Method and apparatus for identifying supercooled liquid precipitation

Abstract

To identify supercooled liquid precipitation, the temperature of an object (3) having a precipitation impact surface (2) is measured, and it is detected whether precipitation has occurred onto the precipitation impact surface (2). When the temperature below 0°C is raised due to the occurred precipitation, then an alarm of supercooled liquid precipitation is output.

Description

Technical Field

[0001] This invention relates to a method for identifying supercooled liquid precipitation, wherein the temperature of an object having a precipitation impact surface is measured, and whether precipitation has occurred on the precipitation impact surface is detected. Furthermore, this invention relates to an apparatus for identifying supercooled liquid precipitation, comprising: an object having a precipitation impact surface; a temperature measuring device for measuring the temperature of the object; a precipitation detection device for detecting whether precipitation has occurred on the precipitation impact surface; and an evaluation device.

[0002] The most common form of supercooled liquid precipitation is supercooled or frozen rainwater, which is called freezing rain in English and has the METAR-Code FZRA. Therefore, as it is used herein, the concept of supercooled liquid precipitation includes not only supercooled rainwater but also supercooled liquid precipitation with smaller droplet sizes, such as frozen drizzle, which is called freezing drizzle in English and has the METAR-Code FZDZ.

[0003] Supercooled liquid precipitation has a temperature below 0°C before impacting the ground. For example, supercooled liquid precipitation occurs when rain falls through a layer of air near the ground, and the temperature of this supercooled liquid precipitation is below 0°C. If the raindrops are very fine, the water does not crystallize in the air but cools to the surrounding air temperature below 0°C without a phase change. Upon impact with the ground, supercooled liquid precipitation can freeze very rapidly and form a closed ice surface. Therefore, supercooled liquid precipitation is a concern in road and air traffic. It is therefore important to quickly and reliably identify supercooled liquid precipitation so that the associated hazards can be alerted. Background Technology

[0004] Known methods and apparatus for detecting supercooled liquid precipitation are based on the identification of icing on an object subjected to precipitation, where unfrozen liquid precipitation flows away from the object, or precipitation that has frozen in the air does not adhere to the object. Specifically, an increase in effective mass is detected as an indication of icing on the object, for example, by directly detecting a decrease in mechanical resonant frequency, an increase in moment of inertia, or an increase in effective mass, as the effective mass increases. Air temperature is additionally measured, as supercooled liquid precipitation typically occurs only within a limited range of air temperatures from -2°C to -20°C.

[0005] EP 3 196 676 A1 discloses a method for identifying supercooled liquid precipitation and an apparatus for identifying supercooled liquid precipitation. The apparatus includes a Yagi-Uda antenna whose response to an excitation signal changes with precipitation deposited on the antenna surface. Furthermore, temperature is detected using a temperature sensor arranged in a region of the Yagi-Uda antenna. By correlating information from the response signal of the Yagi-Uda antenna with a temperature profile, the presence of immediately frozen supercooled liquid precipitation is inferred in cases where liquid precipitation freezes on the Yagi-Uda antenna only after the air temperature has decreased. Summary of the Invention

[0006] The object of the present invention is to provide a method and an apparatus by which supercooled liquid precipitation has been identified and thus reliably identified very early based on very little precipitation.

[0007] The objective of this invention is achieved by a method having the characteristics of a technical solution and by an apparatus having the characteristics of a technical solution for implementing the method. Preferred embodiments of the method according to the invention and preferred embodiments of the apparatus according to the invention are determined in other technical solutions.

[0008] In a method for identifying supercooled liquid precipitation according to the present invention, the temperature of an object having a precipitation impact surface is measured, and it is detected whether precipitation has occurred on the precipitation impact surface. An alarm for supercooled liquid precipitation is output when the temperature below 0°C rises due to the occurrence of precipitation.

[0009] In the method according to the invention, that is, if the temperature of the object below 0°C rises due to precipitation, an alarm for supercooled liquid precipitation is issued. When supercooled liquid precipitation impacts the precipitation impact surface of the object and freezes there, the heat of crystallization is released. The heat of crystallization of water is almost 80 times the hydrothermal capacity per Kelvin. When supercooled liquid precipitation freezes, this large heat of crystallization is released very rapidly and thus a significant increase in the measured temperature of the object is caused by a very small amount of supercooled liquid precipitation. Specifically, the temperature in the corresponding frozen water droplets of supercooled liquid precipitation rises and thus also rises suddenly to 0°C directly on the precipitation impact surface and remains there for such a long time that all the heat of crystallization of the water droplets is completely consumed, i.e., dissipated. If not a very large amount of supercooled liquid precipitation freezes on the precipitation impact surface, the increase in the temperature of the entire object and thus also the increase in the measured temperature of the object is, in principle, less pronounced due to the heat capacity of the object. However, due to the object's limited thermal conductivity, even in situations where the object has a very large heat capacity near the surface of the precipitation impact, a significant temperature rise occurs. This rise is easily detected when measuring the object's temperature at this location and can be assessed as an indication of supercooled liquid precipitation freezing on the precipitation impact surface. In the presence of this indication, an alarm for supercooled liquid precipitation is output.

[0010] When supercooled liquid precipitation begins to appear on the precipitation impact surface, the precipitation can remain liquid despite being supercooled on the impact surface. This is applicable, for example, in the case of drizzle; when the falling velocity of the precipitation is too low to trigger crystallization by vibration upon impact with the precipitation impact surface; or if the precipitation impact surface is very clean after a longer period of rainfall and correspondingly only a small amount of dirt exists as possible crystallization nuclei for freezing the supercooled liquid precipitation. In the method according to the invention, the precipitation impact surface can therefore be excited to reciprocate, particularly in the sense of vibration, in order to induce the supercooled liquid precipitation to freeze on the precipitation impact surface. The phenomenon that vibration can freeze supercooled liquids is well known in principle. This well-known phenomenon can be fully utilized in the method according to the invention so that if an increase in temperature begins with the excited motion of the precipitation impact surface, the alarm regarding the importance of the supercooled liquid precipitation is escalated. Only when precipitation is supercooled liquid precipitation that has frozen due to excited motion and thus released heat of crystallization, does the measured temperature rise below 0 °C result from the excited motion of precipitation carrying precipitation impacting the surface.

[0011] When it is mentioned herein and in the claims, that precipitation has occurred on the precipitation impact surface, it is possible, but not necessary, to detect the impact of precipitation on the precipitation impact surface. However, it is sufficient, for example, to detect whether precipitation is on the precipitation impact surface and, in particular, how much precipitation is on the precipitation impact surface and to infer from the changes determined herein that precipitation has occurred on the precipitation impact surface during this period.

[0012] When mentioned herein and in the claims, it is stated that the temperature below 0 °C rises due to precipitation that occurs and is detected in this respect, meaning that this includes not only the situation where the temperature rise occurs at least almost simultaneously with the precipitation. More precisely, the temperature rise can be delayed relative to the precipitation, especially because the freezing of the precipitation begins delayed and may have to be initiated first. In any case, the temperature rise in this invention is associated with the precipitation in order to identify supercooled liquid precipitation.

[0013] In the method according to the invention, other or additional indications of supercooled liquid precipitation can also be identified and used to escalate the alarm regarding its importance. The indication is that the measured temperature rise of the object exceeds a predetermined limit relative to the amount of precipitation detected. In principle, non-supercooled liquid precipitation with a temperature higher than that of the object can also cause an increase in the object's temperature when it appears on the precipitation impact surface. Once the measured temperature rises to >0°C, the alarm regarding the importance of supercooled liquid precipitation is downgraded. However, if non-supercooled liquid precipitation also freezes on the precipitation impact surface and releases the same heat of crystallization as supercooled liquid precipitation does when freezing, a detectable difference is obtained. Supercooled liquid precipitation freezes much faster than non-supercooled liquid precipitation. In the case of supercooled liquid precipitation, freezing spontaneously begins throughout the volume along the dendritic structure within the corresponding droplet; in the case of non-supercooled liquid precipitation, freezing initially begins only at the interface between the non-supercooled liquid precipitation and the precipitation impact surface. Thus, during the freezing of supercooled liquid precipitation, such a large heat of crystallization is released that all the corresponding water droplets are heated to 0°C directly on the precipitation impact surface and held there until the heat of crystallization is completely dissipated, i.e., dissipated to the object and the corresponding water droplets in their surrounding environment. In the case of non-supercooled liquid precipitation, the temperature on the precipitation impact surface may briefly rise to 0°C. The 0°C isotherm rapidly moves away from the precipitation impact surface into the corresponding water droplets as the ice boundary layer grows, and the temperature on the precipitation impact surface similarly drops rapidly back below 0°C. Therefore, in the case of supercooled liquid precipitation, a greater increase in the measured temperature of the object is caused during the freezing of the precipitation. If the thermal capacity of the temperature sensor used is ignored, the rate and magnitude of this increase are essentially related to the relative position of the object's temperature measurement location with respect to the freezing point of the precipitation on the precipitation impact surface and to the temperature change curve on the precipitation impact surface. Here, the relative position is determined by the thermal conductivity generated between the measurement location and the freezing point relative to the thermal conductivity between the measurement location and the remaining object and the heat dissipation medium affecting it, such as the cold air in the object's surrounding environment. The temperature change curve on the surface impacted by precipitation is determined not only by the type of precipitation (supercooled or non-supercooled) but also by the amount of precipitation. If the temperature increase with respect to the amount of detected precipitation exceeds a limit not reached by non-supercooled precipitation, this is a strong indication of the presence of supercooled liquid precipitation and therefore forms the basis for escalating the alarm regarding its importance. To achieve high sensitivity in distinguishing between supercooled and non-supercooled precipitation, the thermal conductivity between the measurement location and the freezing point should be as high as possible relative to the thermal conductivity between the measurement location and the remaining object and the heat sinks affecting it.

[0014] If the temperature rises to a plateau temperature with a temperature ≤ 0 °C, this is also a meaningful basis for escalating the alarm regarding the importance of supercooled liquid precipitation. At the point where supercooled liquid precipitation directly impacts the surface, the heat of crystallization released when the supercooled liquid precipitation freezes causes the temperature to rise to a plateau temperature with a temperature of 0 °C. However, in temperature measurements taken at intervals, the effective thermal conductivity results in a plateau temperature with a temperature less than 0 °C, as mentioned above. The duration for which the measured temperature plateau is maintained depends on the effective heat capacity of the object, the amount of supercooled liquid precipitation, and environmental conditions. For example, air humidity and wind speed are considered environmental conditions, determining the rate of temperature re-descent. If a further decrease in temperature occurs after the temperature has risen to a plateau temperature less than 0 °C due to precipitation, this can be assessed as another indication of supercooled liquid precipitation, indicating that escalating the alarm regarding its importance is appropriate.

[0015] As already mentioned, supercooled liquid precipitation occurs within a typical range of air temperatures. Therefore, it is advantageous in the method according to the invention to measure the air temperature in the surrounding environment of the object, and to escalate the alarm regarding the importance of supercooled liquid precipitation when the measured air temperature is in the range of -20°C to -2°C, and particularly in the range of -10°C to -5°C.

[0016] In addition to the time-varying curve of the temperature rise and the subsequent drop of the measured temperature, the spatial variation curve of the measured temperature along the plane of the precipitation impact surface, i.e., within the plane of the precipitation impact surface, can be detected in the method according to the invention. It is understood that for this purpose, the temperature must be measured at different points along the precipitation impact surface of the object. If the rise in the measured temperature of the object begins locally and gradually ends over time along the precipitation impact surface, the alarm regarding the supercooled liquid precipitation can be escalated in terms of its importance. The gradual spatial end of the measured temperature rise along the precipitation impact surface is evidence of localized input of heat of crystallization at the location where the precipitation impacts the precipitation impact surface or where the precipitation freezes on the precipitation impact surface.

[0017] In the method according to the invention, after identifying that the temperature below 0 °C has risen due to precipitation, the object can be heated with a determined power. If a temperature plateau caused by the continued rise in the measured temperature of the object appears at 0 °C, this proves that ice has formed on the precipitation impact surface, and that the heat of crystallization initially released on the object must be input into the precipitation as melting heat before the precipitation impact surface rises above 0 °C. This provides evidence of supercooled liquid precipitation, which indicates that escalating the alarm regarding its importance is appropriate.

[0018] In one embodiment of the method according to the invention, a reference object having an additional precipitation impact surface is maintained at a temperature above the air temperature of the object and its surrounding environment, and precipitation is detected on the additional precipitation impact surface. The additional precipitation impact surface at this additional temperature above the air temperature is protected from dew, so that dew or frost, i.e., condensed water vapor, and especially frost, i.e., sublimated water vapor, does not condense on the additional precipitation impact surface. If precipitation is detected on the precipitation impact surface of an unheated object, but no precipitation is detected on the additional precipitation impact surface, the precipitation is dew, frost, or frost. If, simultaneously, an increase in temperature below 0°C is observed due to precipitation on the object, the precipitation is frost. Accordingly, in this embodiment of the method according to the invention, a frost alarm is output.

[0019] In the method according to the invention, the object can also be heated to above 0°C, and it can be detected whether an increase in the capacitance and / or conductivity of the object at the precipitation impact surface is observed. If an increase is observed, it can be inferred that snow or ice is present on the precipitation impact surface. As the ice or snow melts on the heated precipitation impact surface, the dielectric constant increases, thereby increasing the capacitance of the object at the precipitation impact surface. The conductivity of the object at the precipitation impact surface also increases.

[0020] The detection of precipitation impacts on a precipitation impact surface can be performed in different ways according to the method of the invention. This includes continuous detection of the mass of an object having a precipitation impact surface. However, in the method of the invention, it is preferred that precipitation impacts on the precipitation impact surface be detected by detecting whether the capacitance and / or conductivity of the object at the precipitation impact surface changes. Corresponding measuring components for detecting precipitation are known in principle. The magnitude of the change in capacitance and / or conductivity of the object at the precipitation impact surface can be used to infer the portion of the precipitation impact surface wetted by the detected precipitation and thus infer the amount of precipitation detected. It is indicated here that supercooled liquid precipitation frozen on the precipitation impact surface results in a capacitance or conductivity that changes continuously with the amount of said precipitation but remains constant in the absence of additional precipitation. In contrast, precipitation flowing particularly through the precipitation impact surface, i.e., water flowing through the precipitation impact surface, causes a change in said value. This difference can also be used as a basis for escalating alarms regarding the importance of supercooled liquid precipitation.

[0021] In the method according to the invention, the detection of whether precipitation occurs on the precipitation impact surface can also be performed indirectly by detecting whether the temperature of the object changes gradually. This gradual change suggests heat dissipation or heat input through individual water droplets of precipitation, particularly through heat input from crystallization caused by the freezing of individual supercooled liquid water droplets. In contrast, convective heating or convective cooling, as well as evaporative cooling, cause a continuous change in the temperature of the object at the precipitation impact surface. At least in the case of supercooled liquid precipitation, the relatively large heat of crystallization allows the amount of precipitation occurring on the precipitation impact surface to be deduced from the magnitude of the gradual temperature change of the object.

[0022] An apparatus for identifying supercooled liquid precipitation according to the present invention comprises: an object with a precipitation impact surface; a temperature measuring device for measuring the temperature of the object; a precipitation detection device for detecting whether precipitation has occurred on the precipitation impact surface; and an evaluation device designed to identify an increase in temperature below 0 °C due to the occurrence of precipitation and for implementing the method according to the present invention.

[0023] In one embodiment of the device according to the invention, the device includes an actuator that acts on an object having a precipitation impact surface and is designed to excite the precipitation impact surface to reciprocate. In particular, the actuator is designed to vibrate the precipitation impact surface in a vibratory sense in order to induce freezing of supercooled liquid precipitation on the precipitation impact surface. The actuator is particularly energy-efficient if it excites the object to mechanically inherent vibrations at a natural frequency determined by the object's elasticity and / or its support.

[0024] The temperature measuring device according to the invention is preferably designed for locally measuring the temperature of an object near the surface impacted by precipitation. The temperature measuring device may for this purpose have an array of temperature sensors extending along the surface impacted by precipitation. Specifically, the temperature sensors may be arranged on the underside of the object, which is planarly designed, away from the surface impacted by precipitation.

[0025] The temperature measuring device can be additionally designed to measure the air temperature in the environment surrounding the object. For this purpose, the temperature measuring device preferably has an air temperature sensor protected against precipitation. This temperature sensor, unlike the temperature sensor that detects the temperature of the object, is unaffected by heat input or dissipation due to precipitation.

[0026] The device according to the invention may also include a heating element to determine the power required to heat the object, particularly after identifying a temperature rise below 0°C during precipitation. As already described, the change curve caused by the heat input can be used to infer whether precipitation impacts the surface and causes icing, since significant heat input at 0°C is exhausted through melting heat. Furthermore, the melting and dissipation of snow on the sensor surface enables the reconstruction of the sensor's measurement capabilities.

[0027] Alternatively or additionally, the device according to the invention may have a heating device to heat a reference object with a defined power. The reference object may correspond entirely to an object having a precipitation impact surface. In any case, the reference object has an additional precipitation impact surface, and additional temperature measuring devices and additional precipitation detection devices are connected to the evaluation device, the additional temperature measuring devices being designed to measure the temperature of the reference object, and the additional precipitation detection devices being designed to detect whether precipitation has occurred on the additional precipitation impact surface. As described above for the method according to the invention, dew, frost, and white frost can be identified by means of the reference object, and a distinction can be made between dew and frost on the one hand, and white frost on the other.

[0028] In the device according to the invention, the precipitation impact surface is typically oriented at an angle relative to the horizontal plane that allows precipitation to adhere but prevents a large amount of liquid precipitation from remaining on the precipitation impact surface. The angle can generally be in the range of 10° to 80°. Preferably, the angle is between 50° and 70° relative to the horizontal plane, i.e., approximately 60°.

[0029] The precipitation detection device according to the invention can be designed to detect the capacitance and / or conductivity of an object at the surface impacted by precipitation. As already described, the precipitation detection device can also, in principle, be designed to detect the mass of the object so as to infer the amount of precipitation on the surface impacted by precipitation. The distribution of precipitation on the surface impacted by precipitation can be additionally inferred from the detection of the capacitance and / or conductivity of the object at the surface impacted by precipitation, at least when the capacitance and / or conductivity are detected along the surface impacted by precipitation with significant resolution. In particular, capacitance can be detected by detecting the vibration frequency of an RC oscillator comprising the capacitance, the vibration frequency being linearly related to the reciprocal of the capacitance.

[0030] Advantageous further aspects of the invention are derived from the claims, description and drawings.

[0031] The advantages mentioned in the specification regarding the features and combinations thereof are merely exemplary and may work alternatively or additionally, and the advantages are not necessarily enforceable by embodiments of the invention.

[0032] The following applies to the disclosures (excluding the scope of protection) in the original application documents and patents: Additional features can be derived from the drawings (particularly the geometry and relative dimensions of the plurality of components relative to each other, and the relative arrangement and functional connections of said components). Features of different embodiments of the invention, or combinations of features of different claims, can also differ from and be inspired by the chosen backreference relationships of the claims. This also applies to features shown in separate drawings or mentioned in the description of said drawings. These features can also be combined with features of different claims. Features listed in the claims can also be omitted for other embodiments of the invention; however, this does not apply to the independent claims of the granted patents.

[0033] The quantity of features mentioned in the claims and specification can be understood as exactly the quantity or a greater quantity, without the need for the specific use of the adverb "at least". That is, when referring, for example, to an air temperature sensor, this is understood to mean that there is exactly one air temperature sensor, two air temperature sensors, or more air temperature sensors. Features referenced in the claims may be supplemented by other features or be unique features possessed by the corresponding method or device.

[0034] The reference numerals included in the claims do not limit the scope of the subject matter protected by the claims. These reference numerals are used merely to make the claims easier to understand. Attached Figure Description

[0035] The present invention will be further illustrated and explained below with reference to the preferred embodiments shown in the accompanying drawings.

[0036] Figure 1 A first embodiment of the apparatus according to the invention for implementing the method according to the invention is shown.

[0037] Figure 2 This is a rear view of the sensor circuit board of the device according to Figure 1.

[0038] Figure 3 It is a graph of different measurement parameters, which are determined according to... Figure 1 The device detects when supercooled liquid rainwater hits the sensor circuit board of the device and freezes there.

[0039] Figure 4 This is a perspective view of the sensor circuit board of another device according to the present invention.

[0040] Figure 5 A schematic top view of a sensor circuit board according to another embodiment of the device of the present invention.

[0041] Figure 6 The cross-sectional view of the sensor circuit board in Figure 5 is obtained by cutting along the cutting line VI-VI shown in Figure 5.

[0042] Figure 7 This is a schematic top view of yet another sensor circuit board according to yet another embodiment of the device according to the invention.

[0043] Figure 8 Along Figure 7 The section line VIII-VIII shown in the figure is based on Figure 7 A cross-sectional view of the sensor circuit board; and Figure 9 This is a flowchart of one embodiment of the method according to the present invention. Detailed Implementation

[0044] exist Figure 1 The device 1, shown in a simplified three-dimensional side view, is used to detect meteorological data, particularly regarding precipitation, which impacts the device 1 on its precipitation impact surface 2. The device 1 has a pyramidal arrangement of a total of four precipitation impact surfaces 2 on its upper side. Each precipitation impact surface 2 is inclined at 60° relative to the horizontal plane. Precipitation can thus adhere to these precipitation impact surfaces. However, a larger amount of liquid precipitation flows downwards from the precipitation impact surfaces 2. The precipitation impact surfaces 2 are the outer surfaces of sensor circuit boards 3, which are arranged in openings within a rigid frame 4 and supported thereon. The rigid frame 4 is connected at its upper part to the device housing 5, in which the evaluation device is located, and an air temperature sensor 6 is arranged on the outer side of the housing. The air temperature sensor 6 is protected upwards from the influence of precipitation by the frame 4 and the sensor circuit board 3 arranged therein. The air temperature sensor 6 is protected from solar radiation by oriented northwards during the operation of the device 1, see the azimuth mark 7 on the device 1. To protect the air temperature sensor from wind and blown-up precipitation, the air temperature sensor 6 is also arranged between baffles 8 in the circumferential direction around the housing 5. The interface area 9 of the device, which has mechanical and electrical interfaces (not specifically shown here), is connected to the housing 5.

[0045] The arrangement of the three temperature sensors 10 distributed on the precipitation impact surface 2 can be seen in the rear view of the sensor circuit board 3 shown in Figure 2, based on Figure 1. The temperature of the sensor circuit board 3, which is the object with the precipitation impact surface 2, is locally detected by means of the temperature sensors 10. Additionally, the wetting of the precipitation impact surface 2 by precipitation is identified by a precipitation detection device (not shown), and thus the impact of precipitation on the precipitation impact surface 2 is identified.

[0046] Figure 3 shows the variation curves of different parameters for a time period of approximately 30 seconds, during which a total of 12 water droplets from supercooled liquid water impact the sensor circuit board 3, which is oriented at an angle of 60° relative to the horizontal plane, in the area opposite the temperature sensor shown above in Figure 2, on the rain impact surface 2. Here, the vertical line indicated by the dashed line shows the impact time of each of the two water droplets. The line extending upwards in Figure 3 shows the variation curve of the vibration frequency 11 of the RC oscillator, which includes a capacitor formed at the rain impact surface 2. The capacitance increases by wetting the rain impact surface with the appearing rainwater, and the vibration frequency 11 of the electronic RC oscillator decreases accordingly. The rising line in Figure 3 shows the variation curve of the temperature 12 of the sensor circuit board 3, which is determined by... Figure 2 The upper temperature sensor of the three temperature sensors 10 is measured. The horizontal line represents the water temperature of the supercooled liquid water before it impacts the precipitation impact surface 2; and the other horizontal line 14 represents the air temperature in the environment surrounding the sensor circuit board 3, for example, the air temperature is detected by means of the air temperature sensor 6 in the device 1 according to FIG. 1. As shown by the progressively decreasing vibration frequency 11, the wetting of the precipitation impact surface increases as each of the 12 water droplets impacts the precipitation impact surface 2. Specifically, the increased wetting is wetting with ice, as the supercooled liquid water freezes into ice on the precipitation impact surface 2. The freezing releases heat of crystallization, which causes the temperature 12 of the sensor circuit board 3 in the impact area of ​​the corresponding water droplet to rise. After each of the 12 water droplets impacting the precipitation impact surface 2 freezes, line 21 rises accordingly. The rise 15 occurs at temperatures below 0°C and approaches 0°C, the temperature at which the water droplet rewarms to due to the heat of crystallization released during freezing. The rapid increase 15 below 0 ℃ is caused by the impact of water droplets on the precipitation impact surface 2, as indicated by the decreasing vibration frequency 11. This increase is clear evidence of the presence of supercooled liquid precipitation, and thus the evaluation device of equipment 1 outputs a corresponding alarm signal.

[0047] With each of the 12 water droplets impacting the surface, the vibration frequency 11 decreases in principle in a stepwise manner. However, immediately after the impact of a single droplet of the 12 water droplets, the vibration frequency 11 initially decreases very sharply before stabilizing at the level it had reached after the initial decrease. This is attributed to the fact that the portion of the precipitation impact surface 2 wetted by the respective water droplet is larger immediately after the impact, before the corresponding water droplet has slightly contracted before freezing on the more hydrophobic precipitation impact surface 2.

[0048] from Figure 3It can be clearly seen that the heat of crystallization released by the freezing of each of the 12 water droplets upon impact with the surface 2 is still sufficient, despite the heat capacity of the sensor circuit board 3, to cause a distinguishable increase in temperature on the back side of the sensor circuit board 3, which can be detected by means of one of the temperature sensors 10 according to FIG. 2. It is understood that the heat capacity of the sensor circuit board can be limited in order to observe the effect. However, no special measures are required, i.e., a particularly low heat capacity of the sensor circuit board is not necessary.

[0049] Figure 4 shows a sensor circuit board 3 of another device according to the present invention. Although the sensor circuit board 3 has a different basic geometric shape, i.e., not triangular but rectangular, it is in principle implemented according to... Figure 1 and 2 The sensor circuit board 3 operates on the same measurement principle. According to... Figure 4The sensor circuit board 3 is specifically based on a substrate 16 made of alumina with a typical thickness ranging from 0.2 to 1 mm, and the substrate has a glass passivation layer typically 5 to 15 µm thick on its surface. A sensor assembly 17 is constructed beneath the glass passivation layer of the precipitation impact surface 2, and the sensor assembly has two electrodes 18 and 19 arranged in a comb-like pattern and mating with each other along the precipitation impact surface 2, but spaced apart from each other. The capacitance between electrodes 18 and 19, for example made of a silver-palladium alloy, determines the vibration frequency of an RC oscillator of the precipitation detection device (not shown further here), the capacitance being affected by the wetting of the precipitation impact surface 2 by precipitation. A temperature sensor 10 and a heating element 20 are arranged on the underside of the substrate 16. The heating element 20 is part of a heating device by means of which the sensor circuit board 3 can be heated to a defined power. If a temperature plateau of 0 °C occurs when heating the sensor circuit board 3 below 0 °C, this indicates that the precipitation impact surface 2 is frozen, and the ice melts only when the required melting heat is applied. The required heat of melting is exactly the same as the heat of crystallization released during freezing. One of the multiple sensor circuit boards, also serving as a reference, can be heated to a temperature slightly above air temperature, i.e., several Kelvin higher, and held there by means of the heating element 20. Therefore, this sensor circuit board 3 is equipped with a dew-proof wetting device, and the presence of dew or frost can only be inferred when precipitation occurs on another sensor circuit board 3 that is not heated to above air temperature by the heating element 20. However, frost only exists when a temperature rise of 15 below 0°C occurs due to precipitation only on the sensor circuit board 3 that is not heated by the heating element 20. Temperature sensors 10 are arranged in a planar grid on the back side of the substrate 16. Thus, a temperature sensor 10 is attached at each point of the precipitation impact surface 2. That is, each water droplet from supercooled liquid water frozen on the precipitation impact surface 2 that impacts the precipitation impact surface 2 causes a local temperature rise in the substrate 16, which is large at least at the location of one of the temperature sensors 10, so that the temperature rise can be reliably detected. The distribution of temperature rise on the surface of substrate 16 is also an indication of supercooled liquid precipitation droplets impacting the precipitation impact surface 2 and freezing there. The accurate curve of the distribution is related to the heat capacity and thermal conductivity of substrate 16.

[0050] An actuator 21 is provided to ensure that supercooled liquid precipitation freezes on the precipitation impact surface 2. This actuator acts on the side edge of the substrate 16 and agitates the substrate 16 to move back and forth. This movement causes vibration of the precipitation impact surface 2 and the supercooled liquid precipitation on the surface, triggering the freezing of the supercooled liquid precipitation. The actuator 21 can be designed as a microelectromechanical system (MEMS) and the sensor circuit board 3 is positioned at a mechanically natural frequency determined by the elasticity and / or elastic support of the sensor circuit board. In this manner, sufficient vibration of the precipitation on the precipitation impact surface 2 is achieved with minimal energy consumption to trigger the freezing of the precipitation.

[0051] In the embodiment of sensor circuit board 3 according to Figures 5 and 6, substrate 16 is made of a thermally conductive and sufficiently weather-resistant metal, or passivated on its surface, with a typical material thickness of 10 µm to 1 mm. An array of temperature sensors 10 is arranged on the underside of substrate 16 on a common circuit board 22. The free space between temperature sensors 10 can be filled with insulating material 23. Heating elements 20 of heating device 24 are arranged here on the opposing side edges of substrate 16. Actuator 21 is also engaged on the side edges of substrate 16.

[0052] In the embodiment of sensor circuit board 3 according to Figures 7 and 8, substrate 16 is made of insulating material 23. Highly thermally conductive contact pads 25 are arranged on the rain impact surface 2, and these contact pads are connected to a temperature sensor 10 arranged on the underside of substrate 16 via highly thermally conductive connecting portions 26. Thus, when a droplet of water from supercooled rain falls onto one of the contact pads 25 and freezes there, the detected temperature rise and the reduction of the heat capacity of sensor circuit board 3 to the heat capacity of a single contact pad 25, a single connecting portion 26, and a single temperature sensor 10 can be suppressed.

[0053] The method according to the invention, illustrated in flowchart form in Figure 9, begins with step 27 measuring the temperature T of the sensor circuit board 3, including the corresponding precipitation impact surface 2, and step 28 detecting precipitation occurring on the precipitation impact surface 2. If, in check 29, an increase in the measured temperature T below 0°C is temporally correlated with the detection of precipitation, an alarm for supercooled liquid precipitation is output in step 30. Additionally, in step 31, a boundary condition analysis is performed where an increase in the measured temperature T below 0°C is detected under these boundary conditions. When it is determined in check 32 that an additional criterion has been met, thus providing further indication of the presence of supercooled liquid precipitation, the alarm for supercooled liquid precipitation is escalated in step 33 regarding its importance. This step is implemented whenever the criterion is met. The following conditions apply: the measured temperature rise begins only with the motion excited by the impact of precipitation on the surface; the measured temperature rise exceeds a predetermined limit with respect to the amount of detected precipitation; the measured temperature rise proceeds to a temperature plateau with a temperature plateau of ≤ 0 °C; the measured air temperature in the surrounding environment of the object is in the range of -20 °C to -2 °C or more particularly -10 °C to -5 °C; the measured temperature rise of the sensor circuit board is localized and gradually ends along the precipitation impact surface; heating of the sensor circuit board after identifying a measured temperature rise below 0 °C causes a continued rise in the measured temperature of the sensor circuit board, the continued rise having a temperature plateau at 0 °C; and the capacitance and / or conductivity at the precipitation impact surface either continuously change or remain constant during the measured temperature rise. When verifying whether the final criterion is met, short-term effects of capacitance and / or resistance at the precipitation impact surface are disregarded. These short-term effects are determined by the self-contraction of water droplets from liquid precipitation on a hydrophobic precipitation impact surface or by the recent dispersion of liquid precipitation on a hydrophilic precipitation impact surface. In a specific embodiment of the method according to the invention, only one of the criteria may be verified. Other criteria may remain unnoticed.

[0054] List of reference numerals

Claims

1. A method for identifying supercooled liquid precipitation, - Among them, the temperature (12) of the object (3) with the surface impacted by precipitation (2) is measured, and - in, Detect whether precipitation occurs on the precipitation impact surface (2). The feature is that when the temperature (12) below 0°C rises (15) due to precipitation, an alarm for supercooled liquid precipitation is output.

2. The method according to claim 1, characterized in that, The precipitation impacts the surface (2) and induces a back-and-forth motion, and if the temperature (12) rises (15) with the induction of the motion, the alarm for the supercooled liquid precipitation is escalated in relation to its importance.

3. The method according to claim 1, characterized in that, - If the increase in temperature (12) exceeds a predetermined limit with respect to the amount of detected precipitation, and / or - If the temperature (12) rises (15) to a temperature plateau with a temperature plateau of ≤ 0 °C, the alarm for the supercooled liquid precipitation will be upgraded in terms of its importance.

4. The method according to claim 1, characterized in that, The air temperature (14) in the surrounding environment of the object (3) is measured, and when the air temperature (14) is measured in the range of -20 ℃ to -2 ℃, the alarm for the supercooled liquid precipitation is upgraded in terms of its importance.

5. The method according to claim 1, characterized in that, When the measured temperature (12) of the object (3) rises (15) locally and gradually ends along the surface (2) where the precipitation impacts, the alarm for the supercooled liquid precipitation is escalated in relation to its importance.

6. The method according to any one of claims 1 to 5, characterized in that, After identifying that the temperature (12) below 0 °C rises (15) when precipitation occurs, the object (3) is heated with a determined power, and when the temperature plateau that causes the measured temperature (12) of the object (3) to continue to rise is at 0 °C, the alarm for the supercooled liquid precipitation is upgraded in terms of its importance.

7. The method according to any one of claims 1 to 5, characterized in that, - A reference object (3) having an additional precipitation impact surface (2) is maintained at a temperature above the air temperature (14) of the object (3) and its surrounding environment, and precipitation is detected on the additional precipitation impact surface (2), wherein the object (3) is not heated, and - When the temperature (12) below 0°C rises (15) due to precipitation on the object (3), a frost alarm is output if no additional precipitation impacting the surface (2) of the reference object is detected at the same time.

8. The method according to any one of claims 1 to 5, characterized in that, The object (3) is heated to above 0°C, and it is detected whether there is an increase in the capacitance and / or conductivity of the object (3) at the precipitation impact surface (2), wherein if an increase is found, it is inferred that snow or ice is on the precipitation impact surface (2).

9. The method according to claim 2, characterized in that, The back-and-forth motion is motion in the sense of vibration.

10. The method according to claim 4, characterized in that, When the air temperature is measured to be in the range of -10 °C to -5 °C (14), the alarm for supercooled liquid precipitation will be upgraded in terms of its importance.

11. A device (1) for identifying supercooled liquid precipitation, comprising: - Object (3) with a surface impacted by precipitation (2). - Temperature measuring device, which is designed to measure the temperature (12) of the object (3). - A precipitation detection device, designed to detect whether precipitation occurs on the precipitation impact surface (2), and - Evaluation device, Its features are, The evaluation device is designed to identify temperature increases below 0 °C due to precipitation and to implement the method according to any one of the preceding claims.

12. The device (1) according to claim 11, characterized in that, The actuator (21) of the device (1) acts on the object (3) having the precipitation impact surface (2) and is designed to excite the precipitation impact surface (2) to move back and forth.

13. The device (1) according to claim 11, characterized in that, The temperature measuring device is designed to locally measure the temperature (12) of the object (3) near the surface (2) impacted by the precipitation.

14. The device (1) according to claim 11, characterized in that, The temperature measuring device is designed to measure the air temperature (14) in the surrounding environment of the object (3).

15. The device (1) according to claim 11, characterized in that, The heating device of the device (1) is designed for, - To heat the object (3) at a determined power, and / or - A reference object (3) is heated by a defined power, wherein the reference object has an additional precipitation impact surface (2) wherein an additional temperature measuring device and an additional precipitation detection device are connected to the evaluation device, the additional temperature measuring device being designed to measure the temperature (12) of the reference object (3), and the additional precipitation detection device being designed to detect whether precipitation occurs on the additional precipitation impact surface (2).

16. The device (1) according to any one of claims 11 to 15, characterized in that, The precipitation impact surface (2) is oriented at an angle between 10° and 80° relative to the horizontal plane.

17. The device (1) according to any one of claims 11 to 15, characterized in that, The precipitation detection device is designed to detect the capacitance and / or conductivity of the object (3) at the precipitation impact surface (2).

18. The device (1) according to claim 12, characterized in that, The back-and-forth motion is motion in the sense of vibration.

19. The device (1) according to claim 13, characterized in that, The temperature measuring device has an array of temperature sensors (10) extending along the precipitation impact surface (2), the temperature sensors being arranged on the underside of the planar object (3) facing away from the precipitation impact surface (2).

20. The device (1) according to claim 14, characterized in that, The temperature measuring device has an air temperature sensor (6) that is protected from precipitation.

21. The device (1) according to claim 16, characterized in that, The precipitation impact surface (2) is oriented at an angle between 50° and 70° relative to the horizontal plane.

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