EP2183943A1

EP2183943A1 - Heating device, method for operating a heating device and electric heating apparatus of such a heating device

Info

Publication number: EP2183943A1
Application number: EP08785645A
Authority: EP
Inventors: Franci Kovacic; Herbert Schinko; Wolfgang Thimm
Original assignee: EGO Elektro Geratebau GmbH
Current assignee: EGO Elektro Geratebau GmbH
Priority date: 2007-08-24
Filing date: 2008-08-20
Publication date: 2010-05-12
Also published as: DE102007040891A1; WO2009027042A1

Abstract

A heating device (11) comprising a water guiding element (12, 13) and a heating element (15) attached to the outside has a temperature sensor (17). The temperature sensor (17) is a part or section of the heating element (15) and thus the same heating element current (I) flows through it. The temperature sensor (17) is used to monitor the temperature of the heating device (11). Through connections (20, 21) on the temperature sensor, the applied voltage can be detected by means of a controller (23) and thus the electric resistance and consequently the temperature can be determined. An instance of a critical overtemperature can thus be recognized and prevented.

Description

description

Heating device. A method of operating a heater and electric heater with such a heater

Field of application and state of the art

The invention relates to a heater with heating element, a method for operating such a heater and an electric heater with such a heater.

To hedge such heaters, such as those in kettles, hobs or the like. are used against overtemperature so far separate thermal fuses are used to prevent the case of an inadmissible excess temperature on the heating element by galvanic interruption and thus disconnecting the power supply or thereby react. However, this is expensive in many cases, both constructive and in terms of manufacturing costs.

Another type of heater, in which a separate temperature fuse element can be saved, uses so-called PTC heating elements. It is exploited that the heat conductor guasi itself regulates and reacts to a temperature increase with a strong increase in resistance. The following examples, which describe the prior art, are explicitly mentioned. A hotplate in which BaTiO3 is used to control heating power is EP 853 444 A1. A hotplate with PTC heating elements is described in WO 2004/080127 A1. The materials mentioned are tungsten (resistivity 0.056 ohm mnτ7m), Vacon CF 25 cobalt alloy (resistivity 0.056 ohm mm ² / m), and resistivity iron typically in the range 0.1-0.15 ohms mm ² / m. A typical sensor material, which as Heating conductor could be used is platinum with a resistivity of 0.1 ohm mm ² / m.

A disadvantage of these solutions are sometimes very special and therefore usually expensive materials in which it is for various reasons just not common Heizleiterlegierungen, as they can be easily used in heating elements. In particular, the low resistivity of these alloys is disadvantageous. Attempts to circumvent the problems that the above-mentioned materials are combined with known Heizleiterlegierungen are known from EP 621 738 A1 and DE 10 2004 063207 A1. However, such combinations are associated with considerable design effort.

Task and solution

The invention has for its object to provide an aforementioned heating device and an aforementioned method for operating such a heater with which problems of the prior art can be avoided and in particular novel, simple and technically advantageous ways to monitor the temperature of a heating element or Heating device can be created.

This object is achieved by a heating device with the features of claim 1 and a method having the features of claim 23 and an electric heater with the features of claim 25 or 26. Advantageous and preferred embodiments of the invention are the subject of further claims and will become more apparent in the following explained. Some features are explained only for the heater, the method or the electric heater. However, you should be able to apply regardless of both the heater as well as the process or the electric heater. Of the The wording of the claims is incorporated by express reference into the content of the description. Furthermore, the wording of the priority application DE 1020070040891.0 of August 24, 2007 of the same Applicant is incorporated by express reference into the content of the present specification.

The heating device has a temperature sensor or an element serving as a temperature sensor, with which it or the heating element can be monitored during heating operation to an inadmissibly high overtemperature. In this case, a heating element current flows during operation of the heating element through it. The heating element is at least partially itself formed as a temperature sensor for temperature measurement by evaluating the course of the Heizelementstroms over time with determination of the temperature by an evaluation of Heizelementspannung and / or Heizelementstrom at a known value for the electrical resistance. According to the invention, it is also provided that the temperature sensor is always flowed through by the heating element current or lies in the current path provided for the heating element. Furthermore, the material of the heating element is a material having a resistivity of greater than 0.2 ohm mm ² / m at 20 ° C without further materials with a resistance increase greater than the resistance increase of pure metals with 3.9 / 1000 K and / or without parallel or series connection of smaller specific resistances. Particularly advantageous is a metallic material. This results in a number of possibilities for temperature monitoring, both in terms of a temperature detection per se and a shutdown of the heating element or the heater, so as to prevent the case of a critical overtemperature after detection. These possibilities are explained below.

According to a basic embodiment of the invention, the heating element or a part thereof may itself be designed as a temperature sensor or used and evaluated as such. examples For example, the course of the heating element current over time can be evaluated for temperature measurement. Then, at least partially serving as a temperature sensor heating element is already flowed through by the Heizelementstrom.

In an embodiment of the invention, the specific resistance is greater than 0.9 ohm mm ² / m at 20 ⁰ C.

The PTC material is designed such that when the temperature increases, in particular when the temperature of the PTC material approaches a critical temperature limit that would be detrimental to the heater or electrical appliance, the electrical resistance of the PTC material increases so much, a limitation of the heating element current leads to a reduction of the electric power of the heating element, for example by at least 20%, so that the temperature decreases again due to the reduced power. In addition, an increase in the electrical resistance of the PTC material does not even have to be too steep. Alternatively, just a very steep rise from a threshold temperature take place, through which the Heizelementstrom and thus the heating power are greatly reduced.

Such PTC materials are known to the person skilled in the art. For the advantageously usable PTC materials is essentially only a positive increase in electrical resistance. BaTiO ₃ should be explicitly excluded. As will be explained below, conventional heat conductors, with a generally relatively low temperature coefficient compared to pure metals, can also be used for the invention. It is advantageous that such materials have a specific electrical resistance, which is generally greater than that of pure metals (at about 1 ohm mm ² / m), which is contrary to the use as a heating element. In an embodiment of the invention, the PTC material may be designed so that in a temperature range between 150 ⁰ C and 250 ⁰ C, an increase in the resistance is at least 10%, advantageously even more than 20%. This increase can be carried out substantially over some 10 ⁰ C, for example over 20 ⁰ C to 30 ⁰ C. This is considered sufficient for a significant reduction in heating power and thus a resulting reduction in temperature.

In a further embodiment of the invention, the material of the heating element may contain components having a ferromagnetic phase transition. A Curie point can advantageously be between 200 ⁰ C and 1000 ° C. It may be particularly advantageous Fe, Ni, or Co contained.

In a further embodiment of the invention, voltage and / or current can be evaluated on the heating element to determine its temperature, in which case the heating element itself is the temperature sensor. This can be done either for the entire heating element or just for one section. In this case, the temperature can be detected independently of a heating operation via the heating element, so that, for example, in an intended heating break, the heating element can also be used as a pure temperature sensor for a pure temperature measurement. Furthermore, this can also be used in a heating operation extra heating breaks to allow a better and trouble-free temperature measurement.

An evaluation of the temperature sensor or the heating element as a temperature sensor is advantageously carried out electronically. The values for current or voltage are detected and, in particular via a signal transmission or signal conditioning to a controller such as a microcontroller or the like. given.

Further materials for the heating element are iron-nickel alloys, for example available from Fa. Kanthai as Nifethal 52 or Nifethal 70. Alternative materials for the heating element may also be selected from the group of FeCrAI alloys and NiCr heating conductor alloys. Yet other alternative materials for the heating element may have a coefficient of resistance between that of NiCr3020 and that of tungsten. Thus, good properties of the heating element can be achieved both during heating operation and for a temperature measurement.

Likewise, the heating element may have as additive at least one material from the group Cr ₁ Ni or Fe. Also additives such as tungsten, molybdenum, or an alloy containing tungsten or molybdenum are possible. Another possible additive is carbon in various modifications, for example in the form of carbon or so-called carbon nanotubes.

On the heating element may be a layer of CT ₂ O ₃ or Al ₂ O ₃ . The heating element itself can be insulated, wherein the insulation can have a high thermal conductivity greater than 1 W / mK. Insulation may consist essentially of SiO ₂ , in particular of glass or glass ceramic, alternatively of MgO or of Al ₂ O ₃ .

With a sufficiently large signal amplification can be used as further alternative materials and conventional Heizleiterlegierungen with a melting point of greater than 1000 ⁰ C and a resistivity in the order of 1-2 ohm mnrvVm. Such Heizleiterlegierungen are described for example in EP 542 128 A1, to which reference is explicitly made.

As another alternative material, the heating element may consist of a ceramic material. Advantageously, it may be a doped ceramic material doped with Ce or La. Alternatively, a high temperature superconductor such as YBCO-1-2-3 may be used. A further embodiment of the invention with a temperature sensor which is at least functionally separate from the heating element can provide for this, although similar to a safety fuse, to be self-destructive when a limit temperature is exceeded. However, in the present case an admissible high limit temperature of the temperature sensor due to the choice of material already at a few 100 ⁰ C begin to oxidize, such as tungsten under normal atmosphere. Advantageously, the temperature sensor is designed so that it oxidizes after a few seconds, for example, 5 seconds to 15 seconds, at this temperature, so it self-destructing and thereby interrupts the flow of current. So there is no melting of a corresponding breaker element, but there is another, temperature-related destruction mechanism, but with the same result. This has, inter alia, the advantage that, on the one hand, a response time or interruption time is longer, that is, for example, 5 seconds to 15 seconds. On the other hand, since this is not so significant in the case of thermally rather sluggish heating devices, on the other hand, the advantage prevails that thermal protection is not triggered by only short-term temperature peaks.

As can be seen from the previously explained, either an electrical resistance of the heating element can be evaluated for temperature measurement or a resistance of the temperature sensor itself, which is then part of the heating resistor or serves for heating.

An inventive electric heater with such a heater may for example be a water heater or an aforementioned kettle. The heating device can thus be designed to heat water in direct contact or indirectly. Alternatively, it may be a hot plate or substantially only a heating element such as a tubular heater, which may then be installed in one of the aforementioned devices. In a tubular heater is arranged the heating element in a tube jacket and electrically insulated. The serving as a temperature sensor part may advantageously be provided close to an end or electrical connection or a housing serving for it or in a connection housing. A tube can be made of metal or glass or quartz glass.

These and other features will become apparent from the claims but also from the description and drawings, wherein the individual features each alone or more in the form of sub-combination in one embodiment of the invention and in other areas be realized and advantageous and protectable Represent embodiments for which protection is claimed here. The subdivision of the application into individual sections and subheadings does not limit the statements made thereunder in their generality.

Brief description of the drawings

Embodiments of the invention are shown schematically in the drawings and are explained in more detail below. In the drawings show:

1 is a schematic representation of a water heater with wound heating element including series-connected temperature sensor,

Fig. 2 is a greatly simplified circuit diagram of the electrical wiring of FIG. 1 and

Fig. 3 is a schematic representation of a so-called tubular heater with extending therein elongated heating element, of which a portion serves as a temperature sensor.

Detailed description of the embodiments In Fig. 1, a heater 11 is shown having a water guide 12, which consists of a water-carrying pipe 13. Such heaters are known and are used for example in the manner of a water heater for washing machines or dishwashers.

On the tube 13 and the water guide 12, a heating element 15, advantageously a heating wire, applied, and wound. Instead of a so-called exposed heating element 15 in a wound-up form, it would also be possible to provide a printed thick-film heating element, possibly also a plurality of alternatively sheathed tubular heating elements. These are explained below with reference to FIG. 3.

At its right in Fig. 1 end, the heating element 15 is connected to a temperature sensor 17 in the form of a resistor. At its left end, the heating element 15 is provided with a first connection 19 as a main electrical connection, through which in particular the heating element current flows. The other main electrical connection is made via the second connection 20 at the right end of the heating device 11, namely at the temperature sensor 17, so that there is always a series connection of heating element 15 and temperature sensor 17.

At the other end of the temperature sensor 17 or at the connection to the heating element 15, an intermediate tap 21 is provided. In particular, here the temperature sensor is formed by the intermediate tap 21, the heating element 15 and the forming this conductor is divided into two parts functional, namely on the one hand in the functional part of the heating element, which heats only. The second part also heats up and, by means of the intermediate tap 21 and the connection 20, additionally forms a described temperature sensor. The production of the conductor can be in one piece, and by an applied contact field to get the intermediate tap 21. Alternatively, two Parts or suitable conductors are connected to each other at the contact pad for the intermediate tap.

The electrical equivalent circuit diagram in FIG. 2 shows how, on the one hand, the series connection of heating element 15 and temperature sensor 17 is flowed through by heating current I. Furthermore, a control 23 is provided, which can detect the voltage across the part as a temperature sensor 17 via the intermediate tap 21 and via a connection to the second connection 20.

For operation, it should be said that the heating element current I is controlled or applied by a control, not shown, of the heating element 15. In operation, the heating element 15 heats the water flowing through the water guide 12, as is well known. Part 17 contributes, albeit with a small share, as it is much shorter. In order to provide the aforementioned temperature fuse, 17 different possibilities can be provided for the temperature sensor. In accordance with the electrical circuit diagram, the controller 23 can determine the voltage and thus the electrical resistance of the temperature sensor 17 when the heating element current I is known. For this purpose, the controller 23 may also be additionally connected to the first terminal 19 under certain circumstances. If an impermissibly high temperature is detected, the controller 23 can throttle or switch off the heating element current I.

Another possibility for a thermal fuse is that the temperature sensor 17 has the above-mentioned PTC properties. In particular, these are such that when the temperature of the heater 11 and the water guide 12, especially of course in the area monitored by the temperature sensor 17 to a predetermined limit temperature of the electrical resistance of the temperature sensor at this limit temperature increases so much that the temperature sensor 17th throttles the heating element current I. In turn, the heating element 15 generates less heating power and the heater 11 can cool down again. Thus, the temperature sensor 17 can thus serve not only to detect the present temperature as an evaluable measured value, as has been explained above, but to capture the temperature so to speak automatically and to limit it automatically. The limit temperature may for example be between 150 ⁰ C and 250 ⁰ C. The material may be any of the foregoing.

In a further embodiment, which has also been described above, this start of the strong PTC behavior of the temperature sensor 17 can also be detected and evaluated by means of a controller 23. The controller 23 then causes no temperature limitation.

Furthermore, it is possible that the temperature sensor 17 consists of an aforementioned material which begins to oxidize at a specified temperature of a few 100 ⁰ C, again as a kind of limit temperature, under normal atmosphere. Likewise, the entire conductor, including the part of the heating element or the part with the main heating function, consist of this material. If a named impermissible high temperature limit is maintained for several seconds, at least the temperature sensor 17 is thereby destroyed, similar to a fuse, the duration is up to the destruction of the temperature sensor is greater than a fuse and in particular from 5 to 30 seconds. Such a destruction of the temperature sensor does not need to be detected by means of a control connected in parallel therewith, because a power interruption necessarily takes place and the heating element current does not start to flow again by itself. This can also be detected in another control as a case of over-temperature and destruction of the thermal fuse. In Fig. 3, a so-called tubular heater 11 ^{'is shown} as a heater. Such tubular heaters are known for example from DE-OS 24 21 842 or DE 10356914 A1. The tubular heater 11 'has a jacket 13 ^' of appropriate metal on as usual and contains a fine-grained insulating sand or ceramic powder, a schematically illustrated, elongated heating element 15 ^' as a heating element.

The heating conductor 15 ^' is still divided by a kind of contact field or contact tap, and so the temperature sensor 17 ^{' is formed} as a separate or own area. Here goes the intermediate tap 21 ^' , which is led out as a thin conductor from the jacket 13 ^' for connection according to FIG. 1 to a controller 23, not shown.

At the right end 25 ^' , the conductor of the heating element or the temperature sensor 17' to the terminal 20 'and the other conductor to the intermediate tap 21 ^' out, and both from there to said control.

So here heating element and temperature sensor are made of the same material or from the same conductor. The distinction is made only by the additionally attached contact tap for the intermediate tap 21 ^' . The temperature sensor also works as a heater.

In a manner similar to that in FIG. 1, that is, for example with a circuit according to FIG. 2, another heating may be formed, for example a heating base for a kettle, which may even have a plurality of heating elements in any interconnections. Even thick-film constructions are possible. Likewise, a hotplate with one or more of these heating elements or even such a tubular heater may be provided, since the heater on the underside of a cooking plate constructive similarity with such tubular heaters. Then it is just to at least one of the heating elements to invented A temperature sensor according to the present invention is connected in series or has such a section. Further overtemperature safeguards can be dispensed with, in particular thermomechanical systems or those with a completely separate temperature sensor which has no further function, in particular has no heating effect.

Claims

claims

A heating device (15), wherein a temperature sensor (17) is provided for monitoring the temperature of the heating device or heating element during heating operation, wherein a heating element current (I) flows through the heating element and the temperature sensor (17) and the heating element (15 ) are formed such that the temperature sensor (17) is always flowed through by the Heizelementstrom (I), wherein the heating element is at least partially itself formed as a temperature sensor for temperature measurement by evaluating the course of Heizelementstroms over time with determining the temperature by an evaluation of Heating element voltage and / or Heizelementstrom (I) at a known value for the electrical resistance, characterized in that the material of the heating element is a preferably metallic material having a resistivity greater than 0.2 ohm mm ² / m at 20 ⁰ C without further Materials with a resistance increase greater than the Widersta nsanstieg pure metals with 3.9 / 1000 K and / or without parallel or series connection of smaller resistors.

2. Heating device according to claim 1, characterized in that the resistivity is greater than 0.9 ohms mm ² / m at 20 ⁰ C.

3. Heating device according to claim 1 or 2, characterized in that the heating device is designed for heating water in direct contact with the heating device or the heating element.

4. Heating device according to claim 1 or 2, characterized in that the heating device is designed for heating water in a container, in particular in a cooking vessel, to which the heating device is attached, preferably on the underside.

5. Heating device (11) according to any one of the preceding claims, characterized by a water guide (12, 13), wherein a heating element (15) is arranged on or in the water guide.

6. Heating device according to one of the preceding claims, characterized by an electronic evaluation.

7. Heating device according to one of the preceding claims, characterized in that the temperature sensor (17) or the heating element (15) is a material with PTC properties such that a change in resistance of the PTC M aterials with increase in electrical resistance when approaching a critically high limit temperature is sufficiently large for reducing the electric power of the heating element (15) by at least 20% or for switching off, wherein preferably the material of the temperature sensor (17) is designed so that an increase in the resistance in the temperature range from 150 ⁰ C to 250 ⁰ C is at least 10%, preferably more than 20%.

8. Heating device according to one of the preceding claims, characterized by a determination of the temperature independent of an operating state of the heating element.

9. Heating device according to one of the preceding claims, characterized in that the material of the heating element (15) is an alloy having a melting point greater than 1000 ⁰ C.

10. Heating device according to one of the preceding claims, characterized in that the heating element (15) additionally comprises at least one material from the following group: Cr, Ni, Fe.

11. Heating device according to one of the preceding claims, characterized in that the heating element (15) additionally comprises a material from the following group: tungsten, molybdenum, or an alloy containing tungsten or molybdenum.

A heater according to any one of the preceding claims, characterized in that the material of the heating element (15) is selected from the group consisting of: FeCrAI, NiCr heating conductor and iron-nickel alloy.

13. Heating device according to one of the preceding claims, characterized by a layer of Cr2Ü3 or AI2O3 on the heating element (15).

14. Heating device according to one of the preceding claims, characterized in that the temperature sensor (17) at least partially consists of a few 100 ⁰ C oxidizing material, wherein the temperature sensor and thus the heating element (15) upon reaching this temperature of a few 100 ⁰ C. Oxidize in a few seconds to interrupt the flow of current.

15. Heating device according to one of the preceding claims, characterized in that the heating element (15) additionally comprises a material from the following group: pure carbon, carbon in various modifications or carbon nanotubes.

16. Heating device according to one of the preceding claims, characterized in that the coefficient of resistance of the material of the heating element (15) is between that of NiCr3020 and that of tungsten.

17. Heating device according to claim 16, characterized in that the linear resistance coefficient is in the range of the precious metals of 3 to 4.5 / 1000 K.

18. A heating device according to claim 17, characterized in that the material of the heating element (15) contains components having a ferromagnetic phase transition with a Curie point between 200 ⁰ C and 1000 ⁰ C ₁ in particular Fe, Ni, or Co contains.

19. Heating device according to one of the preceding claims, characterized in that the heating element (15) is insulated and the insulation has a high thermal conductivity greater than 1 W / mK, wherein preferably the insulation consists essentially of SiO 2, MgO or Al ₂ O ₃ ,

20. Heating device according to one of the preceding claims, characterized in that the heating element is applied as a thick-film or thin-film heating on an electrically insulating substrate.

21. Heating device according to one of the preceding claims, characterized in that it is designed as a tubular heating element, in particular tubular heating element or rod shape, preferably with the heating element in a tube.

22. Heating device according to claim 21, characterized in that the tube consists of metal or quartz glass.

23. A method for operating a heating device according to one of the preceding claims, characterized in that the electrical resistance of the heating element (15) and the temperature sensor (27) is evaluated for temperature measurement, wherein it is preferably evaluated electronically.

24. The method according to claim 23, characterized in that a measurement of the temperature of the heating element (15) or the heating device takes place in phases in which the heating element is not active or operated.

25. Electric heater for hot water preparation with a water guide (12, 13), characterized in that it comprises a heating device (11) according to one of claims 1 to 22, wherein it is in particular a water heater.

26. Electric heating device (11), which has a heating device according to one of claims 1 to 22, characterized in that it is designed for contact with a vessel, preferably for carrying the vessel, wherein it is in particular a cooking plate.

27. Electrical heating device according to claim 25 or 26, characterized in that in addition to electronic protection means by the electrical temperature measurement or by interruption does not contain any electro-mechanical protection.