System and sensor for measuring the urea concentration in a urea solution

Abstract

The invention relates to a system (100) for measuring the urea concentration in a urea solution, in particular for monitoring the quality and degree of degradation of diesel exhaust fluid (DEF) or AdBlue fluids, comprising a sensor (10) and a data processing module (70), wherein the sensor (10) comprises a cylindrical glass tube (40) with a glass wall (43) and a capacitor (20) with a first electrode (23) and a second electrode (25) is arranged circumferentially on the outer surface of the glass wall (43), wherein the length (I) of the first electrode (23) is shorter than the length (L) of the second electrode (25), and wherein the real and / or imaginary component of the impedance of the capacitor (20) is measured by means of a measuring circuit (50) as a measure of the quality of the urea solution and the measurement signals are transmitted as sensor data (15) to the data processing module. (70) are transferred, and wherein the data processing module (70) is configured,to generate output data (75) for controlling the urea concentration from the sensor data (15).

Description

[0001] The invention relates to a system and a sensor for measuring the urea concentration in a urea solution, in particular to regulate the quality of the diesel exhaust fluid (AdBlue fluid).

[0002] AdBlue is a registered trademark for the exhaust aftertreatment of diesel engines using selective catalytic reduction (SCR). It is a clear, non-toxic, and non-flammable solution consisting primarily of urea and demineralized water. AdBlue is used in diesel engines to reduce emissions of harmful nitrogen oxides (NOx), which contribute significantly to air pollution. During diesel combustion, nitrogen and atmospheric oxygen combine to form NOx. The vehicle's SCR system treats the exhaust gases by injecting a precisely metered amount of AdBlue into the exhaust stream.

[0003] In the SCR catalyst, the AdBlue solution decomposes into ammonia (NH3) and carbon dioxide (CO2). The ammonia then reacts with the nitrogen oxides in the exhaust gas, converting them into harmless nitrogen (N2) and water vapor (H2O). This chemical reaction contributes to significantly reducing pollutant emissions into the atmosphere. AdBlue and SCR technology are increasingly being used in diesel vehicles, particularly commercial vehicles such as trucks, buses, and heavy machinery. It is also used in some passenger cars to meet strict emissions standards.

[0004] To ensure effective operation of the SCR system, vehicles with SCR technology have a separate AdBlue tank, usually located near the fuel tank. The AdBlue tank must be refilled regularly, usually during regular vehicle maintenance. AdBlue consumption varies depending on engine size, vehicle load, and operating conditions.

[0005] The use of AdBlue and SCR technology can significantly reduce vehicle nitrogen oxide emissions, contributing to cleaner air and improved environmental performance in the transport sector.

[0006] To monitor the quality of diesel exhaust fluid (DEF) or AdBlue, a system for measuring the quality and degree of degradation is used. Such a system includes various sensors, components, and algorithms to evaluate the composition and degree of degradation of the DEF. Conductivity sensors are known to be used for this purpose. Since DEF typically contains a precise concentration of urea, a conductivity sensor can measure the electrical conductivity of the fluid, which is directly related to the urea concentration. Any deviation from the expected conductivity value can indicate a potential quality problem. Another option is to use a pH sensor, since the pH of the DEF is an indicator of its quality. A pH sensor measures the acidity or alkalinity of the fluid, and significant deviations from the expected pH range can indicate contamination or deterioration.In addition, optical sensors, such as those in the near-IR range, can be used to detect visible contaminants or particles in the DEF. This can help identify contaminants that may compromise fluid quality.

[0007] A comprehensive monitoring and control system can integrate data from the various sensors mentioned above. The system can continuously monitor parameters, compare them with predefined thresholds, and issue warnings in case of deviations. The system can also forward information to the vehicle's on-board diagnostic system and display information about the DEF quality to the driver. Diagnostic and maintenance alerts can also be issued to ensure timely DEF replacement or system maintenance.

[0008] WO 2010 151327 A12 discloses a sensor for measuring the level, composition, and contamination of a liquid. The sensor generates an RF signal via an oscillating circuit containing a variable inductance and a capacitor. The resulting electromagnetic radiation propagates through the liquid. Changes in the impedance and resonance of the oscillating circuit, which result from changes in the conductivity and dielectric properties of the liquid and are proportional to the liquid content and volume, are detected. The conductivity and dielectric properties of the liquid are measured and compared with the changed impedance and resonance of the oscillating circuit.

[0009] DE 101 02 237 A1 discloses a device for dosing urea solutions, wherein a sensor unit is provided for detecting one or more physical state variables, which sensor unit has two electrodes with two comb-shaped, interlocking structures.

[0010] EP 2 517 004 B1 discloses a device and method for measuring physical properties of a urea solution. A conductivity sensor with two electrodes is immersed in the urea solution to detect the electrical conductivity of the urea solution.

[0011] The invention is based on the object of creating possibilities for improving the measurement of the urea concentration in a urea solution, in particular in order to regulate the quality of the diesel exhaust fluid (AdBlue fluid).

[0012] The system according to the invention can monitor the quality and consumption of the AdBlue solution, since the capacity of the AdBlue fluid sensor is influenced by contaminants such as metal salts in the AdBlue fluid. The measuring system includes a temperature sensor to measure the temperature of the electrolyte and use this to calculate the AdBlue fluid concentration.

[0013] The sensor according to the invention exhibits a linear transfer characteristic because interference from stray capacitance (e.g., metallic objects in the vicinity of the sensor) is avoided. It is possible to modify the sensor design while maintaining the sensor constant by only keeping the length of the shorter electrode unchanged. Furthermore, changes in the liquid level have a negligible influence on the sensor capacitance. The arrangement of the electrodes circumferentially on the non-metallic glass wall of the glass tube eliminates distortion effects that can be caused by the double-layer capacitance at the interface between the electrolyte (AdBlue) and the metal electrodes. Furthermore, the sensor is characterized by a simple and cost-effective manufacturing process.

[0014] This object is achieved according to the invention with respect to a system by the features of patent claim 1 and with respect to a sensor by the features of patent claim 3. The further claims relate to preferred embodiments of the invention.

[0015] According to a first aspect, the invention provides a system for measuring the urea concentration in a urea solution, in particular for monitoring the quality and degree of degradation of diesel exhaust fluid (DEF) or AdBlue liquids.The system comprises a sensor and a data processing module, wherein the sensor comprises a cylindrical glass tube with a glass wall and a capacitor with a first electrode and a second electrode is arranged circumferentially on the outer surface of the glass wall, wherein the length of the first electrode l is smaller than the length of the second electrode, and wherein the real and / or imaginary component of the impedance of the capacitor is measured by means of a measuring circuit as a measure of the quality of the urea solution and the measurement signals are transmitted as sensor data to the data processing module; and wherein the data processing module is designed to generate output data for controlling the urea concentration from the sensor data.

[0016] In a further development, the capacitance C of the sensor is determined by the formula C=εrε0πl ln 2 where ε0 = 8.85 - 10 -12 FM -1the dielectric constant of the vacuum and ε r is the relative dielectric constant of the urea solution.

[0017] According to a second aspect, the invention provides a sensor for measuring the urea concentration in a urea solution, in particular for monitoring the quality and degree of degradation of diesel exhaust fluid (DEF) or AdBlue fluids. The sensor comprises a cylindrical glass tube with a glass wall, wherein a capacitor with a first electrode and a second electrode is arranged circumferentially on the outer surface of the glass wall. The length of the first electrode is shorter than the length of the second electrode. By means of a measuring circuit, the real and / or imaginary component of the capacitor's impedance is measured as a measure of the quality of the urea solution.

[0018] In a further development, the capacitance C of the sensor is determined by the formula C=εrε0πl ln 2 where ε0 = 8.85 · 10 -12 FM -1 the dielectric constant of the vacuum and ε r is the relative dielectric constant of the urea solution.

[0019] In an advantageous embodiment, it is provided that the outer surface of the glass wall of the glass tube is provided with a shield, which is applied in particular by vapor deposition of a copper layer in a vacuum onto the outer surface of the thin-walled glass wall of the glass tube, wherein a thin air gap is provided between the shield and the surface of the first electrode and the second electrode.

[0020] In a further embodiment, it is provided that a temperature sensor is provided, which is arranged in particular on an upper cover of the glass tube.

[0021] In particular, the length of the second electrode is at least three times greater than the length of the first electrode.

[0022] To avoid stray capacitances, the lines to the two electrodes of the capacitor are advantageously shielded and grounded.

[0023] In an advantageous embodiment, it is provided that the input electrode is connected to a voltage source with low output resistance via a shielded line with low capacitance, so that no significant voltage drop occurs in the voltage source.

[0024] Advantageously, the capacitance of the shielded line leading to the input of an operational amplifier is equal to the virtual zero voltage of the operational amplifier, so that it has a negligible influence on the output voltage of the operational amplifier.

[0025] The invention is explained in more detail below with reference to embodiments shown in the drawing.

[0026] It shows: Fig. 1 is a block diagram illustrating an embodiment of a system according to the invention; Fig. 2 a representation of the impedance of a coaxial cylindrical sensor according to the prior art with non-linear dependence as a function of an AdBlue concentration; Fig. 3 a schematic representation of a capacitor stray field that is suppressed by a grounded guard ring; Fig. 4 a perspective view of the sensor according to the invention; Fig. 5 shows an electrical circuit for the sensor according to the invention; Fig. 6 a representation of a strip capacitor; Fig. 7 a schematic representation of a conformal transformation of a Z-plane into a W-plane.

[0027] Additional features, aspects and advantages of the invention or embodiments thereof will become apparent from the detailed description taken in conjunction with the claims.

[0028] Fig. 1 shows a system 100 according to the invention for measuring the urea concentration in a urea solution, in particular for monitoring the quality and degree of degradation of diesel exhaust fluid (DEF) or AdBlue liquids. The system 100 comprises a sensor 10 according to the invention, which is designed as a capacitive sensor with an electrode arrangement according to the invention for performing impedance measurements, and a data processing module 70 for processing the sensor data 15 measured by the sensor 10 into output data 75. The AdBlue concentration can be regulated using the output data 75. Furthermore, further components, parts, and algorithms, such as artificial intelligence algorithms, in particular neural networks, can be provided.

[0029] The sensor 10 and the data processing module 70 can each be provided with a processor and / or a storage unit. In particular, the data processing module 70 can be designed as a standalone computer unit or as a cloud-based solution. The data processing module 70 can be connected to a database 80. The term "database" refers both to a storage algorithm and to the hardware in the form of a storage unit. In particular, the database 80 can be designed as a cloud computing infrastructure. Further data in the form of images, graphics, time series, parameters, etc. can also be stored in the database 80. For example, target and target values ​​that define a safety standard can be stored in the database 80.

[0030] In the context of the invention, a "processor" can be understood to mean, for example, a machine or an electronic circuit. A processor can in particular be a main processor (Central Processing Unit, CPU), a microprocessor or a microcontroller, e.g. an application-specific integrated circuit or a digital signal processor, optionally in combination with a memory unit for storing program instructions, etc. A processor can also be a virtualized processor, a virtual machine or a soft CPU. It can also be, for example, a programmable processor that is equipped with configuration steps for carrying out the aforementioned method according to the invention or is configured with configuration steps such that the programmable processor implements the inventive features of the method, the sensor 10, the modules or other aspects and / or sub-aspects of the invention.In particular, the processor can contain highly parallel computing units and powerful graphics modules.

[0031] In the context of the invention, a "storage unit" or "storage module" and the like can be understood to mean, for example, a volatile memory in the form of random access memory (RAM), a permanent memory such as a hard disk or a data storage device, or, for example, a removable storage module. The storage module can also be a cloud-based storage solution.

[0032] In the context of the invention, a "module" can be understood, for example, as a processor and / or a memory unit for storing program instructions. For example, the processor is specifically configured to execute the program instructions in such a way that the processor and / or the control unit performs functions to execute or implement the method according to the invention or a step of the method according to the invention.

[0033] Impedance is a measure of the resistance to the flow of alternating current (AC) in an electrical circuit. It is a complex quantity containing both resistive and reactance components. Impedance is denoted by the symbol Z and is measured in ohms (Ω). In an AC circuit, impedance is affected by the resistance of the circuit elements (e.g., resistors, conductors, and loads) and by the reactance caused by inductors and capacitors. The resistive component of impedance, called the real part, represents the resistance to current flow through purely resistive elements and is denoted by R. The reactance component, called the imaginary part, represents the resistance caused by inductive or capacitive elements and is denoted by jX, where j is the imaginary unit.

[0034] The total impedance Z of a circuit is the vector sum of resistance and reactance: Z=R+jX

[0035] The magnitude of the impedance |Z| represents the total resistance to the current flow, while the phase angle θ represents the phase relationship between voltage and current in the circuit.

[0036] Impedance plays a crucial role in the analysis and design of AC circuits. It influences the voltage and current ratios, power transfer, and overall performance of electrical and electronic systems. Matching the impedance of various components and devices in a circuit is important for efficient power transfer and to avoid signal reflections or losses.

[0037] In Fig. Figure 2 shows the reactance component of the impedance of a typical coaxial cylindrical sensor from the prior art as a nonlinear function of the AdBlue concentration in wt.%. Due to the inventive design of the sensor 10, however, the impedance is completely linear with the AdBlue concentration.

[0038] In contrast to the capacitance C of an ideal coaxial cylindrical capacitor, in a real capacitor the stray field changes both the capacitance C of the capacitor and the nonlinearity of the relationship C=f(ε), where ε is the dielectric constant.

[0039] In a capacitor, the stray field is the electric field that extends beyond the area between the capacitor plates. When a voltage is applied to the plates of a capacitor, an electric field builds up between them. However, this electric field does not end abruptly at the edges of the plates, but spreads somewhat into the surrounding space. The stray field is created because the electric field lines bend or diverge as they approach the edges of the capacitor plates. The electric field lines in the stray field are weaker than the field between the plates, but are still present near the capacitor. The shape and strength of the stray field depend on the geometry of the capacitor, e.g., the shape and size of the plates and the distance between them.

[0040] The presence of the stray field has practical implications for the design and operation of capacitors. It influences the capacitance value and the distribution of the electric field within the capacitor.

[0041] The stray field can lead to capacitance fluctuations, particularly in capacitors with closely spaced or irregularly shaped plates. The influence of the stray field is generally less pronounced in capacitors with larger plate areas and smaller plate spacing. Therefore, the stray field must be considered when designing capacitors for specific applications through factors such as plate spacing, plate geometry, and dielectric properties to minimize the effects of the stray field and optimize capacitor performance.

[0042] Understanding the stray field is therefore crucial for the accurate modeling and analysis of capacitors in various electronic systems and devices, as this is the only way to ensure the correct function and reliable performance of capacitors in their intended applications.

[0043] In Fig. Figure 3 illustrates the deformation of the electric field 30 caused by the action of the stray field 32 on a planar capacitor 20 with a first upper electrode 23 and a second lower electrode 25. A grounded guard ring 27 and a shield 29 suppress the field strength of the stray field 32 so strongly that it drops very quickly to almost zero.

[0044] Fig. 4 shows the sensor 10 according to the invention, which is designed as a cylindrical sensor with a glass tube 40. The glass tube 40 has a glass wall 43. A capacitor 20 with a first arc-shaped electrode 23 and a second arc-shaped electrode 25 is arranged circumferentially on the outer surface of the glass wall 43 of the glass tube 40. The length of the first electrode is 1 and the length of the second electrode 25 is L, wherein the length 1 of the first electrode 23 is shorter than the length L of the second electrode 25. In particular, the length of the second electrode, with L ≥ 3 1, is three times as long as the length of the first electrode 23. Furthermore, a temperature sensor 47 is provided, which is arranged in particular on an upper cover of the glass tube 40. The circumference of the glass tube 40 is divided into four 90° sections.The entire outer surface of the glass wall 43 of the glass tube 40 of the sensor 10 is coated with a shield 49 in the form of a metal layer. The shield 49 is separated from the first electrode 23 and the second electrode 25 by a thin insulating air gap. The shield is applied, in particular, by a vapor deposition process. To create the thin air gap between the electrodes 23, 25 and the metal layer, a covering technique can be used. The electrodes 23, 25 are covered with a material that prevents the coating of the electrodes 23, 25, thereby creating the desired air gap between the electrodes 23, 25 and the shield 49. The shield 49 must always be grounded for proper operation. The temperature sensor 47 has low power consumption and high accuracy at the analog output.

[0045] Fig. Figure 5 shows the electrical measuring circuit 50 of the sensor 10. The operation of the sensor 10 is based on the Lampard theorem. The measurement of the AdBlue concentration depends on the real and imaginary components of the impedance between the first electrode 23 and the second electrode 25 of the capacitor 20. Fig. The measuring circuit 50 shown in Figure 5 preferably measures the imaginary component of the impedance, ie the reactance or capacitance between the first electrode 23 and the second electrode 25. The capacitance corresponding to the thin glass wall 43 of the glass tube 40 is connected in series with the measured impedance of the interior 21 of the capacitor 20.

[0046] Since the thickness of the glass wall 43 is substantially smaller than the geometry of the interior space 21 between the first electrode 23 and the second electrode 25, the impedance of the glass wall 43 is also substantially smaller than the impedance of the electrolyte located in the interior space 21 between the first electrode 23 and the second electrode 25.

[0047] In addition, glass has a relatively high dielectric constant in the range of approximately 3.7 - 10, which further reduces the impedance of the glass wall 43. Furthermore, measurements can be performed at high frequencies, where the impedance of the glass wall 43 is further reduced. The final formula for the capacitance C of the cylindrical sensor 10 according to the invention can be represented as follows: C=εrε0π / ln 2 where ε0= 8.85 · 10 -12 FM -1 the dielectric constant of the vacuum and ε ris the relative dielectric constant of a liquid.

[0048] This formula is derived below for the capacitance C of the sensor 10. The calculation of the sensor capacitance of the sensor 10 according to the invention is based on the conformal transformation of the representation of the stray field in the Z-plane into a circular representation in the W-plane. Fig. Figure 6 shows a strip capacitor. A strip capacitor is a capacitor in which the capacitance results from the overlap of two opposing strip-shaped electrodes with different potentials. The two strips E1, E2 are separated by an insulating layer and are manufactured either as a flat foil or as a cylindrical component. The capacitance C of the Fig. The strip capacitor shown in Figure 6 can be described as follows: C=ε0εrπln(cosh(π2d,(x3−x0)cosh(π2d(x2−x1)))cosh(π2d,(x2−x0))cosh(π2d(x3−x1))) for πxd>>1coshπxd≈eπxd Equation (2) simplifies to: C≅ε0επl

[0049] If all surrounding areas of the first electrode E1 and the second electrode E2 are grounded, the parameter I in Fig. 6 shows the overlap area of ​​the two electrodes E1, E2. The parameter I corresponds to the length of the smaller electrode E1. The arrangement of the strip capacitor can thus be used to eliminate the stray field effect in order to obtain a linear dependence of the capacitance C on the dielectric constant ε (permitivity). However, for measuring the dielectric constant ε of AdBlue fluids, the cylindrical shape of the capacitor offers many advantages over the rectangular shape.

[0050] The conversion of a rectangular capacitive strip capacitor into a cylindrical capacitor 20, as in Fig. 4, can be achieved by a conformal transformation of the geometry of the rectangular capacitor in the Z-plane into a circular W-plane, as shown in Fig. 7 shown.

[0051] The appropriate conformal transformation w=−jtan(z2−π4) forms the interior of the strip 0 ≤ x ≤ π in the Z-plane on the interval of the unit circle w = ρe jΦ , ρ ≤ 1 in the W-plane.

[0052] Equation 1 for a rectangular capacitor can be written down using the following substitutions π2(xi−x0d)=φicoshxi=jsin(xi+π2)yi=πdxi} with i = 0,1,2,3 can be changed to: C=ε0επ / ln(jsin(y302+π2)jsin(y212+π2)jsin(y202+π2)jsin(y312+π 2))=ε0επ / ln(sin(y302+π2)sin(y212+π2)sin(y202+π2)sin(y312+π2))

[0053] The rotation of the strip capacitor in Fig. 2 by 90° is taken into account by subtracting π / 2 from the arguments of the sine functions in formula (6).

[0054] Using the following relationships corresponding to the angles of the electrodes of the sensor 10 in the Fig. 4 correspond, 12y30=φ3−φ02=π212y21=φ2−φ12=π212y20=φ2−φ02=14π12y31=φ3−φ12=14π the final formula for the capacitance C of the cylindrical sensor 10 according to the invention can be represented as follows: C=εrε0π / ln 2

[0055] It is noteworthy that the capacitance C of the sensor 10 is not determined by the length L of the longer electrode, nor by the radius R of the glass tube 43, but only by the length l of the shorter electrode 23, measured along the cylinder of the glass tube 43. This represents an important advantage of the sensor 10 according to the invention. If all surrounding areas of the two electrodes 23, 25 are grounded by the shield 49, the parameter l represents the area of ​​the overlapping electrodes 23, 25. By arranging the capacitor 20 as a strip capacitor, the stray field effect is eliminated and a linear dependence of the capacitance C of the sensor 10 on the dielectric constant ε r the liquid in the interior 21 of the condenser 20.

[0056] The sensor constant K used for calibration of the sensor is given by equation (7): K=ε0π / ln2

[0057] The relative dielectric constant ε r can then be easily calculated from the capacity: C=Kεr

[0058] Specific dilutions of an AdBlue fluid are available for calibrating a sensor 10.

[0059] In order to keep the impedance of the glass wall 43 as low as possible, it is advisable to measure at high frequencies,

[0060] To avoid stray capacities in the Fig.To avoid interference with the measuring circuit 50 shown in Figure 5, the lines to the electrodes 23, 25 of the capacitor 20 must always be shielded. The measuring circuit 50 can measure both the real and imaginary parts of the impedance. By combining both impedance components, additional information about the measured AdBlue fluid concentration can be obtained. In particular, the input electrode is connected to a voltage source 17 with a low output resistance via a shielded, low-capacitance line 24, so that no significant voltage drop occurs in the voltage source 17. The capacitance of the shielded line 26 leading to the input of the operational amplifier (OA) 19 is equal to the virtual zero voltage of the operational amplifier 19 and has a negligible influence on the output voltage Uv of the operational amplifier 19.

[0061] The sensor 10 according to the invention thus enables the measurement of the concentration of urea in a urea solution, in particular the exhaust fluid (AdBlue) with an electrode arrangement according to the invention for impedance measurement of the electrolyte concentration in the interior 21 of the capacitor 20.

[0062] The advantages of the sensor 10 according to the invention are a linear transfer characteristic C = f(wt), particularly at higher temperatures, where the nonlinearity of the transfer function of prior art sensors is higher due to the greater interference effect of the stray field. The measuring circuit 50 according to the invention avoids the interfering effect of stray capacitances through lines by using shielded lines 24, 26 to the electrodes 24, 25, with the shielding being grounded.

[0063] Furthermore, the design of the sensor 10 according to the invention can be changed while maintaining the sensor constant, since the sensor constant is determined only by the length of the shorter electrode l and the fulfillment of the condition L ≥ 9l and the positioning of the electrode I in the middle of the glass tube 40.

[0064] In addition, fluctuations in the liquid level in the glass tube 40 of the sensor 10 have only a minor influence on the measurement result if the liquid level has exceeded a value of approximately 3*l above the upper edge of the first electrode 23.

[0065] In addition, a temperature sensor 47 can be used which is insensitive to level changes and does not impair the function of the capacitive part of the sensor 10.

[0066] The sensor 10 can be manufactured simply and inexpensively. The shield 49 can be applied by vacuum-depositing a copper layer onto the outer surface of the thin-walled glass wall 43 of the glass tube 40. Furthermore, galvanic processes can be used to insulate the air gap between the electrodes 23, 25.

[0067] The sensor according to the invention exhibits a linear transfer characteristic by avoiding interference from stray capacitances (e.g., metallic objects in the vicinity of the sensor). It is possible to modify the sensor design while maintaining the sensor constant by only keeping the length of the shorter electrode unchanged. Furthermore, changes in the liquid level have a negligible influence on the sensor capacitance. The arrangement of the electrodes circumferentially on the non-metallic glass wall of the glass tube eliminates distortion effects that can be caused by the double-layer capacitance at the interface between the electrolyte (AdBlue) and the metal electrodes. Furthermore, the sensor is characterized by a simple and cost-effective manufacturing process.

[0068] Electrolyte impedance measurement is therefore a suitable method when direct contact between a metal electrode and an electrolyte leads to negative interference and other adverse effects. The sensor according to the invention avoids the influence of metallic foreign bodies in the vicinity of the electrodes. Since the sensor electrodes are not in direct contact with the electrolyte of the diesel exhaust fluid, no effects occur due to electrolyte reactions with the electrodes. The influence of the fluid level on the impedance is thus prevented by the sensor geometry.

[0069] The diesel exhaust fluid system according to the invention can monitor the quality and consumption of the AdBlue solution, since the capacity of the AdBlue fluid sensor is influenced by contaminants such as metal salts in the AdBlue fluid. The measuring system includes a temperature sensor to measure the temperature of the electrolyte and use this to calculate the AdBlue fluid concentration. Reference symbol 10 Sensor 15 Sensor data 17 Voltage source 19 operational amplifiers 20 Capacitor 21 Interior 23 first electrode 24 shielded cable 25 second electrode 26 shielded cable 27 Protective ring 29 Shielding 30 electric field 32 stray field 40 glass tubes 43 glass wall 47 Temperature sensor 49 Shielding 50 measuring circuit 70 Data processing module 75 Output data 80 database 100 systems QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2010 151327 A1

[0008] DE 101 02 237 A1

[0009] EP 2 517 004 B1

[0010]

Claims

[1] System (100) for measuring the urea concentration in a urea solution, in particular for monitoring the quality and degree of degradation of diesel emission fluid (DEF) or AdBlue liquids, comprising a sensor (10) and a data processing module (70), wherein the sensor (10) comprises a cylindrical glass tube (40) with a glass wall (43) and a capacitor (20) with a first electrode (23) and a second electrode (25) is arranged circumferentially on the outer surface of the glass wall (43), wherein the length (I) of the first electrode (23) is smaller than the length (L) of the second electrode (25), and wherein the real and / or imaginary component of the impedance of the capacitor (20) is measured by means of a measuring circuit (50) as a measure of the quality of the urea solution and the measurement signals are transmitted as sensor data (15) to the data processing module (70) be transferred;and wherein the data processing module (70) is designed to generate output data (75) for controlling the urea concentration from the sensor data (15); [2] System (100) according to claim 1, wherein the capacitance (C) of the sensor (10) is given by the formula C=εrε0π / ln 2 where ε0 = 8.85 · 10 -12 FM -1 the dielectric constant of the vacuum and ε r is the relative dielectric constant of the urea solution. [3] Sensor (10) for measuring the urea concentration in a urea solution, in particular for monitoring the quality and degree of degradation of diesel emission fluid (DEF) or AdBlue liquids, wherein the sensor (10) comprises a cylindrical glass tube (40) with a glass wall (43) and a capacitor (20) with a first electrode (23) and a second electrode (25) is arranged circumferentially on the outer surface of the glass wall (43), wherein the length (I) of the first electrode (23) is smaller than the length (L) of the second electrode (25), and wherein the real and / or imaginary component of the impedance of the capacitor (20) is measured by means of a measuring circuit (50) as a measure of the quality of the urea solution. [4] Sensor (10) according to claim 3, wherein the capacitance (C) of the sensor (10) is given by the formula C=εrε0π / ln 2 where ε0 = 8.85 · 10 -12 FM -1the dielectric constant of the vacuum and ε r is the relative dielectric constant of the urea solution. [5] Sensor (10) according to claim 3 or 4, wherein the glass wall (43) of the glass tube (40) is provided with a shield (49) which is applied in particular by vapor deposition of a copper layer in a vacuum onto the outer surface of the thin-walled glass wall (43), wherein a thin air gap is provided between the shield and the surface of the first electrode and the second electrode. [6] Sensor (10) according to one of claims 3 to 5, wherein a temperature sensor (47) is provided, which is arranged in particular on an upper cover of the glass tube (40). [7] Sensor (10) according to one of claims 3 to 6, wherein the length (L) of the second electrode (25) is at least three times greater than the length (I) of the first electrode (23). [8] Sensor (10) according to one of claims 3 to 7, wherein to avoid stray capacitances the lines (24, 26) to the two electrodes (23, 25) of the capacitor (20) are shielded and grounded. [9] Sensor (10) according to one of claims 3 to 8, wherein the input electrode is connected via a shielded line (24) with low capacitance to a voltage source (17) with low output resistance, so that no significant voltage drop occurs in the voltage source (17). [10] Sensor (10) according to one of claims 3 to 9, wherein the capacitance of the shielded line (26) leading to the input of an operational amplifier (OA) (19) is equal to the virtual zero voltage of the operational amplifier (19) and has a negligible influence on the output voltage (Uv) of the operational amplifier (19).

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