EP1615469A2 - Cooking apparatus with temperature detection and method for detecting temperature in a cooking apparatus - Google Patents

Abstract

The cooking device has a support for a cooking pot (15), a heating device for the cooking pot and a temperature detection device for the pot at a point on the outside of the pot. The temperature detection device has at least one quotient pyrometer (20a,20b) and a controller with a memory for processing the signal of the pyrometer to determine the temperature of the pot using data from the memory. An independent claim is also included for a method of detecting the temperature of a cooking pot.

Description

Field of application and state of the art

The invention relates to a cooking appliance with a device for detecting the temperature of the cookware on its outside and a method for detecting the temperature.

It is known, for example from EP 690 659 A, to query the temperature on the outside of a cookware via an IR sensor. From this temperature on the outside of the cookware can be closed to the temperature of the cookware or a food therein. As a result, a so-called temperature-controlled or automatic cooking is possible. The IR sensor is arranged upwardly extendable at the rear edge of a hob and measures over an air gap across the heat radiation, which emanates from the cookware. From this, the temperature is calculated.

Here, however, there is the problem that as far as possible defined properties should be present at the location on the cookware on which the heat radiation is measured, since otherwise the temperature determination on fluctuating values of the radiation properties can become inaccurate. Although it has been proposed here by the application of films or the like. to create these defined properties. But this is expensive and must be made individually for each cookware. Furthermore, there is the danger that such films lose or change their properties over time, which can falsify measurements.

Task and solution

This object is achieved by a cooking appliance with the features of claim 1 and a method having the features of claim 8. 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 made explicit reference to the content of the description. The features that are described with respect to the cooking appliance, in their generality apply regardless of the process.

According to the invention, the cooking appliance, which is preferably a hob, a carrier and a heater for the cookware. Advantageously, the cookware can be placed on the carrier. Furthermore, a temperature detection device is provided, which detects or interrogates the temperature at a location on the outside of the cookware. This device has at least one quotient pyrometer, which is directed to the cookware or a specific location. Furthermore, the device has a control with which the temperature of the cookware can be determined using the signals or information that the Quotient pyrometer delivers. The controller is connected to or has a memory. In this data are stored, which are used to process the signals or to determine the temperature. In particular, these are physical data or stored measurement curves, which will be discussed in more detail below.

The advantage of using a quotient pyrometer is that the intensity of the thermal radiation is measured in two temperature ranges which are of interest or to be expected for the measurement in two wavelength ranges which are very close to one another, and the quotient is determined therefrom. It is assumed that the course of the radiation intensity in this wavelength range can be approximated by a straight line according to Planck's law of radiation. By forming the quotient, the slope of this line can be determined. The curves of Planck radiation intensity versus wavelength are known and have a characteristic characteristic of the temperature. So they are different, each with its own, specific slope at each wavelength. The curves are stored for example in the memory. Thus, from the slope of this line the curve in question and thus the temperature can be determined. By the formation of the quotient or the approximation of the curves as a straight line, the size of the emissivity of the surface of the cookware as well as a possible attenuation by other conditions in the measuring path is negligible. Such an error would be the same in both measurements and cancel out insofar as the absolute values of the radiation intensity are lower than actually come out. In absolute terms, the straight line is lower than the actual radiation intensity of the cookware. However, from the slope it corresponds to this. Of course, care should be taken that a wavelength range is used in which the distinctness The different temperature curves based on their slope is well possible.

In a further embodiment of the invention, it is possible that the carrier for the cookware is a plate of at least partially radiation-permeable material. Here are glassy materials, in particular toughened glass or glass ceramic. Especially for cooktops glass ceramic has prevailed, but can also be used as a carrier or wall in an oven. Thus, the temperature measurement in a corresponding manner by glass ceramic or a similar material is also possible with an oven.

On the aforementioned plate is the cookware, wherein advantageously the heating device is arranged underneath. Especially with a hob, it may be a so-called radiant heating or induction heating. Particularly advantageous in an aforementioned embodiment, the quotient pyrometer is arranged below the plate and directed to the cookware or the aforementioned location at which the temperature is to be detected. Usually this is the bottom of the cookware. Depending on the type of cookware may be provided to select either a central area or a circumferential area at which the temperature detection is to take place.

The quotient pyrometer may be disposed between the plate and the heater, and should have thermal insulation if it is in the heating area of the heater. It may also be located adjacent to the heater and directed obliquely to a location above it. Likewise, it may be directed through a passage in the heater.

In order to reduce or even exclude influences of the plate or the glass ceramic on the measured radiation intensity as possible, it is advantageous to set the quotient pyrometer to a wavelength range in which the transmittance of the plate is very large and tends towards one. It is of course advisable to turn it off on the expected or to be measured temperature range, in a cooktop in about 80 ° C to 300 ° C. For glass ceramics, for example, a wavelength range of about 2.5 μm lends itself to this, since a maximum transmission is usually possible here.

In a preferred embodiment of the invention, a second quotient pyrometer may be provided which detects the temperature of the plate on which the cookware is standing. This is done with the aim of eliminating the heat radiation generated by the heating of the plate itself so that it can not distort the intensity measurement with the first quotient pyrometer. For this purpose, the second quotient pyrometer is set to a wavelength range in which the transmittance of the plate is relatively low or even tends to zero. In the case of the abovementioned materials, such as glass-ceramic, a wavelength range below 0.5 μm lends itself here. The sequence of the corresponding method will be explained below.

As previously mentioned, data may be stored in the memory, in particular, so to speak curves of the radiation intensity over the wavelength for different temperatures. At least, this should be for the wavelength range to which the first quotient pyrometer is set. For the use of the second quotient pyrometer, these data are also advantageously available for its wavelength range.

In the method according to the invention is measured with the first quotient pyrometer in the wavelength range of about 2.5 microns, which is particularly advantageous in a measurement through glass ceramic throughout. By way of example, a measuring method can proceed in such a way that a total radiation intensity of the cookware and the plate is detected together with the first quotient pyrometer. With the second quotient pyrometer, the radiation intensity of only the plate is detected. The wavelength ranges are chosen so that the transmission of the plate on the one hand as high as possible and on the other hand is almost zero. Stored data are used to calculate the temperature of the plate and, either via this step or directly from the measured radiation intensity of the plate, to calculate the radiation intensity of the plate at the wavelength at which the first quotient pyrometer measures. Thus, the proportion is determined in the wavelength range of the first quotient pyrometer, which is due to the radiation of the plate. This proportion is deducted from the total measured radiation intensity, which has been determined by the first quotient pyrometer. From the obtained value, the temperature can be determined, which then rests on the outside of the cookware.

Thus, with this method, both the advantage of the measurement with a quotient pyrometer can be used as well as by the implementation of the two measurements with two quotient pyrometers a disturbing or distorting influence of the glass ceramic, through which is measured, can be reduced.

These and other features will become apparent from the claims and from the description and drawings, wherein the individual features each alone or more in the form of sub-combinations in one embodiment of the invention and in other fields be realized and advantageous and protectable Represent embodiments 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.

Description of the drawings

Fig. 1

eine schematische Ansicht eines erfindungsgemäßen Kochfeldes mit zwei Quotienten-Pyrometern,

Fig. 2

die Kurven der Strahlungsintensität über der Wellenlänge gemäß dem Planck'schen Strahlungsgesetz für verschiedene Temperaturen und

Fig. 3

eine Kurve der Transmission über der Wellenlänge für Glaskeramik.

An embodiment of the invention is shown schematically in the drawings and will be explained in more detail below. In the drawings shows:

Fig. 1

a schematic view of a hob according to the invention with two quotient pyrometers,

Fig. 2

the radii intensity versus wavelength curves according to Planck's Law of Radiation for different temperatures and

Fig. 3

a curve of transmission over the wavelength for glass-ceramic.

Detailed description of the embodiment

In Fig. 1, a hob 11 is shown, in which a cookware 15 is placed on a glass ceramic plate 13. The cookware 15 is a so-called saucepan and contains a food 16, such as soup or potatoes to be cooked.

Below the glass ceramic plate 13, as in a conventional hob with radiant heating, a heater 18 is arranged. This is designed according to a conventional radiant heater. The generated heat radiation is directed upward in the direction of the cookware 15 and penetrates the glass ceramic plate 13 with a substantial proportion. This reaches the bottom of the cookware 15 and heats it up.

Two quotient pyrometers 20a and 20b are arranged in a region on the underside of the glass ceramic plate 13 with shield 21. The shield 21 protects the quotient pyrometers 20a and 20b against unwanted extraneous radiation from the side and from the heater 18. So may also possibly harmful overheating of the ratio pyrometer 20a and 20b are avoided because the temperature just above the heater 18 can be up to 700 or 800 ° C. Alternatively, quotient pyrometers 20 'are shown, which are arranged to the left of the heating device 18. They are directed obliquely in the same place as the quotient pyrometers 20a and 20b. This would solve the problem of possible undesired influence or damage by the heater 18 itself. Furthermore, they are not visible from above for a user and do not shield a portion of the heater 18 from the cookware 15 from. With an obliquely arranged arrangement of the quotient pyrometers 20a and 20b, it is also possible to direct them substantially to exactly one point on the glass ceramic plate. Thus, both measurements can actually be made for the same location.

As a further alternative, the quotient pyrometers 20 "are shown, which are arranged below the heating device 18. Their direction of action is through the heating device 18 or a corresponding passage, in which case a small opening may already be sufficient.

The left quotient pyrometer 20a is set to a wavelength at which the transmission of the glass-ceramic plate 13 is as large as possible. According to the diagram of FIG. 2, this applies to a wavelength of about 2.5 μm. Radiation with this wavelength is more than 80% through the glass ceramic plate 13 therethrough. This is indicated by the symbolic heat radiation in FIG. 1, which, starting from the underside of the cookware 14, passes through the glass-ceramic plate 13 to the left-handed quotient pyrometer 20a.

The right-hand quotient pyrometer 20b is set to a wavelength at which the transmission of the glass-ceramic plate is as low as or equal to zero. This is the case, for example, at a wavelength of 0.5 μm, to which the quotient pyrometer 20b is set. As a result of the symbolic thermal radiation also drawn in, it can be seen that only thermal radiation emanating from the underside of the glass-ceramic plate 13 falls on the quotient pyrometer 20b.

The two quotient pyrometers 20a and 20b are connected to a controller 24. The controller 24 in turn is connected to a memory 26 and a switch 28, with which the power supply to the heater 18 can be controlled. Furthermore, it should be noted, above all, that the controller 24 makes it possible to evaluate the data of the quotient pyrometers 20a and 20b. Therefore, it can generally be regarded as an evaluation.

function

For the theoretical understanding, reference is made to the curves of the Planck radiation intensity E over the wavelength λ in accordance with FIG. 2. It can be seen that the curves of the radiation intensity at a certain temperature over the wavelength λ have a characteristic course. The curves are given for different radiating body temperatures, from 300K at the lowest curve to 700K at the top curve. The solid curves go from bottom to top in 100K increments. The two dashed curves represent 50K steps, so that for Temperatures of 300K, 350K, 400K, 450K, 600K and 700K curves are plotted.

In the aforementioned wavelength range of 2.5 microns, in which the curves have approximately a maximum change in slope, they additionally have a respectively well distinguishable slope. The gradients at a wavelength of 2.5 microns are indicated by the dash-dotted tangents for the lowest and the highest curve. This means that at the wavelength of 2.5 μm or very close to it each curve of the radiation intensity can be approximated by a straight line and these lines are clearly distinguishable at each curve.

If the slope of this straight line can be determined by measuring or calculating an intensity at an unknown temperature, the temperature can be determined from this. This will, as explained below, used for temperature determination.

The basic operating principle of a quotient pyrometer is sufficiently well known to the person skilled in the art and has been outlined at the outset. Further explanations are not necessary. The left quotient pyrometer 20a is set to the wavelength range of 2.5 μm and measures the total radiation intensity at two wavelengths around 2.5 μm, which are for example only about 10 to 100 nm apart. By the quotient formation, which can be made by the quotient pyrometer 20a itself or the controller 24, two slightly spaced values for the intensity E for two closely spaced wavelengths can be determined. These define a straight line which corresponds to one of the dash-dotted lines and thus tangents according to FIG. 2. Thus, approximately the temperature can be determined.

However, with this measured radiation intensity, it should be noted that both the hot bottom of the cookware 115 radiates downwards and the heated glass ceramic plate 13 itself. Desired is only the intensity of the cookware. On the one hand, the proportion of the glass-ceramic plate 13 can be eliminated from empirical values for specific temperatures via correction data stored in the memory 26. Alternatively, the second quotient pyrometer 20b is used, as described below.

The second quotient pyrometer 20b is set at a wavelength of about 0.5 μm. Referring to Fig. 3, with the basic method of quotient formation as described above, the intensity and thus temperature of only the glass-ceramic plate 13 in a spatial region near the first quotient pyrometer 20a is measured. If the temperature of the glass-ceramic plate 13 is known therefrom, it can again be determined according to the diagram from FIG. 2 which radiation intensity the glass-ceramic plate 13 has at the wavelength of 2.5 μm. This radiation intensity of the glass-ceramic plate 13 can be subtracted from the total radiation intensity measured by the quotient pyrometer 20a, so that the radiation intensity, which goes back exclusively to the cookware 15, can be determined. Based on this, in turn, the temperature of the cookware 15 can be determined by using the curves of FIG. 2.

Depending on the determined temperature on the underside of the cookware 15, for example, in turn, can be closed by stored in the memory 26 empirical values on the temperature of the cooking product 16. It is usually a few K lower. If, for example, a so-called cooking program is to be used with temporal regulation of the temperature according to predetermined values, the controller 24 can directly via the switch 28 to supply energy to Heating device 18 and thus control the heating of the cooking product 16. Alternatively, the control or evaluation 24 may be connected to an overall control for the cooking money 11 or even be integrated therein and thus influence the energy supply to the heating device 18.

Another advantage of a quotient pyrometer 20 mounted under the glass ceramic plate 13 is that it is protected against contamination or damage. Furthermore, it is rigid and immovable, which is very simple in construction.

Claims (9)

Cooking appliance, in particular hob (11), with: a carrier for a cookware (15), - A heater (18) for the cookware (15) and - a temperature detecting means (20, 24, 26) for the cookware (15) at a location on the outside of the cookware,
characterized in that the temperature detecting means comprises at least one quotient pyrometer (20a) and a controller (24) having a memory (26) adapted to process the signals of the quotient pyrometer for determining the temperature of the cookware (15) using data from memory. Cooking appliance according to claim 1, characterized in that the carrier is a plate (13) made of at least partially radiation-permeable material, in particular glass ceramic, on which the cookware (15) and below which the heating device is arranged, preferably as a radiant heater (18) or induction heating. Cooking appliance according to claim 2, characterized in that the quotient pyrometer (20a) is arranged below the plate (13) and is directed to the cookware (15), preferably on its underside. Cooking appliance according to claim 3, characterized in that the quotient pyrometer (20a) is set to a wavelength range in which the transmittance of the plate (13) is very high is large, preferably nearly one, in particular to a wavelength range of about 2.5 microns. Cooking appliance according to one of claims 2 to 4, characterized by a second quotient pyrometer (20b) for detecting the temperature of the plate (13) in the area on which the cookware (15) stands or on which the first quotient pyrometer (20a ), wherein preferably the second quotient pyrometer (20b) is arranged below the plate (13) and in particular adjacent to the first quotient pyrometer (20a). Cooking appliance according to claim 5, characterized in that the second quotient pyrometer (20b) is set to a wavelength range in which the transmittance of the plate (13) is very low, in particular equal to zero, wherein preferably the wavelength range below 0, 5 microns is. Cooking appliance according to one of the preceding claims, characterized in that in the memory (26) data of the curves of the radiation intensity over the wavelength for different temperatures at least in the wavelength range are stored, to which the first quotient pyrometer (20a) is set, preferably also for the wavelength range to which the second quotient pyrometer (20b) is set. Method for detecting the temperature of a cookware (15) with a cooking appliance (11) according to one of the preceding claims, characterized in that the quotient pyrometer (20a) is measured in a wavelength range of approximately 2.5 μm. Method according to claim 8, with a cooking appliance according to one of claims 3 to 7, characterized by the following steps: - with the first quotient pyrometer (20a) a total radiation intensity of cookware (15) and plate (13) is detected, the second quotient pyrometer (20b) detects the radiation intensity of the plate (13) at a wavelength at which the transmittance of the plate is almost zero, the temperature of the plate is calculated via stored data and, assuming the radiation intensity of the plate at the wavelength at which the first quotient pyrometer measures (20a) is calculated from the stored data on the basis of the measured radiation intensity of the plate (13) or its calculated temperature, the calculated radiation intensity of the plate (13) is subtracted from the total radiation intensity (E) of the first quotient pyrometer (20a) to determine the radiation intensity emanating from the cookware (15), and - Based on the stored data is determined from the cookware radiation intensity, the temperature on the outside of the cookware (15).

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