DE10337543A1 - Temperature measuring device for heater of hob has longitudinal sensor made from ferromagnetic material running along active region of heating device connected to evaluation unit - Google Patents

Abstract

Device for measuring the temperature of a heating device (13) comprises a longitudinal sensor (20) made from ferromagnetic material running along the active region of the heating device connected to an evaluation unit (24) which is structured in such a way that the Curie temperature of the sensor is acquired by measuring an electrical property of the sensor, especially the inductance or electrical resistance. An independent claim is also included for a process for measuring the temperature of a heating device using the above device.

Description

field of use and state of the art

The The invention relates to an apparatus and a method for measuring the temperature of a heater, wherein a sensor of ferromagnetic Material is used.

From the DE 195 26 091 A1 It is known to provide for a temperature limiting a sensor with a coil, in the region of ferromagnetic material is arranged. In the region of limit temperature of the ferromagnetic material, the so-called Curie temperature, a magnetic phase transition is performed. As a result, the inductance of the coil changes greatly, indicating an exceeding of the limit temperature. This can then be evaluated electronically.

adversely in this solution and in the other prior art is that a sensor with a additional Coil needed which is a not inconsiderable expense, or due to high Ambient temperatures are technically difficult or impossible to realize is.

Task and solution

Of the Invention is based on the object, an aforementioned device as well as to create a named method with which the disadvantages of the prior art can be avoided and in particular a Temperature detection in a heater easy and safe as well as possible is.

Is solved this object by a device with the features of the claim 1 and a method having the features of claim 11. Advantageous As well as preferred embodiments of the invention are the subject of further claims and will be closer in the following explained. The wording of the claims is by express Reference made to the content of the description.

A inventive device has an elongated sensor made of ferromagnetic Material exists. The sensor runs in the heating area of the heating device, advantageously relatively close to the heater. He should, however closer to the temperature to be monitored Surface, such as. the glass ceramic plate, run. The sensor or the ferromagnetic Material have a Curie temperature which is in the range of a maximum temperature the heater or other temperature to be measured the heater is located. Furthermore, the sensor with an evaluation, For example, an evaluation, connected. This evaluation is designed to detect the Curie temperature of the sensor. For this purpose, at least one electrical property of the sensor is measured, in particular its inductance or its electrical resistance, advantageously also both.

In the context of the invention, it has been shown that the already used in the past even effect of passing the magnetic Pha senübergangs in a ferromagnetic material at the Curie temperature can also be detected directly on a sensor when it is a passive sensor, so to speak. So in the above DE 195 26 091 A1 described detour via a further coil, in the magnetic field region, a corresponding ferromagnetic material is disposed, can be saved. Effort and susceptibility to errors reduce considerably. Depending on the required accuracy, a sufficiently good measurement can also be carried out. The range of Curie temperature at which the relative permeability of the ferromagnetic material changes during the phase transition is relatively narrow.

Basically the Curie temperature of a ferromagnetic material in one wide range selected become. Advantageous, especially for use for temperature measurement in a heating device, for example in a radiant heater under a glass ceramic plate, the Curie temperature is between 150 ° C and 900 ° C. Especially Advantageously, it is between 400 ° C to 600 ° C and 800 ° C, preferably at 700 ° C. This is, for example when used under a glass ceramic plate, including their permissible maximum temperature and the distance to it depends.

Of Furthermore, it is advantageous if the sensor is resistant to high temperatures. For this purpose, it can consist of a FeCrAl alloy. The aluminum content it may be less than 6%, advantageously about 3% to 4%. Such a material has many advantages. On the one hand, it is ferromagnetic. Furthermore, it is also resistant to high temperatures.

It can be provided, the sensor for your own protection or due from electrical safety regulations in an electrical insulating shell to arrange. This should be tubular its shape may be both straight and curved. The case consists of some of a ceramic material or glass, for example also quartz glass.

Of the Sensor can be elongated and straight, using a wire or a pipe can be. Advantageously, a constant cross-section, thus a temperature measurement due to local increase each location, essentially point-like, as well as integrally over longer areas can take place.

in the Operation, the sensor is directly energized. Advantageous this is an alternating current with frequencies between 20 kHz and 150 kHz.

A mentioned device or such a sensor can in a variety of applications are used. An advantageous Application is an installation in a hob with at least one hotplate, advantageous four cooking rings or more. Such a hob can in particular a plurality of radiant heaters and a glass ceramic plate exhibit.

In addition to the task of measuring the temperature can be provided that the function of a pot detection can be realized with the sensor. Such pan detection sensors are for example from the DE 19603845 A1 or the DE 10135270 A1 known. For this purpose, a corresponding pot detection evaluation is provided, which is designed as a circuit. This pan detection circuit can also be implemented together with a temperature evaluation circuit.

On the one hand Is it possible, punctiform with the sensor and cover smaller areas of a heater. on the other hand However, it is possible in the invention, with a corresponding long and running sensor larger or all areas of one or to cover several rer heating elements of a radiant heater. In still another Embodiment of the invention may be provided with such Sensor several radiant heaters to cover a hob. Thus, with a single or several such sensors, a temperature monitoring for a whole Hob with several burners and corresponding heaters, for example radiant heaters, be created.

There in many cases the use of such a temperature sensor under a glass ceramic plate this is to prevent too high temperature and consequent damage protect, it is beneficial to place the sensor relatively close to the bottom of the To arrange glass ceramic plate. Here, however, should be provided that the sensor is sufficiently mechanically secured against being closed strong beating against the underside of the hob or the glass ceramic plate, For example, in so-called drop tests for finished hobs.

at a method according to the invention a sensor whose possible Properties mentioned above have been supplied with current or alternating current. It will be at least one electrical property of the sensor, for example inductance or electrical resistance, measured. Upon reaching the Curie temperature is from the current or current flow, which is appropriate concise changed this temperature determines. Therefor can For example, different slope values of the temperature curve determined as authoritative be, as well as the subsequent Waste.

Of further it is possible an aforementioned sensor with a correspondingly adapted evaluation to use a pot detection function on a hob to realize. Therefore can be provided various evaluation algorithms.

It can be provided for more accurate determination of the temperature, distorting influences other ferritic parts or ferromagnetic materials in the Calculate the environment of the sensor, if they are known. This applies for example the material of the Heizleiter band, which is also a FeCrAl alloy is with ferromagnetic properties. Corresponding correction values can be found in be stored in a memory.

These and other features go out the claims also from the description and the drawings, wherein the individual features each for alone or in the form of subcombinations an embodiment of the Invention and other fields be realized and advantageous also for protectable versions can represent for the protection is claimed here.

Summary the drawings

One embodiment the invention is shown schematically in the drawings and will be closer in the following explained. In the drawings show:

1 a functional design of a hob with heater and an overlying sensor, including wiring and

2 Curves of the inductance and the resistance of the sensor over the temperature.

detailed Description of the embodiment

In 1 is highly schematic a hob 11 shown. Below is a heater 13 arranged with heating effect upwards. This heater 13 can be a radiant heater, such as in the DE 42 29 375 A1 is described.

Furthermore, the hob has 11 a glass ceramic plate 15 on, which also corresponds to a usual structure. On the hob 11 is above the heater 13 , which forms a cooking place, a pot 18 , This is done by the heater 13 heated.

at Cooktops, especially with glass ceramic plates, there is the problem that the glass ceramic is not allowed to reach temperatures above 600 ° C, as a rule even less. Therefore are overtemperature fuses provided, mostly so-called rod regulator.

The invention will now be a sensor 20 between heater 13 and bottom of the glass ceramic plate 15 arranged. The sensor is advantageous 20 while closer to the glass ceramic plate 15 arranged. It can be seen that the sensor 20 with a control 22 and an evaluation 24 connected is. It can be controlled, as shown, by being directly traversed by an alternating current. Thus, it forms a kind of passive sensor element. These signals are from the evaluation 24 evaluated. As indicated, the evaluation may 24 at least one microcontroller include, advantageously also memory for comparison values and the like. An evaluation is advantageously carried out via frequency measurement, for example by integrating the sensor into a resonant circuit or via impedance measurement.

In the diagram in 2 is roughly approximated the course of both the inductance and the ohmic resistance of the sensor 20 shown above the temperature. These measurements were made at a frequency of about 50 kHz. The sensor 20 consists of a FeCrAl alloy, which is also known as material 1.4770. The alloy is on the one hand ferromagnetic with the previously counted on properties. It also contains 3% aluminum, which is less than standard FeCrAl alloys. The ferromagnetic properties of this material of the sensor 20 can be found in the diagram in 2 read off. It should be noted that the ohmic resistance, the inductance or impedance, due to the change in the so-called equivalent penetration depth of the electromagnetic wave in the skin effect results.

It it can be seen how the inductance increases with increasing temperature to a certain point, namely the Curie point or the Curie temperature. While the rise is relatively flat with increasing slope near the Curie point, the garbage is after steeper. something similar applies to the ohmic resistance. It can be seen, as with a corresponding Adjustment absolute values of the measured quantities these curves would be very similar, in particular from the slope course ago. Especially the slightly steeper climb and the much steeper decline of the courses shortly before and shortly after The Curie temperature is suitable for a relatively accurate determination the temperature based on the known Curie temperature of the special Material.

In the present example, the Curie temperature is about 630 ° C. For known geometric dimensions of the hob 11 , In particular a known distance of the heater 13 to the bottom of the glass ceramic plate 15 , the operating temperatures and the maximum temperature of the glass ceramic, can be a predetermined limit temperature over the distance of the sensor 20 to the heater 13 and glass ceramic plate 15 be adjusted as it were based on this Curie temperature. This means that the limit temperature of the glass-ceramic plate is reached or is not quite reached by the temperature conditions, if the sensor 20 reached its Curie temperature of about 630 ° C. Thus, there are two ways to influence this relationship. On the one hand, for the sensor 20 a material with a certain Curie temperature can be selected. Furthermore, can over the distance and the resulting temperature drop between the heater 13 and glass ceramic plate 15 the temperature of the glass-ceramic plate prevailing when the Curie temperature is reached can be set.

For control and evaluation need not be explained much here. Suitable controls and evaluations both for a measurement of the ohmic resistance and for a measurement of the inductance are known and easy to realize for the skilled person. For this purpose, for example, on the from the DE 195 26 091 recourse to known circuit or circuit principles.

An attachment of the sensor 20 It can be made dependent on how it is executed. In a relatively self-stable design, he can, similar to currently known rod controller, on the heater 13 or one in the 1 Not shown insulating edge be attached. It should be noted that the sensor is not too close to the glass ceramic plate that he can strike at this. In a design as a wire in turn, this risk is lower.

Furthermore, it is possible, as previously mentioned, the sensor 20 next to the Tem peraturkennungsfunktion also train for pan detection. Possible training for this purpose are for example in the DE 101 35 270 to which reference is expressly made in this regard. The functions of the temperature measurement on the one hand and pan detection on the other hand can be done in alternating operation.

In addition to the in 1 illustrated embodiment of a sensor 20 which, so to speak, the temperature of a single heater 13 he summarizes, embodiments are conceivable in which a sensor spans several heaters or all heaters of a hob and thus measures their temperature. In this case, it can be used as an advantage that the sensor can measure areas or associated heating devices both quasi pointwise via small heating elements or heating element areas as well as integrating over its entire length. In many cases, such a temperature measurement is not mainly used for control operations, but as overtemperature protection, which should avoid major damage, especially on a glass ceramic plate. In this respect, these over-temperature fuses often respond in practice, but otherwise are not primarily involved in control processes for the heaters. For this purpose, other temperature detections are advantageously used.

Claims (12)

Device for measuring the temperature of a heating device ( 13 ), in particular a radiant heater under a glass ceramic plate ( 15 ), with a sensor ( 20 ) in elongated form made of ferromagnetic material, which extends in the effective range of the heating device, wherein the sensor has a Curie temperature in the range of a maximum temperature of the heater and wherein the sensor with an evaluation circuit ( 24 ), which is designed to detect the Curie temperature of the sensor by measuring an electrical property of the sensor, in particular the inductance or the electrical resistance. Device according to claim 1, characterized in that the Curie temperature of the sensor ( 20 ) between 150 ° C and 900 ° C, in particular between 600 ° C and 800 ° C. Device according to claim 1 or 2, characterized in that the sensor ( 20 ) is high temperature resistant, preferably consisting of a FeCrAl alloy. Device according to claim 3, characterized in that the FeCrAl alloy contains less than 6% aluminum, preferably about 3%. Device according to one of the preceding claims, characterized in that the sensor ( 20 ) is in an electrically insulating sheath, which is preferably tubular and in particular consists of a material of the following group: ceramic, glass or quartz glass. Device according to one of the preceding claims, characterized in that the sensor ( 20 ) has a cylindrical cross-section, in particular a wire or a tube. Device according to one of the preceding claims, characterized in that the sensor ( 20 ) is flowed through directly, in particular flows through an alternating current. Device according to one of the preceding claims, characterized in that it is suitable for installation in a hob ( 11 ) is formed with at least one cooking point, in particular with a radiant heater ( 13 ) and a glass ceramic plate ( 15 ), wherein preferably the device is designed for carrying out the function of pot detection and for this purpose with a corresponding pan detection evaluation circuit ( 24 ) connected is. Device according to claim 8, characterized in that the sensor ( 20 ) at least larger areas of one or more heating elements of a radiant heater ( 13 ), wherein it preferably covers the entire hob length. Device according to claim 8 or 9, characterized in that the sensor ( 20 ) at a short distance to the underside of the hob ( 11 ), in particular the glass ceramic plate ( 15 ) is arranged. Method for measuring the temperature of a heating device, in particular a radiant heater ( 13 ) under a glass ceramic plate ( 15 ), with a sensor ( 20 ) in elongated form of ferromagnetic material, which extends in the range of action of the heater, wherein the sensor has a Curie temperature in the range of a maximum temperature of the heater, wherein the sensor, a current, in particular alternating current is applied, wherein an electrical property of the sensor ( 20 ), in particular the inductance and / or the electrical resistance, are measured and the current is used when determining the Curie temperature for determining the temperature. Method according to claim 11, characterized in that the sensor ( 20 ) for the realization of a pan detection function in a hob ( 11 ) is used and evaluated with various evaluation algorithms.