Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02291896 2005-03-17
METHOD AND APPARATUS OF CONTROLLING fll'ERATION OF R ANGE
TOP HEATING ELEMENTS FOR COOHING
This invention relates to the method and the device for controlling the
temperature
of all utensils for cooking on a burner element particularly on the surface
burner element
of a range. There are many types of ranges equipped with surface burner
elements
presently in use. Some surface burner elements of electric ranges are in the
form of spiral
sheathed heating elements, while others have a flat heat transfer tap made of
either glass,
metal alloy, or ceramic with the heating elements located underneath such top.
Others use
natural gas for heating. The challenge is to create a regulating device which
can provide
safe control of the cooking temperature of the utensil placed on the heating
element. Most
electric ranges in use nowadays do not have any cooking temperature control
per se; a
device commonly referred to as a heat switch is used to regulate the current
to the burner
element so as to vary its heating power. The heat switch may be in the form of
a
mechanical switch provided with a current coil or a current control electronic
circuit
which operates to vary the heating power of the burner element. Malfunction of
such
current control would inevitably result in a run away operation of the burner
element,
namely the burner element would operate continuously with ever increasing
power to
result ultimately in a fire hazard. In cooking, it is, in fact, the
temperature of the utensil
that actually cooks the food contained within it. However, by controlling the
heating
powei output of the burner element, the actual cooking temperature is unknown.
Since
utensils of various sizes and volumes may be used for cooking and also various
types and
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amount of food. The user has to estimate the appropriate setting of the
heating power of a
burner element, depending on the size of the utensil, and the amount of food
to be cooked in
the utensil. The heat switch varies the current to the burner element with a
series of ON and
OFF cycles so as, in turn, to vary its heating power. Such method of merely
varying the
S heating power does not provide a satisfactory cooking operation when using
utensils of
different shapes and sizes for cooking foods having various masses of liquids
and/or solids
so that the heat losses, as well as the thermal capacities may vary widely;
therefore, the same
amount of heat applied to two very different utensils will result in two very
different actual
cooking temperatures. Furthermore, the heat required to raise the temperature
of the utensil
is often much higher than the heat required to maintain the utensil at a
desired cooking
temperature. Most users would turn the heat switch control dial to the maximum
heat setting
in order to save time in heating the utensil to the desired cooking
temperature quickly; and
it is intended to turn the control dial down to a lower maintenance heat
setting after the
utensil has attained the desired temperature. However, often time, the user
forgets to do so,
resulting in dire consequences in which the cooking pot may become overheated,
or even
melted, or the cooking oil or similar flammable substance inside the pot may
be ignited.
Kitchens and whole houses have been known to burn down in many cases due to
such
negligence.
In U. S. Patent No.4,492,336 to Takata et al and U. S. Patent No.4,470,888 to
Ceste
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et al, temperature controls for particular types of cooking vessels are shown.
Such
temperature controls do not cater to universal applications for cooking with
different types
of cooking utensils such as boiling water in a kettle, or heating a large stew
pot; and they
cannot be used for controlling common cooking utensils intended for use in
cooking with
different types of conventional surface burner elements.
There have been attempts to sense directly the temperature of the utensil
during
cooking by means of infrared devices, such as those shown in U. S. Patents
4,734,553 to
Noda and U. S. Patent No.4,499,357 to Kojima. However, these methods and
devices suffer
the critical drawback that the infrared waves can be blocked by the lid,
handle, or other parts
ofthe utensil to render them inoperative. Thus, there is a great demand that
the temperature
sensing method and device must be capable of sensing directly the actual
cooking temperature
of any cooking utensil which is heated on all types of conventional burner
elements so that
the application of the method and device is universal. Furthermore, the method
and device
must be capable of turning off the burner element when there is no cooking
utensil placed
thereon or to prevent the burner element from operating in a runaway
condition.
It is the principal object of the present invention to provide a method and
device
for controlling the actual cooking temperature of any utensil to be heated on
a common
burner element of a cooking heater.
It is another object of the present invention to provide a heat control device
having
an integral fail safe circuits which is operative to turn offthe burner
element in case of
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some critical components failure in the device due to unforeseeable
circumstances.
It is another object of the present invention to provide a reliable
temperature control
device which may be incorporated into existing cooking heaters with simple
modification
to the latter.
It is another object of the present invention to provide a heat control device
which
has a protective cover for the heating elements of the cooking heaters so as
to alleviate the
likelihood of any fire hazard.
It is yet another object of the present invention to provide a method and
device which
is capable of sensing the presence or absence of a utensil placed on the
cooking heater and
to switch off the heating elements automatically when the utensil is absent.
Briefly, the device according to the present invention includes a temperature
sensing
means mounted in close contact with the cooking utensil such as on a heat
transfer plate
mounted to the burner element on which the utensil is located.. A switching
means is
connected in series with the temperature sensing means. The switching means
has switching
elements connected in series to the current control switch and the surface
burner element.
The switching means has actuation element therein connected to the temperature
sensing
means. The actuation means is operative in response to the actual temperature
of the
cooking utensil sensed by the temperature sensing means for selectively
operating the
switching elements for energizing the burner element.
The device may have a battery powered transmitter mounted directly on the
utensil
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and the switching means is located in a receiver means. The actual cooking
temperature of
the utensil is sensed by a thermocouple having a heat sensing junction which
is either in
direct contact with the side wall of the utensil or mounted to the heat
transfer plate. The
thermocouple will generate a voltage signal relative to the actual cooking
temperature of
the utensil. A temperature selector in provided in the transmitter for
selecting the desired
cooking temperature. The transmitter operates to compare the actual cooking
temperature and the selected temperature to transmit a control signal to the
receiver for
actuating the switching means for turning the burner element in a series of on
and off
cycles so that the actual cooking temperature is equal to the desired cooking
temperature.
Figure 1 is a bottom elevation of the burner element of a cooking heater
having the
component of the heat control according to the present invention mounted
thereon.
Figure 2 is an exploded elevation view of Figure 1 showing the various
components therein.
Figure 3 is a schematic circuit diagram of the electrical control circuit of
the device
according to the present invention.
Figure 4 is a schematic diagram of a preferred embodiment of the heat control
electrical circuit in the device according to present invention.
Figure 5 is a schematic diagram of an alternate electrical circuit of the
control
according to the present invention using a battery operated remote sensing and
control
transmitter.
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Figure 6 is a schematic diagram of the electrical circuit of the receiver when
the
remote sensing transmitter is used.
Figure 7 is a side elevation view of the temperature remote control unit
according to
the present invention..
Figure 8 is a top elevation view of the temperature remote control unit.
Figure 9 is a side elevation showing the mounting of the temperature remote
control
unit to a cooking utensil.
The invention will now be described with reference to the accompanying
drawings
wherein corresponding parts are identified with the same reference numerals
and/or
alphanumerals. The heat sensing assembly of the present device for mounting to
a
conventional burner element is best shown in Figures 1 and 2. Only one heat
sensing
assembly is shown for the simplicity of illustration purposes. It can be
appreciated that the
assembly is similar for all surface burner elements in an electric range in
which, commonly,
four surface burner elements are provided. The heat sensing assembly of the
present
invention includes a heat transfer plate 10 mounted to the burner element 11
such as a
spiral sheath-type surface burner element. A removable burner element is shown
as an
example. The assembly may similarly be applied to tiltable burner elements
which are
permanently mounted to the range top but they may be tilted upwards to
facilitate cleaning
of any food spillage to a burner box area located below the burner elements.
The heat
transfer plate 10 has a diameter larger than the opening in the range top
surrounding the
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burner element such that any spillage due to boil over during cooking will be
diverted by
the heat transfer plate 10 to the range top rather than running into the
burner box so as to
facilitate easy cleaning up in the event of such spillage. The heat transfer
plate 10 may be
molded of aluminum or other metal or alloy having a high thermal conductivity
and its
S surface may be anodized to resist abrasion. The heat transfer plate 10 is
mounted to the
burner element 11 by a Y-shaped mounting plate 12 which is secured to the heat
transfer
plate 10 by three bolts 13, 14 and 15 af~lxed to the under side of the heat
transfer plate 10
together with associated nuts 16, 17 and 18 respectively.
A thermostat 19 is also mounted to the heat transfer plate 10 by the bolts 14
and
15 with separate nuts so that it abuts tightly against the surface of the heat
transfer plate
10 for sensing its surface temperature. Alternatively, a thermocouple may be
mounted to
either one of the bolts 14 and 15 by welding to a washer which is secured to
the bolt by a
nut so that it is held tightly against the heat transfer plate 10 for sensing
its surface
temperature. The opening in the bifurcation of the mounting plate 12 permits
ready access
to the electrical connection terminals of the thermostat 19.
The electrical circuit for use with the heat sensor of the device for
controlling the
temperature of all four burner elements is shown in Figure 3 . The supply of
power from
the power lines L1 and L2 to the four burner elements EL1, EL2, EL3 and EL4
are
controlled by four heat switches HC1, HC2, HC3, and HC4 respectively in a
conventional
electric ranges, which, in fact, only control the current flowing through the
burner
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elements. The actuation of the burner elements are indicated by pilot lights
PL1 and PL2.
According to the present invention, four relays RL1, RL2, RL3 and RL4 are
incorporated
to control the operation of the burner elements EL1, EL2, EL3 and EL4
respectively. The
terminals of the switching contacts RS1, RS2, RS3 and RS4 of the relays RL1,
RL2, RL3
and RL4 respectively are connected in series with the burner elements EL1,
EL2, EL3 and
EL4. The direct current operating power for the relays EL1, EL2, EL3 and EL4
is supplied
from the power lines L1 and L2 by a rectification circuit consisting of a
stepdown
transformer TX, rectifier diodes D 1 and D2, and modulating capacitor C 1.
Temperature
control thermostats TS1, TS2, TS2 and TS4 are connected in series with the
operating
coils of the relays. The thermostats TS1, TS2, TS3 and TS4 correspond to the
thermostat
12 mounted to the heat transfer plate 10 of each of the burner elements EL1,
EL2, EL3 and
EL4 respectively as shown in Figures 1 and 2. Since the cooking utensil is
placed on the
heat transfer plate 10, its mass becomes integral with the cooking utensil
such that the
temperature of the heat transfer plate 10 is equal to the actual cooking
temperature of the
utensil. As long as the thermostats are closed, the relays are energised and
power can be
applied to the burner elements. The thermostats are preset so that their
contacts will be
opened at a safe temperature which is below the ignition temperature of oil,
paper or such
similar substances commonly present in the kitchen thereby reducing the risk
of fire.
In the beginning of the cooking operation, the thermostat is closed . When the
temperature of the heat transfer plate 10 is increased to higher than the
preset opening
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temperature of the thermostat, the thermostat contacts become opened thereby
deactivating
the relay and, in turn, turning off the associated burner element so that the
heat transfer
plate as well as the utensil will cool down in a short period of time.
An electrical control circuit for use with thermocouple sensors mounted to the
heat
transfer plate is best shown in Figure 4 in which Ll and L2 are incoming AC
line voltages
to which most electric ranges are commonly connected. The primary PR of a
stepdown
transformer TX is connected to the power lines L1 and L2. The low voltage
secondary SR
of the transformer TX is connected to diodes D 1 and D2 for rectification of
the AC
voltage so as to produce a DC positive voltage V 1 which is modulated by a
capacitor C7.
The center tap CT of the secondary of the transformer TX is connected to the
negative pin
of the capacitor which, in turn, is connected to a common negative voltage
ground line G.
The positive voltage V1 is applied to the input of a regulator REG which has
one pin
grounded and has a regulated output voltage V2 . The regulated output V2 which
powers
most of the circuit is switched to the circuit when the potentiometer P2 is
turned on for
setting a required temperature of the utensil located on the burner element,
by the switch
S 1 which is a part of a potentiometer P2. A capacitor C 1 is provided to
reduce the
possibility of spurious oscillation of the integrated circuits present in the
circuit. As soon
as the potentiometer P2 is turned on, the light emitting diodes D3 and D4 will
be turned on
by the resistors R20 and R21 to emit a light of mixed color from this diode
assembly
which has two diodes, D3 and D4 each emitting a different color. The
integrated circuits
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A1, A2, B1 and B2 have their positive voltage terminal connected to a
regulated output
line V2 and their negative voltage terminal connected to the ground line G.
The resistors
R2 and R3 and the capacitor C2 produce a divided voltage V3 which is arranged
to be
substantially equal to the voltage across the collector and emitter of the
transistor Q1. A
thermocouple TC 1 is provided for sensing the temperature of the heat transfer
plate PT
which is substantially identical to the temperature of the utensil placed on
the heat transfer
plate. When the hot junction of the thermocouple TC1 is heated up with respect
to the cold
junction CON1 and CON2, there is a voltage generated at the cold junction. The
amount of
voltage generated is proportional to the temperature difference between the
hot and cold
junctions. The negative wire of the thermocouple is connected to the divided
voltageV3
and the positive voltage of the thermocouple is applied to the non-inverting
input NIV of
an operational amplifier A1 via the resistor R5. A capacitor CS is connected
between NIV
and V3 while the feedback capacitor C3 attenuates unwanted pick-up voltage at
the output
of the amplifier. To compensate for the variation in temperature of the cold
junction, the
transistor Q1 with its base and collector are joined together to output line
V2. The base
and collector volt is applied to the inverting voltage IV of the amplifier A1
by the resistor
R11; and by selecting appropriate value for the resistor Rl 1, the effect of
the variation of
the cold junction temperature can be greatly reduced. The resistor R4 is
connected between
CON1 and V2 so that if there is an open circuit in the thermocouple, the NIV
voltage of
Al will go high, resulting in a high voltage at the output of integrated
circuit Al, thus
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switching off the relay RL1 and resulting in the removal of the power to the
burner
element EL1. The resistors R7 and R6 and the potentiometer are used to adjust
the output
of the operational amplifier so that its output is zero when the temperature
of the
thermocouple is at zero. The resistors R9 and R8 and the potentiometer P4 sets
the gain of
the amplifier. Resistor R12 and the capacitor C8 roll off the frequency
response of the
circuit and further reduce the value of pick-up voltage; and the output of the
integrated
circuit A1 is applied to the IV input of the amplifier which serves as a
comparator. Resistor
R13 provides a voltage drop across the control potentiometer P2 so that the
maximum
required temperature which is set as voltage on potentiometer P2 does not
exceed the
selected safe level. Resistors R14, R15, R16 and R17 provide a positive
feedback to allow
a small hysteresis in the operation of this comparator. If the selected
voltage of slider of
the potentiometer representing the required temperature, which is applied to
the non-
inverting input NIV of the comparator, is higher than the voltage of the
output of amplifier
representing the utensil temperature, the output of the comparator is high. In
this condition,
the transistor Q2 is turned on by the resistor R18, while the resistor R19
acts as a shunt .
When the transistor Q2 turns on, it applies an operating voltage to the coil
of the relay RL1
to energize it, and the contact RS 1 of relay RL1 will become closed so that
power is
applied to the element EL1 for heating up the heat transfer plate and the
utensil placed
thereon. When the transistor Q2 is on, it shorts out the diode D4 to draw
current away
from it, which changes the color output of the light emitting diode assembly.
The diode D6
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CA 02291896 1999-12-07
ensures that the diode D4 is properly turned off. Diode D8 is across the relay
to limit the
back EMF generated by the coil of the relay RL 1 in order to protect the
transistor from
breaking down. If for any reason the temperature of the heat transfer plate
rises too high,
the thermostat TS 1 will become opened, thus terminating the current to the
coil of the
relay and , in turn, the switch RS 1 becomes opened so that power is removed
from the
burner element EL1. If the temperature of the utensil is higher than the
required
temperature set by the potentiometer P2, the output of the integrated circuit
A2 is low, and
it will turn offthe transistor so that the relay is de-energized and the power
to the burner
element is again removed. The output of the amplifier is connected to the
capacitor C4,
while the other end of which is connected to the NIV input of the amplifier B
1 and also to
the resistor R24. In this arrangement the voltage at the NIV input terminal of
the amplifier
is proportional to the rate of rise of temperature of the heat transfer plate.
The gain of this
amplifier is set by the resistors R26 and R25. R23, R22 and the potentiometer
P3 which is
adjusted to substantially zero for the output of the amplifier when there rate
of rise of
1 S temperature is substantially zero. This circuit functions to switch off
the burner element
EL1 in the absence of the utensil on the heat transfer plate. When there is no
utensil on the
plate, the rate of rise of temperature of the plate is high, this results in a
high voltage level
at the output of amplifier B l, and this voltage is applied to the NIV input
terminal of the
amplifier B2 which serves as a comparator. The resistor R29 and potentiometer
PS are
used to set the rate of rise of temperature to detect the absence of a utensil
and this voltage
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is applied to input terminal IV of the amplifier B2. If the rate of rise of
the temperature of
the plate is higher than the set level, it makes the output of amplifier high
which turns on
the transistor Q3 via the resistor R30, and the resistor R31 acts as a shunt.
When the
transistor Q3 is turned on, it places a short circuit on the base emitter
junction of the
transistor Q2, thus de-energizing the relay and removing the power from the
burner
element EL1. The capacitor C6 and resistor R28 is selected to have a
sufficient time
constant so that the plate can cool down adequately until the next attempt to
switch it on
A battery-operated remote-controlled circuit for the device of the present
invention
is best shown in Figure 5 in which the power supply voltage is provided by
batteries BAT.
The battery voltage V4 is applied to the circuit by operating a control switch
S8. The
required temperature of the utensil is set by adjusting the potentiometer P7 ,
and the switch
S8 forms a part of the potentiometer P7. When the switch S8 is closed, it
applies the supply
voltage to the power line V5, which will activate the light emitting diode D21
to turn on
briefly via the capacitor C14 and resistor R59. The regulated voltage for the
circuit is
1 S provided by the reference diode RF and the resistor R33. The control unit
operates with
the heat sensing thermocouple TCR. The operation of the circuit for this unit
is similar to
that described in Figure 4. Resistors R37,R39 and transistor Q4 provide the
cold junction
compensation circuit. Resistors R34, R35 and capacitor C17 provide the voltage
divider
whose voltage is substantially equal to the voltage across Q4. C 11 is the
smoothing
capacitor. Resistors R36, R38and capacitors C18 and C19 provide the
attenuation of
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spurious signals and open circuit detection for the thermocouple TCR. R61 and
P6 provide
the zeroing circuit for the amplifier AAl, while resistors R40, R41, R42 and
R43 set the
gain for the amplifier. Resistor R44 and capacitor provides a further
attenuation for
unwanted signals. The required temperature is set on the potentiometer P7, and
the set
operating voltage is applied to the positive or NIV input terminal of the
comparator AA2
via the resistor R45. This voltage is compared with the output of AA1 which
represents
the temperature of the utensil which is applied to the negative or inverting
input terminal of
the comparator AA2 . R48, R49, R47, R46 act as voltage selection means for the
positive
feedback for the comparator AA2. When the utensil temperature is higher than
the required
set temperature, the output of the comparator is low. The output of the
comparator is
inverted by the inverter H6 . H1-H6 are CMOS inverters. When the comparator is
low, the
output of the inverter H6 is high and it back biases a diode D23 to activate
an oscillator
composed of inverters H1 and H2 and resistor R60 and capacitor C15. During the
sample
time of inverter H1, the diode D22 is also back biased. An amplifier E 1 is
used to provide
an oscillator having a relatively long operating time period. The resistors
R50, R51 and
R52 provide a positive feedback and the resistor R53 and capacitor C 12
provide a
negative feedback to produce the required oscillation . Each time the output
of amplifier E 1
goes from negative to positive the amplifier E2 emits a negative pulse at is
output. The
period of this pulse depends upon the time constant of the capacitor C 13 and
resistor R54
and is chosen to be small to conserve power, as its period determines the
length of time of
CA 02291896 1999-12-07
the transmission. The resistors R57, R56and R55 provide a positive feedback so
that the
edges of the pulse are rapid in transition. The negative pulse is inverted by
the inverter H1.
If the duration the pulse is high at the output of the inverter H1, the light
emitting diode
D21 is turned on via the resistor R58 for indicating that the unit is in
operation. When there
is a positive pulse at the output of the inverter H1, the diode D23 is back
biassed, and the
oscillator composed of inverters Hland H2 plus other associated components can
oscillate.
This oscillation is amplified by the inverters H4 and HS and applied to the
induction coil
COIL,2 or ultra-sonic piezo-electric transducer UT for transmission .
A receiver unit for operating with the remote-controlled unit of Figure 5 is
best shown
in Fig.6. A regular control signal is received by the receiver to turn off a
particular burner
element as long as the temperature of the utensil is higher than the required
set temperature.
In the absence of the control signal, the burner element is turned on. The
control signal is
received by the coil COIL2 or the ultra-sonic piezo-electric transducer UR .
This control signal
is amplified by a CMOS inverter J1, where R60 and C21 are the coupling
components and R61
and C22 are the feedback components. The following stages of amplification are
of the type
commonly termed Sallen-Key filter amplifiers . Three stages are shown in the
Figure 6;
however, more stages may be added for greater filtering. In the first stage
resistors R76 ,R63
R62 and associated capacitors C24 and C23 are provided. The gain , bandwidth
and the center
frequency of the receiver can be set by selecting the values of these
components. Similarly,
resistors R64, R65, R66, R67, R68, R69 and associated capacitors C24, C23,
C26, C25, C28
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and C27 are used as the components for the other two stages. The output
voltage of the
inverter J4 is applied to rectifying diodes D 14 and D 15 by a capacitor C29.
The resultant DC
voltage is smoothed by a capacitor C30, and a resistor R70 is used as a
bleeder resistor. The
rectified DC voltage is applied to the base of the transistor Q5, the emitter
of which is
connected to the capacitor C31 and the resistor R71, and the time constant of
which is chosen
so that if the turn off pulse does not arrive in time the capacitor is
discharged and the output
is a low voltage. If the pulse are received at regular time the voltage at the
input terminal IV
of the amplifier K is low . R74, R73 and R72 are positive feedback resistors .
The output of
amplifier K is coupled to the base of transistor Q6 ,and when the output of
the amplifier K is
low, the transistor Q6 is turned off. In such condition, the relay RL1 is de-
energized, and the
burner elements are turned off . When a signal is not received in time, the
output of the
amplifier K is high which energizes the relay RL1 so that the burner elements
are turned on.
D 11 is the diode across the relay RL 1 for breakdown protection. As described
previously, the
transformer provides the rectified low voltage which is smoothed by the
capacitor C33. A
regulator REG provides the regulated voltage for the receiver unit. A
capacitor C32 is
connected across the regulated voltage for stability. The transformer and the
regulator may be
selectively shared by all the controls or may be used individually.
The transmitter box 20 of the remote-controlled device of the present
invention is best
shown in Figures 7 and 8. The transmitter box 20 has a rectangular enclosure
21. An adjustable
knob 22 located at the top of the unit is mounted to the adjustable shaft of
the temperature
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CA 02291896 1999-12-07
setting potentiometer in the unit. The knob 22 is operative rotatably to set
the required
temperature of the cooking utensil shown on a scale 23. The operation
indicator of the device
is provided by a light emitting diode 24. The enclosure has an extension base
25, and the top
of the enclosure 21 has an upstanding ridge 26 therein adjacent to the
extension base 25. A
substantially T-shaped clamping member 27 is provided. The clamping member 27
has an
upstanding arm 28, and the base portion perpendicular to the clamping member
27 which
consists of a longer side arm 29 and a shorter side arm 30. The shorter side
arm 30 has an L-
shaped side edge 31. The clamping member 27 is coupled to the transmitter box
20 with the
L-shaped side edge 31 engaging with the upstanding ridge 26 at the top of the
enclosure 21
and the longer arm 29 extending downwards in a sloping manner down to the
extension base
25. The clamping member 27 is pivotally retained in place by a torsion spring
30 such that the
extension base 25 and the longer arm 29 form a clamp which is operative by
pulling the
upstanding arm 28 against the spring force of the torsion spring 30 for
mounting the
transmitter unit 20 on the handle of a cooking utensil as best shown in Figure
9. The
thermocouple 32 provided with a flexible tube extending outwards from the
transmitter box
may be positioned with its thermal junction free end 33 contacting the side of
the cooking
utensil to sense its temperature. The extension base 25 and the longer arm 29
of the clamping
member 27 may be curved in shaped and may include a flexible moderately high
temperature
material surface liner so as to provide a better grip of the handle of the
utensil.
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It will be appreciated by persons skilled in the art that the present
invention is not
limited to what has been particularly shown and described hereinabove. Rather,
the scope
of the present invention is defined only by the claims that follow:
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