DE102012206476A1 - Method for operating ordinary wide band lambda probe for detecting e.g. oxygen portion of exhaust gas in exhaust gas tract of motor car, involves performing calibration of sense element using water vapor pressure and portion of water vapor - Google Patents

Abstract

The method involves determining a reference water vapor pressure, and determining a portion of a water vapor in a gas electrochemically using a sense element that comprises two electrodes i.e. inner and outer pumping electrodes, where the electrodes are connected over solid electrolytes. Calibration of the sense element is performed using the water vapor pressure and the specific portion of the water vapor in the gas. An oxygen portion in the gas is electrochemically determined using the sense element using a standard operation. A pumping voltage (134) between the electrodes is adjusted. An independent claim is also included for a device for detecting an oxygen portion of a gas in a gas measuring chamber.

Description

State of the art

From the prior art, a plurality of devices, in particular sensor elements, and methods for operating these devices for detecting an oxygen content of a gas in a measuring gas space are known. The oxygen content can be detected, for example, in the form of a partial pressure and / or in the form of a percentage. In particular, ceramic sensor elements are known from the prior art, which are based on the use of electrolytic properties of certain solids, ie ion-conducting properties of these solids. In particular, these solids can be ceramic solid electrolytes, such as, for example, zirconium dioxide, in particular yttrium-stabilized zirconium dioxide (YSZ) and / or scandium-doped zirconium dioxide (ScSZ). For example, such sensor elements may be configured as so-called lambda probes, as they are, for example, in Robert Bosch GmbH: Sensors in the motor vehicle, 1st edition 2010, pages 160-165 are described. With broadband lambda probes, in particular with planar broadband lambda probes, it is possible, for example, to determine the oxygen content in an exhaust gas in a large range and thus to infer an air-fuel ratio in the combustion chamber. The air ratio λ usually describes this air-fuel ratio. Planar broadband lambda probes, which are preferably operated as a limiting current probe, can be constructed in particular as a single cell or as a double cell.

In the case of a broadband lambda probe, in particular a broadband lambda sensor, the amount of O ₂ or fat gas diffusing into a measuring cavity is measured either on the basis of a limiting current, in particular in unicellular organisms, or by means of a pumping current necessary for regulating a cavity concentration to λ = 1, in particular in the case of double cells. A flowing electric current, in particular a flowing measuring current and / or a pumping current through a pump cell of a broadband lambda probe, is usually proportional to an O ₂ content and / or fat gas content in the exhaust gas. A measurement of the cavity concentration is usually carried out by determining a Nernst voltage between a Nernst electrode in the measuring cavity, for example in a cavity, and an oxygen and / or air-purged reference electrode in a reference space. For example, a measurement of the oxygen partial pressure and / or the oxygen content in the exhaust gas can be carried out from an example of a linear relationship of a limiting current, in particular an Grenzpumpstroms, with the oxygen content, in particular with the oxygen partial pressure. A slope of this linear relationship and / or a sensitivity of the sensor element, in particular of the sensor, may for example depend on a manufacturing tolerance of a diffusion barrier, in particular with regard to a thickness and / or a length and / or a permeability and / or a pore diameter. To compensate for the manufacturing tolerance, for example, in known from the prior art sensor elements, in particular in known sensors, for example, a trim resistor as a current divider in a plug, in particular the sensor element, particularly preferably the broadband lambda probe, adjusted. Alternatively or additionally, an appropriate resistance readable by an engine control unit (ECU) in the plug can be trimmed and / or a bypass to the diffusion barrier can be opened by laser light and / or the length of the diffusion barrier can be shortened by grinding a contour of the sensor element.

A comparison of a characteristic in a thrust, in particular in air, is also known from the prior art, in which a factor in a control unit is used to convert a pitch. It is also known to consider a decay of outgassing of gasoline vapors from an oil sump.

It is also known to inflate the cavity electrochemically and to close after a diffusion time from an emptying integral to a diffusion resistance of the diffusion barrier. Out DE 10 2008 007 238 A1 a method for balancing a sensor element for a probe is known, wherein by means of a pumping electrode, a gas mixture of predetermined, defined composition is set, then the gas component to be determined is converted by the arranged on the side remote from the exhaust side of a diffusion barrier pump electrode, and wherein the In this case, the resulting pumping current and / or the time profile of the pumping current is closed at a balance value.

Also known are two-cell lambda probes, in which a pumping voltage can be regulated such that λ = 1 sets in a cavity. Furthermore, single-cell probes are known which have a gas-side electrode (GE) in the exhaust gas and a reference electrode (RE) in a reference-facing volume.

It is also known from the prior art to change a Nernst voltage of a controlled operated probe to allow a distinction of the gas composition and a modulation of a sensor element temperature.

Furthermore, a selective decomposition of water from the prior art in the field of electrolysis is basically known. Furthermore, methods are known in which a composition of gas mixtures is determined by varying a pumping voltage and evaluating the pumping current.

Furthermore, methods are known in which current values are evaluated as a function of predetermined pump voltages for the electrochemical detection of various gases. In GB 2 443 951 A For example, a method of operating an electrochemical gas sensor is known wherein a voltage pulse is applied across a pair of measuring electrodes and a current through the measuring electrode pair is detected while the voltage pulse decays before the current to a constant state level.

DE 39 90 187 C2 describes an electrochemical gas sensor, wherein all the electrodes are arranged and formed so that the ion conductivity is improved at least by increasing the effective surface area of an active electrode. This sensor according to the invention is capable of selectively detecting and indicating the presence of CO, H ₂ and other gases by means of electrolysis performed at a certain potential, the sensor having small dimensions, high sensitivity and excellent stability.

Furthermore, a method is known in which the vapor pressure and the relative humidity can be calculated from the oxygen partial pressure measured with a lambda probe, the total pressure and the temperature.

Usually, a pumping voltage of the sensor element, in particular the probe, is adjusted so that the Nernst voltage is constant 450 mV.

In EP 1 710 568 A2 a sensor element for measuring a concentration of NO _{x is described} as a gas component of a sample gas, wherein in particular a heater is embedded in an aluminum oxide insulating layer. US 6,695,964 B1 describes a method and a sensor for measuring an accurate determination of NO _x concentration in an exhaust gas comprising O _2, H ₂ O, CO ₂ and NO _x and a NO _x gas concentration sensor. A voltage which is applied across a pair of electrodes of a second oxygen ion pumping cell is set such that there is no dissociation of H ₂ O and CO ₂ in a second measuring chamber.

The known methods and devices of the prior art have some disadvantages. For example, known matching methods require a costly process. A thrust balance, as described in the prior art, is only partially usable in automatic vehicles and for gasoline vehicles usually significantly falsified due to a closed throttle by gasoline vapors from an oil pan. The methods of the prior art usually provide, in particular in the case of dynamic balancing, only one signal proportional to a void volume multiplied by the sought-after limiting current and are falsified, in particular, by an electrode capacity. It would therefore be desirable to have a method and a device which can measure the influence of the production spread on the limit current of the lambda probe, in particular an alternative balancing method.

Disclosure of the invention

Accordingly, a method and a device are proposed which at least largely avoid the disadvantages of known methods and devices. It is proposed a method for operating a sensor element for detecting an oxygen content of a gas in a sample gas space. The method can be carried out, for example, as a dynamic adjustment, for example one or more times before and / or during the detection of the oxygen content of the gas in the measurement gas space. The method may in particular comprise at least one calibration. In principle, the sensor element may be any device which is set up to detect the oxygen content of the gas in the measurement gas space. The sensor element may particularly preferably be an electrochemical sensor element. The detection of the oxygen content may in principle be a qualitative detection, particularly preferably a quantitative detection. The oxygen content may be, for example, at least one oxygen concentration and / or at least one oxygen volume fraction and / or at least one oxygen partial pressure and / or at least one air ratio λ. The gas may in principle be any gas. Particularly preferably, the gas may be an exhaust gas, for example an internal combustion engine, particularly preferably in a motor vehicle and / or in a heating system. In principle, the measurement gas space can be any space which is exposed to the gas. Particularly preferably, the measuring gas space can be an exhaust gas tract, in particular of a combustion power plant. The sensor element may in particular be a sensor element for detecting oxygen in an exhaust gas of an internal combustion engine.

The sensor element comprises at least a first electrode and at least one second electrode. The terms "first" and "second" and, if appropriate, "third" are used here and below as designations, without reference to the fact that, if appropriate, further elements of the type mentioned, for example further electrodes, may exist and without reference to an order. The first electrode and the second electrode are connected via at least one solid electrolyte. The solid electrolyte may in particular be understood as meaning a ceramic solid electrolyte, preferably an oxygen ion-conducting ceramic solid electrolyte, for example a zirconium dioxide-based solid electrolyte. By way of example, the sensor element may comprise at least one third electrode. The second electrode may, for example, be connected to at least one cavity and / or at least one reference gas space and / or at least one reference gas channel, for example a reference air channel. The third electrode can preferably be designed as a reference electrode and be connected, for example, to the reference gas space and / or the reference gas channel and / or the reference air channel. The gas can be applied to the first electrode and / or the second electrode, for example via at least one diffusion barrier. The cavity may be understood to mean a space within the sensor element which, although structurally separated from the measurement gas space, can nevertheless be exposed to the gas from the measurement gas space, for example via at least one gas access path and / or via the diffusion barrier. The cavity and / or the reference gas space and / or the reference gas channel may be wholly or partially open, but may also be wholly or partially filled with at least one gas-permeable medium, for example a porous medium, for example porous alumina. The cavity and / or the reference gas space may in particular be designed to store a supply of a gas component, for example of oxygen and / or air, for example, before this supply can optionally be delivered to another room. The third electrode can, for example, be connected to at least one solid electrolyte, for example the solid electrolyte as described above, in particular be connected in an ion-conducting manner. The third electrode may preferably be arranged in the reference gas space. For example, the diffusion barrier can be understood as meaning a layer of a material which suppresses a flow of a gas and / or a fluid, during which the layer promotes diffusion of a gas and / or a fluid and / or ions. The sensor element may further comprise at least one heating element. The heating element can in particular serve to regulate the temperature of the sensor element, in particular of at least part of the sensor element. The heating element may preferably serve to improve the catalytic activity of the electrodes comprising the first electrode and / or the second electrode and / or the third electrode, in particular on the solid electrolyte.

• • mindestens einen Dampfdruckbestimmungsschritt, wobei in dem Dampfdruckbestimmungsschritt mindestens ein Referenzwasserdampfdruck bestimmt wird,
• • mindestens einen Kalibrationsmessschritt, wobei in dem Kalibrationsmessschritt mindestens ein Anteil an Wasserdampf in dem Gas elektrochemisch mit dem Sensorelement bestimmt wird.

The method comprises the following steps:

• At least one vapor pressure determining step, wherein in the vapor pressure determining step at least one reference water vapor pressure is determined,
• At least one calibration measuring step, wherein in the calibration measuring step at least one portion of water vapor in the gas is determined electrochemically with the sensor element.

For example, the steps including the vapor pressure determining step and / or the calibration measuring step may be repeated a plurality of times, for example, alternately or in other orders. For example, the method may include further additional steps, in particular steps that differ from the above-mentioned steps.

The vapor pressure determining step may be performed, for example, temporally independently of the calibration measuring step. For example, the vapor pressure determination step may occur simultaneously with the calibration measurement step.

For example, the vapor pressure determination step may at least partially overlap with the calibration measurement step in time. For example, the calibration measurement step and / or the vapor pressure determination measurement step may be performed as soon as the vapor pressure determination step and / or the calibration measurement step are completed, preferably completed completely. For example, at least one time delay, in particular a waiting pause, may be performed between the vapor pressure determination step and / or the calibration measurement step and / or a repetition of the vapor pressure determination step and / or a repetition of the calibration measurement step and / or a further step.

The reference water vapor pressure may be, for example, a vapor pressure in Torr and / or bar and / or a water vapor concentration and / or a partial pressure of water vapor and / or a humidity. The proportion of water vapor may be, for example, a vapor pressure in Torr and / or mbar or a partial pressure of water vapor and / or a percentage by steam and / or an atmospheric moisture. The determination of the reference water vapor pressure and / or the proportion of Steam may preferably be quantitative. The determination of the reference water vapor pressure may in particular be a determination which is not and / or can not be carried out electrochemically, in particular not by the sensor element. In particular, the determination of the reference water vapor pressure and the determination of the proportion of water vapor in the gas may preferably differ with respect to the measurement method. By the term "determine electrochemically" it can be understood, for example, that a determination is made, wherein both electrical and chemical processes take place and / or be exploited. For example, in the case of an "electrochemical determination", at least one chemical reaction can be linked to at least one electric current. For example, at least one galvanic element may be involved in the "electrochemical determination". The expression "with the sensor element" may in particular mean that the proportion of water vapor in the gas can be determined by means of the sensor element, at least partially. In the electrochemical determination of the proportion of water vapor in the gas, the proportion of water vapor alone can be determined. Alternatively, a combined fraction can also be determined electrochemically, the combined fraction comprising, in addition to water vapor, at least one further gas component. For example, in the calibration measurement step, a combined fraction of water vapor and oxygen in the gas can be determined electrochemically, for example a combined partial pressure (p (H ₂ O) + p (O ₂ )) of water vapor and oxygen.

In the context of the present invention, a calibration can generally be understood as a comparison of at least two variables determined in different ways and independently of one another, in particular measured variables. Based on the comparison, the calibration can furthermore comprise at least one method step which compensates for deviations of these variables from one another, which are caused by the conditions for determining the detection of these variables, for example due to the apparatus. In this way, for example, systematic deviations or deviations in apparatus can be compensated. At least one of the sizes may be used as a reference, and the system to be calibrated may be modified to match at least one other size to the reference size. The compensation can be done for example by changing the hardware and / or a mathematical influencing or influencing a software of the system.

Calibration of the sensor element is performed using the reference water vapor pressure and the portion of water vapor determined in the calibration measurement step. The calibration may be, for example, a recalibration and / or an adjustment and / or a dynamic adjustment and / or an adjustment. For example, the calibration can serve the operability of the sensor element and / or a measurement accuracy. For example, the calibration can be carried out when the sensor element is re-commissioned and / or after an exchange of the sensor element and / or during operation, for example in order to compensate for aging effects.

During calibration, for example, the reference water vapor pressure can be compared with the proportion of water vapor determined in the calibration measurement step. For example, at least one arithmetic operation, in particular using the reference water vapor pressure and / or the proportion of water vapor determined in the calibration measuring step, can be carried out. For example, at least one difference between the reference water vapor pressure and the proportion of water vapor determined in the calibration measuring step can be formed. For example, at least one comparison of the reference water vapor pressure with the determined in the calibration measuring portion of water vapor at least one characteristic of the sensor element can be adjusted, for example, with respect to a change in the slope of the characteristic and / or with respect to an addition of at least one offset, for example a constant and / or one offsets dependent on the oxygen content.

In the vapor pressure determining step, at least one temperature of at least a part of the sensor element and / or an environment of the sensor element may be detected. The temperature of the at least one part of the sensor element may, for example, be at least one temperature and / or at least one average temperature of at least part of the motor vehicle and / or the exhaust tract and / or the sensor element and / or the cavity. By way of example, the temperature of the at least one part of the sensor element may also be an average temperature of different temperatures of different parts of the sensor element and / or the surroundings of the sensor element. The detection of the temperature of the at least one part of the sensor element and / or the surroundings of the sensor element can be carried out, for example, by at least one thermometer, in particular by at least one NTC (negative temperature coefficient thermistor), and / or by at least one temperature sensor. For example, the temperature of the sensor element may also be one Outside temperature, in particular outside of the sensor element and / or the exhaust gas tract, and / or to a gas temperature, in particular a temperature of the gas act. The temperature may in particular be an average temperature, for example averaged over several measuring points, for example via measuring points measured at different times and / or measuring points measured at different places. For example, the temperature of the at least one part of the sensor element and / or the environment of the sensor element can also be detected via at least one thermal imaging camera. For example, the temperature can also be detected externally, for example, provided by a weather service, and / or via at least one Internet connection and / or radio connection and / or satellite connection. From the temperature, the reference water vapor pressure can be particularly preferably concluded, in particular in the vapor pressure determination step. For example, it is possible to deduce the reference water vapor pressure from the temperature by means of at least one calibration curve. For example, the reference water vapor pressure can be calculated from the temperature, in particular in the presence of a saturated water vapor. The detection of the temperature and / or the vapor pressure determination step and / or the calibration measuring step can be carried out in particular during a cold start of the sensor element and / or the vehicle and / or during another time point, to which at least part of the sensor element and / or the environment of the sensor element are in a temperature equilibrium and / or a saturated water vapor is present, in particular the gas is saturated with water vapor. For example, the reference water vapor pressure can be determined with the aid of the temperature from at least one characteristic curve.

The method may be performed in at least one state of the sensor element. In the state, the sensor element can be at least partially acted upon by saturated steam. The state may particularly preferably be a stable state. For example, the state may be a physical state. In particular, the state may be characterized in that the sensor element and / or the gas and / or the environment of the sensor element are in a temperature equilibrium and / or the gas is saturated with water vapor. The state can be, for example, a cold start, for example, a state in or directly after a break in operation of the sensor element and / or the exhaust tract and / or the motor vehicle. For example, the state of the cold start can also be generated artificially. For example, the state and / or the exposure of the sensor element to saturated steam can be artificially generated, for example by at least one humidifier and / or at least one water reservoir and / or at least one water-saturated wick and / or at least one heating element and / or at least one fuel cell, in particular a hydrogen-oxygen fuel cell. The state is particularly preferably a state in which all components of a vehicle and / or the sensor element are at the same temperature, in particular at the same temperature as the gas.

In the calibration measuring step, a first pumping voltage between the first electrode and the second electrode can be adjusted. Furthermore, in the calibration measuring step, in particular when the first voltage is present, a first pumping current can be detected. In particular, the first pumping current can be detected in order to determine the proportion of water vapor in the gas electrochemically with the sensor element. The first pumping current may be at least partially a pumping current, which may be present between the first electrode and the second electrode as an ionic current, in particular as a current of oxygen ions. The first pumping voltage may in particular be an electrical voltage which is sufficient to generate a water decomposition at the first electrode, in particular in the calibration measuring step.

The method may further include at least one standard operating step. The standard operating step may, for example, be a regulating operation for setting and / or regulating the oxygen content, for example an air ratio. The standard operating step may particularly preferably be an operating step in which an oxygen content in the gas is detected by means of the sensor element. For example, in the standard operating step, the oxygen content in the gas can be determined electrochemically with the sensor element. The standard operating step may in particular be a step in conventional standard operation, as known from the prior art, for example, and in particular in US Pat Robert Bosch GmbH: Sensors in the motor vehicle, 1st edition 2010, pages 160-165 described.

In the calibration measuring step, for example, at least one first pumping voltage between the first electrode and the second electrode can be set, wherein at least one first pumping current can be detected. In the standard operating step, at least one second pumping voltage can be set between the first electrode and the second electrode, wherein at least one second pumping current can be detected. at The first pumping voltage may in particular be an electrical voltage which, as described above, is sufficient to decompose water. The second pumping voltage may in particular be a voltage which is preferably insufficient to decompose water. The first pumping current may be, for example, a pumping current as described above. The first pumping current may be a pumping current, which is usually higher than the second pumping current. The first pumping voltage may preferably differ from the second pumping voltage, in particular in magnitude and / or in sign. In particular, the first pumping current can be detected to determine the proportion of water vapor in the gas.

The first pumping voltage may be, for example, higher by 1 mV to 10 kV, preferably by 500 mV to 1 kV higher, particularly preferably by 800 mV, higher than the second pumping voltage. Other differences in size between the first voltage and the second voltage may be possible in principle. The difference in size between the first voltage and the second voltage may in particular be temperature-dependent. In comparison to the second pumping voltage, the first pumping voltage can be higher in particular such that water decomposition takes place at the first pumping voltage and oxygen decomposition takes place at the second pumping voltage without water decomposition. The first pumping voltage may be particularly preferably chosen such that no decomposition of zirconium dioxide or another constituent of the gas, except oxygen and / or water, and / or the sensor element can take place. Particularly preferably, the first pump voltage and / or the second pump voltage may have a value at which a pump current-pump voltage diagram in each case has a plateau of the pump current, for example a range of a substantially constant pump current.

In the calibration measuring step and / or in the standard operating step, an at least temporally constant pumping voltage, in particular a constant first pumping voltage and / or a constant second pumping voltage, can be applied in each case. For example, several, for example mutually different, first pump voltages and / or second pump voltages can be detected in the calibration measuring step and / or in the standard operating step, for example to determine whether there is a plateau of the pumping current at the first pumping voltages and / or the second pumping voltages / or to form an average of the first pumping voltages and / or the second pumping voltages.

In the calibration measuring step and / or in the standard operating step, an at least temporally changing pump voltage can be applied in each case, in particular a time-varying first pump voltage and / or a time-varying second pump voltage. For example, the first pumping voltage and / or the second pumping voltage can be alternately changed and / or "wobbled". By way of example, the first pumping voltage and / or the second pumping voltage may be a periodic voltage in time, for example, the first pumping voltage and / or the second pumping voltage may be at least one sinusoidal voltage and / or one rectangular voltage and / or a sawtooth-shaped voltage and / or a triangular voltage. In particular, the first pumping voltage and / or the second pumping voltage may be a pump voltage which varies at least temporarily, for example to determine whether the first pumping voltage and / or the second pumping voltage are at a plateau of the pumping current as a function of the pumping voltage located. For example, in the calibration measuring step and / or in the standard operating step, an at least temporarily time-varying pumping voltage can be applied in such a way that both the first pumping voltage and the second pumping voltage are swept by the temporally changing pumping voltage. For example, in a period of the changing pump voltage, both the first pump voltage and the second pump voltage can be swept so that both the calibration measurement step and the standard operation step can be performed within a period. For example, the changing pumping voltage can sweep over two current plateaus, particularly preferably with the first pumping voltage and / or the second pumping voltage. For example, while the changing pumping voltage is applied, a changing pumping current, in particular the first pumping current and / or the second pumping current, can be detected, for example continuously and / or as discrete values.

For example, the method may include at least one additional step. The vapor pressure determining step and / or the calibration measuring step and / or the standard operating step and / or the additional steps may be carried out several times in succession, in particular in different orders and / or recurring consecutively. In the method, at least one characteristic curve, for example a characteristic curve of the sensor element, can be adjusted.

In particular, the method according to the invention may comprise a procedure, the procedure comprising a measurement of the proportion of water and oxygen (p (H ₂ O) + p (O ₂ )), in particular in the calibration measuring step, and / or a measurement of the proportion of oxygen p (O ₂ ), in particular in the calibration _measurement step and / or in the standard operation step, and / or a determination of the proportion of water p (H ₂ O) _measurement , in particular in the vapor pressure determination step, and / or a correction of the characteristic, for example in the Calibration. p (H ₂ O) can for example be determined from (p (H ₂ O) + p (O ₂ )), in particular by at least one arithmetic operation and / or by the comparison, for example by a subtraction. The correction of the characteristic curve and / or the calibration can be carried out in such a way that after the correction of the characteristic curve p (H ₂ O) _measurement = p (H ₂ O) is fulfilled. This correction of the characteristic, in particular the characteristic correction and / or the adjustment, applies to all gas species and / or can be carried out for all gas species, in particular also for a regular probe operation, in particular for the detection of p (O ₂ ).

In a further aspect of the present invention, an apparatus for detecting an oxygen content of a gas in a measurement gas space is proposed. The device comprises at least one sensor element. The device may preferably comprise one sensor element or two sensor elements. The sensor element comprises at least a first electrode and at least one second electrode. The first electrode and the second electrode are connected via at least one solid electrolyte, for example a solid electrolyte as described above. The device furthermore has at least one activation. The drive is set up to carry out a method according to the invention as described above. The control can be connected to the sensor element and / or connectable, for example. The activation can be understood to mean a device which is set up to support and / or control at least one function of the device, in particular of the sensor element, for example the detection of the proportion of water vapor in the calibration measurement step and / or the detection of the reference water vapor pressure. By "connectable", for example, a property can be understood in which an electrical connection can be made or already exists. The control may be wholly or partially designed separately from the sensor element, but may also be fully or partially integrated into the sensor element, for example in at least one plug of the sensor element and / or the device. The drive may comprise at least one voltage measuring device and / or at least one current measuring device for detecting the first pumping current and / or the second pumping current and / or the first pumping voltage and / or the second pumping voltage and / or for regulating the first pumping voltage and / or for regulating the second Pump voltage include. Alternatively or additionally, the drive and / or the sensor element and / or the device may have at least one loading device. The application device may in particular comprise at least one voltage source and / or at least one current source. For example, the loading device may be configured to apply the first pumping current and / or the first pumping voltage and / or the second pumping current and / or the second pumping voltage to the sensor element. The drive may be further configured to perform the calibration measurement step and / or the standard operation step and / or the vapor pressure determination step and / or to perform the calibration of the sensor element. The drive may further comprise at least one data processing device.

The method and apparatus of the present invention have a number of advantages over known methods and apparatus. For example, in the method according to the invention, no other adjustment methods, for example at least one connector adjustment and / or at least one thrust adjustment and / or at least one laser adjustment, are more necessary, but in principle can additionally be performed. By means of the method according to the invention, furthermore, a dynamic adjustment can be realized, for example an aging of the sensor element, for example a probe, can be compensated, preferably during operation.

Brief description of the drawings

Embodiments of the invention are illustrated in the figures and are explained in more detail in the following description.

Show it:

1 a pumping current-pumping voltage diagram of a first embodiment of a method according to the invention;

2 a dependence of the vapor pressure of a temperature for use in an embodiment of a method according to the invention;

3A an embodiment of a device according to the invention during a standard operating step of an embodiment of a method according to the invention;

3B a pumping current-pumping voltage diagram for different oxygen partial pressures in a standard operating step of an embodiment of a method according to the invention;

4A an embodiment of a device according to the invention during a calibration measuring step of an embodiment of a method according to the invention;

4B a pumping current-pumping voltage diagram for different proportions of water vapor in a gas in a calibration measuring step of an embodiment of a method according to the invention;

5A a further embodiment of a device according to the invention when performing a standard operating step of an embodiment of a method according to the invention; and

5B the further embodiment of a device according to the invention when performing a calibration measuring step of an embodiment of a method according to the invention.

Embodiments of the invention

In the figures, particular embodiments of the inventive method for operating a sensor element 110 for detecting an oxygen content of a gas in a sample gas space 112 shown. In the 3A . 4A . 5A and 5B are further embodiments of a device according to the invention 114 shown. The device 114 is a device for detecting an oxygen content of a gas in a measuring gas space 112 , The device 114 includes at least one sensor element 110 , The sensor element 110 includes at least a first electrode 116 and at least one second electrode 118 , The first electrode 116 and the second electrode 118 are about at least one solid electrolyte 120 connected, in particular ion-conducting connected. The device 114 also has at least one control 122 on. The control 122 is set up to perform a method according to the invention. The device according to the invention 114 can continue at least one heating element 124 and / or at least one cavity 126 exhibit. In the sensor element 110 it may be, for example, at least one lambda probe. The sensor element 110 For example, at least one diffusion barrier 128 exhibit. At the first electrode 116 For example, it may be an outer pumping electrode 130 act. At the second electrode 118 For example, it may be an internal pumping electrode 132 act.

For example, the device 114 , in particular the sensor element 110 , at least one third electrode, in particular at least one Nernst electrode 133 ,

• • mindestens einen Dampfdruckbestimmungsschritt, wobei in dem Dampfdruckbestimmungsschritt mindestens ein Referenzdampfdruck bestimmt wird,
• • mindestens einen Kalibrationsmessschritt, wobei in dem Kalibrationsmessschritt mindestens ein Anteil an Wasserdampf in dem Gas elektrochemisch mit dem Sensorelement 110 bestimmt wird.

In the 1 . 2 . 3A . 3B . 4A . 4B . 5A and 5B are exemplary embodiments of the method according to the invention for operating the sensor element 110 , in particular of the sensor element 110 as described above, for detecting an oxygen content in a gas in the measurement gas space 112 shown. The sensor element 110 may for example be configured as described above. The sensor element 110 includes at least a first electrode 116 and at least one second electrode 118 , The first electrode 116 and the second electrode 118 are about at least one solid electrolyte 120 connected. The method comprises the following steps:

• At least one vapor pressure determination step, wherein at least one reference vapor pressure is determined in the vapor pressure determination step,
• At least one calibration measuring step, wherein in the calibration measuring step at least one portion of water vapor in the gas electrochemically with the sensor element 110 is determined.

A calibration of the sensor element 110 is performed using the reference water vapor pressure and the proportion of water vapor determined in the calibration measurement step. The proportion of water vapor, in particular the vapor pressure p (H ₂ O), can in particular by a lambda probe as a sensor element 110 be measured. By measuring the reference water vapor pressure and the proportion of water vapor in the gas with the sensor element 110 For example, at least one resistance of the diffusion barrier 128 , in particular a diffusion resistance, are detected and is thus known thereafter. This allows the sensor element 110 , in particular the lambda probe, are adjusted, ie manufacturing variations can in the control 122 , In particular in a control unit, be compensated by adjusting at least one characteristic. In the vapor pressure determining step, at least one temperature of at least a part of the sensor element 110 and / or an environment of the sensor element 110 be recorded. From the temperature can be concluded on the reference water vapor pressure. For example, during a cold start, the temperature of the exhaust system may be known. This can for example be due to the fact that during cold start all components of the sensor element 110 and / or the vehicle, which is an outside air are usually located at a same temperature, thus the exhaust system is usually at the same temperature. For example, numerous sensors, in particular temperature sensors, on the sensor element 110 and / or in the vicinity of the sensor element 110 located, for example in the vehicle, in particular in an air conditioner and / or in a turbocharger and / or in an exhaust tract. With these temperature sensors, for example, the temperature can be detected. As a result, the temperature, in particular the temperature of the exhaust system, can be known, a temperature of the exhaust pipe inner wall, for example, the manifold is usually known. As a result, the vapor pressure in the exhaust pipe can be known and / or recorded and / or calculated, for example via the in 2 shown relationship between a temperature in ° C and a vapor pressure, for example, a water vapor pressure p (H ₂ O) in Torr. From the detected temperature can thus, for example by means of in 2 As shown, the reference water vapor pressure in the vapor pressure determining step can be determined. 2 in particular shows a dependence of the vapor pressure of water on the ambient temperature in a possibly relevant temperature range, in particular between -10 ° C and 60 ° C. Further influences on the vapor pressure can, for example, be disregarded, but can also be detected and / or taken into account in the context of the method according to the invention, for example in the context of an error calculation and / or a correction and / or a disturbance calculation. In particular, influences on the vapor pressure, in particular on the reference water vapor pressure, can be taken into account, for example a deviation from a state with a saturated water vapor pressure and / or influences by the exhaust gas and / or influences by temperature differences and / or by temperature gradients and / or influences by changes in air pressure. 2 in particular shows the dependence of the water vapor pressure, for example the reference water vapor pressure, p (H ₂ O), with respect to the temperature T in ° C. For example, the relationship between the temperature and the reference water vapor pressure can be adjusted, for example in the case of a change in the relative humidity, for example, depending on the weather and / or air conditioning, for example a Abstellortes.

The method can in particular in a state of the sensor element 110 be performed. The sensor element 110 may be at least partially acted upon in the state with saturated water vapor.

In the calibration measuring step, a first pumping voltage 134 , such as in the 1 and 4B shown, between the first electrode 116 and the second electrode 118 set and / or charged and / or created. In this case, at least one first pumping current 136 be recorded.

The method may further include at least one standard operating step. In the standard operating step, the oxygen content in the gas may be electrochemical with the sensor element 110 be determined. The method according to the invention can comprise, for example, a measuring method, in particular a measuring method of the lambda probe, by means of which both the oxygen content, for example an oxygen partial pressure, and a proportion of water vapor, in particular a partial pressure of water vapor, in particular in internal combustion engines, can be determined. For example, according to the inventive method, the sensor element 110 , In particular, a common broadband lambda probe, are used as a moisture sensor, this can be in particular the proportion of water vapor in the gas, in particular a humidity measure.

In the calibration measuring step, the first pumping voltage 134 between the first electrode 116 and the second electrode 118 be set. At least the first pumping current 136 can be detected. In the standard operating step, at least one second pumping voltage 138 between the first electrode 116 and the second electrode 118 be set. In this case, for example, at least a second pumping current 140 be recorded. The first pumping voltage 134 may preferably be from the second pumping voltage 138 differ and / or the first pumping current 136 may be different from the second pumping current 140 differ.

For example, the first pumping voltage 134 by 1 mV to 10 kV higher, preferably by 500 mV to 1 kV higher, more preferably by 800 mV higher than the second pumping voltage 138 , In the method according to the invention, in addition to an oxygen signal, in particular in addition to the second pumping current 140 in a controlled operation of the sensor element 110 , In particular the probe, also directly the proportion of water vapor, in particular a moisture, preferably a cathode branch, are detected. For this purpose, a pump voltage to a sensor cell of the probe, in particular of the sensor element 110 , For example, a pumping voltage between the first electrode 116 and the second electrode 118 be increased to a value above the decomposition voltage of the water.

For example, in particular in a limit current operation, the probe signal, for example the first pumping current 136 and / or the second pumping current 140 and / or one hereby correlating size, as described below and in the 1 . 3B and 4B shown, put together. The standard operating step may, for example, be a conventional control operation of the sensor element 110 , in particular the probe. In this case, the probe signal, for example the second pumping current 140 and / or a corresponding quantity, for example an electrical voltage, with the oxygen content in the gas, in particular with the O ₂ concentration, correlate. The calibration measuring step may in particular at least one probe operation at elevated pumping voltage, in particular at the first pumping voltage 134 , include. In the calibration measuring step, in particular in the probe mode, the probe signal, for example the first pumping current 136 , with the sum of the oxygen content in the gas, in particular the O ₂ concentration, and the proportion of water vapor in the gas, in particular a H ₂ O concentration, correlate. For example, the sensor element 110 , in particular as described above, over at least one operating cycle, for example a complete operating cycle, a profile of the proportion of water vapor in the gas, in particular at least one moisture concentration, and / or the oxygen content in the gas, in particular the oxygen concentration detect. In 1 In particular, a numerical example of a method according to the invention is shown. 1 shows in particular a schematic pumping current profile of a pumping current I _p over a pumping voltage U _p with two limiting current plateaus, in each case a limiting current plateau for O ₂ 142 and a limiting current plateau for H ₂ O + O ₂ 144 , in particular for H ₂ O and O ₂ . The pump voltage may be the first pump voltage 134 and / or the second pumping voltage 138 act. The pumping current may be the first pumping current 136 and / or the second pumping current 140 act. The indicated pumping voltage, in particular the width of the limiting current plateau for O ₂ 142 of about 0.8V, can be considered as an example value.

In the method according to the invention, in particular in the standard operating step, for example in the conventional control mode, the pumping current, in particular the second pumping current, can be used 140 , at a pumping voltage, in particular at the second pumping voltage 138 of approximately U _p = 400 mV, a maximum, in particular its maximum, preferably a local maximum, particularly preferably a saddle point. Here, in particular, the Grenzstromplateau for O ₂ 142 be achieved, such as in the 1 . 3B and 4B shown in 3B especially for different oxygen levels in the gas. The required pumping voltage, for example for the oxygen decomposition, in particular the second pumping voltage 138 , is usually composed of: U _p = Ig _O2 · R _iDC + U _{O2 reduction} + U _{O2 oxidation} · Up stands for the pumping voltage, in particular for the second pumping voltage 138 , Ig _O2 stands for the second pumping current 140 , in particular for a limiting current at the diffusion barrier 128 for O ₂ , R _iDC stands for an internal resistance of the sensor element 110 , In particular an internal resistance of the lambda probe and / or the sensor element 110 , R _iDC = R _IPN + R _electrolyte + R _APE , where R _{IPN is} the resistance of an internal pumping electrode (IPN) 132 , R _electrolyte for the resistance of the solid electrolyte 120 , in particular an electrolyte, and R _APE for the resistance of an external pumping electrode (APE) 130 stands. At the inner pump electrode 132 in particular, it may be the second electrode 118 act, at the outer pumping electrode 130 in particular, it may be the first electrode 116 act. At different oxygen partial pressures at the electrodes, a Nernst voltage may result, which is referred to herein as U _{O2 reduction} and U _{O2 oxidation} . A reduction voltage at the second electrode 118 , in particular on the inner pumping electrode 132 , and an oxidation voltage at the first electrode 116 , in particular on the outer pumping electrode 130 , can be of the same magnitude, so that the following applies: U _{O2 reduction} + U _{O2 oxidation} = 0 mV. Usually, all resistors and voltages are temperature dependent. This temperature dependency can be taken into account, for example, in the method according to the invention, for example by using non-constant pump voltages, in particular by a first pump voltage which varies over time 134 and / or a time-varying second pumping voltage 138 , The operation of the sensor element 110 in this standard operating step, in particular the operation of the probe, may preferably be via at least one Nernstspannungsregelung, for example as part of the control 122 , take place, preferably with a control on λ = 1.

The calibration measuring step may in particular include a probe operation with increased pumping voltage. At the increased pumping voltage, in particular compared to the second pumping voltage 138 , it may be, for example, the first pumping voltage 134 act. The pumping current, as in 1 or 4B shown, for example, as the first pumping current 136 at a pumping voltage of approximately ΔU _p = 600 mV after reaching the limit current plateau of O ₂ 142 , preferably after ΔU _p = 800 mV, reach a second maximum, in particular a second limiting current plateau, for example a limiting current plateau for H ₂ O + O ₂ 144 , preferably a second saddle point. In the calibration measuring step, for example, in addition to the limiting current plateau for O ₂ 142 , also the limiting current plateau for H ₂ O + O ₂ 144 be achieved. The required pumping voltage, in particular the first pumping voltage 134 , especially preferably the pump voltage for the Kalibrationsmessschritt, can be composed of: U _p = (Ig + _O2 Ig _H2O) · R _iDC U + _{H2O reduction} (IPN) + U _{O2 oxidation} (APE). Ig _H2O stands for the limiting current at the diffusion barrier 128 for H ₂ O, U _{H2O reduction} stands for the reduction voltage of H ₂ O at the inner pumping electrode (IPN) 132 and U _{O2 oxidation} here stands for the oxidation voltage at O ₂ at the outer pumping electrode (APE) 130 , This reduction voltage and this oxidation voltage are usually different in magnitude. A numerical example of the decomposition of water may be especially: U _p> 0.8 V + (Ig Ig _O2 + _H2O) · R _iDC. The operation of the sensor element 110 , in particular the probe, can, in particular in the calibration measuring step, take place via a pump voltage control which, for example, depends on the activation 122 can be included. 1 shows in particular the limiting current of O ₂ , in particular the limiting current at the limiting current plateau for O ₂ 142 (Ig _O2 ), and the limiting current H ₂ O + O ₂ , in particular at the limiting current plateau for H2O + O ₂ 144 (Ig _H2O ). The limiting current plateau for O ₂ 142 For example, it can be about 0.8V wide. In the limiting current plateau for H ₂ O + O ₂ 144 For example, in the normal operation, for example in the standard operating step, the pumping current Ig _O2 may preferably be a second pumping current 140 , be read. Further shows 1 the current Ig _H2O , in particular in the operation with increased pumping voltage, in particular in the calibration measuring step, for example for water decomposition, particularly preferably as part of the first pumping current 136 , Furthermore, an increase in the pumping current is indicated by a further increase in the pumping voltage, in particular up to a decomposition of ZrO ₂ .

In the 3A and 3B is an embodiment of a standard operating step, in particular a lambda probe in an XO ₂ measurement operation shown. X here preferably stands for the oxygen content in the gas and / or for the proportion of water vapor in the gas. 3A shows in particular an embodiment of a device according to the invention 114 , Wherein by arrows a pumping current, in particular the second pumping current 140 , is shown. 3B shows a diagram of the pumping current, in particular the second pumping current 140 , above the pumping voltage, in particular the second pumping voltage 138 , in particular for different levels of oxygen in the gas, preferably for different high pressures, in particular for increasing pressures of p ₁ over p ₂ to p ₃ .

At the in 3A and 4A illustrated embodiments of inventive devices 114 in particular, these may be broadband lambda probes. For example, it may be in 4A and 5A to the same embodiment of the device according to the invention 114 act. In the 4A and 4B 1 shows an exemplary embodiment of a calibration measuring step of the method according to the invention, in particular a lambda probe in a (XO ₂ + XH ₂ O) measuring mode. In 4A is an embodiment of a device according to the invention 114 in particular, a pumping current, particularly preferably the first pumping current 136 , is shown and / or, as well as in 3A , an application of the sensor element 110 with the gas. In the 3A . 3B . 4A and 4B are in particular modes of operation of the device according to the invention 114 shown. 4B shows pumping currents I _p , in particular first pumping currents 136 against a pumping voltage, in particular the first pumping voltage 134 and the second pumping voltage 138 , in particular for different proportions of water vapor in the gas, in particular increasing from (1), via (2) to (3). Shown is, inter alia, the limiting current plateau for O ₂ 142 and various boundary current plateaus for different levels of water vapor in the gas 144 ,

In 5A are in particular a reduction mechanism of oxygen (O ₂ ) of an embodiment of a method according to the invention, for example a standard operating step, and an embodiment of a device according to the invention 114 shown. 5B shows a reduction mechanism for water (H ₂ O), for example, a calibration measuring step of an embodiment of the method according to the invention. In the 5A and 5B are in particular reduction mechanisms in a cavity 126 a lambda probe shown.

In the calibration measuring step and / or in the standard operating step, in each case an at least temporarily temporally constant pumping voltage can be applied, in particular a first pumping voltage 134 and / or a second pumping voltage 138 , In particular, a pump voltage, for example the first pump voltage, may be provided under a pump voltage that is constant in time 134 and / or the second pumping voltage 138 , the amount of the pumping voltage remaining substantially constant at least over a period of at least 1 ms, preferably 10 ms, particularly preferably 100 ms. By "substantially constant", in particular a constancy of the pumping voltage can be understood within a range of a few V, preferably less than 100 mV, particularly preferably less than 1 mV.

In the calibration measuring step and / or in the standard operating step, a pump voltage which changes at least temporarily with respect to time, in particular the first pumping voltage 134 and / or the second pumping voltage 138 , are applied, in particular between the first electrode 116 and the second electrode 118 and / or the second electrode 118 and the third electrode. For example, alternatively or additionally, a pump voltage, in particular the first pump voltage 134 and / or the second pumping voltage 138 , alternating and / or "wobbling" increase, for example, with an amplitude of 1 mV to 1 V, preferably from 100 mV to 200 mV, more preferably of about 150 mV, in particular controlled by the drive 122 , In particular, the pump voltage can increase and / or the pump voltage can be increased, preferably regulated by the control 122 , until a second time a change in current, in particular the first pumping current 136 and / or the second pumping current 140 , is reached less than 100 mA, preferably less than 1 mA, particularly preferably less than 0.5 mA, and / or can be detected. In particular, it may be assumed that the limiting current plateau for H ₂ O + O ₂ 144 is reached, in particular is achieved safely. However, this alternative mode of operation, in particular with a pump voltage that changes at least temporarily over time, may under certain circumstances have reduced dynamics. In particular, the first pumping voltage 134 and / or the second pumping voltage 138 and / or the Nernst voltage in the probe operation and / or in the standard operating step and / or in the calibration measuring step are varied such that at least two operating points result: for example, at least one control operation, preferably at a Nernst voltage of about U _N = 450 mV, in particular for a measurement of the oxygen content p (O ₂ ), in particular in the standard operating step, and at least one control operation, preferably at about U _N = 1000 mV, in particular in a measurement of p (O ₂ ) + p (H ₂ O), in particular in the Kalibrationsmessschritt. The vapor pressure determining step and / or the calibration measuring step and / or the standard operating step may be carried out several times in succession, for example in different orders. At least one characteristic curve can be adjusted here. Particularly preferably, the method according to the invention, comprising in particular the calibration measuring step and / or the standard operating step, with a sensor element 110 be performed. For example, the inventive method can also be used with two sensor elements 110 and / or with two devices according to the invention 114 be performed. For example, the calibration measuring step can be performed with a first sensor element 110 and the standard operating step with a second sensor element 110 , For example, a lambda probe can be used for a measurement and / or detection of p (O ₂ ), in particular for the standard operating step, and a further lambda probe for the measurement and / or detection of p (O ₂ + steam), in particular for the calibration measuring step. A vapor pressure, in particular the proportion of water vapor in the gas, may result from: p (vapor) = p (O ₂ + steam) - p (O ₂ ). Alternatively or additionally, a lambda probe can be used for an alternating and / or simultaneous measurement of p (O ₂ ) and p (O ₂ + steam). For example, the vapor pressure can also be calculated and / or recorded using the equation described above. A dynamic of the measurement, in particular of the method according to the invention, in particular one cycle of the method according to the invention, for example comprising at least one vapor pressure determination step and / or at least one calibration measurement step and / or at least one standard operation step, can be for example less than 1 s, preferably less than 500 ms, particularly preferred less than 100 ms. The method according to the invention may in particular be an autonomous adjustment. The method according to the invention can be based, in particular, on the recognition that there is usually a reproducible relationship between a diffusion resistance for oxygen and a diffusion resistance for water vapor, in particular a well reproducible relationship. The diffusion resistance may in particular be a diffusion resistance of the diffusion barrier 128 and / or the solid electrolyte 120 act.

The device according to the invention 114 in particular, at least one heating element 124 include. The heating element 124 may be arranged to, for example, in one embodiment of the method according to the invention, regulate an operating temperature and / or to control. The process according to the invention can be carried out, for example, at a temperature of from 500 to 1000.degree. C., preferably from 700 to 800.degree. C., more preferably from approximately 780.degree. For example, an operating temperature of T = 780 ° C can be sought. As a result, for example, a lower decomposition voltage and / or a shift of the plateaus, in particular the Grenzstromplateaus, for example, towards lower voltages, in particular to a lower first pumping voltage 134 and / or to a lower second pumping voltage 138 , revealed. An alternative mode of operation with an at least temporarily time-varying pump voltage can be used, for example, if a user and / or the control 122 the first pumping voltage 134 and / or the second pumping voltage 138 , in particular for measuring the limiting current plateau for O ₂ 142 and / or the limiting current plateau for H ₂ O + O ₂ 144 , does not know and / or this has shifted, for example, by at least one temperature change of at least a portion of the sensor element 110 and / or the environment and / or by aging, for example of the sensor element 110 ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008007238 A1 [0004]
• GB 2443951 A [0008]
• DE 3990187 C2 [0009]
• EP 1710568 A2 [0012]
• US 6695964 B1 [0012]

Cited non-patent literature

• Robert Bosch GmbH: Sensors in the motor vehicle, 1st edition 2010, pages 160-165 [0001]
• Robert Bosch GmbH: Sensors in the motor vehicle, 1st edition 2010, pages 160-165 [0027]

Claims (10)

Method for operating a sensor element ( 110 ) for detecting an oxygen content of a gas in a measuring gas space ( 112 ), wherein the sensor element ( 110 ) at least one first electrode ( 116 ) and at least one second electrode ( 118 ), wherein the first electrode ( 116 ) and the second electrode ( 118 ) via at least one solid electrolyte ( 120 at least one vapor pressure determination step, wherein at least one reference vapor pressure is determined in the vapor pressure determination step; at least one calibration measurement step, wherein in the calibration measurement step at least a portion of water vapor in the gas is electrochemically coupled to the sensor element; 110 ), wherein a calibration of the sensor element ( 110 ) using the reference water vapor pressure and the portion of water vapor determined in the calibration measurement step. Method according to the preceding claim, wherein in the vapor pressure determining step at least one temperature of at least a part of the sensor element ( 110 ) and / or an environment of the sensor element ( 110 ) is detected, being closed from the temperature to the reference water vapor pressure. Method according to one of the preceding claims, wherein the method in a state of the sensor element ( 110 ) is carried out, wherein the sensor element ( 110 ) is in the state at least partially acted upon by saturated water vapor. Method according to one of the preceding claims, further comprising at least one standard operating step, wherein in the standard operating step, the oxygen content in the gas electrochemically with the sensor element ( 110 ) is determined. Method according to the preceding claim, wherein in the calibration measuring step a first pumping voltage ( 134 ) between the first electrode ( 116 ) and the second electrode ( 118 ), wherein at least one first pumping current ( 136 ), wherein in the standard operating step at least one second pumping voltage ( 138 ) between the first electrode ( 116 ) and the second electrode ( 118 ), wherein at least one second pumping current ( 140 ), wherein the first pumping voltage ( 134 ) from the second pumping voltage ( 138 ) is different. Method according to the preceding claim, wherein the first pumping voltage ( 134 ) by 1 mV to 10 kV higher, preferably by 500 mV to 1 kV higher, more preferably by 800 mV higher than the second pump voltage ( 138 ). Method according to one of the three preceding claims, wherein in each case an at least temporarily temporally constant pumping voltage is applied in the calibration measuring step and / or in the standard operating step. Method according to one of the four preceding claims, wherein in the calibration measuring step and / or in the standard operating step in each case an at least temporarily temporally changing pumping voltage is applied. Method according to one of the preceding claims, wherein the vapor pressure determining step and / or the calibration measuring step and / or the standard operating step are carried out several times in succession, wherein at least one characteristic curve is adjusted. Contraption ( 114 ) for detecting an oxygen content of a gas in a measuring gas space ( 112 ), the device ( 114 ) at least one sensor element ( 110 ), wherein the sensor element ( 110 ) at least one first electrode ( 116 ) and at least one second electrode ( 118 ), wherein the first electrode ( 116 ) and the second electrode ( 118 ) via at least one solid electrolyte ( 120 ), the device ( 114 ) at least one control ( 122 ), wherein the control ( 122 ) is arranged to perform a method according to any one of the preceding claims.

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