EP3096585A1 - Heating device for heating fluids and a method for operating such a heating device - Google Patents

Abstract

A heating device for heating liquids, comprising: a flat carrier having a surface on which heating elements are arranged distributed over a surface and are divided into a plurality of separately operable heating circuits, a temperature sensor device with a sensor layer which covers the surface of the heating elements, wherein the Sensor layer at least two sensor electrodes are applied in an electrode layer, which are electrically separated from each other and finger-like or winding-like sensor electrode sections which extend at a distance of less than 2cm to each other, wherein the width of each two juxtaposed sensor electrode sections is less than 2cm, and a Control device for evaluating the temperature sensor device.

Description

Field of application and state of the art

The invention relates to a heating device for heating fluids, in particular liquids, and a method for operating such a heating device.

From the WO 02/12790 A1 a cooking appliance with steam generation by means of a heating device is known, which has a steam generating container in the form of a vertical tube. Outside of the steam generating container, a flat heating element is arranged. A water supply to the steam generator tank is from below, while the generated steam can escape upwards and is used in the cooking appliance for steam cooking.

From the WO 2007/136268 A1 and the DE 102013200277 A1 It is known to carry out a temperature detection over a dielectric insulating layer in heaters with flat distributed heating elements. In this case, the so-called leakage current or leakage current is measured at electrodes, which flows through the insulating layer of the heating elements. This insulating layer has a decreasing with increasing temperature electrical resistance. For example, local overheating can be detected over a large area without the need for temperature sensors as discrete components.

Task and solution

The invention has for its object to provide an aforementioned heating device and a method for their operation, with which problems of the prior art can be solved and it is in particular possible, a temperature or an excess temperature at a heating circuit of the heater or at the to capture the entire heater safely.

This object is achieved by a heating device with the features of claim 1 and by a method having the features of claim 11. Advantageous and preferred embodiments of the invention are the subject of further claims and are explained in more detail below. Some of the features are described only for the heater or only for the method. However, they should be independent of both the heater as well as for the procedure independently. The wording of the claims is incorporated herein by express reference.

It is envisaged that the heating means for heating fluids, in particular for heating liquids to operate a steamer, has the following features. It has a flat carrier with a surface, wherein the carrier may be either substantially or completely flat as a kind of plate. Alternatively, the support may be bent and particularly advantageously a closed tube or a tubular container in which the fluid to be heated is located. On the surface of the carrier, advantageously on an outer side, which does not come into contact with the fluid to be heated, heating elements are arranged distributed over a surface. They advantageously cover a large part of the carrier or its surface, preferably at least 50% or even at least 70%. The heating elements are divided into one or more separately operable heating circuits. Each heating circuit has at least one heating element, in which case a heating element is thus to be understood as a section of a heating circuit. Particularly advantageously, each heating circuit has a plurality of individual heating elements which are connected together in parallel, series or mixed or can be interconnected.

Furthermore, a temperature sensor device is provided with a sensor layer, which is advantageously electrically insulating. The sensor layer is applied with a surface which covers at least the surface of the heating elements, particularly advantageously completely covered. It can be provided that the sensor layer is formed over the entire surface and closed. It is preferably applied above the heating elements, and if it is preferably applied directly to the heating elements, it should be electrically insulating. This sensor layer has the abovementioned temperature-dependent properties with respect to its electrical resistance, that is to say it is a type of sensor element. Particularly advantageous is formed as in the aforementioned prior art of WO 2007/136268 A1 and the DE 102013200277 A1 described with a large drop in resistance at temperatures of 200 ° C to 300 ° C, for example from about 250 ° C. These temperatures are considered critical for such heaters. If exceeded, the heater may otherwise be damaged or destroyed.

At least two sensor electrodes are applied to the sensor layer, advantageously in an electrode layer, specifically directly on the sensor layer. These two sensor electrodes are electrically separated from each other and, unlike the sensor layer, are not simply large in area formed, but have finger-like or winding-like and elongated sensor electrode sections. These sensor electrode sections extend at a distance of less than 2 cm from one another, advantageously less than 1 cm or even less than 0.5 cm, for example only 1 mm to 3 mm. In sections, the sensor electrode sections should have the same width or constant width. The width of two juxtaposed sensor electrode sections, ie of one of the two sensor electrodes, is advantageously less than 2 cm. Particularly advantageously, it is less than 1 cm and more than 1 mm.

Finally, a control device for evaluating the temperature sensor device is provided. This control device can be provided only for the temperature sensor device. Alternatively, it may be provided in a controller for the other heater or the entire electric appliance in which the heater is installed. Then, a good interaction with the operation of the heater is possible due to information or data from the temperature sensor device. However, it may also be provided a separate control device only for the temperature sensor device or only for the heater.

By providing two sensor electrodes in the temperature sensor device, which together cover the surface of the heater or at least the heating circuits, a surface monitoring of local overheating or overheating, so-called hot spots, is possible, which is not actually possible with individual discrete temperature sensors , Such local overtemperatures usually have a maximum expansion range of 2 cm to 3 cm with very high critical temperatures, so that a very narrow network of discrete temperature sensors would have to be applied. By providing two sensor electrodes, increased fault tolerance or two-fault safety can be achieved. Even if one of the two sensor electrodes fails or is damaged, over-temperature monitoring is still possible so that the heater can continue to operate. In addition to increased reliability and fault tolerance, a significantly improved safety can be achieved in detecting such an excess temperature. Namely, if both sensor electrodes detect an increased fault current, then such an over-temperature actually occurs in an area with a very high probability.

In an advantageous embodiment of the invention can be provided that juxtaposed sensor electrode sections of the two sensor electrodes are parallel to each other. Advantageously, they also have the same or constant width, a sensor electrode section should therefore have the same and constant width. Particularly advantageous alternate sensor electrode sections of the two sensor electrodes, so are arranged alternately side by side.

In an embodiment of the invention, it is possible to divide the temperature sensor device into a plurality of, at least two, and preferably three, detection regions. The division should be such that each detection area corresponds to a heating circuit or is assigned to a heating circuit. This is advantageous in that a detection area is congruent with a heating circuit. Thus each area of each heating circuit is individually monitored for overtemperature.

In one embodiment of the invention, the sensor electrode sections may extend in the manner of elongated tracks on the carrier, so to speak bifilar. The sensor electrode sections of the two sensor electrodes again run parallel to one another and next to one another or alternately. Particularly advantageously, its course corresponds to a so-called meander shape in a flat carrier. In the case of a carrier in tubular form, the sensor electrode sections with a bifilar course can also correspond to fully rotating turns with a spiral course.

In an alternative embodiment of the invention, the sensor electrode sections may be formed so that they mesh in a comb-like manner or in a comb-like manner, in areas that overlap with the heating circuits, as described above. Here, too, the sensor electrode sections of the two sensor electrodes should be arranged alternately.

As a result of the arrangement of the sensor electrode sections alternately next to one another and close to one another, it is possible for a region with an excess temperature to cover, so to speak, sensor electrode sections of both sensor electrodes due to their local extent. Thus, the overtemperature can actually be detected on both sensor electrodes and thus with double certainty.

In the interlocking configuration of the sensor electrode sections, the sensor electrode sections may advantageously be designed in the manner of fingers. They may protrude from continuous and substantially obliquely or at right angles thereto base portions of the sensor electrodes. On the surfaces of the heating circuits can relate the continuous base portions extend at opposite end portions of a surface monitored by the sensor electrodes and the sensor electrode portions extend toward these base portions. In this case, the sensor electrode sections of one sensor electrode can reach from its base section to shortly before the base section of the other sensor electrode, particularly advantageously at a distance of 1 mm to 10 mm. This distance can also be the same distance as between two adjacent sensor electrode sections, particularly preferably it is the same.

It is particularly advantageous if the width of the sensor electrode sections of a respective sensor electrode remains the same in the region of a heating circuit. This preferably applies to exactly one heating circuit. If, in fact, all the sensor electrode sections of both sensor electrodes are of equal width, the total presence of an excess temperature can be recognized with twice the reliability of error, but localization is not possible. However, if the sensor electrode sections of the two sensor electrodes have different widths in an area over at least one heating circuit, preferably with a difference of between 10% and 500%, then even with only two sensor electrodes an overtemperature occurring can occur at least one heating circuit or one area above a heating circuit of each be assigned to several. This can be done by measuring the leakage currents or fault currents at both sensor electrodes and setting them in relation to one another. If the widths of the sensor electrode sections of the sensor electrodes differ significantly, for example, the width of only one 50% of the width of the other, then due to the higher surface coverage of the sensor layer at the sensor electrode with the wider sensor electrode sections and the much larger leakage current can be detected. If the widths of the sensor electrode sections are below the aforementioned 1 cm, then it is to be assumed that a region of excess temperature covers at least two adjacent sensor electrode sections and generates a fault current dependent thereon from the overlap surface. If, then, the fault current is significantly greater at one sensor electrode than at the other, the overtemperature will be present in the region of the heating device in which this sensor electrode has the wider sensor electrode sections.

Advantageously, the widths of the sensor electrode sections should differ by at least 50%, particularly advantageously by at least 100%. Then a safe distinction is possible, even if the area with the excess temperature is not equal to the two sensor electrodes or their sections is distributed.

In a preferred embodiment of the invention, the heating device may have three heating circuits.

In the region of one of the heating circuits, the sensor electrode sections of both sensor electrodes can have the same width. Thus, if approximately equal fault currents are detected at both sensor electrodes, then there is an excess temperature in this area or at the corresponding heating circuit. In the region of the other two heating circuits, the sensor electrode sections of the two sensor electrodes may each have different, advantageously significantly different, widths. Thus, even in the case that a significantly larger fault current is detected at one sensor electrode than at the other, it is possible to distinguish the presence of the excess temperature at one of these two heating circuits. A subdivision into even more than three areas or heating circuits is possible. At the same time, however, the good and certainty of distinctness as regards the location of the overtemperature is decreasing.

For good coverage of the heating circuits and, above all, for differentiation with sensor electrode sections of different widths, it is considered advantageous if, over each heating circuit, each sensor electrode has at least two sensor electrode sections, preferably at least three. Then, the widths of the respective sensor electrode sections are not so large, and it is ensured that an excess temperature at least two, advantageously at least three, sensor electrode sections by the increase of the fault currents.

On the one hand, it is possible, as described above, to make the support flat, for example as a kind of plate, and to connect to a container or channel, in particular thermally connect, in which a fluid to be heated, in particular a liquid, or flows therethrough. Examples of this are in a boiler and in a kettle as a floor.

On the other hand, the carrier of the heating device is particularly advantageously designed as a tube and thus a container for liquid to be heated by this, so to speak permanent. It is evaporated by heating, for example for use in a steamer. By the contact with the fluid, in particular a liquid, the heat can generally be removed very well from the heating elements of the heating circuits. Only when problems arise here or, for example, when heating water occur calcifications that worsen the decrease of heat, the aforementioned excess temperatures can occur. This is just to recognize and then to avoid the operation with such an excess temperature, otherwise a permanent damage to the heater may occur. In a tubular support, the heating circuits are advantageously separated along the longitudinal axis of the tube educated. They should largely revolve around the carrier, advantageously in the manner of a sleeve, so that the largest possible area of the carrier is covered with the heating circuits or their heating elements for the best possible and uniform power input. It is possible that the sensor electrode sections extend to a large extent, in particular all sensor electrode sections, at a right angle to the longitudinal axis of the tube. In particular, when water is to be heated with the heater, the sensor electrode sections, possibly also the heating elements of the heating circuits should run parallel to a water surface. Thus, a meaningful division of the heating circuits for coordinated heating depending on the level in the pipe is possible.

An overtemperature can generally be detected when a fault current at a sensor electrode increases by at least 10% to 50% or is more than 10 mA to 50 mA. Should it rise only at one sensor electrode, then there is very likely to be a fault with the other sensor electrode. This should be signaled to a user and then after a certain time, if the user does not intervene, for example, after one minute to five minutes, the heating power can be reduced or even completely shut off.

In an embodiment of the invention, it is possible for two protective circuits each having two resistors to be arranged in an electrical input circuit of an evaluation for the temperature sensor device. As a result, the evaluation or a corresponding control device can be protected.

In a further embodiment of the invention, it is possible to perform a short circuit or cable breakage test. In this case, a high-frequency signal can be fed into one of the two sensor electrodes. This is advantageously done via a capacitive decoupling means of a capacitor or the like. The signal is then read back via the other of the two sensor electrodes by means of a control device and should correspond to the fed signal when the temperature sensor device is functioning. If a deviation of the signal shape and / or the signal level is detected by, for example, at least 5%, this is regarded as an error. Then, a signal can be output to a user and the operation of the heater can be changed, in particular, a power reduction is made, or an entire heating circuit or even the entire heater is turned off.

These and other features are apparent from the claims and from the description and drawings, wherein the individual features in each case alone or to several be realized in the form of sub-combinations in one embodiment of the invention and in other fields and can represent advantageous and protectable versions for which protection is claimed here. The subdivision of the application into individual sections and intermediate headings does not limit the statements made thereunder in their generality

Brief description of the drawings

• Fig. 1 eine Draufsicht auf eine erfindungsgemäße Heizeinrichtung mit drei nebeneinander angeordneten Heizkreisen mit Heizelementen und einer Temperatursensoreinrichtung,
• Fig. 2 eine schematisierte Ansicht der Heizeinrichtung aus Fig. 1 mit detaillierter Darstellung der Temperatursensoreinrichtung samt deren Ansteuerung,
• Fig. 3 eine Abwandlung der Heizeinrichtung aus Fig. 2 mit unterschiedlich breiten Sensorelektrodenabschnitten und
• Fig. 4 in weiterer Abwandlung eine Heizeinrichtung entsprechend Fig. 1 mit anders ausgebildeter Temperatursensoreinrichtung.

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

• Fig. 1 a top view of a heating device according to the invention with three heating circuits arranged side by side with heating elements and a temperature sensor device,
• Fig. 2 a schematic view of the heater off Fig. 1 with detailed representation of the temperature sensor device including its control,
• Fig. 3 a modification of the heater Fig. 2 with different width sensor electrode sections and
• Fig. 4 in a further modification, a heating device accordingly Fig. 1 with differently designed temperature sensor device.

Detailed description of the embodiments

In the Fig. 1 an upright heater 11 according to the invention is shown, comprising a round cylindrical tubular container 12 made of metal. On an outer side 13 of the container 12, strip-like heating elements 15 are provided which, as shown, run along approximately 75% to 90% of the outer circumference of the container 12. Upper heating elements 15a and the uppermost heating element 15a 'form an upper heating circuit 16a. Middle heating elements 15b form a middle heating circuit 16b, and lower heating elements 15c form a lower heating circuit 16c. Here, the middle heating elements 15b of the middle heating circuit 16b and the lower heating elements 15c of the lower heating circuit 16c and the heating circuits 16b and 16c are formed identical to each other. The upper heating circuit 16a is different in that than that here the uppermost heating element 15a 'at a distance of about 60% of a width of the normal heating elements 15a extends over it, so having increased distance.

The heating circuits 16a to 16c are electrically contacted via contact fields 18, specifically the upper heating circuit 16a via the contact fields 18a and 18a '. The middle heating circuit 16b has the contact fields 18b and 18b ', and the lower heating circuit 16c the contact fields 18c and 18c'. Furthermore, additional contacts 20a 'and 20a to 20c are provided, specifically for the middle heating circuit 16b and the lower heating circuit 16c, in each case one additional contact 20b or 20c. The upper heating circuit 16a has an auxiliary contact 20a with an arrangement similar to the middle heating circuit 16b. At the top heating element 15a 'is still another additional contact 20a' is provided.

In the left-hand area, SMD temperature sensors 21a to 21c, which form the discrete temperature sensors described above, are provided on the heating circuits 16a to 16c. For each SMD temperature sensor 21a to 21c, two temperature sensor contact pads 22a and 22a ', 22b and 22b' and 22c and 22c 'are provided. They are completely separated electrically from the heating circuits 16a to 16c. While these discrete temperature sensors are well suited for determining the temperature of the water in the heater 11, they are not suitable for locating a region of overtemperature. In addition, their surveillance area is far too small.

In the middle of the container 12, a strip region 27 is provided along its longitudinal axis, in which a weld 28 extends, since the tubular container 12 is formed from a sheet and the adjacent edges are welded together. At the bottom of the container 12, a so-called outer side contact 30 is mounted, for example, for grounding.

As already explained, it is either possible to produce a dielectric sensor layer on the heating elements 15 or the heating circuits homogeneously or from the same material or glass. Alternatively, however, two differently conductive materials or glasses can be used. These can even be superimposed and / or applied to each other, each of which must be contacted individually. The sensor layer forms, as it were, a planar, temperature-dependent electrical resistance which has a very high electrical resistance at temperatures up to about 80 ° C., this temperature being adjustable, and thus no current flows via the insulating layer. If the temperature continues to increase even in a small range and reaches, for example, 100 ° C., the electrical resistance decreases. At temperatures of for example 150 ° C or 200 ° C, the resistance have decreased so far in this small area that, although still the electrical insulation properties are given sufficient to operate the heating circuits 16a to 16c easily. However, it is already possible to reliably detect a leakage current or fault current which can flow in the range of these temperatures.

To such high and significantly above 100 ° C temperatures may occur during operation of the heater 11 or a vaporizer provided with it and the evaporation of water actually only when on the one hand by emptying no more water or on the other hand by strong calcification on a Place the heat loss is no longer large enough, so that it comes to overheating. In the first case that there is generally no more water in such a region, a countercheck can be made with the state of the respective SMD temperature sensor 21a to 21c, especially the uppermost temperature sensor 21 a. If this also determines a temperature of over 100 ° C, then obviously the level of the water has dropped. If, however, even the uppermost SMD temperature sensor 21a still determines a temperature of at most 100 ° C., then a significantly higher temperature, determined by the sensor electrodes together with the sensor layer 25, than overtemperature due to excessive calcification on the inside of the container 12 in front. Depending on the size of the area or on the amount of excess temperature, the corresponding heating circuit 16 can continue to be operated or switched off. In any case, an initially described signaling to an operator to make attentive that the heater 11 and the evaporator must be descaled.

The highly schematic representation of the heater 11 in the Fig. 2 should be, so to speak, a plan view of the carrier in the unwound state or if the support tube of the container 12 would be cut, so it lies flat. Evident are the three heating circuits 16a to 16c, wherein the subdivision into the individual heating elements is not shown here, because it plays no role for this aspect of the invention. The contacting of the control of the heating circuits 16a to 16c is not shown here. Only for the heating circuit 16c whose contact fields 18c and 18c 'are shown schematically. From this Fig. 2 It can be clearly seen that the three heating circuits 16a to 16c occupy separate areas.

On the heating circuits 16a to 16c, the temperature sensor device 30 is applied, namely first the entire surface of the aforementioned sensor layer 32 directly to the heating circuits 16. This sensor layer 32 has at least the surfaces of the three heating circuits 16a to 16c, it is advantageous a full-surface or continuous sensor layer. It may, for example, slightly overlap the surfaces of the heating circuits 16a to 16c and extend to or just before the edge of the container 12 as a carrier. The sensor layer is applied directly to the heating circuits 16 a to 16 c and consists of an aforementioned electrically insulating material, advantageously a known from the prior art glass material. This is at room temperature and also at temperatures in the operation of the heater 11 for cooking or evaporation of water, ie about 100 ° C, electrically insulating with a nearly infinite electrical resistance. In the case of the aforementioned excess temperatures above 150 ° C., advantageously between 200 ° C. and 300 ° C., the electrical resistance and a prescribed fault current, also referred to as the leakage current, can pass through the sensor layer 32. Such overtemperatures can occur if there is no longer any water either in the region on a heating element or on a heating circuit 16a to 16c which reduces the heat generated. Alternatively, a strong calcification may have come about on the inside of the container 12, which also makes a heat loss difficult. Typically, the areas of such overtemperatures have a diameter between 0.5cm and 1.5cm to a maximum of 2cm when the container 12 is about 20cm to 30cm long and has a diameter of about 6cm to 10cm. Very small local excess temperatures occur more rarely, since here the thermal cross-conduction of the container 12 ensures sufficient heat distribution. Significantly larger areas with excess temperature also occur very rarely, because then in their central area already much earlier an overtemperature would have occurred, which should be detected and prevented.

In turn, sensor electrodes 34a and 34b are applied to the sensor layer 32, specifically in an electrode layer. The sensor electrodes 34a and 34b are separated from each other at a distance of 1 mm to 3 mm or a maximum of 5 mm. In principle, the sensor electrodes 34a and 34b have the same configuration, and the sensor electrode sections 37ac, 37ab and 37aa and 37bc, 37bb and 37ba come off each other from a base-side base section 36a and 36b. Their width is about 5mm to 1.2cm. A comb-like structure of the interdigitated sensor electrode sections 37 is created. It can be seen that these sensor electrode sections 37 cover the surfaces of the heating circuits 16a to 16c in a fairly accurate manner, and no overtemperatures can occur in the gaps or next to the heating circuits anyway. Shown here are each three sensor electrode sections 37 of the two sensor electrodes 34a and 34b of the temperature sensor device 30 per heating circuit 16. But it could also be more sensor electrode sections 37. It should not be less than two. It can also be seen that all Sensor electrode sections 37 have the same width and the same distance from each other.

Sensor leads 39a and 39b of the sensor electrodes 34a and 34b lead to protection circuits 41a and 41b, respectively. Each of these protection circuits 41 a and 41 b has two series-connected resistors R1a and R2a and R1b and R2b. Behind each are connected a diode Da and Db and a Zener diode ZDa and ZDb. The protection circuits 41a and 41b are connected to a possibly remote control device 43 for evaluation of the temperature sensor device 30. Thus, it is possible that the protection circuits 41a and 41b are even arranged on the container 12 as a carrier, but the control device is separate and is combined or integrated, for example, with a control for an entire electrical appliance in which the heating device is installed.

The control device 43 has series resistors and precondensers upstream of a microcontroller 44. Downstream of the microcontroller 44 is a further circuit, which leads to outputs L, SL, SN and N.

In the heating circuit 16a an overtemperature region 46 is located. Its center lies above the central sensor electrode section 37ba, but also simultaneously overlaps the central sensor electrode section 37aa and also the one to the left thereof. Thus, a fault current ib and ia can be registered at both sensor electrodes 34a and 34b. These fault currents ia and ib flow depending on the change in resistance of the sensor layer 32 in the overtemperature region 46. However, not only does the areal coverage of the over-temperature region 46 over the sensor electrode sections 37 count, but also the respectively existing temperature. If a detected fault current exceeds a fault current threshold that has been set, this is detected as an overtemperature and triggers an error. In this case, a signal can be output, possibly also a prescribed reduction of the heating power or even a shutdown can be made. A fault current should not exceed 0.7mA. A fault current threshold may be selected to be, for example, 0.2mA to 0.5mA.

From the Fig. 2 It can also be seen that even with one of the sensor electrodes 34a or 34b or their sensor electrode sections 37, a case of such an overtemperature or an excess temperature region 46 could be detected. Thus, a two-fault safety can be achieved, the temperature sensor device 30 thus only works with one of them Temperature sensors. The two protective resistors in the protective circuits 41 serve to avoid damage or electrical destruction of the control device 43 in the event of a fault. The Zener diodes ZD limit the sensor voltage to low signal level.

Based on Fig. 2 It is also easy to see that in each case two such sensor electrodes with comb-like interdigitated sensor electrode sections could be provided separately for each heating circuit 16. Then, however, both the connection costs and the cost of the protective circuits and on the control device 43 triples, at least with respect to their wiring. In this respect, this is possible, but associated with significant additional effort. Nevertheless, it would of course be desirable to be able to limit such a case of an excess temperature range to the corresponding heating circuit 16, so that only this can be reduced in power or switched off. A power reduction can, for example, take place so far that while heating power is still generated and heat is introduced into the fluid to be heated, but just a dangerous excess temperature no longer exists.

In order to enable this possibility of locating an over-temperature range for one of the heating circuits, the configuration of sensor electrodes 134a and 134b corresponding to the heater 111 in the case of FIG Fig. 3 to get voted. Both sensor electrodes 134a and 134b correspond to FIG Fig. 2 Sensor leads 139 a and 139 b and base portions 136 a and 136 b on. However, the sensor electrode portions 137 projecting therefrom are formed differently.

Above the rightmost heating circuit 116a, the three sensor electrode portions 137aa projecting downward from the base portion 136a of the sensor electrode 34a are relatively thin and narrower than in FIG Fig. 2 , On the other hand, the respective sensor electrode portions 137ba of the other sensor electrode 134b, which are upwardly projected from the lower base portion 136b, are wider than those in FIG Fig. 2 in the embodiment shown here they are about twice as wide. Above the middle heating circuit 116b, the respective sensor electrode portions 137ab and 137bb are the same width. Above the left heating circuit 116c, the conditions are reversed as above the right heating circuit 116a. The top-to-bottom sensing electrode portions 137ac are significantly wider and, in particular, twice as wide as the bottom-up sensor electrode portions 137bc.

As a result of this configuration of the widths of the sensor electrode sections via a respective one of the heating circuits 116, the sizes of the fault currents ia and ib can be compared with one another and the conclusion drawn in the area of which heating circuit 116 there is an excess temperature region 146. Namely, an over-temperature region 146 is again corresponding to the Fig. 2 has occurred over the right heating circuit 116a, so due to the greater width of the sensor electrode sections of the sensor electrode 134b whose affected by the overtemperature or covered area is much larger. Thus, the fault current ib will be significantly greater than the fault current ia, for example, about twice as large. By a correspondingly differently selected size ratio, in particular 2: 1 as here or even more different, cases can be clearly identified in which a center of the overtemperature region is indeed directly over a narrower sensor electrode section 137, but just significantly larger surface areas of the sensor electrode sections of covered by another sensor electrode.

If the fault current ia is significantly greater than the fault current ib, an over-temperature range will probably be above the left-hand heating circuit 116c. If the two fault currents are approximately the same, then an excess temperature range will probably be above the middle heating circuit 116b. As stated above, after detecting the affected heating circuit, its power can be reduced, for example, by 20% to 50%. Then, in most cases, the temperature in the overtemperature region will still be higher than usual, but no longer in a critical range. Incidentally, this achievement of a critical area could certainly and definitely be recognized. Thus, the heating power of the entire heater need not be reduced or switched off.

By dividing the size ratios of the sensor electrode sections to one another, even more than three surface areas could be monitored or distinguished. However, this makes little sense in a heater shown here with three heating circuits. It would only make sense if more heating circuits were available or if they were again subdivided among each other. At the same time, however, it should also be noted that the safety of detecting an overtemperature should in any case take precedence over, so to say, additional functions such as the localization of the overtemperature. In any case, a localization of an overtemperature shown here is easily possible because the fault currents ia and ib are approximately proportional to the area ratios of the respective sensor electrodes.

Furthermore, it is also easy to see how an aforementioned short-circuit or cable break test can be performed. For this purpose, a correspondingly suitable high-frequency signal from the frequency connection 149 is fed to the microcontroller 144 via a coupling 150 by means of the sensor feed line 139b into the sensor electrode 134b. The coupling 150 has a capacitor for capacitive decoupling. The signal can then be read back via the other sensor electrode by means of the control device 143, via its normal connection. If no signal comes back or a significantly changed, for example, by at least 5% to 25% changed, so there is an error. This corresponds to a conventional short-circuit or cable break test. This can either lead to power reduction or to switch off the heating device 111 or at least to output a corresponding error message to a user, advantageously optically and / or acoustically. In the Fig. 4 a further heater 211 is shown, not in the unwound state of the support tube as in the Fig. 2 and 3 , but as a support tube accordingly Fig. 1 per se. While at the Fig. 2 and 3 the sensor electrode sections are configured comb-like or finger-like interlocking, extending sensor electrode sections 237a and 237b of sensor electrodes 234a and 234b continuously side by side, so to speak bifilar. Three heating circuits 216a, 216b and 216c are also applied here to a container 212 or its outer side 213 in separate regions. The sensor electrode sections 237a and 237b run, so to speak, into two double turns via one of the heating circuits 216. The free strip between two heating circuits is directly crossed by the sensor electrode sections, which in practice does not have to be rectangular, as shown here, but can also be oblique.

Again, it can be seen that the sensor electrode sections 237a and 237b, similar to the Fig. 2 and 3 , Cover substantially the entire surface of the heating circuits 216a to 216c, so can monitor for excess temperatures. This can also be made even better in terms of area. Would the heater 211 an over-temperature range as in the Fig. 2 and 3 It could also be detected by the sensor electrode sections 237a and 237b.

The constant width of the sensor electrode sections 237, which is the same here in each case and which is the same for both sensor electrodes 234a and 234b, corresponds approximately to Fig. 2 Thus, it is not possible to localize an over-temperature range over one of the heating circuits. By way of derogation, the widths of the sensor electrode sections 237a and 237b extending thereabove in the region of one of the heating circuits 216a to 216c, respectively, could be determined in accordance with FIG Fig. 3 vary. Thus, above the heating circuit 216a, the sensor electrode sections 237b may be twice as wide as the sensor electrode sections 237a, over the heating circuit 216b they may be the same width, and above the heating circuit 216c, the sensor electrode sections 237a may be twice as wide as the sensor electrode sections 237b. How to Fig. 3 described, by comparing the magnitudes of the fault currents that can be detected at the sensor electrodes 234a and 234b and their sensor leads 239a and 239b, the localization of an over-temperature region again take place.

Also in the heater 211 of Fig. 4 should a distance between the sensor electrode sections 237 always be the same and, furthermore, relatively small, for example between 1 mm and 3 mm.

Claims (16)

Heating device for heating fluids, characterized by : a flat carrier with a surface, Heating elements distributed on the surface of the carrier, - The heating elements are divided into one or more separately operable heating circuits, a temperature sensor device with a sensor layer which covers at least the surface of the heating elements, on the sensor layer at least two sensor electrodes are applied in an electrode layer, the two sensor electrodes are electrically separated from one another and have finger-like or winding-type sensor electrode sections which run with a distance of less than 2 cm from one another, the width of each two adjacent sensor electrode sections is less than 2 cm in each case, - A control device for evaluation of the temperature sensor device. Heating device according to claim 1, characterized in that juxtaposed sensor electrode sections parallel to each other and preferably have the same width. Heating device according to claim 1 or 2, characterized in that the temperature sensor device is divided into at least two, preferably three, detection areas, wherein in particular each detection area corresponds to a heating circuit or is associated with a heating circuit and is congruent with this. Heating device according to one of the preceding claims, characterized in that sensor electrode sections in the manner of elongated paths bifilar, in particular in a meandering form, extend on the support. Heating device according to claim 1 to 3, characterized in that sensor electrode sections mesh in a comb-like manner or are interlocked in areas which overlap with the heating circuits. Heating device according to claim 5, characterized in that the sensor electrode sections protrude in the manner of fingers of continuous base portions of the sensor electrodes, wherein preferably the continuous base sections relative to the surfaces of the heating circuits relative to opposite end portions and in particular the sensor electrode sections of a sensor electrode to the base sections of the other Touch sensor electrode. Heating device according to one of the preceding claims, characterized in that in the region of a heating circuit, the width of the sensor electrode sections in each case a sensor electrode remains the same, preferably exactly one heating circuit. Heating device according to claim 7, characterized in that the ratio of the widths of the sensor electrode sections of the two sensor electrodes to each other in the area over at least one heating circuit is different, preferably between 10% and 500%, in particular the heater has three heating circuits and sensor electrode sections in the region of a heating circuit both sensor electrodes have the same width and in the region of the other two heating circuits sensor electrode sections of both sensor electrodes each have different widths. Heating device according to one of the preceding claims, characterized in that over each heating circuit each sensor electrode has at least two sensor electrode sections, preferably three. Heating device according to one of the preceding claims, characterized in that the carrier is designed as a tube and the heating circuits along the longitudinal axis of the tube separated from each other substantially circumferentially around the carrier are arranged, preferably sensor electrode sections to a large extent, preferably all sensor electrode sections, at right angles the longitudinal axis of the tube. Method for operating a heating device according to one of the preceding claims, characterized in that for detecting a region of the heating elements with an excess temperature, in which a fault current between an electrical conductor, in particular a heating element and / or a metallic carrier, and one of the sensor electrodes exceeds a predetermined threshold value, in each case a fault current is measured at both sensor electrodes and when a fault current threshold value of at least one fault current is exceeded an overtemperature is detected and then a signal is output to a user and / or the operation of the heating device is changed. A method according to claim 11, characterized in that in an electrical input circuit of an evaluation for the temperature sensor device two protective circuits are arranged with two resistors to protect the evaluation. A method according to claim 11 or 12, characterized in that in a heating device according to claim 8, a detection of the location of the overtemperature in the region of one of the heating circuits by comparing the size of the fault currents at the two sensor electrodes, wherein the sizes of the fault currents to each other behave like the sizes of the surfaces of the sensor electrode sections of the sensor electrodes in the region of this heating circuit. Method according to one of claims 11 to 13, characterized in that upon detection of an excess temperature, the operation is changed by at least reducing or switching off the power, in particular the heating circuit, in the area of which the overtemperature has been detected. Method according to one of claims 11 to 14, characterized in that a short-circuit and cable breakage test is performed by a high-frequency signal is fed into one of the two sensor electrodes, preferably via a capacitive decoupling means of a capacitor or the like, wherein the signal on the other the two sensor electrodes is read back by means of a control device, wherein at a deviation of the signal shape and / or signal height by at least 5% an error is detected and a signal is output to a user and / or the operation of the heater is changed. Method according to one of claims 11 to 15, characterized in that a change in the operation of the heater after detecting an excess temperature is at least a reduction in power or a shutdown of the heating circuit, in whose Area the overtemperature has been detected, preferably the entire heater is turned off.

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