WO2019162086A1 - Operating a domestic appliance with a defrosting function - Google Patents

Abstract

A method (S1-S7) serves to determine a defrosting state operating a domestic appliance (1) with a defrosting function, wherein at the start of a defrosting process microwave radiation at different frequencies is irradiated (S1) into a treatment space (2), reflected microwave radiation is measured (S1) for each of the irradiated frequencies, and on the basis of the reflected microwave radiation at least one frequency is selected (S2) as a measuring frequency, and the defrosting state is subsequently determined (S3-S5) on the basis of an evaluation of reflective microwave measurement radiation of only the at least one selected measuring frequency. A domestic appliance is configured to enable the method to run. The invention can be applied particular advantageously to cooking devices or freezing devices, specifically to cooking devices with a microwave function, also for heating foodstuffs, particular microwave ovens and combined baking/microwave ovens.

Description

 Operating a home appliance with defrost function

The invention relates to a method for operating a household appliance with a thawing function. The invention also relates to a household appliance, which is set up to carry out the method. The invention is particularly advantageously applicable to cooking appliances or freezers, in particular to cooking appliances with a microwave function also for heating food, especially microwave ovens and combined back / microwave ovens.

US 4,520,250 discloses a heater in which a signal wave is directed to a frozen food and the change in the absorption rate of the signal wave due to a dielectric loss of the food is measured to automatically control a heating process for thawing based on the measurement result.

WO 2012001523 A2 discloses a method for processing an object. The method includes heating the object by applying radio frequency (RF) energy, monitoring a value for an absorption rate of RF energy through the object during heating, and adjusting the RF energy in accordance with changes in one time derivative of the monitored signal value.

It is the object of the present invention to overcome the disadvantages of the prior art, at least in part, and in particular to provide an improved possibility of determining a thawing state of frozen material to be treated in a domestic appliance, in particular cooking appliance.

This object is achieved according to the features of the independent claims. Advantageous embodiments are the subject of the dependent claims, the description and the drawings.

The object is achieved by a method for operating a domestic appliance with a defrosting function, in which microwave radiation with different frequencies enters a treatment chamber of the household appliance at the beginning of a thawing process. is irradiated, a reflected microwave radiation is measured for each of the irradiated frequencies, based on the reflected microwave radiation at least one frequency is selected as a measurement frequency and the thawing condition is determined based on an evaluation of a reflected microwave measurement radiation only the at least one selected measurement frequency.

The fact that at the beginning of a thawing process the microwave measuring radiation with different measuring frequencies is irradiated into a treatment chamber of the domestic appliance and that a reflected microwave measuring radiation is measured for each of the irradiated measuring frequencies can also be referred to as an "initial scan".

This method has the advantage that a thawing condition of frozen treatment material (for example, food or other objects) in a domestic appliance can be detected particularly quickly and precisely. For an initial selection of the measurement frequencies by means of the initial scan makes it possible for the expected course of the reflected microwave measurement radiation to have sufficient dynamics (change potential) in order to be easily evaluable. By appropriate selection of certain measurement frequencies of the microwave radiation, the risk of a wrong decision during thawing is significantly reduced. The thawing condition may include, in particular, the states "not thawed" and "thawed". The thawing condition may also include the condition "thawing".

The domestic appliance is in particular an electrically operated domestic appliance that is set up to specifically introduce or input heating power for heating laundry to be treated in the treatment room. For this purpose, the treatment chamber can be designed, in particular, as a resonance chamber for the microwave radiation with electrically conductive surfaces.

It is a development that the household appliance is a cooking appliance. The treatment room can then be a cooking chamber or be referred to as a cooking chamber.

It is still a development that the household appliance is a refrigerator, in particular freezer. The treatment room can then be a refrigerator or freezer or be referred to as a refrigerator or freezer. The microwave measuring radiation can be introduced into the treatment room by means of a microwave transmitter of the household appliance. The microwave transmitter can have a microwave generator such as a magnetron or a semiconductor microwave generator for generating the microwave radiation and possibly a microwave guide and / or an antenna, etc.

The fact that the microwave radiation is radiated into the treatment space at different frequencies during an initial scan comprises in particular that microwave radiation having different frequencies is irradiated in succession into the treatment space. For this purpose, the microwave generator can be adjusted according to the respective frequencies. This can also be referred to as a "sweep", in particular if the microwave radiation is irradiated with temporally ascending or descending measuring frequencies.

It is a further development that the microwave radiation used for carrying out the initial scan or its frequency band determined by the frequencies lies in at least one ISM band, e.g. between 902 MHz and 928 MHz, between 2.4 GHz and 2.5 GHz and / or between 5.725 GHz and 5.875 GHz.

A start of a thawing process can be understood to mean a period of time during which no heating power is still radiated into the treatment space, which is specifically provided for heating the material to be treated. Also, a start of a defrosting operation may be understood as a period of which the beginning coincides with a beginning of an introduction of heating power.

The fact that at least one measurement frequency is selected on the basis of the reflected microwave radiation may include that the measurement frequency is selected on the basis of at least one with the measured power of the reflected microwave radiation and / or on the basis of at least one quantity derived therefrom. A derived quantity can be, for example, a reflectance of the microwave measurement radiation, ie a ratio of the power of the reflected microwave radiation to a power of the irradiated microwave radiation. In general, instead of the degree of reflection, the degree of absorption can be determined and used analogously. Is hereafter from a degree of reflection the speech, can be used analogously, the degree of absorption for determining the thawing state. The performance and the quantities derived from it are also collectively referred to as "performance quantities" below.

The evaluation of the reflected microwave measuring radiation can be carried out based on at least one output of the reflected microwave measuring radiation. In this case, the at least one performance variable used to select the measurement frequency (s) need not correspond to the at least one performance variable used for the subsequent determination of the thawing condition, but it may.

The reflected microwave measuring radiation can be measured by a microwave measuring device. The microwave measuring device may e.g. have a (microwave) antenna and a measuring unit connected downstream of the antenna. It is advantageous that the antenna of the microwave measuring device is not in a direct beam path to the microwave transmitter. However, in principle it is also possible (in particular when using a plurality of microwave transmitters) that in addition to the reflected microwave measuring radiation, transmitted microwave radiation is also measured.

The antenna of the microwave measuring device may correspond to an antenna of the microwave transmitter or be a separate antenna. The measuring unit may be or have a bolometer or a (measuring) diode. In general, the microwave transmitter and the microwave measuring device can be separate devices or integrated in a device.

It is a further development that only microwaves or microwave measurement radiation are irradiated into the treatment room to determine a thawing state during operation of the household appliance, which have the at least one selected measuring frequency. This provides the advantage that a time duration for generating the microwave radiation and its evaluation is particularly short. Alternatively, it is also possible to irradiate microwaves into the treatment space which do not have the at least one selected measuring frequency, and subsequently an evaluation is carried out only for the microwave measuring radiation having the at least one selected measuring frequency. Based on the determination of the thawing condition (in particular a determination that the material to be thawed or is in the process of thawing), a thawing operation of the household appliance can be controlled, eg a thawing process can be ended, in the case of a cooking appliance a transition between a thawing process and cooking, etc.

It is an embodiment that the at least one measurement frequency is selected according to the fact that the associated reflected microwave radiation fulfills at least one of the following selection criteria:

 - she belongs to a group with highest reflections;

 - It belongs to a group with highest reflected microwave power;

 - she belongs to a group with the lowest levels of reflection;

 it belongs to a group with the lowest reflected microwave power;

- Their reflectance reaches or exceeds at least a predetermined first ("upper") threshold;

 - Their reflected microwave power reaches or exceeds at least a predetermined upper threshold value;

 - Their reflectance reaches or falls below at least a predetermined second ("lower") threshold;

 - Their reflected microwave power reaches or falls below at least a predetermined lower threshold.

These selection criteria make it possible to select measurement frequencies in a particularly easy-to-understand manner, with which the thawing state can be determined particularly precisely.

A group may comprise an element or member (ie, microwave radiation of exactly one measurement frequency) or multiple elements or members (ie, microwave radiation of multiple measurement frequencies). Thus, the group with the highest reflectivities can comprise only the highest reflectivity microwave radiation or the highest two, three, ... reflectance microwave radiations, etc. It is an embodiment that at least one measurement frequency is or has been selected and a thawing state based on a change of at least one performance variable of the associated reflected microwave measurement radiation (ie, the reflected micro-radiation) determined over a time course of a thawing process or a portion thereof. wave power and / or at least one derived therefrom such as a degree of reflection) is determined. It is exploited that a phase transition of water from solid to liquid takes place spatially in macroscopic domains, and takes place within the water domains practically abruptly. This is accompanied by a significant change in the dielectric properties of the material to be treated. The quality factor of the treatment space, which in a good approximation represents a resonance chamber, is significantly influenced here. The reflectance of the microwave measuring radiation reflects the change in the quality factor. The microwave measurement radiation does not directly indicate the absorption capacity of the material to be treated, but the quality of the coupling between the microwave transmitter and the treatment room. This quality of the coupling decisively determines the reflection behavior.

The change of the time profile may be a reduction or an increase of the at least one power quantity of the reflected microwave measuring radiation. In particular, the change is an abrupt change ("step response"), i.e. that it occurs within a comparatively short period of time compared to the thawing process, e.g. within a period of 5, 10, 15, 20, 25 or 30 seconds. The change may be e.g. at least 40%, in particular at least 50%, in particular at least 70%, in particular at least 80%, in particular at least 90%, of an initial value of the at least one output quantity.

It is an embodiment that a plurality of measurement frequencies are selected or are and the thawing state is based on a change in at least one power quantity of the reflected microwave measurement radiation (ie, the reflected microwave power and) determined over a time course of a thawing or section thereof / or at least one derived quantity such as a reflectance) per selected measurement frequency. This way, the thawing condition can be detected very precisely. It is a further development that heating power is introduced into the treatment space during a thawing process in order to heat the material to be treated, and measurements are carried out by the microwave measuring radiation, in particular several times in a row, which show a temporal course of the at least one performance variable of the reflected Generate microwave measuring radiation. If the performance variable changes noticeably over a short period of time in the course, for example abruptly, a transition from a frozen state to a thawed state (phase transition from solid to liquid) can be concluded.

In this embodiment, therefore, the curves of the at least one power variable are evaluated separately for each of the selected measurement frequencies. A thawing state can then be determined from the fact that one or more of the courses belonging to different measuring frequencies (in particular of all courses) show a change in the output quantity indicating a phase transition.

The change in the power quantity can be determined, for example, from a percentage change in an initial value and / or from a time derivative (slope) of the power quantity. For example, a thawing or thawing condition may be inferred when a percentage decrease in reflectance within a predetermined short period of time (eg, 5, 10, 20, or 30 seconds) reaches a predetermined threshold or is minimized (or absolute values maximum) and / or the slope reaches a predetermined threshold or becomes minimal (or maximum in absolute values).

It is a further development, which is particularly advantageous for determining a change of the thawing state, that, for recording the course, a plurality of successively determined performance quantities are averaged, e.g. the last five or ten performance variables. In this way fluctuations in the course can be reduced or the progression curve can be smoothed.

It is an embodiment that a plurality of measurement frequencies are selected or are and the thawing state is determined on the basis of a change of at least one performance variable of the common reflected microwave measurement radiation of at least one group comprising several measurement frequencies over a time course. selected measuring frequencies is determined. In one variant, the at least one performance variable determined for several measurement frequencies of a measurement process or measurement section (also referred to as a "measurement cycle") can be considered together, eg averaged. In another variant, the measured values measured by the microwave measuring device for a plurality of measuring frequencies of a measuring process or measuring section (also referred to as "measuring cycle") can be linked, eg averaged, and from this at least one common or summarized output quantity can be considered together. Both allow a particularly robust evaluation. This configuration may include that the thawing state is determined on the basis of the reflected microwave measuring radiation of all selected measuring frequencies of a measuring cycle, for example by averaging the measured values over all measuring frequencies. However, it is also possible that at several measuring frequencies only microwave measuring radiation of one or more sub-groups of all measuring frequencies of a measuring cycle are combined. This embodiment can be further developed analogously to the above embodiment with separate evaluation at different measurement frequencies.

It is an embodiment that the domestic appliance is set up to heat treatment material in the treatment room by means of at least one of the following types of heating:

 - Microwave irradiation by microwave useful radiation;

 - Irradiation of further electromagnetic energy

 - heat radiation through at least one resistance heater;

 - Heat treatment by hot air introduction and / or steam injection.

This results in the advantage that the method can be carried out on a large number of household appliances. The household appliance may be, for example, a microwave oven, an oven or a combination thereof, a freezer, etc. If the household appliance is equipped for microwave radiation by microwave useful radiation, the microwave measuring radiation and the microwave useful radiation can be generated by different microwave transmitters or by the same microwave transmitter. For example, the useful microwave radiation can be generated in a frequency band between 902 MHz and 928 MHz or between 2.4 GHz and 2.5 GHz. By the microwave measuring device, the power of the microwave useful radiation can then be measured. In a further development, the microwave measuring radiation and the microwave useful radiation is measured by different microwave measuring devices.

It is an embodiment that treatment items located in the treatment room are heatable by means of microwave useful radiation (ie the household appliance has a microwave heating function, eg a microwave oven or a baking oven / microwave oven combination) and a frequency comprising the measuring frequencies. Frequency range of the microwave measuring radiation and a frequency range of microwave useful radiation are different. This reduces possible crosstalk between microwave measurement radiation and microwaveable useful radiation provided for heating the material to be treated and also allows simultaneous measurement of the thawing state by microwave measurement radiation and heating by microwave useful radiation, in particular if the microwave measurement radiation and the microwaves Use radiation generated by different microwave generators. The frequency ranges of the microwave radiation and the microwave useful radiation can be in the same ISM band or in different ISM bands. In a specific example, the microwave useful radiation can be generated in a frequency band between 902 MHz and 928 MHz or between 2.4 GHz and 2.5 GHz, while the microwave measurement radiation is generated in a frequency band between 5.725 GHz and 5.875 GHz. A measuring device measuring the microwave measuring radiation can, in particular for this embodiment, have a protective network which protects the measuring device against power peaks of microwave useful radiation reflected from the cooking chamber. This can e.g. be implemented by providing a filter that is permeable to the microwave measurement radiation, but blocks the microwave useful radiation.

It is an embodiment that treatment material located in the treatment space can be heated by means of microwave useful radiation and a frequency range of the microwave measurement radiation which encompasses the measurement frequencies and a frequency range of the microwave useful radiation are the same. This embodiment has the advantage that only one microwave generator is needed. In particular, the selected measurement frequencies can be used during a measurement section or measurement cycle for generating and measuring the reflected microwave radiation and during a warm-up section or warm-up cycle separated therefrom for heating the treatment good, possibly with different power levels. It is an embodiment that heating power with m (m> 2) different predetermined sets of heating parameters in the treatment room can be introduced, the heating power for different sets of heating parameters located in the treatment room befindliches material to be heated locally different and in the during the thawing process

 a) the heating power is radiated with one of the sets of heating parameters and a time profile of at least one power quantity of the reflected microwave radiation is determined,

 b) when, for this thawing section, a thawed state is or has been detected by means of the time profile of the at least one performance variable, following

 c) repeating steps a) and b) for heating power with at least one other of the sets of heating parameters.

This embodiment has the advantage that the material to be treated is particularly uniformly defrostable, since the distribution of the energy input into the frozen product is changed by the change in the heating parameters and, as a result, particularly even power is introduced into the material to be treated. Thus, a large-volume material to be treated can be thawed uniformly reliable. The thawing process can have a chronological sequence of several thawing sections with different heating parameters.

The heat output corresponds to the heat output, which is intended to heat the treatment good, while the microwave measuring radiation is assigned virtually no heating power. This can be implemented in such a way that the microwave measurement radiation is irradiated into the treatment room with low power and / or only for a short period of time. If a measurement cycle takes only a short period of time (for example, less than one second), this can optionally also be done at the power level of the heating power, since there is no significant change in the material to be treated by the measurement process in this short period of time.

Depending on the configuration of the domestic appliance, the heating output may comprise, for example, a microwave power, a heating power generated by electrical resistance heaters, etc. Heating parameters can generally be understood as meaning all device parameters. those which influence or adjust a local distribution of the heating power in the treatment room. The heating parameters can therefore also be referred to as heating power localization parameters.

However, the heating parameters applied or used during a thawing section need not be constant until the thawing is detected and may be dynamic and may be e.g. also not be determined repeatedly. A set of heating parameters may thus comprise a group of constant or a group of non-constant heating parameters. The heating parameters of a block can be preset or dynamically adjusted.

For example, in the case of microwave power input, the heating parameters may include one or more of the following parameters:

 - frequency,

 - phase,

 Amplitude,

 - antenna position,

 - wobble frequency.

In the case of introduction of heat by irradiation of further electromagnetic energy, this may involve the introduction of electromagnetic radiation having a frequency of not more than 900 MHz, in particular radiation having a frequency between 1 MHz and 900 MHz, especially in a range between 30 and 50 MHz.

For example, if heat is introduced through at least one resistance heater, the heating parameters may include, for example, one or more of the following parameters:

 - type of radiator activation (top heat, bottom heat, hot air etc. or a combination thereof),

 - Activation of a recirculation fan.

It is an embodiment that the thawing process is terminated when - the steps a) and b) have been carried out for all m sets of microwave parameters; and or

 - if in at least one of steps b) initially no frozen state has been detected.

The fact that in step b) initially no frozen or already thawed state is detected in one of the thawing sections can be established, for example, during a first measuring cycle or during several initial measuring cycles within a thawing section, the power quantity of the reflected Microwave measuring radiation is less than a predetermined threshold, with values above this threshold corresponding to a frozen state. The threshold value may have been empirically determined and given or determined at the beginning of the thawing process, e.g. during the initial measurement.

Another possibility for determining a thawed state is in comparison with the reflection values of the selected measurement frequencies determined during the initial scan. If, at all or almost all measurement frequencies, the abrupt change in the value of the reflected microwave measurement radiation indicative of the phase transition has been established, it can be assumed that there are no longer any areas with frozen material to be treated.

It is a development that the steps a) to c) are performed repeatedly for all m sets of microwave parameters.

It is an embodiment that in step b), when for this thawing section, a thawing state (or a phase change from solid to liquid) resulting during the thawing section is detected, the heating power is reduced until a Re-freezing is determined or detected, and subsequently step c) is performed. By reducing the heating power re-freezing of a locally particularly heated area of the material to be treated is made possible by its possibly still frozen environment. The change of the heating parameters together with the determination of a re-freezing results in particular in the advantage that many zones or domains can be generated in the material to be treated whose water fractions after re-freezing immediately before thawing or before a phase transition from solid to be too fluid. The re-freezing can be detected, for example, by means of an opposite change following the sharp change in the power quantity of the reflected microwave measuring radiation, for example, by increasing the reflectance after a large reduction in the reflectance. The purpose of re-freezing is to heat up areas that are already too hot, so that even liquid areas are not disproportionately heated due to the higher absorption capacity of water compared to ice under microwave irradiation. This achieves improved power regulation during a thawing process.

That the heating power is reduced with the detection of the thawing in step b) may include that the heating power is switched off or reduced to zero.

It is an embodiment that the defrosting operation is terminated when no re-freezing is recognized for at least one of the defrosting sections.

It is an embodiment that when a thawing condition is detected for a thawing portion, the energy of the microwave measuring radiation is reduced until the end of thawing-out portion. Thus, the re-freezing retarding or preventing effect of the microwave measuring radiation can be suppressed.

It is an embodiment that in step a) a high heating power is radiated during a defrosting section of the thawing process. The high heating line may be a maximum heating power or a high percentage of the maximum heating power (e.g., 70%, 80% or 90% of the maximum heating power). This development provides the advantage that the thawing can be done very quickly.

It is a development that, when a thawed state has been detected, heating power is additionally introduced into the treatment room for a short time in order to be able to ensure the thawed state particularly reliably. In particular, the thawing state of the material to be treated can thus be effected particularly reliably from a state shortly before thawing to a thawed state. It is particularly preferred for the irradiation of useful microwave power that microwave useful radiation with m (m> 2) different predefined sets of microwave parameters can be introduced into the treatment space and that

 in step a) the useful microwave radiation is irradiated with one of the sets of microwave parameters and a time profile of at least one output of the reflected microwave measuring radiation, e.g. the reflectance,

 in step b), if a thawed state is detected for this thawing section by means of the course of the at least one performance variable

- in step c) the steps a) and b) is repeated for microwave useful radiation with at least one other of the sets of microwave parameters.

The object is also achieved by a household appliance, which is set up to run the method according to one of the preceding claims.

It is a development that the household appliance has at least:

 at least one microwave transmitter for irradiating microwave measuring radiation into the treatment room,

 at least one microwave measuring device for measuring microwave measuring radiation reflected from the treatment space and

 a data processing device for selecting the at least one measuring frequency of the microwave measuring radiation at least on the basis of measured data of the microwave measuring device and for determining the thawing state.

The household appliance can be designed analogously to the method and has the same advantages.

The data processing device can be integrated into a control device of the household appliance or a control device can have a data processing function for carrying out the method. In particular, in this case, the control device can be set up to control the microwave transmitter, for example, with regard to its microwave power and possibly the microwave parameters used in the irradiation of the microwaves. It is a development that the at least one microwave transmitter and the at least one microwave measuring device are separate components or components.

It is a further development that each one microwave transmitter and one microwave measuring device each represent a component ("microwave transceiver"). In this case, a microwave transmitter can measure the reflected power. The (transmitting) antenna used to irradiate the microwaves into the treatment space can also serve as a measuring or receiving antenna for the reflected microwave radiation in this development.

It is a development that the household appliance has a microwave transmitter and several microwave measuring devices. The microwave measuring devices are associated with respective microwave receiving antennas, which are spatially spaced apart. This has the advantage that the reflected microwaves are particularly precise detectable. In particular, the household appliance can then also be set up to evaluate the reflected microwaves in a spatially resolved manner. The spatial resolution is based on the position of the microwave receiving antennas. Another advantage is that the measured values generated by the plurality of microwave measuring devices can be interlinked, which enables a particularly precise determination of the thawing state.

In the event that the household appliance has a plurality of microwave transmitters, in particular the reflected and possibly transmitted microwave radiation generated by all microwave transmitters is measured and added to a measuring device.

In the event that the household appliance has a plurality of microwave transmitters, they can radiate in particular monofrequent microwaves in the treatment room, ie, that at any time all microwave transmitters irradiate microwaves of the same frequency in the treatment room. The use of multiple microwave transmitters gives the advantage of a particularly uniform heating of the material to be treated and / or a particularly high irradiated microwave power. It is one in the event that the household appliance has several microwave transceivers, advantageous development that at least one of the microwave transceivers is operated at least during at least one measurement cycle only as a microwave transmitter and at least one other of the microwave transceiver only is operated as a microwave receiver or microwave measuring device. During a heating cycle, for example, microwave transceivers, which serve only as a microwave measuring device in a measuring cycle, can also be used as microwave transmitters. The assignment of the microwave transceiver as a microwave transmitter or microwave measuring device can remain the same or change in the course of the process, especially within a measuring cycle. A change of such a function assigned to the microwave transceivers during a measurement cycle can further improve an accuracy of the determination of a thawing state, for example by a spatial resolution of the determination of the thawed regions.

For example, in the case of introduction of heat by at least one resistance heater, the household appliance may contain one or more of the following components or components:

 - top heaters,

 - grill radiator,

 - bottom heating radiator,

 - Ring radiator convection heating,

 - Recirculation fan.

In the case of introducing steam to heat a material to be treated, the domestic appliance may comprise a steam generator, e.g. an outside of the treatment room existing steam generator, a heated water bowl within the treatment room, etc.

The above-described characteristics, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following schematic description of an embodiment which will be described in more detail in conjunction with the drawings. 1 shows a sectional side view of a possible inventive household appliance in the form of a cooking appliance;

 FIG. 2 shows a plot of a power quantity derived from a reflected microwave measurement radiation versus the time for a thawing process; FIG. and FIG. 3 shows a flowchart for a possible operation of the cooking appliance

 Fig.1.

1 shows a sectional side view of a possible household appliance according to the invention in the form of a microwave oven 1. The microwave oven 1 has a cooking chamber 2 which can be loaded with foodstuffs L (i.e., one or more foods). The microwave oven 1 comprises a microwave transmitter 3 having a microwave generator 4 (e.g., a magnetron) and an antenna 5. Microwaves generated by the microwave generator 4 are fed via the antenna 5 into the cooking chamber 2. A control device 6 activates the microwave transmitter 3 and can, in particular, instruct the microwave generator 4 to generate the microwaves with certain microwave parameters, e.g. with respect to their microwave frequency, phase and / or amplitude. The control device 6 can also be set up to control a rotation of the antenna 5.

The antenna 5 is further coupled to a microwave measuring device 7, which, possibly together with the antenna 5, serves as a microwave receiver and measures microwave radiation reflected from the cooking chamber 2. The measuring device 7 may for this purpose comprise a bolometer or a diode used for the measurement. The microwave measuring device 7 is further coupled to the control device 6 in order to transmit measured data generated by the microwave measuring device 7, which represent a measure of the power of the reflected microwave radiation, to the control device 6. The control device 6 is also designed as a data processing device to process the measurement data, to determine a thawing state and to control the microwave oven 1, for example to control the microwave generator 4 accordingly.

2 shows a plot of a time curve V of a power quantity of a reflected microwave measurement radiation in the form of a reflectance R (in arbitrary units) versus time t in minutes for a thawing or thawing section. During the thawing process microwave useful radiation is radiated into the cooking chamber 2 in order to heat the foodstuff L. As long as the foodstuff L is still frozen or not yet thawed, the reflectance R determined from the reflected microwave radiation changes only slightly. With the phase transition of the water in the foodstuff L from frozen to liquid (thawing), the degree of reflection R within a phase transition time range PZ drops in a short time (for example within 12 seconds by more than 50% from R = 47 to R = 20) strongly, as shown here at t = about 6 minutes. This drop in the reflectance R can be clearly recognized and can also be described as a step response. However, if the microwave useful radiation does not penetrate the food L uniformly, it may occur that the drop in the reflectance R is caused due to only local phase transition or local thawing only, so that portions of the food L are already thawed other parts of the food L are still in a frozen (thawing) state.

In order to determine the thaw even more precisely, it is advantageous not to determine the degree of reflection R on the basis of all the microwave frequencies generated or generated by the microwave generator 4, but only by means of a selection thereof. The microwave useful radiation can then use more microwave frequencies than a microwave measuring radiation.

In particular, at the beginning of a thawing process, an initial scan can be performed on all microwave frequencies used or usable by the microwave generator 4. In this case, the microwave radiation is irradiated individually or at different times for all possible microwave frequencies and their reflection is measured by the measuring device 7. For example, a time window of 100 ms can be provided for each of the microwave frequencies. The control device 6 selects therefrom at least one measurement frequency, in particular a plurality of measurement frequencies, based on at least one stored selection criterion for the following use as measurement frequency (s). A frequency range of the microwave measurement radiation encompassing the measurement frequencies and a frequency range of the microwave useful radiation are thus identical. This also includes that the frequency range encompassing the measurement frequencies lies within the frequency range of the microwave useful radiation. The at least one selection criterion may include that the reflected microwave radiation

 - belongs to a group with highest reflections;

 - belongs to a group with highest reflected microwave powers;

 - belongs to a group with the lowest reflectivities;

 - belongs to a group with the lowest reflected microwave power;

 - their reflectance reaches or exceeds at least a predetermined upper threshold value;

 - Their reflected microwave power reaches or exceeds at least a predetermined upper threshold value;

 - Their reflectance reaches or falls below at least a predetermined lower threshold value;

 - Their reflected microwave power reaches or falls below at least a predetermined lower threshold.

The thawing state of the foodstuff L is subsequently determined on the basis of an evaluation of the degree of reflection R of the microwave measuring radiation. For example, alternating microwave useful radiation and microwave measuring radiation can be radiated into the cooking chamber 2 alternately during a thawing process.

In a variant in which a plurality of measuring frequencies have been selected, the microwave measuring radiations can be evaluated individually for different measuring frequencies, and the achievement of the phase transition can be detected by a drop in the reflectance R at one, several or all measuring frequencies.

In another variant, in which a plurality of measuring frequencies have been selected, the measured values of the microwave measuring device 7 can be linked for different measuring frequencies, e.g. averaged or added, a reflectance R for the associated measured values are determined and the thawing or reaching of the phase transition can be detected by dropping this one reflectance R.

3 shows a flowchart for a possible operation of the cooking appliance 1. In a first step S1, an initial scan is carried out under the control of the control device 6 by emitting microwave measuring radiation with different measuring frequencies into the cooking chamber 2 at the beginning of a thawing process by means of the microwave transmitter 3 and by means of the microwave measuring device 7 reflected microwave measuring radiation is measured for each of the radiated measuring frequencies.

In a second step S2, at least one measuring frequency is selected by the control device 6 on the basis of the reflected microwave measuring radiation.

In a third step S3, controlled by the control device 6, the microwave useful radiation is irradiated in a first thawing section with a first set of microwave parameters from a group of m (m> 2) microwave parameters in the cooking chamber 2 until a Phase transition is detected, eg In this first thawing section, the irradiation of the microwave useful radiation and the microwave measuring radiation alternately alternate to form the curve V of the reflectance R with a high temporal resolution to be able to record. The microwave useful radiation is irradiated with high power, in particular with maximum power.

In a fourth step S4, if a phase transition or a thawed state is detected or has been determined on the basis of the gradient V of the reflectance R, the heating power is set to zero until re-freezing is determined on the basis of the course V of the reflectance R, eg by a noticeable increase in the reflectance R. following the phase transition

Subsequently, steps S3 and S4 may be repeated for all other predetermined m sets of microwave parameters as indicated by step S5, alternatively only for some of the sets.

The thawing process may be e.g. be ended in a step S6, if

- the steps S3 and S4 have been performed for all m or a few predetermined sets of microwave parameters; - no re-freezing has been detected in at least one of steps S4; and or

 - if in at least one of steps S3 initially no frozen state has been detected.

The steps S3 to S5 can also be run through several times, in particular if re-freezing is or has been detected even at the last of the predetermined sets of microwave parameters. Optionally, the step S6 may be followed by a step S7, in which the foodstuff L is briefly irradiated in time by microwave useful radiation ("heating pulse"), e.g. to eliminate the presence of small frozen areas and / or to transfer the food L to a completely thawed state in a particularly reliable manner. Of course, the present invention is not limited to the illustrated embodiment.

In general, "on", "an", etc. can be understood to mean a singular or a plurality, in particular in the sense of "at least one" or "one or more", etc., unless this is explicitly excluded, e.g. by the expression "exactly one", etc.

Also, a numerical value may include exactly the specified number as well as a customary tolerance range, unless this is explicitly excluded.

LIST OF REFERENCE NUMBERS

1 microwave oven

 2 cooking space

 3 microwave transmitters

 4 microwave generator

 5 antenna

 6 control device

 7 microwave measuring device

 L food

 PZ phase transition time domain

 R reflectance

 S1-S7 process steps

t time

 V course

Claims

claims A method (S1-S7) for operating a household appliance (1) with a thawing function, in which  microwave radiation having different frequencies is irradiated into a treatment space (2) of the domestic appliance (1) at the beginning of a thawing process (S1),  a reflected microwave radiation is measured for each of the irradiated frequencies (S1),  on the basis of the reflected microwave radiation at least one frequency is selected as a measuring frequency (S2) and  the thawing state is determined on the basis of an evaluation of a reflected microwell radiation only of the at least one selected measuring frequency (S3-S5). 2. Method (S1-S7) according to claim 1, wherein the at least one measuring frequency is selected according to the fact that the associated reflected microwave radiation fulfills at least one of the following selection criteria:  she belongs to a group with highest reflections;  it belongs to a group with the highest reflected microwave power; she belongs to a group with the lowest reflections;  it belongs to a group with the lowest reflected microwave power; their reflectance reaches or exceeds at least a predetermined upper threshold value;  its reflected microwave power reaches or exceeds at least one predetermined upper threshold value;  their reflectance reaches or falls below at least one predefined lower threshold value;  their reflected microwave power reaches or falls below at least a predetermined lower threshold. 3. Method (S1-S7) according to one of the preceding claims, in which at least one measurement frequency is selected and a thawing state based on a via a temporal course (V) determined, in particular jump-like, change of at least one power quantity (R) of the reflected microwave measurement radiation is determined. 4. Method (S1-S7) according to claim 3, in which a plurality of measurement frequencies are selected and the thawing state is determined on the basis of a temporal progression (V), especially a sudden change in at least one output variable (R) of the reflected microwave radiation. Measuring radiation per selected measurement frequency is determined. 5. Method (S1-S7) according to claim 3, wherein a plurality of measurement frequencies are selected and the thawing state based on a temporal course (V) determined, in particular sudden change of at least one performance variable (R) of the common reflected microwaves Measuring radiation is determined at least one group of selected measuring frequencies comprising a plurality of measuring frequencies. 6. Method (S1-S7) according to one of the preceding claims, in which the domestic appliance (1) is set up to heat treatment items (L) located in the treatment room (2) by means of at least one of the following types of heating:  Microwave irradiation by microwave useful radiation;  Irradiation of further electromagnetic energy  Heat radiation through at least one resistance heater; Heat treatment by hot air introduction and / or steam injection. 7. Method (S1-S7) according to claim 6, in which treatment material (L) located in the treatment space (2) can be heated by means of microwave useful radiation and wherein the frequency range of the microwave measurement radiation encompassing the measurement frequencies and a frequency range of the microwaves Useful radiation are different. 8. Method (S1-S7) according to claim 5, in which treatment material (L) located in the treatment space (2) can be heated by means of microwave useful radiation and in which a frequency range encompassing the measurement frequencies of the microwave measurement radiation and a frequency range of the microwave useful radiation are the same. 9. Method (S1-S7) according to one of the preceding claims, in which heating power with m (m> 2) different predetermined sets of heating parameters can be introduced into the treatment space (2), the heating power for different sets of heating parameters in the treatment room (2) located treat- ment (L) locally heated differently and in the  a) the heating power is radiated with one of the sets of heating parameters and a time profile of at least one power quantity of the reflected microwave measuring radiation is determined (S3),  b) if, for the thawing section, a thawed state is detected by means of the course of the at least one performance variable (S3), then c) the steps a) and b) for heating power are repeated with at least one other of the set of heating parameters (S5). 10. The method (S1-S7) according to claim 9, wherein the thawing operation is ended (S6) when  the steps a) and b) have been carried out for all m sets of microwave parameters; and or  if in at least one of steps b) initially no frozen state has been detected. 1 1. The method (S1-S7) according to any one of claims 9 to 10, wherein in step b), when for a thawing a thawing in the course of thawing revealed thawed state is detected (S3), the heating power is reduced until freezing is recognized (S4), and following step c) is executed (S5). 12. The method (S1-S7) according to claim 11, wherein the thawing operation is ended (S6) when no re-freezing is detected for at least one of the thawing sections. 13. The method (S1-S7) according to any one of claims 1 1 to 12, wherein when a thawing condition is detected for a thawing section, the energy of the microwave stray radiation is reduced to the end of this thawing section (S4). 14. The method (S1-S7) according to any one of claims 11 to 13, wherein in step a) a high heating power is radiated. 15. Domestic appliance (1) which is adapted to run the method (S1-S7) according to one of the preceding claims, wherein the household appliance (1) comprises:  at least one microwave transmitter (3) for irradiating microwave measuring radiation into the treatment space (2),  at least one microwave measuring device (7) for measuring microwave measuring radiation reflected from the treatment space (2), and - a data processing device (6) for selecting the at least one Measuring frequency of the microwave measuring radiation at least based on measurement data of the microwave measuring device (7) and for determining the thawing state.