clement sheath arrangements whereby the heating load is spread across the surface of the heating plate, thus alleviating potential hot spots,
Figure 34a illustrates a twin sheathed element incorporating two concentric C-shaped sheaths 202 mounted on the substrate 20 L
Figure 34b illustrates two sheaths 202 mounted on a substrate 201. The outer sheath is C shaped, with die inner sheajh convoluted in shape (e.g. star shaped) for fuaber spreading (he heating load across the substrate 201.
The benefits of the embodiments of Figures 34a and 34b include one or more of;
1. The heat is spread across more of the substrate.
2. The power density, and therefore miming temperature of the two sheaths will be lower than a single C-shaped element.

3. The switching may be configured so lhat one of the element sheaths 202 is switched off as the milk approaches the required temperature so that there is less overshoot after the thermostat 128 has switched off.
Figure 34c illustrates a single convoluted (e.g. star-shaped) element sheath 202 mounted on a substrate 201. This shape may spread the heating load more evenly over the substrate 201 and the increased length may reduce the power density at any given-point.
Postponing of thermostats
There are two main areas to consider with the temperature selection of thermostat!;: the break
temperature and the remake temperature.
Ideally the thermostat should break just at the point that the milk has reached the desired temperature and remake when further cool milk is added to the heating chamber for subsequent cycles:
Generally the lowest perceived acceptable temperature for the milk is 60°C and it is usual that the thermostat would have a differential of at least 10 °C between the break and the remake temperature. Lower differentials are possible but these invariably increase the stress on the bimetal blade and shorten the effective life of the component, or a mure expensive component is needed,.
With milk frcthers there are known mechanical and physical properties that complicate the specification and performance of the thermostat, for example:
a) The high mass mechanical sheathed element stores heal during the heating cycle and continues to dissipate heat into the milk after the element has been deenergised.
b) The thermal time lag between the temperature of the milk and the thermostat mounted on the dry side.
c) The effect on the thermostat of the conducted heat from the heating clement,
If the thermostat is to switch the appliance off acting only on the temperature of the milk then the thermostat would need to be positioned apart from the influence of the element substrate and also take into account the temperature lag between the position of the thermostat and the actual temperature of me milk; also to allow for the amount of beat that is dissipated after the appliance has switched off. The effect of c) can be alleviated by cutting or forming a hole in the substrate 201 and mounting the thermostat directly onto (he element plate 12. One eould also compensate for a) and b) by lowering the set temperature by a few degrees iti each case,

but this in turn may effectively lower the reset temperature, and subsequent time to cool, to a point that is unacceptable to the user.
Alternatively and preferably, the break temperature of the thermostat should be higher than the actual temperature of the milk so that the appliance cools down to the remake temperature faster ensuring a rapid energising of the appliance for subsequent use. This can be achieved if the ttiermoslat is subjected to an additional heat source during the heating cycle, which, combined with the influence of the heat sink effect of the milk, combine to give a reliable switching time.
The applicant manufactures thermostats that combine the function of temperature sensing with some form of self heating, for example, in plastic water heating appliances where the thermal lag is even greater than metal appliances; however, the manufacturing costs of these thermostats ate comparatively high, uierefore it is preferred that the elevated temperature of die dry side of the element substrate is used as the additional heat source for tins purpose.
It is well known that the element substrate can be 'tuned' so as tu improve the relationship between the temperature of the thermostat on the sheath and that of die liquid to be heated -however it is known that this 'tuning' disrupts the even temperatures required in milk heaters.
Investigations by the inventors have shown that .by taking steps to even out the temperature on the wet.side, the thermostat can be mounted on the dry side without further modifications.
Fig 48b illustrates a cross section of a heating chamber 110 for a miik frother. In this case the mechanical sheathed element 202 is attached to an aluminium substrate 201 which in turn is attached directly onto the base 12 of a metal chamber 110; the substrate 201 is configured as per the substrate 201 in Figure 11a. The thermostat 128 is mounted directly in the centre of the substrate 201 so that the thermostat 128 will benefit from the elevated temperature of the substrate 202 at the end of" the heating cycle and will be furthest away from the sheath 202 so it is less affected by any residual heat on the dry side when the appliance needs to be reenergised-
An additional thermostat may be positioned in good thermal contact with a location on the base at which burning of a liquid such as milk is most likely to huppen, for example offset from the centre of the substrate 201.
Figure 33a shows a cross section of a heating chamber 110 in an embodiment similar in construction to that of Figure 32a with the thermostat 128 mounted against both the side wall 200 of the reservoir 110 and also the substrate 201. Ideally the thermostat 128 should be

mounted in a position below the spout of the reservoir 110, as this area is the last pail of the reservoir 110 from which, ihe milk is removed and therefore the least likely to be affected by any lesidual heat in the heating plate 12. The inventors have discovered that the thermostat 128 can be set at a temperature! that is elevated from the required milk temperature and the wall 200 quickly reduces in temperature as the milk is poured away and new milk added.
Figure 33b shows a variant of the embodiment of Figure 33a whereby the thermostat 128 is mounted on the outside of me appliance on an element substrate 201 as detailed in Figure 32b. In this embodiment it is expected (hat (he substrate 201 below the thermostat 128 may run at a higher temperature man in the position in Figure 33a. Klevating the break and remake temperatures further will benefit appliances where the desired temperature is lower than 60° Ci so that the appliance may still reset in an ambient temperature.
Tn all the reEevant embodiments it is preferred thai the acting part of (he thermostat 128, for
example the bimetal, is in direct contact with me appliance, so as to ensure good thetmal
contact.
Position, Speed and Running Time of the Stirrer
Milk fro there normally have a frothcr attachment for fronting the milk and a stirrer attachment for stirring the milk whilst warming it. It is dommonly understood in the industry tiiat milk frothing or stirring is improved if the irother or stirrer is offset from the centre of the heating chamber. The inventors disagree with this theory, and have ascertained that positioning the forther or stirrer concentric to the element plate, which in turn is central to the appliance heating chamber 110, allows stirring of milk direcdy over the element sheath and thus a lower running temperature of the heater. Hence the preferred position for the stirrer is central within the appliance. By positioning die frother or stirrer dose to the element plate, the temperature immediately above the sheath is reduced.
Figures 29a to 29c schematically illustrate respective different embodiments'of a stainless steel reservoir 110 in which there is attached a substrate 201 and element sheath 202 which form the heating plate 12.
The reservoir 110 includes a removable cover 220, which in turn incorporates a shaft 210, and frother/sturer 136. The cover may include a bearing case 211 to act as a support for the shaft and an electric motor (not shown). Alternatively, as shown in Figure 29c, the frother/stirrer 136 may have magnetic portions 301 at its radially outer portions, driven by an electromagnetic coil 300 located outside the wall 200 at the approximate height of the

frother/stirrer. The coil 300 is arranged as an armature of an eletric motor, of which the frother/fltirrer 136 is the rolor.
In each case the frolher/atinrier 136 is concentric to the element sheath 202. In each case the preferred height of the frother/stirrer above the dement phite is a maximum 15 mm and a minimum of 4 mm.
The speed of the frother/stirrer 136 also plays a large part in the milk warming or frothing process. It has been ascertained that the optimum speed for a frother 136 as illustrated in Figure 29b is between 2p00 and 3,000 revs per mki with no load, or l,500 rpm when stirring a lypkal load, for example when heating 150 ml of milk with a 450 Watt element. If the speed is too slow then little or no frothing occurs; if too fast, milk may be ejected from the reservoir 110 by the frothing process-Increasing the radial length of the stirrer 136 will increase the peripheral velocity of the stirrer therefore it is possible to utilise a lower speed motor with the longer stirrer 135 illustrated in Figure 29a. The slower speed will reduce the vibration due to any imbalance or eccentricity of the shaft or stirrer which will result in a quieter, more stable appliance.
Figures 29d, 29e and 29f respectively show variants of irolhers 136, each nf which include a shaft 2I0? a paddle 139 and a coil 138. The paddles in Figure 29d are solid and are suitable for thinner liquids. The paddles in Figure 29e are hollow which will allow a srnoower flow in thicker liquids. In Figure 29f, the paddles are set at an angle so as to act like a propeller in order to impart an axial velocity to the liquid and encourage agitation of the liquid. In other embodiments the puddles may include other features, for example small holes or a fine mesh, to assist in mixing or agitating the liquid. The coil 138 may be arranged on the upper surface of the paddles 139, rather than on The radially outer surface as shown. Where frothing is not required for essunple for heating milk for latte coffee, the coil 13B may be omitted altogether to form a stirrer.
Larger diameter fmthers allow the coil 138 or associated paddle 139 to be placed over the lieater; however, as there is wore resistance to How, a higher power motor is required to aehieve the necessary minimum speed to satisfactorily froth milk. This is also the case with a radially largt paddle 139 and a radially smaller coil 138. as shown In Figure 29k, If a lower power motor is required then a smaller paddle 139 would be preferred, as shown in Figure 29j. Alternatively, using backward curved rather than radial paddles 139, as shown in Figures 29g and 29h, will also increase the speed required lor a given resistance and increase the

radial flow of the liquid, giving improved mixing of liquid and thus cooling of the element plate 32 above the demerit sheath.
For milk warming without frothing, a paddie 139 may he used without a coil 138. Preferably. the paddle 139 lias a larger vertical than horiamEul dimension. In one example, the paddle 139 is 30-40 mm in diameter, 2-4 mm in the horizontal direction and 5-10 mm in the vertical direction, In the embodiment shown in Figure 29i, iJie paddle 139 comprises radially outer blades 139a that are relatively tall in the vertical direction, eonneeted to the shaft 21Q by radially inner connecting portions .139b that are relatively short in the vertical direction for achieving good mixing over the heater while mtrtimiiing resistance. The stirrer 136 may include a temperature sensor towards the distal end of the shaft 210 e.g. around the area of the paddle 139. The temperature sensor may be a thermocouple, for example. The temperature sensor may be elcctrica lly connected a long the shaft 210 to a contro 1.
An alternative or additional solution to prevent overheating of the liquid in the appliance is a control to control the stiner 136 to carry on running for a short period, for example 30 seconds, after the thermostat has switched off the element- This ensures that all the residual heat in the clement is transferred to the milk before the rntlk is poured, which reduces wasted energy and lowers overshoot temperature. In turn this also has a positive effect on the reset time as the element plate has not reached an elevated temperature.
Thick Film or Printed Elements
Some of the above embodiments are directed at lower cost mechanical elements. Generally:, die manufacturing costs of thick film heating elements are greater than mechanical elements, however the performance of thick film heating elements is better, for one or more of the following reasons;
a) Lower mass, so that there is less residual energy to dissipate after the element has been deenergiscd and less likelihood of burning me residual milk after boiling,
b) Better distribution of the heat across the el erne nt, ensuring an equal temperature distribution across the element plate.
c) Better dry boil control. The thick firm element may include overheat protection, such as the E-tast™ protection disclosed in WO-A-2006/DS3162 or Parallel E-Fast as disclosed in WO-
A-2008/150172.
Investigations carried out by the applicant tiave shown that there may be further advantages in

the use of thick film printed elements with additional PTC sensor tracks as described above. It is now proposed that these same sensing means can be used lo assist in increasing the
performance of milk heating appliances.
The PTC tracks are sensitive to the rate of rise uf Ihe liquid in the appliance, with the result that as the temperature increases, so does the resistance measured within the PTC track.
Experimental results will now be disclosed, showing the resistance change (measured in Ohms per second) during hearing of milk The resistance when cold is very low, bait rises quicldy during the initial heat up period; then the rate of resistance rise decreases as the temperature on the dry side of the element is stabilised by heat dissipation into the milk. The dissipation of heat into the milk can change quite dramatically under certain conditions, for example if burning is taking place or if the stirrer is not functioning.
Mote that the actual measurements taken arc specific to the test appliances in which the experiments were carried out and are used for explanation purposes only. It is expected that the phenomena behind the results can be exploited in other appliance types, size, and power rating and also for other liquids to be heated and processed.
The object of the tests is to formulate an algorithm that will form the basis of an. electronic control module for heating milk and other liquids,
i :
In order to understand how to exploit this phenomenon it ia important to understand how a PTC sensor reacts under normal conditions.
figure 37 shows the PTC sensor output for a normal milk heating cycle with a clean element surface. It can be seen is that there is an initial rapid rise in temperature for the first 3.5 seconds. In this, example the rate of rise is approx 105 Ohms/sec. After this initial rapid rises the sensor signal climbs up at an almost constant rate of rise of approximately 12 Ohms/sec. The peak resistance at the point of cut-off is 12150 Ohms.
For comparison, further work has been carried on the same appliance with different fill levels from 65 ml to 130 tnl and with different power ratings from 495 watts to 577 watts. It has been found that the critical measurements of rate of rise of resistance are only marginally different There is a factor of 1.4 between the maximum and minimum fill levels and factor of 1.2 between the maximum and minimum. wattages.
Figure 38 shows the sensor response during a 10 second dry-boil test in which the appliance is energised without any milk inside the heating chamber. A horizontal hatched line is

superimposed on the graph at 12150 Ohms, which is the maximum level seen in normal conditions.
In order to ascertain that there is no milk present the algorithm could use either a rate of change detection or a threshold detection or a combination of both methods.
Figure 38 shows that the rate of change for the first 3,5 seconds is 270 Ohms/sec, which is significantly higher than the initial rate of change in the normal milk heating mode which way measured at 105 Ohms/sec, An electronic control baaed on this rate of rise algorithm may terminate the power if the rate of rise was substantially greater than that seen in normal operation, for instance two times the initial rate of rise which is 210 Ohms/sec. The control could calculate the rate of rise in 1 second intervals. and detect a dry boil condition very rapidly.
Alternatively it may be advantageous to introduce, for example, a 3.5 second delay into the control process so that (he detection does not commence until after the point at which the rate of rise would have stabilised if there had been liquid present. This is because the user may, for cleaning purposes, heat up a different liquid, for example, water and may remove or disengage the stirrer during the heating process; each of which could cause the rate of rise to increase to a point at which nuisance tripping may occur. In this case the control would then sense if the rate of rise had started to stabilise nfter the 3.5 second delay and if this did not occur within, for example, a 1.5 second time frame, then the power to the element would be interrupted. At this stage the rate of rise will be slower in the dry boil state but still considerably greater than the rate or rise when a liquid is present so that it is expected that a rate of rise of 75 Ohms/sec will be the level at which the appliance would be deenergised. The time to switch off the power would be approximately 5 seconds.
In a further embodiment a threshold detection can be used with the threshold level set above the maximum level attained during a normal milk heating cycle. A threshold set at 12400 Ohms would interrupt the power after approximately 7 seconds, which is dower than the rate of rise response time, however this is well within the design performance/requirements of thick film elements and still considerably faster than equivalent electromechanical controls.
Advantageously both the extended rate of rise and threshold detection means will provide further safety protection if, for whatever reason, the appliance fails to switch off when the milk has been heated. When a sufficient quantity of the milk has boiled away, the element temperature will increase considerably. In the experiment detailed in Figure 40 the power was

switched off manually soon after the failure mode was detected but it tan be seen rliat the resistance quickly increased above the 12400 Ohm threshold at a rate of rise of 150 Ohms per second so that either the rale of rise or threshold method would provide adequate protection in this safety critical failure mode.
In each of these examples the difference in rate of change is considerably greater than that experienced during the maximum and minimum volume and wartage tests, so it is expected that this method will be reliable across the full range of usage.
Detecting burnt milk deposits on the wet side of the element plate is more difficult to achieve, In order to understand the problems an experiment was set up whereby a milk heater was subjected to five consecutive milt frothing cycles in conditions that caused milk residue to be deposited after each cycle and without any cleaning between the cycles. In these conditions uhe milk deposits wj|] be showing considerable signs of overheating by the fifth cycle.
Figure 41 shows that the rates of rise during the latter part of the five cycles are essentially the same, however the initial starting resistance of the element, is higher, the initial high rate of rise lasts longer and the final PTC sensor signal is significantly higher.
Figure 42 shows a snapshot of the first 20 seconds of each cycle and it is advantageous to concentrate on the 6 second period (between 6 and 12 seconds) of each cycle. This is the period after the rapid rate of rise and before the rate of rise stabilises. It can be seen that on cycle 1, by (he end of this 6 second period the rate of rise has settled to approx 12 Ohms/s which is very close to the rate of rise that it will sustain for the rest of the cycle, whereas the rate of rise for the 5"1 cycle is higher at 31 Ohms/sec and it has not yet started to stabilise.
The increases in the rate of rise during this 6 second lime period and the increased offset from the initial resistance are a result of the milk deposits on the wet side of the element. The gradient of me 5th cycle is 2.6 times greater than the first cycle.
Earlier it was mentioned that the ratio for ranges of fill level and power rating was 1.4 and 1.2 respectively so it is expected that there is smflieient safety margin to enable this detection means to he used as a basis for identifying the build up of milk deposits on the element. This method could be combined with a threshold detection measured over the complete heating cycle. For example in Figure 41 in the first cycle the initial sensor value was 10860 Ohms which increased to 12] 61 Ohms during the cycle: a range of 1301 Ohms. Cycle 2 had a range of 1446 Ohms, wi increase of 15% over the first cycle and this increased to a range of 1860 Ohms by the fifth cycle, an increase of +3% over the first cycle

it would be possible to set a threshold during a function test cycle on the production line. Once the base range is known then a setting of 30% for instance above this base range would be seen at around cycle 3 to 4 and a warning would be given to the user. The algoritlim could be set so that it allows the cycle to be .completed, but that it gives a signal to the user that the vessel needs to be cleaned, for example with a flashing LED.
An example of such an algorithm that contains these features is shown in flow chart of Figures 43a and 43b, The algorithm assumes that a reference value (or reference values) is stored during the first production line operation of the unit It may also be possible for the control utiit to calculate a second set of references during the first 'out of me box' operation by the customer.
In addition to this, it would be beneficial to cross reference the resistance values of the NTC thermistor 14 and PTC sensor track 30 during an initial start up of the unit on the production line, which would help to determine the room temperature value for the PTC sensor track resistance. This single point cross reference would help to reduce the effective spread Fn sensor offset that would be experienced across a batch duo to variations in the print process, The slope of the sensor characteristic is set by the TCR of the material which will not vary much over the batch, but will vary from batch to batch.
One of the problems with using printed sensors is that the variations in materials and process can make for fairly significant differences in the room temperature resistance (resistivity variation) of the sensor track 30 and the rate of" change of resistance with temperature (TCR variation).
One way to improve this is to perform a two point reference check. The NTC sensor 14 will have a much tighter tolerance than the printed PTC sensor tracks 30. When the appliance is being tested OH the production line, the testing software takes an initial reading of the resistances of botii the NTC and PTC sensors 14, 30 before the eEement 12 is energised. The PTC sensor resistance value could then be taken as the equivalent temperature as the NTC sensor resistance value, giving a first reference point. This would not be a specific temperature, but would be a far more accurate representation of the room temperature value. The element is then energised to heat a quantity of water. The heating and stirring process proceeds and then once the NTC sensor 14 has detected the target temperature (approx 70°c for a milk fro (her, for example) the element is turned off At this point, ii second reference value is taken from the PTC sensor 30. The actual temperature of the PTC sensor 30 is likely to be higher than the NTC sensor temperature, because the PTC sensor is adjacent to the

heater tracks. Nevertheless, the testing software can thereby derive two reference values for the PTC sensor that will allow calculation of threshold values of either a fixed value or a rate of change. These threshold values- may he used in the algorithm above to detect dry-boil or . milk burning.
Tests have shown that the initial rate of use differed depending on whether the liquid was stirred or not, for example 140 Ohms/sec stirred, 190 Ohms/sec not stirred. Advantageously this difference could be used to detect whether the stirrer of frothet is inactive, for example because the stirrer or frother rotor has not been assembled onto the unit. In response to tins detection, further heating may be inhibited or reduced, or an indication may he made to the user that the sti rrer is not present, for example by illuminating an LED.
Alternative Embodiments
The present invention is not limited to kettles, milk brothers or stirrers, and heating elements therefor; aspects of the invention may be applied to other liquid heating and/or stirring frothing appliances such as wasserkochers., coffee makers such as tnoka and espresso makers, Turkish tea makers, samovars, water boiling urns, pans, sauce makers, hobs, steamers, chocolate fountains, fondues, steamers, pressure cookers., slow cookers, electric irons, food processors, blenders, juicers, smoothie makers, for example. Aspects of the invention are applicable to liquid dispensers, for example which dispense liquid using a pump or spray.
The above specific embodiments are described by way of reference only, and that many modifications and variations are possible within the scope of the enclosed claims.

We claim:
1. A liquid heating and stirring appliance comprising a liquid reservoir having a healing element plate in (he base thereof and a Totaiable stirrer for stirring the liquid within the reservoir, the healing clement plate comprising a heater substantially concentric with the rotatable stirrer.
2. The appliance of claim 1, wherein the stirrer is located above the element ptale, with a smaJl clearance therebetween.
3. The appliance of claim 1 or 2, wherein the stirrer includes a portion directly opposite the heater,
4. The appliance of claim 3, wherein the stirrer includes a. radially outer portion opposite the heater and a radially inner connecting portion having means for reducing the resistance (hereof
5. The appliance of claim 4, wherein the radially inner connecting portion is axially shorter than the radially outer portion.
6. The appliance of claim 4, wherein the radially inner connecting portion is perforated.
7. The appliance of any one of claims 1 to 6, wherein the stirrer extends radially proximate a side wall of the reservoir.
3. The appliance of any one of claims 1 to 7, wherein the stirrer is mounted above the reservoir and extends downwardly into the reservoir towards the element plate.
9, The appliance of any one of claims 1 to £, wherein the stirrer includes means for promoting flow of the liquid in an axial direction of the stirrer.
10, The appliance of any one of claims 1 to 9, wherein the stirrer includes means for promoting flow of the liquid in a radial direction of the stirrer,
11, The appliance of claim 9 or 10, wherein the means for promoting liquid flow comprises one or more rotatable blades.
12, The appliance of any one of claims 1 to 10, wherein the stirrer includes a frothing portion.
13, The appliance of claim 12, wherein the frothing portion is positioned radially inwardly of the periphery of the stirrer.
14. The appliance of claim 12, wherein the frothing portion is axially positioned away

from the element plate.
15. The appliancer of any preceding claim, wherein the heater comprises a sheathed heater.
16. The appliance of any one of claims 1 to 14, wherein the heater comprises a thick film heater.
17. The appliance of any one of claims 1 to 14, wherein the heating element plate is inductively heated.
IS. A liquid heating and stirring appliance, comprising a. liquid reservoir for heating liquid within the reservoir and a stirrer for stirring the liquid within the reservoir, the stirrer comprising a stirring element within the reservoir, electromagnetically coupled to a driving means outside the reservoir.
19. An appliance as claimed in claim 18, wherein ihe driving means comprises an electromagnetic coil.
20. A stirrer for an appliance as claimed in any preceding claim.
21. A liquid heating appliance comprising a first liquid chamber, electrically powered heating means operable to heat a first liquid within the first chamber, and a second chamber in thermal contact with the first chamber such that a second liquid within the second chamber is heated indirectly by the hearing of the first liquid, the appliance including means for introducing steam and/or vapour from the heated first liquid from the first chamber into the second chamber so that the steam and/or vapour passes through the second liquid.
2 J, The appliance of claim 21, wherein the second chamber is located substantially within the first chamber, so as to enhance the thermal contact therebetween.
iy. The appliance of claim 21 or claim 22, wherein the second chamber is removable from within the first chamber.
24. The appliance of any one of claims 21 to 23, wherein the means for introducing steam and/or vapour into the second chamher comprises a passage extending above the liquid level in the second chamber.
25. The appliance of any oae of claims 21 to 23, wherein the means for introducing steam and/or vapour into the second chamber comprises one or more one-way valves.
26. The appliance of any one of claims 21 to 25, including a stirrer for stirring the second

liquid within the second chamher.
27, A heated liquid dispensing appliance having a liquid reservoir, a heater for healing liquid within the reservoir and a pump for dispensing liquid from the reservoir, the dispenser having pump inhibiting means for inhibiting operation of the pump until the viscosity of the liquid heated within the reservoir is sufficiently low for the liquid to be dispensed.
28, The appliance of claim 27, wherein the pump inhibiting means comprises a temperature sensor for sensing the temperature of the heated liquid.
29. The appliance of claim 27, wherein the pump inhibiting means comprises a linxer for determining the duration of heating of the heated liquid.
30. The appliance of claim 27, including a stirrer for Stirling the heated liquid within the reservoir, Ihe pump inhibiting means coniprishig vistosuy sensing means for sensing the viscosity of the heated liquid by actuating the stirrer.
31- The appliance of claim 30; wherein the viscosity sensing means comprises load detecting means for detecting load on a motor for driving the stirrer.
32. The appliance of claim 31, wherein the load detecting means comprises a cut-out for switching off the motor under excessive load..
33. A heated liquid dispensing appliance having a liquid reservoir and a detachable assembly, the assembly being electrically powered by attachment to the reservoir, the assembly comprising a plurality of discrete electrical functions.
34. The appliance of claim 33, wherein said discrete electrical functions comprise one or more of a stirrer and a pumped dispenser.
35. The appliance of claim 33 or 34, wherein the reservoir includes an electrical beater for heating liquid withia the reservoir.
36. A liquid heater comprising an element plate fin contacting the liquid to be heated, and a localised heating elemenl arranged in thermal contact with the element plate through a substrate located between the element plate and the heating element, the substrate being [bicker in the vicinity of die heating element than in another portion thereof, so
as lo distribute heat evenly over the element plate.
37- The liquid heater of claim 36, wherein the substrate is thicker in a portion of The

substrate between the element plate and the heating element
38- The liquid heater of claim 36, therein the substrate is thicker in a portion of the substrate adjacent the heating element.
39. The liquid heater of any one of claims 36, wherein said another portion of the substrate further decreases in thickness towards the centre thereof.
40. A liquid heater comprising an element plate for contacting the liquid to be heated, and a Localised hearing element arranged! ill thermal contact with the element plate through a substrate located between the element plate and the heating element, the substrate having a void in the vicinity or the heating element, so as to distribute heat evenly over the element plate.
41. The liquid heater of claim 40, wherein the void comprises a channel in the surface of the substrate facing towards the element plate.
42. The liquid heater of uluim 43, wherein the channel extends substantially congruently with the localised heating element.
43. The liquid heater of any one of claims 40 to 42, wherein the void is filled with a material of low thermal conductivity.
44. The liquid heater of claim 43, wherein the material of low thermal conductivity is integrated with the element plate.
45. The liquid heater of any one of claims 36 to 44, including a thermostat fur controlling the heating of the liquid heater, the thermostat being in thermal contact with a central portion of the element plate.
46. The liquid heater of claim 45, wherein the thermostat is in contact with a central portion of the substrate.
47- A liquid heater comprising an element plate for contacting the liquid to be heated, and a localised healing element arranged in thermal contact with the element plate through a substrate located between the element plate and the heating element, the substrate extending outwardly beyond the element plate so as to distribute heat evenly over the element plate.
48. The liquid heater of claim 40, wherein the outward extension of the substrate is substantially coplanar with an inner part of the substrate.

49. The liquid heater of cfaim 40, wherein the outward extension of the substrate extends out of the plane of an inner part of the substrate.
50. The liquid heater of claim 49, wherein the clement plate has a thermally conductive sidcwall blending therefrom, and the outward extension of the substrate is in thermal contact with the sidewalk
51. The liquid heater of any one of claims 47 to 50, including a thermostat for controlling the heating of the liquid heater, the thermostat being in thermal contact with, the outward extension of the substrate.
52.A liquid heater comprising an element plate having a localised heating element arranged in (hernial contact therewith, the localised heating clement having an elongate- convoluted shape so as to distribute heat evenly over ihe element plate.
53- The heater of claim 52, including a second localised heating element in thermal contact therewith, located outward of the first localised heating element.
54. The heater of claim 52 or 53, wherein the localised healing element comprises a
sheathed heating element.
55, A liquid heating and stirring appliance, comprising a liquid reservoir having a heater.
for heating liquid within the reservoir and a stirrer for stirring the liquid within The
reservoir, the appliance including a control for actuating the stirrer after the heating of
the heater is reduced or switched off.
56- The appliance of claim 55, including a timer for determining a period for which the stirrer is. actuated after the heating of the heater is reduced or switched off.
57, The appliance of claim 55, including a thermostat for determining a thermal condition at which the stirrer is no longer actuated after the heating of the heater is reduced or switched off.
58, A liquid heating and stirring appliance, comprising a liquid reservoir having a heating element for heating liquid within the reservoir and a stirrer for stirring the liquid within the reservoir, the appliance including a control for detecting the rate of temperature rise of the element plate during heating, determining that the stirrer is absent or inoperative if the rate of rise exceeds a threshold value.
59, A heated liquid dispensing appliance comprising a liquid heating portion including
liquid heating means, a dispensing portion and a further portion, the portions being

removably conncctable together.
60. The appliance of claim 59, -wherein the further portion is connectabie between the heating portion and the dispensing portion,
61. The appliance of claim 59 or claim 60, having a liquid reservoir defined by one or more or said portions.
62. The appliance of claim 61, wherein the heating portion comprises a floor of the reservoir.
63. The appliance of any one cf claims 59 to 62, wherein the further portion comprises first and second further portions removably conncctable together.
64. The appliance of any one of claims 61 to 63, wherein a part of the volume of the reservoir is contained within each of the heating portion and the further portion.
65. The appliance of any one of claims 59 to 64, wherein one or more of said portions are conncctable together so as to align said portions iri a predetermined alignment.
66. The appliance of any one of claims 59 to 65, wherein at least one of the portions comprises a thermatry msnlating material or means.
67. The appliance of any one of claims 59 to 66, comprising a plurality of interchangeable said portions.
68. The appliance of any one of claims 59 to 67, wherein the further portion is disposable.
69. The appliance of any one of claims 59 to 68, wherein the dispensing portion is disposable.
70- A heated liquid dispensing appliance comprising a reservoir, heating means operable to heat the contents of the reservoir, and dispensing means for dispensing the contents of the reservoir, wherein a plurality of different said dispensing means are removably conncctable to the reservoir or to the heating means.
71. A heated liquid dispensing appliance comprising a plurality of interchangeable reservoir portions, healing means operable to heat the contents of any one of said reservoir portions, and dispensing means for dispensing the contents of said one reservoir portion,
72. The appliance of claim 70 or 71t including a support or housing for said plurality of
interchangeable portiuna.

73. A heated liquid dispensing appliance comprising a reservoir, heating means operable
to heat the conLents of the reservoir, and dispensing means for dispensing the contents
of the reservoir, wherein the reservoir includes a disposable container for the contents
of the reservoir.
74, A heated liquid dispensing appliance comprising a reservoir, heating rneans operable
to heat the comenLs of the reservoir, and dispensing means for dispensing the contents
of the reservoir, wherein the dispensing means includes, a flexible conduit,
75. A heated liquid dispensing appliance comprising a reservoir, heating means operable to heat the contents of the reservoir, and dispensing means for dispensing the contents of the reservoir, who:ein the reservoir is. tillable when inverted.
76. A heated liquid dispensing appliance comprising a reservoir, beating means operable to heat the contents of the reservoir, .and electrically powered dispensing means for dispensing the contents of the reservoir.
77. The dispensing appliance of claim 76, electrically connected or connecatable to a cordless power base, and including an electrical power source for providing power to the dispensing means when the dispensing appliance is disconnected from the power base,
78. A heated liquid dispensing appliance comprising a reserving heating means operable to heat the contents of the reservoir, dispensing means for dispensing the contents of the reservoir, and means for stirring or agitating the contents of the reservoir,
79. The dispensing appliance of claim 78, wherein the stirring or agitating means is drivable by a motor.
80. The dispensing appliance of claim 79, wherein the motor is mechanically coupled to a stirrer within the reservoir.
SL The dispensing appliance of claim 80, wherein the motor and stirrer are integrated in an assembly removably mountable in or on the appliance
82. The dispensing appliance of claim 80, wherein one or both of the motor and stirrer are removably mountable in or on the dispensing appliance.
83. The dispensing appliance of claim 79, wherein the motor is magnetically coupled to a stirrer within the reservoir.

84. The dispensing appliance of claim 78, wherein the stirring or agitating means is manually drivable.
85. The dispensing appliance of any one of claims 78 to 84, electrically connected or connectable to a cordless power base, and including an electrical power source for providing power to the stirring or agitating means when the dispensing appliance is disconnected from the power base.
86. A liquid dispensing appliance comprising a reservoir, means for stirring or agitating the contents of the reservoir, and means for dispensing the contents of the reservoir.
87. A thick film heating element comprising a substrate having a thick film heating track and a temperature sensor comprising a thick film -temperature sensing track formed thereon, wherein, the temperature sensing track comprises one or more first sections of a first material having a high resistivity and/or a high temperature coefficient of resistance, and one or more second sections of a second material having a low resistivity and/or a low temperature coefficient of resistance.
88. The element of claim 87, wherein the one or more second sections are of the same material as the heating track.
89. The element of any one of claims 87 to 8 8, -wherein the resistivity of said first sections is in the range 1-100 ft/square.
90. The element of any one of claims 87 to 89, wherein the temperature coefficient of resistance of the first sections is in the range 1500-3000 ppm.
91. The element of any one of claims 87 to 90, wherein the Tesistivity of said second sections is in the range 20-200 mΩ/squarc
92. The element of any one of claims 87 to 91, wherein the second sections have a positive temperature coefficient of resistance.
93. The element of any one of claims 87 to 92, wherein the sensing track comprises a plurality of said first sections, mutually distributed around the element.
94. A thick film heating element comprising a substrate having a thick film heating track and a temperature sensor comprising a thick film temperature sensing track formed thereon, wherein die heating track comprises at least a pair of substantially parallel heating sections connected at one end, wherein the temperature sensing track extends between said pair of substantially parallel sections and comprises substantially parallel

sensor sections connected adjacent said one end.
95. A thick film beating element comprising a substrate having a thick film heating track and a temperature sensor comprising a thick film temperature; sensing track formed Thereon, wherein the heating track and the temperature sensing track are formed of the same thick film material.
96. A thick film heating element comprising a substrate having a thick film heating track and a steam sensor formed integrally thereon,
97. The element of claim 96, wherein the steam sensor is formed as a thick film.
98. The element of any one of claims 96 to 97, wherein the steam sensor is sensitive to humidity,
99. The element of claim 98, wherein the steam sensor is a capocitative sensor.
100- The element of claim 99, wherein the steam sensor comprises a plurality of
interdigitated electrodes.
101 The element of claim 100, wherein the electrodes comprise silver,
102. The element of claim 101, wherein the electrodes include a high level of
palladium, .
103. The element of any one of claims 96 to 97, wherein the steam sensor is
sensitive to temperature.
104. The clement of claim 103, wherein the steam sensor comprises a long, thin, thick film track confined to a small area of the substrate,
105. The clement of any one of claims 96 to 104} including means for drying the steam sensor,

106, The element of claim 105, wherein said means comprises a second, discrete heating track,
107, The element of claim 105, wherein said means is arranged to pass a heating
current through the steam sensor.
108, The element of any one of claims 96 to 107, including means for directing
steam onto the steam sensor.
109. The element of claim 108, wherein said means includes a steam tube.

110. The element of claim 108 or 109, wherein said means includes a steam chamber arranged to segregate the steam senior from its surroundings.
111. The element cf any one of claims 87 to 110, wherein said substrate is substantially planar.
112. The element of any one of claims 87 to 111, wherein said substrate is substantially circular,
113. The element cf any one of claims S7 to 112, wherein said sub&trate comprises steel with a dielectric; surface layer.
114. The element of claim 113, wherein stud steel comprises stainless steel
115. The element of any one of claims 87 to 114, including a. sensing circuit connected to the sensor so as to generate a sensing signal.
116. The element of claim 115, wherein said sensing circuit comprises an analog to digital converter.
117. The element of claim 116, wherein the sensing circuit is arranged to apply a periodic dithering signal to the sensing signal prior to digital conversion.
118. The element of claim 116 or 117, wherein the sensing circuit is arranged to .
calculate amoving average of the digitally converted sensing signal.
119. A liquid heating vessel including an element according to any one of claims 87
to 118.
120, A flow-through heater including an element according to any one of claims 87
to 118.
121. A method of detecting deposition of solids in a liquid heater For heating milk
or similar liquids by means of a detected temperature, comprising comparing the rate
of temperature rise with time after an initial heating period with a first threshold value
and, if the rate of temperature rise exceeds the threshold and the absolute temperature
exceeds a second threshold value, determining a solid deposition condition.
122, A method of detecting deposition of solids in a liquid heater for heating milk
or similar liquids by means of a detected temperature, comprising comparing the rate
of temperature rise with time after an initial heating period with a threshold value and,
if the rate of temperature rise exceeds the threshold value, determining a dry boh

condition,
123. The method of claim 121 or 122, wherein the rate of temperature rise is determined by a PTC sensor.
124. The method of any one of claims 121 to 123, wherein said threshold value is determined by reference to an NTC sensor.
125. The method of any one of claims 121 to 124, wherein the liquid heater composes a liquid heating clement as claimed in any one of claims 87 to 1 IS.
126. A method of setting a target temperature reference value for a liquid healing apparatus arranged to heat liquid to a target sub-boiling temperature,. the apparatus having first. and second temperature sensors comprising respectively an NTC resistor and a PTC resistor, the, method comprising heating liquid within the apparatus utitil the target temperature is determined by means of the NTC resistor, and setting a corresponding value for the PTC resistor.
127. The method of claim 126, wherein the second temperature sensor is thermaily coupled to a heater of the apparatus.
128. The method of claim 127, wherein Lhe second temperature sensor comprises an elongate PTC sensor track adjacent a heater track.
12?. The method of any one of claims 126 to 12S, therein the apparatus comprises
a heated liquid frother or stirrer.
130. A liquid heating appliance including a control arranged to perform the method of any one of claims 121 to 128.
131. The appliance of any one of claims 16,18 to 32, 35, 55 to 57, 5S, 62, and 70 to 86. having a liquid heating element as claimed in any one of claims 87 to 1 IS.
132. The appliance of any one of claims 15,18 to 32, 35, 55 to 57, 58, 62. and 70 to 86P having a liquid heater as claimed in any one of claims 36 to 54.