CA2213381A1 - Improvements to liquid boiling apparatus - Google Patents
Improvements to liquid boiling apparatusInfo
- Publication number
- CA2213381A1 CA2213381A1 CA 2213381 CA2213381A CA2213381A1 CA 2213381 A1 CA2213381 A1 CA 2213381A1 CA 2213381 CA2213381 CA 2213381 CA 2213381 A CA2213381 A CA 2213381A CA 2213381 A1 CA2213381 A1 CA 2213381A1
- Authority
- CA
- Canada
- Prior art keywords
- temperature
- rate
- change
- electrical
- liquid
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- A—HUMAN NECESSITIES
- A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
- A47J—KITCHEN EQUIPMENT; COFFEE MILLS; SPICE MILLS; APPARATUS FOR MAKING BEVERAGES
- A47J27/00—Cooking-vessels
- A47J27/21—Water-boiling vessels, e.g. kettles
- A47J27/21008—Water-boiling vessels, e.g. kettles electrically heated
- A47J27/21016—Water-boiling vessels, e.g. kettles electrically heated with heating elements immersed in the water
-
- A—HUMAN NECESSITIES
- A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
- A47J—KITCHEN EQUIPMENT; COFFEE MILLS; SPICE MILLS; APPARATUS FOR MAKING BEVERAGES
- A47J27/00—Cooking-vessels
- A47J27/21—Water-boiling vessels, e.g. kettles
- A47J27/21008—Water-boiling vessels, e.g. kettles electrically heated
- A47J27/21158—Devices to detect overheating or boiling with a single control element or unit
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- Engineering & Computer Science (AREA)
- Food Science & Technology (AREA)
- Cookers (AREA)
Abstract
In a liquid heating apparatus (10) such as an electric kettle, a method is provided of controlling operation of an electrical element (11), for example to switch off the power supply to the element on boiling of the liquid. In the method, the temperature of the element (11) is measured at regular predetermined intervals by a sensor (14). A microprocessor (15) is provided linked to the sensor (14) and to a timer (16) and is capable of determining the rate of change of the temperature of the element (11) at any given time after the element (11) has been switched on. The microprocessor (15) can thereby detect when the rate of change in the temperature of the element (11) exceeds a predetermined threshold, which has been calculated according to the power rating of the electrical element, subsequent to a predetermined initial heating period for the element (11). Thus, the microprocessor (15) can control the means (12) for cutting-off or varying the electrical power supply to the element (11) dependent on the difference between said actual rate of change and said predetermined value. In this way, the apparatus can be used to detect an initial boiling of the liquid when the bubbles of vapour which initially form within the liquid congregate over the surface of the element and insulate it from the liquid for a short time causing the temperature of the element at this period of time to increase more rapidly.
Description
. CA 02213381 1997-08-19 ~_............................. . . ........ .. .. ~ -- .. ... --' ~ ' . - . . - - . -.. . - . ~ ~ . ....
~ 1 ~- --- ------- ..-IMPROVEMENTS TO LI~UID BOILING APPARATUS
The present invention relates to a liquid boiling apparatus incorporating an electrical element and in particular but not exclusively to water boiling apparatus such as an electric kettle.
In a conventional apparatus used for boiling liquid, such as an electric kettle, boiling of the liquid is detected by detecting the presence of the vapour produced as the liquid boils. Typically in an electric kettle, the pressure of the steam produced is used to operate a switch to cut off the electricity supply to the electrical element. However, one disadvantage with such an arrangement is that a considerable quantity of steam has to be produced before the pressure-responsive switch operates, particularly if only a small quantity of water is boiled in a large volume kettle. This increases the risk of the kettle boiling dry. In addition, to detect a dry boil condition, a thermal fuse is usually employed.
In various conventional cooking apparatus comprising an electrical heating element and a control circuit, it has ~een proposed that the temperature within the apparatus should be detected and this information used to control the supply of power to the element thereby to control the cooking proces~.
-For example, in DE 3642 181 C1 is disclosed a means of30 controlling the simmering or /cookinq time in a cooking vessel which is heated by an electrical element associated with a control circuit. The temperature in the cooking vessel is determined and utilized by the control circuit to regulate the heat output of the heating element in order that the simmering or cooking time can be set. This is accomplished ~y shuttins off the heating element a length h~h~FG S~ic~
of time before the completion of the predetermined simmering or cooking time and by using the heat content contained in the cooking material after shutting off the element to complete the preset simmering or cooking time.
DE 33 38 788 Cl discloses a method for deriving a measuring signal proportional to the temperature rise of a temperature-time characteristic curve in such a cooking vessel in which the temperature within the vessel is measured by means of a temperature sensor.
EP 0348 298 discloses a similar arrangement wherein for the purpose of effecting the thermal control of a heating apparatus its temperature is allowed to rise to a value lower than a predetermined maximum temperature, whereupon, after stopping the heating the temperature is allowed to rise through thermal inertia until the aforesaid maximum temperature is substantially reached. Here, the difference between the maximum temperature and the temperature at which heating is stopped is determined in accordance with the profile of the temperature rise curve during the heating period.
Such arrangements are particularly suitable for use in cooking utensils wherein it is desired to cook food for predetermined periods of time such as by simmering them in water. However, they are not so suitable for use in boiling apparatus such as kettles where it is desired to brin~ a liquid to a full rolling boil for the preparation of beverages and the like.
Kettles are known in which a temperature sensor is formed integrally with an electric element, for example by using thick film resistive tracks formed on a substrate, whereby over-heating of the heating element is avoided by directly sensing any excessive increase in the temperature ~ CA 02213381 1997-08-19 ~, ~ 7'~
3 ~ .7 of the substrate and taking appropriate action to shut off the power supply to the element. Such an arrangement is described in EP 0 585 015.
In addition to the prevention of over-heating of an electrical element, in EP 0 380 369 is additionally disclosed the used of a thermistor to effect electrical control of a heating element in a liquid heating vessel such as a kettle whereby the power supply to the element can be cut-off when the liquid boils. The functions of the control are effected in dependence on the provision of a thermistor located in association with a hot spot on a dry side of the head plate of the heating element of the vessel. The thermistor is therefore in close heat transfer relationship with the heating element and when a boil condition occurs within the vessel, the thermistor temperature stabilizes after an initial normal rate of rise. The electrical control is therefore programmed to detect rates of temperature rise in the thermistor below those caused by normal heating and to remove power from the element when the temperature stops risin~. However here again rapid boiling, producing large quantities of ~team, must occur before the temperature of the element stabi 1 izes .
It has been found, however, that when a liquid being heated by an electrical element in direct contact with the liquid begins to boil, the bubbles of vapour which initially form within the liquid congregate over the surface of the element before rising and discharging into the atmosphere. These bubbles insulate the element from the liquid for a short time but once a condition of rapid boiling occurs and the liquid is agitated, bubbles of vapour are formed throuqhout the liquid and any formed over the surface of the element rapidly rise to be replaced by liquid. It will be appreciated that boiling of the liquid 4 '~
could, therefore, be deduced by detection of the period at which the element is insulated by the first bubbles to be formed within liquid for, if the power supply to the element is kept constant, the rate of rise in the temperature of the element at this period of time will increase as the element is unable to discharge its heat into the liquid. Once rapid boiling occurs, however, the temperature of the element will level off as a steady state condition is reached.
It is an object of the present invention to make use of this phenomenon to enable the supply of power to a liquid boiling apparatus to be controlled. Such an apparatus overcomes the aforementioned disadvantages of conventional apparatus and enables boiling of a liquid to be detected without it being necessary to produce significant quantities of vapour and irrespective of the mass of liquid being heated.
According to a first aspect of the present invention there is provided a method of controlling the operation of an electrical element for boiling a liquid wherein the rate of change of the temperature of the element is determined at regular intervals, and the electrical power supply to the element is cut-off or varied when the rate of change of the temperature varies in a predetermined manner thereby to control the subseguent quantity of heat imparted to the liq~id by the element, and characterised in that it comprises the steps of measuring the temperature of the element at regular predetermined intervals; calculating the rate of change of the temperature of the element as aforesaid at each of said predetermined intervals;
monitoring the rate of change in the temperature of the element; and after a predetermined initial heating period sufficient to determine that a dry boil condition has not occurred, cutting-off or varying the electrical power supply to the element a predetermined time after said rate of change in the temperature of the element increases to a value which is predetermined accordinq to the power ratinq of the electrical element and is indicative of insulation of the element by bubbles of liquid vapour.
Thus, in the present invention the temperature of the electrical element itself is directly measured rather than the temperature of either the interior of the apparatus or a head portion of the element. Thus the rate of change of temperature of the heating element is directly monitored durinq the heating period in order that insulation of the element by bubbles of liquid vapour can be detected. In this way, any increase in the value of this rate of change can be used to infer that rapid boiling of the liquid in the apparatus is imminent rather than waiting until the rate of change of the temperature of the element levels off after commencement of the boiling of the liquid. The power supply to the heating element can thus be cut off or adjusted as desired as a consequence sooner than would otherwise be the case.
Preferably, in a water heating apparatus with a 2 kW
electrical element said predetermined value comprises a rate of rise of temperature of 40~C per second.
Preferably also, the predetermined initial heating period comprises at least one second.
Preferably also, if the electrical power supply to the element has been switched off after the rate of chanqe in the temperature of the element has reached the predetermined value and thereafter if the rate of decrease in the temperature of the element is slower than a predetermined rate of change for any given liquid, a warning siqnal is given whereby a user can be alerted to 4b clean the element.
Preferably also, in a water heating apparatus with a 2 kW electrical element said predetermined rate of chanse comprises a rate of decrease in the temperature of the element of substantially 30~C per second.
Alternatively, if the initial rate of chanse of the temperature of the element immediately subsequent to said initial heatins period for the element is greater than a predetermined rate of change for any given liquid but less than said predetermined value, a warning signal is given to prompt a user to clean the element.
Preferably also, in a water heating apparatus with a 2 kW electrical element, said warning signal is given if said initial rate of change of the temperature of the element immediately subsequent to said initial heating period is greater than 20~C per second but less than 40~C per second.
According to a second aspect of the present invention there is provided a liquid heating apparatus comprising an electrical element; a temperature sensor; means for cutting-off or varying the electrical power supply to the element; a timer; and a microprocessor linked to the sensor and to the timer; and characterised in that the temperature sensor can detect the temperature of the element; and in that the microprocessor is capable of determining the rate of change of the temperature of the element at any given time after the element is switched on and is programmed to compare said rate of change to a stored predetermined value and to control said means for cutting-off or varying the electrical power supply to the element dependent on the difference between said actual rate of change and said predetermined value in a such manner that the apparatus is controlled in accordance with the first aspect of the ~ CA 02213381 1997-08-19 ; ' " s 4c present invention.
Preferably, the temperature sensor comprises a thermistor located peripherally of the electrical element.
Advantageously, the electrical element comprises a conductive track of a thick film printed circuit formed on a substrate and the temperature sensor comprises a thermistor formed by a conductive track of measurable resistance on the same substrate.
Preferably also, the conductive track comprising said thermistor extends parallel to and in close proximity with at least a part of the conductive track comprising the electrical element.
Preferably also, the substrate comprises a ferromagnetic steel which will vibrate in use to mitigate the effect of limescale deposition thereon.
The present invention will now be described by way of example with reference to the accompanying drawings in which:-W 096/25869 PCT/~kYG/Q0~70 Figure 1 is a graph showing the rise in temperature against time of water contained within a liquid boiling apparatus and of an electrical element of such an apparatus;
Figure 2 is a schematic block diagram of circuitry for use in controlling the operation of an electrical element in an apparatus according to the present invention;
Figure 3 is a schematic view of a substrate incorporating an electrical element and a temperature sensor for use in an apparatus according to the present invention; and Figure 4 is a graph similar to Figure 1 showing the change in temperature against time of an electrical element in a water boiling apparatus in both a scaled and unscaled condition when the water is heated to boiling point and then subsequently permitted to cool.
The scientific phenome~on underlying the present invention will firstly be described in detail with reference to Figure 1. Whilst Figure 1 shows the conditions in a water boiling apparatus such as an electric kettle it should be appreciated that a similar phenomenon would occur in a boiling apparatus for any liquid.
Figure 1 is a graph illustrating ideal conditions when a litre of water is heated to boiling point by a 2 kW
electrical element in an apparatus such as a kettle. The element itself can be of any conventional type. The rise in the temperature of the water against time is shown by the dashed line 1; the rise in the temperature of the electrical element heating the water is shown by the unbroken line 2; and the rise in the temperature of the electrical element in a dry kettle, ie. in a dry boil condition is shown by the unbroken line 3.
As can be seen, when the electrical element is powered the water temperature rises linearly from ambient to boiling point at 100~C before levellinq off and remaining at boiling point for as long as heat is supplied to it by the element. The length of time taken for the water to reach boiling point is dependent on the mass of water being heated and the power rating of the element but the relative gradients of the lines 1, 2 and 3 are always the same. In contrast to line 1, the temperature of the element rises rapidly initially at approximately 40~C per second, dependent on its thermal mass, until it reaches a point A
when the temperature begins to rise more slowly and its rate of rise becomes the same as that of the water.
However, just before boiling of the water occurs, the gradient of the line 2 again rises rapidly at a point B to a higher value before levelling off at a temperature of approximately 130~C at a point C.
The point B in the line 2 occurs when the bubbles of vapour which initially form within the water are lying over the surface of the element and are thereby insulating it from the water. This causes the temperature of the element to rise sharply. However, as the water begins to boil more rapidly, the insulating layer of bubbles is dispersed as the water becomes agitated and the temperature of the element levels off at point C and remains thereafter in a steady state condition.
Line 3 of the graph shows the rise in temperature of the element in a dry boil condition when no water is present in the kettle. Here at point A, the rate of rise in the temperature of the element does not fall but continues to rise sharply. It can be seen that the gradient of the line 3 from the point A onwards has a value which is -7 ~ .
similar to that of the line 2 between points B and C when the element is being insulated by the bubbles of vapour.
For a 2 kW element, this comprises a rate of approximately 40~C per second.
The present invention uses the fact that the gradient of the line 2 increases rapidly just prior to and at the initial boiling of a liquid because of the aforementioned phenomenon in order to provide a means of controlling the power supply to an electrical element. In addition, dry boil conditions can be monitored. For example, if a 2kW
element sustains a rate of temperature rise of 40~C per second for more than approximately a second either after the initial heating period of the element, that is after point A has been reached, or after point B has been reached, then a dry boil condition can be inferred. In these circumstances the power supply to the element can be cut off until the apparatus is manually re-set.
With reference to Figure 2, a liquid heating apparatus 10, such as an electric kettle, comprises at electrical element 11 which can linked by a power switch 12 to a source of electricity 13 such as a mains supply. Within the apparatus 10 and in close proximity to the element is a tempèrature sensor 14 for detecting the running temperature of the element 11. The output from the temperature sensor 14 is connected to a microprocessor 15 which can control the power supply to the element 11 via the switch 12. The microprocessor 15 is also linked to or incorporates a timer 16 which measures the elapsed time from the point at which the element 11 is first activated.
In normal operation of the apparatus, the apparatus 10 is at least partially filled with water and the element 11 is activated by operation of the switch 12 to heat the water. As the microprocessor 15 is linked to both the -') CA 02213381 1997-08-19 8 .~
temperature sensor 14 and the timer 15 it can calculate at predetermined intervals the instantaneous rate of change of the temperature of the element 11. In other words it can calculate the gradient of the line 2 in Figure 1 at any given elapsed time. The microprocessor 15 is programmed to make this calculation at predetermined intervals of a second or less throughout the period during which the element 11 is activated and by this means it is then possible to detect the condition of the element 11 when the rate of change of its temperature has a value which is between points B and C as shown in Figure 1. It is known, therefore that at point C and beyond the water must be at boiling point. Thus, it is possible to program the microprocessor 15 either to cut-off the electrical supply to the element 11 altogether after a further predetermined time when rapid boiling will have been achieved, or if the switch 12 is of a sophisticated type such as a TRIAC, relay or other voltage controlling means, to reduce the power supplied to the element 11 to permit the water in the apparatus to be kept, for example, in a simmering mode.
Also, as previously described the microprocessor can be programmed to take action if a dry boil condition is suspected at any time.
In order for apparatus accordin~ to the invention to operate satisfactorily, the temperature of the element 11 must be detected with some accuracy. It is therefore important for the sensor 14 to be in close proximity to the element 11. With a conventional wire wound electrical element the temperature sensor could comprise a thermistor wound around the periphery of the element. However, the invention is particularly suited for use with an electrical element which compri~es a conductive track of a thick film printed circuit formed on a substrate. The temperature sensor can then comprise a thermistor formed by a second conductive track of measurable resistance on the same substrate whereby the temperature of the element can be accurately detected. Such an element will now be described in more detail with reference to Figure 3.
As shown in Figure 3, a substrate 17 is provided to which a thick film circuit layout has been applied, in known manner, by printing. The circuit layout comprises a first conductive track 18 constituting the electrical element 11 and a second conductive track 19 constituting the temperature sensor 14 which takes the form of a thermistor. An earth tag 20 is also provided, in conventional fashion, for the element.
Preferably, the substrate 17 comprises a ferromagnetic steel. Such a substrate will vibrate slightly in use when an electrical current is passing through the track 18. This is advantageous for use with water heating apparatus as the vibration prevents significant layers of limescale being deposited on the substrate 17 because such layers are eventually broken up by the energy of the vibrations.
-The track 18 follows a tortuous path over the majorityof the area of the substrate 17 to maximize the heated area of the element 11. At its ends, the track 18 terminates in respective contact portions 21 and 22 which are adapted to make electrical connection with an electrical control device which comprises the switch 12 as shown in Figure 2.
A third contact portion 23 is also provided connected to the track 18 which is used to take power from the element to power the control circuitry comprising the microprocessor 15 and the timer 16.
The track 19 constituting the temperature sensor extends in close proximity with the track 18 around its periphery between first and second terminal pads 24 and 25.
These pads 24, 25 are used to connect the track to the microprocessor 15.
Up to this point, a water heating apparatus has been described wherein it is expected that the rates of rise of both the water and the element itself will closely follow an ideal, such as described with reference to Figure 1.
However, in reality the operation of the element and therefore the efficient heating of the water within the apparatus will be affected by the presence of limescale.
As is known, in any water heating apparatus which heats water above 65~C and which is used in hard water areas, limescale tends to build up as a layer within the apparatus. In particular, limescale builds up as a coating over the element itself. Thick film printed circuits formed on substrates are not immune from such limescale build-up but as previously described, those formed on a substrate of ferromagnetic steel tend to be self-cleaning once a significant layer of limescale is present. However, the presence of a limescale layer on an electrical element affects the rate of rise of its temperature when powered.
In Figure 4 is shown the change in temperature against time of an electrical element in a water heating apparatus in both a scaled and unscaled condition when the water is heated to boiling point and then subsequently permitted to cool. Unbroken line 4 is equivalent to line 3 in Figure 1 and shows the change in temperature against time of the element in an unscaled condition. Here, however, a short time after a steady state position is reached once the water is boiling, the power to the element is switched off.
This occurs at point D and it can be seen that the effect of turning the power off results in a rapid cooling of the element until it reaches the temperature of the water, at 3S point E. Thereafter, the water and the element together cool much more slowly at a rate which will be determined by factors that are of no relevance to the present invention and that are dependent on the environment of the kettle itself and the quantity of water heated initially.
Should the element have a layer of limescale, its performance is significantly affected and the change of its temperature against time is shown by line 5. The limescale acts as an insulator placed between the element and the water. When the element is switched on, the temperature of the element again rises rapidly but at point A where the initial rapid rate of rise in the temperature of the unscaled element falls to track that of the water, the rate of rise in the temperature of the scaled element continues to rise for a further short time before reducing. When it does reduce, at point F, the actual running temperature of the element is greater by approximately 20-C over that of the unscaled element. Between point A and point F if the rate of change of the temperature of a 2 kW element is greater than 20-C per second but less than 40-C per second then it can be deduced that it re~uires de-scaling.
Points B and C occur at the same time for the scaled element as the unscaled element so that detection of the boiling of the water is not affected. However, after the power to the element is switched off at point D, the scaled element takes a significantly longer time to cool down to the same temperature, which occurs at point G. In particular it is estimated that in a water heating apparatus with a 2 kW electrical element a rate of decrease in the temperature of the element of less than 30-C per second after point D indicates that the element requires de-scaling.
Hence, it is possible by detecting a higher running temperature of the element after the initial period up to point A than would normally be expected, or by detecting CA 022l338l l997-08-l9 W 096/25869 PCT/~b,''00~70 either a higher rate of increase in the temperature of the element immediately after point A or a slower rate of decrease in the temperature of the element after the power has been switched of at point D than would otherwise be expected to deduce that the element needs de-scaling or cleaning. It is possible, therefore, to include in the control circuitry shown in Figure 3 a warning signal such as a light which can be illuminated to prompt a user to clean the element.
Thus, the invention provides a means whereby the boiling of a liquid in a vessel can be detected by monitoring the temperature of the element without reference to the liquid itself. This means that the use of conventional vapour pressure switches and the thermal fuses used to detect dry boil conditions can be avoided and, combined with the use of thick film elements, that all the element control circuitry can be made solid state. This significantly reduces the quantity of wiring required for such an apparatus and thereby simplifies its assembly.
The detection of boiling also enables the apparatus to be simply adapted to incorporate built-in simmer controls and other variable temperature controls.
In addition, for a water heating apparatus, such as a kettle, or for other apparatus used for boiling liquids resulting in the deposition of a sediment or scale further analysis of the rates of change in the element temperature can be carried out to enable users to be prompted into cleaning or de-scaling the element to ensure the apparatus operates at maximum efficiency.
~ 1 ~- --- ------- ..-IMPROVEMENTS TO LI~UID BOILING APPARATUS
The present invention relates to a liquid boiling apparatus incorporating an electrical element and in particular but not exclusively to water boiling apparatus such as an electric kettle.
In a conventional apparatus used for boiling liquid, such as an electric kettle, boiling of the liquid is detected by detecting the presence of the vapour produced as the liquid boils. Typically in an electric kettle, the pressure of the steam produced is used to operate a switch to cut off the electricity supply to the electrical element. However, one disadvantage with such an arrangement is that a considerable quantity of steam has to be produced before the pressure-responsive switch operates, particularly if only a small quantity of water is boiled in a large volume kettle. This increases the risk of the kettle boiling dry. In addition, to detect a dry boil condition, a thermal fuse is usually employed.
In various conventional cooking apparatus comprising an electrical heating element and a control circuit, it has ~een proposed that the temperature within the apparatus should be detected and this information used to control the supply of power to the element thereby to control the cooking proces~.
-For example, in DE 3642 181 C1 is disclosed a means of30 controlling the simmering or /cookinq time in a cooking vessel which is heated by an electrical element associated with a control circuit. The temperature in the cooking vessel is determined and utilized by the control circuit to regulate the heat output of the heating element in order that the simmering or cooking time can be set. This is accomplished ~y shuttins off the heating element a length h~h~FG S~ic~
of time before the completion of the predetermined simmering or cooking time and by using the heat content contained in the cooking material after shutting off the element to complete the preset simmering or cooking time.
DE 33 38 788 Cl discloses a method for deriving a measuring signal proportional to the temperature rise of a temperature-time characteristic curve in such a cooking vessel in which the temperature within the vessel is measured by means of a temperature sensor.
EP 0348 298 discloses a similar arrangement wherein for the purpose of effecting the thermal control of a heating apparatus its temperature is allowed to rise to a value lower than a predetermined maximum temperature, whereupon, after stopping the heating the temperature is allowed to rise through thermal inertia until the aforesaid maximum temperature is substantially reached. Here, the difference between the maximum temperature and the temperature at which heating is stopped is determined in accordance with the profile of the temperature rise curve during the heating period.
Such arrangements are particularly suitable for use in cooking utensils wherein it is desired to cook food for predetermined periods of time such as by simmering them in water. However, they are not so suitable for use in boiling apparatus such as kettles where it is desired to brin~ a liquid to a full rolling boil for the preparation of beverages and the like.
Kettles are known in which a temperature sensor is formed integrally with an electric element, for example by using thick film resistive tracks formed on a substrate, whereby over-heating of the heating element is avoided by directly sensing any excessive increase in the temperature ~ CA 02213381 1997-08-19 ~, ~ 7'~
3 ~ .7 of the substrate and taking appropriate action to shut off the power supply to the element. Such an arrangement is described in EP 0 585 015.
In addition to the prevention of over-heating of an electrical element, in EP 0 380 369 is additionally disclosed the used of a thermistor to effect electrical control of a heating element in a liquid heating vessel such as a kettle whereby the power supply to the element can be cut-off when the liquid boils. The functions of the control are effected in dependence on the provision of a thermistor located in association with a hot spot on a dry side of the head plate of the heating element of the vessel. The thermistor is therefore in close heat transfer relationship with the heating element and when a boil condition occurs within the vessel, the thermistor temperature stabilizes after an initial normal rate of rise. The electrical control is therefore programmed to detect rates of temperature rise in the thermistor below those caused by normal heating and to remove power from the element when the temperature stops risin~. However here again rapid boiling, producing large quantities of ~team, must occur before the temperature of the element stabi 1 izes .
It has been found, however, that when a liquid being heated by an electrical element in direct contact with the liquid begins to boil, the bubbles of vapour which initially form within the liquid congregate over the surface of the element before rising and discharging into the atmosphere. These bubbles insulate the element from the liquid for a short time but once a condition of rapid boiling occurs and the liquid is agitated, bubbles of vapour are formed throuqhout the liquid and any formed over the surface of the element rapidly rise to be replaced by liquid. It will be appreciated that boiling of the liquid 4 '~
could, therefore, be deduced by detection of the period at which the element is insulated by the first bubbles to be formed within liquid for, if the power supply to the element is kept constant, the rate of rise in the temperature of the element at this period of time will increase as the element is unable to discharge its heat into the liquid. Once rapid boiling occurs, however, the temperature of the element will level off as a steady state condition is reached.
It is an object of the present invention to make use of this phenomenon to enable the supply of power to a liquid boiling apparatus to be controlled. Such an apparatus overcomes the aforementioned disadvantages of conventional apparatus and enables boiling of a liquid to be detected without it being necessary to produce significant quantities of vapour and irrespective of the mass of liquid being heated.
According to a first aspect of the present invention there is provided a method of controlling the operation of an electrical element for boiling a liquid wherein the rate of change of the temperature of the element is determined at regular intervals, and the electrical power supply to the element is cut-off or varied when the rate of change of the temperature varies in a predetermined manner thereby to control the subseguent quantity of heat imparted to the liq~id by the element, and characterised in that it comprises the steps of measuring the temperature of the element at regular predetermined intervals; calculating the rate of change of the temperature of the element as aforesaid at each of said predetermined intervals;
monitoring the rate of change in the temperature of the element; and after a predetermined initial heating period sufficient to determine that a dry boil condition has not occurred, cutting-off or varying the electrical power supply to the element a predetermined time after said rate of change in the temperature of the element increases to a value which is predetermined accordinq to the power ratinq of the electrical element and is indicative of insulation of the element by bubbles of liquid vapour.
Thus, in the present invention the temperature of the electrical element itself is directly measured rather than the temperature of either the interior of the apparatus or a head portion of the element. Thus the rate of change of temperature of the heating element is directly monitored durinq the heating period in order that insulation of the element by bubbles of liquid vapour can be detected. In this way, any increase in the value of this rate of change can be used to infer that rapid boiling of the liquid in the apparatus is imminent rather than waiting until the rate of change of the temperature of the element levels off after commencement of the boiling of the liquid. The power supply to the heating element can thus be cut off or adjusted as desired as a consequence sooner than would otherwise be the case.
Preferably, in a water heating apparatus with a 2 kW
electrical element said predetermined value comprises a rate of rise of temperature of 40~C per second.
Preferably also, the predetermined initial heating period comprises at least one second.
Preferably also, if the electrical power supply to the element has been switched off after the rate of chanqe in the temperature of the element has reached the predetermined value and thereafter if the rate of decrease in the temperature of the element is slower than a predetermined rate of change for any given liquid, a warning siqnal is given whereby a user can be alerted to 4b clean the element.
Preferably also, in a water heating apparatus with a 2 kW electrical element said predetermined rate of chanse comprises a rate of decrease in the temperature of the element of substantially 30~C per second.
Alternatively, if the initial rate of chanse of the temperature of the element immediately subsequent to said initial heatins period for the element is greater than a predetermined rate of change for any given liquid but less than said predetermined value, a warning signal is given to prompt a user to clean the element.
Preferably also, in a water heating apparatus with a 2 kW electrical element, said warning signal is given if said initial rate of change of the temperature of the element immediately subsequent to said initial heating period is greater than 20~C per second but less than 40~C per second.
According to a second aspect of the present invention there is provided a liquid heating apparatus comprising an electrical element; a temperature sensor; means for cutting-off or varying the electrical power supply to the element; a timer; and a microprocessor linked to the sensor and to the timer; and characterised in that the temperature sensor can detect the temperature of the element; and in that the microprocessor is capable of determining the rate of change of the temperature of the element at any given time after the element is switched on and is programmed to compare said rate of change to a stored predetermined value and to control said means for cutting-off or varying the electrical power supply to the element dependent on the difference between said actual rate of change and said predetermined value in a such manner that the apparatus is controlled in accordance with the first aspect of the ~ CA 02213381 1997-08-19 ; ' " s 4c present invention.
Preferably, the temperature sensor comprises a thermistor located peripherally of the electrical element.
Advantageously, the electrical element comprises a conductive track of a thick film printed circuit formed on a substrate and the temperature sensor comprises a thermistor formed by a conductive track of measurable resistance on the same substrate.
Preferably also, the conductive track comprising said thermistor extends parallel to and in close proximity with at least a part of the conductive track comprising the electrical element.
Preferably also, the substrate comprises a ferromagnetic steel which will vibrate in use to mitigate the effect of limescale deposition thereon.
The present invention will now be described by way of example with reference to the accompanying drawings in which:-W 096/25869 PCT/~kYG/Q0~70 Figure 1 is a graph showing the rise in temperature against time of water contained within a liquid boiling apparatus and of an electrical element of such an apparatus;
Figure 2 is a schematic block diagram of circuitry for use in controlling the operation of an electrical element in an apparatus according to the present invention;
Figure 3 is a schematic view of a substrate incorporating an electrical element and a temperature sensor for use in an apparatus according to the present invention; and Figure 4 is a graph similar to Figure 1 showing the change in temperature against time of an electrical element in a water boiling apparatus in both a scaled and unscaled condition when the water is heated to boiling point and then subsequently permitted to cool.
The scientific phenome~on underlying the present invention will firstly be described in detail with reference to Figure 1. Whilst Figure 1 shows the conditions in a water boiling apparatus such as an electric kettle it should be appreciated that a similar phenomenon would occur in a boiling apparatus for any liquid.
Figure 1 is a graph illustrating ideal conditions when a litre of water is heated to boiling point by a 2 kW
electrical element in an apparatus such as a kettle. The element itself can be of any conventional type. The rise in the temperature of the water against time is shown by the dashed line 1; the rise in the temperature of the electrical element heating the water is shown by the unbroken line 2; and the rise in the temperature of the electrical element in a dry kettle, ie. in a dry boil condition is shown by the unbroken line 3.
As can be seen, when the electrical element is powered the water temperature rises linearly from ambient to boiling point at 100~C before levellinq off and remaining at boiling point for as long as heat is supplied to it by the element. The length of time taken for the water to reach boiling point is dependent on the mass of water being heated and the power rating of the element but the relative gradients of the lines 1, 2 and 3 are always the same. In contrast to line 1, the temperature of the element rises rapidly initially at approximately 40~C per second, dependent on its thermal mass, until it reaches a point A
when the temperature begins to rise more slowly and its rate of rise becomes the same as that of the water.
However, just before boiling of the water occurs, the gradient of the line 2 again rises rapidly at a point B to a higher value before levelling off at a temperature of approximately 130~C at a point C.
The point B in the line 2 occurs when the bubbles of vapour which initially form within the water are lying over the surface of the element and are thereby insulating it from the water. This causes the temperature of the element to rise sharply. However, as the water begins to boil more rapidly, the insulating layer of bubbles is dispersed as the water becomes agitated and the temperature of the element levels off at point C and remains thereafter in a steady state condition.
Line 3 of the graph shows the rise in temperature of the element in a dry boil condition when no water is present in the kettle. Here at point A, the rate of rise in the temperature of the element does not fall but continues to rise sharply. It can be seen that the gradient of the line 3 from the point A onwards has a value which is -7 ~ .
similar to that of the line 2 between points B and C when the element is being insulated by the bubbles of vapour.
For a 2 kW element, this comprises a rate of approximately 40~C per second.
The present invention uses the fact that the gradient of the line 2 increases rapidly just prior to and at the initial boiling of a liquid because of the aforementioned phenomenon in order to provide a means of controlling the power supply to an electrical element. In addition, dry boil conditions can be monitored. For example, if a 2kW
element sustains a rate of temperature rise of 40~C per second for more than approximately a second either after the initial heating period of the element, that is after point A has been reached, or after point B has been reached, then a dry boil condition can be inferred. In these circumstances the power supply to the element can be cut off until the apparatus is manually re-set.
With reference to Figure 2, a liquid heating apparatus 10, such as an electric kettle, comprises at electrical element 11 which can linked by a power switch 12 to a source of electricity 13 such as a mains supply. Within the apparatus 10 and in close proximity to the element is a tempèrature sensor 14 for detecting the running temperature of the element 11. The output from the temperature sensor 14 is connected to a microprocessor 15 which can control the power supply to the element 11 via the switch 12. The microprocessor 15 is also linked to or incorporates a timer 16 which measures the elapsed time from the point at which the element 11 is first activated.
In normal operation of the apparatus, the apparatus 10 is at least partially filled with water and the element 11 is activated by operation of the switch 12 to heat the water. As the microprocessor 15 is linked to both the -') CA 02213381 1997-08-19 8 .~
temperature sensor 14 and the timer 15 it can calculate at predetermined intervals the instantaneous rate of change of the temperature of the element 11. In other words it can calculate the gradient of the line 2 in Figure 1 at any given elapsed time. The microprocessor 15 is programmed to make this calculation at predetermined intervals of a second or less throughout the period during which the element 11 is activated and by this means it is then possible to detect the condition of the element 11 when the rate of change of its temperature has a value which is between points B and C as shown in Figure 1. It is known, therefore that at point C and beyond the water must be at boiling point. Thus, it is possible to program the microprocessor 15 either to cut-off the electrical supply to the element 11 altogether after a further predetermined time when rapid boiling will have been achieved, or if the switch 12 is of a sophisticated type such as a TRIAC, relay or other voltage controlling means, to reduce the power supplied to the element 11 to permit the water in the apparatus to be kept, for example, in a simmering mode.
Also, as previously described the microprocessor can be programmed to take action if a dry boil condition is suspected at any time.
In order for apparatus accordin~ to the invention to operate satisfactorily, the temperature of the element 11 must be detected with some accuracy. It is therefore important for the sensor 14 to be in close proximity to the element 11. With a conventional wire wound electrical element the temperature sensor could comprise a thermistor wound around the periphery of the element. However, the invention is particularly suited for use with an electrical element which compri~es a conductive track of a thick film printed circuit formed on a substrate. The temperature sensor can then comprise a thermistor formed by a second conductive track of measurable resistance on the same substrate whereby the temperature of the element can be accurately detected. Such an element will now be described in more detail with reference to Figure 3.
As shown in Figure 3, a substrate 17 is provided to which a thick film circuit layout has been applied, in known manner, by printing. The circuit layout comprises a first conductive track 18 constituting the electrical element 11 and a second conductive track 19 constituting the temperature sensor 14 which takes the form of a thermistor. An earth tag 20 is also provided, in conventional fashion, for the element.
Preferably, the substrate 17 comprises a ferromagnetic steel. Such a substrate will vibrate slightly in use when an electrical current is passing through the track 18. This is advantageous for use with water heating apparatus as the vibration prevents significant layers of limescale being deposited on the substrate 17 because such layers are eventually broken up by the energy of the vibrations.
-The track 18 follows a tortuous path over the majorityof the area of the substrate 17 to maximize the heated area of the element 11. At its ends, the track 18 terminates in respective contact portions 21 and 22 which are adapted to make electrical connection with an electrical control device which comprises the switch 12 as shown in Figure 2.
A third contact portion 23 is also provided connected to the track 18 which is used to take power from the element to power the control circuitry comprising the microprocessor 15 and the timer 16.
The track 19 constituting the temperature sensor extends in close proximity with the track 18 around its periphery between first and second terminal pads 24 and 25.
These pads 24, 25 are used to connect the track to the microprocessor 15.
Up to this point, a water heating apparatus has been described wherein it is expected that the rates of rise of both the water and the element itself will closely follow an ideal, such as described with reference to Figure 1.
However, in reality the operation of the element and therefore the efficient heating of the water within the apparatus will be affected by the presence of limescale.
As is known, in any water heating apparatus which heats water above 65~C and which is used in hard water areas, limescale tends to build up as a layer within the apparatus. In particular, limescale builds up as a coating over the element itself. Thick film printed circuits formed on substrates are not immune from such limescale build-up but as previously described, those formed on a substrate of ferromagnetic steel tend to be self-cleaning once a significant layer of limescale is present. However, the presence of a limescale layer on an electrical element affects the rate of rise of its temperature when powered.
In Figure 4 is shown the change in temperature against time of an electrical element in a water heating apparatus in both a scaled and unscaled condition when the water is heated to boiling point and then subsequently permitted to cool. Unbroken line 4 is equivalent to line 3 in Figure 1 and shows the change in temperature against time of the element in an unscaled condition. Here, however, a short time after a steady state position is reached once the water is boiling, the power to the element is switched off.
This occurs at point D and it can be seen that the effect of turning the power off results in a rapid cooling of the element until it reaches the temperature of the water, at 3S point E. Thereafter, the water and the element together cool much more slowly at a rate which will be determined by factors that are of no relevance to the present invention and that are dependent on the environment of the kettle itself and the quantity of water heated initially.
Should the element have a layer of limescale, its performance is significantly affected and the change of its temperature against time is shown by line 5. The limescale acts as an insulator placed between the element and the water. When the element is switched on, the temperature of the element again rises rapidly but at point A where the initial rapid rate of rise in the temperature of the unscaled element falls to track that of the water, the rate of rise in the temperature of the scaled element continues to rise for a further short time before reducing. When it does reduce, at point F, the actual running temperature of the element is greater by approximately 20-C over that of the unscaled element. Between point A and point F if the rate of change of the temperature of a 2 kW element is greater than 20-C per second but less than 40-C per second then it can be deduced that it re~uires de-scaling.
Points B and C occur at the same time for the scaled element as the unscaled element so that detection of the boiling of the water is not affected. However, after the power to the element is switched off at point D, the scaled element takes a significantly longer time to cool down to the same temperature, which occurs at point G. In particular it is estimated that in a water heating apparatus with a 2 kW electrical element a rate of decrease in the temperature of the element of less than 30-C per second after point D indicates that the element requires de-scaling.
Hence, it is possible by detecting a higher running temperature of the element after the initial period up to point A than would normally be expected, or by detecting CA 022l338l l997-08-l9 W 096/25869 PCT/~b,''00~70 either a higher rate of increase in the temperature of the element immediately after point A or a slower rate of decrease in the temperature of the element after the power has been switched of at point D than would otherwise be expected to deduce that the element needs de-scaling or cleaning. It is possible, therefore, to include in the control circuitry shown in Figure 3 a warning signal such as a light which can be illuminated to prompt a user to clean the element.
Thus, the invention provides a means whereby the boiling of a liquid in a vessel can be detected by monitoring the temperature of the element without reference to the liquid itself. This means that the use of conventional vapour pressure switches and the thermal fuses used to detect dry boil conditions can be avoided and, combined with the use of thick film elements, that all the element control circuitry can be made solid state. This significantly reduces the quantity of wiring required for such an apparatus and thereby simplifies its assembly.
The detection of boiling also enables the apparatus to be simply adapted to incorporate built-in simmer controls and other variable temperature controls.
In addition, for a water heating apparatus, such as a kettle, or for other apparatus used for boiling liquids resulting in the deposition of a sediment or scale further analysis of the rates of change in the element temperature can be carried out to enable users to be prompted into cleaning or de-scaling the element to ensure the apparatus operates at maximum efficiency.
Claims (12)
1. A method of controlling the operation of an electrical element (11) for boiling a liquid wherein the rate of change of the temperature of the element (11) is determined at regular intervals, and the electrical power supply to the element (11) is cut-off or varied when the rate of change of the temperature varies in a predetermined manner thereby to control the subsequent quantity of heat imparted to the liquid by the element, and characterised in that it comprises the steps of measuring the temperature of the element (11) at regular predetermined intervals;
calculating the rate of change of the temperature of the element (11) as aforesaid at each of said predetermined intervals;
monitoring the rate of change in the temperature of the element (11); and after a predetermined initial heating period sufficient to determine that a dry boil condition has not occurred, cutting-off or varying the electrical power supply to the element (11) a predetermined time after said rate of change in the temperature of the element (11) increases above a value which is predetermined according to the power rating of the electrical element (11) and is indicative of insulation of the element by bubbles of liquid vapour.
calculating the rate of change of the temperature of the element (11) as aforesaid at each of said predetermined intervals;
monitoring the rate of change in the temperature of the element (11); and after a predetermined initial heating period sufficient to determine that a dry boil condition has not occurred, cutting-off or varying the electrical power supply to the element (11) a predetermined time after said rate of change in the temperature of the element (11) increases above a value which is predetermined according to the power rating of the electrical element (11) and is indicative of insulation of the element by bubbles of liquid vapour.
2. A method as claimed in Claim 1, characterised in that in a water heating apparatus (10) with a 2 kW electrical element (11) said predetermined value comprises a rate of rise of temperature of 40°C per second.
3. A method as claimed in Claim 1 or Claim 2, characterised in that the predetermined initial heating period comprises at least one second.
4. A method as claimed in any one of Claims 1 to 3, characterised in that if the electrical power supply to the element (11) has been switched off after the rate of change in the temperature of the element (11) has reached the predetermined value and thereafter if the rate of decrease in the temperature of the element is slower than a predetermined rate of change for any given liquid, a warning signal is given whereby a user can be alerted to clean the element (11).
5. A method as claimed in Claim 4, characterised in that in a water heating apparatus (10) with a 2 kW electrical element (11), said predetermined rate of change comprises a rate of decrease in the temperature of the element (11) of substantially 30°C per second.
6. A method as claimed in any one of Claims 1 to 3, characterised in that if the initial rate of change of the temperature of the element (11) immediately subsequent to said initial heating period for the element (11) is greater than a predetermined rate of change for any given liquid but less than said predetermined value, a warning signal is given to prompt a user to clean the element (11).
7. A method as claimed in Claim 6, characterised in that in a water heating apparatus (10) with a 2 kW electrical element (11), said warning signal is given if said initial rate of change of the temperature of the element (11) immediately subsequent to said initial heating period is greater than 20°C per second but less than 40°C per second.
8. A liquid heating apparatus (10) comprising an electrical element (11);
a temperature sensor (14);
means (12) for cutting-off or varying the electrical power supply to the element;
a timer (16); and a microprocessor (15) linked to the sensor (14) and to the timer (16); and characterised in that the temperature sensor (14) can detect the temperature of the element; and in that the microprocessor (15) is capable of determining the rate of change of the temperature of the element (11) at any given time after the element (11) is switched on and is programmed to compare said rate of change to a stored predetermined value and to control said means (12) for cutting-off or varying the electrical power supply to the element (11) dependent on the difference between said actual rate of change and said predetermined value in a such manner that the apparatus is controlled in accordance with the method as claimed in any one of Claims 1 to 7.
a temperature sensor (14);
means (12) for cutting-off or varying the electrical power supply to the element;
a timer (16); and a microprocessor (15) linked to the sensor (14) and to the timer (16); and characterised in that the temperature sensor (14) can detect the temperature of the element; and in that the microprocessor (15) is capable of determining the rate of change of the temperature of the element (11) at any given time after the element (11) is switched on and is programmed to compare said rate of change to a stored predetermined value and to control said means (12) for cutting-off or varying the electrical power supply to the element (11) dependent on the difference between said actual rate of change and said predetermined value in a such manner that the apparatus is controlled in accordance with the method as claimed in any one of Claims 1 to 7.
9. An apparatus as claimed in Claim 8, characterised in that the temperature sensor (14) comprises a thermistor located peripherally of the electrical element (11).
10. An apparatus as claimed in Claim 8, characterised in that said electrical element (11) comprises a conductive track of a thick film printed circuit formed on a substrate (17) and the temperature sensor (14) comprises a thermistor formed by a conductive track (19) of measurable resistance on the same substrate (17).
11. An apparatus as claimed in Claim 10, characterised in that the conductive track (19) comprising said thermistor extends parallel to and in close proximity with at least a part of the conductive track (18) comprising the electrical element (11).
12. An apparatus as claimed in Claim 11 or Claim 12, characterised in that the substrate (17) comprises a ferromagnetic steel which will vibrate in use to mitigate the effect of limescale deposition thereon.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9503256.1 | 1995-02-20 | ||
| GBGB9503256.1A GB9503256D0 (en) | 1995-02-20 | 1995-02-20 | Improvements to liquid boiling apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2213381A1 true CA2213381A1 (en) | 1996-08-29 |
Family
ID=10769871
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2213381 Abandoned CA2213381A1 (en) | 1995-02-20 | 1996-02-19 | Improvements to liquid boiling apparatus |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0810836A1 (en) |
| AU (1) | AU4725396A (en) |
| CA (1) | CA2213381A1 (en) |
| GB (1) | GB9503256D0 (en) |
| WO (1) | WO1996025869A1 (en) |
Families Citing this family (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1999027828A1 (en) * | 1997-12-02 | 1999-06-10 | Koninklijke Philips Electronics N.V. | Heating vessel and method of controlling the heating element of such a vessel |
| FR2791857B1 (en) * | 1999-03-30 | 2002-04-19 | Moulinex Sa | ELECTRICALLY CONTROLLED LIQUID HEATING ELECTRIC HOUSEHOLD APPLIANCE |
| GB2358576B (en) * | 2000-01-27 | 2003-08-06 | Otter Controls Ltd | Improvements relating to liquid heating appliances |
| GB2402322B (en) * | 2003-05-09 | 2006-09-27 | Cannon Rubber Ltd | Babycare heating apparatus |
| GB2429124B (en) * | 2005-08-11 | 2010-10-20 | Otter Controls Ltd | Scale detection on water heating elements |
| WO2007033530A1 (en) * | 2005-09-26 | 2007-03-29 | Crastal Technology (Shenzhen) Co., Ltd | Method of controlling the temperature of electrical heating jug |
| US7728263B2 (en) * | 2005-09-27 | 2010-06-01 | Mohan Zhang | Process of controlling an operation of electric kettle |
| GB2431784B (en) * | 2005-11-18 | 2007-12-05 | Crastal Technology | Anti-dry burning control methods and apparatus |
| DE102008016442A1 (en) * | 2008-03-31 | 2009-12-24 | Peter Huber Kältemaschinenbau GmbH | Apparatus and method for monitoring heated liquid baths for overheating and dry running |
| AT514681B1 (en) * | 2013-08-05 | 2015-06-15 | Vaillant Group Austria Gmbh | Method for detecting and avoiding boiling in heat exchangers |
| WO2015084294A1 (en) * | 2013-12-02 | 2015-06-11 | Richards Corporation | Aircraft kettle temperature control system |
| US10969141B2 (en) | 2018-03-13 | 2021-04-06 | Ngb Innovations Llc | Regulating temperature and reducing buildup in a water heating system |
| EP3870004A4 (en) * | 2018-10-23 | 2022-08-03 | Breville Pty Limited | Kettle |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3338788C1 (en) * | 1983-10-26 | 1985-05-15 | Kurt Wolf & Co Kg, 7547 Wildbad | Arrangement for deriving a measurement signal dependent on the rise in temperature of a temperature-time characteristic in a heating system |
| DE3642181C1 (en) * | 1986-12-10 | 1988-04-14 | Wolf & Co Kg Kurt | Arrangement for influencing the cooking or cooking time in a cooking vessel |
| FR2633481B1 (en) * | 1988-06-22 | 1996-04-26 | Seb Sa | METHOD FOR THERMAL REGULATION OF A HEATER, DEVICE FOR IMPLEMENTING SAME AND HEATER COMPRISING THE SAME |
| AU633042B2 (en) * | 1989-01-26 | 1993-01-21 | Otter Controls Limited | Controls for electrically powered heating elements |
| GB2269980B (en) * | 1992-08-13 | 1996-07-03 | Ist Lab Ltd | Apparatus for heating liquid |
-
1995
- 1995-02-20 GB GBGB9503256.1A patent/GB9503256D0/en active Pending
-
1996
- 1996-02-19 WO PCT/GB1996/000370 patent/WO1996025869A1/en not_active Application Discontinuation
- 1996-02-19 CA CA 2213381 patent/CA2213381A1/en not_active Abandoned
- 1996-02-19 EP EP96903102A patent/EP0810836A1/en not_active Withdrawn
- 1996-02-19 AU AU47253/96A patent/AU4725396A/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| WO1996025869A1 (en) | 1996-08-29 |
| GB9503256D0 (en) | 1995-04-12 |
| AU4725396A (en) | 1996-09-11 |
| EP0810836A1 (en) | 1997-12-10 |
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