Sensor assembly for determining the temperature state in an area of a heating surface

A sensor assembly is disclosed for determining the temperature state in an area of a heating surface heated by a heat source and disposed between the heat source and the heating surface in parallel relationship to the heating surface. The sensor assembly includes a first sensor having a carrier and a temperature-dependent resistor web which is attached to the carrier and confronts the heating surface and which is electrically contacted at a contact zone outside a temperature-measuring zone, and a second sensor having a carrier and a temperature-dependent resistor web which is attached to the carrier and electrically contacted at a contact zone outside the temperature-measuring zone and which confronts the heat source.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of Austrian Patent Application, Serial No. GM 241/2005, filed Apr. 19, 2005, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates, in general, to a sensor assembly for determining the temperature state in an area of a heating surface.

Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.

In typical electric stoves, particularly those having a ceramic cooktop, an electromechanical protective temperature limiter is provided per heater to limit it to the maximum temperature. If the cooking platform is controlled using an electronic system, a substitution of the mechanical temperature limiter by electronic temperature sensors is possible, since the necessary circuit breaker (relay) is already provided. In the electronic control units used, a sensor is frequently also positioned in the region of the electronics of an electric stove.

Conventional temperature sensors are insufficient to provide a true representation of the temperature distribution underneath the heating surface. As a result, the electronic control circuits receive only incomplete data so that the heating surface can only controlled poorly, causing excessive amount of energy to be unnecessarily converted into heat.

It would therefore be desirable and advantageous to provide an improved sensor assembly to obviate prior art shortcomings and to allow precise temperature control of a heating surface to thereby enhance efficiency and lower energy consumption.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a sensor assembly for determining the temperature state in an area of a heating surface heated by a heat source and disposed between the heat source and the heating surface in parallel relationship to the heating surface, includes a first sensor having a carrier and a temperature-dependent resistor web which is attached to the carrier and confronts the heating surface and which is electrically contacted at a contact zone outside a temperature-measuring zone, and a second sensor having a carrier and a temperature-dependent resistor web which is attached to the carrier and electrically contacted at a contact zone outside the temperature-measuring zone and which confronts the heat source.

A sensor assembly according to the present invention enables a temperature measurement in the entire heating space so that prior art problems are resolved and an added safety feature is realized as far as temperature control is concerned in the event one sensor malfunctions or is incorrectly controlled. Moreover, the temperature measurement is more accurate. By knowing the temperature of the heat source, the temperature of the heating surface can be ascertained before it reaches the desired level so that the temperature or the heat source can be fine-tuned. As a result, the desired temperature of the heating surface can be reached more quickly or energy can be saved when maintaining the heating surface at the desired temperature because the heating surface temperature and the heat source temperature can be suited to one another in an optimum manner. The temperature sensors used for a sensor assembly according to the present invention can be manufactured cheaply so that the addition of a second temperature sensor is of no financial consequence. Operating safety and efficiency of the cooking platform is much enhanced as both the heating surface temperature and the heat source temperature can be ascertained at any time and determination of a characteristic temperature graph inside the heating unit is possible using a processor. This in turn can be used for calibrating and self-adjusting the heating unit.

According to another feature of the present invention, the heating surface may be a glass ceramic hot plate, and the carrier of the first and second sensors may be made of ceramic.

According to another feature of the present invention, the resistor web of the first sensor and/or the resistor web of the second sensor may be shaped in the form of a meander. Suitably, the resistor web of the first sensor and/or the resistor web of the second sensor may be made through a thick-film technique. In this way, the resistance pattern can be best suited in an easy manner to the application at hand.

According to another feature of the present invention, the first sensor and the second sensor may be made substantially identical in construction. Manufacture and storage are thus simple and cost-effective. As an alternative, the second sensor may be sized greater than the first sensor. In this way, the second sensor is able to protect the first sensor from exposure to heat radiating from the heat source so that the temperature measurement by the first sensor becomes more accurate. In addition, the second sensor may be constructed to absorb radiation to further shield the first sensor from the heat source.

According to another feature of the present invention, the resistor web of the first sensor and/or the resistor web of the second sensor may be greater, e.g. twice, in cross section in a transition zone than in an area of the temperature-measuring zone. As a result, the electric resistance per length of the resistor web is significantly reduced in this area so that the temperature measurement in this area is hardly affected.

According to another feature of the present invention, the sensor assembly may be constructed to have a configuration tapering toward a free end distal to the contact zone for improving mechanical stability. Thus, the carrier can be constructed light and in a material saving manner while still exhibiting sufficient mechanical stability, whereby shading of the heating coil in particular on the contact-distal end can be kept to a minimum by the carrier or can be selected great and dimensioned specific to a local in order to set the desired temperature gradient on the cooking platform and heating surface.

According to another feature of the present invention, the sensor assembly may be constructed to have a wide zone in an area of the contact zone, and a transition curved to a remaining narrow zone. Suitably, the transition is concave. In this way, material can be utilized efficiently without adversely affecting stability.

According to another feature of the present invention, the resistor web of the first sensor and/or the resistor web of the second sensor may have a length of at least 200 mm in the temperature-measuring zone. As a result, temperature is absorbed across an area of great spatial range, thereby further enhancing the accuracy of measurement.

According to another feature of the present invention, a contact piece of elastically yielding material may be provided for establishing contact of the resistor web of the first sensor and/or the resistor web of the second sensor in the contact zone, with the contact piece being connected, e.g. riveted, to the carrier of the resistor web of the first sensor and/or the resistor web of the second sensor. Sufficient contacting is hereby realized, even when exposed to frequent changing temperature stress.

According to another feature of the present invention, a closed thermally conductive passivation layer may be provided for insulating the resistor web of the first sensor and/or the resistor web of the second sensor. The resistor web is thus protected reliably from chemical impacts and retains its thermoelectric characteristic for a longer period so that a drift over time of the measuring range is minimized. In this way, rivets may also be shielded or covered.

According to another feature of the present invention, a retention element may be provided between the first sensor and the second sensor. In this way, a defined distance can be maintained. The provision of such a retention element insulates also the first sensor. The retention element may be implemented in the form of a bracket or may have the shape of a trough. Suitably, the bracket or the trough defines hereby a space for receiving insulating material. As a result, the retention element is simple in structure and stiff and has space for insulation material. As an alternative, the retention element may have a trough bottom which is formed with reinforcing grooves to define pockets for providing insulation. This effectively improves the insulation in a simple manner.

According to another feature of the present invention, a spring tongue may be attached to the second sensor and/or retention element and supported by the first sensor. As a result, the first sensor is precisely placed on the heating surface.

According to another feature of the present invention, the second sensor may, at least regionally, be connected to the retention element, and/or the retention element may have a receptacle for accommodating the first sensor. Thus, the second sensor can be supported precisely while being supported by the planar disposition of the first sensor. The disposition in the receptacle effects also a sealing of a void in the receptacle so that trapped air in the void can provide insulation.

According to another feature of the present invention, an elastically yielding connection element may be provided for connecting the first sensor, in particular the carrier thereof, in the area of the contact zone to the second sensor and/or retention element. Examples of a connection element include a spring, e.g. a metal spring, U-shaped spring, or Z-shaped spring. In this way, the first sensor can be precisely placed upon the heating surface. Suitably, the connection element may be connected thermally to the first sensor, second sensor, and/or retention element, in particular by using bolts and/or rivets. This ensures a secure connection of the elastically yielding connection element in the space between heating surface and heat source, even when subjected consistently to high temperatures.

According to another feature of the present invention, the retention element may have a receptacle for accommodating the first sensor, with the first sensor having a step-shaped configuration in an area of the contact zone to define a recessed zone which extends at a lower level than the connection element, wherein the resistor web of the first sensor extends in substantial parallel relationship to the resistor web of the second sensor, when the first sensor is disposed completely in the receptacle of the retention element. In this way, the first sensor can be securely placed flatly on the heating surface, even when using bolts and rivets because the heads of the bolts or rivets are prevented from bearing upon the heating surface. Suitably, the carrier of the first sensor may be made of several parts in an area of the recessed zone. This results in a particularly simple configuration of the carrier.

According to another feature of the present invention, a substantially angular restraining bracket may be connected, e.g. bolted or riveted, to the second sensor and/or retention element. This allows easy and flexible attachment to the surroundings or heating space or oven.

According to another feature of the present invention, the first sensor rests flatly on the heating surface in operative position and defines a wedge-shaped gap in combination with heads of rivets. As a consequence, the first sensor is coupled directly to the heating surface and the temperature indication is accurate.

According to another feature of the present invention, the restraining bracket may have a receptacle for accommodating the second sensor. In particular, the restraining bracket may have a bay for insertion of the second sensor.

According to another feature of the present invention, the restraining bracket in operative position may have a vertical surface formed with a vertical oblong hole for installation and adjustment. This allows easy assembly and adjustment of the sensor assembly.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 to 23depict various embodiments and details of a sensor assembly according to the present invention for determining a temperature state in the area of a heating surface15which has been heated by a heat source16and may be a glass ceramic hot plate for example. The sensor assembly is intended for use in particular for glass ceramic areas of kitchen stoves and has dimensions that can be suited to the application at hand. The sensor assembly is positioned between the heat source16and the heating surface in parallel relationship to the heating surface. The heating surface15and the heat source16are shown in detail inFIGS. 19 and 20.

FIGS. 1 to 3show the basic principle of a sensor assembly according to the present invention. The sensor assembly includes a first sensor1arranged on a first carrier26and a second sensor2arranged on a second carrier26′. Carrier26bears a resistor web23. Likewise, carrier26′ also bears a resistor web of similar construction which is, however, not shown in the drawings. The resistor web23is in electrical contact with two of contact elements8via rivets6, contact pieces5and rivets7. The resistor web of sensor2provided on carrier26′ is in direct contact with two of contact elements8. In the particular embodiment ofFIGS. 1 to 3, the contact pieces5are S-shaped. The sensor assembly further has a retention element3with a receptacle4. For reasons of mounting, the sensor assembly has a mounting bracket9with a hole10.

FIGS. 4 to 6show another embodiment of the present invention. For sake of simplicity, identical and similar features that have already be described with regard toFIGS. 1 to 3will not be explained again. For ease of illustration, the resistor web23actually provided on sensor1is not shown inFIGS. 4 to 20. It is however to be understood that a temperature sensitive web has to be provided for proper functioning of the sensor assembly. The embodiment ofFIGS. 4 to 6differs from the one shown inFIGS. 1 to 3in that the contact pieces5are U-shaped. Hence, the first sensor carrier26is longer and covers rivets7(seeFIG. 6).

FIGS. 7 to 9show yet another embodiment of the present invention. Sensor1has two carrier parts31and32. It therefore has a recess33and a recessed zone17.

FIGS. 10 to 12show yet another embodiment of the present invention. Sensor1has a single carrier26. It also has a recess33and a recessed zone17. However, recess33and recessed zone17form integral parts of the carrier26.

FIGS. 13 and 14show yet another embodiment of the present invention. A spring tongue11is provided here between sensor1and sensor2. This tongue11urges sensor1upwards and hence—in use—towards the heating surface15. It therefore ensures proper contact to the heating surface15which allows more accurate temperature measurements. This embodiment includes a retention element3isolating the sensor1from the heat source16(the latter being shown inFIG. 20but not inFIGS. 13 and 14).

FIGS. 15 to 17show yet another embodiment of the present invention. This embodiment is similar in structure than the embodiment ofFIGS. 13 and 14, with the difference residing in the absence of the retention element. Therefore, this embodiment is very simple in structure.

FIG. 18shows a detail of yet another embodiment of the present invention. In this embodiment a particular shape of the retention element3is shown. The retention element3has grooves1forming reinforcement ribs having voids14therein. This particular shape provides both enhanced stability and, due to the voids14, better insulating properties.

FIGS. 19 and 20shows a sensor assembly according to the present invention installed in an electric stove with a heating surface15and a heat source16.

FIGS. 21 to 23show top views of different embodiments of the first sensor1of a sensor assembly according to the invention. In particular, different shapes of the carrier26are shown. Although the different zones are only depicted inFIG. 21, each of the three carriers ofFIGS. 21 to 23comprises, in principle, a temperature measuring zone28with a resistor web23thereon, a transition zone29and a contact zone30provided with contact pieces8. While the carrier26inFIG. 21has a general rectilinear shape, the carrier26inFIGS. 22 and 23are of smaller diameter at the distal end34of the carrier26. In the embodiment ofFIG. 22the transition from the wider to the narrower carrier region is realized by a step35while in the embodiment ofFIG. 23the transition continues. Both arrangements reduce the weight of the carrier26at the distal end34. This in turn provides less distortion and hence better stability and enhanced measuring accuracy of the sensor.

The sensor assembly according to the present invention essentially includes a first sensor1and at least one second sensor2. The sensor1has a carrier26, which may be made of ceramic, and at least one temperature-dependent resistor web23, which is shown by way of example inFIGS. 1 and 21and arranged on the carrier26. The resistor web23is not shown in the other figures for reasons of better comprehensibility of the drawings. The resistor web23of the sensor1faces the heating surface15and is electrically contacted outside a temperature-measuring zone28of the sensor1to a contact zone30with contact pieces8. The sensor2has a carrier26′, which may be made of ceramic, and at least one temperature-dependent resistor web (not shown but similar to that on sensor1), which is arranged on the carrier26′ of the sensor2and faces the heat source16(FIG. 20). When assembled, the sensor1rests as flatly as possible and directly upon an underside of the heating surface15.

As indicated inFIGS. 1 and 21, the resistor web23of the sensor1and/or sensor2may have a meandering configuration and is made preferably through thick-film technique. Any configuration of meander shape may be possible. As a result of the meander shape, the temperature-measuring zone28which is especially temperature-sensitive can be defined. Although the meander shape is currently preferred, any other configuration of the resistor web23is, of course, possible as well. While the application of thick-film technique, using especially a screen printing process, is currently preferred, thin-film technique or other processes at the disposal of the artisan are, of course, also conceivable. The sensors1,2may be of substantially identical construction for cost-saving reasons; currently preferred is however a configuration in which the sensor2is made of greater size than the sensor1so that the sensor2is able to shield the sensor1from heat radiating from the heat source16, as shown by way of example inFIGS. 1 to 20. Shielding of the sensor1can further be enhanced by making the sensor2radiation-absorbent.

The temperature measuring zone28can be further adjusted by making the resistor web23of the sensor1and/or the resistor web of the sensor2in a transition zone29between the contact zone30and the temperature-measuring zone28of a cross section23awhich is greater than, in particular twice, a cross section in the temperature-measuring zone28. Greater cross section23ameans smaller resistance and less temperature sensitivity which is desired in the transition zone29.

The stability of the sensor assembly can be enhanced by tapering the sensor carrier26and/or26′ assembly in a direction to a free end which is distal to the contact zone30. As a result, only a small portion of the heat source16is shielded from the heating surface15. In addition, this effect can be further enhanced by providing the sensor assembly in the area of the contact zone30with a wider portion25(FIGS. 22,23), with a transition from the wider portion25to the remaining narrower portion24of the sensor assembly being curved, suitably concavely curved.

Suitably, the resistor web23of the sensor1and/or sensor2has a length of at least 200 mm in the temperature-measuring zone28so as to be able to suit the temperature sensitivity. The resistor web(s)23must be securely electrically contacted consistently even when exposed to widely varying thermal conditions. Suitably, the resistor web(s)23is contacted by at least one contact piece5which is made of elastically yielding material and connected, e.g. riveted, to the respective carrier. It is also possible to insulate the resistor web(s)23by a closed thermally conductive passivation layer (not shown) which, when having sufficient width, is able to cover or screen any unevenness, caused, e.g., by bolt heads and/or rivets6,7. As a result, the sensor1rests flatly against the heating surface15.

In view of the affect that the heat source16may have on the sensor1, the sensor1is isolated from the heat source16by disposing a retention element3between the sensor1and sensor2, seeFIGS. 1 to 14,18and20. The retention element3may be configured as a bracket or have a trough shape to define a receptacle4for accommodating insulating material (not shown). The retention element3may be made of any suitable thermally stable material, e.g. ceramic or stainless steel. As shown inFIG. 18, the retention element3has a bottom formed with grooves13to provide reinforcement ribs with voids14for insulation.

FIGS. 13 and 14show an embodiment of a sensor assembly, having a spring tongue11for urging the sensor1against the heating surface15. The spring tongue11is connected to the sensor2. In the sensor assembly ofFIGS. 15,16and17, the sensor1is biased by a spring tongue12which is secured to the sensor2. The spring tongue11,12may be a metal spring.

The sensor2is at least regionally connected to the retention element3and bears flatly against the retention element3.

The retention element3has preferably the shape of a trapezoidal frame or the shape of a trough with trapezoidal or rectangular configuration, with an underside and inner side of the trough having preferably plane-parallel plates. As a result, the sensors1,2bear against the retention element3. The receptacle4of the retention element3may be provided in either variation, i.e. when the retention element3is configured as frame or as trough.

As the sensor1should rest flatly upon the heating surface15, the sensor1, in particular the carrier26of the sensor1, is connected in the area of the contact zone30to the sensor2and/or retention element3by at least one elastically yielding contact piece5, e.g. a spring such as a metal spring, U-shaped spring (FIGS. 4-6,7-9,10-12,13,14,15-17), or Z-shaped spring (FIGS. 1-3). To connect the elastically yielding contact piece5reliably and consistently to the sensor1, sensor2, and/or retention element3, the use of thermally stable connection means are provided, such as bolts and/or rivets6,7. Rivets in particular are reliable, thermally stable, cheap, and allow automatic installation.

When using rivets6,7or bolts or like fasteners, the heads of the fasteners6,7jut out beyond the surface of the sensor1to prevent a flat abutment of the sensor1. While this may be acceptable is some instances whereby the heads of the fasteners6,7form a wedge-shaped gap, it is however preferred to implement a flat abutment of the sensor1against the heating surface15. This may be attained by applying a thermally conducting passivation layer upon the surface of the sensor1, with the passivation layer covering also the heads of the fasteners6,7. As an alternative, or in addition, the sensor1is formed in the area of the contact zone30with a step-shaped recessed zone17which extends at a lower level as the thermally stable connection means, as shown inFIGS. 7 and 9. When the sensor1is completely received in the receptacle4of the retention element3, the resistor web23of the sensor1extends in substantial parallel relationship to the sensor2. The step-shaped recessed zone results in a flat abutment of the sensor1upon the heating surface15in the absence of any interference by the heads of the fasteners6,7.

Suitably, the carrier of the sensor1is of multipart configuration in the area of the recessed zone17. In this way, the part that is relevant for the measurement, i.e. the part of the carrier26with the measuring zone28, can be configured as a flat part that can be connected to a further part to form a step, as shown inFIGS. 7 and 9.

In the embodiment shown inFIGS. 7 to 9, the sensor1is made up of two carrier parts31and32. By arranging the two carrier parts31and32as shown inFIGS. 7 and 8a recess33and hence recessed zone17is formed.

FIGS. 10 to 12show an alternative to form the recess33and hence a recessed zone17. As shown inFIGS. 10 and 12, the sensor1has a single piece carrier26. The recess33is already an integral part of the carrier26and can be applied by grinding or other abrasive treatment of the carrier26.

With regard toFIGS. 1 to 20, installation and adjustment in a heating space formed by the heat source16and the heating surface15is realized by using a mounting bracket9of substantially angular shape. The mounting bracket9is connected to the sensor2and/or the retention element3, e.g. by riveting ort bolting. When connected to the retention element3, the mounting bracket9can have a pocket or bay (not shown) for receiving the sensor2. This allows easy installation of the sensor2. The mounting bracket9has a vertical oblong hole10to facilitate assembly and adjustment.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and include equivalents of the elements recited therein: