CA1148599A - Thermostat control system for an electric kettle - Google Patents
Thermostat control system for an electric kettleInfo
- Publication number
- CA1148599A CA1148599A CA000340987A CA340987A CA1148599A CA 1148599 A CA1148599 A CA 1148599A CA 000340987 A CA000340987 A CA 000340987A CA 340987 A CA340987 A CA 340987A CA 1148599 A CA1148599 A CA 1148599A
- Authority
- CA
- Canada
- Prior art keywords
- heating means
- kettle
- main
- bias
- temperature
- 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.)
- Expired
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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
- A47J27/21058—Control devices to avoid overheating, i.e. "dry" boiling, or to detect boiling of the water
Abstract
Case 2716 THERMOSTAT CONTROL SYSTEM FOR AN ELECTRIC KETTLE
ABSTRACT OF THE DISCLOSURE
A control circuit for an electric kettle is provided which turns the kettle off after water in the kettle boils. The control circuit includes a main thermostat for controlling the operation of the heating element. The control circuit further includes an auxiliary thermostat and a bias heating element for heating the main thermostat, being electrically connected in such a manner that precludes current from flowing through the bias heating element until the boiling condition is approached. When the auxiliary thermostat senses a predetermined value of temperature from the kettle shell, it effectively energizes the bias heating element which drives the value of temperature sensed by the main thermostat rapidly upward to a higher, predetermined temperature value. When the main thermostat reaches the predetermined higher value it turns the kettle off. Prior control circuits for kettles have not employed an auxiliary thermostat in this manner.
ABSTRACT OF THE DISCLOSURE
A control circuit for an electric kettle is provided which turns the kettle off after water in the kettle boils. The control circuit includes a main thermostat for controlling the operation of the heating element. The control circuit further includes an auxiliary thermostat and a bias heating element for heating the main thermostat, being electrically connected in such a manner that precludes current from flowing through the bias heating element until the boiling condition is approached. When the auxiliary thermostat senses a predetermined value of temperature from the kettle shell, it effectively energizes the bias heating element which drives the value of temperature sensed by the main thermostat rapidly upward to a higher, predetermined temperature value. When the main thermostat reaches the predetermined higher value it turns the kettle off. Prior control circuits for kettles have not employed an auxiliary thermostat in this manner.
Description
~1~8599 - 1 - Case 2~16 THERMOSTAT CONTROL SYSTEM FOR AN E~ECTRIC KETTLE
This invention relates to an electric kettle for boiling water. In particular it relates to a control circuit that turns the kettle off relative to water in the kettle beginning to boil.
In a boil and off electric kettle it is known to locate a heat sensor, which forms part of a control circuit for the kettle, either in the kettle handle or in an electrical housing adjacent the handle. In either location, the heat sensor is positioned in close proximity to an opening in the upper shell portion of the kettle so as to ~detect" the presence of steam which is generated when water in the kettle begins to boil.
When the heat sensor detects the steam, it activates the control circuitry of the kettle which turns the kettle off. This is usually accomplished by opening a pair of contacts which are connected in series with the heating element of the kettle. The water level in the kettle generally has to be above the opening where the spout meets the kettle shell to ensure a pressure build-up of steam within the kettle. After the generation of steam within the kettle ceases and the heat sensor cools to a temperature at which it can again function, then and only then can the kettle be reset for operation. Thus, the term "boil and off" when used to describe an electric kettle means an electric kettle that automati-cally shuts itself off sometime after water contained ` ,r .. .. ..................
.
11'~8599 Case 2716 in the kettle begins to boil.
A disadvantage common to most boil and off electric kettles is the lengthy period of time that is required to allow the heat sensor to cool to a temperature at which it can again ~unction and thus permit the control circuitry of the kettle to be reset. It can be appreciated that in certain circumstances the lengthy time delay, which may be in the order of a few minutes, can ~e a nuisance. Ano,her disadvantage occurs when a small amount of water is to be boiled and the water level is below the opening where the spout meets the kettle shell. When this occurs the steam generated when the water boils escapes out of the spout resulting in long boiling times before the kettle turns off.
lS It is therefore an object of the present invention to provide in a boil and off electric kettle a control circuit that requires a relatively short period of time for the heat sensor to cool to a temper-ature at which it can again function permitting the control circuit of the kettle to ~e reset.
It is another object of the present invention - to provide a boil and off electric kettle that can be filled through its spout and not have to rely on the pressure build-up of steam in the kettle to turn it off.
Briefly, the present invention provides in an electric ketcle a control circuit that includes a main thermoresponsive switching device connected in series with a main resistance heating means. The main switching device senses the temperature of the main heating means, which heats water contained in the kettle. Connected to the main device is a bias heating means which raises the temperature of the main switching device above that normally attained by it when the main heating alone is on.
An auxiliary thermoresponsive switching device electrically li48599 _ 3 _ Case 2716 connected to the bias heating means controls the passase of current therethrough. During the heating of water in the kettle the auxiliary switching device precludes current from flowing through the bias heating means. The auxiliary device indirectly senses the temperature of the water by sensing the temperature of a shell portion of the kettle.
As the water is heated it reaches a predetermined temper-ature value below the boiling temperature of water which causes the auxiliary switching device to effectively energize the bias heating means. The temperature of the main switching device then rapidly rises to a pre-determined temperature value above that sensed when boiling water.At this latter predetermined temperature value the main switching device open-circuits. When the main device open-circuits, the heating means causes to heat the water in the kettle. The two predetermined temperature values and increased rate of temperature rise of the main switching device, due to the bias heating means being in circuit therewith, are chosen such that during the time elapsed between the auxiliary device permitting current flow through the bias heating means and the main device becoming open-circuited, the water in the kettle will come to the boil.
One advantage in the control circuit lies in the ability of the main switching device to rapidly cool down to a temperature at which it can again function. This is possible because the predetermined temperature value at which the main switching device open-circuits is above the boiling temperature of the water and above the temperature of the heating means. After the main heating means is turned off, the water in the kettle rapidly cools the main heating means which in turn cools the main switching device to a reset condition. Another advantage is the kettle can be spout filled because the control circuit is not dependent upon a pressure build-up of steam.
11'~8599 4 Case 2716 In one embodiment it is envisaged that the bias heating means and the auxiliary switching device are electrically connected in mutual series relation. The series arrangement is electrically connected in parallel with the main switching device and the main heating means. In this embodiment the auxiliary switching device will normally be open-circuited and will close when it senses the lower one of the predetermined temperature values. In another embodimemt, the preferred one, it is envisaged that the bias heating means and the auxiliary switching device are electrically connected in mutual parallel arrangement. ~his parallel arrangement is electrically connected in series with the main switching device. In this preferred embod-iment the auxiliary device is normally close-circuited and will become open-circuited when it senses the lower one of the predetermined temperature values.
In accordance with a broad aspect of the preser..
invention there is provided in a boil and off electric kettle a control circuit therefor comprising: a resistance main heating means; a main thermoresponsive switching device connected in heat transfer relation with and electrically in series with the main heating means, the main switching device switching from a closed condition permitting electrical current to flow through the heating means to an open condition precluding current from flowing through the main heating means when the main switching device senses a first predetermined value; a bias resistance heating means connected in electrical and heat transfer relation with the main switching device for raising the temperature of the main device to the first predetermined value when the bias heating means is effectively energized; and, an auxiliary thermoresponsive switching device connected in electrical relation with the main device and the bias heating means, the auxiliary device being connected in heat transfer relation with a shell portion of the kettle and switching from a first Case 2716 condition precluding effective energization of the bias heating means to a second condition providing effective energization of the bias heating means when the auxiliary switching device senses a second predetermined temperature value from the shell portion.
For a better understanding of the nature and objects of the present invention reference may be had by way of example, to the accompanying diagrammatic drawings in which:
Figure 1 is a plan view of a boil and off electric kettle as disclosed herein;
Figure 2 is a bottom view taken from direction
This invention relates to an electric kettle for boiling water. In particular it relates to a control circuit that turns the kettle off relative to water in the kettle beginning to boil.
In a boil and off electric kettle it is known to locate a heat sensor, which forms part of a control circuit for the kettle, either in the kettle handle or in an electrical housing adjacent the handle. In either location, the heat sensor is positioned in close proximity to an opening in the upper shell portion of the kettle so as to ~detect" the presence of steam which is generated when water in the kettle begins to boil.
When the heat sensor detects the steam, it activates the control circuitry of the kettle which turns the kettle off. This is usually accomplished by opening a pair of contacts which are connected in series with the heating element of the kettle. The water level in the kettle generally has to be above the opening where the spout meets the kettle shell to ensure a pressure build-up of steam within the kettle. After the generation of steam within the kettle ceases and the heat sensor cools to a temperature at which it can again function, then and only then can the kettle be reset for operation. Thus, the term "boil and off" when used to describe an electric kettle means an electric kettle that automati-cally shuts itself off sometime after water contained ` ,r .. .. ..................
.
11'~8599 Case 2716 in the kettle begins to boil.
A disadvantage common to most boil and off electric kettles is the lengthy period of time that is required to allow the heat sensor to cool to a temperature at which it can again ~unction and thus permit the control circuitry of the kettle to be reset. It can be appreciated that in certain circumstances the lengthy time delay, which may be in the order of a few minutes, can ~e a nuisance. Ano,her disadvantage occurs when a small amount of water is to be boiled and the water level is below the opening where the spout meets the kettle shell. When this occurs the steam generated when the water boils escapes out of the spout resulting in long boiling times before the kettle turns off.
lS It is therefore an object of the present invention to provide in a boil and off electric kettle a control circuit that requires a relatively short period of time for the heat sensor to cool to a temper-ature at which it can again function permitting the control circuit of the kettle to ~e reset.
It is another object of the present invention - to provide a boil and off electric kettle that can be filled through its spout and not have to rely on the pressure build-up of steam in the kettle to turn it off.
Briefly, the present invention provides in an electric ketcle a control circuit that includes a main thermoresponsive switching device connected in series with a main resistance heating means. The main switching device senses the temperature of the main heating means, which heats water contained in the kettle. Connected to the main device is a bias heating means which raises the temperature of the main switching device above that normally attained by it when the main heating alone is on.
An auxiliary thermoresponsive switching device electrically li48599 _ 3 _ Case 2716 connected to the bias heating means controls the passase of current therethrough. During the heating of water in the kettle the auxiliary switching device precludes current from flowing through the bias heating means. The auxiliary device indirectly senses the temperature of the water by sensing the temperature of a shell portion of the kettle.
As the water is heated it reaches a predetermined temper-ature value below the boiling temperature of water which causes the auxiliary switching device to effectively energize the bias heating means. The temperature of the main switching device then rapidly rises to a pre-determined temperature value above that sensed when boiling water.At this latter predetermined temperature value the main switching device open-circuits. When the main device open-circuits, the heating means causes to heat the water in the kettle. The two predetermined temperature values and increased rate of temperature rise of the main switching device, due to the bias heating means being in circuit therewith, are chosen such that during the time elapsed between the auxiliary device permitting current flow through the bias heating means and the main device becoming open-circuited, the water in the kettle will come to the boil.
One advantage in the control circuit lies in the ability of the main switching device to rapidly cool down to a temperature at which it can again function. This is possible because the predetermined temperature value at which the main switching device open-circuits is above the boiling temperature of the water and above the temperature of the heating means. After the main heating means is turned off, the water in the kettle rapidly cools the main heating means which in turn cools the main switching device to a reset condition. Another advantage is the kettle can be spout filled because the control circuit is not dependent upon a pressure build-up of steam.
11'~8599 4 Case 2716 In one embodiment it is envisaged that the bias heating means and the auxiliary switching device are electrically connected in mutual series relation. The series arrangement is electrically connected in parallel with the main switching device and the main heating means. In this embodiment the auxiliary switching device will normally be open-circuited and will close when it senses the lower one of the predetermined temperature values. In another embodimemt, the preferred one, it is envisaged that the bias heating means and the auxiliary switching device are electrically connected in mutual parallel arrangement. ~his parallel arrangement is electrically connected in series with the main switching device. In this preferred embod-iment the auxiliary device is normally close-circuited and will become open-circuited when it senses the lower one of the predetermined temperature values.
In accordance with a broad aspect of the preser..
invention there is provided in a boil and off electric kettle a control circuit therefor comprising: a resistance main heating means; a main thermoresponsive switching device connected in heat transfer relation with and electrically in series with the main heating means, the main switching device switching from a closed condition permitting electrical current to flow through the heating means to an open condition precluding current from flowing through the main heating means when the main switching device senses a first predetermined value; a bias resistance heating means connected in electrical and heat transfer relation with the main switching device for raising the temperature of the main device to the first predetermined value when the bias heating means is effectively energized; and, an auxiliary thermoresponsive switching device connected in electrical relation with the main device and the bias heating means, the auxiliary device being connected in heat transfer relation with a shell portion of the kettle and switching from a first Case 2716 condition precluding effective energization of the bias heating means to a second condition providing effective energization of the bias heating means when the auxiliary switching device senses a second predetermined temperature value from the shell portion.
For a better understanding of the nature and objects of the present invention reference may be had by way of example, to the accompanying diagrammatic drawings in which:
Figure 1 is a plan view of a boil and off electric kettle as disclosed herein;
Figure 2 is a bottom view taken from direction
2-2 of Figure 1 showing the preferred embodiment of the control circuit of the kettle;
Figure 3 is a schematic drawing of the preferred electrical circuit shown in Figure 2;
Figure 4 is a graph showing the temperature vs. time relations of the auxiliary and main thermostats in relation to the temperature rise of water contained in the kettle; and Figure 5 is a schematic drawing of an alternate control circuit for the invention.
- Referring to Figure 1 there is shown a boil and off electric kettle 10 having a shell portion 12, a combined nandle and spout 14 and a base cover 16.
The kettle 10 is provided with an outlet 18 to which an electric plug ~not shown) may be connected.
Referring now to Figures 2 and 3, outlet 18 is electrically connected to the interior of kettle 10 by 30 line terminals 20, 24 and ground terminal 22. Ground terminal 22 is connected by wire 22a to post 26 so as to ground the ground terminal 22 to the inner bottom 19 of the kettle shell 12. Ground terminal 22 is employed in the kettle 10 for use in a 240 volt system and may be eliminated to adapt the kettle for use in a 120 volt system. Line terminal 24 is connected by wire 24a to . , Case 2716 connection point F, which comprises a post 25 extending through inner bottom 19 connected to the heating means. The heating means comprises a sheathed heating element 28 (shown in Figure 3).
Line terminal 20 is connected by wire 20A to connection point A.
An auxiliary thermoresponsive switching device comprising auxiliary thermostat 30 is electrically connected by link arms 32 and 34 between connection points A and C. Link arm 32 is connected to a first contact of thermostat 30 and link arm 34 is connected to a second contact of thermostat 30. Auxiliary thermostat 30 is connected in heat transfer relation at 31 with a portion of shell 12 which is inner bottom 19. Thermostat 30 indirectly senses the temperature of the water in the kettle 10 by sensing the temperature of the inner bottom 19 .
Also connected to connection point C is a first input terminal 36 of a main thermoresponsive switching device which comprises main thermostat 38. The first input terminal 36 is electrically connected to a first contact of thermostat 38. A
bias heating means comprising a bias heater 40 forms the second input terminal for thermostat 38 and is electrically connected between the first contact of thermostat 38 and connection point A.
The bias heater 40 comprises a metal strip element having a tip portion welded to the first contact of thermostat 38 in heat transfer relation with thermostat 38. The second contact of thermostat 38 is electrically connected by output terminal 42~to connection point D. Bar 44 interconnects connections points D and E. Connection point E comprises a post 46 extending through inner ~1~8599 Case 2716 bottom 19 connected to heating element 28. Thus, main thermostat 38 is electrically connected in series with heating element 28. The main thermostat 38 senses by conduction the temperature of heating element 28 through a stud 47 brazed to heating element 28. Stud 47 connects thermostat 38 in heat transfer relation with heating element 28. Auxiliary thermostat 30 and bias heater 40 are electrically connected in series with main thermostat 38 and in parallel to one another.
In alternate embodiments the main and auxiliary thermoresponsive switching devices may comprise devices other than thermostats such as, for example, thermistors or other forms of electronic devices.
A lamp 48 is shown connected by wires 50,52 between connection points A,D. When the contacts of main thermostat 38 open, lamp 48 turns on giving a visual indication that the kettle 10 has turned off. Lamp 48 has a high resistance in circuit therewith so as to limit the current flowing through heating element 28 when the contacts of main thermostat 38 open.
A manually operated reset mechanism 54 is provided to reset the contacts of main thermostat 38 to a closed position after the contacts have opened. Reset mechanism 54 may be activated by depressing reset button 54a.
Referring now to Figures 3 and 4 the operation of the control circuit will now be described. The contacts of auxiliary thermostat 30 are set to open when thermostat 30 senses a predetermined tempeature value slightly less than the boiling temperature of water.
Main thermostat 38, which senses the temperature~of heating element 28, is set to cpen its contacts at a predetermined temperature value above the boiling temperature of water.
When the contacts of thermostats 30,38 are closed, the thermostats are $aid to be in their closed position and when the contacts are open, the thermostats are said to ~ 8S99 Case 2716 be in their open position. The auxiliary thermostat 30 is chosen such that it has a thermal time constant which allows it to closely match the rate of temperature rise of water in the kettle. Because the auxiliary thermostat senses the temperature of the shell and the shell experiences heat losses, the auxiliary thermostat does not sense the actual water temperature. The main thermostat 38 senses the actual temperature of the heating element 28 which is usually slightly above the temperature of the water in the kettle. However the temperature of the heating element 28 does not rise to the predetermined temperature at which main thermostat 38 open-circuits. Bias heater 40, when activated, pushes the temperature of the main thermostat 38 rapidly up to the predetermined temperature at which thermostat 38 open-circuits.
Assuming the thermostats 30,38 are in their closed positions as shown in Figure 3 and electrical current is supplied to the kettle terminals 20,24, then electrical current flows through thermostats 30, 38 and heating element 28. Current flowing through resistance heating element 28 generates heat which warms the water in the kettle. Because auxiliary thermostat 30 is in its closed position electrical current is substantially precluded from passing through bias heater 40. Thus the rate of temperature rise of water, the main thermostat 38, and auxiliary thermostat 30 will approximate that respectively shown by curves 98, 100 and 102 over time period Pl. It should be understood that when the auxiliary thermostat 30 is in its closed position the main thermostat 38 is precluded from rising in temperature to its predetermined temperature at which main thermostat 38 open-circuits. This is because main thermostat 38 senses by conduction only the temperature of the heating element 28 which is always slightly above the temperature of water in the kettle. When a . ~
~48599 Case 2716 _ g _ predetermined temperature Tl, which is less than the boiling temperature of water, is sensed by auxiliary thermostat 30, thermostat 30 switches from its closed to its open position thereby permitting electrical current to flow through bias heater 40. The time rate of temperature rise of main thermostat 38 is then increased as shown by the portion of curve 100 over time period P2. It is to be noted that during time period P2 water represented by curve 98 reaches its boiling temperature Tw. The main thermostat continues to rise rapidly in temperature until it reaches pre-determined temperature T2 which is above the boiling temperature Tw and the temperature of the heating element 28. When main thermostat 38 reaches temperature T2 it switches from its closed to its open position there-by turning the kettle off. The temperature of main thermostat 38 rapidly decreases as shown in curve 100 over period P4 because the thermostat 38 senses the temperature of heating element 28 which rapidly cools to the temperature of the water after the kettle is switched off. Period P4 has a time duration in the order of about 10 to 15 seconds. Period P3, the time duration in which the kettle remains on after the water boils, has a time duration in the order of 10 to 90 seconds.
The duration of period P3 is dependent upon the volume of water in the kettle.
Referring now to Figure 5, an alternate embodiment for the present invention is shown.
Auxiliary thermostat 100 is electrically connected in series with bias heating element 102. The series arrangement of auxiliary thermostat 100 and bias heating element 102 is shown connected across line terminals 108,110. The series arrangement is also connected in parallel with the series combination of main thermostat 104 and heating element 106. In Figure S, auxiliary thermostat 100 is shown in its open position and main 1~8599 Case 2716 thermostat 104 in its closed position. In operation, current passes through closed thermostat 104 and heating element 106. When the temperature sensed by the auxiliary thermostat 100 reaches a predetermined value, auxiliary S thermostat 100 closes permitting current to flow through bias heating element 102. As a result, heat is radiated from element 102 to thermostat 104 causing the temperature of thermostat 104 to rise rapidly to a predetermined temperature at which temperature thermostat 104 opens, 10 precluding current flow through element 106.
It will be appreciated that alternate embodiments will be readily apparent to a man skilled in the art in light of the present disclosure.
Accordingly the present invention is to be limited only 15 to that which is claimed in the accompanying claims.
One particular alternate embodiment may comprise locating the auxiliary thermostat in the handle of the kettle so as to sense the temperature of the top portion of the kettle shell. Such an 20 arrangement is primarily influenced by the presence of steam in the kettle and is relatively insensitive to changes in water volume.
Figure 3 is a schematic drawing of the preferred electrical circuit shown in Figure 2;
Figure 4 is a graph showing the temperature vs. time relations of the auxiliary and main thermostats in relation to the temperature rise of water contained in the kettle; and Figure 5 is a schematic drawing of an alternate control circuit for the invention.
- Referring to Figure 1 there is shown a boil and off electric kettle 10 having a shell portion 12, a combined nandle and spout 14 and a base cover 16.
The kettle 10 is provided with an outlet 18 to which an electric plug ~not shown) may be connected.
Referring now to Figures 2 and 3, outlet 18 is electrically connected to the interior of kettle 10 by 30 line terminals 20, 24 and ground terminal 22. Ground terminal 22 is connected by wire 22a to post 26 so as to ground the ground terminal 22 to the inner bottom 19 of the kettle shell 12. Ground terminal 22 is employed in the kettle 10 for use in a 240 volt system and may be eliminated to adapt the kettle for use in a 120 volt system. Line terminal 24 is connected by wire 24a to . , Case 2716 connection point F, which comprises a post 25 extending through inner bottom 19 connected to the heating means. The heating means comprises a sheathed heating element 28 (shown in Figure 3).
Line terminal 20 is connected by wire 20A to connection point A.
An auxiliary thermoresponsive switching device comprising auxiliary thermostat 30 is electrically connected by link arms 32 and 34 between connection points A and C. Link arm 32 is connected to a first contact of thermostat 30 and link arm 34 is connected to a second contact of thermostat 30. Auxiliary thermostat 30 is connected in heat transfer relation at 31 with a portion of shell 12 which is inner bottom 19. Thermostat 30 indirectly senses the temperature of the water in the kettle 10 by sensing the temperature of the inner bottom 19 .
Also connected to connection point C is a first input terminal 36 of a main thermoresponsive switching device which comprises main thermostat 38. The first input terminal 36 is electrically connected to a first contact of thermostat 38. A
bias heating means comprising a bias heater 40 forms the second input terminal for thermostat 38 and is electrically connected between the first contact of thermostat 38 and connection point A.
The bias heater 40 comprises a metal strip element having a tip portion welded to the first contact of thermostat 38 in heat transfer relation with thermostat 38. The second contact of thermostat 38 is electrically connected by output terminal 42~to connection point D. Bar 44 interconnects connections points D and E. Connection point E comprises a post 46 extending through inner ~1~8599 Case 2716 bottom 19 connected to heating element 28. Thus, main thermostat 38 is electrically connected in series with heating element 28. The main thermostat 38 senses by conduction the temperature of heating element 28 through a stud 47 brazed to heating element 28. Stud 47 connects thermostat 38 in heat transfer relation with heating element 28. Auxiliary thermostat 30 and bias heater 40 are electrically connected in series with main thermostat 38 and in parallel to one another.
In alternate embodiments the main and auxiliary thermoresponsive switching devices may comprise devices other than thermostats such as, for example, thermistors or other forms of electronic devices.
A lamp 48 is shown connected by wires 50,52 between connection points A,D. When the contacts of main thermostat 38 open, lamp 48 turns on giving a visual indication that the kettle 10 has turned off. Lamp 48 has a high resistance in circuit therewith so as to limit the current flowing through heating element 28 when the contacts of main thermostat 38 open.
A manually operated reset mechanism 54 is provided to reset the contacts of main thermostat 38 to a closed position after the contacts have opened. Reset mechanism 54 may be activated by depressing reset button 54a.
Referring now to Figures 3 and 4 the operation of the control circuit will now be described. The contacts of auxiliary thermostat 30 are set to open when thermostat 30 senses a predetermined tempeature value slightly less than the boiling temperature of water.
Main thermostat 38, which senses the temperature~of heating element 28, is set to cpen its contacts at a predetermined temperature value above the boiling temperature of water.
When the contacts of thermostats 30,38 are closed, the thermostats are $aid to be in their closed position and when the contacts are open, the thermostats are said to ~ 8S99 Case 2716 be in their open position. The auxiliary thermostat 30 is chosen such that it has a thermal time constant which allows it to closely match the rate of temperature rise of water in the kettle. Because the auxiliary thermostat senses the temperature of the shell and the shell experiences heat losses, the auxiliary thermostat does not sense the actual water temperature. The main thermostat 38 senses the actual temperature of the heating element 28 which is usually slightly above the temperature of the water in the kettle. However the temperature of the heating element 28 does not rise to the predetermined temperature at which main thermostat 38 open-circuits. Bias heater 40, when activated, pushes the temperature of the main thermostat 38 rapidly up to the predetermined temperature at which thermostat 38 open-circuits.
Assuming the thermostats 30,38 are in their closed positions as shown in Figure 3 and electrical current is supplied to the kettle terminals 20,24, then electrical current flows through thermostats 30, 38 and heating element 28. Current flowing through resistance heating element 28 generates heat which warms the water in the kettle. Because auxiliary thermostat 30 is in its closed position electrical current is substantially precluded from passing through bias heater 40. Thus the rate of temperature rise of water, the main thermostat 38, and auxiliary thermostat 30 will approximate that respectively shown by curves 98, 100 and 102 over time period Pl. It should be understood that when the auxiliary thermostat 30 is in its closed position the main thermostat 38 is precluded from rising in temperature to its predetermined temperature at which main thermostat 38 open-circuits. This is because main thermostat 38 senses by conduction only the temperature of the heating element 28 which is always slightly above the temperature of water in the kettle. When a . ~
~48599 Case 2716 _ g _ predetermined temperature Tl, which is less than the boiling temperature of water, is sensed by auxiliary thermostat 30, thermostat 30 switches from its closed to its open position thereby permitting electrical current to flow through bias heater 40. The time rate of temperature rise of main thermostat 38 is then increased as shown by the portion of curve 100 over time period P2. It is to be noted that during time period P2 water represented by curve 98 reaches its boiling temperature Tw. The main thermostat continues to rise rapidly in temperature until it reaches pre-determined temperature T2 which is above the boiling temperature Tw and the temperature of the heating element 28. When main thermostat 38 reaches temperature T2 it switches from its closed to its open position there-by turning the kettle off. The temperature of main thermostat 38 rapidly decreases as shown in curve 100 over period P4 because the thermostat 38 senses the temperature of heating element 28 which rapidly cools to the temperature of the water after the kettle is switched off. Period P4 has a time duration in the order of about 10 to 15 seconds. Period P3, the time duration in which the kettle remains on after the water boils, has a time duration in the order of 10 to 90 seconds.
The duration of period P3 is dependent upon the volume of water in the kettle.
Referring now to Figure 5, an alternate embodiment for the present invention is shown.
Auxiliary thermostat 100 is electrically connected in series with bias heating element 102. The series arrangement of auxiliary thermostat 100 and bias heating element 102 is shown connected across line terminals 108,110. The series arrangement is also connected in parallel with the series combination of main thermostat 104 and heating element 106. In Figure S, auxiliary thermostat 100 is shown in its open position and main 1~8599 Case 2716 thermostat 104 in its closed position. In operation, current passes through closed thermostat 104 and heating element 106. When the temperature sensed by the auxiliary thermostat 100 reaches a predetermined value, auxiliary S thermostat 100 closes permitting current to flow through bias heating element 102. As a result, heat is radiated from element 102 to thermostat 104 causing the temperature of thermostat 104 to rise rapidly to a predetermined temperature at which temperature thermostat 104 opens, 10 precluding current flow through element 106.
It will be appreciated that alternate embodiments will be readily apparent to a man skilled in the art in light of the present disclosure.
Accordingly the present invention is to be limited only 15 to that which is claimed in the accompanying claims.
One particular alternate embodiment may comprise locating the auxiliary thermostat in the handle of the kettle so as to sense the temperature of the top portion of the kettle shell. Such an 20 arrangement is primarily influenced by the presence of steam in the kettle and is relatively insensitive to changes in water volume.
Claims (16)
1. In a boil and off electric kettle a control circuit therefor comprising:
a main resistance heating means;
a main thermoresponsive switching device conducted in heat transfer relation with and electrically in series with said main heating means, said main switching device in operation switching at a first predetermined temperature value from a closed position permitting electrical current to flow through said main heating means to an open position precluding current from flowing through said main heating means ;
a bias resistance heating means connected in heat transfer relation with said main device to assist in raising the temperature sensed by said main device to said first predetermined value when said bias heating means is effectively energized; and, an auxiliary thermoresponsive switching device connected in controlling electrical energizing relation with said bias heating means, said auxiliary device being connected in heat transfer relation with a portion of said kettle for switching to an effective energizing condition of said bias heating means on sensing a second temperature value less than said first value to thereby energize said bias heating means so as to assist in raising the temper-ature of said main switching device to said first value, whereupon said main switching device is switched to an open circuit condition.
a main resistance heating means;
a main thermoresponsive switching device conducted in heat transfer relation with and electrically in series with said main heating means, said main switching device in operation switching at a first predetermined temperature value from a closed position permitting electrical current to flow through said main heating means to an open position precluding current from flowing through said main heating means ;
a bias resistance heating means connected in heat transfer relation with said main device to assist in raising the temperature sensed by said main device to said first predetermined value when said bias heating means is effectively energized; and, an auxiliary thermoresponsive switching device connected in controlling electrical energizing relation with said bias heating means, said auxiliary device being connected in heat transfer relation with a portion of said kettle for switching to an effective energizing condition of said bias heating means on sensing a second temperature value less than said first value to thereby energize said bias heating means so as to assist in raising the temper-ature of said main switching device to said first value, whereupon said main switching device is switched to an open circuit condition.
2. The kettle of claim 1, wherein said bias heating means and said auxiliary device are electrically connected in series relation arrangement, the which arrangement is connected in parallel with said main switching device and said main heating means.
- 12 - Case 2716
- 12 - Case 2716
3. The kettle of claim 1, wherein said bias heating means and said auxiliary device are electrically in mutual parallel connected arrangment, which arrangment is connected in series with said main switching device.
4. In a boil and off electric kettle a control circuit therefor comprising:
a resistance main heating means through which electric current flows for heating water contained within said kettle;
a thermoresponsive main switching device connected in heat transfer relation with and electrically in series with said main heating means, said main switching device having a closed condition permitting current to flow through said main heating means and an open position condition precluding current from flowing through said main heating means, said main switching device switching from its closed to its open condition in response to it sensing a first predetermined value of temperature greater than values of temperature sensed by it from said heating means;
a bias resistance heating means connected electrically and in heat transfer relation with said main device for raising the value of temperature sensed by said main device to said first predetermined value when current flows through said bias heating means; and, an auxiliary thermoresponsive switching device electrically connected in series with the bias heating means, such that the series arrangment of the auxiliary device and bias heating means is electrically connected in parallel with said main device and heating means, said auxiliary device having an open condition precluding current from flowing through said bias heating means and a closed condition permitting current to flow through said bias heating means, said auxiliary device being connected in heat transfer relation with a portion of said kettle and switching from its open condition to its - 13 - Case 2716 closed condition in response to sensing a second predetermined value of temperature from the kettle portion.
a resistance main heating means through which electric current flows for heating water contained within said kettle;
a thermoresponsive main switching device connected in heat transfer relation with and electrically in series with said main heating means, said main switching device having a closed condition permitting current to flow through said main heating means and an open position condition precluding current from flowing through said main heating means, said main switching device switching from its closed to its open condition in response to it sensing a first predetermined value of temperature greater than values of temperature sensed by it from said heating means;
a bias resistance heating means connected electrically and in heat transfer relation with said main device for raising the value of temperature sensed by said main device to said first predetermined value when current flows through said bias heating means; and, an auxiliary thermoresponsive switching device electrically connected in series with the bias heating means, such that the series arrangment of the auxiliary device and bias heating means is electrically connected in parallel with said main device and heating means, said auxiliary device having an open condition precluding current from flowing through said bias heating means and a closed condition permitting current to flow through said bias heating means, said auxiliary device being connected in heat transfer relation with a portion of said kettle and switching from its open condition to its - 13 - Case 2716 closed condition in response to sensing a second predetermined value of temperature from the kettle portion.
5. In a boil and off electric kettle a control circuit therefor comprising:
a resistance main heating means through which electric current flows for heating water contained within said kettle;
a main thermoresponsive switching device connected in heat transfer relation with and electrically in series with said heating means, said main device having a closed condition permitting current to flow through said heating means and an open condition precluding current from flowing through said heating means, said main device switching from its closed to its open condition in response to sensing a first predetermined value of temperature, greater than values of temperature sensed from said heating means;
a bias resistance heating means connected in heat transfer relation with and electrically in series with said main switching device for raising the value of temperature sensed by said main switching device to said first predetermined value when said bias heating means is effectively energized; and, an auxiliary thermoresponsive switching device electrically connected in series with the main device and in parallel with the bias heating means, said auxiliary device having a closed condition substantially precluding current from flowing through said bias heating means and an open condition causing effective energization of said bias heating means, said auxiliary device being connected in heat transfer relation with a portion of said kettle and being switched from its closed condition to its open condition in response to sensing a second predetermined value of temperature from the kettle portion.
a resistance main heating means through which electric current flows for heating water contained within said kettle;
a main thermoresponsive switching device connected in heat transfer relation with and electrically in series with said heating means, said main device having a closed condition permitting current to flow through said heating means and an open condition precluding current from flowing through said heating means, said main device switching from its closed to its open condition in response to sensing a first predetermined value of temperature, greater than values of temperature sensed from said heating means;
a bias resistance heating means connected in heat transfer relation with and electrically in series with said main switching device for raising the value of temperature sensed by said main switching device to said first predetermined value when said bias heating means is effectively energized; and, an auxiliary thermoresponsive switching device electrically connected in series with the main device and in parallel with the bias heating means, said auxiliary device having a closed condition substantially precluding current from flowing through said bias heating means and an open condition causing effective energization of said bias heating means, said auxiliary device being connected in heat transfer relation with a portion of said kettle and being switched from its closed condition to its open condition in response to sensing a second predetermined value of temperature from the kettle portion.
6. The kettle of claim 4 or 5, wherein said - 14 - Case 2716 second predetermined value of temperature is less than the boiling temperature of water.
7. The kettle of claim 5, wherein the auxiliary device is located in the handle for sensing the temperature of an upper shell portion of said kettle.
8. The kettle of claim 7, wherein the switching of said auxiliary device from its closed to its open condition is a function substantially independ-ent of water volume.
9. The kettle of claim 5, wherein said auxiliary device is located adjacent an inner bottom shell portion of the kettle for sensing the temperature of said shell bottom portion.
10. The kettle of claim 9, wherein the switching of said main device from its closed condition to its open condition is affected by the level of water present in the kettle.
11. The kettle of claim 4 or claim 5, wherein said main switching device and said auxiliary switching device each comprises a thermostat.
12. The kettle of claim 4 or claim 5, wherein said bias heating means comprises a metal strip element having a tip portion welded to a contact of said main thermostat.
13. The kettle of claim 4 or claim 5, wherein said main heating means comprises a metal sheathed heating element.
14. The kettle of claim 5, wherein a lamp is connected across said bias heating means and said main device, said lamp giving a visual indication that said main device is in its open position.
15. The kettle of claim 14, wherein said lamp has a high resistance in series therewith to limit current flow therethrough to the heating means.
16. The kettle of claim 4 or claim 5, wherein Case 2716
16. The kettle of claim 4 or claim 5, wherein Case 2716
Claim 16 continued:
said auxiliary switching device has a thermal time constant that closely matches the normal rate of temp-erature rise of water in said kettle when full.
said auxiliary switching device has a thermal time constant that closely matches the normal rate of temp-erature rise of water in said kettle when full.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000340987A CA1148599A (en) | 1979-11-30 | 1979-11-30 | Thermostat control system for an electric kettle |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000340987A CA1148599A (en) | 1979-11-30 | 1979-11-30 | Thermostat control system for an electric kettle |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1148599A true CA1148599A (en) | 1983-06-21 |
Family
ID=4115725
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000340987A Expired CA1148599A (en) | 1979-11-30 | 1979-11-30 | Thermostat control system for an electric kettle |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1148599A (en) |
-
1979
- 1979-11-30 CA CA000340987A patent/CA1148599A/en not_active Expired
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| Date | Code | Title | Description |
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| MKEX | Expiry |