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EP1198741A1 - Improvements relating to water heating vessels - Google Patents

Improvements relating to water heating vessels

Info

Publication number
EP1198741A1
EP1198741A1 EP00946184A EP00946184A EP1198741A1 EP 1198741 A1 EP1198741 A1 EP 1198741A1 EP 00946184 A EP00946184 A EP 00946184A EP 00946184 A EP00946184 A EP 00946184A EP 1198741 A1 EP1198741 A1 EP 1198741A1
Authority
EP
European Patent Office
Prior art keywords
heating element
track
thick film
auxiliary heater
vessel
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.)
Ceased
Application number
EP00946184A
Other languages
German (de)
French (fr)
Inventor
Robert Andrew O'neill
Robin Keith Moore
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Otter Controls Ltd
Original Assignee
Otter Controls Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Priority claimed from GBGB9917131.6A external-priority patent/GB9917131D0/en
Priority claimed from GBGB9926533.2A external-priority patent/GB9926533D0/en
Priority claimed from GB0013545A external-priority patent/GB2354927B/en
Application filed by Otter Controls Ltd filed Critical Otter Controls Ltd
Publication of EP1198741A1 publication Critical patent/EP1198741A1/en
Ceased legal-status Critical Current

Links

Classifications

    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B1/00Details of electric heating devices
    • H05B1/02Automatic switching arrangements specially adapted to apparatus ; Control of heating devices
    • H05B1/0202Switches
    • H05B1/0213Switches using bimetallic elements
    • GPHYSICS
    • G05CONTROLLING; REGULATING
    • G05DSYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00Control of temperature
    • G05D23/19Control of temperature characterised by the use of electric means
    • G05D23/275Control of temperature characterised by the use of electric means with sensing element expanding, contracting, or fusing in response to changes of temperature
    • G05D23/27535Details of the sensing element
    • G05D23/2754Details of the sensing element using bimetallic element
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B2203/00Aspects relating to Ohmic resistive heating covered by group H05B3/00
    • H05B2203/013Heaters using resistive films or coatings
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B2203/00Aspects relating to Ohmic resistive heating covered by group H05B3/00
    • H05B2203/017Manufacturing methods or apparatus for heaters

Definitions

  • This invention concerns improvements relating to electrically powered
  • the vessel are well known, and commonly operate by responding to the
  • actuator a bimetal or shape memory effect device for example, is located.
  • thermal contact with the heating element and is calibrated to operate at a
  • heating appliance to be selected by the user, and bimetallic arrangements are
  • operating temperature of the bimetal is controllable by the user, or which
  • mechanism can be adjustable.
  • the creep bimetal is arranged to interact with the trip lever of the control
  • a thick film heating element comprises
  • heating track or layer on at least one side thereof, electrically
  • thermosensor is to have a thermal sensor associated therewith to be selectively adjusted
  • volume of water being heated will change correspondingly.
  • electrically powered water heating vessel has a thick film heating element, a
  • thermally-responsive control is located in thermal contact with a
  • Thick film heating elements are commonly manufactured by printing
  • the track temperature is related to the water temperature
  • the track temperature will be about 160°C, that is 60°C above the
  • control bimetal is normally set at about 180°C. If, on the
  • cordless vessel was lifted off its base and reset. On the X46 (auto cycling) or
  • bimetal senses the heater temperature.
  • variable resistor separate from the heating element
  • control knob accessible to the user of the appliance, but such a
  • control could be electronic, since the control of a
  • element m the form of a resistive track p ⁇ nted on the element, and to provide
  • resistive track included in circuit with the auxiliary heater there could also be
  • auxiliary track is the same as in the adjacent main power track so that both
  • va ⁇ able resistors with sliding contacts are well known and would be directly applicable to this construction.
  • the resistive track could be an arc preferably
  • adjustment arm could project from a slot in the wall of the vessel body and be
  • the arc could be formed as a
  • This sensor should have a low thermal
  • PTC sensor take the form of a PTC sensor, with an electronic control system, or preferably
  • contactstat would be approximately 105°C to avoid nuisance tripping du ⁇ ng
  • auxiliary heater track could be arranged to be adjustable to
  • a further aspect of the invention useful to maintain water at a preset
  • the heating is proposed to be
  • variable remake bimetal that is to say an adjustable
  • bimetal could be used with an adjustable auxiliary track power, in which case
  • thick film heating element of an electrically powered water heating vessel has
  • the thick film heating element so that, in use, its operation is dependent upon
  • Switching off the appliance on boil can be done by any of the known
  • heating element provided with an auxiliary heating track at a location whereat
  • thermocontrol for example a bimetallic control
  • both functions and preferably comprise respective variable resistance elements
  • the slider control preferably has an off position
  • a water heating vessel provided with such a heating element and with
  • heating element track and by the keep warm track can have an on/off control
  • the abovementioned slider or, more preferably, can have the two such controls
  • Such a water heating vessel can, with the tracks and
  • the keep warm track keeps the vessel contacts close to boiling, and a heat and keep warm mode wherein the slider control is positioned at an
  • Figure 1 illustrates in plan view an exemplary track layout of a thick
  • Figure 2 is a schematic circuit diagram showing a thick film heating
  • Figure 3 is a plan view of an alternative thick film heating element
  • Figures 4A, 4B, 4C and 4D show how a modified form of our X4
  • Figures 5 and 6 are plan views of yet further alternative thick film
  • Figure 7 is a plan view of yet another thick film heating element
  • Figure 8 is a circuit diagram illustrating the use of a thick film heating
  • the heating element proper 3 is made up of
  • heater track sections 4 which are joined by conductive b ⁇ dges 5 at their
  • the heating element shown is adapted for use with an X4 control having two
  • heating element m good heat transfer relationship therewith generally in the
  • heater track 11 is provided in the region 7 of the heating element which
  • resistive track section 13 which, in use,
  • auxiliary heater track 11 is coupled at one end to mam heater
  • the wiper 14 along the resistive track section determines the heat output of the
  • auxiliary heater 1 1 determines the operation of that bimetallic actuator of the X4 control that registers with
  • auxiliary heater 11 to be switched off when the vessel is to be used for boiling
  • knob is preferably such that contact between the resistive track section 14 and
  • the wiper 14 is made and broken with a snap action so as to minimize arcing
  • provided at the high resistance end thereof, may be configured to withstand
  • Figure 2 shows the thick film heating element of Figure 1 in an
  • boil control such as our aforementioned X4 control and with a steam control
  • controls are designated 21 and 22 and are designed to register with the regions
  • slider track 13 is designated 24, this position of the wiper serving to isolate
  • FIG. 3 shows an alternative thick film track layout designed
  • the thick film heating element of Figure 3 has regions 7 and 8
  • auxiliary heater track 11 which is connected to a track
  • Figures 4A to 4D illustrate the attachment of a modified X4 control to
  • FIG. 3 a thick film heating element as shown in Figure 3.
  • Figure 4A merely shows
  • control are affixed to the metal substrate 1 of the heating element, the
  • variable resistance track section 13 adapted to be contacted by a
  • the X4 control comprises a cordless vessel inlet connector 41 of the 360° type pioneered by us which enables a cordless vessel to be set
  • first and second heating element protector controls generally
  • Figures 4B, 4C and 4D show the modification to the X4 control.
  • metal chassis of the control has an extended part 51, which has a central pivot
  • a plastics moulding 55 has a pivot peg 56 and an overlapping arm 57 and is
  • chassis extension to prevent the moulding coming off its pivot and acts as a
  • pigtail of the brush assembly has a quick connect receptacle attached which is
  • moulding is greater than the angle subtended by the slider track so that at one
  • FIGS 5 and 6 show yet further alternative thick film track layouts
  • thick film heating elements of Figures 5 and 6 each have regions 7 and 8 designed to register with the bimetals of the X4 control and the region 7 has
  • auxiliary heater track 11 which is connected to a track
  • section 13 designed to cooperate with a control slider of the X4 control to
  • auxiliary track 1 1 is somewhat narrower, since it is of lower power and thus
  • the silver pads 15 have two purposes Firstly, it is known that making
  • auxiliary track is arranged to be the same as in the adjacent main power track
  • this arrangement enables a kettle or hot water
  • jug for example, selectively to provide boiling water, or water which has been
  • element 1 has arcuate main heater track sections 4 connected at their ends by
  • section 1 1 is connected between a tapping point 20 of the main heater track
  • An additional track section 21 is provided in the centre of the heating
  • the control that is used with the heating element of Figure 7 is a
  • the variant X4 has a third spring contact 22, in
  • the control is fitted with a high temperature bimetal blade
  • the potentiometer slider has
  • the slider contacts are not connected to anything, they have no
  • track 21 provides the maximum power to that track which is
  • the water may be any suitable material (thermostat) associated with it to operate.
  • the water may be any suitable material (thermostat) associated with it to operate.
  • the water may be any suitable material
  • the track is preferably targeted always to give a
  • thermostat bimetal will cycle occasionally, as
  • Dry boil protection of the system is provided by the dry boil bimetal of
  • the keep warm track 21 is positioned centrally to
  • auxiliary track 11 will operate, albeit somewhat more slowly because of the
  • buttons could be provided, one for the boil control, and one for the slider.
  • auxiliary heater 11 could be formed to exhibit a PTC (positive temperature coefficient of resistance) characteristic whereas the auxiliary heater 11 could be formed with
  • bimetallic actuators For example, an underfloor heating element of the metal

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Automation & Control Theory (AREA)
  • Cookers (AREA)

Abstract

A water boiling vessel has a thick film heating element (3) provided with a bimetallic overtemperature protection control for switching off the heating element if it overheats, for example because the vessel is switched on empty and, to enable the vessel selectively to be operated to produce hot water at a selected temperature lower than boiling, an auxiliary heater (11) is provided on the thick film heating element in the region thereof to which the bimetallic control is responsive and a resistive track is connected in series with the auxiliary heater and is contactable selectively along its length so as to vary its effective resistance and thereby vary the current through the auxiliary heater. The auxiliary heater increases the heating of the bimetallic control above that normally received in operation of the vessel so that it operates at a lower temperature than it normally would, thereby switching off the vessel prematurely before it had time to boil. Also disclosed is an integrated 360° cordless appliance inlet connector and dry boil control which includes a means to connect selectively to the resistive track.

Description

IMPROVEMENTS RELATING TO WATER HEATING VESSELS
Field of the Invention:
This invention concerns improvements relating to electrically powered
water heating vessels such as domestic kettles and hot water jugs for example,
and, more particularly, concerns arrangements whereby such vessels may be
switched off or their power supply reduced at a water temperature below
boiling.
Background of the Invention:
Steam controls which operate to switch off or reduce the power supply
to the electric heating element of a water boiling vessel when water boils in
the vessel are well known, and commonly operate by responding to the
generation of steam when water boils in the vessel, the stem venting from the
vessel interior into a region of the vessel whereat a thermally-sensitive switch
actuator, a bimetal or shape memory effect device for example, is located.
Controls are also well known which are intended to protect the heating
element of a water boiling vessel from overheating, for example as a result of
the vessel being switched on empty or being allowed to boil dry, and
commonly comprise a bimetallic switch actuator which is held in close
thermal contact with the heating element and is calibrated to operate at a
certain overtemperature.
It has also been proposed to provide a water heating vessel with means
whereby hot water can be provided at a temperature lower than boiling, for example for use m making coffee Electronic control arrangements have been
proposed which enable the temperature of the hot water produced by a water
heating appliance to be selected by the user, and bimetallic arrangements are
known which operate similarly to an adjustable thermostat, in that the
operating temperature of the bimetal is controllable by the user, or which
operate by varying the heat transfer relationship between the heating element
and the bimetal, for example by moving the bimetal relative to the heating
element
The bimetals that are employed m controls for water heating vessels
are nowadays commonly of a stressed, snap-acting type m view of the fact that
such bimetals have well defined characteπstics which are stable over a peπod
of time So-called creep acting bimetals were previously employed but are not
nowadays widely used, mamly on account of their relative lack of stable
operating characteπstics Creep acting bimetals, which exhibit a progressive
deflection or deformation as a function of increasing temperature, as opposed
to the snap-acting type which exhibits a change from one stable state to
another at a predetermined temperature, are however useful in applications
where the operating temperature of a control is required to be adjustable It is
however, disadvantageous to use a creep-acting bimetal to operate switch
contacts directly since the relatively slow movement of the bimetal (as
compared to a snap-actmg bimetal) will give πse to arcmg at the switch
contacts with disadvantageous consequences and for this reason, where creep-acting bimetals are proposed to be used in present day controls, it would
be good design practice to isolate the bimetal from the switch contacts of the
control by means of a snap-acting mechanism, an overcentre lever for
example, which translates the slow movement of the bimetal into a
snap-action at the switch contacts. For obtaining temperature adjustability,
the mechanical relationship between the creep bimetal and the snap-acting
mechanism can be adjustable.
One such arrangement as abovedescribed is proposed in Strix
Limited's GB-A-2 329 523. A standard U18 control as presently available
from Strix has a creep bimetal riveted to the metal carrier plate of the control
and the creep bimetal is arranged to interact with the trip lever of the control
by way of a manually operable selector which provides for adjustability of the
mechanical relationship between the creep bimetal and the trip lever. The
arrangement of GB-A-2 329 523 provides the U18 control with the additional
facility of an adjustable means for switching off the power supply to a heating
element at a temperature below boiling which is selectable, in dependence
upon the calibration and adjustment of the creep bimetal, by operation of the
manually operable selector.
For the reasons abovementioned, creep bimetals are, in our considered
opinion, an undesirable component for inclusion in a control for a water
boiling appliance. It is in the nature of creep acting bimetals that some form
of initial temperature calibration is required during manufacture, and it is notable that the embodiment described in GB-A-2 329 523 includes set screws
which have to be adjusted to determine the action of the creep bimetal. This
adds to the cost and renders the control susceptible to variation of its operating
temperature as the calibration and adjustment changes as the control ages.
Objects and Summary of the Invention:
It is thus the principal object of the present invention to provide for
adjustability of the water temperature at which a control will operate to switch
off or reduce the power supply of the heating element of a water boiling vessel
without evoking the disadvantages that are inherent in the arrangement that is
described in GB-A-2 329 523 abovementioned.
Whilst the arrangement of GB-A-2 329 523 is not restricted in its
application to any particular kind of electric heating element, its greatest
application at the present time is to electric kettles and hot water jugs utilizing
so-called thick film heating elements. A thick film heating element comprises
a generally planar substrate, commonly but not essentially formed of metal,
such as stainless steel for example, which carries a printed or otherwise
formed heating track or layer on at least one side thereof, electrically
insulating layers being provided as necessary between the heating track or
layer and the substrate and overlying the heating track or layer. In accordance
with the present invention, in one of its aspects, we propose to make use of
the properties inherent in thick film heating elements to achieve adjustability
of the operating temperature of a thermally sensitive control associated with a thick film heating element. More particularly, we propose to enable the
thermal output of a predetermined part of a thick film heating element which
is to have a thermal sensor associated therewith to be selectively adjusted,
whereby the performance characteristics of the sensor in relation to the
volume of water being heated will change correspondingly.
According to the present invention, in one of its aspects, therefore, an
electrically powered water heating vessel has a thick film heating element, a
thermally-responsive control is located in thermal contact with a
predetermined part of the thick film heating element, and means are provided
for enabling the thermal output of that part of the thick film heating element to
be selectively adjusted.
Thick film heating elements are commonly manufactured by printing
with conductive ink onto the surface of a substrate formed of stainless steel
and provided with one or more insulating layers, commonly of glass. On such
a printed element the track temperature is related to the water temperature,
normally exceeding it by an amount which depends on the power density of
the track and on the thermal conductivity of the substrate and dielectric. In the
case of our X4 control described in our GB-A-2 339 088 on a 2.5 to 3kW
element the track temperature will be about 160°C, that is 60°C above the
boiling water temperature. In order to avoid nuisance tripping of the control
during boiling the control bimetal is normally set at about 180°C. If, on the
track portion which heats the bimetal, the heat output is increased, then the bimetal can be made to nuisance trip at a water temperature below boiling
point. If the amount of additional power applied to that part of the track were
arranged to be controlled, then the temperature at which the control "nuisance
tripped" could be controlled to give water at a controlled temperature below
boiling. In application to a cordless vessel, because of the latch out function
of the X44 (latched) variant, the control would remain off until the associated
cordless vessel was lifted off its base and reset. On the X46 (auto cycling) or
X48 (auto cycling with thermal fuse) variants, the control would cycle to
maintain the water at the preselected temperature. Of course, the present
invention is not limited in its application to our X4 series of controls.
The means by which the heat output of the track beneath the bimetal
may be adjusted could take a number of forms, but the preferred means is to
add an auxiliary track beside the main heater track at the location where the
bimetal senses the heater temperature. The current through the auxiliary track
could be controlled by connecting it via a variable resistance to the power
supply. It is anticipated that a power of around 20W would be necessary to
give a range of about 20°C depression of switch off point. This could be done
by provision of a variable resistor separate from the heating element and
having a control knob accessible to the user of the appliance, but such a
resistor would be costly and would dissipate a considerable amount of heat,
making it inefficient. The control could be electronic, since the control of a
power of 20W is well within the capability of low cost components. However the preferred option is to form the vaπable resistor on the thick film heating
element m the form of a resistive track pπnted on the element, and to provide
an arm carrying a brush or sliding contact arranged to make electπcal
connection to the resistive track at any selected position along the track or to
any selected one of a plurality of contacts connected to predetermmed track
locations which preferably are spaced apart from each other unequally to
provide a linear change of power to the auxihary track as the brush or sliding
contact is moved, the arrangement thus increasing or decreasing the amount of
resistive track included in circuit with the auxiliary heater There could also
be a "boil" position where the sliding contact made no contact with the
resistive track, providing a setting where the auxiliary heater track has no
effect and the vessel boils water normally Such an arrangement would
however mean that with the sliding contact in its "boil" position, no heat
would be generated by the auxiliary track and thus no contπbution to the
overall element power would be available from that area of the heater This is
inefficient use of the available space on the heating element and would lead to
an unnecessaπly large and costly heater, and to avoid this it is preferred in
accordance with the present invention to arrange that the "boil" position
places the entire resistive track in circuit and that the power density in the
auxiliary track is the same as in the adjacent main power track so that both
operate at the same temperature The techniques of pπnting tracks for
vaπable resistors with sliding contacts are well known and would be directly applicable to this construction. The resistive track could be an arc preferably
concentπc with the element substrate disc (and/or the appliance), and the
adjustment arm could project from a slot in the wall of the vessel body and be
arranged to slide around the body. Alternatively the arc could be formed as a
small diameter arc of more than 180°, as would be normal in a conventional
potentiometer, in which case the sliding arm could be pivoted from the centre
of the arc and a lever could be connected to the sliding arm and project from
the side of the appliance
In the above embodiment which contemplates the use of an X4 control
in the practice of the invention, the bimetal actuator of the control would also
continue to function as a dry boil protector. However if a more flexible lower
power solution is desired, then a thermal sensor separate from those provided
on the X4 control could be provided. This sensor should have a low thermal
capacity to reduce the power required from the auxiliary heater track It could
take the form of a PTC sensor, with an electronic control system, or preferably
it could be a small contactstat. Such a contactstat would require a smaller (m
area) heater track to make it function and, since the temperature of the heater
depends on its power density (not the absolute power), then a small track will
only require a small amount of power. The temperature setting of the
contactstat would be approximately 105°C to avoid nuisance tripping duπng
boiling, and the auxiliary heater track could be arranged to be adjustable to
provide between 0° and 65°C temperature πse to provide water selectively at temperatures from 40°C for heating babies bottles up to boiling. A further
advantage of this approach is that the auxiliary heater track would normally be
run at very low or no power, which would limit the amount of scale build up.
Scale build up over the main bimetal heater area results in a rise in running
temperature, which could affect the switch off point of a temperature control
based on the main bimetal. This is, after all, the reason why the bimetal is set
higher than the running temperature to avoid nuisance tripping.
A further aspect of the invention, useful to maintain water at a preset
temperature, for example simmering, or for maintaining a water bath at a set
low temperature, makes use of the principle disclosed in our GB-A-2 248 144
which describes how a temperature may be controlled by the reset temperature
of an automatically resetting bimetal control by ensuring that the bimetal
differential is less than the self heating caused by the current flow through the
bimetal. In the case of the present invention, the heating is proposed to be
supplied not by through current but by the auxiliary heater track, which raises
the bimetal through its differential until it switches off. The track then rapidly
falls to the water temperature and, if this is below the remake temperature of
the bimetal, then the control switches the heater back on and repeats the cycle.
This cycling action continues, with the water being heated intermittently, until
the water reaches the bimetal remake temperature, whereafter the bimetal will
cycle slowly to maintain the heater and the water at its remake temperature
just as in GB-A-2 248 144. To take best advantage of this effect it would be desirable to have a variable remake bimetal, that is to say an adjustable
bimetal, with a fixed auxiliary track power, but a variable (adjustable) remake
bimetal could be used with an adjustable auxiliary track power, in which case
one of these adjustments, possibly the power of the auxiliary heating power,
might be factory set and the other enabled to be determined by the user of the
appliance by provision of an appropriate control on the appliance.
Adjustability of the remake temperature of a bimetal, particularly a dished,
snap-acting bimetal as best contemplated for use in the practice of the present
invention, is readily provided for example by provision of an adjustable
back-stop for the bimetal and/or by provision of adjustability of the stressing
of the bimetal.
In the practice of this aspect of the invention, the controlled
temperature would be unaffected by any scale build up, since at the controlled
temperature there is no temperature drop across the dielectric/substrate/scale
sandwich. It should be noted in connection with the previously mentioned
example of the cycling X46, that if the normal remake temperature (which is
above 100°C) of such a control is used in the practice of this further aspect of
the invention, then the water temperature would tend to rise steadily until it
boiled. For this reason the alternative contactstat version with its lower
setting and remake below 100°C, is to be preferred where a controlled
maintained water temperature is desired. In accordance with this further aspect of the invention, therefore, the
thick film heating element of an electrically powered water heating vessel has
a predetermined part thereof provided with an auxiliary heater and a
snap-acting bimetallic actuator is arranged in thermal contact with such part of
the thick film heating element so that, in use, its operation is dependent upon
the heat output of said auxiliary heater, said snap-acting bimetallic actuator
being adjustable as regards it remake temperature.
Switching off the appliance on boil can be done by any of the known
ways, such as by use of our Jl or Z5 controls described in GB-A-2 212 664
and GB-A-2 331 848 respectively, or by means of the concept described in
GB-A-2 265 070, or by sensing the rate of rise of the water temperature as in
our electronic kettle control described in GB-A-2 228 634.
According to yet another optional feature of the invention a thick film
heating element provided with an auxiliary heating track at a location whereat
a thermal control, for example a bimetallic control, is to be juxtaposed with
the heating element and with means enabling the heat output of the auxiliary
track to be adjusted, all as aforesaid, additionally has a keep warm track and
means enabling the heat output of the keep warm track to be adjusted. The
means enabling the heat outputs of the auxiliary and keep warm tracks are
preferably commoned so that one and the same manual operation can perform
both functions and preferably comprise respective variable resistance elements
juxtaposed with each other and arranged to be adjusted by means of one and the same slider control, and the slider control preferably has an off position
where no contact is made with either variable resistance element so that
neither the auxiliary heater nor the keep warm heater is operative.
A water heating vessel provided with such a heating element and with
an X4 element protector control monitoring the condition of the heating
element, with one of its bimetallic actuators located to be responsive to the
heat developed by the main heating element track and by the auxiliary track
and the other located to be responsive to the heat developed by the main
heating element track and by the keep warm track, can have an on/off control
constituted by the reset switch of a boil sensing control such as our
aforementioned Jl or Z5 steam controls and a further control constituted by
the abovementioned slider or, more preferably, can have the two such controls
commoned together. Such a water heating vessel can, with the tracks and
bimetals appropriately configured, demonstrate different modes of operation,
namely a boil mode wherein the slider control is in its off position so that
neither the auxiliary heater track nor the keep warm track is operative and the
vessel is controlled by operation of the boil sensing control, a boil and keep
warm mode wherein the slider control is positioned so that the keep warm
track provides its maximum power output and the auxiliary track its minimum
whereby the vessel contents are initially heated to boiling by operation of the
main heater track which is then switched off by the Z5 steam control
whereafter the keep warm track keeps the vessel contacts close to boiling, and a heat and keep warm mode wherein the slider control is positioned at an
intermediate position so that the auxiliary heater operates to switch off the
power supply to the main heating element track when the vessel contents are
at some selected sub-boiling temperature and the keep warm track then
maintains the vessel contents at that selected temperature. By selection of the
appropriate mode, the user of such a water heating vessel can obtain boiling
water, or water that has boiled and which has been maintained close to
boiling, or water that has just been heated to some selected intermediate
temperature, and the mode selection is simple and uncomplicated.
The above and further features of the present invention are set forth in
the appended claims and will be further explained by reference to the
following detailed description of exemplary embodiments which are
illustrated in the accompanying drawings.
Description of the Drawings:
Figure 1 illustrates in plan view an exemplary track layout of a thick
film heating element for an electrically powered kettle or hot water jug
embodying the present invention.
Figure 2 is a schematic circuit diagram showing a thick film heating
element, for example as in Figure 1, in a water heating vessel provided with
dual dry-boil protection and with a steam control;
Figure 3 is a plan view of an alternative thick film heating element
embodying the present invention; Figures 4A, 4B, 4C and 4D show how a modified form of our X4
control interfaces with the heating element of Figure 3, Figure 4A illustrating
the areas of the heating element that are required to register with specific parts
of the control, Figure 4B showing a plan view of the modified X4 control
assembled with the heating element, Figure 4C showing an enlarged
perspective view illustrating the modification of the X4 control and Figure 4D
being a scrap cross-sectional view of the modified part of the control,
Figures 5 and 6 are plan views of yet further alternative thick film
heating elements embodying the present invention,
Figure 7 is a plan view of yet another thick film heating element
embodying the present invention which additionally includes a controllable
keep warm track, and
Figure 8 is a circuit diagram illustrating the use of a thick film heating
element according to Figure 7 with a control substantially as shown in Figures
4 A, 4B, 4C and 4D
Detailed Descnption of the Embodiments
Referring to Figure 1 , a circular thick film heating element is shown in
plan view as compπsing a stainless steel disk 1 upon which there is formed an
electπcally insulating layer 2 upon which a conductive ink pπnted heating
element proper 3 is provided The heating element proper 3 is made up of
heater track sections 4 which are joined by conductive bπdges 5 at their
extremities to avoid current crowding where the track changes direction The heating element shown is adapted for use with an X4 control having two
generally similar bimetallic switch actuators which, when the control is
affixed to the heating element by spot welding of metal mounting feet of the
control to the stainless steel disk 1 at the three locations 6, register with the
heating element m good heat transfer relationship therewith generally in the
regions 7 and 8 thereof The main power supply terminals to the heating
element compπse conductive pads 9 and 10 which are arranged to be
contacted by spπng terminals of the X4 control
In accordance with the teachings of the present invention, an auxiliary
heater track 11 is provided in the region 7 of the heating element which
co-operates with one of the bimetals of the X4 control and, coupled thereto by
means of a conductive section 12, is a resistive track section 13 which, in use,
will serve to enable the thermal output of auxiliary heater track 11 to be
adjusted The auxiliary heater track 11 is coupled at one end to mam heater
terminal 9 and resistive track section 13 has associated therewith a
schematically illustrated wiper 14 which is connected to that pole of the power
supply which supplies terminal 10 of the main heating element 3 In use, the
seπes-connected resistive track section 13 and auxiliary heater track 1 1 are
connected in parallel with the mam heating element track 3 and the position of
the wiper 14 along the resistive track section determines the heat output of the
auxiliary heater 1 1 and thus, as hereinbefore described, determines the operation of that bimetallic actuator of the X4 control that registers with
region 7 of the thick film heating element
The position of wiper 14 on the resistive track section 13 is made
controllable by the user of the vessel and preferably, to enable the effect of the
auxiliary heater 11 to be switched off when the vessel is to be used for boiling
water, has a control position whereat it makes no contact with the resistive
track section 13 The mechanical arrangement of the wiper 14 and/or its slider
knob is preferably such that contact between the resistive track section 14 and
the wiper 14 is made and broken with a snap action so as to minimize arcing,
and the respective part of the resistive track section, which will preferably be
provided at the high resistance end thereof, may be configured to withstand
such arcing as might occur
Figure 2 shows the thick film heating element of Figure 1 in an
electrically heated water boiling vessel provided with a dual-protection dry
boil control such as our aforementioned X4 control and with a steam control
such as our aforementioned Jl or Z5 controls In the figure, the two dry boil
controls are designated 21 and 22 and are designed to register with the regions
7 and 8 of the thick film heating element, and the steam control is designated
23 The control position of wiper 14 where it does not make contact with
slider track 13 is designated 24, this position of the wiper serving to isolate
auxiliary heater track 1 1 so that the vessel operates as a water boiling vessel Figure 3 shows an alternative thick film track layout designed
specifically for use with a modified form of our X4 control which is described
hereinafter. Employing the same reference numerals as were used in relation
to Figure 1, the thick film heating element of Figure 3 has regions 7 and 8
designed to register with the bimetals of the X4 control and the region 7 has
associated therewith an auxiliary heater track 11 which is connected to a track
section 13 which is designed to co-operate with a control slider 14 to
constitute a variable resistance enabling the thermal output of the auxiliary
track 11 to be controlled by the vessel user.
Figures 4A to 4D illustrate the attachment of a modified X4 control to
a thick film heating element as shown in Figure 3. Figure 4A merely shows
the regions of the heating element which are required to register with specific
parts of the control, namely the regions 6 whereat the feet of the metal chassis
of the control are affixed to the metal substrate 1 of the heating element, the
regions 7 and 8 whereat the bimetals of the X4 control thermally contact the
heating element track, the terminal regions 9 and 10 whereat the spring
terminals of the X4 control make electrical contact with the heating element
track, and the variable resistance track section 13 adapted to be contacted by a
control wiper of the X4 control.
Referring to Figure 4B, this shows a modified X4 control 40 affixed to
the heating element. As is known, and as described in GB-A-2 339 088
aforementioned, the X4 control comprises a cordless vessel inlet connector 41 of the 360° type pioneered by us which enables a cordless vessel to be set
down upon its base in any relative rotational orientation and, integrated
therewith, first and second heating element protector controls generally
designated 42 and 43 which can be bimetallic or a combination of one
bimetallic and one fusible material as described in our abovementioned
application. Provision is made at location 44 of the control for the attachment
of a Z5 steam control to the X4 control.
Figures 4B, 4C and 4D show the modification to the X4 control. The
metal chassis of the control has an extended part 51, which has a central pivot
hole 52 at the centre of the arc of an arc shaped section 53 with end stops 54.
A plastics moulding 55 has a pivot peg 56 and an overlapping arm 57 and is
designed to snap into place as shown, so that the pivot peg 56 locates in the
pivot hole 52 of the chassis extension. The overlapping arm 57 fits under the
chassis extension to prevent the moulding coming off its pivot and acts as a
guide as the moulding is rotated. At the outer end of the moulding is a box
section 58 with a snap fitting lid 59. A carbon brush assembly 60 fits into the
box section, with the brush projecting towards the element surface. The braid
pigtail of the brush assembly has a quick connect receptacle attached which is
fitted to the tab 61 of the X4. This tab is connected to the neutral supply point
of the element via the neutral side dry boil thermal control, as shown in the
circuit diagram of Figure 2. As is also seen from the circuit diagram of Figure 2, the boil control,
which may be either directly plugged into the X4 or remotely mounted (as is
the case in the Figures, plugging into the receptacles marked 62 and 63 on the
isometπc view), will act to switch off the power to the element, independently
of the connection of the brush assembly This will ensure that in the event of
a failure of the lower temperature feature, the boil control will always prevent
the water boiling continuously
When the X4 control is mounted to the heating element, the brush
makes contact with the arc shaped slider track 13 The angle of rotation of the
moulding is greater than the angle subtended by the slider track so that at one
extreme of travel the brush is not in contact with the slider track In this
position the auxiliary heating track 12 is not energised and the appliance w l
behave as a normal automatic kettle This is the "Boil Position" in Figure 2
As the brush engages the slider track, current w l flow m the auxiliary track,
causing the live side dry boil blade to operate at a temperature depending on
the power in the auxiliary track, as already descπbed, and varying the position
of the brush on its slider track will vary the power in the auxiliary track, and
hence the water temperature at which the control will switch off
Figures 5 and 6 show yet further alternative thick film track layouts
designed for use with the aforementioned modified X4 control Employing
the same reference numerals as were used in relation to Figures 1 and 3, the
thick film heating elements of Figures 5 and 6 each have regions 7 and 8 designed to register with the bimetals of the X4 control and the region 7 has
associated therewith an auxiliary heater track 11 which is connected to a track
section 13 designed to cooperate with a control slider of the X4 control to
constitute a vaπable resistance enabling the thermal output of the auxiliary
track 11 to be controlled by the user of the vessel
In both of the heating element layouts of Figures 5 and 6 the mam
power track 4 is shown reasonably wide, whereas the temperature control
auxiliary track 1 1 is somewhat narrower, since it is of lower power and thus
higher resistance The arc shaped control track 13 is moved away from the
stroke of the sliding brush contact and has a seπes of silver hnks 14' pπnted
over (or under) it The silver links lead to a seπes of closely spaced silver
pads 15 which he in an arc beneath the path of the brush contact The spacing
of the pads ensures that the brush is always in contact and may bπdge two
pads with little loss of contact area
The silver pads 15 have two purposes Firstly, it is known that making
contact to resistive areas of a thick film pπnted heater can cause problems
from localised overheating, which may burn out the track or the contacting
component Although the current through the track m this case is relatively
low, the mateπal of the track has a much higher resistivity than the mam track
and may cause problems Thus it has been our practice always to provide
silver pads when making spπng contact to a thick film heater The problem
may be worse with the proposed sliding contact when the point of contact is moving and any arcmg could damage the track surface Secondly, it will be
noticed that the segments of the arc shaped track 13 between the silver links
14' are not of equal length This allows a linear change of power to the
auxiliary track as the brush is rotated, rather than the hyperbolic relationship
that would occur with equal length segments or with direct contact with the
arc shaped track This will allow a linear temperature scale on the appliance
A further feature of the design of Figures 5 and 6 is that there is no
"boil" position where the brush is isolated from the arc shaped track Such a
position would mean that no heat is generated in the auxiliary track, and thus
no contπbution to the overall element power would be available from that
area of the heater This is inefficient use of the available space and would
lead to an unnecessaπly large and costly heater In the present layout, m the
"boil" position, which is with the whole arc included, the power density m the
auxiliary track is arranged to be the same as in the adjacent main power track
Thus the auxiliary track will run at the same temperature as the mam boil
track, not causing nuisance tπppmg and contπbuting both to the normal power
output of the element and to providing the necessary dry boil response from
the bimetal blade at that position As the brush is moved to the minimum
included arc length, so the power density in the auxiliary heater track is
increased leading to the bimetal being actuated at progressively low er
temperatures, according to the invention Referring now to Figure 7, shown therein is yet another embodiment
of a thick film heating element according to the present invention which, in
addition to incorporating an auxiliary track and associated arc shaped slider
track enabling the heat output of the auxiliary track to be controlled, also
incorporates a keep warm track and an associated control enabling the heat
output of the keep warm track to be controlled. The control for the keep
warm track is actually commoned with the control for the auxiliary track by
virtue of comprising an arc shaped slider track parallel to and concentric with
the arc shaped slider track that is associated with the auxiliary track and by
virtue of employing the same control to determine the position of respective
carbon brushes associated with the respective arcuate slider tracks. As will be
explained more fully hereafter, this arrangement enables a kettle or hot water
jug, for example, selectively to provide boiling water, or water which has been
boiled and then has its temperature maintained close to boiling, or water
which is heated to a selected temperature lower than boiling and then is
maintained substantially at that temperature. Furthermore the arrangement
hereinafter described enables this to be achieved by use of just one manual
control.
The same reference numerals are used in Figure 7 as were used to
denote like parts in previous embodiments. As shown, the thick film heating
element 1 has arcuate main heater track sections 4 connected at their ends by
conductors 5 so as to avoid cuπent crowding, the main heater track extending between neutral and live terminals 9 and 10 respectively. An auxiliary track
section 1 1 is connected between a tapping point 20 of the main heater track,
selected to apply the required sub-mains voltage to the auxiliary track section,
and an adjustable resistance defined by the track section 13 with its associated
contact points 14' and tapping points 15 to be contacted selectively by a
sliding brush contact. As shown, an end tapping point 15' is provided upon
which the brush contact can be parked out of electrical contact with the track
section 13; when the brush contact is in this position, the auxiliary track 11 is
not powered.
An additional track section 21 is provided in the centre of the heating
element and serves as a keep warm track. As shown, the keep warm track 21
is connected at one end to an additional power supply terminal 22 provided on
the heating element by means of a conductor 23 and, at its other end, is
connected by means of a conductor 24 to a further adjustable resistance 25
configured similarly to and physically in parallel with the adjustable resistance
that is associated with the auxiliary track section 11. The provision of the two
adjustable resistances physically in parallel and closely proximate to each
other enables both to be operated by means of one and the same control slider.
The control that is used with the heating element of Figure 7 is a
variant of the X4 control described hereinbefore with reference to Figures 4A
to 4D. According to this variant, the sliding brush mechanism of the Figure 4
proposal is provided with two separate brushes (or a single broader one) attached to a flexible lead or braid, which in turn is connected to one terminal
of the boil control Z5 by means of the standard X4 tabs and receptacles
provided for the purpose. The variant X4 has a third spring contact 22, in
addition to the standard live and neutral element contacts, which is located
beside the auxiliary track 1 1. Figure 8 shows how the control connects to and
interacts with the heating element.
The control is fitted with a high temperature bimetal blade
(180/190°C) on its neutral side to protect the main and auxiliary tracks. A low
temperature blade (110/120°C) is fitted to the live side to act as a keep warm
thermostat and provide secondary protection. The potentiometer slider has
either one or two contacts (depending on the design, to ensure that both
resistance tracks have good contact pressure), which contact the two variable
tracks, so that as one resistance increases, the other is reduced. At one end of
the travel there is an isolated position, to act as an "Off. The auxiliary track
1 1 is shown being fed from a tapping, part of the way along the main track, to
give a lower voltage which is better suited to the available resistive materials
used to print its heater track. This is simply for convenience, and the auxiliary
track could be fed from the full supply voltage if desired.
The heating element of Figure 7 when combined with the
abovedescribed control enables the following selectable modes of operation,
namely: . Boil: With the slider in the Off position, the kettle may be
switched on by means of the Z5 control, which functions as
usual, and switches the kettle off when the water boils. Since
the slider contacts are not connected to anything, they have no
effect and the auxiliary and keep warm tracks are inoperative.
2. Boil and Keep Warm: With the slider position in the max
position, when the Z5 is switched on the water will come to the
boil and switch off the Z5. The slider contact of the keep warm
track 21 provides the maximum power to that track which is
designed to keep the water close to boiling. The slider contact
of the auxiliary track 11 gives a very low heat to its associated
heater track, which is insufficient to cause the bimetal
(thermostat) associated with it to operate. The water may be
re-boiled by operating the Z5 at any time.
3. Heat and Keep Warm: With the slider positioned between max
and min, and when the Z5 is switched on, the main track will
heat the water until the thermostat bimetal is tripped by the
auxiliary track 1 1. After this the keep warm track 21 will
maintain the water temperature. The two variable resistors are
arranged so that the "keep warm" setting follows the
"Vari-Temp" setting determined by auxiliary track 11 as the
slider is moved, so that the maintained temperature is close to the Van-Temp temperature There wfll clearly be some
vaπation in the temperature given by the keep warm track,
depending on ambient conditions and the amount of water in
the kettle, so the track is preferably targeted always to give a
slightly lower temperature than the Van-Temp track This
means that the thermostat bimetal will cycle occasionally, as
necessary, to switch on the mam heater and return the water
temperature to the required value This avoids the possibility
of the water temperature slowly πsmg m an uncontrolled
manner, and at the same time limits the cycling rate of the
thermostat to increase its fespan
Dry boil protection of the system is provided by the dry boil bimetal of
the X4 which locates m the region 8 of the heating element This will switch
off the main tracks, but leave the keep warm track 21 energised if the slider is
not at the off position The keep warm track 21 is positioned centrally to
ensure that its heat does not cause damage to seals or the vessel wall In the
event of failure of the dry boil bimetal, the other bimetal associated with
auxiliary track 11 will operate, albeit somewhat more slowly because of the
lower track power density Even if the slider is set to off, there will be
sufficient thermal transfer from the main tracks to ensure that this low set
bimetal will operate Should the keep warm track remain energised, it is
probable that it will act to maintain the Van-Temp bimetal in an operated condition, giving a form of manual latch, to be reset by disconnecting the
kettle from the supply. However this action is dependent on the slider
position and is not relied on in the design of the system.
The design of the "user interface" is a matter of choice. Two separate
controls could be provided, one for the boil control, and one for the slider.
However this would still leave the dilemma of having two "Off positions,
and a simple user may not realise that both controls must be off to completely
switch off the appliance. A better scheme is to have a single, sliding, control,
which has three states: Off, where both the Z5 and the sliders are in their
"Off positions; a Boil position, where the Z5 is switched on, and can return
the control of the "Off state, the sliders remaining in their "Off position; and
a Simmer range of positions, where the Z5 is on, and can have no effect on the
sliding control, and the sliders are between Max and Min. The status of the
appliance would be indicated by indicating lamps. Such a mechanism would
be within the capability of a reasonably skilled mechanism designer, and
might make use of lost motion and Geneva wheel type functions.
The invention having been described herein by reference to specific
arrangements and an exemplary embodiment, it is to be understood that
modifications and variations thereto would be possible without departure from
the scope of the invention. For example, in accordance with the teachings of
GB-A-2 340 367, the main track portions 3 of the thick film heating element 1
could be formed to exhibit a PTC (positive temperature coefficient of resistance) characteristic whereas the auxiliary heater 11 could be formed with
an NTC characteristic for the purpose of compensating for supply voltage
variations. Furthermore, whereas in the foregoing the auxiliary heater is
formed as an integral part of a thick film heating element, the invention is
applicable to the control of other kinds of heating elements by means of
bimetallic actuators. For example, an underfloor heating element of the metal
sheathed, mineral insulated, resistance wire type could be controlled in
accordance with the teachings of the present invention by means of a
bimetallic control by provision of a separate auxiliary heater, for example a
small thick film heater, in close thermal contact with the bimetal and by
provision of a variable resistance to control the auxiliary heater output. The
metal mounting plate of an X4 control (item 27 in Fig ID of GB-A-2 339 088
for example) could even be provided with a small thick film heater on a part
thereof extending under one of the bimetals for this purpose.

Claims

Claims:
1. In or for an electrically powered water heating vessel, a thick film
heating element having a predetermined part thereof adapted to be
juxtaposed with the bimetallic actuator of a thermally-responsive
control, and means enabling the thermal output of that part of the thick
film heating element to be selectively adjusted.
2. A heating element as claimed in claim 1 wherein said part of the
heating element has an auxiliary heater track formed thereon, and said
adjustment means is such as to enable the current through the auxiliary
heater track to be selectively adjusted.
3. A heating element as claimed in claim 2 wherein said adjustment
means comprises an adjustable resistance including a resistive track
section formed on the thick film heater.
4. A heating element as claimed in claim 3 wherein said resistive track
section has an associated plurality of contact portions coupled thereto
at spaced apart locations.
A heating element as claimed m claim 4 wherein said locations are
unequally spaced apart so as to enable the output of the auxiliary
heater track to be linearly adjusted
An electπcally powered water heating vessel including a thick film
heating element, a thermally responsive control for protecting the
heating element against overheating, said control including a
bimetallic actuator juxtaposed with the thick film heating element, an
auxiliary heater associated with said bimetallic actuator, and means
enabling the heat output of said auxiliary heater to be adjusted
A water heating vessel as claimed in claim 6 wherein the bimetalhc
actuator is juxtaposed with a predetermined part of the thick film
heating element which is provided with an auxiliary heater track
constituting said auxiliary heater
A water heating vessel as claimed in claim 7 wherein said adjustment
means compnses an adjustable resistor connected in seπes with said
auxiliary heater track, said adjustable resistor compπsing a resistive
track section formed on the thick film heating element and means
enabling the operatι\ e length of said resistive track section to be
adjusted
9. A water heating vessel as claimed in claim 8 wherein a movable wiper
is associated with the resistive track section for enabling the operative
length thereof to be adjusted.
10. A water heating vessel as claimed in claim 9 wherein the wiper
cooperates with a plurality of contacts coupled to respective locations
of said resistive track section.
11. A water heating vessel as claimed in claim 10 wherein said locations
are unequally spaced apart whereby adjustment of the wiper linearly
adjusts the output of the auxiliary heater track.
12. A water heating vessel as claimed in claim 9 or 10 or 1 1 wherein the
wiper is additionally selectively movable to a position whereat it
makes no contact with the resistive track thereby disconnecting said
auxiliary heater.
13. A water heating vessel as claimed in claim 9 or 10 or 1 1 wherein the
power output of the auxiliary heater track matches that of the main
heater track when the maximum length of resistive track section is
selected.
14. An electrically powered water heating vessel including a heating
element, a thermally-responsive control associated with the heating
element for protecting the same against overheating, an auxiliary
heater associated with said control, and means enabling the heat output
of said auxiliary heater to be selectively adjusted thereby to adjust the
vessel temperature at which said control will operate.
15. A water heating vessel as claimed in claim 14 wherein said control
comprises a snap-acting bimetallic element and means are provided
enabling the operating characteristics of said bimetallic element to be
adjusted.
16. A water heating vessel as claimed in claim 15 wherein the heating
element is a thick film heating element, the auxiliary heater comprises
a track formed on said thick film heating element, and for adjusting the
heat output of said auxiliary heater, a resistive track is provided on the
thick film heating element in series with the auxiliary heater and a
wiper is associated with said resistive track for adjusting the resistance
thereof by adjusting the effective length thereof.
17. A water heating vessel as claimed in claim 16 wherein the wiper
cooperates with a plurality of contacts connected to respective
locations of said resistive track section.
18. A water heating vessel as claimed in claim 17 wherein said locations
are unequally spaced apart whereby linear adjustment of the wiper
linearly adjusts the output of the auxiliary heater.
19. A water heating vessel as claimed in claim 16 or 17 or 18 wherein the
power output of the auxiliary heater track matches that of the main
heater track when the maximum length of resistive track section is
selected.
20. An electrically powered water heating vessel including a thick film
heating element having associated therewith a temperature-sensitive
control comprising an automatically resetting snap-acting bimetallic
actuator in thermal contact with the heating element, an auxiliary
heater being associated with the bimetallic actuator for causing the
same to snap from its cold to its hot configuration in a relatively short
time period, and the remake temperature setting of the bimetallic
actuator being adjustable, the aπangement being such as to enable water to be heated in the vessel to the remake temperature of the
bimetallic actuator and maintained at that temperature.
21. A water heating vessel as claimed in claim 20 wherein the auxiliary
heater comprises a track formed on the thick film heating element.
22. A water heating vessel as claimed in claim 20 or 21 wherein the heat
output of the auxiliary heater is aπanged to be adjustable.
23. A water heating vessel as claimed in claim 22 as dependent upon
claim 22 wherein an adjustable resistance is provided on the thick film
heating element in series with the auxiliary heater.
24. A water heating vessel as claimed in claim 23 wherein said adjustable
resistance is aπanged so that adjustment thereof enables the output of
the auxiliary heater to be controlled linearly.
25. A water heating vessel as claimed in claim 23 or 24 wherein the heat
output of the auxiliary heater at one adjustment of the adjustable
resistance matches that of the main heater track of the thick film
heating element.
26. A thick film heating element as claimed in any of claims 2 to 5, or a
water heating vessel incorporating such a thick film heating element,
or a water heating vessel as claimed in any of claims 6 to 13, 16 to 19
and 20 to 25, wherein the major part of the thick film heating element
has a PTC characteristic and the auxiliary heater has an NTC
characteristic.
27. A thick film heating element as claimed in any of claims 2 to 5 and 26,
or a water heating vessel incorporating such a thick film heating
element, or a water heating vessel as claimed in any of claims 6 to 13,
16 to 19 and 20 to 26, wherein the heating element further comprises a
"keep warm" track portion.
28. A thick film heating element as claimed in claim 27 wherein means
are provided for enabling the power output of said "keep warm" track
portion to be adjusted.
29. A thick film heating element as claimed in claim 28 wherein said
adjustment means comprises an adjustable resistance including a
resistive track section formed on the thick film heater.
30. A thick film heating element as claimed in claim 29 wherein said
resistive track section has an associated plurality of contact portions
coupled thereto at spaced apart locations.
31. A thick film heating element as claimed in claim 28 or 29 or 30
wherein the adjustment means of the "keep warm" track portion is
adjacent to a corresponding adjustment means for the auxiliary heater
track whereby both adjustment means may be adjusted together.
32. A thick film heating element as claimed in claim 31 wherein
adjustment of the power output of the auxiliary heater track such as to
increase the same is effected commonly with adjustment of the power
output of the "keep warm" track portion, and vice versa.
33. A thick film heating element comprising a main heater track portion,
an auxiliary heater track portion located at a position whereat a
thermal control is to be juxtaposed with the heating element, a "keep
warm" track portion, a first adjustable track portion connected to the
auxiliary heater track and configured to enable its resistance to be
selectively adjusted for selectively adjusting the power output of the
auxiliary heater track, and a second adjustable track portion connected
to the "keep warm" track portion and configured to enable its resistance to be selectively adjusted for selectively adjusting the power
output of the "keep warm" track.
34. A thick film heating element as claimed in claim 33 wherein said first
and second adjustable track portions extend alongside one another so
as to be adjustable simultaneously by one and the same manual
control.
35. A thick film heating element as claimed in claim 34 wherein the first
and second track sections are simultaneously adjustable in opposite
senses so that as the resistance of one increases, so the resistance of
the other reduces.
36. A thick film heating element as claimed in any of claims 33 to 35 in
combination with a thermally-responsive control comprising a first
bimetallic actuator juxtaposed with the heating element at said
position thereof, a second bimetallic actuator juxtaposed with the
heating element so as to be responsive to the temperature of said "keep
warm" track portion, and adjustment means enabling said first and
second adjustable track portions to be manually adjusted.
37. A liquid heating vessel incorporating a heating element and
thermally-responsive control as claimed in claim 36.
38. A liquid heating vessel as claimed in claim 37 further comprising a
boil control responsive to the boiling of liquid in the vessel to
switch-off the power supply to the main heater track portion.
39. A thermally responsive control for a water heating vessel, said control
including a bimetallic actuator arranged so as in use of the control to
be responsive to the temperature of a heating element so as to protect
the same against overheating, and wherein the control further
comprises a selectively operable member enabling the heating of said
bimetallic actuator to be controlled for adjusting the heating element
temperature at which the control will operate.
40. A thermally responsive control as claimed in claim 39 which is
adapted for use with a thick film heating element having an auxiliary
heater located to interact with said bimetallic actuator and wherein
said selectively operable member comprises part at least of an
adjustable resistor for determining the current in said auxiliary heater.
A thermally responsive control as claimed in claim 40 which is
adapted for use with a thick film heating element further having a
resistive track coupled in senes with the auxiliary heater and wherein
said selectively operable member compnses a slider mechanism for
co-operation with said resistive track to vary the effective resistance
thereof
A thermally responsive control as claimed m claim 39 or 40 or 41
wherein the control compnses first and second bimetallic actuators and
only one of said actuators is arranged to be effected by said selectively
operable member
A thermally responsive control as claimed in claim 39 or 40 or 41
further compπsing a fusible component actuator
A thermally responsive control as claimed in any of claims 39 to 43
which is integrated with an appliance mlet connector
A thermally responsive control as claimed in claim 44 wherein the
appliance inlet connector is for a cordless appliance and enables the
appliance proper to be set onto its base with any relative rotational
oπentation
46. A thick film heating element substantially as herein described with
reference to any of Figures 1, 3, 5, 6 and 7 of the accompanying
drawings.
47. A thermally responsive control substantially as herein described with
reference to Figures 4B, 4C and 4D of the accompanying drawings.
48. A thermally responsive control as claimed in claim 47 in combination
with a thick film heating element as claimed in claim 46, in or for a
water heating vessel.
49. An electrically powered water heating vessel wherein the electrical
circuit of the vessel heating element and its associated controls is
substantially as herein described with reference to Figure 2 of the
accompanying drawings.
50. An electrically powered water heating vessel wherein the electrical
circuit of the vessel heating element and its associated controls is
substantially as herein described with reference to Figure 8 of the
accompanying drawings.
EP00946184A 1999-07-21 2000-07-20 Improvements relating to water heating vessels Ceased EP1198741A1 (en)

Applications Claiming Priority (9)

Application Number Priority Date Filing Date Title
GBGB9917131.6A GB9917131D0 (en) 1999-07-21 1999-07-21 Improvements relating to water heating vessels
GB9917131 1999-07-21
GB9918183 1999-08-02
GBGB9918183.6A GB9918183D0 (en) 1999-07-21 1999-08-02 Improvements relating to water heating vessels
GBGB9926533.2A GB9926533D0 (en) 1999-07-21 1999-11-09 Improvements relating to water heating vessels
GB9926533 1999-11-09
GB0013545A GB2354927B (en) 1999-07-21 2000-06-02 Improvements relating to water heating vessels
GB0013545 2000-06-02
PCT/GB2000/002814 WO2001006334A1 (en) 1999-07-21 2000-07-20 Improvements relating to water heating vessels

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EP1198741A1 true EP1198741A1 (en) 2002-04-24

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GB2466219A (en) * 2008-12-12 2010-06-16 Otter Controls Ltd Thick film heating element
CN102434971A (en) * 2011-12-28 2012-05-02 九阳股份有限公司 Instant heating type water boiler and control method thereof
KR102476376B1 (en) * 2017-08-31 2022-12-12 현대자동차주식회사 Cooling water heating apparatus of electric vehicle
CN109932930B (en) * 2017-12-15 2021-07-20 佛山市顺德区美的电热电器制造有限公司 Heating control method, heating control device, heating appliance and computer-readable storage medium

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GB2305233A (en) * 1995-09-15 1997-04-02 Welwyn Components Ltd Water heater with thick film printed circuit
GB2318713B (en) * 1996-10-22 2000-07-12 Strix Ltd Electric heaters

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CN100373280C (en) 2008-03-05
CN1373866A (en) 2002-10-09
WO2001006334A1 (en) 2001-01-25
AU6005700A (en) 2001-02-05

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