HEATING DEVICE COMPRISING A TEMPERATURE MEASURING DEVICE AND METHODS FOR TEMPERATURE MEASUREMENT AT THE HEATING DEVICE AND FOR PRODUCTION

Abstract

A heating device comprising a temperature measuring device has a sheet-like carrier, at least one heating conductor on said sheet-like carrier, an elongate electrode on the sheet-like carrier and a layer structure on the carrier with an insulation layer between the heating conductor and the electrode. A measuring apparatus for detecting local high temperatures at the heating device is connected to the electrode and to the heating conductor. Said measuring apparatus detects a temperature-dependent leakage current through the insulation layer between the heating conductor and the electrode and evaluates this as a measure of a local change in temperature at the heating device. The electrode consists of a material with a temperature dependence of its electrical resistance of between 0.0005/° C. and 0.01/° C. in a temperature range of between 0° C. and 200° C. A temperature measuring device is connected to the electrode for the purpose of measuring a temperature at the electrode using the temperature dependence of the electrical resistance of the electrode.

Claims

1. A heating device comprising a temperature measuring device for said heating device, where said heating device has: a sheet-like carrier, at least one heating conductor on said sheet-like carrier, an elongate electrode on said sheet-like carrier, a layer structure on said carrier with an insulation layer between said heating conductor and said electrode, a measuring apparatus for detecting local high temperatures at said heating device, where said measuring apparatus is connected to said electrode and to said heating conductor and is designed to detect a temperature-dependent leakage current through said insulation layer between said heating conductor and said electrode and to evaluate said temperature-dependent leakage current as a measure of a local change in temperature at said heating device, wherein: said electrode consists of an electrode material having an electrical resistance and having a temperature dependence of said electrical resistance, where said temperature dependence lies between 0.0005/° C. and 0.01/° C. or between 500 ppm/K and 10,000 ppm/K in a temperature range of between 0° C. and 500° C., said temperature measuring device is connected to said electrode for a purpose of measuring a temperature at said electrode using said temperature dependence of said electrical resistance of said electrode.

2. The heating device as claimed in claim 1, wherein said temperature dependence of said electrical resistance of said electrode material lies between 0.0015/° C. and 0.005/° C. or between 1,500 ppm/K and 5,000 ppm/K in said temperature range of between 0° C. and 500° C.

3. The heating device as claimed in claim 1, wherein said electrode is at least partially covered by said heating conductor, with said insulation layer therebetween.

4. The heating device as claimed in claim 3, wherein a section of said electrode, covered by said heating conductor, runs along a direction of a longitudinal extent of said heating conductor.

5. The heating device as claimed in claim 4, wherein a section of said electrode, covered by said heating conductor, runs along at least 70% or 90% of a length of said longitudinal extent of the heating conductor.

6. The heating device as claimed in claim 1, wherein said electrode has a width being relatively small in comparison to a length of said electrode, where said length of said electrode is at least 20 times of said width.

7. The heating device as claimed in claim 1, wherein said insulation layer has an electrical resistance between a top side and a bottom side or between said heating conductor and said electrode of at least 1 MΩ in a temperature range of between 0° C. and 150° C.

8. The heating device as claimed in claim 1, wherein said electrode has a total electrical resistance of between 50Ω and 100 kΩ in said temperature range of between 0° C. and 500° C.

9. The heating device as claimed in claim 1, wherein said electrode has a longitudinal extent and has a constant width along said longitudinal extent.

10. The heating device as claimed in claim 1, wherein said electrode has a longitudinal extent and has a constant thickness along said longitudinal extent.

11. The heating device as claimed in claim 1, wherein said electrode has a content of silver of up to at most 95% as said electrode material.

12. The heating device as claimed in claim 1, wherein said electrode material has a variable temperature coefficient of said electrical resistance.

13. The heating device as claimed in claim 1, wherein said heating conductor has a plurality of partial heating conductors, wherein said partial heating conductors are interconnected with one another, wherein each of said partial heating conductors covers one said electrode or an electrode section.

14. The heating device as claimed in claim 13, wherein connecting sections are provided between said individual partial heating conductors, wherein said connecting sections are composed of a conductor material, said conductor material having a specific electrical resistance, said specific electrical resistance being lower at least by a factor of 10 than in said heating conductor.

15. The heating device as claimed in claim 1, wherein at least one additional electrode composed of the same material as said electrode is provided, said additional electrode not being covered or overlapped by one said heating conductor, where a lateral distance between said additional electrode and one said heating conductor is at least 1 mm or at least 2 mm or is twice a width of said electrode.

16. The heating device as claimed in claim 15, wherein said additional electrode is also connected to said temperature measuring device.

17. The heating device as claimed in claim 1, wherein a carrier insulation layer is applied to said carrier, said at least one electrode is applied to said carrier insulation layer, said insulation layer is applied to this electrode, said heating conductor is applied to said insulation layer, and a covering layer is applied to said heating conductor.

18. The heating device as claimed in claim 1, wherein a carrier insulation layer is applied to said carrier, said heating conductor is applied to said carrier insulation layer, an insulation layer or a dielectric layer is applied to said heating conductor, an electrode is applied to said insulation layer or to said dielectric layer, and a covering layer is applied to said electrode.

19. A method for temperature measurement at a heating device as claimed in claim 1, wherein in a first step a temperature detection takes place by means of a temperature-dependent leakage current flowing through said insulation layer between said heating device and said electrode, and wherein in a second step temperature measurement takes place at said heating device by way of a change in temperature at said electrode alone being measured.

20. The method as claimed in claim 19, wherein a change in temperature at said electrode is evaluated as a change in temperature over time.

21. A method for producing a heating device as claimed in claim 1, wherein said heating device has a plurality of said heating conductors, where all of said heating conductors and possibly also partial heating conductors of said heating device are applied in the same method step and from the same heating conductor material.

22. The method as claimed in claim 21, wherein said heating conductor has a plurality of partial heating conductors which are interconnected with one another, where each of said partial heating conductors covers an electrode or an electrode section, where all of said heating conductors and possibly also said partial heating conductors of said heating device are applied in said same method step and from said same heating conductor material.

23. A method for producing a heating device as claimed in claim 1, wherein said heating device has a plurality of said electrodes, where all of said electrodes of said heating device are applied in the same method step and from the same electrode material.

24. The method as claimed in claim 23, wherein said heating device has at least one additional electrode composed of said same material as said electrode and not being covered or overlapped by a heating conductor, wherein a lateral distance between said additional electrode and one said heating conductor is at least 1 mm or at least 2 mm or is twice a width of said electrode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Exemplary embodiments of the invention are schematically illustrated in the drawings and will be explained in greater detail below

[0026] FIG. 1 shows a plan view of a first refinement of a heating device according to the invention comprising a sheet-like heating conductor and a meandering electrode,

[0027] FIG. 2 shows a section through the heating device from FIG. 1 with the layer structure, and

[0028] FIG. 3 to FIG. 6 show various modifications of heating devices similar to FIG. 1 with different refinements for the heating conductor and the electrode.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0029] FIG. 1 shows a plan view of a heating device 11 according to the invention. Here, said heating device has a rectangular shape, but can also have any desired shape. In addition to planar refinements of a heating device 11, curved and tubular heating devices are also conceivable. In particular, the heating device 11 is produced using thick-film technology.

[0030] The heating device 11 has a carrier 12 which consists either of electrically insulating ceramic or of metal. Said layer structure is located on a carrier top side 13 which, in the case of a carrier 12 composed of metal, is provided with a functional insulation 27. Two contact tracks 15a and 15b composed of very highly electrically conductive material and situated parallel at a distance from one another are arranged on the carrier top side 13. Said contact tracks merge with contact areas 16a and 16b on the left. The contact tracks 15a and 15b make contact with a wide heating conductor 18 of sheet-like design between them. In this respect, reference is made, for example, to EP 3250003 A1. The current flow direction through the heating conductor 18 is at a right angle to the longitudinal extent of the contact tracks 15a and 15b here.

[0031] A supply voltage source 20 is connected to the contact areas 16a and 16b by means of contact lines 17a and 17b. This is known per se from the prior art. The supply voltage source is advantageously a domestic AC mains voltage of 230 V. Use in the automotive sector or in an automobile, that is to say a DC voltage of 12 V or 48 V or even more, is also possible.

[0032] An electrode 22 runs in a meandering manner in six parallel tracks in the area of the heating conductor 18. The tracks can each be at approximately the same distance from one another, but they can also be at different distances from one another, for example for different power densities or in order to be able to evaluate defined regions more precisely. The topmost track and the bottommost track can also run even closer to the contact tracks 15a and 15b. The electrode 22 has, on the left, two electrode connections 23a and 23b. A resistance measuring device 25 is connected by means of electrode lines 24a and 24b. Therefore, the electrical resistance of the electrode 22 can be measured, and the temperature can be determined on account of the temperature dependence of said electrical resistance. For this purpose, the electrode 22 consists of a material mentioned at the outset with a silver content of 10% to 90% or 80% to 90%. However, a material mentioned at the outset can also be used for the electrode.

[0033] It can be seen that the temperature measurement, on account of the temperature-dependent variable electrical resistance of the electrode 22, does not allow local temperature measurement at a single point, but rather temperature measurement as it were distributed or averaged over the area covered by the electrode 22. Leakage current detection, as is known from the prior art mentioned at the outset, is used for local temperature measurement, in particular for detecting dangerous local overtemperatures. The leakage current detection means is then connected by means of the contact lines 17a and 17b and electrode lines 24a and 24b.

[0034] For explanatory purposes, reference is explicitly made to FIG. 2 and primarily to the abovementioned prior art. According to FIG. 2, the carrier 12 has a carrier top side 13 with the layer structure and has a carrier bottom side 14. Here, the carrier bottom side 14 is in contact with water W which is intended to be heated by the heating device 11. The layer structure, produced by means of thick-film technology, on the carrier top side 13 has, as the lowermost layer, said functional insulation 27 of the carrier 12. The electrode 22 is applied to the functional insulation 27 in the desired form. Variations of this form have been explained at the outset and will be described further below with reference to FIGS. 4 to 5. The electrode 22 has, on the right, an electrode connection 23 to which an electrode line 24 is connected, here for example welded. Said electrode line can also be soldered; as an alternative, contact-connection by means of pressed-on contacts or by means of a clamping plug is possible.

[0035] The electrode 22 is covered by an insulation layer 29 which has the dielectric properties mentioned at the outset. These include that, at a specific relatively high temperature, for example 350° C. to 400° C., the electrical resistance drops sharply and a leakage current can flow. Here, this leakage current can flow from the heating conductor 18 applied to the insulation layer 29 to the electrode 22. The heating conductor 18 in turn has, on the right, a contact area 16 applied to it, which contact area can be connected by means of a contact line 17. At this temperature, there is a risk of permanent damage if it prevails over a time period of more than 1 minute or more than 20 seconds.

[0036] A covering layer 31 is in turn applied to the heating conductor 18. Said covering layer leaves out the contact area 16 for subsequent attachment of the contact line 17, similarly to the way in which, when applying the insulation layer 29, the electrode connection 23 remains free. The covering layer 31 serves to protect the structure of the carrier device 11 to the outside, in particular to protect the heating conductor 18 against the surrounding atmosphere and in particular against oxidation.

[0037] At this point, the functional principle of the leakage current measurement and temperatures at which it can be carried out are not discussed further here since this can be sufficiently gathered from the prior art. With reference to FIG. 1, this means that the leakage current flows from the heating conductor 18 to the electrode 22 at a particular hotspot of the insulation layer 29 between the two. No leakage current or no appreciable leakage current flows in the range considerably below said critical temperature.

[0038] Measurement of the temperature of the heating device 11 by way of the temperature-dependent electrical resistance of the electrode 22 can take place at any time. This can advantageously also take place at the same time as the leakage current monitoring.

[0039] FIG. 3 shows an alternative structure. The heating device 111 with a carrier 112 has three parallel contact tracks 115a, 115ab and 115b on the carrier top side. Said contact tracks have, on the left, respective contact areas 116a, 116ab and 116b. This is still similar to the case as in FIG. 1. A continuous area can be covered by the heating conductor 118, that is to say from the upper contact track 115a down to the lower contact track 115b. The middle contact track 115ab runs in the middle and forms a kind of intermediate tap. Depending on the application of a supply voltage to the contact areas 116a, 116ab and 116b, the two heating conductors 118a and 118b can be connected in series or in parallel with one another, possibly also at different supply voltages, as partial heating conductors.

[0040] An upper electrode 122a runs in a single loop above the upper partial heating conductor 118a between the contact track 115a and the contact track 115ab. Said upper electrode can be electrically contacted, on the left, via two electrode connections 123a and can be connected, for example in accordance with FIG. 1, to a resistance measuring device, not illustrated here. Similarly, a leakage current detection means can be connected in the abovementioned way. A lower electrode 122b of identical design runs above the lower partial heating conductor 118b between the contact track 115ab and the contact track 115b. Said lower electrode can be electrically contacted via electrode connections 123b, provided on the left, in said way. Therefore, not only is leakage current detection possible via the two partial heating conductors 118a and 118b, but also respective detection of the absolute temperature.

[0041] A further alternative structure of a heating device 211 according to the invention is shown in FIG. 4. Four parallel strip-like partial heating conductors 218a, 218b, 218c and 218d are provided here. They are connected to one another in series by means of contact tracks 215 and have two contact areas 216a and 216b. In turn, two electrodes, specifically an upper electrode 222a and a lower electrode 222b, are provided. The upper electrode 222a runs, as it were, in a loop virtually entirely centrally along the two partial heating conductors 218a and 218b. Said upper electrode can be electrically contacted via electrode connections 223a at its ends. In a similar way, the lower electrode 222b runs along virtually the entire length of the two lower partial heating conductors 218c and 218d. Said lower electrode is electrically contacted by means of electrode connections 223b at its ends. Therefore, here, leakage current detection is possible in two regions since there are just two electrodes 222a and 222b separated from one another. Similarly, even though the four partial heating conductors are always operated in the same way in series, temperature measurement can take place by way of the temperature-dependent electrical resistance of the electrodes 222a and 222b both in the upper half and in the lower half separately.

[0042] A yet further alternative structure of a heating device 311 is shown in FIG. 5. Two spaced-apart and parallel partial heating conductors 318a and 318b are provided on a carrier 312 with a carrier top side 313, in a seemingly simplified manner in relation to FIG. 4. Said partial heating conductors are connected, on the right, by means of a contact track 315. At the left-hand side ends, said partial heating conductors can be electrically connected in the abovementioned manner by means of a short contact track 315 and contact areas 316a and 316b. The distance between said partial heating conductors is relatively large, but can also be smaller, in particular even only twice to four times the width of a single partial heating conductor.

[0043] Similarly to the situation in FIG. 4, an outer electrode 322a runs over virtually the entire length both of the upper partial heating conductor 318a and of the lower partial heating conductor 318b. In so doing, it also runs below the right-hand-side contact track 315 where, however, a leakage current is not expected. Nevertheless, temperature measurement can also take place here. This outer electrode 322a can be electrically contacted by means of contact areas 323a.

[0044] An inner electrode 322b with two electrode connections 323b runs in a loop within the free area between the two partial heating conductors 318a and 318b. Said inner electrode can also be used for leakage current measurement, where it can hardly be assumed that a leakage current occurs on the inner electrode 322b given this large distance from the partial heating conductors 318a and 318b. For this purpose, the outer electrode 322a is finally provided. The inner electrode 323b can be provided exclusively for temperature measurement. Said inner electrode can advantageously be applied in the same production step as the outer electrode 322a, so that a temperature measuring device or a kind of temperature sensor can thus be created in the same step in which the outer electrode 322a required for leakage current detection is also applied. All of the layers, as can be seen in FIG. 2, are advantageously applied by thick-film processes, in particular by means of screen printing. Therefore, the complexity of the method is very low, and costs are incurred substantially only due to the additional electrode material. Furthermore, owing to this inner electrode 322b, temperature measurement somewhat at a distance from the partial heating conductors 318a and 318b is possible, this being regarded as advantageous. Therefore, corruption of a temperature, for example a temperature of the water heated by the heating device 311 similarly to FIG. 2, due to the inherent relatively high temperature of the heating conductor is reduced per se or even prevented.

[0045] FIG. 6 shows, in a simplified manner, a heating device 11 with a carrier 12, in which heating device a heating conductor 18 of large surface area runs between two contact tracks 15, similarly to FIG. 1. Various possible designs of electrodes 22A to 22E are applied in the area between the contact tracks 15. Said electrodes are each illustrated only in a manner reduced in size and by way of example for basic illustration. Said electrodes have two electrode connections 23. There could also be at least two electrode connections in the sense that an additional center tap would possibly still be present.

[0046] The electrode 22A is of sheet-like design. Even though said electrode is shown with only a small surface area here, in particular covers a smaller area than the area of the heating conductor 18 between the two contact tracks 15, it can have a considerably larger surface area in practice. In particular, said electrode can take up virtually the entire area of the heating conductor 18 between the two contact tracks 15. Therefore, the electrode 22A is an example of a sheet-like design or design of large surface area.

[0047] The electrode 22B is designed in a similar manner to in FIG. 1. Said electrode is relatively narrow and meandering and long. The electrode 22C is of sheet-like design similarly to the electrode 22A and somewhat larger.

[0048] The electrode 22D is of elongate design but considerably wider than the electrode 22B and also the narrow electrode 22E above it. Said electrode is intended to illustrate that an elongate electrode that is designed as an electrode track can also have a certain width. The width can be provided so that the electrode covers a certain area or so that it has a certain quantity of resistance material, that is to say it has a certain electrical resistance, given a defined or prespecified thickness. Therefore, the width of the electrode can be used as a parameter for achieving a specific electrical resistance given a prespecified resistance material.