Method for determining the humidity within a cooking chamber of a cooking appliance and cooking appliance

Abstract

Method for determining the humidity within a cooking chamber (12) of a cooking appliance (10), comprising the following steps: a) an acoustic vibration is generated in a resonance chamber (24) in the cooking appliance (10), b) a control unit (38) receives the signals picked up by a microphone (34) in the resonance chamber (24), c) the control unit (38) determines the frequency spectrum of the acoustic vibrations present in the resonance chamber (24) on the basis of the received signals and the speed of sound within the cooking chamber (12) on the basis of the frequency spectrum, d) the control unit (38) receives a temperature value, e) the control unit (38) determines the humidity inside the cooking chamber (12) using the temperature value and the speed of sound.

Description

[0001] The invention relates to a method for determining the humidity within a cooking chamber and a cooking appliance therefor.

[0002] Such cooking appliances can be designed as so-called combi steamers, i.e., cooking appliances in which the food to be cooked is cooked using hot air and / or steam. For such cooking appliances, it is necessary to know the humidity in the cooking chamber, i.e., the water content of the atmosphere within the cooking chamber, for optimal food preparation.

[0003] Various methods are commonly used to measure humidity, such as measuring a pressure drop at the fan wheel of the cooking appliance.

[0004] DE 906 023 B discloses a device for measuring the moisture content of gases above an evaporation temperature by measuring the speed of sound in the gas by means of standing waves, wherein an acoustic transmitter and receiver are positioned opposite one another in a measuring chamber and the electrical excitation voltage supplied to the transmitter and the electrical voltage supplied by the receiver are adjusted to phase equality by changing the frequency of the transmitter for the purpose of resonance.

[0005] DE 12 91 916 A describes a device for measuring temperatures, in particular for nuclear reactors, using a resonance frequency of a resonator arranged in a measuring chamber, wherein an energy source for exciting the resonator and a receiver for the oscillation excited in the resonator are arranged outside the measuring chamber and connected to the resonator via a coupling tube.

[0006] US 2012 / 0 225 179 A1 discloses a device for estimating the humidity in an oven by using ultrasonic waves with at least two different frequencies.

[0007] From US 5 689 060 A, an oven is known with a humidity measuring device, comprising an air-filled hollow chamber for measuring sound waves and a reference chamber, wherein a difference in the phase of the sound waves in the two chambers is detected, from which the humidity state can be determined.

[0008] Furthermore, EP 1 300 079 A2 discloses a cooking appliance with a cooking chamber, a temperature measuring device, and a device for generating acoustic waves arranged in a tube. Acoustic standing waves are generated in the tube through resonance excitation, and the humidity is determined from their frequency, together with the data from the temperature measuring device.

[0009] However, the results of such methods also depend on other external factors, such as air pressure, which can lead to measurement inaccuracies.

[0010] It is therefore an object of the invention to provide a cooking appliance and a method for determining the humidity within a cooking chamber of a cooking appliance, which can precisely determine the humidity within the cooking chamber using simple means.

[0011] The task is solved by a procedure with the following steps: a) an acoustic vibration is generated in a resonance chamber in the cooking appliance, b) a control unit receives the signals recorded by a microphone in the resonance chamber, c) the control unit uses the received signals to determine the frequency spectrum of the acoustic vibrations present in the resonance chamber and, based on the frequency spectrum, the speed of sound within the cooking chamber, d) the control unit receives a temperature value, e) the control unit uses the temperature value and the speed of sound to determine the humidity inside the cooking chamber.

[0012] The vibrations in the resonant chamber are generated by a broadband sound source. These vibrations are eigenfrequencies of the resonant chamber, i.e., standing waves of the fundamental or higher order within the resonant chamber, also called fundamental vibrations or overtones.

[0013] Humidity is determined by determining or indirectly measuring the speed of sound in the resonant chamber. The speed of sound in the resonant chamber depends on the temperature and the composition of the atmosphere in the resonant chamber. To determine the speed of sound, the frequencies of the vibrations excited in the resonant chamber, especially the frequency of the fundamental vibration, are determined. From this, the speed of sound can be determined using the known wavelength of the fundamental vibration.

[0014] Because the frequency spectrum of the vibrations present in the resonance chamber is determined to determine the speed of sound, the frequency of the fundamental vibration can be determined very precisely because the determined frequencies of the overtones can be used to correct the determined frequency value of the fundamental vibration. Secondly, the determination of the fundamental frequency and thus the determination of the humidity is independent of the control of the sound source. This eliminates the need for complicated and in-phase coupling of the sound from the sound generator to the resonance chamber because the broadband excitation is sure to cause natural vibrations, i.e. resonances, in the resonance chamber. In this way, the humidity can be determined precisely using simple means, some of which are already present in the cooking appliance.

[0015] Preferably, the temperature value corresponds to the temperature in the resonance chamber, and / or the control unit can determine the temperature in the resonance chamber based on the temperature value. The temperature value is, for example, a measured value from a temperature sensor in the resonance chamber or in the cooking chamber. However, it is also conceivable that the temperature value is another value from which the control unit can determine the temperature in the resonance chamber, for example, the target temperature of the cooking appliance's heating device. In this way, the temperature in the resonance chamber can be determined very precisely.

[0016] For example, the control unit determines the frequency spectrum by means of Fourier analysis and / or by determining the correlation function, whereby the frequency spectrum can be reliably determined.

[0017] Furthermore, the object is achieved by a cooking appliance comprising a resonance chamber, a sound generator, a microphone associated with the resonance chamber, a temperature value unit capable of generating a signal dependent on the temperature of the atmosphere in the cooking appliance, and a control unit to which the microphone and the temperature value unit are connected. The control unit includes a spectral analysis module, in particular a Fourier analysis and / or correlation function module. The spectral analysis module enables the control unit to precisely determine the frequency spectrum of the vibrations occurring in the resonance chamber.

[0018] Preferably, the cooking appliance has a fan wheel, with the fan wheel serving as the sound generator. Thus, no additional components beyond those already present in the cooking appliance are required to generate the required sound.

[0019] The cooking appliance may have a loudspeaker, wherein the loudspeaker represents the sound generator, so that the humidity can also be determined independently of the operation of the cooking appliance, in particular independently of the operation of the fan wheel.

[0020] In one embodiment of the invention, the cooking appliance has a loudspeaker control that can control the loudspeaker so that the loudspeaker emits noise or performs a frequency sweep. The noise can be white noise. In a frequency sweep, the loudspeaker generates an oscillation of a frequency, with the frequency of this oscillation sweeping through a frequency range over a specific time interval. This also ultimately generates a broadband signal.

[0021] This type of control eliminates the need to precisely adjust the amplitude and phase of the loudspeaker signal to the resonant chamber, which is particularly difficult when the loudspeaker is located far from the resonant chamber. Broadband control of the loudspeaker eliminates this complex adjustment, allowing the loudspeaker's position to be chosen independently of the position of the resonant chamber.

[0022] In one design variant, the cooking chamber of the cooking appliance is the resonance chamber, which means that no additional component is necessary to create the resonance chamber.

[0023] In a further embodiment of the invention, the resonance chamber is located within a resonator that is open to the cooking chamber of the cooking appliance. The resonator is a geometrically clearly defined space that is comparatively small compared to the cooking chamber, for example, in the shape of a cylinder or a rectangular cavity. This allows the dimensions and geometries of the resonance chamber to be freely selected.

[0024] For example, the resonator is located in the cooking chamber of the cooking appliance. This allows for excellent thermal and acoustic coupling between the cooking chamber and the resonator. The resonator can be open at its lower end and / or positioned so that the resonator is also cleaned by the washing solution of the cooking appliance when the cooking chamber is cleaned. The temperature sensor can also be located on the resonator.

[0025] The resonator is preferably designed as a tube, which makes it simple and cost-effective to manufacture. For example, the tube is 20 cm long and / or has an inner diameter of 1.5 cm to 2 cm. The tube can also be open on one or both sides and / or be arranged vertically in the cooking chamber. It is also conceivable to provide at least one opening in the wall of the tube to influence the vibrations generated in the resonator.

[0026] In one embodiment of the invention, the cooking appliance has a cavity that is acoustically coupled to the resonance chamber at a coupling point, with the microphone provided in the cavity. This allows the microphone to be arranged outside the resonance chamber and the cooking chamber.

[0027] The cavity can be formed by another tube or hose. The diameter of the hose or pipe differs from the diameter of the resonator at the coupling point in order to create an impedance jump at the coupling point, thereby reducing the coupling between the cavity and the resonator and thus coupling less energy out of the resonator. The length of the cavity can also be selected such that the resonance frequency of the system consisting of the resonance chamber and cavity differs significantly from the resonance frequency of the resonance chamber, so that a clear distinction can be made in the frequency spectrum between the vibrations in the resonance chamber alone and any vibrations occurring in the system consisting of the cavity and resonance chamber.

[0028] Preferably, the cavity has a membrane arranged in the coupling point to protect the microphone from water vapor, dirt and heat.

[0029] For example, the cavity can be shaped to dampen or absorb vibrations at its end facing away from the coupling point, in particular tapering towards the end, in particular tapering to a point, so that vibrations in the cavity are dampened and no standing waves can form in the cavity.

[0030] The cavity can also be provided with sound-absorbing material, particularly at its end facing away from the coupling point, so that vibrations in the cavity are not reflected.

[0031] In one design variant, the cavity widens in a funnel shape toward the coupling point. This allows for the use of a thin membrane with a large surface area and prevents reflections at the coupling point.

[0032] In a further embodiment of the invention, the microphone is provided in the resonance chamber, whereby the amplitudes of the vibrations in the resonance chamber can be measured directly and accurately.

[0033] Preferably, the microphone or coupling point is positioned in the region of the maximum sound pressure of one or more of the natural oscillations of the resonant chamber, thereby achieving good coupling of the microphone to the resonator, thus improving the quality of the measurement. Other positions for the microphone or coupling point that provide favorable coupling are also conceivable. One possible position for the microphone or coupling point is the center of the tube relative to its longitudinal axis.

[0034] Further features and advantages of the invention will become apparent from the following description and the accompanying drawings, to which reference is made. In the drawings: - Fig. 1 a first embodiment of a cooking appliance according to the invention schematically in section, - Fig. 2 an enlarged view of a part of the cooking appliance according to Fig. 1, - Fig. 3 an exemplary control unit of the cooking appliance according to the invention according to Fig. 1 determined frequency spectrum, - Fig. 4 a schematic flow diagram of the method for determining moisture, - Fig. 5 is an enlarged view of part of a second embodiment of a cooking appliance according to the invention, and - Fig. 6 a third embodiment of a cooking appliance according to the invention schematically in section.

[0035] In Fig. Figure 1 shows a cooking appliance 10 intended for professional use in commercial kitchens and large-scale catering. This appliance is, for example, a combi steamer that can prepare various foods using hot air and / or hot steam. For this purpose, an atmosphere is created in the cooking chamber 12 that has the desired temperature and humidity for cooking. The temperature and humidity are controlled by a cooking appliance control system, which controls a heating device and an evaporator. For reasons of clarity, the cooking appliance control system, the heating device, and the evaporator have been omitted.

[0036] The cooking chamber 12 and the technical chamber 14 are separated from each other by a rear wall 16 of the cooking chamber 12.

[0037] A fan wheel 18 and a resonator 20 are arranged on the rear wall 16 on the cooking chamber side, wherein the fan wheel 18 represents a sound generator 22.

[0038] The resonator 20 is attached to the rear wall 16 by means of a fastening 23. The area of ​​the cooking appliance 10 around the resonator 20 is in Fig. 2 shown enlarged.

[0039] The resonator 20 is designed as a tube and has, for example, a length L of 20 cm and an inner diameter between 1.5 cm and 2 cm. Both ends of the tube are open, so that the resonator 20 is a resonator open on both sides. However, it is also conceivable that only one side of the resonator 20 is open.

[0040] The resonator 20 defines a resonance chamber 24 within the tube. The resonance chamber 24 is thus located within the cooking chamber 12 and is open toward the cooking chamber 12.

[0041] The tube and thus the resonator 20 are arranged vertically in the cooking chamber 12. As a result, when cleaning the cooking appliance 10, the washing solution also penetrates the tube of the resonator 20 and thus cleans the resonator 20.

[0042] A cavity 26 is provided on the resonator 20, which can be formed by a hose or another tube.

[0043] The cavity 26 opens into the resonance chamber 24 of the resonator 20, wherein the point at which the cavity 26 merges into the resonance chamber 24 is referred to as the coupling point 28.

[0044] At the coupling point, a thin membrane 30 is provided which closes the cavity 26 from the resonance chamber 24 so that neither hot air, nor water vapor, nor dirt can penetrate into the cavity 26.

[0045] At the same time, however, the membrane 30 can vibrate, so that vibrations can be transmitted from the resonance chamber 24 into the cavity 26. The cavity 26 and the resonance chamber 24 are thus acoustically coupled.

[0046] In the embodiment shown, the cavity 26 opens centrally into the resonance chamber 24, viewed in the longitudinal direction of the resonator 20. In other words, the coupling point 28 in the embodiment shown is located halfway along the length L / 2 of the resonator 20.

[0047] The diameter of the cavity 26 at the coupling point 28 differs from the diameter of the resonance chamber 24. For example, the diameter of the cavity 26 is significantly smaller.

[0048] The cavity 26 extends in the other direction, ie from the resonator 20 through the rear wall 16 into the technical room 14.

[0049] At the end of the cavity 26 facing away from the resonator 20, the tube or pipe defining the cavity 26 tapers to a point and is closed. Thus, the cavity 26 is shaped to dampen and absorb vibrations at its end facing away from the coupling point 28.

[0050] Sound-absorbing material 32 can also be provided in the cavity 26.

[0051] In the embodiment shown, a microphone 34 is provided in the area of ​​the cavity 26 which is located within the technical room 14.

[0052] In addition, in the embodiment shown, a temperature value unit 36 ​​in the form of a temperature sensor is provided on the resonator 20.

[0053] A control unit 38 is located in the technical room 14 and is connected to the microphone 34 and the temperature sensor 36. The control unit 38 receives signals from both the microphone 34 and the temperature sensor 36.

[0054] The control unit 38 has a module 40 that receives the signals from the microphone 34 and can perform a spectral analysis of the received signal using a Fourier analysis and / or a correlation function. In this way, the module 40 can determine the frequency spectrum ( Fig. 3) of the signal from the microphone 34 and thus determine the frequency spectrum of the vibrations in the resonance chamber 24.

[0055] By means of one or more openings 42 in the wall of the resonator 20 or the tube of the resonator 20, it is possible to influence which overtones can develop in the resonator 20.

[0056] To determine the humidity during operation of the cooking appliance 10, sound is first generated in the cooking chamber 12 (S1). In the embodiment shown, this is done by the fan wheel 18, which generates a broadband noise during operation, thus serving as a sound generator 22 with a broadband spectrum.

[0057] The sound generated by the sound generator 22 propagates to the resonator 20 and excites the natural vibrations of the resonator 20, i.e., the resonance chamber 24. This creates standing acoustic waves in the resonance chamber 24. In addition to the fundamental vibration or fundamental tone of the resonator 20, one or more overtones can also be excited in the resonance chamber 24 (S2).

[0058] It is also conceivable that only overtones are excited if the frequency of the fundamental vibration lies outside the range generated by the sound generator 22.

[0059] The fundamental oscillation of the resonator 20 has pressure nodes at the two openings of the resonator tube 20 and a pressure antinode at half the length L / 2. This pressure antinode thus forms at the coupling point 28 and causes the oscillations to propagate through the membrane 30 into the cavity 26.

[0060] In the cavity 26, the acoustic vibrations are then recorded by the microphone 34 and transmitted as an electrical signal to the control unit 38, more precisely to the module 40 for spectral analysis (S3).

[0061] In order to prevent a standing wave from forming within the cavity 26, the cavity 26 is provided with the sound-absorbing material 32 and tapers at its end facing away from the coupling point 28.

[0062] In addition, the diameter of the cavity 26 is selected to be smaller than that of the resonance chamber 24 or the resonator 20, so that the coupling between the system consisting of the cavity 26 and the resonance chamber 24 and the resonance chamber 24 alone is reduced. If the coupling is too high, and especially if the cavity 26 is too large, too much power would be extracted from the natural oscillation in the resonance chamber 24, thereby damping this natural oscillation.

[0063] In addition, by a suitable choice of the length of the cavity 26, the resonance frequency of the system consisting of cavity 26 and resonance chamber 24 can be selected sufficiently far away from the resonance frequency of the resonance chamber 24 alone.

[0064] The spectral analysis module 40 receives the signals recorded by the microphone 34 and, using a Fourier analysis and / or correlation function, determines the frequency spectrum of the signal and thus the frequency spectrum of the oscillations excited in the resonance chamber 24 (S4).

[0065] Such a determined spectrum is in Fig. 3. Based on the determined frequency spectrum, the module 40 determines the frequency F0 of the fundamental vibration or the fundamental tone of the natural vibrations of the resonance chamber 24 (S5).

[0066] In Fig. In the case shown in Figure 3, the frequency F0 of the fundamental oscillation can be easily read from the frequency spectrum. If necessary, the read value F0 can be compared with the frequencies F1, F2, and F3 and corrected.

[0067] In the event that the fundamental oscillation was not excited in the resonance chamber 24 and is therefore not present in the frequency spectrum, the module 40 determines the frequency F0 of the fundamental oscillation based on the distances between the frequencies F1, F2, F3 of the overtones occurring in the frequency spectrum.

[0068] Because the entire spectrum of vibrations generated in the resonant chamber 24 is determined continuously or at regular intervals, it is irrelevant how precisely the sound generator 22 is operated or controlled. The sound generator 22 only needs to generate a broadband signal that excites acoustic vibrations in the resonant chamber 24. Adjusting the phase of the generated sound or anything similar is not necessary. The determination of the humidity and the frequency spectrum is thus independent of the control of the sound source.

[0069] Based on the frequency F0 determined by the spectral analysis module 40, the control unit 38 now determines the speed of sound within the resonance chamber 24 using the formula c = λ0 · F0, where λ0 is the wavelength of the fundamental oscillation. The wavelength of the fundamental oscillation λ0 is known due to the geometry of the resonance chamber 24 and is stored in the control unit 38. In the embodiment shown, the wavelength λ0 corresponds approximately to twice the length 2L of the resonator 20 (S6).

[0070] In order to determine the humidity within the cooking chamber, the control unit 38 requires the value of the temperature T in the resonance chamber 24.

[0071] For this purpose, a temperature value is first generated by the temperature value unit 36 ​​in a step S7.

[0072] In the embodiment shown, the temperature value unit 36 ​​is the temperature sensor on the resonator 20, so that the temperature value is generated by measuring the temperature of the resonator 20.

[0073] However, it is also conceivable that the temperature value unit 36 ​​generates the temperature value from data from the cooking appliance control system. For example, the temperature value unit 36 ​​obtains the target temperature of the heating device from the cooking appliance control system.

[0074] The control unit 38 receives the temperature value in step S8 and adjusts the temperature value if necessary. This may be necessary if the resonator 20 is located outside the cooking chamber 12 but is connected to it, so that it is filled with the cooking chamber atmosphere, while the temperature sensor is provided inside the cooking chamber 12, so that the temperature T in the resonance chamber 24 is lower than the measured temperature in the cooking chamber 12. In this case, the control unit 38 can correct the value received from the temperature value unit 36. The control unit 38 also corrects the temperature value if necessary if the temperature value was generated by the temperature value unit 36 ​​in a different way, as described above, for example if the temperature value 36 is the target temperature of the heating device.

[0075] In the embodiment shown, however, the temperature value corresponds directly to the temperature of the resonator 20 and thus to the temperature T of the resonance chamber 24 and can be used immediately.

[0076] Now, in step S9, the control unit 38 determines the humidity in the cooking chamber 12 using the determined speed of sound c and the temperature T in the resonance chamber 24. The speed of sound c depends on the temperature T and the composition of the atmosphere within the resonance chamber 24: c=(κatmo⋅Rmol⋅T)Matmo, where R moı is the universal gas constant, K atmo the adiabatic exponent and M atmo the molar mass of the gas mixture of water vapor and air in the cooking chamber atmosphere.

[0077] M atmo and K atmo or their ratio can be determined, since the speed of sound c, the universal gas constant R mol and the temperature T are known.

[0078] In this way, the composition of the atmosphere in the resonance chamber 24 can be determined, ie the proportion of water vapor to air in the atmosphere, which also determines the humidity in the atmosphere in the cooking chamber 12.

[0079] Of course, the two equations can also be inserted into each other and solved for the ratio of M atmo to K atmo Other ways of calculating this ratio are also conceivable.

[0080] The humidity value determined in this way can now be transferred from the control unit 38 to the cooking appliance control of the cooking appliance 10.

[0081] Further embodiments of the cooking appliance according to the invention are described below, which essentially correspond to the first embodiment. Identical or functionally equivalent parts are provided with the same reference numerals, and only the differences will be discussed.

[0082] Fig. Figure 5 shows an enlarged view of a part of a cooking appliance 10 according to a second embodiment of the invention. The representation of the Fig. 5 corresponds to the representation of the Fig. 2 to the first embodiment.

[0083] In contrast to the first embodiment, no cavity 26 is provided, but the microphone 34 is arranged directly in the resonator 20, i.e. in the resonance chamber 24.

[0084] The microphone 34 can be arranged at the location where the coupling point 28 was arranged in the first embodiment, ie in the longitudinal direction of the tube of the resonator 20 approximately at half the length L / 2.

[0085] By arranging the microphone 34 in the resonance chamber 24, the temperature in the resonance chamber 24 can be measured directly. However, in this embodiment, the microphone 34 is also exposed to the hot and sometimes greasy atmosphere in the cooking chamber, which significantly increases the demands on the load capacity of the microphone 34.

[0086] In Fig. 6 shows a third embodiment of a cooking appliance 10 according to the invention.

[0087] In the third embodiment according to Fig. 6, no separate resonator 20 is provided, but the cooking chamber 12 itself serves as a resonance chamber 24.

[0088] The method for generating acoustic vibrations in the resonance chamber 24 also differs from that of the first embodiment.

[0089] In the embodiment according to Fig. 6, the sound generator 22 is a loudspeaker 44.

[0090] The loudspeaker 44 is provided in a loudspeaker room 46 which is located within the technical room 14 and which is connected to the cooking chamber 12 by a line 48.

[0091] A further membrane 50 is provided in the line 48, which enables an acoustic coupling between the cooking chamber 12 and the loudspeaker chamber 46, but at the same time protects the loudspeaker 44 from the atmosphere of the cooking chamber 12.

[0092] It is of course also conceivable that the loudspeaker 44 is arranged in the cooking chamber 12.

[0093] A loudspeaker control 52 is electrically connected to the loudspeaker 44 and controls the loudspeaker 44.

[0094] In the embodiment shown, the microphone 34 is arranged centrally on the floor of the cooking chamber 12. It is, of course, also conceivable to mount the microphone 34 on a side wall or the ceiling of the cooking chamber 12.

[0095] The loudspeaker control 52 controls the loudspeaker 44 so that it emits white noise, i.e. a broadband sound signal.

[0096] Alternatively, the loudspeaker 44 can perform frequency sweeps by controlling the loudspeaker controller 52. In this case, the loudspeaker 44 generates acoustic oscillations each with a single frequency, i.e., pure tones, with the pitch, i.e., the frequency, of these oscillations repeatedly sweeping through a predetermined frequency band. Thus, the output of the loudspeaker 44 is also broadband in this case, since tones are generated at different frequencies.

[0097] Stimulated by the loudspeaker 44, standing waves are now formed in the cooking chamber 12, similar to the resonator 20 of the first embodiment, which correspond to the fundamental vibration and / or overtones of the resonance chamber 24.

[0098] In this embodiment, the vibrations are also detected by the microphone 34, and the determination of the frequency F0 of the fundamental vibration of the cooking chamber 12 and the determination of the humidity within the cooking chamber 12 are carried out in the same manner as described for the first embodiment.

[0099] Naturally, the features of the embodiments shown can be combined with each other as desired. In particular, it is conceivable that the embodiment according to Fig. 1 can also be designed without a separate resonator 20 and / or the cooking chamber 12 is also used as a resonance chamber 24.

[0100] In the first embodiment, a loudspeaker 44 can also serve as the sound generator 22.

[0101] It is also conceivable that the control unit 38 and / or the loudspeaker control 52 are integrated into the cooking appliance control.

Claims

[1] Method for determining the humidity within a cooking chamber (12) of a cooking appliance (10), comprising the following steps: a) an acoustic vibration is generated in a resonance chamber (24) in the cooking appliance (10), b) a control unit (38) receives the signals picked up by a microphone (34) in the resonance chamber (24), c) the control unit (38) determines the frequency spectrum of the acoustic vibrations present in the resonance chamber (24) on the basis of the received signals and the speed of sound within the cooking chamber (12) on the basis of the frequency spectrum, d) the control unit (38) receives a temperature value, e) the control unit (38) determines the humidity inside the cooking chamber (12) using the temperature value and the speed of sound. [2] Method according to claim 1, characterized bythat the temperature value corresponds to the temperature in the resonance chamber (24) and / or the control unit (38) can determine the temperature in the resonance chamber (24) based on the temperature value. [3] Method according to claim 1 or 2, characterized by that the control unit (38) determines the frequency spectrum by means of a Fourier analysis and / or by determining a correlation function. [4] Cooking appliance (10) with a resonance chamber (24), a sound generator (22), a microphone (34) associated with the resonance chamber (24), a temperature value unit (36) which can generate a signal dependent on the temperature of the atmosphere in the resonance chamber (24), and a control unit (38) to which the microphone (34) and the temperature value unit (36) are connected, wherein the control unit (38) contains a module (40) for spectral analysis, in particular a Fourier analysis and / or a correlation function module. [5] Cooking appliance (10) according to claim 4, characterized bythat the cooking appliance (10) has a fan wheel (18), wherein the fan wheel (18) represents the sound generator (22). [6] Cooking appliance (10) according to claim 4, characterized by that the cooking appliance (10) has a loudspeaker (44), wherein the loudspeaker (44) represents the sound generator (22). [7] Cooking appliance (10) according to claim 6, characterized by that the cooking appliance (10) has a loudspeaker control (52) which is designed such that it controls the loudspeaker (44) such that the loudspeaker (44) emits noise or carries out a frequency sweep. [8] Cooking appliance (10) according to one of claims 4 to 7, characterized by that the cooking chamber (12) of the cooking appliance (10) is the resonance chamber (24). [9] Cooking appliance (10) according to one of claims 4 to 7, characterized by that the resonance chamber (24) is located within a resonator (20) which is open to the cooking chamber (12) of the cooking appliance (10). [10] Cooking appliance (10) according to claim 9, characterized bythat the resonator (20) is arranged in the cooking chamber (12) of the cooking appliance (10). [11] Cooking appliance (10) according to claim 9 or 10, characterized by that the resonator (20) is designed as a tube. [12] Cooking appliance (10) according to one of claims 4 to 11, characterized by that the cooking appliance (10) has a cavity (26) which is acoustically coupled to the resonance chamber (24) at a coupling point (28), wherein the microphone (34) is provided in the cavity (26). [13] Cooking appliance (10) according to claim 12, characterized by that the cavity (26) has a membrane (30) which is arranged in the coupling point (28). [14] Cooking appliance (10) according to claim 12 or 13, characterized by that the cavity (26) is shaped to dampen or absorb vibrations at its end facing away from the coupling point (28), in particular tapers from the coupling point (28), in particular tapers to a point. [15] Cooking appliance (10) according to one of claims 12 to 14, characterized by that the cavity (26), in particular at its end facing away from the coupling point (28), is provided with sound-absorbing material (32). [16] Cooking appliance (10) according to one of claims 12 to 15, characterized by that the cavity (26) widens in a funnel shape towards the coupling point (28). [17] Cooking appliance (10) according to one of claims 4 to 11, characterized by that the microphone (34) is provided in the resonance chamber (24). [18] Cooking appliance (10) according to one of claims 4 to 17, characterized by that the microphone (34) or the coupling point (28) is arranged in the region of the maximum of the sound pressure of one or more natural oscillations of the resonance chamber (24).

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