CN115552218A

CN115552218A - Sensor for detecting at least one property of a measurement gas and method for operating a sensor

Info

Publication number: CN115552218A
Application number: CN202180034703.4A
Authority: CN
Inventors: M·舍尔
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2020-05-12
Filing date: 2021-04-29
Publication date: 2022-12-30
Also published as: KR20230008808A; EP4150318A1; DE102020205944A1; WO2021228565A1

Abstract

A sensor (10) for detecting at least one property of a measurement gas, in particular for detecting particles of the measurement gas in a measurement gas chamber, 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) further comprises at least one controller (20), wherein the controller (20) comprises a measuring device (22), wherein the measuring device (22) is connected to the first electrode (16) and/or the second electrode (18) and is provided for detecting at least one electrical signal, wherein the controller (20) further comprises 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 is provided for applying a variable voltage to the first electrode (16) and/or the second electrode (18).

Description

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

Background

A multiplicity of sensor elements for detecting particles of a measurement gas in a measurement gas chamber are known from the prior art. For example, the measurement gas can be an exhaust gas of an internal combustion engine. In particular, the particles can be carbon black particles or dust particles. In the following, the invention is described with particular reference to a sensor element for detecting carbon black particles, without limiting further embodiments and applications.

It is known from practice to measure the concentration of particles, such as soot particles or dust particles, in exhaust gases by means of two electrodes arranged on a substrate, such as ceramic. This can be done, for example, by measuring the resistance of the ceramic material separating the two electrodes. More precisely, the current flowing between the electrodes when a voltage is applied to them is measured. Carbon black particles are deposited between the electrodes due to electrostatic forces and, over time, form conductive bridges between the electrodes. The more such bridges are present, the more the measured current rises. Thus creating more and more short circuits of the electrodes. The sensor element is periodically regenerated (regenereriert) in that it is brought to at least 700 ℃ by means of an integrated heating element, thereby burning off the carbon deposits.

Such sensors are used, for example, in the exhaust system of internal combustion engines, for example diesel internal combustion engines. These sensors are usually located downstream of the exhaust valve or soot particle filter.

DE102010030634A1 describes a method and a device for operating a particle sensor.

Despite the many advantages of the devices and methods known from the prior art, they still have potential for improvement. As such, ceramic sensor elements used in exhaust gas technology or similar environmental conditions are mostly exposed to moisture in the form of liquid or condensed water, which may limit the point in time of use or even damage the sensor if water comes into contact with the sensor element at the wrong point in time. Thus, the particle sensor operates under protective heating to be protected from the necessary regeneration of the sensor in order to evaporate the water present on the sensor element. Regeneration is initiated after the dew point is released by the motor control. Dew point release is a modeled quantity and assumes that the exhaust system has been heated dry and that there is no longer liquid water at and before the important relevant points in the exhaust system. However, it has been demonstrated that: such dew point release is not always properly applied in a series and therefore sensors in the field can fail due to thermal shock (i.e., liquid water suddenly hits the thermal sensor element with the result that the sensor element ceramic is damaged). If water is still present on the sensor element after the dew point release, i.e. at the beginning of regeneration, damage to the sensor element and thus sensor failure may result due to the locally high temperature gradient in the ceramic.

Disclosure of Invention

In a first aspect of the invention, therefore, a sensor is proposed for detecting at least one property of a measurement gas, in particular for detecting particles of the measurement gas (such as soot particles) in a measurement gas chamber, which sensor at least largely avoids the disadvantages of known sensors and is designed to recognize liquid water on the surface of a sensor element in the region of an electrode structure by means of electronic measurement and thus to extend a protective heating duration in order to evaporate the water, or to interrupt this protective heating duration and return to a protective heating mode during a sensor regeneration that is already in progress in order to evaporate the water at low temperatures. The sensor can be used in particular for detecting soot particles in the exhaust gas of an internal combustion engine. Without limiting further possible fields of application, the invention is described below in terms of a sensor for detecting particles of a measurement gas in a measurement gas chamber. Alternatively, the sensor can, however, also be configured, for example, as a gas sensor, in particular as a resistive gas sensor, for example based on SnO, for example ₂ The semiconductor metal oxide gas sensor of (1). The at least one property of the measurement gas can thus be, for example, a chemical and/or physical property in general, in particular a property that can be detected by means of a resistive sensor. For example, it may be a measurement of the concentration of at least one force component in the gas chamber or a measurement of the concentration of moisture in the gas.

The sensor comprises at least one sensor element, wherein the sensor element has a substrate as a carrier, at least one first electrode and at least one second electrode, wherein the first electrode and the second electrode are arranged on the substrate, wherein the sensor further has 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 provided for detecting at least one electrical signal, wherein the controller further has at least one voltage source, wherein the voltage source is connected to the first electrode and/or the second electrode and is provided for applying a variable voltage to the first electrode and/or the second electrode.

Within the scope of the present invention, a "sensor" is understood to mean, in general, a device which is provided for detecting a measured variable, for example at least one measured variable, which characterizes a state and/or a property. Within the scope of the present invention, a "sensor element" is understood to be any device, the device is adapted to detect qualitatively and/or quantitatively at least one property of the measurement gas. For example, the sensor element can be provided for detecting the concentration and/or the amount of particles. The sensor element can generate an electrical measurement signal corresponding to the detected particles, for example by means of a suitable operating unit and suitably configured electrodes. Typically, the sensor element is capable of generating at least one electrical measurement signal, such as a voltage or a current. Here, a DC signal and/or an AC signal can be used. Further, for example, in order to perform signal analysis processing from impedance, a resistance portion and a capacitance portion can be used. The particles detected can be, in particular, carbon black particles and/or dust particles. With regard to possible configurations of the sensor element, reference can be made, for example, to the above-mentioned prior art. However, other configurations are possible.

The sensor element can be provided in particular for use in a motor vehicle. The measurement gas can be, in particular, an exhaust gas of a motor vehicle. In principle, other gases and gas mixtures are also possible. The measurement gas chamber can in principle 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 chamber can be an exhaust gas line of an internal combustion engine, for example of an internal combustion engine.

The electrical signal can preferably be influenced by at least one detectable property of the measurement gas, in particular by the particle loading of the electrodes.

The electrodes can be arranged in particular on the surface of the substrate or accessible from the surface of the substrate by the measurement gas. The electrodes can in particular form at least one interdigital electrode, i.e. a structure of two measuring electrodes which engage in one another and which each have electrode fingers which engage in one another. However, other arrangements of the electrodes are also possible in principle, for example a configuration in which two measuring electrodes are guided at least in sections in parallel and together form a meandering pattern, as will be described in more detail below.

The electrodes can in particular comprise platinum and/or be made completely or partially of platinum. In principle, alloys are also possible. Other metals can also be used instead of or in addition to platinum.

Within the scope of the present invention, a "substrate" is understood in principle as any substrate which is suitable for carrying an electrode and/or to which an electrode can be applied. The substrate can be of single-layer or else of multi-layer construction. The substrate can comprise, in particular, at least one ceramic material as a carrier material. In particular, the substrate can comprise an oxide ceramic, preferably alumina, in particular Al ₂ O ₃ . However, other oxides, such as zirconia, are also possible. Furthermore, the substrate may comprise at least one electrically insulating material. The substrate can have a substrate surface. Within the scope of the present invention, a "substrate surface" is understood to mean in principle any layer which separates the substrate from its surroundings and to which electrodes are applied.

Within the scope of the present invention, an "electrode" is understood to mean in principle any electrical conductor which is suitable for current and/or voltage measurement and/or which can be used to apply a voltage and/or a current to at least one element which is in contact with the electrode arrangement.

In general, it should be noted that: within the scope of the present invention, the terms "first", "second" or "third", and corresponding variants thereof, are used as a plain label and nomenclature, not for numbering purposes. Thus, for example, a first element and a third element can be present without necessarily requiring a second element; alternatively, a second element can be present, without the first element; alternatively, a first element can be present without a second or third element.

Within the scope of the present invention, a "control" is understood here in general to mean a device which is provided for starting, stopping, controlling or regulating one or more processes in another device. The controller can for example comprise at least one microcontroller. However, alternatively or additionally, the controller can also comprise other hardware, such as at least one hardware component selected from the group consisting of: comparator, current source, voltage source, current measuring equipment, voltage measuring equipment, resistance measuring equipment.

In this context, a "measuring device" is to be understood within the scope of the present invention as meaning, in general, a device which is able to generate at least one measuring signal from which at least one property of the measuring gas can be inferred. The measuring device can be configured in particular as a particle measuring device and can accordingly be provided for generating at least one measurement signal from which a particle load, in particular a particle concentration in the measurement gas, can be deduced. With regard to possible configurations of the particle measuring device, reference can be made, for example, to the above-mentioned prior art. In particular, the measuring device, in particular the particle measuring device, can comprise at least one current measuring device, wherein the electrodes can be acted upon by a voltage source of the controller, for example, with a voltage, and wherein the current can be measured here by means of the current measuring device. For example, the electrodes can be designed to each have 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 the other 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 one of the two first ends, for example. Then, for example, at least one property, in particular the particle loading of the electrode, can be deduced from the intensity of the current and/or a property, for example the concentration of particles in the measurement gas, can be deduced from the time profile of the current.

Here, "end of an electrode" is generally understood to mean a point or region within the electrode, via which electrical contact can be made to the electrode. The outermost ends of the electrodes may be, but need not be, involved here, and may for example be the ends of conductor loops of straight or curved conductors.

For detecting the at least one electrical signal (also referred to as measurement signal), the controller can comprise 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, current measuring devices can be used here, since the particle load is usually detected in the form of an electric current.

In this context, a "voltage source" is to be understood within the scope of the present invention as meaning, in general, a device which has at least one terminal with a variable potential. The potential source can thus have, for example, a fixed or adjustable voltage source, at least one pole of the voltage source forming the terminal. A "variable voltage" is generally understood to mean a voltage which is able to assume at least two values. For example, the voltage source can be provided for varying the voltage between the at least one first value and the at least one second value in a single-stage, multistage or stepless manner.

Accordingly, the voltage source can be provided for applying at least one first and one second voltage to the first and/or second electrode, wherein the second voltage is different from the first voltage.

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

The controller can be configured to vary the voltage in dependence on the temperature of the sensor element.

The controller can have at least one voltage divider for varying the voltage. Alternatively, the voltage source is adjustable.

The first and second electrodes can be arranged as interdigitated electrodes or meander on the substrate.

The voltage source can be arranged for loading the first electrode and/or the second electrode with an electrical measurement voltage for detecting particles, wherein the variable voltage is smaller than the measurement voltage.

The sensor can also have at least one heater for heating the sensor element. A "heater" is generally understood here to mean a device which is provided for heating at least one element, for example a sensor in this case. 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 of the heater) and at least one heating resistor connected to the electrical energy source, which can, for example, be configured to heat a meandering structure.

The sensor can also have at least one thermocouple (thermocouple fur), for example at least one temperature-dependent resistance, for example a temperature-measuring meander. In this case, the voltage source can also be identical to the at least one thermocouple as a complete or partial component and/or be electrically connected to the at least one thermocouple.

In a further aspect of the invention, a method is proposed for operating a sensor for detecting at least one property of a measurement gas, in particular for detecting particles (in particular soot particles) of the measurement gas in a measurement gas chamber. The sensor can in particular be a sensor according to the invention, for example a sensor according to one of the configurations described above or according to one of the configurations which will still be described further below. The sensor comprises at least one sensor element, wherein the sensor element has a substrate as a carrier, at least one first electrode and at least one second electrode, wherein the first electrode and the second electrode are arranged on the substrate, wherein the sensor further has 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 provided for detecting at least one electrical signal, wherein the controller further has at least one voltage source, wherein the voltage source is connected to the first electrode and/or the second electrode and is provided for applying a variable voltage to the first electrode and/or the second electrode.

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

The method can further include: the first and second electrodes are subjected to at least one first voltage and a first electrical signal is detected, and the first and/or second electrodes are subjected to at least one second voltage and a second electrical signal is detected, wherein the second voltage is different from the first voltage.

The method can further include: if a non-linear relationship is detected between the detected electrical signal and the varying voltage, a liquid, in particular water, is detected on the sensor element.

The method can further include: defining a threshold for a plurality of (ein Anzahl von) events of the liquid detected on the sensor element, and detecting a change in a quality state of the first and second electrodes above the threshold.

The method can be performed during protective heating of the sensor, during regeneration of the sensor and/or during a measurement phase of the sensor.

Advantages of the invention

The proposed sensor and the proposed method have a number of advantages with respect to known sensors and methods of the mentioned type. In general, the concepts of the present invention can be applied to many sensor concepts. Reliable detection of water on the electrode structure is achieved before regeneration and thus avoidance or reduction of thermal shock faults is achieved. The water on the detection electrode structure is achieved before the measurement phase and thus the avoidance of strong electrolysis is achieved when a measurement voltage of about 45V is applied. Otherwise, a measurement zone stop (Messbereichsanschlag) of the current measurement signal occurs due to electrolysis, which would result in a sensor reporting a fault. The service life of the sensor is prolonged. Furthermore, a reduction of customer complaints is achieved.

Drawings

Further optional details and features of the invention result from the following description of preferred embodiments, which are schematically illustrated in the drawings.

The figures show:

FIG. 1 is an embodiment of a sensor according to the present invention;

FIG. 2 is a time course of voltage and current in the presence of water;

FIG. 3 is a time course of the voltage at a first value;

FIG. 4 is a time course of the voltage at a second value and in the absence of water;

FIG. 5 is a time course of the voltage at a second value and in the presence of water;

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

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

fig. 8 is a flow chart of a method according to the invention before the measurement phase.

Detailed Description

In fig. 1, 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 chamber is represented. The measurement gas can in particular be an exhaust gas of an internal combustion engine, and correspondingly the measurement gas chamber can in particular be an exhaust gas line of an internal combustion engine. The sensor 10 is particularly configured for detecting particles. Particles can be present in the measurement gas chamber. The microparticles can be, for example, carbon black particles. However, it is explicitly emphasized that the sensor 10 can be a sensor for detecting moisture.

In this embodiment, the sensor 10 comprises a sensor element 12 having a substrate 14 and (in this embodiment exemplarily) two

electrodes

16, 18 applied directly or indirectly on the substrate 14 or exposable to a measurement gas. The

electrodes

16, 18 are also referred to hereinafter as first electrode 16 and second electrode 18. The first electrodes 16 and the second electrodes 18 are arranged as interdigitated electrodes on the substrate 14. The first electrode 16 illustratively functions as a positive electrode, and the second electrode 18 functions as a negative electrode.

The sensor 10 also has at least one controller 20. The controller 20 is a sensor control device. However, it may also relate to a motor control device of an 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 provided for detecting 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 intercept electrical signals via a measuring resistor 26. The electrical signal can be the resistance value and/or the current of the electrical measuring resistor 26. For example, the electrical signal can be a current which is determined on the basis of the voltage drop across the measuring resistor 26 and its resistance value.

The controller 20 also has at least one voltage source 28. A voltage source 28 is connected to the first electrode 16 and/or the second electrode 18 and is arranged for applying a variable voltage to the first electrode 16 and/or the second electrode 18. 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 provided for applying at least one first and one second voltage to the first and

second electrodes

16, 18, wherein the second voltage is different from the first voltage. The voltage source 28 is arranged for loading the first electrode 16 and the second electrode 18 with an electrical measurement voltage for detecting particles, wherein the variable voltage is smaller than the measurement voltage. To vary the voltage, the voltage source 28 can be adjusted. The voltage source 28 is provided, for example, for generating a signal by means of pulse width modulation and smoothing the signal into a dc 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. Furthermore, a first resistor 32 and a second resistor 34 are connected in series with the first line 30. Between the first resistor 32 and the second resistor 34, the second line 36 branches off to a voltage remeasurement device (spannungsruckmessvorticichung) 38, by means of which voltage remeasurement can be carried out on the first electrode 16.

In order to detect water on the sensor element 12, the following method is proposed according to the invention. A voltage is applied to the first electrode 16 of the sensor element 12 and the current at the measuring resistance 26 is measured, which current flows as a result of the applied voltage. In order to distinguish between water and solid shunts (e.g. carbon black), it is proposed to vary the voltage in order to identify a highly non-linear characteristic curve of the water at the start of electrolysis, whereas a (maximally) linear characteristic curve can be expected at the solid shunt.

Fig. 2 shows the time course of the voltage and current in the presence of water. Time is plotted on the X-axis 40. The current in μ a is plotted on the left Y-axis 42. The voltage in V is plotted on the right Y-axis 44. To verify the function, the sensor element 12 has been wetted with water on the first electrode 16 and the second electrode 18. The voltage at the

electrodes

16, 18 rises linearly from 0V to 2V and the current has been recorded by means of a Keysight 34465a multimeter. Here, the voltage rises within a few seconds. It is explicitly emphasized that the exact duration for the voltage rise has no significant effect on the result, so that no exact time specification on the X-axis 40 is given in fig. 2. Curve 46 illustrates the voltage profile. Curve 48 illustrates the course of the current. The measurement data have been evaluated and a change in the current change 48, which increases sharply toward a higher voltage 46, can be detected. With regard to the course of the resistance characteristic curve with voltage, it can be determined that: the course of the sharp increase in current toward higher voltages is also reflected in the resistance characteristic curve.

Thus, the method allows detecting a liquid, in particular water, on the sensor element 12 if a non-linear relationship between the detected electrical signal and the varying voltage is detected. In order to improve the grading precision

The voltage can be adapted to the temperature of the sensor element 12 in order to take into account the temperature dependence during electrolysis. Since electrolysis on the sensor element 12 would in principle reduce the service life of the sensor element, but would not destroy it as abruptly as a consequence of the liquid water to be detected on the sensor element surface, the method can only be used after dew point release has been completed (since previously the water on the sensor element 12 could have been taken into account), and the measurement time for detecting water is kept as short as possible. In the event of water being detected, the measurement voltage should be switched off immediately and the measures described below (a) are carried out before the measurement is restartedProtective heating for a minimum duration). It is also possible to define a threshold value for a plurality of events of the liquid detected on the sensor element 12 and thus to detect a change in the mass state of the first electrode 16 and the second electrode 18 above this threshold value. In this way, for example, a threshold value can be defined which is the upper limit for the number of recognized moisture events, from which further electrolytic loading can lead to a severe degradation of the

electrodes

16, 18. It is also possible to record the number of occurrences of water in the fault memory in order to gain insights into the field.

In principle, the sensor 10 can be operated by means of a static method. The variable voltage can thus be realized by means of at least one voltage divider. For example, two fixed voltages are used for the evaluation, which can be provided, for example, by two voltage dividers (optionally with downstream impedance converters).

The method is described in more detail below with reference to fig. 3 to 5. Fig. 3 shows the time profile of the voltage at the first value. Fig. 4 shows the time profile of the voltage at the second value and in the absence of water. Fig. 5 shows the time course of the voltage at the second value and in the presence of water. In fig. 3 to 5, the time in ms is plotted on the X-axis 56, respectively. In fig. 3 to 5, the voltages in mV are plotted on the Y-axis 58, respectively. In fig. 3 to 5, curves 60 illustrate the differential voltage between the first electrode 16 and the second electrode 18, respectively. In fig. 3 to 5, curves 62 illustrate the voltage at the first electrode 16, respectively. In fig. 3 to 5, curves 64 respectively illustrate the voltages at the second electrodes. In the method, a settable differential measurement voltage at the

electrodes

16, 18 is output via the first electrode 16 from a nominal (nominal) higher voltage, for example 5V to 8V, in the controller 20 by means of a pulse-width-modulated signal.

Fig. 3 shows a first measurement point. At the first measurement point, a differential measurement is made with a differential voltage of 0.5V between the first electrode 16 and the second electrode 18, which can be parameterized and is indeed below the electrolysis threshold. In addition, the current between the first electrode 16 and the second electrode 18 is determined at the measuring resistor 26 by the measuring device 22 as an electrical signal at this voltage difference. The voltage at the second electrode 18 can be converted to a current by a known measuring resistor 26.

Fig. 4 shows a second measuring point in the case of no 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 measurement point, a differential measurement is made with a differential voltage of 2V between the first electrode 16 and the second electrode 18, which can be parameterized and is indeed above the electrolysis threshold. In addition, the current between the first electrode 16 and the second electrode 18 is determined at the measuring resistor 26 by the measuring device 22 as an electrical signal at this voltage difference. The voltage at the second electrode 18 can be converted to a current by a known measuring resistor 26.

An electrical shunt is present if a linear or substantially linear relationship occurs between the current inversely calculated from the voltage at the second electrode 18 and the known measuring resistance 26 and the differential voltage between the first electrode 16 and the second electrode 18, as shown in fig. 4. However, if there is a non-linear relationship due to the start of electrolysis in the form of a sharp increase in measured current at a differential voltage of 2V between the first electrode 16 and the second electrode 18, it can be concluded that there is water and countermeasures can be taken.

In the following, some applications of the method according to the invention are exemplarily described.

Fig. 6 shows a flow chart of the method according to the invention before the measurement or during the protective heating. In step S10, a moisture check during protective heating is started. In a subsequent step S12, a first voltage is applied to the

electrodes

16, 18. In a subsequent step S14, a first measured value of the electrical signal is detected with the application of a first voltage. In a subsequent step S16, a second voltage, which is different from the first voltage, is applied to the

electrodes

16, 18. In a subsequent step S18, a second measured value of the electrical signal is detected with the application of a second voltage. In a subsequent step S20, an actual check is made as to whether moisture is present on the sensor element 12. The test is performed according to the method as described above with reference to fig. 2 to 5. If in step S20 it is sought that moisture is present, the method proceeds to step S22. In step S22, the protective heating duration is extended by a minimum duration when moisture is detected, and a matching protective heating strategy (with reduced heating power) is applied if necessary in order to minimize deposits. After the expiration of the minimum duration in the protective heating, a new check is made and the method returns to step S10. If no moisture is detected in step S20, the method proceeds to step S24 and a regeneration of the sensor 10 or the sensor element 12 can be carried out.

Fig. 7 shows a flow chart of the method according to the invention during regeneration. In step S30, a moisture check during regeneration is started. In a subsequent step S32, a first voltage is applied to the

electrodes

16, 18. In a subsequent step S34, a first measured value of the electrical signal is detected with the first voltage applied. In a subsequent step S36, a second voltage, which is different from the first voltage, is applied to the

electrodes

16, 18. In a subsequent step S38, a second measured value of the electrical signal is detected with the second voltage applied. In a subsequent step S40, an actual check is made as to whether moisture is present on the sensor element 12. The test is performed according to the method as described above with reference to fig. 2 to 5. If in step S40 it is sought that moisture is present, the method proceeds to step S42. In step S42, the regeneration is aborted upon identification of moisture and the protective heating minimum duration is returned, and a matching protective heating strategy (with reduced heating power) is applied if necessary, in order to minimize deposits. After the minimum duration in the protective heating has expired, a new check is made and the method returns to step S30. If no moisture is detected in step S40, the method proceeds to step S44 and the regeneration of the sensor 10 or the sensor element 12 can be continued.

Fig. 8 shows a flow chart of the method according to the invention before the measurement phase. In step S50, a moisture check is started before the measurement phase, i.e. before the measurement voltage is applied and in particular in the case of direct measurement. In a subsequent step S52, a first voltage is applied to the

electrodes

16, 18. In a subsequent step S54, a first measured value of the electrical signal is detected with the first voltage applied. In a subsequent step S56, a second voltage, which is different from the first voltage, is applied to the

electrodes

16, 18. In a subsequent step S58, a second measured value of the electrical signal is detected with the application of a second voltage. In a subsequent step S60, an actual check is made as to whether moisture is present on the sensor element 12.

The test is performed according to the method as described above with reference to fig. 2 to 5. If in step S60 it is sought that moisture is present, the method proceeds to step S62. In step S62, upon identification of moisture, a new measurement cycle with protective heating and subsequent regeneration is started before the measurement voltage is applied in the described manner. Subsequently, the method returns to step S50. If no moisture is sought in step S60, the method proceeds to step S64 and the measurement phase can begin.

The invention can be demonstrated in the following way: water is introduced on the electrode structure of the sensor element, measurements are taken on the electrode probe line, and it is checked whether the operating strategy has changed compared to a sensor without water.

Claims

1. A sensor (10) for detecting at least one property of a measurement gas, in particular for detecting particles of the measurement gas in a measurement gas chamber, 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) further has at least one controller (20), wherein the controller (20) has a measuring device (22), wherein the measuring device (22) is connected to the first electrode (16) and/or the second electrode (18) and is provided for detecting at least one electrical signal, wherein the controller (20) further 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 is provided for applying a variable voltage to the first electrode (16) and/or the second electrode (18).

2. The sensor (10) according to the preceding claim, wherein the voltage source (28) is arranged for loading the first electrode (16) and/or the second electrode (18) with at least one first voltage and a second voltage, wherein the second voltage is different from the first voltage.

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

4. The sensor (10) according to any one of the preceding claims, wherein the controller (20) is configured for varying the voltage in dependence on a temperature of the sensor element (12).

5. The sensor (10) of any one of the preceding claims, wherein the controller (20) has at least one voltage divider for varying the voltage, or wherein the voltage source (28) is adjustable.

6. The sensor (10) according to any of the preceding claims, wherein the first electrode (16) and the second electrode (18) are arranged as interdigitated electrodes or meander on the substrate (14).

7. The sensor (10) according to any one of the preceding claims, wherein the voltage source (28) is arranged for loading the first electrode (16) and the second electrode (18) with an electrical measurement voltage for detecting particles, wherein the variable voltage is smaller than the measurement voltage.

8. A method for operating a sensor (10) for detecting at least one property of a measurement gas, in particular for detecting particles of the measurement gas in a measurement gas chamber, wherein the sensor (10) has 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) further has at least one controller (20), wherein the controller (20) has a measuring device (22), wherein the measuring device (22) is connected with the first electrode (16) and/or the second electrode (18) and is provided for detecting at least one electrical signal, wherein the controller (20) further has at least one voltage source (28), wherein the voltage source (28) is connected with the first electrode (16) and/or the second electrode (18) and is provided for applying the first electrode (16) and/or the second electrode (18) with a variable voltage, wherein the method comprises applying a varying voltage to the first electrode (16) and/or the second electrode (18) and detecting an electrical signal.

9. The method according to the preceding claim, the method further comprising: -applying at least one first voltage to the first electrode (16) and the second electrode (18) and detecting a first electrical signal, and-applying at least one second voltage to the first electrode (16) and/or the second electrode (18) and detecting a second electrical signal, wherein the second voltage is different from the first voltage.

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

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

12. Method according to any of the four preceding claims, wherein the method is performed during protective heating of the sensor (10), during regeneration of the sensor (10) and/or during a measurement phase of the sensor (10).