WO2021228565A1

WO2021228565A1 - Sensor for detecting at least one property of a measurement gas, and method for operating a sensor

Info

Publication number: WO2021228565A1
Application number: PCT/EP2021/061241
Authority: WO
Inventors: Michael Scholl
Original assignee: Robert Bosch Gmbh
Priority date: 2020-05-12
Filing date: 2021-04-29
Publication date: 2021-11-18
Also published as: DE102020205944A1; CN115552218A; EP4150318A1; KR20230008808A

Abstract

A sensor (10) for detecting at least one property of a measurement gas, in particular for detecting particles of a measurement gas in a measurement gas compartment, is proposed. The sensor (10) comprises a sensor element (12), wherein the sensor element (12) has a substrate (14), at least one first electrode (16), and at least one second electrode (18), wherein the first electrode (16) and the second electrode (18) are arranged on the substrate (14). The sensor (10) additionally has at least one controller (20), wherein the controller (20) has a measuring device (22), and the measuring device (22) is connected to the first electrode (16) and/or the second electrode (18) and is designed to detect at least one electric signal. The controller (20) additionally has at least one voltage source (28), said voltage source (28) being connected to the first electrode (16) and/or the second electrode (18) and being designed to apply a variable electric voltage to the first electrode (16) and/or the second electrode (18).

Description

description

title

SENSOR FOR DETERMINING AT LEAST ONE PROPERTY OF A MEASURING GAS

AND METHOD OF OPERATING A SENSOR

State of the art

A large number of sensor elements for detecting particles of a measurement gas in a measurement gas space are known from the prior art. For example, the measurement gas can be exhaust gas from an internal combustion engine. In particular, the particles can be soot or dust particles. The invention is described below, without restricting further embodiments and applications, in particular with reference to sensor elements for the detection of soot particles.

It is known from practice to measure a concentration of particles, such as soot or dust particles, in an exhaust gas by means of two electrodes which are arranged on a substrate, such as, for example, a ceramic. This can be done, for example, by measuring the electrical resistance of the ceramic material separating the two electrodes. More precisely, the electrical current that flows between the electrodes when an electrical voltage is applied is measured. The soot particles are deposited between the electrodes due to electrostatic forces and over time form electrically conductive bridges between the electrodes. The more of these bridges there are, the more the measured current increases.

An increasing short circuit of the electrodes is thus formed. The sensor element is periodically regenerated by bringing it to at least 700 ° C using an integrated heating element, which burns away the soot deposits. Such sensors are used, for example, in an exhaust line of an internal combustion engine, such as an internal combustion engine of the diesel type. These sensors are usually located downstream of the outlet valve or the soot particle filter.

DE 102010030 634 A1 describes a method and a device for operating a particle sensor.

Despite the numerous advantages of the devices and methods known from the prior art, they still have room for improvement. Ceramic sensor elements that are used in exhaust technology or similar environmental conditions are mostly exposed to moisture in the form of liquid water or condensate, which restricts the time of use or can even damage the sensor if the water comes into contact with the sensor element at the wrong time . The particle sensor is therefore operated in protective heating to protect against a necessary sensor regeneration in order to evaporate any water present on the sensor element. The regeneration only begins after the dew point has been released by the engine control unit. The dew point release is a modeled variable and it is assumed that the exhaust system has been heated to dryness and that there is no longer any liquid water at or in front of the relevant point in the exhaust system. However, it has been shown that this dew point release was not always applied correctly in the series and as a result the sensors in the field fail due to thermal shock, i.e. sudden impact of liquid water on a hot sensor element with the consequence of damage to the sensor element ceramics. If, after the release of the dew point, there is still water on the sensor element at the beginning of the regeneration, the resulting locally high temperature gradients in the ceramic can damage the sensor element and thus cause the sensor to fail.

Disclosure of the invention

In a first aspect of the present invention, there is therefore a sensor for detecting at least one property of a measurement gas, in particular for Detection of particles, such as soot particles, of a measuring gas in a measuring gas chamber, which at least largely avoids the disadvantages of known sensors and which is designed to detect liquid water on the sensor element surface in the area of the electrode structure by means of electronic measurement and, as a result, the protective heating duration in order to evaporate the water, or if the sensor is already being regenerated, interrupt it and return to protective heating mode in order to evaporate the water at low temperatures. The sensor can in particular be used to detect soot particles in an exhaust gas of an internal combustion engine. Without restricting further possible areas of application, the invention is described below with regard to a sensor for detecting particles of a measurement gas in a measurement gas space. Alternatively, however, the sensor can also be designed, for example, as a gas sensor, in particular as a resistive gas sensor, for example as a gas sensor based on semiconducting metal oxides such as Sn0 ₂ . In general, the at least one property of the measurement gas can be, for example, a chemical and / or physical property, in particular a property that can be detected by means of a resistive sensor. For example, this can be a concentration of at least one force component in the measurement gas space or a moisture content of the measurement gas.

The sensor comprises at least one sensor element, wherein the sensor element has a substrate serving as a carrier, at least one first electrode and at least one second electrode, the first electrode and the second electrode being arranged on the substrate, the sensor furthermore having at least one controller, wherein the controller has a measuring device, wherein the measuring device is connected to the first electrode and / or the second electrode and is set up to detect at least one electrical signal, the controller furthermore having at least one voltage source, the voltage source being connected to the first electrode and / or or is connected to the second electrode and is set up to apply a variable electrical voltage to the first electrode and / or the second electrode. In the context of the present invention, a sensor is generally understood to mean a device which is set up to detect a measured variable, for example at least one measured variable, which characterizes a state and / or a property. In the context of the present invention, a sensor element is understood to mean any device which is suitable for qualitatively and / or quantitatively detecting the at least one property of the measurement gas. For example, the sensor element can be set up to detect a concentration and / or number of particles. The sensor element can, for example, generate an electrical measurement signal corresponding to the detected particles with the aid of a suitable control unit and suitably configured electrodes. In general, the sensor element can generate at least one electrical measurement signal, for example a voltage or a current. DC signals and / or AC signals can be used here. Furthermore, a resistive component and / or a capacitive component can be used, for example, for signal evaluation from the impedance. The detected particles can in particular be soot particles and / or dust particles. With regard to possible configurations of the sensor element, reference can be made, for example, to the prior art mentioned above. However, other configurations are also possible.

The sensor element can in particular be set up for use in a motor vehicle. In particular, the measurement gas can be exhaust gas from the motor vehicle. Other gases and gas mixtures are also possible in principle. The measurement gas space can basically be any open or closed space in which the measurement gas is received and / or through which the measurement gas flows. For example, the measurement gas space can be an exhaust tract of an internal combustion engine, for example an internal combustion engine.

The electrical signal can preferably be influenced by the at least one property of the measurement gas that is to be detected, in particular by particle loading of the electrodes. The electrodes can in particular be arranged on a surface of the substrate or be accessible to the measurement gas from a surface of the substrate. The electrodes can in particular form at least one interdigital electrode, that is to say a structure of two interlocking measuring electrodes which each have interlocking electrode fingers. However, a different arrangement of the electrodes is also possible in principle, for example, as will be described in more detail below, a structure in which two measuring electrodes are guided in parallel at least in sections and together form a meander pattern.

The electrodes can in particular comprise platinum and / or consist entirely or partially of platinum. In principle, an alloy is also possible. As an alternative or in addition to the use of platinum, other metals can also be used.

In the context of the present invention, a substrate is basically understood to be any substrate that is suitable for carrying the electrodes and / or on which the electrodes can be applied. The substrate can have a single layer or a multilayer structure. The substrate can in particular comprise at least one ceramic material as the carrier material. In particular, the substrate can comprise an oxidic ceramic, preferably aluminum oxide, in particular Al ₂ O _3. However, other oxides, for example zirconium oxide, are possible. Furthermore, the substrate can comprise at least one electrically insulating material. The substrate can have a substrate surface. In the context of the present invention, a substrate surface is basically understood to be any layer which delimits the substrate from its surroundings and to which the electrodes are applied.

In the context of the present invention, an electrode is generally understood to mean any electrical conductor that is suitable for current measurement and / or voltage measurement and / or that applies a voltage and / or current to at least one element in contact with the electrode devices can. In general, it should be pointed out that in the context of the present invention, the terms “first”, “second” or “third”, as well as corresponding modifications thereof, are used purely as designations and naming, without the purpose of numbering. For example, a first element and a third element can be present without a second element being absolutely necessary, or a second element can be present without a first element being present, or a first element can be present without a second element or a third element are present.

In the context of the present invention, a controller is generally understood to mean a device which is set up to start, end, control or regulate one or more processes in another device. The controller can for example comprise at least one microcontroller. Alternatively or additionally, however, the controller can also comprise other hardware, for example at least one hardware component selected from the group consisting of: a comparator, a current source, a voltage source, a current measuring device, a voltage measuring device, a resistance measuring device.

In the context of the present invention, a measuring device is generally understood to mean a device which can generate at least one measuring signal from which at least one property of the measuring gas can be inferred. The measuring device can in particular be designed as a particle measuring device and can accordingly be set up to generate at least one measuring signal from which a particle load, in particular a particle concentration in the measuring gas, can be inferred. With regard to possible configurations of the particle measuring device, reference can be made, for example, to the prior art mentioned above. In particular, the measuring device, in particular the particle measuring device, can comprise at least one current measuring device, wherein a voltage can be applied to the electrodes, for example, by means of the voltage source of the controller, and a current using the current measuring device can be measured. For example, the electrodes can each be designed with a first end and a second end, wherein one pole of the voltage source can be connected to a first of the two first ends and another pole of the voltage source can be connected to a second of the two first ends and wherein the current measuring device can be connected to, for example can be connected to one of the first two ends. From a strength of the current, for example, conclusions can be drawn about the at least one property, in particular particle loading of the electrodes, and / or from a change in the current over time, conclusions can be drawn about the property, for example a concentration of the particles in the measurement gas.

An end of an electrode is generally understood to be a point or area within the electrode via which electrical contact can be made with the electrode. This can, but does not necessarily have to be, an outermost end of the electrode, for example an end of a conductor loop of a straight or curved conductor.

To detect the at least one electrical signal, also referred to as a measurement signal, the controller can include the at least one measurement device, as will be explained in more detail below, for example a current measurement device and / or a voltage measurement device. In particular, this can be a current measuring device, since particle loadings are usually recorded in the form of currents.

In the context of the present invention, a voltage source is generally understood to mean a device which has at least one connection with a variable electrical potential. For example, the potential source can have a fixed or a controllable voltage source, with at least one pole of the voltage source forming the connection. A variable electrical voltage is generally to be understood as an electrical voltage which can assume at least two values. For example, the voltage source can be set up to change the electrical voltage between at least one first value and at least one second value in one stage, in several stages or continuously. Correspondingly, the voltage source can be set up to apply at least a first electrical voltage and a second electrical voltage to the first electrode and / or the second electrode, the second electrical voltage differing from the first electrical voltage.

The electrical signal can be a resistance value of an electrical measuring resistor and / or an electrical current.

The controller can be designed to vary the electrical voltage as a function of a temperature of the sensor element.

The controller can have at least one voltage divider for varying the electrical voltage. Alternatively, the voltage source can be regulated.

The first electrode and the second electrode can be arranged as interdigital electrodes or in a meandering shape on the substrate.

The voltage source can be designed to apply an electrical measurement voltage to the first electrode and / or the second electrode for detecting particles, the variable electrical voltage being smaller than the measurement voltage.

The sensor can furthermore have at least one heater for heating the sensor element. A heater is generally understood to mean a device which is set up to heat at least one element, for example in this case the sensor. The heater can in particular be an electric heater. The heater can, for example, as will be explained in more detail below, have at least one electrical energy source, also referred to as a supply or electrical supply for the heater, and at least one heating resistor connected to the electrical energy source, which can be configured, for example, as a heating meander. The sensor can furthermore have at least one temperature sensor, for example at least one temperature-dependent resistor, for example a temperature measuring meander. In this case, the voltage source can also have a completely or partially identical component to the at least one temperature sensor and / or be electrically connected to the at least one temperature sensor.

In a further aspect of the present invention, a method for operating a sensor for detecting at least one property of a measurement gas, in particular for detecting particles, in particular soot particles, of a measurement gas in a measurement gas space is proposed. The sensor can in particular be a sensor according to the invention, for example in accordance with one of the configurations described above or in accordance with one of the configurations described in more detail below. The sensor comprises at least one sensor element, wherein the sensor element has a substrate serving as a carrier, at least one first electrode and at least one second electrode, the first electrode and the second electrode being arranged on the substrate, the sensor furthermore having at least one controller, wherein the controller has a measuring device, wherein the measuring device is connected to the first electrode and / or the second electrode and is set up to detect at least one electrical signal, the controller furthermore having at least one voltage source, the voltage source being connected to the first electrode and / or or is connected to the second electrode and is set up to apply a variable electrical voltage to the first electrode and / or the second electrode.

The method comprises applying a varying electrical voltage to the first electrode and / or the second electrode and detecting an electrical signal.

The method can also apply at least one first electrical voltage to the first electrode and / or the second electrode and detect a first electrical signal, and apply at least a second electrode to the first electrode and / or the second electrode electrical voltage and detecting a second electrical signal, wherein the second electrical voltage is different from the first electrical voltage.

The method can furthermore include the detection of liquid, in particular water, on the sensor element, provided that a non-linear relationship between the detected electrical signal and the varying electrical voltage is detected.

The method can further include defining a threshold value for a number of events of detected liquid on the sensor element and detecting a change in a qualitative state of the first electrode and the second electrode when the threshold value is exceeded.

The method can be carried out during protective heating of the sensor, during regeneration of the sensor and / or during a measuring phase of the sensor.

Advantages of the invention

The proposed sensor and the proposed method have numerous advantages over known sensors and methods of the type mentioned. In general, the idea of the present invention can be applied to numerous sensor concepts. A reliable detection of water on the electrode structure before regeneration and thus avoidance or reduction of thermal shock failures is made possible. A detection of water on the electrode structure before a measuring phase and thus an avoidance of strong electrolysis when applying the measuring voltage of approx. 45 V is made possible. Otherwise, as a result of the electrolysis, the measuring range limit of the current measurement signal occurs, which leads to the sensor being reported as defective. An increase in the service life of the sensor is made possible. Furthermore, a reduction in customer complaints is made possible.

Brief description of the drawings Further optional details and features of the invention emerge from the following description of preferred exemplary embodiments, which are shown schematically in the figures.

Show it:

Figure 1 shows an embodiment of a sensor according to the invention;

FIG. 2 shows a time profile of electrical voltage and electrical current in the presence of water;

FIG. 3 shows a time profile of the electrical voltage at a first value;

FIG. 4 shows a time profile of the electrical voltage at a second value and without the presence of water;

FIG. 5 shows a time profile of the electrical voltage at a second value and the presence of water;

FIG. 6 shows a flow chart of the method according to the invention before a measurement or during protective heating;

FIG. 7 shows a flow chart of the method according to the invention during a regeneration; and

FIG. 8 shows a flow chart of the method according to the invention before a measurement phase.

Embodiments of the invention

FIG. 1 shows a first exemplary embodiment of a sensor 10 according to the invention for detecting at least one property of a measurement gas in a measurement gas space. The measurement gas can be, in particular, exhaust gas from an internal combustion engine, and the measurement gas space accordingly, in particular, an exhaust tract of the internal combustion engine. The sensor 10 is designed in particular for the detection of particles. The particles can be present in the measurement gas in the measurement gas space. The particles can be soot particles, for example. However, it is explicitly emphasized that the sensor 10 can be a sensor for detecting moisture.

In this exemplary embodiment, the sensor 10 comprises a sensor element 12 with a substrate 14 and, as an example in this exemplary embodiment, two electrodes 16, 18 applied directly or indirectly to the substrate 14 and exposed to the measurement gas. The electrodes 16, 18 are also referred to below as the first electrode 16 and second electrode 18 designated. The first electrode 16 and the second electrode 18 are arranged as interdigital electrodes on the substrate 14. The first electrode 16 is used, for example, as a positive electrode and the second electrode 18 is used as a negative electrode.

The sensor 10 also has at least one controller 20. The controller 20 is a sensor control device. However, it can also be an engine control unit of the internal combustion engine. The controller 20 has a measuring device 22. The measuring device 22 is connected to the first electrode 16 and / or the second electrode 18 and is set up to acquire at least one electrical signal. For example, the measuring device 22 is connected to the second electrode 18 via a measuring line 24 and can pick up the electrical signal via a measuring resistor 26. The electrical signal can be a resistance value of the electrical measuring resistor 26 and / or an electrical current. For example, the electrical signal can be an electrical current that is determined based on a voltage drop across the measuring resistor 26 and its resistance value.

The controller 20 also has at least one voltage source 28. The voltage source 28 is connected to the first electrode 16 and / or the second electrode 18 and is used to apply a variable electrical voltage to the first electrode 16 and / or the second electrode 18 set up. For example, the voltage source 28 is connected to the first electrode 16 by means of a first line 30. In particular, the voltage source 28 is set up to apply at least a first electrical voltage and a second electrical voltage to the first electrode 16 and the second electrode 18, the second electrical voltage differing from the first electrical voltage. The voltage source 28 is set up to apply an electrical measurement voltage to the first electrode 16 and the second electrode 18 for detecting particles, the variable electrical voltage being smaller than the measurement voltage. The voltage source 28 can be regulated to vary the electrical voltage. The voltage source 28 is set up, for example, to generate a signal by means of pulse width modulation and to smooth it into a direct voltage signal by means of a downstream low-pass filter, not shown in detail. Alternatively, the voltage can also be generated by means of a digital-to-analog converter. A first resistor 32 and a second resistor 34 are also connected in series to the first line 30. A second line 36 branches off between the first resistor 32 and the second resistor 34 to a voltage back measurement device 38, by means of which a voltage back measurement at the first electrode 16 can take place.

For the detection of water on the sensor element 12, the following method is proposed according to the invention. Applying an electrical voltage to the first electrode 16 of the sensor element 12 and measuring the electrical current at the measuring resistor 26, which flows as a result of the applied voltage. In order to differentiate between water and solid shunts such as soot, it is proposed to vary the voltage in order to recognize the strongly non-linear characteristic of water during the onset of electrolysis, while a (largely) linear characteristic is to be expected in the case of a solid bypass.

FIG. 2 shows a time curve of electrical voltage and electrical current in the presence of water. The time is plotted on the X axis 40.

The current in mA is plotted on the left Y-axis 42. The electrical voltage in V is plotted on the right Y axis 44. For proof of functionality a sensor element 12 on the first electrode 16 and the second electrode 18 was wetted with water. The electrical voltage at the electrodes 16, 18 was ramped up linearly from 0 to 2 V and the current was recorded using a Keysight 34465A multimeter. The tension was increased in the range of seconds. It is explicitly emphasized that the exact time period for increasing the voltage has no significant influence on the result, so that the exact time information on the X-axis 40 was not given in FIG. The curve 46 indicates the course of the electrical voltage. The curve 48 indicates the course of the current. The measurement data have been evaluated and in the current profile 48 a profile that increases sharply towards higher voltages 46 can already be seen. With regard to the course of a resistance characteristic curve over the electrical voltage, it should be noted that the rapidly increasing course of the current towards higher voltages is also reflected in the resistance characteristic curve.

Thus, the method allows the detection of liquid, in particular water, on the sensor element 12, provided that a non-linear relationship between the detected electrical signal and the varying electrical voltage is detected. In order to increase the selectivity, the electrical voltage can be adapted as a function of the temperature of the sensor element 12 in order to take into account the temperature dependency during the electrolysis. Since electrolysis on the sensor element 12 principally reduces the service life of the sensor element, but does not suddenly destroy it, as is the case with the liquid water to be detected on the sensor element surface, the method can only be used after the dew point has already been released, as there is potential for water on the sensor element beforehand 12 is to be expected, and to keep the measuring time for the water detection as short as possible. If water is detected, the measuring voltage must be switched off immediately and the measures described below (protective heating for a minimum period) must be carried out before resuming the measurement. It is also possible to define a threshold value for a number of events of detected liquid on the sensor element 12 and thus to detect a change in a qualitative state of the first electrode 16 and the second electrode 18 when the threshold value is exceeded. For example, a threshold value can be used as an upper limit for the number of detected Moisture occurrences are defined, from which a further electrolysis load would lead to excessive degradation of the electrodes 16, 18. It can also record the number of water occurrences in the fault log in order to gain insights from the field.

In principle, the sensor 10 can be operated by means of a static method. The variable electrical voltage can thus be implemented by means of at least one voltage divider. For example, two fixed voltages are used for evaluation, which can be made available via two voltage dividers, if necessary with downstream impedance conversion.

The method is described in more detail below with reference to FIGS. 3 to 5. FIG. 3 shows a time profile of the electrical voltage at a first value. FIG. 4 shows a time profile of the electrical voltage at a second value and without the presence of water. FIG. 5 shows a time profile of the electrical voltage at a second value and the presence of water. In FIGS. 3 to 5, the time in ms is plotted on the X axis 56 in each case. In FIGS. 3 to 5, the electrical voltage is plotted on the Y axis 58 in mV. In FIGS. 3 to 5, curve 60 indicates the differential voltage between first electrode 16 and second electrode 18. In FIGS. 3 to 5, the curve 62 in each case indicates the electrical voltage at the first electrode 16. In FIGS. 3 to 5, curve 64 in each case indicates the electrical voltage at the second electrode. In the method, an adjustable differential measurement voltage is output at the electrodes 16, 18 by means of a pulse-width-modulated signal via which the first electrode 16 from a nominally higher voltage of, for example, 5 V to 8 V in the controller 20.

Figure 3 shows a first measurement point. At the first measuring point, there is a differential measurement with a differential voltage between first electrode 16 and second electrode 18 of 0.5 V, which can be parameterized and is safely below the electrolysis threshold. Furthermore, the electrical signal is the current between the first electrode 16 and the second electrode 18 through the measuring device 22 at the measuring resistor 26 at this voltage difference determined. The voltage at the second electrode 18 can be converted into a current via the known measuring resistor 26.

FIG. 4 shows a second measuring point without water on the sensor element 12. FIG. 5 shows a second measuring point in the presence of water on the sensor element 12. At the second measuring point, a differential measurement is carried out with a differential voltage between the first electrode 16 and the second electrode 18 from FIG V, which can be parameterized and is safely above the electrolysis threshold. Furthermore, the current between first electrode 16 and second electrode 18 is determined as an electrical signal by measuring device 22 at measuring resistor 26 at this voltage difference. The voltage at the second electrode 18 can be converted into a current via the known measuring resistor 26.

If there is a linear or almost linear relationship between the current, calculated back from the voltage at the second electrode 18 and the known measuring resistor 26, and the differential voltage between the first electrode 16 and the second electrode 18, as shown in FIG Shunt before. However, if there is a non-linear relationship due to the onset of electrolysis in the form of a sharp increase in the measured current at 2 V differential voltage between first electrode 16 and second electrode 18, it can be concluded that water is present and countermeasures can be taken.

Some application cases for the method according to the invention are described below by way of example.

FIG. 6 shows a flow chart of the method according to the invention before a measurement or during protective heating. At step S10 a humidity test begins during protective heating. In a subsequent step S12, a first electrical voltage is applied to the electrodes 16, 18. In a subsequent step S14, a first measured value of the electrical signal is recorded for the first electrical voltage applied. In a subsequent step S16, a second electrical voltage that differs from the first electrical voltage is applied to the electrodes 16, 18 differs. In a subsequent step S18, a second measured value of the electrical signal is recorded when the second electrical voltage is applied. In a subsequent step S20, the actual check takes place as to whether there is moisture on the sensor element 12. The check is carried out according to the method described above with regard to FIGS. 2 to 5. If it is determined in step S20 that there is moisture, the method proceeds to step S22.

In step S22, when moisture is detected, the protective heating duration is extended by a minimum duration and, if necessary, an adapted protective heating strategy is used with a reduction in the heating power in order to minimize deposits. After the minimum duration in protective heating has elapsed, a new check takes place and the method returns to step S10. If no moisture is determined in step S20, the method proceeds to step S24 and the sensor 10 or sensor element 12 can be regenerated.

FIG. 7 shows a flow chart of the method according to the invention during a regeneration. At step S30, a moisture test begins during a regeneration. In a subsequent step S32, electrodes 16,

18 a first electrical voltage is applied. In a subsequent step S34, a first measured value of the electrical signal is recorded for the applied first electrical voltage. In a subsequent step S36, a second electrical voltage that differs from the first electrical voltage is applied to the electrodes 16, 18. In a subsequent step S38, a second measured value of the electrical signal is recorded when the second electrical voltage is applied. In a subsequent step S40, the actual check takes place as to whether there is moisture on the sensor element 12. The check is carried out according to the method described above with regard to FIGS. 2 to 5. If it is determined in step S40 that there is moisture, the method proceeds to step S42. In step S42, if moisture is detected, regeneration is aborted and a return to protective heating for a minimum duration and, if necessary, application of an adapted protective heating strategy with a reduction in the heating power in order to minimize deposits. After the minimum duration in protective heating has elapsed, a new test takes place and the method returns to step S30. If no moisture is determined in step S40, the method proceeds to step S44 and the regeneration of the sensor 10 or sensor element 12 can be continued. FIG. 8 shows a flow chart of the method according to the invention before a measurement phase. In step S50, a moisture test begins before a measurement phase, ie before the measurement voltage is applied, and especially during direct measurement. In a subsequent step S52, a first electrical voltage is applied to the electrodes 16, 18. In a subsequent step S54, a first measured value of the electrical signal is recorded for the applied first electrical voltage. In a subsequent step S56, a second electrical voltage that differs from the first electrical voltage is applied to the electrodes 16, 18. In a subsequent step S58, a second measured value of the electrical signal is recorded when the second electrical voltage is applied. In a subsequent step S60, the actual check takes place as to whether there is moisture on the sensor element 12. The check is carried out according to the method described above with regard to FIGS. 2 to 5. If it is determined in step S60 that there is moisture, the method proceeds to step S62. In step S62, when moisture is detected before the measurement voltage is applied, a new measurement cycle with protective heating and subsequent regeneration begins with the method described. The method then returns to step S50. If no humidity is determined in step S60, the method advances to step S64 and the measurement phase can be started.

The invention can be demonstrated by introducing water on the electrode structure of a sensor element and measuring on the electrode probe lines and checking whether the operating strategy changes compared to the sensor without water.

Claims

Expectations

1. Sensor (10) for detecting at least one property of a measurement gas, in particular for detecting particles of a measurement gas in a measurement gas space, comprising a sensor element (12), wherein the sensor element (12) has a substrate (14), at least one first electrode (16 ) and at least one second electrode (18), wherein the first electrode (16) and the second electrode (18) are arranged on the substrate (14), wherein the sensor (10) furthermore has at least one controller (20), wherein the controller (20) has a measuring device (22), the measuring device (22) being connected to the first electrode (16) and / or the second electrode (18) and being set up to detect at least one electrical signal, the controller ( 20) furthermore has at least one voltage source (28), the voltage source (28) being connected to the first electrode (16) and / or the second electrode (18) and for applying the first electrode (16) and / or the two th electrode (18) is set up with a variable electrical voltage.

2. Sensor (10) according to the preceding claim, wherein the voltage source (28) for applying the first electrode (16) and / or the second electrode (18) is set up with at least a first electrical voltage and a second electrical voltage, wherein the second electrical voltage differs from the first electrical voltage.

3. Sensor (10) according to one of the preceding claims, wherein the electrical signal is a resistance value of an electrical measuring resistor (26) and / or an electrical current.

4. Sensor (10) according to one of the preceding claims, wherein the controller (20) is designed to vary the electrical voltage as a function of a temperature of the sensor element (12).

5. Sensor (10) according to one of the preceding claims, wherein the controller (20) for varying the electrical voltage has at least one voltage divider or wherein the voltage source (28) can be regulated.

6. Sensor (10) according to one of the preceding claims, wherein the first electrode (16) and the second electrode (18) are arranged as interdigital electrodes or in a meandering shape on the substrate (14).

7. Sensor (10) according to one of the preceding claims, wherein the voltage source (28) is set up for applying an electrical measurement voltage to the first electrode (16) and the second electrode (18) for detecting particles, the variable electrical voltage being smaller than the measurement voltage is.

8. A method for operating a sensor (10) for detecting at least one property of a measurement gas, in particular for detecting particles of a measurement gas in a measurement gas space, the sensor (10) having a sensor element (12), the sensor element (12) being a substrate (14), at least one first electrode (16) and at least one second electrode (18), the first electrode (16) and the second electrode (18) being arranged on the substrate (14), the sensor (10) furthermore has at least one control (20), the control (20) having a measuring device (22), the measuring device (22) being connected to the first electrode (16) and / or the second electrode (18) and for detecting at least an electrical signal is set up, wherein the controller (20) furthermore has at least one voltage source (28), wherein the voltage source (28) is connected to the first electrode (16) and / or the second electrode (18) and to act beating the first electrode (16) and / or the second electrode (18) is set up with a variable electrical voltage, the method applying the first electrode (16) and / or the second electrode (18) with a varying electrical voltage and detecting an electrical signal.

9. The method according to the preceding claim, further comprising applying at least a first electrical voltage to the first electrode (16) and the second electrode (18) and detecting a first electrical signal, and applying the first electrode (16) and / or the second Electrode (18) with at least one second electrical voltage and detection of a second electrical signal, the second electrical voltage differing from the first electrical voltage.

10. The method according to any one of the two preceding claims, further comprising detecting liquid, in particular water, on the sensor element (12), provided that a non-linear relationship between the detected electrical signal and the varying electrical voltage is detected.

11. The method according to the preceding claim, further comprising defining a threshold value for a number of events of detected liquid on the sensor element (12) and detecting a change in a qualitative state of the first electrode (16) and the second electrode (18) when the Threshold.

12. The method according to any one of the four preceding claims, wherein the method is carried out during protective heating of the sensor (10), during regeneration of the sensor (10) and / or during a measuring phase of the sensor (10).