EP3409371B1 - Domestic appliance with filter unit, method for determining the saturation of a filter unit of a domestic appliance - Google Patents

Description

The present invention relates to household appliance with a filter unit, in particular an extractor hood, with at least one filter unit. The invention further relates to a method for determining the saturation of a filter unit.

In the case of air-carrying household appliances, it is known to filter out impurities from the air. Mechanical filters can be used here, such as fleece mats, porous foam media, expanded metal filters or perforated plate filters. In household appliances that represent extractor hoods that are operated in a kitchen, liquid and solid contaminants are filtered out from the vapors and vapors produced during cooking. Expanded metal filters, perforated plate filters, baffle filters, which can also be referred to as eddy current filters, edge suction filters and porous foam media are used in particular as mechanical filters. The saturation of these filters must be determined based on the operating time of the extractor hood.

From the US 2016/236131 A1 a projector with a dust collector is known. The dust collector has a housing, a fan, a filter element, an electric field generator and an electrostatic separator in which plates are arranged. A detection unit is provided in the dust collector. The detection unit is arranged around the separator and consists of conductive material, in particular metal.

In the CN105203602A describes a soot separator which comprises a metallic oil guide channel and a metal grid. The oil channel and the metal grille can be connected and the capacity between them can be measured.

In the WO 2013/166794 A1 describes a fume cleaning machine in which an electrical cleaner is used. The cleaner has an ionization unit and a separation unit in which positive and negative electrodes are arranged alternately.

In addition, for example, from the DE 2146288 A an extractor hood is known in which an electrostatic filter unit is used. In this extractor hood, the electrostatic filter unit consists of plate-shaped separating and counter electrodes as well as wire-shaped ionization electrodes. The plate-shaped separating and counter electrodes are connected to one another via electrically conductive webs and are arranged in such a way that the air entering the filter element first flows against the separating electrodes with wire-shaped ionization elements lying between them and then reaches the counter electrodes offset upwards. The separating electrodes are attached to the housing of the extractor hood via a partition. In addition, a high-voltage device is provided in the housing of the extractor hood, which is connected to the electrodes of the electrodes of the filter unit.

US 4,861,356 A . CN205925302U , and EP 1 860 391 A2 disclose further prior art.

A disadvantage of this filter unit is that, even with this filter unit, it is not apparent to the user when the filter unit needs to be cleaned.

According to the current status, the saturation detection of a filter is not recorded directly by a measurement solution. At most, the saturation is determined indirectly via the number of switch-on processes or the operating time in hours of the household appliance. This method is inaccurate and does not take into account the real conditions to which the household appliance is exposed. If the degree of saturation is determined by the operating time, the next cleaning interval of a filter is usually concluded. If the household appliance is, for example, an extractor hood, a disadvantage of these methods is that the cooking behavior of the user of the extractor hood is not shown here. For example, if someone does not cook intensively, such as in a single household, you could significantly extend the cleaning cycle for a fat filter in this case, although it cooks as frequently / regularly as a multi-person household.

The invention is therefore based on the object of providing a solution by means of which the saturation of a filter unit can be reliably determined in a simple manner.

According to a first aspect, the invention relates to a household appliance with at least one filter unit, which has an ionization unit and a separation unit with at least one precipitation electrode and at least one counter electrode and in which the precipitation electrode and the counter electrode are arranged alternately and at a distance from one another. The household appliance is characterized in that the household appliance has at least one capacitive measuring unit for measuring the capacitance between the precipitation electrode and the counter electrode.

According to the invention, an air-conducting household appliance is referred to as a household appliance. In particular, the household appliance represents a household appliance with air guidance. The household appliance can therefore be, for example, a tumble dryer, a vacuum cleaner or an extractor hood. The household appliance has at least one filter unit. The filter unit is used to filter out impurities from the air that is conveyed through the household appliance. The filter unit is an electrostatic filter unit with an ionization unit and a separation unit. The separation unit is connected downstream of the ionization unit in the direction of flow. The separation unit can also be referred to as a separation area or separation stage and the ionization unit as an ionization area or ionization step.

The ionization stage preferably has at least one ionization element and at least one counter electrode. Voltage, preferably high voltage, is applied to the ionization element. When contaminated air flows through the ionization stage, solid and liquid substances are charged electrostatically by means of the ionization element, which can also be referred to as a spray electrode. The deposition stage comprises at least one precipitation electrode and at least one counter electrode, which are preferably plate-shaped and which are arranged alternately and at a distance from one another in the deposition stage. Due to the electric field generated by the precipitation electrode and counter electrode, the impurities charged in the ionization unit settle on the Surface of the precipitation electrodes and counter electrodes of the separation unit and are thus filtered out of the air.

The separation unit and the ionization unit are preferably accommodated in a common housing. Particularly preferably, at least one contact element accessible from the outside is provided on the housing. An externally accessible electrical contact element is a contact element which can be connected to a voltage source without opening the housing of the filter unit and via which current can be conducted to the electrodes located in the housing.

The filter unit is also referred to as a filter module. The filter unit is a portable filter unit that can be removed from the household appliance and is preferably preassembled. A filter unit is referred to as pre-assembled, which can be inserted into the household appliance as a structural unit and removed from it in a unit.

The household appliance is characterized in that the household appliance has at least one capacitive measuring unit for measuring the capacitance between the precipitation electrode and the counter electrode.

The deposition unit alternately consists of precipitation electrodes under positive voltage, which can also be referred to as electrodes or plates, and negative / grounded counter electrodes, which can also be referred to as electrodes or plates. If several positive precipitation electrodes are provided, these are connected to one another in an electrically conductive manner. The same applies to the negative / grounded counter electrodes. When an electrical voltage is applied to the positive precipitation electrodes, an electric field is formed between the positive precipitation electrodes and negative counter electrodes analogously to a plate capacitor. When filtering the air, i.e. during the separation process, the particles are electrostatically charged in the upstream ionization unit and deposited in the separation unit on the positive precipitation electrodes and negative / grounded counter electrodes. The contaminants settle on the surface of the respective positive precipitation electrodes and negative / grounded counter electrodes of the separation unit.

The capacitance can be measured between the positive precipitation electrodes and negative counter electrodes by means of the capacitive measuring device provided according to the invention. The geometric properties, that is to say the distance d between the adjacent precipitation electrodes and counterelectrodes, and the plate area A of the respective electrodes remain fixed as a function of the structural design of the electrostatic filter and do not change. The electrical field constant, which is also called the dielectric constant, is also a natural constant and does not change.

ändert sich aber in Abhängigkeit der Beladung der Elektroden mit Verunreinigungen die relative Permittivität ε_r. Die relative Permittivität ε_r ist eine temperatur- und materialabhängige, spezifische Größe. Werden nun während des Filtervorgangs die Elektroden der Abscheideeinheit mit Ansammlungen von Verunreinigungen beaufschlagt, so ändert sich dementsprechend die relative Permittivität ε_r und dadurch die Permittivität ε. Während bei der Filtereinheit im Ausgangszustand, in dem keine Verunreinigungen an den Elektroden abgeschieden sind, die relative Permittivität ε_r die Permittivität von Luft ist, bestimmt sich die Permittivität zwischen den Elektroden nach der Abscheidung von Verunreinigungen durch die Permitivität der abgeschiedenen Verunreinigungen und der zwischen den Ansammlungen an den Elektroden befindlichen Luft. Die Änderung der Kapazität kann durch die erfindungsgemäße Messeinrichtung gemessen werden. Hieraus kann dann die Beladungsmenge der Elektroden, das heißt die Menge von Verunreinigungen, die in der Abscheideeinheit abgeschieden wurden, bestimmt werden.According to the equation $$\mathrm{C}={\mathrm{\epsilon }}_0*{\mathrm{\epsilon }}_{\mathrm{r}}*\mathrm{A}/\mathrm{d}$$

however, the relative permittivity ε _r changes depending on the loading of the electrodes with impurities. The relative permittivity ε _r is a temperature-dependent and material-dependent, specific variable. If, during the filtering process, the electrodes of the separation unit are subjected to the accumulation of impurities, the relative permittivity ε _r changes accordingly and thus the permittivity ε. While the relative permittivity ε _{r is} the permittivity of air for the filter unit in the initial state, in which no impurities are deposited on the electrodes, the permittivity between the electrodes is determined by the permittivity of the deposited impurities and that between the electrodes after the deposition of impurities Air at the electrodes. The change in capacitance can be measured by the measuring device according to the invention. From this, the amount of loading of the electrodes, that is the amount of impurities that have been deposited in the deposition unit, can then be determined.

The measuring unit is at least temporarily connected to the filter unit. The connection between the measuring unit and the filter unit can be temporary or permanent. It is thus possible to reliably detect a loading of the filter unit with impurities in a simple manner and thus also to recognize a saturation of the filter unit.

The measurement unit is not limited to any particular type. In principle, any measuring unit by means of which a capacitance can be measured can be used. According to one embodiment, the measuring device has a power supply unit for applying voltage to the precipitation electrodes and the counter electrodes. In particular, AC voltage is applied to the electrodes and the current profile is measured. The current applied is also referred to as the measuring current. Alternatively, the capacitive measuring unit can, for example, also be a unit for charging with constant current and observing the voltage rise rate or a unit for measuring the resonance frequency of an LC resonant circuit formed with the capacitance.

Since the electrodes of the separating unit must be supplied with voltage, in particular high voltage, for filter operation, contact elements are preferably provided on the filter unit which are accessible from the outside. In the case of a measuring unit which is arranged outside the filter unit, the contact elements can be used to apply the measuring current to the electrodes.

According to a preferred embodiment, a plurality of precipitation electrodes and a plurality of counter electrodes are provided, and the precipitation electrodes and counter electrodes are each combined to form a comb profile. In particular, the electrodes are each electrically conductively connected in the comb profile. This simplifies the construction of the filter unit. In addition, the measurement of the capacitance between the precipitation electrodes and counter electrodes can be carried out in a simple manner, since not every electrode has to be connected individually for the measurement of the capacitance. Rather, the two comb profiles can be connected.

According to one embodiment, the measuring unit is integrated in the filter unit. This embodiment has the advantage that the structure of the household appliance does not have to be changed. However, it is also within the scope of the invention that the measuring unit represents a separate unit from the filter unit, which is connected to the filter unit at least temporarily and is preferably arranged in the household appliance. In this case, the connection between the measuring unit and the filter unit is preferably produced when the filter unit is introduced into the household appliance.

According to one embodiment, the measuring unit is connected to an output unit for outputting information and / or a warning. The output unit can be an output unit of the household appliance on which, for example, the settings of the household appliance are displayed to the user or indicated acoustically. At this. Embodiment can be reliably indicated to the user that the filter unit has reached a certain degree of saturation. The user can thus be informed in good time before reaching a maximum degree of saturation, at which the function of the electrostatic filter unit can no longer be carried out, and can clean the filter unit. However, it is also possible to warn the user only when the maximum degree of saturation has been reached.

According to a preferred embodiment, the household appliance represents an extractor hood. In this embodiment, the filter unit preferably represents a fat filter unit.

According to a further aspect, the present invention relates to a method for determining the saturation of a filter unit of a household appliance, which is a household appliance according to the invention. The method is characterized in that the method comprises the step of a reference measurement and at least one operational measurement of the capacitance between the electrodes of the deposition unit.

A reference measurement is a measurement in which the filter unit is either unused or in a cleaned state. An operational measurement is a measurement in which the filter unit has already been used and is not in the cleaned state.

By performing a reference measurement on a new or cleaned filter unit, a change in capacitance can be detected by simple measurement after the filter unit has been operated. The reference measurement is preferably carried out on the filter unit in the installed state. This can ensure that the dimensions, in particular the size of the electrode surfaces and the distance, are the same as in a subsequent operational measurement.

According to a preferred embodiment, the change in the capacitance between the reference measurement and the operational measurement is recorded and is compared with a threshold value. In this embodiment, the threshold value can indicate the value at which the failure of the filter unit is not yet to be feared. The threshold value can be stored in the measuring unit. Alternatively, the threshold value can also be stored in the filter unit or the household appliance.

When the threshold value is exceeded, a warning signal is preferably output via the output unit.

According to one embodiment, the change in the capacitance between the reference measurement and the operational measurement is detected and the degree of saturation of the filter unit is determined from this change. With this embodiment, the current state of saturation of the filter unit can always be displayed to the user of the household appliance.

According to one embodiment, the degree of saturation is determined on the basis of comparison values which are stored in the measuring unit or in a control unit of the household appliance. Each degree of saturation is assigned to a change in capacity. The degree of saturation can thus be determined from a measured change in capacitance.

According to one embodiment, the reference measurement is triggered by inserting the filter unit into the household appliance. This embodiment has the advantage that the method can be carried out automatically. Since the filter unit generally has to be removed from the household appliance for cleaning, it can be assumed that when the filter unit is inserted either a new filter unit is inserted or the filter unit has been cleaned.

According to one embodiment, the operational measurements are carried out after predetermined time intervals, when the household appliance is switched off or by user input. In any case, it is preferred that the operational measurement is not carried out during the operation of the filter unit.

Figur 1:

eine schematische Explosionsansicht einer Ausführungsform einer Filtereinheit zur Verwendung in dem erfindungsgemäßen Haushaltsgerät;

Figur 2:

eine schematische Schnittansicht der Ausführungsform der Filtereinheit nach Figur 1;

Figur 3:

eine schematische Prinzipdarstellung des Messaufbaus;

Figur 4:

eine schematische Ansicht einer Ausführungsform eines erfindungsgemäßen Haushaltsgerätes; und

Figur 5:

eine schematische Ansicht einer weiteren Ausführungsform des erfindungsgemäßen Haushaltsgerätes.

The present invention will be described again below with reference to the accompanying drawings. Show it:

Figure 1:

a schematic exploded view of an embodiment of a filter unit for use in the household appliance according to the invention;

Figure 2:

is a schematic sectional view of the embodiment of the filter unit according to Figure 1 ;

Figure 3:

a schematic diagram of the measurement setup;

Figure 4:

a schematic view of an embodiment of a household appliance according to the invention; and

Figure 5:

is a schematic view of another embodiment of the household appliance according to the invention.

In the Figures 1 and 2 1 shows an embodiment of a filter unit 2, which can also be referred to as an electrostatic filter unit or filter module, which is shown in a household appliance 1 (see Figures 4 and 5 ) can be used. The electrostatic filter unit 2 consists of an upstream ionization unit 22 and a downstream separation unit 21. In the ionization unit 22, which can also be referred to as the ionization region or ionization stage, an ionization element 220 is arranged centrally between two negative or grounded counter electrodes 221, 222. The ionization element 220, which can also be referred to as a spray electrode, is under positive electrical high voltage, for example> 6 kV (> 6000 V).

In the illustrated embodiment, the ionization element 220 is arranged parallel to the bottom of the housing 20 of the filter unit 2 and extends over the entire width of the housing 20. The ionization element 220 is arranged at half the height of the housing 20. The counter electrodes 221, 222 are on the underside of the top wall of the housing 20 and on the top of the bottom of the Housing 220 arranged. The counter electrodes 221, 222 and the ionization element 220 are located in the front area of the housing 20.

The solid and liquid particles are electrostatically charged in the air flow in the ionization unit 22 and separated in the downstream separation unit 21.

The deposition unit 21 consists of precipitation electrodes 211 and counter electrodes 210. The electrodes 210, 211 are arranged parallel to one another at a distance from one another and are located in FIG Figures 1 and 2 Embodiment shown in the vertical, that is aligned perpendicular to the bottom of the housing 20. The precipitation electrodes 211 and counter electrodes 210 are arranged alternately. Electrically charged electrodes 211, 210 are thus alternately present in the deposition unit 21. The positive electrodes 211 are under positive electrical high voltage. An electric field is formed between the alternately arranged positive and negative electrodes 211, 210 in filter operation. This electric field has the effect that the solid and liquid substances already charged in the ionization unit 22 are deflected out of the air flow by the electric field and are deposited or deposited on the precipitation electrodes 211 or counter electrodes 210. These solid and liquid substances settle on the precipitation electrodes 211 and counter electrodes 210 in the form of impurities.

In the embodiment shown, the separating unit 21 consists of two interdigitated comb profiles 212, 213, which can also be referred to as web profiles or rib profiles, which are connected to one another only at the lateral fastening points or are kept at a distance from one another by an insulating material. The individual ribs or plates of the respective comb profiles 212, 213 do not touch each other. The comb profile 213 of the precipitation electrodes 211 and the comb profile 212 of the counter electrodes 210 comprise a multiplicity of electrodes 210, 211 which are parallel to one another and are arranged alternately. If positive electrical voltage is applied to the positive precipitation electrode 213 and the negative counterelectrode 212 is applied to a negative or grounded potential, an electric field is formed between the two comb profiles 212, 213.

In the Figure 3 a schematic diagram of the measuring unit 3 with a part of the filter unit 2 is shown.

The capacitance can be measured between the positive precipitation electrode 211 and the negative counter electrode 210 by means of a capacitive measuring device 3. The geometric properties, namely the distance d between the electrodes 210, 211 and the area A of the respective electrodes 210, 211 remain fixed as a function of the design of the filter unit and do not change. The electrical field constant, the dielectric constant is also a natural constant and does not change.

ändert sich in Abhängigkeit der Schmutzbeladung auf den Elektroden aber die relative Permittivität ε_r. Die relative Permittivität ε_r ist eine temperatur- und materialabhängige, spezifische Größe. Werden nun während des Filtervorgangs die Niederschlagselektroden 211 und Gegenelektroden 210 in der Abscheideeinheit 21 mit Ansammlungen von Verunreinigungen, beispielsweise Wrasenansammlungen belegt, so ändert sich dementsprechend die relative Permittivität ε_r und damit die Permittivität ε. Aufgrund dieser Änderung kann nun durch die kapazitive Messeinrichtung 3 eine elektrische Kapazitätsänderung ΔC [F] festgestellt werden. Hierbei wird vorzugsweise die Kapazität aus einer Referenzmessung und einer Betriebsmessung miteinander verglichen. Anhand dieser Kenngröße wird nun die Beladungsmenge, hervorgerufen durch Verunreingungsansammlungen, detektiert. Die kapazitive Sättigungsmessung erfolgt dabei außerhalb des Filterbetriebes, das heißt wenn die elektrostatische Filtereinheit ausgeschaltet ist.According to the equation $$\mathrm{C}={\mathrm{\epsilon }}_0*{\mathrm{\epsilon }}_{\mathrm{r}}*\mathrm{A}/\mathrm{d}$$

but the relative permittivity ε _r changes depending on the dirt loading on the electrodes _. The relative permittivity ε _r is a temperature-dependent and material-dependent, specific variable. If, during the filtering process, the precipitation electrodes 211 and counterelectrodes 210 in the separation unit 21 are now covered with accumulations of impurities, for example accumulations of vapors, the relative permittivity ε _r and thus the permittivity ε change accordingly. Due to this change, the capacitive measuring device 3 can now determine an electrical capacitance change ΔC [F]. Here, the capacitance from a reference measurement and an operational measurement is preferably compared with one another. On the basis of this parameter, the load quantity, caused by accumulations of impurities, is now detected. The capacitive saturation measurement takes place outside of the filter operation, that is, when the electrostatic filter unit is switched off.

In Figure 4 An embodiment of a household appliance 1 is shown schematically. In the embodiment according to Figure 4 the household appliance 1 represents a clothes dryer 11. In the front of the clothes dryer 11, a door 110 is provided for loading the clothes dryer 11. Inside the dryer 11 is one Filter unit 2 arranged. This is in the Figure 4 provided schematically in the upper area. However, it is also within the scope of the invention that the filter unit 2 is positioned at a different location in the clothes dryer 11. In this embodiment of the household appliance 1, the filter unit 2 serves to filter out solid impurities, such as fluff or dirt. A measuring unit 3 is also provided in the laundry dryer 1. This is connected to the filter unit 2, so that the capacitance between the electrodes 210, 211 provided in the filter unit 2 can be measured via the measuring unit 3.

In the Figure 5 Another embodiment of a household appliance 1 is shown schematically. In this embodiment, the household appliance 1 represents an extractor hood 10. In particular, the extractor hood 10 in the illustrated embodiment is an extractor hood 10 attached to a room ceiling R. The extractor hood 10 has a baffle plate 101 which is offset downward from the underside of the housing of the extractor hood 10. A peripheral edge suction gap 100 is thus formed between the baffle plate 101 and the underside of the housing of the extractor hood 10. In this edge suction gap 100, a plurality of filter units 2 are distributed over the circumference. A measuring unit 3 is arranged inside the housing of the extractor hood 10. This is connected to the filter units 2. In particular, the capacitance between the electrodes 210, 211 of the separating unit 21 of the filter unit 2 can be measured via the measuring unit 3.

Although the invention has been described with reference to filter units with comb profiles, the invention can also be used with any other electrostatic plate filter in which the plates, that is to say electrodes, lie parallel to one another. It is also possible that the household appliance is a vacuum cleaner instead of a tumble dryer or an extractor hood.

With the present invention, a capacitive saturation measurement for an electrostatic filter for extractor hoods and other air-conducting household appliances is created.

With the invention, the capacitive saturation detection and saturation measurement of impurities in an electrostatic filter unit of a household appliance is possible. Here, a dirt load quantity can be determined by measurement. If a maximum degree of contamination of an electrostatic filter unit in a household appliance, for example an extractor hood or a tumble dryer, has been reached, this is recorded by measurement. The user of the household appliance is preferably given the information that the electrostatic filter unit must be cleaned.

With the capacitive saturation determination, which is possible according to the invention, the cleaning interval can be optimally adapted to the cooking behavior of the respective user. This has the advantage that the cleaning interval for an electrostatic filter unit is optimally adapted depending on the cooking behavior and the load.

The present invention has a number of other advantages. If an electrostatic filter unit is overloaded, that is to say the maximum saturation quantity of contamination is exceeded, which can also be referred to as the electrostatic filter unit running full, the filter unit can fail in its function. The reason for this are electrical short circuits between the components which are under high electrical voltage, that is to say electrodes, and the negative / grounded components, that is to say electrodes, in particular along insulation elements.

For optimal filter behavior of an electrostatic filter element, the precipitation electrodes must not be excessively loaded / covered with protective deposits. One reason for this is that as the layer thickness of the dirt deposits on the plates, that is to say the electrodes, increases, the electric field E between the positive precipitation electrodes and negative counter-electrodes is weakened as a result of the higher dielectric constant. Due to the now weaker electric field between the precipitation electrodes and counter electrodes, the filter efficiency drops significantly. With the capacitive saturation measurement possible according to the invention, the optimal time for filter cleaning can be determined in order to avoid a drop in filter efficiency.

LIST OF REFERENCE NUMBERS

1

household appliance

10

Extractor housing

100

suction gap

101

flapper

11

clothes dryer

110

door

2

filter unit

20

casing

21

separation unit

210

counter electrode

211

Collecting electrode

212

Comb profile counter electrode

213

Comb profile precipitation electrode

22

lonisationseinheit

220

lonisationselement

221

counter electrode

222

counter electrode

23

contact element

D

distance

R

ceiling

Claims (14)

1. Household appliance with at least one filter unit, which has an ionisation unit (22) and a separation unit (21) with at least one collecting electrode (211) and at least one counter electrode (210), and in which the collecting electrode (211) and the counter electrode (210) are arranged in an alternating manner and at a distance (d) from one another, characterised in that the household appliance (1) has at least one capacitive measuring unit (3) for measuring the capacitance between the collecting electrode (211) and the counter electrode (210).
2. Household appliance according to claim 1, characterised in that the measuring unit (3) has a power supply unit for applying voltage to the collecting electrodes (211) and the counter electrodes (210).
3. Household appliance according to one of claims 1 or 2, characterised in that a plurality of collecting electrodes (211) and a plurality of counter electrodes (210) are provided and the collecting electrodes (211) and counter electrodes (210) are combined to form a ridged profile (212, 213) in each case.
4. Household appliance according to one of claims 1 to 3, characterised in that the measuring unit (3) is integrated in the filter unit (2).
5. Household appliance according to one of claims 1 to 3, characterised in that the measuring unit (3) represents a separate unit from the filter unit (2), which is connected to the filter unit (2) at least for a time and is preferably arranged in the household appliance (1).
6. Household appliance according to one of claims 1 to 5, characterised in that the measuring unit (3) is connected to an output unit for outputting an item of information and/or a warning.
7. Household appliance according to one of claims 1 to 6, characterised in that it represents an extractor hood (10) and the filter unit (2) represents a grease filter unit.
8. Method for determining the saturation of a filter unit (2) of a household appliance (1) according to one of claims 1 to 7, characterised in that the method comprises the step of a reference measurement and at least one operating measurement of the capacitance between the electrodes (210, 211) of the separation unit (21).
9. Method according to claim 8, characterised in that the change in capacitance between the reference measurement and the operating measurement is detected and is compared with a threshold value.
10. Method according to claim 9, characterised in that a warning signal is output via the output unit when the threshold value is exceeded.
11. Method according to one of claims 8 to 10, characterised in that the change in the capacitance between the reference measurement and the operating measurement is detected and, from this change, the degree of saturation of the filter unit (2) is ascertained.
12. Method according to claim 11, characterised in that the degree of saturation is ascertained on the basis of comparison values, which are stored in the measuring unit (3) or in a control unit of the household appliance (1).
13. Method according to one of claims 8 to 12, characterised in that the reference measurement is triggered by the insertion of the filter unit (2) into the household appliance (1).
14. Method according to one of claims 8 to 13, characterised in that the operating measurements take place according to predetermined time intervals, when switching off the household appliance (1) or by user input.

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