EP1837600B1 - Method for controlling or monitoring or regulating a closed electric heating device - Google Patents

Abstract

The method involves timely processing of signals of temperature acquisition, and processing an amount of heat to be detected in a control device (23). Conditions at a central heating room (15) and/or gases contained in components of the room are determined. Received information is used for monitoring of sensors e.g. temperature sensor (21), provided at an electric heating appliance e.g. baking oven (11), or for controlling and/or regulation of operation of the electric heating appliance.

Description

Field of application and state of the art

The invention relates to a method for monitoring or control or regulation of a closed electric heating appliance with a closed boiler room, in particular an oven, steamer or dryer.

From the DE 101 43 841 A1 It is known to evaluate the differences in the speed of sound between dry and moist air to determine the density. The duration of a sonic pulse is measured and evaluated.

From the DE 101 03 658 A1 is a method for determining the thermal conductivity of gases known, wherein the reaction of a sensor is evaluated for a temperature jump. Here is also explained how far Differences in the thermal conductivity of gases in principle can be used for their characterization.

From the EP 615 400 B1 It is known that different gas sensors can be evaluated in an oven in the preparation of food.

Another method for monitoring, control or regulation discloses the EP-A-0 567 813 ,

Task and solution

The invention has for its object to further develop an aforementioned method so that thus a said electric heater can be operated advantageously and overall advantageous way can be created to operate with so-called gas sensors, an electric heater.

This object is achieved by a method having the feature of claim 1. Advantageous and preferred embodiments of the invention are the subject of further claims and are explained in more detail below. The wording of the claims is incorporated herein by express reference.

According to the invention, it is provided that the electric heating device has a heater and a temperature detection in the heating chamber and a control device including means for detecting the time and the heating power of the heater. The electric heater or its heating are advantageously operated clocking. The time course of at least one signal of the temperature detection and the time course of the heating power are detected in the control device, from which the state in the boiler room or components of gases contained therein are determined. The information obtained in this way is used to monitor sensors present in the oven or to control or regulate the operation of the electric heating appliance.

In particular, this allows the constituents of the atmosphere in the boiler room or the gases contained therein to be recognized in terms of their type and concentration. This in turn can be closed on the one hand on the type of baked goods or the like and on the condition thereof, as for example in the DE 103 40 146 A1 is described. In particular, with the invention, a moisture measurement is possible, which can be dispensed with great advantage on special gas sensors or humidity sensors.

The temperature detection can advantageously have a temperature sensor, wherein the temperature detection detects the reaction of the temperature sensor to a temperature jump in the boiler room. From this reaction or the corresponding information, the thermal conductivity and / or the atmospheric humidity of the atmosphere in the boiler room can be determined via the temperature sensor signals. This can be done particularly advantageously on the basis of the transit time or amplitude of the sensor signals, since these allow a conclusion to the desired information.

Advantageously, the invention can also achieve that existing functional units, for example in an oven, can be used and no further needed. A heater is inevitably and provided by default in an oven, means for temperature detection, such as temperature sensors, also. Although these are partially thermo-mechanically formed with expansion box and capillary tube connection to a temperature sensing device. In some cases, however, electrical temperature sensors are already being used, which can be evaluated electronically by means of a corresponding controller.

On the basis of the obtained sensor signals can be advantageously determined which gases are in the atmosphere of the boiler room, wherein For this purpose, a comparison of the values for transit time and / or amplitude of the sensor signals with values stored in the control device for the sensor signals takes place. If the waveforms are sufficiently similar, the determination of the corresponding gases or their proportions for the expert in a known manner is possible. Also this is on the aforementioned DE 103 40 146 A1 directed.

It is also conceivable according to a first possibility that the aforementioned temperature jumps are generated by a cyclic operation of the heater. In particular, this can be done by a regular continuous operation in continuous operation, as it corresponds, for example, the normal operation of the electric heater. This means, for example, in a conventional oven, that there also the heating is operated clocking, namely switched on at full load or off. The advantage of this is that in one of the normal modes of operation of the electric heater nothing has to be changed in the process, so that both the operation can go undisturbed and the cost of deviating control methods can be saved.

According to a second possibility, a temperature jump for the temperature detection and determination of the atmosphere in the boiler room can be specifically initiated by a heater deviating from the otherwise currently prevailing operating conditions. This therefore means an opening of the aforementioned normal intended operation of the electrical appliance. The advantage here is that then always the same temperature jump can be performed. In particular, it is always the same insofar as it deviates from a prevailing basic temperature by a certain percentage. Alternatively, it can always deviate by a certain absolute temperature difference. This in turn simplifies the evaluation of the obtained Sensor signals, although for a small disturbance or change in the operation of the electric heater is necessary.

In a preferred embodiment of the invention, the temperature jump is a jump up, so with increasing temperature. Advantageously, only temperature jumps are generated upward. This has the advantage that in contrast to temperature jumps down a larger slope can be achieved because the temperature jump can be targeted upwards influenced by the heating. A temperature jump down is possible only by switching off the heater and subsequent cooling of the boiler room, which is slow due to the usual good thermal insulation.

In a further particularly preferred embodiment, it is also possible that after the temperature jump up and its completion, the cooling or cooling rate is detected at the temperature sensor. Thus, it is possible to effect a faster cooling than usual or to detect both increase in temperature during the temperature jump and cooling or falling of the temperature under certain circumstances. Since the temperature jump is introduced from the top of the heater and can be detected in the atmosphere in the boiler room depending on the distance to the heater, but not necessarily leads to a uniform increase in the total temperature in the boiler room, the subsequent cooling is also stronger than from the normal state the temperature conditions out.

A temperature jump can be generated for a relatively manageable duration, for example a few minutes or even less than a minute. A subsequent cooling with a cooling rate A can last longer, in particular a few minutes, until the "normal" temperature value is reached again after a temperature rise.

The cooling rate A is in the simplest case simply defined by the quotient A = (T1-T2) / (t1-t2), where T1 and T2 are the temperatures at the sensor at times t1 and t2. For a given time interval t1-t2, therefore, the two temperatures T1 and T2 are simply to be determined in order to form the cooling rate A. The specification of the time interval can be based on the one hand on the practical conditions for the times of the oven control on the other hand also on the sensor arrangement with regard to the necessary accuracies. In any case, the time intervals are to be chosen in dependence on the other arrangements in such a way as to ensure that the disturbances in the system are smaller than the effects which are actually due to the different state of the gases.

In a further embodiment of the invention, a plurality of temperature sensors are provided for a temperature detection. They may advantageously have a different distance from the heater in order to detect not only the pure temporal behavior of the temperature but also a local course of the temperature. For example, two to five temperature sensors may be provided, of course, it should be noted that both the cost of the evaluation of the respective sensor signals increases with the number and the additional design effort for the plurality of temperature sensors. This should actually be kept in check.

Particularly interesting is the use of sensors or temperature sensors, which can temporarily perform other functions. This could e.g. Functions as a lamp or to control a door lock be.

In an evaluation of the sensor signals, the thermal conductivity of the atmosphere can be detected in the boiler room. This can also be on the Composition of the atmosphere from different gases are closed by their specific values for their thermal conductivity. These values are stored in the control device and can be retrieved.

According to a further embodiment of the invention can be concluded from the running time of a sensor signal of the temperature detection on properties of the atmosphere or the gases in the boiler room. These properties are thermal conductivity, thermal conductivity and / or density of a carrier medium or the atmosphere. Also for this purpose, a comparison can be made with corresponding values stored in the control device.

According to yet another embodiment of the invention can be concluded from the amplitude of a sensor signal of the temperature detection on properties in the atmosphere in the boiler room, in particular the aforementioned properties. Again, a comparison with values stored in the control device is again possible.

The temperature jumps can not only be provided outside the normal operation of the electric heater, but also be generated by an additional heater. This additional heating can not be provided for the considered normal operation of the electric heater or not for the currently selected mode of operation. Thus, for example, in an oven with recirculation mode, a grill mounted above in the boiler room can be operated for a short time to produce the temperature jump. This is standard installed in the oven, for the operation with circulating air, however, not provided.

As a heater in the boiler room on the one hand a radiant heater may be provided, either with temperatures in the range operated by incandescent heating conductors, for example 800 ° C to 1100 ° C. Such a radiant heater may have, for example, exposed heating conductors and is in the DE 42 29 375 A1 described.

A particularly interesting variant can be achieved in that the electrical resistance of the radiant heater, if this is currently not in operation, has a large temperature dependence and thus the radiant heater or a heating element or heating resistor thereof can be used quasi even as a temperature sensor. More specifically, these are NTC or PTC effect heaters or combinations of both. Which type of heating element is more favorable for the temperature detection depends in particular on the arrangement between the temperature sensor and the heating element, which generates the temperature jump. For relatively low temperatures offers the NTC effect, for relatively high temperatures in turn the PTC effect advantages in the evaluation. NTC-effect heating conductors may be doped semiconducting ceramics, preferably of doped and sintered silicon carbide (SiC), or lamps containing heating conductors, for example based on carbon (carbon fiber or carbon nanotubes). Heating conductor with PTC effect, for example, be designed as a so-called halogen lamps, in which case the embodiment may correspond to a lamp, with a heating conductor preferably made of tungsten or molybdenum or alloys thereof.

As an alternative to a radiant heater, a tubular heater can be provided in the boiler room, in which a heating conductor is arranged in a jacket. As a further alternative, a hot air supply can be used as a heater. A heater of this hot air supply is usually located outside the boiler room and has a fan or the like. to bring the hot air into the boiler room. If the electric heater is an oven, so can one Combination of the above-described types of heaters can be provided. Advantageously, a radiant heater or a tubular heater is provided together with a hot air supply, wherein radiant heater or tubular heater can be used, for example, for a grill function.

Just as described above with radiant heaters, it is also possible to design a tubular heater so that it can temporarily perform sensor functions. Corresponding embodiments of tubular heaters are known in the art. However, it should be explicitly pointed out that the operation of tubular heaters with PTC effect must comply with various flicker standards. A known to those skilled in the field of radiant heater variant, which is under the name HaloLight on the market and the EP 176027 A1 It can be seen in a series circuit of halogen heating elements as PTC heating elements and heating elements with "normal" Widerstandsheizdraht (for example FeCrAl, NiCr 8020 or FeNiCr3020, ...).

With the information obtained about the atmosphere in the boiler room or its composition, for example, gas or humidity sensors can be saved in the electric heater. Thus, the method can then serve to control or regulation of the electric heater. Alternatively, these gas or humidity sensors can be monitored, in particular malfunctions or the like .. Furthermore, an unforeseen or critical condition can be detected in the boiler room, for example, a burning of therein objects or food or food or the emergence of other gases in the this mode of operation should not arise.

These and other features are apparent from the claims and from the description and drawings, wherein the individual features in each case alone or in the form of sub-combinations be realized 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 as well as intermediate headings does not restrict the general validity of the statements made thereunder.

Brief description of the drawings

Fig. 1

eine schematische Innenansicht eines Backofens gemäß einer ersten Ausführungsform der Erfindung mit einer Heizung und Temperatursensor,

Fig. 2

eine Innenansicht eines Backofens gemäß einer zweiten Ausführungsform der Erfindung mit zwei Heizungen und einer Alternativposition für den Temperatursensor und

Fig. 3 bis 6

verschiedene Kurven des Verlaufs der Temperatur über der Zeit bei unterschiedlichen Luftfeuchtigkeiten in Abhängigkeit von unterschiedlichen Temperaturen.

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

Fig. 1

1 is a schematic interior view of a baking oven according to a first embodiment of the invention with a heating and temperature sensor;

Fig. 2

an interior view of a baking oven according to a second embodiment of the invention with two heaters and an alternative position for the temperature sensor and

Fig. 3 to 6

different curves of the course of the temperature over time at different humidities depending on different temperatures.

Detailed description of the embodiments

Fig. 1 shows in a lateral schematic section of a baking oven 11 with a housing 12. A door 13 allows access to the muffle or the heating chamber 15 of the oven 11. In the boiler room 15 can be cooked 17, for example, a casserole or other food, in an oven can be prepared stand.

In the oven 11 there is a heater 19. This is designed as a tubular heater, as it is basically known. It can be laid at least at the top of the boiler room 15 meandering or as a single loop.

Furthermore, a temperature detection 21 projects into the heating chamber 15. It can be designed as a type of temperature sensor and, just like the heater 19, can be connected to a control 23. While the controller 23 can both control the heater 19 and, under certain circumstances, only monitor its operation, the temperature detector 21 is actuated and also evaluated by the controller 23, in particular explicitly as a temperature profile with specific values for the temperature. For this purpose, temperature sensors such as, for example, resistance sensors or PT1000 sensors are suitable. An operating element 25 is connected to the controller 23, for example as a rotary knob for setting a heating power for the heater 19th

In Fig. 2 is in extension of the oven 11 off Fig. 1 an oven 111 is shown, which in addition to the heater 119 also has a second heater 120 in the boiler room 115. Furthermore, in addition to the temperature sensor 121 is similar to Fig. 1 a dashed line another position for a temperature sensor 121 'shown. The position of this dashed temperature sensor 121 'is clearly further away from the upper heater 119 and a little closer to the lower heater 120th It will be discussed in more detail later. On the one hand, this greater distance means a considerably lower value for the recorded temperatures during the temperature detection. On the other hand, there is a somewhat delayed temperature detection, since the heat from the heaters must first spread to the respective position of the temperature sensor.

function

The function of a baking oven 11 or 111 and the course of the method according to the invention will be described with reference to FIG Fig. 3 to 6 for such ovens 11 and 111 explained. The diagrams in the Fig. 3 to 6 contain information on temperatures in ° C as well as the relative humidity defined for them. In total, three temperatures were recorded, namely 30 ° C, 60 ° C and 90 ° C and two humidities, namely 20% and 90%. Based on these initial conditions, temperature jumps were generated by the heaters 19 or 119. The heater 120 for the bottom heat according to Fig. 2 was ignored, and her operation would not fundamentally change anything. Furthermore, the distance of the temperature sensor 21 and 121 was varied by the heater. The various values are a distance of 1 cm, 5 cm and 10 cm, the respective temperature curves are shown in solid, dashed or dotted. For better comparability are in Fig. 6 for both values of the relative humidity all courses with different distances drawn in a diagram, more on this later.

In Fig. 3 It can be seen how, starting from the initial temperature of 90 ° C, a temperature jump is produced by operation of the heater. Thereafter, the temperature at the temperature sensor rises relatively steeply for about the first 25 seconds, and then rises slightly further into a slower rise. The increase is somewhat slower for the two larger distances of 5 cm and 10 cm and, of course, reaches much lower values. After about 60 seconds, the heating is switched off again and the temperature drops accordingly.

Out Fig. 3 It can be seen that the temperature curves have a certain characteristic shape, which of course is not surprising. However, the curve is recognizable basically suitable for a characteristic distinction to other curves.

From the comparison of the diagrams in Fig. 4 and Fig. 5 , both of which start at a starting temperature of 30 ° C and only at different relative humidities, a certain degree of distinctness can be made. Admittedly, the difference in the curve is not very large. On the other hand, if one considers the cooling rates, ie from about 60 seconds after switching off the heating, on the basis of the measured values, then differences become clearer. The temperature values at the higher humidity drop more slowly, which means that the temperature drop is lower or just slower.

Since, as I said, the cooling rates and the cooling behavior are better evaluated, is in Fig. 6 for the initial temperature value 60 ° C only the cooling is shown. The cooling rate can be determined at a fixed time interval based on the temperature difference. Here, especially for the course of the measured value at a distance of one centimeter, it can be seen that, especially for times as short as 50 seconds, the temperature at high humidity drops more slowly than at low air humidity. At least in this area, an evaluation of the measured data can take place. In order to distinguish computationally in the controller 23 whether the differences are a true measuring effect due to the actual physical thermal conductivity in the heating chamber 15 or merely measurement inaccuracies, the mean and standard deviation of the relative differences between the two air humidities can be calculated. If the mean value is smaller than the standard deviation, these are accidental measurement inaccuracies. These in turn can not be used to determine the thermal conductivity and thus not to measure the humidity. If, on the other hand, the mean value is greater than the standard deviations, this is an effect that can be used to determine the air humidity.

Even if the Fig. 6 At first glance, suggesting otherwise, at the distances 1 cm and 5 cm of the temperature sensor 21 from the heater 19, the differences between the measurements are smaller than the standard deviations. Thus, the experimental error is too large here to determine the thermal conductivity clearly. At a distance of 10 cm, on the other hand, the mean difference between the humidities is significantly greater than the standard deviation, so that it is possible to infer the thermal conductivity and thus the air humidity from the measured temperature.

In principle, a good embodiment can be achieved by an optimized arrangement of temperature sensors and heating elements, in particular also with regard to inertia, as well as a suitable sensor resolution, preferably of 1/100 K. However, it also turns out that such an arrangement is not self-evident, which emphasizes the inventive aspect.

Claims (17)

1. A method for monitoring or for open- or closed-loop control of a closed electric heating appliance (11, 111) having a closed heating chamber (15, 115), in particular of an oven (11, 111), steamer or tumble-drier, and having a heater (19, 119, 120) and a temperature detector (21, 121, 121') in the heating chamber and having a control device (23, 123) together with means for recording time and for detecting the heating power of the heater, the electric heating appliance or the heater being operated cyclically, characterised in that the time profile of at least one signal of the temperature detector and the time profile of the heating power are recorded in the control device (23, 123) and the situation in the heating chamber (15, 115) or constituents of gases contained therein is/are determined therefrom, the information obtained in this way being used for monitoring sensors present in the electric heating appliance or for open- or closed-loop control of operation of the electric heating appliance.
2. A method according to claim 1, characterised in that the temperature detector comprises a temperature sensor (21, 121, 121') and in the temperature detector the response of the temperature sensor to a sudden change in temperature in the heating chamber (15, 115) is detected and the thermal conductivity or the atmospheric humidity of the atmosphere in the heating chamber is determined by means of the sensor signals of the temperature sensor (21, 121, 121'), in particular by means of the propagation delay and/or amplitude of the sensor signals.
3. A method according to claim 2, characterised in that the gases in this atmosphere are then determined by means of the sensor signals by comparing the values for propagation delay and/or amplitude with values stored in the controller (23, 123).
4. A method according to claim 2, characterised in that the sudden changes in temperature are caused by cyclical operation of the heater (19, 119, 120), in particular cyclical operation corresponding to the mode of operation of the electric heating appliance (11, 111) provided as normal.
5. A method according to claim 1 or claim 2, characterised in that a sudden change in temperature different from the otherwise currently prevailing operating conditions, in particular a sudden change in temperature which is always identical, is initiated by the heater (19, 119, 120) for temperature detection and determination of the atmosphere in the heating chamber (15, 115).
6. A method according to claim 2 or claim 5 and claim 2, characterised in that the sudden changes in temperature are caused by cyclical operation of an additional heater (19, 119, 120), which is not provided for the mode of operation of the electric heating appliance (11, 111) regarded as normal.
7. A method according to any one of the preceding claims, characterised in that a sudden change in temperature is initiated which takes the form of an increase in temperature, preferably only sudden changes in temperature which take the form of an increase in temperature, the cooling rate at the temperature sensor (21, 121, 121') during the period after the sudden change in temperature then in particular also being detected.
8. A method according to any one of the preceding claims, characterised in that a sudden change in temperature is produced for a duration of less than a minute, in particular in the form of an increase in temperature.
9. A method according to any one of the preceding claims, characterised in that a plurality of temperature sensors (21, 121, 121') are present, in particular at different distances from the heater (19, 119, 120) for the sudden change in temperature, preferably two to five temperature sensors.
10. A method according to claim 2, characterised in that the thermal conductivity of the atmosphere in the heating chamber (15, 115) is detected and a conclusion is drawn therefrom about the atmosphere composed of various gases by means of the specific values thereof for thermal conductivity, these values being stored in the control device (23, 123).
11. A method according to claim 2, characterised in that conclusions may be drawn about characteristics of the atmosphere in the heating chamber (15, 115) from the propagation delay of a sensor signal of the temperature detector, in particular the thermal conductivity, thermal capacity and/or density of the carrier medium.
12. A method according to claim 2, characterised in that conclusions may be drawn about characteristics of the atmosphere in the heating chamber (15, 115) from the amplitude of a sensor signal of the temperature detector, in particular the thermal conductivity, thermal capacity and/or density of the carrier medium.
13. A method according to any one of the preceding claims, characterised by a radiant heating device in the heating chamber (15, 115) as heater.
14. A method according to any one of the preceding claims, characterised in that the heater (19, 119, 120) or a heating element displays NTC characteristics, consisting in particular of sintered SiC or being a carbon fibre lamp.
15. A method according to any one of claims 1 to 13, characterised in that the heater (19, 119, 120) or a heating element displays PTC characteristics, it comprising in particular a halogen lamp.
16. A method according to the preceding claim, characterised in that, for operation of the heater, a heating element with PTC characteristics is connected in series with a heating element of a different heat conducting material.
17. A method according to any one of claims 1 to 12, characterised by a hot air supply as heater, a heating device being arranged therefor outside the heating chamber (15, 115) and the hot air being introduced into the heating chamber.

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