CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to German Application No. 10 2012 213 385.2, filed Jul. 30, 2012, the contents of which are hereby incorporated herein in its entirety by reference.
The invention relates to a heating device for heating a medium, in particular a liquid, as well as to an electric appliance having a flow channel for a medium or a liquid, respectively.
A corresponding heating device is known from EP 1152639 A2 which can be configured either as a flat carrier plate or as a flow heater. There, the temperature sensors are attached to the carrier in flat conductor technology or thick film technology, respectively. Since the heating conductors are attached to the carrier as well in thick film technology, but of a different material, two coating steps are required.
The object underlying the invention is to provide an aforementioned heating device as well as an electric appliance provided therewith, by means of which problems of the prior art can be prevented and by means of which in particular a simple and reliable structure of a heating device for a secure and reliable operation can be achieved.
The object is achieved by a heating device as well as by an electric appliance. Advantageous as well as preferred embodiments of the invention are included in the further claims and will be explained in more detailed in the following. Here, some of the features are only described for the heating device or only for the electric appliance. However, regardless thereof, they shall be applicable to both the heating device and the electric appliance. The wording of the claims is incorporated into the content of the description by explicit reference.
It is provided that the heating device heats the medium or the liquid, respectively, either through-flow or past-flow or, in the type of a cooking plate, it may also be a heating for a stagnant medium, for example in a cooking vessel. The heating device comprises a carrier, wherein heating conductors are attached to the carrier and at least a first and a second temperature sensor are arranged on the carrier. The carrier may be configured as generally known, for example be made of an insulating material such as ceramics or the like, as an alternative be made of metal or steel, respectively, with an insulating layer thereon.
According to the invention, a first temperature sensor is arranged close to the heating conductor, whereby predominantly the heating conductor temperature is to be monitored most directly. Here, a distance may be smaller than twice the heating conductor width, advantageously even smaller than one full heating conductor width, or approximately half a heating conductor width. Another measure for the distance of the first temperature sensor to the heating conductor may advantageously refer to the thickness of the carrier instead of to the heating conductor width, i.e. to the path that the heat flow has into the medium starting from the heating conductor on the one hand and on the other hand to the first temperature sensor as a heat transverse conduction in the carrier. Here, the distance of the first temperature sensor to the heating conductor may preferably be smaller than the ten-fold of the thickness of the carrier, advantageously smaller than the five-fold or even only approximately the three-fold of the thickness of the carrier. Naturally, a sufficient electric insulation distance is to be complied with.
According to the invention, the second temperature sensor has a greater distance to the heating conductor than the first temperature sensor, wherein the two temperature sensors do not necessarily have to be arranged close to one another or it does not necessarily have to be the same location of the heating conductor in the vicinity of which the temperature sensors are arranged, respectively. Advantageously, the distance of the second temperature sensor to the heating conductor is more than twice the heating conductor width or even more than the threefold of the heating conductor width, for example the threefold to fivefold. As an alternative, the distance may be such that it is greater than twice the distance of the first temperature sensor to the heating conductor, advantageously approximately the threefold to fivefold.
Similar to the indications made regarding the first temperature sensor, the thickness of the carrier may be consulted as another measure for the distance of the second temperature sensor to the heating conductor, so that a distance to the heating conductor may be greater than the fifteen-fold of the thickness of the carrier. Particularly advantageous, the distance is greater than the thirty-fold of the thickness of the carrier or it is approximately the thirty-fold to fifty-fold of the thickness of the carrier, respectively.
As a result of the different distances of the two temperature sensors to the heating conductor, predominantly the heating conductor temperature may be detected by the first temperature sensor, which is arranged close to the heating conductor. That way, in particular an undesired high temperature may be detected and corresponding counter measures may be initiated, for example a switching-off of the heating device or a reducing of the electric performance. Naturally, due to the small distance, the temperature at the first temperature sensor is influenced essentially by the heating conductor and to a lesser extent by the environment or by the medium to be heated due to the aforementioned short paths for the heat flow.
In turn, the second temperature sensor is located at a greater distance to the heating conductor so that its temperature is determined essentially by the medium to be heated. The aforementioned distances between the second temperature sensor and the heating conductor are generally considered to be sufficient, in particular if the medium is a liquid, so that the heating conductor temperature does not have a direct influence on the temperature measured at the second temperature sensor. First of all, that becomes clear from the indication of the distances regarding the thickness of the carrier.
Advantageously, exactly the two aforementioned temperature sensors are provided on the heating device no further ones. As an alternative, yet another temperature sensor could be provided such that the second temperature sensor and the additional temperature sensor are most distant to one another in the through-flow direction of the medium. Thereby, a heating of the medium flowing through or a heat flow introduced by the heating device, respectively, can be determined.
The temperature sensors may be positive temperature coefficient (PTC) resistors. In an advantageous embodiment of the invention, the temperature sensors are configured as negative temperature coefficient (NTC) resistors, in particular having a most linear characteristic line in a range between 0° C. and 200° C. or 300° C.
In yet another advantageous embodiment of the invention, the first temperature sensor and the second temperature sensor or all temperature sensors, respectively, are identically constructed.
It is preferred if at least one of the temperature sensors is configured as a surface mounted device (SMD) component, advantageously both sensors. As a result of the small construction type, little space is required on the carrier. As a result of their low heat capacity, a very good and rapid temperature detection may be achieved. They may also easily be attached to the carrier by means of SMD technology and they abut the carrier through the soldering connection and the typical SDM construction type for a most good temperature transfer. Here, a temperature transfer can be improved by means of a heat-conductive paste or the like.
In another embodiment of the invention, it can be provided that one or the temperature sensor(s) is/are attached to the carrier not in a fixed manner or not in a permanent manner, i.e. not soldered thereon as described above. They may, for example, be pressed onto the carrier or applied on the carrier by another mounting device and also be electrically contacted by means of the mounting device. That way, a step of soldering the temperature sensors to the carrier may be omitted.
In another embodiment of the invention, the first temperature sensor may be configured to be elongate and extend essentially parallel to a longitudinal course of that heat conductor that it has the shortest distance to. The arrangement of the temperature sensor is advantageous in that now the heat flow coming from the heating conductor encounters the temperature sensor in a transverse manner, so to say, and the sensor is heated over its length most uniformly. That improves the measuring accuracy as well as the response rate of the first temperature sensor. The first temperature sensor per se may face to any region of the heating conductor or be located very close thereto, respectively. Advantageously, it is a region of a loop of the heating conductor.
The heating conductor may advantageously extend meander-shaped or in loops, respectively, on the carrier. The curvatures of the loops can be configured such that the heating conductor extends around the carrier approximately with its width. Advantageously and for prevention of so-called hot spots as a result of current crowding, the two heating conductor arms of the loop may terminate and their ends may be connected or contacted, respectively, by means of an electrically very well conducting contact bridge. That is known from the prior art, see EP 1905271 B1.
Advantageously, the second temperature sensor is arranged in the region of such an aforementioned curvature or loop, respectively, that means that the heating conductor gets closest to the second temperature sensor with such a curvature or loop, respectively. That is advantageous in that here the generated heating power is slightly lower and thus the second temperature sensor is even slightly less exposed to the direct temperature influence of the heating conductor.
The heating conductor is advantageously formed of a resistance material in thick film technology. A thickness may be at least 5 μm, advantageously at least 20 μm up to more than 50 μm. The width of a heating conductor is advantageously approximately constant over its longitudinal course and may be between 2 mm and 10 mm, advantageously approximately 5 mm to 7 mm. In the case of a parallel connection of the heating conductors, the width may even be smaller.
Advantageously, the electric appliance according to the invention comprises a flow channel for a medium or a liquid, respectively, in particular water. Particularly advantageous, such an electric appliance is a washing machine, a dishwasher or in general a flow heater. A heating device according to the invention is located on the flow channel or it forms the flow channel at least partially, respectively. In one embodiment of the invention, it is possible that the heating device is configured tubular with a tubular carrier. However, it may also be a partial tube. Then, the medium flows through the heating device. In that case, heating conductors and temperature sensors are arranged on the outer face of the heating device or of the carrier, so that they do not get into contact with the medium or the liquid, respectively, and are also easier accessible for an electric contacting. Advantageously, it is possible that the second temperature sensor is arranged behind the first temperature sensor in flow direction of the medium.
In another embodiment of the invention, an electric appliance according to the invention may comprise a heating device according to the invention having a flat or plate-shaped carrier, respectively, for example as a cooking device or cooktop for placing a pot or another vessel.
If a heating device is configured tubular, it is advantageously installed in an electric appliance such that at least one of the temperature sensors is arranged in a vertically topmost region of the heating device. Particularly advantageous that is the first temperature sensor close to the heating conductor. If there is a medium or a liquid, respectively, in the flow channel, with air bubbles or air inclusions therein in turn, they are usually located in the topmost region, if their location can be specified at all. Since in that case the heat transfer from the heating device to the medium is not good due to the air bubbles, there is a risk of a local overheating of the heating device or of the heating conductor, which can then be very well and very rapidly be detected by the temperature sensor arranged there.
The second temperature sensor for detecting the temperature of the medium or of the liquid per se, respectively, can on the one hand also be arranged in a vertically upper region or in the vertically topmost region. As an alternative, the second temperature sensor may be provided far below, in particular because the sensor aims at measuring the temperature of the medium, regardless of such air inclusions or even with such inclusions, respectively.
The above features and further features arise not only from the claims, but also from the description and the drawings, wherein the individual features can be realized on their own or together in the form of sub-combinations in an embodiment of the invention and in other fields and represent advantageous embodiments protectable per se for which protection is hereby claimed. The division of the application into individual sections as well as cross-headings does not limit the general validity of the statements made therein.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Exemplary embodiments of the invention are schematically illustrated in the drawings and will be explained in more detail in the following. In the drawings:
FIG. 1 shows an illustration of a heating device according to the invention with a tubular carrier and heating conductors thereon as well as two temperature sensors,
FIG. 2 shows a slightly modified view of a carrier in a flat form with heating conductors and two temperature sensors thereon,
FIG. 3 shows a lateral section through a heating device with tubular carrier and a pressed-on temperature sensor on an elastic arm,
FIG. 4 shows a dishwasher as electric appliance according to the invention with a pump and a downstream heating device according to the invention having a tubular carrier similar to FIG. 1, and
FIG. 5 shows an illustration of the courses of the resistance values of the two temperature sensors of FIG. 1 plotted against time as well as their difference during a heating procedure with the result of a so-called dry-out.
FIG. 1 shows a heating device 11 according to the invention having a tubular carrier 12 in the form of a metal tube. On the external face of the carrier 12 heating conductors 14 are attached in differently extending paths with a width of approximately 3 to 5 mm and an aforementioned thickness. The two left heating conductors 14 with free ends form a curvature 16 or a loop leading there, wherein the free ends are connected to one another by means of a contact bridge 17 as generally known from the aforementioned prior art. The two right heat conductors 14 are guided on contact fields 18. A contacting that may in principle be of any kind can be effected to the contact fields 18 for example as known from the aforementioned EP 1152639 A2. As an alternative, also in this case individual connecting lugs may be soldered thereon or welded thereto.
Furthermore, on the external face of the carrier 12 a first temperature sensor 20 and a second temperature sensor 22 are arranged. The temperature sensors 20 and 22 are configured as SMD components and soldered on corresponding soldering fields 23. An electric contacting is effected via contact fields 24, wherein also in this case plug-connections or the like may be soldered thereon for electric contact.
It can be seen according to the invention that the distance d1 between the first temperature sensor 20 and the heating conductor 14 is comparatively small, and in particular is approximately in the range of the heating conductor width per se. Furthermore, the longitudinal course of the first temperature sensor 20 is parallel to the longitudinal course of the heating conductor 14 in the region. In practice, that may be a distance of approximately 5 mm, and at an exemplary width of the carrier of 0.7 mm, the distance d1 is approximately the 7-fold of the thickness of the carrier 12, but may also be slightly greater or smaller.
Furthermore it can be seen that the distance d2 of the second temperature sensor 22 to the heating conductor 14, in particular in the region of the curvature 16, is significantly greater than the distance d1, namely approximately the threefold of the distance. Thus, the distance d2 corresponds approximately to the threefold of the heating conductor width or accordingly approximately the twentyfold of the thickness of the carrier 12. Furthermore, as shown here, in general the second temperature sensor 22 is spaced apart in a direction from the heating conductor 14 or a curvature 16 that it does not come closer to other heated regions or heating conductors of the heating device 11. The different contact fields 18 and/or 24 may also spatially be located closer to one another or more combined, respectively, in order to be electrically connected by means of for example a common contact device, as known from the aforementioned EP 1152639 A2.
The heating device 11 may advantageously be installed in a pump as it is known from DE 102011003464 A1. It can thus either, as described above, be a tube as a common flow heater or it may be a part and outer shell of a pump chamber of a pump for heating the water pumped therein.
FIG. 2 shows an enlarged detailed view of a slightly different arrangement of a heating device 111 with a carrier 112 which in this case is to be flat or plate-type, respectively. Again, heating conductors 114 are provided which in the upper region form a type of curvature 116 of a described loop with a contact bridge 117. In the lower region, the heating conductors 114 comprise contact fields 118.
Again a first temperature sensor 120 is soldered on soldering fields 123 as SMD component and has a small distance to the heating conductor 114. Here, in contrast to the illustration in FIG. 1, the longitudinal direction of the first temperature sensor 120 is transverse to the longitudinal direction of the heating conductor 114 in its vicinity. Here, the distance is very small and particularly is less than half the heating conductor width.
A second temperature sensor 122 is also configured in SMD technology and attached to soldering fields 123. Its distance to the heating conductors 114 is significantly greater than that of the first temperature sensor 120, namely slightly more than twice the heating conductor width. The heat transverse conduction in the carrier 112 up to the same is significantly longer than up to the first temperature sensor 120, so that the temperature measured by it is determined to a lesser extent by the heating conductors and in fact significantly more by the medium at the carrier. The temperature sensors 120 and 122 are connected to contact fields 124 for electric contacting as described above. The carrier 112 may in this case be a plate made of ceramics or a metal plate with a corresponding insulation layer thereon. In the embodiments according to FIGS. 1 and 2, the heating conductors are attached in thick film technology as it is known per se from the prior art.
FIG. 3 schematically shows how a heating device 211 with a tubular carrier 212 is flown through by a liquid 213. At the external face of the carrier 212, at the top and at the bottom heating conductors 214 are indicated.
In contrast to the embodiments of FIGS. 1 and 2, a second temperature sensor 222 is not directly attached or soldered, respectively, to the external face of the carrier 212, but it is pressed thereon, what is applicable in general also to a first temperature sensor or to both temperature sensors. For that purpose, the second temperature sensor 222 is attached to or soldered on a spring-elastic carrier arm 226 and electrically contacted on the carrier arm 226 via indicated conductor tracks. By means of its configuration or attachment to the carrier 212, the carrier arm 226 is biased in the direction of the carrier 212 such that it presses against the carrier with the force F. As a result, the second temperature sensor 222 is firmly, permanently and reliably applied on the external face of the carrier 212 and is thus arranged there according to the inventive idea. A direct application also causes a good heat transfer from the carrier 212 to the temperature sensor 222. The advantage in such an arrangement compared to a fixed arrangement of the temperature sensor on the carrier according to FIGS. 1 and 2 lies with the flexible construction type, in particular corresponding soldering steps or the like do not have to be carried out at the carrier after the coating procedure for the heating conductors 214.
In FIG. 4, an electric appliance according to the invention is illustrated as dishwasher 30, in which inner space 32 a flushing arm 33 rotates. The supply of water towards the flushing arm 33 is effected via an outlet 34 from the internal space 32 into a schematically illustrated pump 36, to which a heating device 11 in tubular form according to FIG. 1 is connected downstream. The water heated by means of the heating device 11 is then pumped into the flushing arm 33 again. The heating device 11 comprises indicated heating conductors 14 as well as a first temperature sensor 20 on the upper side. In this case, the position of the second temperature sensor is neither shown nor relevant.
Similar as yet shown in FIG. 3, the position of the first temperature sensor 20 may be at the topmost point of the heating device 11 or of the water guidance formed by it, respectively. That applies to both a heating device 11 behind a pump 36 and first of all to a heating device integrated in a pump according to the aforementioned DE 102011003464 A1. If, here, air bubbles are present besides the water to be pumped, which bubbles may strongly reduce the heat transfer with the risk of an overheating of the heating conductors 14, the air bubbles are usually located at a high point or at the topmost point. If the first temperature sensor 20 for monitoring an excess temperature of the heating device 11 or of the heating conductors 14 is provided at the topmost point, it can very well detect the maximum temperature present at the heating conductors. The temperature sensor 20 as well as the heating device 11 as a whole or the heating conductor 14, respectively, and also the pump 36 are connected to a control 37. If the control 37 detects an inadmissibly high temperature at the heating device 11 in particular also by means of the temperature sensor 20, it may reduce the input heating power or may completely switch it off.
FIG. 5 shows a diagram of the course of the electric resistance of the first temperature sensor 20 and of the second temperature sensor at the heating device 11 of the electric appliance 30 according to FIG. 4 plotted against time, wherein the second temperature sensor is arranged lower than the first one. The two temperature sensors are identically configured. The course of the resistance R is plotted against the time t of the first temperature sensor 20 in a dot-dashed manner, and that of the second temperature sensor is shown in a dashed manner. The solid line shows the absolute difference of the two resistance values. Since the first temperature sensor 20 due to its arrangement close to the heating conductor 14 always measures a higher temperature, its resistance value is always slightly lower and decreases more rapidly due to its configuration as an NTC resistance.
At the time t1, i.e. after approximately 20 seconds, the heating device 11 is switched on and starts heating. The temperature increase effected thereby causes a slow decrease in the resistance values for the two temperature sensors. Simultaneously, also the difference between the resistance values decreases. At the time t2 after approximately 150 seconds, here, in the exemplary case of the dry-out, there is not sufficient water in the heating device 11, namely starting in the topmost region. As a result, sufficient heat is no longer transferred and results in a significant heating. That can be seen from the rapid decrease of the resistance values of the two temperature sensors. As from the time t3, after slightly more than 160 seconds, a so-called abnormal and undesired operation starts. As from the moment, also the difference between the two resistance values increases significantly, so that a control 37 advantageously evaluates the course of the difference, since the changes are most significant and characteristic here.
At a time t4 after approximately 200 seconds, the control 37 did not only detect the change of the resistance values, but is also concluded that an abnormal operation is present and completely switches off the heating device 11. As a result, the temperature at the heating conductor or at the heating device does no longer increase further but decrease comparatively rapidly, which can be seen from an increase in the resistance values of the two temperature sensors. Since new heat, which arrives more intense or causes a more intense heating at the first temperature sensor, is no longer generated by the heating conductor, the characteristic curves of the resistance values of the two temperature sensors run increasingly rapid towards one another, so that also the difference characteristic curve rapidly goes down close to zero.
As a result, not only a practicable arrangement for providing a temperature at a heating device or an electric appliance with such a heating device may be provided by means of the invention, but also an advantageous, simple and secure method of temperature evaluation may be achieved.