Temperature limiter

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a division of prior filed copending U.S. application Ser. No. 10/037,253, filed Jan. 3, 2002, which claims the priority of European Patent Application Serial No. 018 90 007.6, filed Jan. 10, 2001.

BACKGROUND OF THE INVENTION

The present invention relates to a switch head for attachment to a temperature sensor with elongated expansion elements having different thermal expansion coefficients and for receiving a device for evaluating the relative movement of the expansion elements.

Cooking areas are frequently made of a glass ceramic plate (Ceran plate) that forms a resting surface for cooking utensils and has a heating space disposed below. Such cooking areas can be heated in different ways, for example with an electric resistive heating element, halogen lamps, gas and the like. Regardless of the heating mode, the Ceran plate can be damaged or destroyed by excess heat, so that overheating has to be avoided.

For this purpose, temperature limiters are frequently used, which comprise a temperature sensor and a switch head of the type described above, which is connected with the temperature sensor. The temperature sensor is arranged in the heating space underneath the Ceran plate and is therefore exposed to substantially the same temperature as the Ceran plate.

When the temperature sensor heats up, the sensor component which can move relative to the switch head is displaced relative to the switch head, and the relative movement is transmitted to a switch via a mechanical connection—which can be a simple ram. When the temperature sensor senses that the temperature of the Ceran plate may become too high, the aforedescribed relative movement becomes so large that the switch is actuated, which decreases or disconnects the heating power supplied to the heating element.

When the cooking area is heated electrically, power can be disconnected simply by forming the switch as a normally closed switch connected in series with the heater. When the cooking area is heated with gas, then actuation of the switch closes a valve arranged in the gas supply line.

AT 404 776 describes combined switch heads which satisfy the aforedescribed function to prevent overheating. These switch heads also provide a so-called “heat indicator” which warns the user not to touch a section of the cooking area that is too hot. In addition, switch heads for temperature limiters are known which combine different additional functions.

All these embodiments, however, have in common that the switch head is formed as a single piece, which makes it impossible to enhance a switch head by adding additional functions. As a result, dedicated production lines and inventory have to be provided for each combination of those functions.

It would therefore be desirable and advantageous to provide an improved switch head which obviates the prior art shortcomings and allows easy implementation of additional functions. It would also be desirable to provide a modular temperature controller in which additional functions can be incorporated.

SUMMARY OF THE INVENTION

The invention is directed to a switch head and a temperature controller/limiter with such switch head, wherein additional functions can be the added or removed.

According to an aspect of the invention, attachment means are provided for attaching at least one additional switch head to an existing switch head. Moreover, at least one opening is provided adapted to receive a transfer member for transferring the relative movement of the expansion elements to the at least one additional switch head. In this way, the switch head can be used as an additional module for a temperature limiter.

According to one embodiment of the invention, the opening can be formed by eliminating a sidewall of the switch head, allowing a lightweight construction of the component.

According to another embodiment of the invention, an electric switching contact can be installed in the switch head for evaluating the relative movement. This arrangement provides a very simple temperature limiter, for example by connecting the switching contact in series with the resistive heating element for the cooking area.

According to yet another embodiment of the invention, the relative displacement of the expansion elements can be transferred to a device for evaluating the relative displacement. A transfer member in the form of a ram can be implemented which is moveable along with longitudinal axis in the switch head. This allows advantageously a particularly rigid and simple construction and makes it unnecessary to install an additional transfer member when the additional switch head is attached to a first switch head.

According to another embodiment of the invention, the switch heads can be covered by a cover that can be easily removed. This cover protects the first switch head from contamination and debris if no other switch head is attached to the first switch head.

According to another aspect of the invention, a temperature limiter includes a temperature sensor with elongated expansion elements having different thermal expansion coefficients and a switch head arranged in a second end region of the temperature sensor, wherein the switch head includes a device that evaluates the relative displacement of the expansion elements.

As mentioned above, such temperature limiters are known for overtemperature protection of glass ceramic cooking areas. A combination of a temperature limiter with a heat indicator is also known. However, these conventional devices do not allow a modular extension or any change in the functionality of the switch heads, such as adding or subtracting functions.

The temperature limiter of the invention includes an additional switch head with an additional device for measuring the relative displacement of the expansion elements, which the additional switch head connected to the first switch head.

In this way, the temperature limiter can be easily modified by removing the second switch head. Alternatively, additional modules can be attached to the temperature limiter.

According to another embodiment of the invention, an additional module can be provided which includes a basic module preferably made of ceramic and provided with a bore, wherein the additional module is placed over the temperature sensor by means of the bore. This provides additional functions in the region of the temperature sensor.

According to another embodiment of the invention, the additional module can be connected directly with the switch head. This provides a particularly rigid connection between the additional module and the temperature limiter.

According to another embodiment of the invention, a resistor, preferably an ohmic resistor with a temperature-dependent resistance value, can be attached to the basic module of the additional module. This enables very precise temperature measurements.

According to another embodiment of the invention, the resistor can be formed by a resistive paste which is printed onto the basic module, preferably by screen printing, which advantageously makes the design very compact. Moreover, the resistor in this embodiment can be manufactured in a single manufacturing step and attached on the basic module, thereby obviating the need for a separate process for attaching the resistor. A suitable range for the resistance value and its temperature dependence can be defined by selecting a suitable material and resistive path of the paste.

According to another embodiment of the invention, the resistor can be shielded by a heat shield to prevent the resistor from heating too quickly during the heat up process.

According to yet another embodiment of the invention, the additional module can include two electrodes attached to the basic module and forming an arc gap therebetween. This makes it possible to provide in the gas-heated cooking areas not only a aforedescribed temperature limiter, but also a device for igniting the gas inside the heating space.

According to another embodiment of the invention, the additional module can include a resistive heating element which can be attached to the basic module and implemented preferably as a helical coil. This type of heating element has a particularly simple construction and is therefore more reliable and more easily controlled as compared to other arrangements, such as a spark plug.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:

FIG. 1

shows a cross-sectional view through a cooking area with a temperature limiter taken along the line I—I shown in

FIG. 2

;

FIG. 2

is a top view of the cooking area of

FIG. 1

;

FIG. 3

is a longitudinal cross-section through a first embodiment of the conventional temperature sensor, wherein the rod has a larger thermal expansion coefficient than the tube;

FIG. 4

is a longitudinal cross-section through a second embodiment of the conventional temperature sensor, wherein the tube has a larger thermal expansion coefficient than the rod;

FIG. 5

is a partial cross-section of an embodiment of a temperature limiter according to the invention with a first switch head and a second switch head, with both switch heads uncovered;

FIG. 6

is another embodiment of the second switch head according to the invention;

FIG. 7

is another embodiment of the second switch head according to the invention, with a strain gauge for measuring the relative displacement of the expansion elements;

FIG. 8

is a schematic diagram of another embodiment of a temperature limiter according to the invention with several switch heads secured to the first switch head;

FIG. 9

is a schematic diagram of an embodiment of a temperature limiter according to the invention having a modular construction;

FIG. 10

is a schematic diagram of an embodiment of the modular temperature limiter of the invention for a gas-heated Ceran cooking area;

FIG. 11

is a schematic diagram of an embodiment of the temperature limiter according to the invention, wherein the second switch head is not connected to the side of the switch head

8

opposite the temperature sensor;

FIG. 12

is another schematic diagram of an embodiment of the temperature limiter according to the invention, wherein the second switch head is not connected to the side of the switch head located opposite the temperature sensor;

FIG. 13

is a schematic diagram of a temperature limiter according to the invention, wherein the openings in two switch heads are formed by eliminating a side wall of the switch heads;

FIG. 14

is a schematic diagram of a temperature limiter according to the invention, wherein two switch heads are connected by threads;

FIG. 15

is a schematic diagram of a switch head according to the invention and closed by a cover;

FIG. 16

shows a cross-sectional view through a cooking area taken along the line I—I shown in

FIG. 17

, with a temperature limiter having a sensor module for indicating the temperature; and

FIG. 17

is a top view of the cooking area of FIG.

16

.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to a switch head which can be secured to a temperature sensor. The temperature sensor has elongated expansion elements with different thermal expansion coefficients and is adapted to receive a device for evaluating the relative displacement of the expansion elements.

For a better understanding of the invention, the basic construction and a preferred application of temperature limiters provided with such switch heads will now be described.

FIGS. 1 and 2

show a possible application for a temperature sensor

7

in connection with a switch head

8

according to the invention. It will be understood, however, that the invention is not limited to this application.

Referring now to

FIG. 1

, a radiant heating element

1

includes a cup

2

in which a helically wound heater coil

3

, which is embedded in a packing material, is received. The radiant heating element

1

is located below the plate

5

which forms a cooking surface

6

and can be made of metal, glass ceramic and the like. The temperature sensor

7

connected with the switch head

8

is located between the cooking surface

6

and the heater coil

3

. The temperature sensor

7

can be simply inserted through openings in the radiant heating element

1

.

The temperature sensor

7

is exposed to the temperature that exists below the cooking surface

6

in the radiation space between the cooking surface

6

and the heater coil

3

, and can hence measure this temperature.

Referring now to

FIGS. 3 and 4

, the temperature sensor

7

is made of two elongated expansion elements

9

,

10

with different thermal expansion coefficients. These expansion elements

9

,

10

can also be in form of a spring or can be arranged side-by-side. Preferably, a first expansion element

10

is implemented as a tube having, for example, an annular cross-section, whereas the second expansion element

9

is implemented as a rod with a preferably circular cross-section. The rod

9

can hereby be placed inside the tube

10

.

As shown in

FIGS. 3 and 4

, the tube

10

and the rod

9

are held in a fixed spatial relationship in a first end region

100

, while they are able to move relative to one another in the second end region

110

, i.e., in the region of the switch head.

In the embodiment depicted in

FIG. 3

, the expansion coefficient of the rod

9

is greater than that of the tube

10

, which can be achieved, for example, by making the rod

9

of a metal and the tube

10

of a ceramic material, such as Cordierit.

The rod

9

is fixedly secured to the tube

10

in the first end region

100

by a limit stop

19

′ affixed on the rod

9

. The first end of the rod can hereby be supported on the first end of the tube. This limit stop

19

′ can also be formed, for example, by a component, which is non-releasably connected with the rod

9

, for example by welding or glueing. The limit stop

19

′ can also be formed by a nut

19

which is screwed onto the first end of the rod

9

which has a thread, and by a shim washer

17

disposed between the nut

19

and the first end of the tube.

A spring

11

, for example a helical compression spring, is arranged in the second end region

110

, biasing the second end of the rod

9

in a direction away from the second end of the tube

10

.

This bias always urges the limit stop

19

′ against the first end of the tube, thereby keeping the rod

9

and the tube

10

in the first end region

100

in a fixed relationship relative to one another.

When heat is applied to the temperature sensor

7

, the rod

9

expands more than the tube

10

. As a result, the second end of the rod can move away from the second end of the tube, as indicated by the arrow +T in FIG.

3

.

The resulting relative displacement between the second end of the rod and the second end of the tube can provide a measurement value which is directly proportional to the temperature of the sensor

7

and therefore also for the temperature of the environment of the sensor. The length change of the rod

9

is indicated in the Figures by the reference symbol &Dgr;L. The change in length of the tube

10

can essentially be neglected, since the tube is made of ceramic. The measurements can be evaluated in different ways. Most frequently used is a method depicted schematically in the Figures, wherein the second end of the tube activates a switching contact

22

′ via a transfer element

20

. Other devices, such as inductive measurement devices, as described in

FIGS. 5

,

6

and

7

for the second switch head

8

′, can also be used for such measurements.

The switching contact

22

′ can be connected in series with a resistive heating element that heats the surroundings of the temperature sensor

7

, in particular the cooking area depicted in

FIGS. 1 and 2

. This allows the temperature produced in this area to be limited and/or controlled.

The switching contact

22

′ and transfer element

20

are hereby supported in the switch head

8

, on which the second end of the tube

10

is also secured. The second end of the tube and the switching contact

22

′ are hereby maintained in a fixed relationship with respect to one another. The switching contact

22

can be activated by the second end of the rod that is movably supported in the switch head

8

. The transfer element

20

can be implemented as a ram; however, springs or rods of various shapes can also be used as transfer elements.

The relative displacement between the second end of the tube and the second end of the rod can be measured in different ways, for example, by measuring the expansion of the rod with a strain gauge, by inductive sensors (for example, solenoid rams attached to the second end of the rod) or by optical sensors (light barrier). The required elements can be housed in the switch head

8

.

The measurement results can also be used for other purposes, for example for indicating the temperature or for signaling that the temperature has exceeded a certain value.

The embodiment of

FIG. 4

operates according to the same basic principle. In this embodiment, however, the tube

10

has a greater thermal expansion coefficient than the rod

9

. In the first end region

100

, the tube

10

is closed, for example, with a plug

17

′ made of metal and welded to the tube

10

, with the end face of the rod

9

contacting the plug

17

′. The second end of the tube

10

is again secured to the switch head

8

, whereas the second end of the rod

9

is movably supported in the switch head

8

and urged into the tube

10

by a spring

11

.

When the temperature increases, the tube

10

expands, whereby the second end of the rod

9

is moved towards the tube

10

(see arrow +T). This relative movement can be processed in different ways, and used, for example, to activate a switching contact

22

′.

According to the present invention, a temperature limiter can be constructed in a modular fashion to include a temperature sensor

7

of the aforedescribed type and a switch head

8

connected thereto. In other words, an additional switch head

8

′ which has an additional device

80

′ for measuring the relative displacement of the expansion elements

9

,

10

, can be coupled to the switch head

8

.

FIG. 5

illustrates a switch head

8

according to the invention with a temperature sensor

7

and an attached second switch head

8

′. As seen in

FIG. 5

, the switch head

8

includes attachment means

200

in form of threaded bores

201

disposed on a side of the switch head

8

opposite to the side of the temperature sensor

7

. The second switch head

8

′ is attached by screws

203

which engage with the threaded bores

201

via bores

201

′ disposed in the housing of the second switch head

8

′. In addition, bores

210

and

210

′ are provided through which a second transfer element

20

′ is guided, which transmits the relative displacement of the rod

9

relative to the measurement device

80

′ located in the second switch head

8

′.

The temperature sensor

7

has again a rod

9

guided in a tube

10

, wherein the rod and the tube have different thermal expansion coefficients. Rod

9

and tube

10

are held in the aforedescribed manner in the first end region

100

so that they are unable to move relative to one another, and in the second end region

110

in the switch head

8

so that they can move relative to one another.

The measurement device

80

is implemented in

FIG. 5

by a switching contact

22

′. The switching contact

22

′ includes a contact

22

fixedly attached in the switch head

8

and connected via a contact support

24

with a terminal lug

23

. The fixed contact

22

cooperates with a moveable contact

25

which is held on a contact spring

26

supported on a contact support

27

and connected electrically with another terminal lug

28

. The contact spring

26

includes a stamped tab

29

which is supported by a support

30

connected with a contact support

29

and the contact spring

26

.

The transfer member

20

contacts the contact spring

26

approximately in the center region of the contact spring

26

where a transverse shoulder

31

is located. The contact system opens and closes, respectively, following displacement of the transfer member

20

due to temperature changes.

With the present invention, a temperature limiter of the aforedescribed type can be expanded by incorporating an additional switch head

8

′ disposed on the switch head

8

. The additional switch head

8

′ includes a measurement device

80

′ which measures the relative displacement of the end of the rod

9

facing the switch head relative to the switch head

8

.

In a preferred embodiment of the invention, the device

80

′ arranged in the second switch head

8

′ is also formed by switching contact

22

″ to which the relative displacement is transferred (see FIG.

9

).

In general, the device

80

′ which is arranged in the second switch head

8

′ and measures the relative displacement, is used to indicate a hot area, for example to warn against touching a hot location on the cooking surface. However, a combination with other measurement devices is also possible. In particular, measurement devices can be implemented wherein the relative displacement is converted into an analog electrical signal (see FIG.

5

). The switch head

8

depicted in

FIG. 5

therefore provides for a modular construction of arbitrary temperature limiters. Temperature limiters consist of a temperature sensor

7

and a switch head

8

which can hence be easily constructed to include various extensions.

To attach the second switch head

8

′, threaded bores

201

engaging with screws

203

are provided in the housing of the first switch head

8

. However, other fastening means, such as tabs or clamps and openings adapted to engage with the tabs or clamps can also be used. Alternatively, the second switch head

8

′ can also be completely enclosed in the switch head

8

(FIG.

13

), or the other switch head

8

′ can be provided with a thread

204

′ adapted to engage with a thread

204

disposed on the first switch head

8

(FIG.

14

). In all these embodiments, a fastening means

200

′ is provided on the second switch head

8

′ that is complementary to the fastening means on the first switch head

8

.

To transfer the relative displacement of the expansion elements

9

,

10

to the second switch head

8

′, there is provided in

FIG. 5

an additional ram serving as an additional transfer member

20

′. However, other elements, such as rods or springs, can also be used as transfer members. The switch heads

8

,

8

′ can be implemented independently of one another, wherein the additional transfer member

20

′ can be either implemented in the first switch head

8

or the second switch head

8

′.

Openings in the form of bores

210

and

210

′ adapted to receive the transfer member

20

′ are provided in the switch heads

8

and

8

′. Alternatively, one or both switch heads

8

,

8

′ can be constructed so that the openings for receiving the transfer member

20

′ is implemented by omitting one side of the housing of the switch head, as indicated schematically in

FIGS. 13 and 14

. In this case, a cover

250

can be provided which closes the respective switch head

8

,

8

′, if no second switch head is secured to the first switch head (FIG.

15

). A cover

250

can be provided for either the first switch head

8

or the second switch head

8

′ or for both. Moreover, the cover

250

can be secured with the existing fastening means

200

and/or

200

′, wherein additional fastening means can be provided for the cover

250

.

FIG. 5

shows a switch head according to the invention, with one additional switch head

8

′ attached to the switch head. However, with a modularly constructed entire module, additional switch heads

8

″ can be secured to the second switch head

8

′ (FIG.

8

). This arrangement can be used to construct, for example, two-step heat indicators based on simple contacts measuring the relative displacement. Conditions, such as “cold”, “warm” and “hot”, of the cooking area could be indicated by multicolored lamps.

FIGS. 5-7

show additional embodiments

80

′ for measuring the relative displacement of the rod

9

in the second module or switch head

8

′. Optionally, these and/or other devices can be located in the first switch head

8

and the additional devices in additional modules. For example, a measurement device providing an analog electrical output signal can be produced.

In an embodiment of a measurement device, an inductive sensor in the form of a simple solenoid ram sensor could be used, as illustrated in FIG.

5

. This solenoid ram sensor is made of a coil

32

with a moveable iron core

33

extending between the transfer member

20

′ and the spring

21

.

The second transfer member

20

′ moves together with the transfer member

207

whereby the rod

9

moves the iron core

33

. This can be achieved, as shown in

FIG. 5

, simply by placing the transfer member

20

′ on the spring

26

. In another embodiment of the invention, the first transfer member

20

can extend past the contact spring

26

, thereby catching the second transfer member

20

′. In this case, the contact spring

26

can have openings through which the transfer member

20

is guided. In this case, the transfer member

20

can have a shoulder located in the region of the transverse shoulder

31

of the contact spring and moving the contact spring

26

.

The measurement device

80

′ is connected via electrical lines

55

,

56

with terminal lugs

37

,

38

, which in turn can be connected with a circuit (not shown) that processes the measurement signal for display.

The inductive sensor of

FIG. 6

is a transverse armature sensor, wherein the coil

32

is located on a leg of a U-shaped core

39

. The magnetic circuit is closed by a transverse armature

40

, which is spaced apart from the core

39

and connected with the transfer member

20

′. A temperature change causes movement of the transverse armature

40

, thereby changing its distance to the core

39

, which in turn changes the inductance of the core

32

.

The fastening means

200

′ depicted in

FIG. 6

are formed by lugs

202

′ which can engage with corresponding openings in the switch head

8

and a thereby enable a rigid releasable connection between the two switch heads

8

,

8

′.

FIG. 7

shows a temperature limiter, wherein a U-shaped spring

48

is provided for pretensioning the transfer member

20

in the direction of the rod

9

. The first leg

49

of the transfer member

20

is supported on the switch head

8

′, and the second leg

50

is supported on the transfer member

20

′. The measurement device is hereby formed by a strain gauge

51

secured to the U-shaped spring

48

.

In all the aforedescribed embodiments, the electrical lines

55

,

56

extending between the measurement device

80

′ and the corresponding terminal lugs

37

,

38

are preferably formed by strip conductors that are directly applied to a thin ceramic plate. The strip conductors can be attached to the ceramic plate by a so-called “direct-copper-bonding” (DCB) method which provides a particularly strong bond between the copper and the ceramic.

Wheatstone bridges, which convert changes in the resistance into changes of the output voltage, can be used to process the signal produced by the measurement device. In embodiments of the measurement device where the resistance value is complex, i.e., includes an inductive or capacitive component (FIGS.

5

and

6

), the Wheatstone bridges are operated with AC voltage.

A display connected after the processing circuit can be implemented by employing, for example, several sequentially arranged lamps, wherein the number of illuminated lamps changes depending on the output signal of the measurement device. Alternatively, an illumination device that changes color depending on the measurement signal can be employed, or an instrument with a moving needle can be used.

In all the aforedescribed embodiments of the invention, the second switch head

8

′ is attached on the side of the switch head

8

opposite from the temperature sensor

7

. However, this is not required, as illustrated in the embodiment depicted in FIG.

11

. Here, the relative displacement of the expansion elements is deflected by a transfer member

120

into a second direction transverse to the original direction of expansion. Additional switch heads

8

′ can also be provided on the side of the temperature sensor

7

, wherein the relative displacement of the expansion elements is deflected accordingly (FIG.

12

). In the embodiment depicted in

FIGS. 11 and 12

, the relative displacement is deflected by a straight or L-shaped beam, which is supported for rotation about a bolt

120

′. With this arrangement, the additional switch heads

8

′,

8

″ can also be attached in other areas of the switch head

8

. The transfer member

120

changes the direction of the relative displacement of the temperature sensor into the direction of the second and/or the additional switch heads.

FIGS. 9 and 10

depict a temperature limiter according to the invention with a modular construction. The temperature limiter includes a switch head

8

according to the invention and a temperature sensor

7

. Additional modules

71

-

75

can be attached in the region of the temperature sensor

7

and additional switch heads

8

′,

8

″ can be attached in the region of the switch head

8

opposite the temperature sensor

7

. The schematically depicted basic module, consisting of the switch head

8

and the temperature sensor

7

, represents a temperature limiter to prevent overheating of a Ceran plate. The indicated contact system

22

′ can interrupt the power to a heater or disconnect the gas supply to a gas heater.

In the embodiment of the invention depicted in

FIG. 9

, additional modules can be added to the basic module by placing these additional modules onto the temperature sensor

7

. For this purpose, the basic module

17

of the additional modules

71

-

75

is provided with bores

220

′. In addition, a connection to the switch head

8

itself is also possible. For example, fastening elements, such as lugs or threads, can be provided for attachment of the additional modules

71

-

75

directly on the switch head

8

. These fastening elements can provided on the switch head

8

and/or on the additional modules

71

-

75

. Alternatively or in addition, the temperature sensor can operate as a fastening element in that the additional modules are press-fitted on the temperature sensor

7

.

In the following, the additional modules depicted in

FIG. 9

will be briefly described. In the sensor module for inductively detecting cooking utensils

71

, the inductance of the coil

71

′ monitors the cooking utensils made of conventional materials, such as steel or copper, and placed on the cooking surface. The presence of the cooking utensils

71

modifies the inductance of the coil

71

′, wherein the change can be detected and evaluated. The material of the cooking utensil as well as its temperature can be characterized from the observed changes in inductance.

The sensor module for analog measurement of the temperature

72

has a temperature-dependent resistor

72

′, whose resistance value is measured and processed, thereby providing information about the actual temperature of the cooking area. The resistor

72

′ is generally an ohmic resistor, however other temperature-dependent impedances can also be used. Advantageously, the resistor can be formed by a resistive paste that is printed onto the basic module

17

, for example by screen-printing.

During initial heat-up, i.e., when the heater is first turned on, the heating space is frequently heated unevenly. This can cause excessive heating of the temperature sensors

72

, which is located closer to the heater coil

3

than the cooking area

5

. This can cause the heater to be turned off prematurely, although the cooking surface

5

is no danger of being overheated. This can be prevented by installing a heat shield

172

on the temperature sensor

72

and/or the resistor

72

′ (see FIG.

16

), which prevents the sensor module or the resistor

72

′ from being heated up too rapidly during heat-up. This can be accomplished by installing heat shielding plates and the like. In a particularly simple embodiment, the mass of the basic module

17

itself forms a heat shield (FIGS.

16

and

17

). The resistor

72

′ is here applied only on one side of the sensor module

72

, and the sensor module is arranged in the cooking area so that the basic module

17

is located between the heater coil

3

and the resistor

72

′, thereby shielding the resistor

72

′. Providing a heat shield

172

also prevents the temperature sensor

7

from heating up too quickly during the heat-up phase.

Alternatively, the temperature of the resistor

72

′ can be made to approximately equal the temperature of the cooking surface

5

by constructing the sensor module

72

and the cooking surface of the same material. Modules made of ceramic/Ceran are particularly advantageous. By using the same material, the resistor

72

′ will heat up at the same rate as of the Ceran plate of the cooking area.

The display module for indicating hot surfaces

73

can include an indicator

73

′. This indicator provides information obtained from close to the dangerous areas if the cooking surface can be touched safely.

The additional modules

74

and

75

represent ignition devices for igniting a gas flame under the Ceran cooking area. Gas-heated cooking areas typically include not only the aforedescribed temperature limiter, but also a device for igniting the gas in the heating space.

An exemplary spark ignition device

74

includes two electrodes

74

′,

74

″ which form a spark gap with a pre-determined spacing. By applying a suitable voltage to the two electrodes

74

′,

74

″, for example between 10 and 20 kV, the generated spark ignites the gas.

An exemplary glow plug device

75

depicted in

FIG. 9

for igniting the gas includes a glow coil in form of a heater coil

75

which is secured to the basic module

70

.

All the additional modules have bores

220

′ adapted to receive the temperature sensor

7

which also secures the additional modules on the temperature limiter of the invention.

The second switch head

8

′ is formed as a residual heat module to indicate when the cooking surface is still hot. The indicated contact

22

″ characterizes the temperature of the cooking area by two values, namely “too hot to touch safely” and “sufficiently cool to touch safely”.

FIG. 10

shows a combination of several modules according to the invention, consisting of a basic module with a temperature sensor

7

and switch head

8

, a residual heat module and/or switch head

8

′, and a spark ignition device

74

. The illustrated combination can be used as temperature limiter for gas-heated Ceran cooking areas.

While the invention has been illustrated and described as embodied in temperature limiter, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and their equivalents: