OPERATING A DOMESTIC STEAM-TREATMENT APPLIANCE, AND DOMESTIC STEAM-TREATMENT APPLIANCE

Abstract

In a method for operating a household steam treatment appliance which includes an evaporator with a heatable water holding chamber and a fill level sensor with at least two measurement electrodes, which are disposed over one another at a distance from each other in the heatable water holding chamber, a water detection measured value provided for indicating wetting of the at least two measurement electrodes with water introduced into the water holding chamber is adapted in an adaptation process to an electrical conductivity of the water in the water holding chamber.

Claims

1.-9. (canceled)

10. A method for operating a household steam treatment appliance including an evaporator with a heatable water holding chamber and a fill level sensor with at least two measurement electrodes, which are disposed over one another at a distance from each other in the heatable water holding chamber, said method comprising: adapting in an adaptation process a water detection measured value provided for indicating wetting of the at least two measurement electrodes with water introduced into the water holding chamber to an electrical conductivity of the water in the water holding chamber.

11. The method of claim 10, wherein the adaptation process comprises the steps of: (a) setting the water detection measured value at a predetermined minimum value, (b) filling the water holding chamber with water, until a minimum value is reached or exceeded, (c) heating the water in the water holding chamber to a boiling point; (d) determining by the fill level sensor a measured value corresponding to a current flowing between the at least two measurement electrodes, and (e) adapting the water detection measured value using the measured value.

12. The method of claim 11, wherein the water holding chamber is filled with water, when the evaporator is dry.

13. The method of claim 11, wherein the water detection measured value is adapted via a formula or a characteristic curve, which provides a link between the measured value determined by the fill level sensor and the water detection measured value.

14. The method of claim 13, wherein the water detection measured value is set at a first, higher value, when the measured value determined by the fill level sensor exceeds a predetermined threshold, or otherwise at a second, lower value.

15. The method of claim 11, wherein, after the fill level sensor has determined the measured value in step (d), the adaptation process comprises the steps of: (d2) removing water from the water holding chamber, until the fill level sensor determines that the measured value has fallen below a predetermined fraction of the measured value, and (d3) subsequently determining by the fill level sensor a further measured value, wherein the water detection measured value is adapted in step (e) by using a value between the measured value measured in step (d) and the further measured value measured in step (d3).

16. The method of claim 11, wherein a presence of a descaling agent is established when the measured value determined in step (d) exceeds a predetermined threshold.

17. The method of claim 16, further comprising: determining the predetermined threshold during a separate descaling process; and rinsing the water holding chamber, when the presence of the descaling agent is established.

18. A household steam-treatment appliance, comprising: an evaporator including a heatable water holding chamber; a fill level sensor including two measurement electrodes, which are disposed over one another at a distance from each other in the water holding chamber; and a control device configured to enable the household steam treatment appliance to carry out a method as set forth in claim 10.

19. The household steam-treatment appliance of claim 18, embodied as a steam cooking appliance.

20. The household steam-treatment appliance of claim 18, wherein the control device is configured to enable the household steam treatment appliance to carry out the steps of: (a) setting the water detection measured value at a predetermined minimum value, (b) filling the water holding chamber with water, until a minimum value is reached or exceeded, (c) heating the water in the water holding chamber to a boiling point; (d) determining by the fill level sensor a measured value corresponding to a current flowing between the at least two measurement electrodes, and (e) adapting the water detection measured value using the measured value.

21. The household steam-treatment appliance of claim 20, wherein the control device is configured to enable the household steam treatment appliance to fill water in the water holding chamber, when the evaporator is dry.

22. The household steam-treatment appliance of claim 20, wherein the water detection measured value is adapted via a formula or a characteristic curve, which provides a link between the measured value determined by the fill level sensor and the water detection measured value.

23. The household steam-treatment appliance of claim 22, wherein the water detection measured value is set at a first, higher value, when the measured value determined by the fill level sensor exceeds a predetermined threshold, or otherwise at a second, lower value.

24. The household steam-treatment appliance of claim 20, wherein, after the fill level sensor has determined the measured value, the control unit is configured to enable the household steam-treatment appliance to carry out the steps of: (d2) removing water from the water holding chamber, until the fill level sensor determines that the measured value has fallen below a predetermined fraction of the measured value, and (d3) subsequently determining by the fill level sensor a further measured value, wherein the water detection measured value is adapted in step (e) by using a value between the measured value measured in step (d) and the further measured value measured in step (d3).

25. The household steam-treatment appliance of claim 20, wherein a presence of a descaling agent is established when the measured value determined in step (d) exceeds a predetermined threshold.

26. The household steam-treatment appliance of claim 25, wherein the predetermined threshold is determined during a separate descaling process and the water holding chamber is rinsed, when the presence of the descaling agent is established.

Description

[0050] The characteristics, features and advantages of this invention as described above and the way these advantages are achieved are described more clearly and understandably by reference to the following schematic description of an exemplary embodiment, which is further explained by reference to the drawings.

[0051] FIG. 1 shows a sectional representation in a side view of a sketch of a household steam treatment appliance;

[0052] FIG. 2 shows the plotting of a measured value x sensed by a fill level sensor against time t for a possible adaptation process; and

[0053] FIG. 3 shows the possible sequence of a method to adapt a water detection measured value.

[0054] FIG. 1 shows as a sectional representation in a side view a sketch of a household steam treatment appliance in the form of a baking oven 1 with steam treatment function. The baking oven 1 has a cooking chamber 3 delimited by an cooking chamber wall 2. An evaporator 4 with a water holding chamber 5 is present outside of the cooking chamber 3. On the bottom of the water holding chamber 5 is a metal plate 6 which can be heated by means of an electric heater 7. By means of the metal plate 6 the water W in the water holding chamber 5 can be heated, in particular to boiling point. The resulting steam reaches the cooking chamber 3 via a steam feed 8.

[0055] The water W can be introduced into the bottom of the water holding chamber 5 by means of a pump 9, namely from e.g. a removable water tank 10. The capacity of the water tank 10 is typically many times greater than the capacity of the water holding chamber 5. The pump 9 can also be operated in such a way that by means of this water W from the water holding chamber 5 can be pumped back into the water tank 10.

[0056] The evaporator 4 also has a fill level sensor 11 or a fill level sensor 11 is associated with the evaporator 4. The fill level sensor 11 has the metal plate 6 as a bottom measurement electrode and a top measurement electrode 12 protruding from above into the water holding chamber, the two of which are connected by an evaluation circuit 13. A voltage is applied to the metal plate 6 and the top measurement electrode 12. The evaluation circuit 13 is connected to a control device 14, which can also control the operation of the pump 10 and the heater 7. In one variant, the evaluation circuit 13 can be integrated into the control device 14, so that the control device 14 takes on the function of the evaluation circuit.

[0057] When introducing the water W into the water holding chamber 5 the metal plate 6 is first covered with water W. As the fill level increases the water W also comes into contact with the top measurement electrode 12, whereby the current flowing between the measurement electrodes 6, 12 rapidly increases. If the evaporator 4 is dry, usually no or very small parasitic leakage currents occur through damp inner walls of the evaporator 4. However, if the evaporator 4 is damp, e.g. due to steam generation being in progress, these leakage currents can be noticeably high. To prevent the leakage currents having an impact, in the evaluation circuit 13 a water detection measured value is therefore advantageously set or specified, that is greater than zero and greater than a measured value generated based on the leakage currents, but smaller than a measured value generated based on contact by the water W introduced.

[0058] This works well until the water detection measured value matches the electrical conductivity of the water W introduced. However, if very soft water (e.g. with an electrical conductivity of less than 50 μS/cm) is introduced into the water tank 10, although the water detection measured value is based on hard water (e.g. with an electrical conductivity of 100 μS/cm or more), there may be occasions when the water detection measured value is reached only late or even not at all, although the top measurement electrode 12 is already noticeably immersed in the water W introduced.

[0059] FIG. 2 shows the plotting of a measured value x (corresponding to a current flowing between the measurement electrodes 6 and 12) sensed by a fill level sensor 11 against the time t for a possible adaptation process.

[0060] First, as also described in more detail in FIG. 3, in a step S1 a water detection measured value x_thr is first set at its minimum value x_thr_min. The minimum value x_thr_min is e.g. selected such that direct contact with the measurement electrodes 6, 12 by water W with an electrical conductivity of between 1 μS/cm and 50 μS/cm can be reliably detected.

[0061] In a step S2, from instant tO via the pump 9, cold water W is pumped from the water tank 10 into the water holding chamber 5, wherein from an instant t1 the presence of water W between the measurement electrodes 6, 12 results in a rapid increase in the measured values x.

[0062] The pump 9 is operated until the measured values x sensed by the fill level sensor 11 at an instant t2 reach or exceed the minimum value x_thr_min, and in a step S3 is then switched off. Due to a short after-run by the pump 9 even after achieving the minimum value x_thr_min water W is still pumped in, whereby the measured value x continues to increase slightly. The after-run can also be precisely set.

[0063] Steps S1 to S3 are preferably carried out with a dry evaporator 4, as in this way leakage currents via e.g. wet or possibly limescale-covered inner walls are avoided.

[0064] In a step S4 from an instant t3 the water W is brought to boiling point by switching on the heater 7, whereby the electrical conductivity of the water W and thus also the measured values x increase at least approximately in proportion.

[0065] At an instant t4 (e.g. 45 s after instant t3) the water W has reliably reached its boiling point, and the heater 7 is switched off.

[0066] In a step S5 within a measuring period from t4 to t5 of e.g. 5 s to 10 s, a series of individual measured values x is now measured and an average measured value x_o determined from these.

[0067] Next, in a step S6, at least on the basis of the average measured value x_o determined in step S5, a new water detection measured value x_thr=x_thr_new is calculated and set in the evaluation circuit 13.

[0068] In one variant, the water detection measured value x_thr_new can be calculated using a characteristic curve or a formula.

[0069] In another variant, in a step S5b, after determining the average measured value x_o (which can then also be referred to as the upper measured value) water W is pumped from the water holding chamber 5, until a lower value x=A.Math.x_o is fallen below, whereby the fraction A can assume e.g. a value in the range [0.1; 0.5], e.g. 0.2.

[0070] Next, in a step S5c, similarly to the average measured value x_o, an average value x_u (which can also be referred to as the lower measured value) is measured. The average value x_u can correspond in particular to a leakage current.

[0071] In step S6 the new or adapted water detection measured value x_thr_new is set to a value between x_u and x_o.

[0072] The adaptation process is thereby ended.

[0073] In a subsequent steam generation operation water W is again pumped into the evaporator 4 until the measured values x of the fill level sensor 11 reach or exceed the water detection measured value x_thr_new. The heater 7 is then switched on in order to bring the water W to boiling point, whereupon evaporated water W reaches the cooking chamber 3 through the steam feed 8. If the measured value x of the fill level sensor 11 drops below the water detection measured value x_thr_new, when the heater 7 is switched on, water W is pumped back until the water detection measured value x_thr_new is again reached or exceeded, and so on.

[0074] Should, during the steam generation operation, the water detection measured value x_thr be set to a value intended for hard water, it may be the case that if very soft water W is used, the measured value x of the fill level sensor 11 would never reach the water detection measured value x_thr. Then e.g. a pump timeout error may be signaled and the evaporator 4 switched off.

[0075] Of course, the present invention is not limited to the exemplary embodiment shown.

[0076] Thus, by evaluating the measured value x of the fill level sensor 11 it is also possible to establish whether a descaling agent is present in the water W.

[0077] In general “a”, “an” etc. can be understood as singular or plural, in particular in the sense of “at least one” or “one or more”, etc., provided this is not explicitly excluded, for example by the expression “precisely one” etc.

[0078] Also, a number can include exactly the specified number as well as a usual tolerance range, provided this is not explicitly excluded.

LIST OF REFERENCE CHARACTERS

[0079] 1 Baking oven [0080] 2 Cooking chamber wall [0081] 3 Cooking chamber [0082] 4 Evaporator [0083] 5 Water holding chamber [0084] 6 Metal plate/bottom measurement electrode [0085] 7 Heater [0086] 8 Steam feed [0087] 9 Pump [0088] 10 Water tank [0089] 11 Fill level sensor [0090] 12 Top measurement electrode [0091] 13 Evaluation circuit [0092] 14 Control device [0093] S1-S6 Method steps [0094] t Time [0095] t1-t5 Instants [0096] W Water [0097] x Measured value [0098] x_o Average measured value/upper measured value [0099] x_thr Water detection measured value [0100] x_thr_min Minimum value [0101] x_thr_new New water detection measured value [0102] x_u Average measured value/lower measured value