Method for operating sensor for detecting at least one property of measurement gas in measurement gas chamber

Abstract

The invention relates to a method for operating a sensor (10) for detecting at least one property of a measurement gas in a measurement gas chamber. The method comprises: measuring a Nernst voltage of the Nernst cell (40) and quantitatively determining a target variable describing the measured gas characteristic based on the Nernst voltage; recording a target variable data packet based on the target variable; assigning a current timestamp to the target variable data packet (68); processing the target variable data packet on a signal processing path (56); querying a current system time (74); correcting a timestamp (68) of the target variable data packet currently being processed based on the predetermined time delay (70) and the current system time (74); converting the corrected timestamps to obtain the number of measured values; ascertaining a time correction index (66) for the target variable on the basis of the number of measured values; and ascertaining a corrected target variable value (90) on the basis of the temporal correction index (66).

Description

Background Art

[0001] A large number of sensors and methods for detecting at least one property of a measurement gas in a measurement gas chamber are known from the prior art. In principle, any physical and / or chemical property of the measurement gas may be involved here, wherein one or more properties may be detected. The invention is described below with particular reference to the qualitative and / or quantitative detection of the contents of gas components of the measurement gas, in particular with reference to the detection of the oxygen content in the measurement gas components. The oxygen content can be detected, for example, in the form of a partial pressure and / or in the form of a percentage. However, other properties of the measurement gas, such as the temperature, may also be detected as an alternative or in addition.

[0002] Ceramic sensors are particularly known from the prior art, which are based on the electrolyte properties of specific solid objects, i.e., on the ion-conducting properties of these solid objects. These solid objects may be, in particular, ceramic solid electrolytes, such as zirconium dioxide (ZrO2), in particular yttrium-stabilized zirconium dioxide (YSZ) and scandium-doped zirconium dioxide (ScSZ), which may contain small amounts of aluminum oxide (Al2O3) and / or silicon dioxide (SiO2) additions.

[0003] For example, such a sensor can be configured as a so-called lambda probe or nitrogen oxide sensor, such as the sensors known from "Kraftfahrtechnisches Taschenbuch" by K. Reif, Deitsche, KH. et al., Springer Vieweg, Wiesbaden, 2014, pp. 1338-1347. With a broadband lambda probe, in particular with a planar broadband lambda sensor, for example, the oxygen concentration in the exhaust gas can be determined over a wide range and the air-fuel ratio in the combustion chamber can be inferred. The air factor I (λ) describes this air-fuel ratio. The nitrogen oxide sensor determines not only the nitrogen oxide concentration in the exhaust gas, but also the oxygen concentration.

[0004] By combining a pump cell, a measuring cell and an oxygen reference cell, the Nernst cell, a sensor for measuring the oxygen content in the ambient gas can be constructed. In a pump cell that works according to the amperometric pump principle, when a voltage or current is applied to the pump electrodes located in different gases, a flow of oxygen ions diffuses ("pumps") through a ceramic body (oxygen-conducting solid electrolyte) that separates the gases from each other. If the pump cell is used to keep the oxygen partial pressure in the cavity into which the ambient gas can diffuse constant, the amount of oxygen transported can be inferred by measuring the current. According to the diffusion law, this pump current is directly proportional to the oxygen partial pressure in the ambient gas. With a Nernst cell, the ratio of the oxygen partial pressure in the cavity to the oxygen partial pressure in another reference gas chamber can be determined by the Nernst voltage that is constructed.

[0005] The electrochemical cell of this sensor can be regarded as a control section in a control loop. The controlled variable of this control loop is the voltage on the pump electrode pair, or optionally the current. The control variable is the measured Nernst voltage. The goal of the regulation is to keep the oxygen partial pressure in the cavity as close to a specific or predetermined value as possible despite changes in the oxygen content in the exhaust gas. The Nernst voltage is used to measure the oxygen partial pressure in the cavity or the ratio of the oxygen partial pressure in the cavity to the partial pressure in the reference cell. The oxygen partial pressure in the cavity can be controlled by the voltage applied to the pump electrode pair. By transporting oxygen ions into the cavity or removing them from the cavity (this is also called pumping), the gas concentration can be actively influenced via the applied pump voltage or pump current. All electrodes in the cavity have a common return conductor. In order to also represent negative voltages, this virtual ground is located at a potential that is increased relative to the electrical ground. The Nernst voltage or the voltage on the first electrode refers to this voltage.

[0006] To determine the oxygen partial pressure or the oxygen content, a pump current signal is evaluated in broadband lambda probes and nitrogen oxide sensors, which pump current signal is approximately linearly dependent on the oxygen concentration present in the ambient gas.

[0007] In internal combustion engines using lambda control, for example Otto engines with a three-way exhaust gas catalytic converter and a lambda probe, the air-fuel ratio is adjusted in homogeneous operation by lambda control so that the lambda mean value of the mixture components of all cylinders is the value lambda=1.0, thus ensuring low-emission operation.

[0008] Due to metering errors when fueling the internal combustion engine, for example, by means of injectors or injection valves, and due to cylinder-specific differences in the mixture composition, that is, in the cylinder charge with fuel and air, caused by system errors, an uneven distribution of the lambda values ​​of the individual cylinders occurs, although the average value of all cylinders reaches the desired lambda value of 1.0. Thus, for example, in the case of a four-cylinder engine, lambda (cylinder 1) = 1.1, lambda (cylinder 2) = 1.1, lambda (cylinder 3) = 1.1 and lambda (cylinder 4) = 0.7 may be obtained, which corresponds to an average lambda value of 1.0 overall.

[0009] This imbalance between the individual cylinders leads to a shortened service life of the components, since, for example, strong pulses act on the crankshaft during abrupt cylinder ignition. Therefore, current regulations in many countries provide for exhaust gas diagnostic strategies or control strategies that counteract or prevent this imbalance.

[0010] A method of this type is known from DE 195 27 218 A1, in which a possible uneven distribution of the cylinder lambda values ​​is derived from detected operating instabilities of the internal combustion engine, that is, changes in the engine torque after a sudden enleanment. The technical effect is based on the fact that there is a clear correlation between the mixture composition and the crankshaft acceleration caused by the combustion. The cylinder-individual lambda differences of the individual cylinders are adjusted by successively enleaning the cylinders and deriving a cylinder-individual characteristic of the impact for the corresponding cylinder from the detected operating instability changes. In addition, a constant lambda mean value of 1.0 is ensured for all cylinders by simultaneously enriching the cylinders that are not enleaned.

[0011] Despite the advantages brought about by these sensors and methods for their functional control, they still have potential for improvement. Therefore, when there is jitter in the pump current signal that serves as the basis on the lambda probe, that is, there is a variable delay component, the current algorithm for identifying the impact of individual cylinders is weak, because due to the jitter, an uncertainty area is generated, which, at a certain speed and jitter, may cause multiple cylinders to be considered for the current impact. Therefore, it is not always possible to reliably determine which cylinder has an impact. In common lambda detection systems, when data is collected, for example, in an interrupt-controlled manner, then further processed as a data packet and finally transmitted to the user at standard intervals (Raster), a significant part of the jitter is generated by the evaluation electronics. Summary of the invention

[0012] Therefore, a method is proposed for operating a sensor for detecting at least one property of a measuring gas in a measuring gas chamber, which method at least largely avoids the disadvantages of known methods for operating these sensors and is particularly suitable for eliminating jitter components from the signal and thus provides a basis for reliable cylinder-individual shock detection.

[0013] According to the invention, a method for operating a sensor for detecting at least one property of a measured gas in a measured gas chamber, in particular for detecting the content of a gas component in the measured gas, wherein the sensor has a sensor element for detecting the property of the measured gas, wherein the sensor element has at least one Nernst cell, the method comprising the following steps, preferably in the order specified:

[0014] - measuring the Nernst voltage of the Nernst cell and quantitatively determining a target variable describing the property of the measured gas based on the Nernst voltage,

[0015] - record a target variable data packet based on the target variable,

[0016] - assign the current timestamp to this target variable data packet,

[0017] - processing the target variable data packet on the signal processing path,

[0018] -Query the current system time,

[0019] - based on the predetermined time delay and the current system time, correct the timestamp of the currently processed target variable data packet,

[0020] - convert the corrected timestamps to the number of measurements,

[0021] - based on the number of measured values, finding a time-corrected index for the target variable, and

[0022] - Obtain the corrected target variable value based on the time correction index.

[0023] Therefore, at the time of the measured value detection, for example in the basic software of the controller, in addition to the already existing measured values, such as the Nernst voltage or the variables derived therefrom, such as the pump current value, the time stamp to be newly introduced is also recorded. The measured value is written to the ring buffer together with the associated time stamp. In the software part that provides the user software with a signal, the measured value is called out from the ring buffer, which is delayed by a certain time offset relative to the current system time. This time offset is greater than the possible worst-case delay due to jitter. The variable part of the time delay (jitter) is thus eliminated.

[0024] The target variable can be the Nernst voltage itself or a variable derived therefrom. Thus, the method can correct the Nernst voltage or a measured variable derived therefrom.

[0025] The sensor element may also have a pump cell. The target variable may be an actuating variable when adjusting the Nernst voltage, which may be a current or a voltage of a pump cell or a Nernst cell of the sensor element. Accordingly, the method may be applied in particular to sprung probes or broadband lambda probes.

[0026] The predetermined time delay can be constant. Thus, jitter can be eliminated particularly reliably starting from a known constant variable.

[0027] The predetermined time delay may be greater than the delay in processing the target variable data packet on the signal processing path. This constant time offset is greater than the possible worst case delay due to jitter. Therefore, the variable part of the time delay (jitter) is eliminated.

[0028] Correcting the timestamp may include adding a predetermined time delay to the timestamp and subtracting the current system time from the timestamp. The timestamp may thus be corrected reliably and correctly by simple calculations.

[0029] The method may further comprise storing the target variable data packets together with the assigned time stamps in a memory so that the values ​​can be traced back multiple times.

[0030] The signal processing path can be part of the user software. The user software can include a ring buffer. This allows fast and multiple access, since the measured value is written to the ring buffer together with the associated time stamp and can be called out of the ring buffer in the software part that provides the user software with a signal.

[0031] “Determining the corrected target variable value based on the time correction index” may include accessing the target variable data packets stored in the ring buffer starting from the last stored target variable data packet. Thus, the correction may be performed starting from the last known measured value, such as the pump current value.

[0032] The corrected target variable value can be obtained by subtracting the correction index from the index of the last stored target variable data packet. Therefore, the correction can be performed by simple calculation.

[0033] The target variable data packets can be recorded at a higher clock rate than the query of the current system time. Thus, the measured values ​​are recorded more frequently than the query of the system time, so that a sufficient number of measured values ​​is available for the method.

[0034] Finally, the present invention also relates to a sensor for detecting at least one property of a measuring gas in a measuring gas chamber, in particular for detecting the content of a gas component in the measuring gas or the temperature of the measuring gas, the sensor comprising a sensor element for detecting the said property of the measuring gas, wherein the sensor element has at least one Nernst cell, wherein the sensor arrangement also has an electronic controller having a computer program according to the invention for executing the method according to the invention.

[0035] For example, the sensor element comprises a solid electrolyte, a first electrode, a second electrode, a third electrode and a fourth electrode, wherein the first electrode and the second electrode are connected to the solid electrolyte in such a way that the first electrode, the second electrode and the solid electrolyte form a pump cell, wherein the third electrode and the fourth electrode are connected to the solid electrolyte in such a way that the third electrode, the fourth electrode and the solid electrolyte form a Nernst cell.

[0036] In the scope of the present invention, a solid electrolyte is understood to be an object or article having electrolyte properties, i.e., having ion-conducting properties. It can be a ceramic solid electrolyte in particular. This also includes the raw materials of the solid electrolyte, and therefore also includes the so-called green or semi-green, which are only transformed into a solid electrolyte after sintering. The solid electrolyte can be constructed in particular as a solid electrolyte layer or composed of a plurality of solid electrolyte layers. In the scope of the present invention, a layer is understood to be a planar extension of the same substance with a certain height, which is above, below or between other elements.

[0037] In the scope of the present invention, an electrode is generally understood to be a component that can contact a solid electrolyte in such a way that a current can be maintained through the solid electrolyte and the electrode. Accordingly, the electrode can include a component on which ions can be incorporated into and / or removed from the solid electrolyte. Typically, the electrode includes a noble metal electrode, which can be applied to the solid electrolyte as a metal ceramic electrode or can be connected to the solid electrolyte in other ways, for example. A typical electrode material is a platinum metal ceramic electrode. However, in principle, other noble metals, such as gold or palladium, can also be used.

[0038] In the scope of the present invention, a heating element is understood to be an element that is used to heat the solid electrolyte and the electrode to at least its functional temperature, preferably to its operating temperature. The functional temperature is the temperature at which the solid electrolyte becomes conductive to the ions and is approximately 350°C. The operating temperature is different from the functional temperature, and it is the temperature at which the sensor element is usually operated and is higher than the functional temperature. The operating temperature can be, for example, 700°C to 950°C. The heating element can include a heating region and at least one feed track. In the scope of the present invention, a heating region is understood to be the region of the heating element that overlaps the electrode in the layer structure in a direction perpendicular to the surface of the sensor element. Typically, the heating region heats up more strongly than the feed track during operation, so that they are distinguishable. This different heating can be achieved, for example, by the following means: the heating region has a higher resistance than the feed track. The heating region and / or the feed track are, for example, constructed as a resistance track and heated by applying a voltage. The heating element can be made of platinum metal ceramic, for example.

[0039] Within the scope of the present invention, a control loop is understood to be a closed-loop process for influencing a physical variable in a process. The key here is that the current value, which is also called the actual value, is returned to the regulator, which continuously compensates for the deviation from the desired value. The control loop consists of a control section, a regulator and a negative feedback of the actual value as a control variable. The control variable is compared with the desired value as a reference variable. The control deviation between the actual value and the desired value is sent to the regulator, which then determines the control variable for the control section in accordance with the desired control loop dynamics. Within the scope of the present invention, a control section is understood to be that part of the control loop: this part contains the control variable that the regulator wants to influence through the control variable or the actuating variable. Within the scope of the present invention, the control section is the electrochemical unit of the sensor.

[0040] Within the scope of the present invention, the measured variable is understood in principle as any physical and / or chemical variable and a signal that equivalently indicates the variable(s), that is, an equivalent signal. Preferably, the measured variable is at least one measurement signal of a sensor element. Preferably, the measured variable can be at least one pump current, such as a boundary current. However, the measured variable can also be a variable related to the pump current. For example, the measured variable can also be a pump voltage and / or a converted charge amount. In this regard, within the scope of the present invention, the expression "detected" is understood to mean that the measured variable is output by the sensor element, for example, as a measurement signal and / or the measured variable is processed and / or evaluated and / or stored by a controller.

[0041] In the context of the present invention, delay is generally understood as the propagation time of a signal. The propagation time is understood as the time difference between a signal entering a (causal) system and leaving the system. Delay is in particular the time interval over which an event is delayed. Processing delay is determined by the time required for further processing of the signal. Processing delay can be reduced by using multiple computing forces. Delay (English: Latency) refers in particular to the propagation time of information (data packet) from its source to its destination. The delay time is measured in the round-trip time (RTT). The RTT value is twice the delay value. RTT values ​​of more than 100ms are no longer acceptable for everyday work and should be as small as possible for real-time applications. However, it should be noted that larger delays are also acceptable for the present invention and only jitter is a problem because the signal is repeated periodically at a constant number of revolutions. Delay times are caused, for example, by the propagation time of the signal on the transmission medium (copper, glass, etc.), the transmission time of the data packet on individual sub-segments with limited bandwidth, the processing of the data packet by the participating network components, queuing due to congestion on the individual sub-segments or due to the characteristics of the transmission protocol (UDP, TCP, RTP, etc.).

[0042] Within the scope of the present invention, jitter is generally understood as the difference in the propagation time of each data packet. The difference caused by the different propagation times of the gas data packet to the detector at different speeds must be eliminated by a characteristic curve family (Kennfelder). However, unlike jitter, the propagation time difference is constant and reproducible during signal processing, because the appearance of the signal peak on the detector for each rotation number at a certain crankshaft angle can be assigned to a certain cylinder. When used in real-time applications on the Internet (such as Internet radio, VoIP, video applications, process control, etc.), the influence of the propagation time difference of each data packet is very disturbing, because it may cause the data packet to arrive too late to be considered in real time. The jitter is reduced by the so-called jitter buffer, but the cost is a further increase in delay. Jitter also refers to the clock jitter (Taktzittern) in time during digital signal transmission, that is, the slight accuracy fluctuation in the transmission clock (English: Clock). Jitter is not desirable as an interference signal under normal circumstances. Generally, jitter is a sudden and undesirable change in signal characteristics in transmission technology. This may involve both amplitude, frequency and phase. Jitter is the first derivative of delay. The spectrum of the time deviation is called phase noise. Jitter should not be confused with quantization error.

[0043] Delay and jitter are particularly important for real-time applications. Poor delay and jitter values ​​can affect the quality of data transmission, i.e. the data packet propagation time itself is too long or individual data packets arrive late, which in turn leads to information losses. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Further optional details and features of the invention emerge from the following description of preferred embodiments which are schematically illustrated in the drawings.

[0045] The accompanying drawings show:

[0046] Figure 1 According to the principle structure of the sensor of the present invention,

[0047] Figure 2 A schematic diagram of the process of the method according to the present invention,

[0048] Figure 3 Block diagram of the storage process of the pump current value,

[0049] Figure 4 A block diagram for calculating the correction index, and

[0050] Figure 5 Table with exemplary calculation variables for the method of the present invention. DETAILED DESCRIPTION

[0051] Figure 1The basic structure of a sensor 10 according to the present invention is shown. Figure 1 The sensor 10 shown in the figure can be used to prove the physical and / or chemical properties of the measured gas, wherein one or more properties can be detected. The present invention is described below with particular reference to the qualitative and / or quantitative detection of the gas components of the measured gas, in particular with reference to the detection of the oxygen content in the measured gas. The oxygen content can be detected, for example, in the form of partial pressure and / or in the form of a percentage. However, in principle, other types of gas components can also be detected, such as nitrogen oxides, hydrocarbons and / or hydrogen. However, other properties of the measured gas can also be detected alternatively or additionally. The present invention can be used in particular in the field of automotive technology, so that the measured gas chamber can be, in particular, an exhaust gas duct of an internal combustion engine, and the measured gas can be, in particular, an exhaust gas. For example, the sensor 10 is constructed as a lambda probe, in particular as a broadband lambda probe, as explained in more detail below. However, it should be clearly emphasized that, alternatively, the sensor 10 can also be a bouncing probe.

[0052] The sensor 10 has a sensor element 12. The sensor element 12 can be constructed as a ceramic layer structure, as described in more detail later. The sensor element 12 has a solid electrolyte 14, a first electrode 16, a second electrode 18, a third electrode 20 and a fourth electrode 22. The solid electrolyte 14 can be composed of a plurality of ceramic layers in the form of a solid electrolyte layer, or include a plurality of solid electrolyte layers. For example, the solid electrolyte 14 includes a pump membrane or pump layer, an intermediate membrane or intermediate layer and a heating membrane or heating layer, which are arranged on top of each other or below each other. The names of the electrodes 16, 18, 20, 22 should not indicate the weight of their importance, but only to conceptually distinguish these electrodes.

[0053] The sensor element 12 also has a gas inlet passage 24. The gas inlet passage 24 has a gas inlet hole 26, which extends from the surface 28 of the solid electrolyte 14 to the interior of the layer structure of the sensor element 12. An electrode cavity 30 is arranged in the solid electrolyte 14, which surrounds the gas inlet hole 26 in an annular or rectangular manner, for example. The electrode cavity 30 is part of the gas inlet passage 24 and is connected to the measurement gas chamber via the gas inlet hole 26. For example, the gas inlet hole 26 extends as a cylindrical blind hole perpendicular to the surface 28 of the solid electrolyte 14 to the interior of the layer structure of the sensor element 12. In particular, the electrode cavity 30 is substantially designed as an annular or rectangular shape and is bounded from three sides by the solid electrolyte 14 when viewed in a cross-sectional view. A channel 32 is arranged between the gas inlet hole 26 and the electrode cavity 30, which is also a component of the gas inlet passage 24. A diffusion barrier 34 is arranged in this channel 32, which reduces or even prevents the subsequent flow of gas from the measurement gas chamber into the electrode cavity 30 and allows only diffusion.

[0054] The first electrode 16 is arranged on the surface 28 of the solid electrolyte 14. The first electrode 16 can surround the gas inlet hole 26 in an annular manner and be separated from the measurement gas chamber by a gas-permeable protective layer, which is not shown in detail. The second electrode 18 is arranged in the electrode cavity 30. The second electrode 18 can also be configured as an annular ring and arranged rotationally symmetrically around the gas inlet hole 26. For example, the first electrode 16 and the second electrode 18 are arranged coaxially with the gas inlet hole 26. The first electrode 16 and the second electrode 18 are connected to the solid electrolyte 14, especially to the pump layer, especially electrically connected, so that the first electrode 16, the second electrode 18 and the solid electrolyte 14 form a pump cell 36. Accordingly, the first electrode 16 can also be referred to as an external pump electrode and the second electrode 18 can also be referred to as an internal pump electrode. The boundary current of the pump cell 36 can be adjusted by the diffusion barrier 34. Therefore, the boundary current is the current flow through the solid electrolyte 14 between the first electrode 16 and the second electrode 18.

[0055] In addition, the sensor element 12 also has a reference gas chamber 38. The reference gas chamber 38 can extend into the interior of the solid electrolyte 14 perpendicularly to the extension direction of the gas inlet hole 26. As described above, the gas inlet hole 26 is constructed as a cylinder, so that the extension direction of the gas inlet hole 26 is parallel to the cylindrical axis of the gas inlet hole 26. In this case, the reference gas chamber 38 extends perpendicularly to the cylindrical axis of the gas inlet hole 26. It should be explicitly mentioned that the reference gas chamber 38 can also be arranged on an imaginary extension line of the gas inlet hole 26, and thus arranged deeper inside the solid electrolyte 14. The reference gas chamber 38 does not have to be constructed as a reference gas chamber visible to the naked eye. For example, the reference gas chamber 38 can be implemented as the mentioned pumped reference, that is, an artificial reference.

[0056] The third electrode 20 is likewise arranged in the electrode cavity 30. For example, the third electrode 20 is located opposite the second electrode 18. The fourth electrode 22 is arranged in the reference gas chamber 38. The third electrode 20 and the fourth electrode 22 are connected to the solid electrolyte 14 in such a way that the third electrode 20, the fourth electrode 22 and the part of the solid electrolyte 14 located between the third electrode 20 and the fourth electrode 22 form a Nernst cell 40. For example, the pump current through the pump cell 36 can be adjusted by means of the pump cell 36 so that the condition λ=1 or another known composition prevails in the electrode cavity 30. This composition is in turn detected by the Nernst cell 40 by measuring the Nernst voltage U between the third electrode 20 and the fourth electrode 22. vs Since there is a known gas composition in the reference gas chamber 38 or the reference gas chamber is exposed to an environment with an excess of oxygen, the composition in the electrode cavity 30 can be inferred from the measured voltage.

[0057] In the extension of the extension direction of the gas inlet hole 26, a heating element 42 is arranged in the layer structure of the sensor element 12. The heating element 42 has a heating area 44 and a feed track 46. The heating area 44 is, for example, configured as a meander. The heating element 42 is arranged between the intermediate layer and the heating layer in the solid electrolyte 14. It should be explicitly mentioned that the heating element 42 is surrounded by a thin layer made of an electrically insulating material, such as aluminum oxide, on both sides, even if this is not shown in detail in the figure. In other words, a thin layer made of an electrically insulating material is arranged between the intermediate layer and the heating element 42 and between the heating element 42 and the heating layer. Since such a layer is known, for example, from the above-mentioned prior art, it is not described in detail here. Therefore, for more details about the layer made of an electrically insulating material, reference is made to the above-mentioned prior art, and its content related to the layer made of an electrically insulating material is incorporated herein by reference.

[0058] like Figure 1 As shown, the sensor 10 is connected to an electronic controller 48. The electronic controller 48 has a Nernst voltage U for regulating the Nernst cell 40. N The sensor 10 and the controller 48 are part of a sensor arrangement 200. The pump voltage U applied to the pump battery 36 P The electronic controller 48 is used to adjust the Nernst voltage U N Here, the Nernst voltage U N In addition, in this way, the pump current I flowing into or out of the pump cell 36, which is dependent on the oxygen concentration, can also be determined. P , the pump current indicates the oxygen content.

[0059] Figure 2 A schematic diagram shows the sequence of a method according to the invention for operating sensor 10. The method enables reliable cylinder-individual impact detection by eliminating jitter components from the pump current signal.

[0060] In step S10, the Nernst voltage U of the Nernst battery 40 is calculated in accordance with the first reference variable in a manner known per se. N In this case, the pump current or the pump voltage of the pump battery 36 is used as the actuating variable. Without being limited thereto, in particular, reference is made to the pump current I P The method is described as an execution variant. If the sensor 10 is a spring detector, step S10 can be omitted. In step S12, the Nernst voltage U of the Nernst cell 40 is detected or measured. N , and quantitatively determine the target variable that describes the characteristics of the measured gas. The target variable is the Nernst voltage U NThe variable signal is in particular a pump current signal, the measured value of which is detected or derived from the Nernst voltage U N In step S14, a target variable data packet is recorded based on the target variable. This target variable data packet includes multiple target variable values, such as 5 pump current values. The recording of the measured value detection is performed, for example, in the basic software 52 of the controller 48 ( Figure 1 ). In step S16, a time stamp is assigned to the target variable data packet. In other words, at the time of the measured value detection, in addition to the already existing pump current value, a time stamp to be newly introduced is recorded. This recording is performed by the memory 54 of the basic software 52 stored in the controller 48. In step S18, the target variable data packet with the assigned time stamp is stored in the memory 54. In other words, the pump current measurement value is written to the memory 54 together with the associated time stamp.

[0061] In the subsequent step S20, the target variable data packet is processed on the signal processing path 56. In other words, the pump current data packet passes through the signal processing path 56, in which different time delays may occur for various reasons. For example, a new value is queried every 2 ms, but only every 2.5 ms to the basic software 52 of the controller 48. The signal processing path 56 is part of the user software 58. The user software 58 can be implemented on an external controller (not shown in detail), for example, an engine control unit. Part of the signal processing, namely the speed-synchronous filtering, is performed in the user software 58. The user software 58 includes a ring buffer 60, to which the measured values ​​with the associated time stamps are written.

[0062] In step S22, the current system time is queried. The system time is queried by the basic software 52. The system time is ahead of the pump current data packet currently being processed by the delay currently existing. The target variable data packet is recorded at a higher clock frequency than the query of the current system time. That is, the target variable is measured every 500 μs and the system time is queried every 2 ms. For this reason, in step S24, the timestamp of the target variable data packet currently being processed is corrected based on the predetermined time delay and the current system time. The predetermined time delay is greater than the delay when the target variable data packet is processed on the signal processing path, that is, the constant time offset is greater than the possible total worst-case delay. The predetermined time delay is constant. Here, "correcting the timestamp" includes: adding the timestamp assigned to the pump current data packet currently being processed to the current system time and subtracting the current system time from the timestamp. In other words, the timestamp of the pump current data packet currently being processed is correspondingly added with a determined constant time delay and subtracted from the current system time.

[0063] In step S26, the corrected timestamp is converted to find the number of measured values. Thus, the time value expressed in time units is converted to the number of measured values, which in the example is a factor of 2, since there are 2 pump current values ​​per 1 ms. Based on the number of measured values, a time correction index is obtained for the target variable. Subsequently, in step S28, the corrected target variable value is obtained based on the time correction index. "Obtaining the corrected target variable value based on the time correction index" includes: starting from the last stored target variable data packet, accessing the target variable data packet stored in the ring buffer 60. The corrected target variable value is obtained by subtracting the correction index from the index of the last stored target variable data packet. Thus, by converting the time value for the timestamp into the number of measured values, a difference in the index is obtained, and in the ring buffer 60, a jump backwards must be made by this difference compared to the last existing target variable value. The past target variable values ​​are stored in the ring buffer 60 itself in such a way that no values ​​that have been overwritten can be accessed by the backward time offset. This is ensured by a suitable buffer size. In this way, in the example described, when processing at 2 ms intervals, the index of the ring buffer 60 is constantly increased by 4 at each function call, which is derived from the fact that there are 4 target variable values ​​every 2 ms. Due to this constant increase, a jitter-free signal is ensured. This is made possible by introducing a constant time delay, which does not bring any disadvantages for the common cylinder individual impact recognition application. The algorithm also works when the functions that provide data to the user functions and the functions that store data in the ring buffer 60 are called at different intervals.

[0064] Figure 3 A block diagram of the storage process is shown for the exemplary use of the pump current value as the target variable value. Figure 3 The left part of the diagram shows a ring buffer 60, which contains stored pump current values. The pump current value is indicated only by way of example at position 3 of the ring buffer 60. As described above, a new pump current value is detected and recorded, as indicated, for example, at position 1, as a target variable data packet or pump current data packet in the form of an array 62 in the basic software 52. As indicated by the addition block 64, the new pump current value is written to the ring buffer 60. In this case, the sum of the previous value, i.e. the value at position 3 of the ring buffer 60 in the example, and the new value, i.e. the pump current data packet at position 1 in the example, is always stored in the ring buffer 60 as a new value. Accordingly, the new pump current value is then located at position 4 in the ring buffer 60.

[0065] These storage steps may be repeated n times, for example at 2 ms intervals. In this case n is an integer. Figure 3 The right part of shows the storage process after it is repeated four times. Figure 3 The pump current value is indicated in the lower right part, for example, at position 7 of the ring buffer 60. As described above, a new pump current value is detected, as indicated, for example, in the array at position 5. The sum of the current value of the pump current data packet 62 (in this example at position 5) and the old value of the ring buffer 60 is written to the new location of the ring buffer 60 (in this example at position 8).

[0066] Figure 4 A block diagram for calculating the correction index is also shown as an example for the pump current as the target variable. Here, the block diagram is presented according to the AUTOSAR standard. The calculation of the correction index, that is, the index offset, is presented on the left side of the array 62 or the ring buffer 60. For the sake of clarity, the array 62 is presented separately because it is a very large array, for example, it may include 192 values. Here, the starting variable of the correction index is marked with 66. As shown by the addition box 72, the determined constant time delay 70 is added to the timestamp 68 of the pump current data packet currently being processed, and as shown by the subtraction box 76, the current system time 74 is subtracted. This time value in time units is converted into a measured value quantity. With reference to the above example, this is achieved by multiplying by a factor of 2, because there are 2 pump current values ​​per 1ms, as shown by the multiplication box 78. Thus, as shown by the subtraction block 80, based on the current index 82 of the ring buffer 60, the difference in the index is obtained, by which a jump must be made in the ring buffer 60 compared to the last existing pump current value. At this index, the segment-synchronous averaging begins. The number of array elements required for the averaging is marked with 84.

[0067] Since the sum of the previous value and the new value is always stored in the array, the start of the segment must finally be subtracted, as shown by the subtraction block 86, and for the final averaging, the number of added values ​​84 must also be divided, as shown by the division block 88, wherein both calculations are shown on the right side of the ring buffer 60. As a result, the corrected target variable value 90 is finally determined as the corrected pump current value. Since the number of array elements 84 used can vary and past target variable values ​​are stored in the ring buffer 60 for a sufficiently long time, the determination of the corrected pump current value as the target variable value 90 can be carried out at intervals that are different from the reading in and sending of the pump current data packets as the target variable data packets 62.

[0068] Figure 5A table with exemplary calculation variables for the method of the present invention is shown. In this regard, reference is made in particular to the above-mentioned example, in which "querying a pump current data packet as a target variable data packet" and "sending a pump current data packet as a target variable data packet" are performed at different clock frequencies. In the first row, the step number 92 for the signal query for the pump current is shown. In the second row, a timestamp 94 of the basic software is shown in seconds, which indicates the current system time. In the third row, a timestamp 96 of the current pump current data packet is shown in seconds. In the fourth row, the acquisition of the pump current value is shown with "yes / no" 98. In the fifth row, the current index 100 of the pump current array is shown. In the sixth row, the array elements 102 considered for the calculation are shown. The table also shows the calculations based on Figure 4 Example calculations performed.

Claims

1. A method for operating a sensor (10) for detecting at least one property of a measurement gas in a measurement gas chamber, in particular for detecting the content of a gas component in the measurement gas, wherein: The sensor (10) comprises a sensor element (12) for detecting the property of the measurement gas, wherein the sensor element (12) comprises at least one Nernst cell (40), wherein the method comprises the following steps: - measuring the Nernst voltage of the Nernst cell (40), quantitatively determining a target variable describing the property of the measurement gas based on the Nernst voltage, - recording a target variable data packet based on the target variable, - assigning a current timestamp (68) to the target variable data packet, - processing said target variable data packet on a signal processing path (56), -Query the current system time (74), - correcting said timestamp (68) of the target variable data packet currently being processed based on a predetermined time delay (70) and said current system time (74), - convert the corrected timestamps to the number of measurements, - determining a time correction index (66) for the target variable based on the number of measured values, and - Determining a corrected target variable value (90) based on the time correction index (66).

2. The method according to the preceding claim, wherein: The target variable is the Nernst voltage or a variable derived from the Nernst voltage.

3. The method according to the preceding claim, wherein: The target variable is an actuating variable when regulating the Nernst voltage, the actuating variable being the current or the voltage of the pump cell (36) of the sensor element (12) or of the Nernst cell (40).

4. The method according to the preceding claim, wherein: The predetermined time delay (70) is constant.

5. The method according to any one of the preceding claims, wherein: The predetermined time delay (70) is greater than a delay in processing the target variable data packet on the time processing path (56).

6. The method according to any one of the preceding claims, wherein: Correction of the timestamp (68) includes adding the timestamp assigned to the pump current data packet currently being processed to the timestamp (68) and subtracting the current system time (74).

7. The method according to any one of the preceding claims, wherein: The method also includes storing the target variable data packet in a memory (54) along with the assigned time stamp (68).

8. The method according to any one of the preceding claims, wherein: The signal processing path (56) is part of user software (58), wherein the user software includes a ring buffer (60).

9. The method according to the preceding claim, wherein: Obtaining the corrected target variable value based on the time correction index (66) includes: accessing the target variable data packets stored in the ring buffer (60) starting from the target variable data packet last stored in the ring buffer (60).

10. The method according to the preceding claim, wherein: The corrected target variable value is obtained by subtracting the correction index (66) from the last stored target variable data packet.

11. A computer program configured to execute each step of the method according to one of the preceding claims.

12. An electronic storage medium on which is stored a computer program according to the preceding claim.

13. An electronic controller (48) comprising an electronic storage medium according to the preceding claim.

14. A sensor arrangement (200) comprising a sensor (10) for detecting at least one property of a measurement gas in a measurement gas chamber, in particular for detecting the content of a gas component in the measurement gas, the sensor arrangement comprising a sensor element (12) for detecting the property of the measurement gas, wherein: The sensor element (12) has at least one Nernst cell (40), wherein the sensor arrangement further comprises an electronic control unit (48) according to the preceding claim.

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