Sensor for a cooking appliance, cooking appliance with such a sensor, and methods for determining the humidity in a cooking chamber atmosphere of a cooking appliance

Abstract

Sensor for a cooking appliance (10), comprising a sensor unit (22) and a filter (28) arranged in the access to the sensor unit (22), characterized in that a second filter (32) is provided, arranged in the access to the first filter (28), wherein the two filters (28, 32) filter, among other things, silanes and / or siloxanes, wherein the first filter (28) is mesoporous and wherein the second filter (32) is designed as a solid plate provided with at least one through-opening (34) to bind a large proportion of the silanes and / or siloxanes contained in the gas stream.

Description

[0001] The invention relates to a sensor for a cooking appliance, comprising a sensor unit and a filter arranged in the access area to the sensor unit. The invention further relates to a cooking appliance with such a sensor and a method for determining the humidity in a cooking chamber atmosphere of a cooking appliance.

[0002] Cooking appliances for professional use, such as in restaurants, canteens, and large-scale catering, are equipped with sensors that can determine various parameters of the cooking chamber atmosphere. Zirconia or semiconductor sensor units, which can be simply referred to as gas sensors, are particularly used for this purpose. For example, such a zirconium dioxide or semiconductor sensor unit can be used to determine the oxygen content of the cooking chamber atmosphere. The oxygen content can then be used to determine the humidity content of the cooking chamber atmosphere. If the oxygen content is 0%, for example, it can be deduced that the cooking chamber atmosphere consists of pure water vapor.

[0003] It is also known in the field of cooking appliances that the commonly used seals (especially silicone seals) release compounds when exposed to higher temperatures that are detrimental to the service life of the gas sensors used, as they coat the active surface of the heated sensor with a quartz deposit. This is referred to as poisoning of the gas sensor, for example, by silanes or siloxanes released by a silicone seal.

[0004] DE 10 2007 054 340 A1 discloses the placement of a filter at the inlet to the semiconductor sensor unit to prevent silanes or siloxanes from reaching the semiconductor sensor unit. A mesoporous filter made of silicon oxide and / or silicate is used as the filter. A coarse filter is also installed upstream of the filter to filter out particles and / or droplets.

[0005] While such a filter can extend the service life of the zirconium dioxide or semiconductor sensor unit, it has been shown that such a filter is insufficient if the cooking appliance in which the sensor is installed is regularly used at high operating temperatures. At high operating temperatures, the amount of silanes or siloxanes released by the cooking appliance's silicone seal increases disproportionately, so it cannot be guaranteed that the sensor will reliably deliver accurate measurement results over the typical service life of a cooking appliance.

[0006] From the subsequently published DE 10 2014 118 153 A1, a gas sensor element with a filter system is known.

[0007] DE 10 2004 037 606 A1 shows a cooking appliance with a gas sensor and an associated filter system for filtering fats and oils.

[0008] The object of the invention is therefore to improve a sensor of the type mentioned at the outset so that it is better protected against poisoning, in particular by compounds released by silicone seals at high temperatures.

[0009] To achieve this object, a sensor of the type mentioned at the outset is provided with a second filter which is arranged in the inlet to the first filter, wherein the two filters filter, among other things, silanes and / or siloxanes, wherein the first filter is mesoporous and wherein the second filter is designed as a solid plate provided with at least one through-opening in order to bind a large proportion of the silanes and / or siloxanes contained in the gas stream. The invention is based on the basic idea of ​​extending the "service life" of the first filter and thus its effectiveness by arranging it in series with a second filter, so that ultimately only "pre-purified" gas reaches the first filter, i.e. gas from which a large proportion of harmful compounds has already been removed by the second filter.

[0010] The sensor unit may in particular be a zirconium dioxide or semiconductor sensor unit.

[0011] The provision of at least one through-hole in a plate as a second filter is based on the realization that a surprisingly good filtering effect can be achieved simply by placing a solid plate with a small number of through-holes in front of the plate. The harmful compounds precipitate on the plate, especially in the area of ​​the through-hole, preventing them from reaching the first filter.

[0012] According to a preferred embodiment of the invention, exactly one through-opening is used. This allows the access cross-section to the first filter to be adjusted very precisely.

[0013] Preferably, the through-opening has a diameter in the range of 0.5 µm to 12 µm, in particular in the range of 3 to 8 µm. A through-opening with this diameter provides, on the one hand, a sufficiently large flow cross-section for access to the first filter and the sensor unit, and, on the other hand, is small enough that, when a gas stream passes through it, the harmful compounds contained in the gas stream can accumulate on the wall of the through-opening.

[0014] Preferably, the through-opening narrows toward the first filter. This improves the filtering effect.

[0015] According to the preferred embodiment, the passage opening is conically tapered. This design is advantageous for the "service life" of the second filter, i.e., the period during which it can effectively remove harmful compounds from the gas stream. With a conical passage opening, it takes a considerable amount of time for even the narrowest cross-section of the passage opening to be closed by the molecules of harmful compounds accumulating there.

[0016] Preferably, a conical through-opening is provided with a diameter of the order of 7 µm on the side facing away from the first filter and a diameter of the order of 4 µm on the side facing the first filter. These values ​​have proven to be a good compromise between good filtering efficiency on the one hand and a long service life of the second filter on the other.

[0017] According to one embodiment of the invention, the first filter and the sensor unit are connected to form a single unit. This prevents the first filter from having to be mounted separately in the sensor.

[0018] The first filter and the sensor unit can, in particular, be firmly connected to one another, for example, by means of a platinum sintered connection or a temperature-resistant glass connection. This allows the components to be connected to one another in a process-reliable manner.

[0019] If the second filter is a through-hole with a plate, the second filter is preferably connected to the first filter, and thus also to the sensor unit, forming a single assembly. The resulting assembly can then be installed in the cooking appliance with minimal effort.

[0020] Alternatively, to achieve this objective, a sensor of the type mentioned above provides a second filter arranged in the inlet to the first filter. The two filters filter, among other substances, silanes and / or siloxanes. The first filter is mesoporous, and the second filter contains a highly porous material with a large internal surface area, for example, activated carbon or surface-activated Norit. This material is particularly suitable for binding harmful compounds such as silanes or siloxanes.

[0021] The second filter can contain a highly porous material, such as activated carbon or Norit, in granular form. This can be replaced at regular intervals if desired.

[0022] Preferably, the second filter is part of a housing that surrounds the sensor unit. This allows the second filter to be arranged at a certain distance from the sensor unit, so that the second filter is exposed to significantly lower temperatures than the first filter.

[0023] It may also be possible to heat the second filter to achieve a better filtering effect.

[0024] The invention also provides a cooking appliance that incorporates the sensor described above. This sensor is very well protected from contamination by harmful compounds such as silanes or siloxanes due to the cumulative effect of the first and second filters, thus resulting in a long service life.

[0025] According to the invention, the sensor described above is also particularly well suited for determining the humidity in the cooking chamber atmosphere of a cooking appliance, where the sensor determines the oxygen content in the cooking chamber atmosphere. Regarding the resulting advantages, reference is made to the above explanations.

[0026] The invention is described below with reference to two embodiments illustrated in the accompanying drawings, in which: - Fig. 1 schematically shows a cooking appliance according to the invention; - Fig. 2 shows a schematic sectional view of a sensor according to a first embodiment of the invention; and - Fig. 3 shows a schematic sectional view of a sensor according to a second embodiment of the invention.

[0027] In Fig. 1 schematically shows a cooking appliance 10 which has a housing 12 in which a cooking chamber 14 is provided.

[0028] Furthermore, a door 16 is provided, which seals off the cooking chamber 14 from the outside when closed. A seal 17, which may be made of silicone, is arranged between the cooking chamber door 16 and the housing 12.

[0029] The cooking appliance is a professional cooking appliance, such as those used in restaurants, canteens, and large-scale catering. A control unit 18, shown schematically here, can run various cooking programs for cooking food in the cooking chamber 14.

[0030] These can be so-called intelligent cooking programs in particular, where the control system can automatically change various parameters of the cooking process (e.g. cooking time, cooking temperature, humidity of the cooking chamber atmosphere) depending on parameters of the food (e.g. caliber).

[0031] The controller 18 receives signals from various sensors that detect certain properties of the cooking chamber atmosphere. As an example, a gas sensor 20 is shown here, which can be used to obtain information about the gas content of the cooking chamber atmosphere. A sensor unit is used for this purpose, which uses a membrane made, for example, of zirconium dioxide.

[0032] In principle, other semiconductor sensor units can also be used.

[0033] An example of a gas sensor 20 is an oxygen sensor, which can be used to determine the oxygen content of the cooking chamber atmosphere. The structure and functionality can generally correspond to the sensors known as lambda sensors for determining the oxygen content in the exhaust stream of an internal combustion engine.

[0034] At the high temperatures that can prevail in the cooking chamber 14 of the cooking appliance 10 (300°C and above), various compounds, particularly silanes and siloxanes, escape from the seal 17. These compounds can poison the zirconium dioxide or semiconductor sensor unit of the gas sensor 20 through quartz deposits. To protect the gas sensor 20 from these compounds, two filters are connected in series.

[0035] In Fig. Figure 2 shows a first embodiment of the sensor 20. Reference numeral 22 denotes the semiconductor sensor unit, which is known per se and has a membrane 24, for example, made of zirconium dioxide. Furthermore, a heater 26, indicated schematically here, is provided, with which the zirconium dioxide or semiconductor sensor unit is brought to its operating temperature. Conventional sensor units can deliver a measurement signal starting at operating temperatures of 300°C, but are usually operated in the range of 500 to 700°C.

[0036] The structure and operation of the sensor unit 22 are basically known and are therefore not explained in more detail below.

[0037] Here, a first filter 28, which can be made of zirconium oxide or aluminum oxide, is placed upstream of the membrane 24. The first filter is particularly mesoporous, meaning it has a pore size between 2 and 50 nm.

[0038] The first filter 28 is designed as an inherently stable plate which is firmly connected to the sensor unit 22 in such a way that any gas reaching the membrane 24 must first flow through the filter 28.

[0039] The first filter 28 can be firmly connected to the sensor unit 22 by being firmly connected to the membrane 24, for example by means of a high-temperature-resistant glass melt 30 or a platinum sintered connection.

[0040] A second filter 32 is positioned upstream of the first filter 28. This filter is designed as a solid plate made of zirconium dioxide or aluminum oxide. The thickness of the filter 32 can be on the order of 300 µm.

[0041] The second filter 32 here has a single through-opening 34, which is conical in the illustrated embodiment. The diameter of the through-opening 34 can be on the order of 7 µm on the side facing away from the sensor unit 22, i.e., on the outside of the sensor 20, while the diameter on the side of the sensor unit 22 is on the order of 4 µm.

[0042] It is also possible for the filter 32 to have more than one through-opening 34.

[0043] The second filter 32 is firmly and tightly connected to the first filter 28, so that any gas flow passing through the first filter 28 to the membrane 24 must first flow through the through-opening 34. The second filter 32 can be firmly connected to the first filter 28, for example, by soldering or sintering. In particular, the same material 30 is used for this as for the connection between the first filter 28 and the membrane 24.

[0044] Harmful compounds and substances contained in the gas to be analyzed partially precipitate on the outside of the second filter 32, and in particular on the wall of the through-opening 34 in the second filter 32. Thus, a "pre-cleaned" gas stream hits the first filter 28, so that it is exposed to a smaller number of molecules of harmful compounds, such as silanes or siloxanes. This results in a longer service life of the sensor 20.

[0045] In Fig. A second embodiment is shown in Figure 3. The same reference numerals are used for components known from the first embodiment, and reference is made to the above explanations.

[0046] The essential difference between the first and the second embodiment is that in the second embodiment, a unit formed from the first filter 28 and the sensor unit 22 is arranged within a sensor housing 40 which is closed off from the environment and in particular from the cooking chamber 14 except for an access opening 41.

[0047] The second filter 32 is arranged in the access opening 41. As a result, the second filter 32 is positioned at a distance from the heater 26, so that it is generally exposed to lower temperatures.

[0048] It is also possible to heat the second filter 32 separately to achieve a better filtering effect.

[0049] The second filter 32 contains a filling made of a highly porous material with a large internal surface area, such as activated carbon or surface-activated Norit. This material is arranged in a suitable container 42, forming an effective gas filter. The filling of the filter 32 can be in the form of granules or as a pressed material.

[0050] It is also possible for the second filter 32 to be replaceable by removing the container 42 and replacing it with a new one.

[0051] The second filter is capable of binding a large proportion of the compounds contained in the gas stream, particularly silanes and siloxanes, so that they do not reach the first filter 28. This extends its service life.

Claims

[1] Sensor for a cooking appliance (10), comprising a sensor unit (22) and a filter (28) arranged in the access to the sensor unit (22), characterized by that a second filter (32) is provided which is arranged in the access to the first filter (28), wherein the two filters (28, 32) filter, among other things, silanes and / or siloxanes, wherein the first filter (28) is mesoporous and wherein the second filter (32) is designed as a solid plate which is provided with at least one through-opening (34) in order to bind a large proportion of the silanes and / or siloxanes contained in the gas stream. [2] Sensor according to claim 1, characterized by that the plate is provided with a small number of through openings (34). [3] Sensor according to claim 2, characterized by that exactly one through opening (34) is provided. [4] Sensor according to one of the preceding claims, characterized bythat the through opening (34) has a diameter in the range of 0.5 µm to 12 µm. [5] Sensor according to claim 4, characterized by that the diameter is in the order of 3 to 8 µm. [6] Sensor according to one of the preceding claims, characterized by that the through opening (34) narrows towards the first filter (28). [7] Sensor according to claim 6, characterized by that the through opening (34) narrows conically. [8] Sensor according to claim 6 or claim 7, characterized by that the through-opening (34) has a diameter of the order of magnitude of 7 µm on the side facing away from the first filter (28) and a diameter of the order of magnitude of 4 µm on the side facing the first filter (28). [9] Sensor according to one of the preceding claims, characterized by that the second filter (32) consists of zirconium dioxide or aluminum dioxide. [10] Sensor according to one of the preceding claims, characterized by that the second filter has a thickness between 100 µm and 2000 µm, in particular in the order of 300 µ. [11] Sensor for a cooking appliance (10), comprising a sensor unit (22) and a filter (28) arranged in the access to the sensor unit (22), characterized by that a second filter (32) is provided which is arranged in the access to the first filter (28), wherein the two filters (28, 32) filter, among other things, silanes and / or siloxanes, wherein the first filter (28) is mesoporous and wherein the second filter (32) contains a surface-activated material, for example activated carbon or Norit. [12] Sensor according to claim 11, characterized by that the second filter (32) contains the filter material in the form of granules. [13] Sensor according to claim 11 or claim 12, characterized by that the second filter (32) is part of a sensor housing (40) which surrounds the sensor unit (22). [14] Sensor according to one of the preceding claims, characterized by that the first filter (28) and the sensor unit (22) are connected to one another to form a unit. [15] Sensor according to one of the preceding claims, characterized by that the first filter (28) is connected to the second filter (32) to form a unit. [16] Sensor according to claim 14 or claim 15, characterized by that the components are soldered or sintered together. [17] Sensor according to claim 16, characterized by that the components are connected to one another by a silver solder (30), a glass solder (30) or a platinum sintered material (30). [18] Sensor according to one of the preceding claims, characterized by that the sensor unit (22) is a semiconductor sensor unit or a zirconium dioxide sensor unit (22). [19] Sensor according to one of the preceding claims, characterized by that the second filter is heated. [20] Cooking appliance with a sensor (20) according to one of the preceding claims. [21] Method for determining the humidity in a cooking chamber atmosphere of a cooking appliance (10), in which a sensor (20) according to one of claims 1 to 19 is used to determine the proportion of oxygen in the cooking chamber atmosphere.

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