EP1565733A2 - Gas measuring device and method for measuring gas with compensation of disturbances - Google Patents

Gas measuring device and method for measuring gas with compensation of disturbances

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Publication number
EP1565733A2
EP1565733A2 EP03785546A EP03785546A EP1565733A2 EP 1565733 A2 EP1565733 A2 EP 1565733A2 EP 03785546 A EP03785546 A EP 03785546A EP 03785546 A EP03785546 A EP 03785546A EP 1565733 A2 EP1565733 A2 EP 1565733A2
Authority
EP
European Patent Office
Prior art keywords
gas
sensor
value
measuring device
pass filter
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP03785546A
Other languages
German (de)
French (fr)
Inventor
Kurt Ingrisch
Markus Niemann
Gerald Hamm
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Paragon AG
Original Assignee
Paragon AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Paragon AG filed Critical Paragon AG
Publication of EP1565733A2 publication Critical patent/EP1565733A2/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
    • G01N27/122—Circuits particularly adapted therefor, e.g. linearising circuits

Definitions

  • the invention relates to a gas measuring device with interference compensation according to the preamble of patent claim 1 and a method with interference compensation according to the preamble of patent claim 10.
  • Semiconductor sensors are used in the automotive sector to measure the gas concentration, in particular the concentration of carbon monoxide CO, nitrogen oxide NO and hydrocarbons CxHy.
  • the majority of semiconductor sensors are conductivity sensors based on Sn02. The measurement result can be used, for example, to open or close a recirculation air flap in a motor vehicle.
  • the sensors mentioned above are also distinguished by good sensitivity to the gas to be measured.
  • Nachteilhafter- however, they also exhibit a number of cross-effects which complicate the signal evaluation.
  • Reducing gases such as carbon monoxide
  • oxidizing gases such as nitrogen dioxide
  • the strong adsorption of water on the surface of the Sn02 semiconductor sensor leads to a disruptive cross effect.
  • the bound water significantly increases the conductivity of the gas-sensitive Sn02 layer.
  • the amount of water adsorbed by the sensitive Sn02 layer is largely dependent on the temperature. The change in the conductivity of the Sn02 layer is therefore strongly temperature-dependent.
  • the semiconductor sensor binds much larger amounts of water than at higher temperatures.
  • the amount of water adsorbed can be demonstrated by means of a TDS measurement. After a certain time, a temperature-dependent equilibrium between adsorbed and desorbed water is established. When there is a change in temperature, the time constant until a new equilibrium is reached is between a few minutes and a few hours. The time constant depends on the previous environmental conditions.
  • This effect is particularly disruptive in the phase after switching on or starting up the semiconductor sensor.
  • the equilibrium of saturation between adsorbed and desorbed water that is valid for this temperature is established during this time. This equilibrium is also referred to below as saturation equilibrium.
  • the sensor In order to be able to carry out gas measurements with the sensor, the sensor is brought to an operating temperature of approx. 330 ° C. The higher temperature of 330 ° C compared to the storage temperature means that water is desorbed until a new saturation equilibrium is formed. During this time, this has the consequence that the conductivity decreases continuously, even if the gas concentration remains constant. The resulting decrease in conductivity correlates with a change in conductivity such as is caused by a large increase in the NO concentration.
  • the gas measuring device according to the invention with interference compensation offers the advantage over the prior art of a high measuring accuracy and immediately after the gas measuring device has been put into operation, that is to say after it has been switched on. was switched.
  • the gas measuring device with interference compensation comprises a gas sensor for generating a gas concentration-dependent measurement signal, which may have an interference component.
  • a high-pass filter with an adjustable cut-off frequency is connected downstream of the gas sensor.
  • the limit frequency can be specified by means of a selection unit depending on the interference component.
  • the method according to the invention for gas measurement with interference compensation with the features specified in claim 10 has the advantage over the prior art that the measurement can be carried out with high accuracy as soon as the gas measuring device is switched on.
  • the method has the following steps. By means of a gas sensor, a measurement signal that is dependent on the gas concentration is generated, which may have an interference component.
  • the measurement signal is then filtered by means of a high-pass filter with an adjustable cut-off frequency, the cut-off frequency being specified by a selection unit as a function of the interference component.
  • a low-pass filter is provided, which is connected between the evaluation unit and the gas sensor.
  • a computing unit is between the evaluation unit and the Low pass filter switched.
  • the computing unit is provided for calculating the slope of a filter output signal originating from the low-pass filter.
  • the selection unit is connected on the output side to a control input of the high-pass filter and is designed such that a value can be selected based on the slope of the filter output signal by means of which the cut-off frequency of the high-pass filter can be set.
  • the selection unit is designed in such a way that a first filter value can be specified if the difference between the sensor value and a target value exceeds a limit value.
  • a second filter value can be specified if the difference between the sensor value and the target value lies within a certain range.
  • a third filter value can be specified if the sensor value corresponds to the target value.
  • the first, the second and the third filter value are time constants.
  • a comparator is advantageously connected to the high-pass filter. This allows the filtered signal to be compared to a threshold value.
  • the gas sensor is an Sn02 gas sensor.
  • the gas sensor can be designed such that nitrogen oxide can be measured with it.
  • FIG. 1 shows the basic procedure for compensating for the disturbance in the form of a signal flow diagram.
  • Figure 2 shows in the form of a block diagram the basic structure of the gas measuring device according to the invention.
  • FIG. 3 shows the course of several signals as they can occur in the gas measuring device according to the invention.
  • a NO sensor 1 supplies a sensor sensor at its output 1.1, also referred to below as a sensor output.
  • signal Sl which in addition to the measured gas concentration can also have an interference component due to a shift in the saturation equilibrium.
  • the sensor signal S1 is evaluated by means of a run-in compensation 2 to determine whether an interference signal component caused by desorption is present and, if appropriate, how high it is. If necessary, the interference signal component in the sensor signal S1 is compensated.
  • a sensor signal S2 which has been freed from the interference signal component is present at the output of the inlet compensation 2.2 and is compared with a threshold value. For this purpose, the threshold value evaluation 3 is provided.
  • a control signal in the form of a switching signal 4 which controls a recirculating air flap, not shown in the figures.
  • the structure of the inlet compensation 2 is shown in FIG. 2 in the form of a further block diagram.
  • the NO sensor 1 is connected to a low-pass filter 5, which filters the sensor signal S1.
  • the low-pass filter 5 has a time constant tv.
  • the filtered sensor signal S5 is present at the output of the low pass 5.
  • the filtered sensor signal S5 is processed further by means of a computing unit 6.
  • the slope S ' is calculated from the filtered sensor signal S5.
  • the slope S ' is fed to a unit 12 for specifying a time constant TH.
  • the unit 12 for setting the time constant TH calculated from those pitch S 'and a parameter a is the time constant TH ⁇ .
  • a time constant TH is calculated from the sensor signal S1 of the NO sensor 1, that time constant in normal operation corresponds, this is fed to the high-pass filter 13 via its control input 13.1. This is the case if the conductance NO-S of sensor 1 lies between p2 * NO limit and NO limit. This is determined by means of a decision unit 7.
  • the time constant TH Tl is switched to the control input 13.1 of the high pass 13. This is only the case at the start of the running-in process of sensor 1. In this case, a large slope S 'of the sensor signal S1 is to be expected. Since no data is available on the start-up of sensor 1 regarding the course of signal S1 until the saturation equilibrium is reached, • based on experience, the difference between the conductance of NO sensor 1 and the limit value NO limit is fixed won cutoff frequency started.
  • the values are stored in a table, hereinafter also referred to as the look-up table. They are updated depending on the current difference during the running-in process. Tl and T2 are adjusted due to the system.
  • the time constant TH T2 is applied to control input 13.1 of the High pass 13 placed. From the slope S 'of the filtered sensor signal S5, the interference amplitude of the signal S2 can be estimated after the high-pass filter 13.
  • the time constant TH for the high pass 13 is set such that a defined limited interference amplitude of the signal S2 occurs at the output of the high pass filter 13. The interference amplitude is selected so that a recirculation damper that can be controlled with signal S2 is not inadvertently closed.
  • the running-in process of the sensor 1 is a monotonous process, which ends when the saturation equilibrium, that is to say the balance between adsorption and desorption of the water, has been reached by the NO sensor 1.
  • the signal form of the logarith ized resistance Ine can be approximated by the function from the time of switching on
  • the measurement signal has a useful signal component and an interference signal component, the latter, due to the desorption of water, having the characteristic of a PTI step function.
  • PT1 a First order delay element understood. In the frequency spectrum of this step function, there are high frequency components at the beginning, which decrease and disappear with increasing time.
  • the interference signal component hereinafter also referred to as interference signal, which is caused by the desorption of water, can therefore be suppressed at the beginning by the high-pass filter 13 with a suitably high selected cutoff frequency for a certain period of time.
  • the high frequency components in the interference signal decrease. This is taken into account by continuously lowering the cut-off frequency of the high-pass filter 13.
  • the cut-off frequency of the high-pass filter 13 remains constant and the initially attenuated measurement signal, which is now a pure useful signal, comes into its own.
  • the signal that can be tapped at the output of the high pass 13 is used to control the recirculation flap.
  • the approximate knowledge about the running-in of the NO sensor 1 is used.
  • a conductivity is established which is referred to as the NO limit.
  • the conductivity of the NO limit thus occurs when there is a balance between desorption and adsorption at the operating temperature of the NO sensor ' 1.
  • the value of the conductivity must be approximately determined by filtering the sensor signal S1 using a low-pass filter 5.
  • the time constant tv is about 30 minutes. The conductivity value obtained in this way is constantly stored in a non-volatile memory during operation.
  • the slope S 'of the sensor signal S1 is shortly after startup of the NO sensor 1, as mentioned, strongly dependent on the storage period of the NO sensor 1. However, the storage period can be provided in the control unit only with great effort Observe the sensor signal Sl for a certain time after switching on the sensor 1 and then conclude that the sensor signal Sl continues. In order to minimize the influence of briefly high gas concentrations, the sensor signal S1 is first filtered by means of the low pass 5 and then its slope S 1 is determined.
  • the amplitude of the interference signal component due to the shift in equilibrium, drops monotonously in the course of the running-in process.
  • the experimental parameters a, b and T depend on the storage period of the sensor 1 ′′ and the sensor itself. These parameters can therefore not be determined in experiments and kept in the run-in compensation.
  • the different signal dynamics between a signal change generated by the gas to be measured and a signal change generated by the desorption of water are used.
  • a change in the concentration of the gas to be measured usually has a time constant between 2 and 30 s.
  • the interference signal caused by the desorption of water has a time constant between a few minutes and several hours, depending on the previous storage period of the sensor.
  • FIG. 3 shows a number of signal curves using a time diagram.
  • the time is plotted on the x-axis of the diagram and the amplitude on the y-axis of the diagram. It can be seen that the amplitude of the —not compensated NO sensor signal S1 initially increases strongly and only slightly increases later.
  • the course of the compensated sensor signal is also shown in FIG. 3 and provided with the reference symbol S2.
  • the threshold value SW, the filtered signal 23, the control signal 24 for the air recirculation flap and the time constant 26 are also shown in FIG. 3.
  • the growing time constant 26 shows how the cut-off frequency of the high-pass filter is adjusted by leasing lower values and thus the system becomes more sensitive to gas pulses.

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  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
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Abstract

Disclosed is a gas measuring device which comprises compensation of disturbances and offers high accuracy of measurement immediately after being activated. Said gas measuring device is provided with a gas sensor (1) for generating a measuring signal (S1) that depends on the gas concentration and can have a spurious component while a high-pass filter (13) having an adjustable limiting frequency is mounted downstream of said gas sensor (1). The limiting frequency can be predefined according to the spurious component by means of a selection unit.

Description

Gas ess orrichtung -und Verfahren mit StörkompensationGas metering device and method with interference compensation

Technisches GebietTechnical field

Die Erfindung betrifft eine Gasmessvorrichtung mit Störkompensation gemäß dem Oberbegriff des Patent- anspruches 1 und ein Verfahren mit Störkompensation gemäß dem Oberbegriff des Patentanspruches 10.The invention relates to a gas measuring device with interference compensation according to the preamble of patent claim 1 and a method with interference compensation according to the preamble of patent claim 10.

Stand der TechnikState of the art

Zur Messung der Gaskonzentration und zwar insbesondere der Konzentration von Kohlenmonoxid CO, Stickoxid NO und Kohlenwasserstoffen CxHy werden im Automobilbereich wegen der geringen Kosten Halblei- tersensoren eingesetzt. Die Mehrzahl der Halbleitersensoren sind Leitfähigkeitssensoren auf der Basis von Sn02. Das Messergebnis kann beispielsweise dazu dienen, eine Umluftklappe im einem Kraftfahrzeug zu öffnen oder zu schließen.Semiconductor sensors are used in the automotive sector to measure the gas concentration, in particular the concentration of carbon monoxide CO, nitrogen oxide NO and hydrocarbons CxHy. The majority of semiconductor sensors are conductivity sensors based on Sn02. The measurement result can be used, for example, to open or close a recirculation air flap in a motor vehicle.

Die oben genannten Sensoren zeichnen sich neben den geringen Kosten auch durch eine gute Empfindlichkeit für das zu messende Gas aus. Nachteilhafter- weise v/eisen sie aber auch eine Reihe von Queref- fekte auf, welche die Signalauswertung erschweren. Reduzierende Gase, wie beispielsweise Kohlenmono- xid, verursachen eine Erhöhung der Leitfähigkeit des Halbleitersensors. Oxidierende Gase, wie beispielsweise Stickstoffdioxid, verursachen hingegen eine Verringerung der Leitfähigkeit des Halbleiter- sensors. Zudem führt die starke Adsorption von Wasser an der Oberfläche des Sn02-Halbleitersensors zu einem störenden Quereffekt. Das gebundene Wasser erhöht die Leitfähigkeit der gassensitiven Sn02- Schicht signifikant. Die von der sensitiven Sn02- Schicht adsorbierte Menge an Wasser ist in erheblichem Maße von der Temperatur abhängig. Damit ist auch die Änderung der Leitfähigkeit der Sn02- Schicht stark temperaturabhängig. Bei einer Temperatur unterhalb von 200 °C werden vom Halbleitersensor wesentlich größere Mengen an Wasser gebunden als bei höheren Temperaturen. Die adsorbierte Was- sermenge lässt sich mittels einer TDS-Messung nachweisen. Nach einer gewissen Zeit stellt sich ein von der Temperatur abhängiges Gleichgewicht zwischen adsorbiertem und desorbiertem Wasser ein. Bei einem Temperaturwechsel liegt die Zeitkonstante bis zum Erreichen eines neuen Gleichgewichts zwischen wenigen Minuten und einigen Stunden. Die Zeitkonstante hängt dabei von den vorherigen Umgebungsbedingungen ab.In addition to the low costs, the sensors mentioned above are also distinguished by good sensitivity to the gas to be measured. Nachteilhafter- however, they also exhibit a number of cross-effects which complicate the signal evaluation. Reducing gases, such as carbon monoxide, cause an increase in the conductivity of the semiconductor sensor. In contrast, oxidizing gases, such as nitrogen dioxide, cause a reduction in the conductivity of the semiconductor sensor. In addition, the strong adsorption of water on the surface of the Sn02 semiconductor sensor leads to a disruptive cross effect. The bound water significantly increases the conductivity of the gas-sensitive Sn02 layer. The amount of water adsorbed by the sensitive Sn02 layer is largely dependent on the temperature. The change in the conductivity of the Sn02 layer is therefore strongly temperature-dependent. At a temperature below 200 ° C, the semiconductor sensor binds much larger amounts of water than at higher temperatures. The amount of water adsorbed can be demonstrated by means of a TDS measurement. After a certain time, a temperature-dependent equilibrium between adsorbed and desorbed water is established. When there is a change in temperature, the time constant until a new equilibrium is reached is between a few minutes and a few hours. The time constant depends on the previous environmental conditions.

Dieser Effekt tritt insbesondere in der Phase nach dem Einschalten oder in Betrieb nehmen des Halblei- tersensors besonders störend in Erscheinung. Wird der Sensor bei Umgebungstemperatur über mehrere Wochen gelagert, stellt sich im Verlauf dieser Zeit das für diese Temperatur geltende Gleichgewicht an Sättigung zwischen adsorbiertem und desor- biertem Wasser ein. Dieses Gleichgewicht wird im folgenden auch als Sättigungsgleichgewicht bezeichnet. Um mit dem Sensor Gasmessungen durchführen zu können, wird der Sensor auf eine Betriebstemperatur von ca. 330 °C gebracht. Die gegenüber der Lager- temperatur erhöhte Temperatur von 330 °C führt dazu, dass solange Wasser desorbiert wird, bis sich ein neues Sättigungsgleichgewicht gebildet hat. Dies hat während dieser Zeit zur Folge, dass die Leitfähigkeit kontinuierlich sinkt, auch wenn die Gaskonzentration konstant bleibt. Die daraus resultierende Abnahme der Leitfähigkeit korreliert mit einer Leitfähigkeitsänderung, wie sie von einem großen Anstieg der NO-Konzentration hervorgerufen wird.This effect is particularly disruptive in the phase after switching on or starting up the semiconductor sensor. If the sensor is stored at ambient temperature for several weeks, the equilibrium of saturation between adsorbed and desorbed water that is valid for this temperature is established during this time. This equilibrium is also referred to below as saturation equilibrium. In order to be able to carry out gas measurements with the sensor, the sensor is brought to an operating temperature of approx. 330 ° C. The higher temperature of 330 ° C compared to the storage temperature means that water is desorbed until a new saturation equilibrium is formed. During this time, this has the consequence that the conductivity decreases continuously, even if the gas concentration remains constant. The resulting decrease in conductivity correlates with a change in conductivity such as is caused by a large increase in the NO concentration.

Dies hat zur Folge, dass die Messung der NO- Konzentration während der Zeit, während der sich ein neues Sättigungsgleichgewicht einstellt, mit einem erheblichen Messfehler behaftet ist.The consequence of this is that the measurement of the NO concentration during the time during which a new saturation equilibrium is established is associated with a considerable measurement error.

Darstellung der ErfindungPresentation of the invention

Die erfindungsgemäße Gasmessvorrichtung mit Stör- kompensation mit den in Patentanspruch 1 angegebenen Merkmalen bietet gegenüber dem Stand der Technik den Vorteil einer hohen Messgenauigkeit und zwar umgehend nachdem die Gasmessvorrichtung in Betrieb genommen wurde, das heißt nachdem sie einge- schaltet wurde. Dies wird dadurch erreicht, dass die Gasmessvorrichtung mit Störkompensation einen Gassensor zum Erzeugen eines gaskonzentrationsab- hängigen Messsignals, welches einen Störanteil auf- weisen kann, umfasst. Dem Gassensor ist ein Hochpassfilter mit einstellbarer Grenzfrequenz nachgeschaltet. Die Grenzfrequenz ist dabei mittels einer Auswahleinheit abhängig vom Störanteil vorgebbar.The gas measuring device according to the invention with interference compensation with the features specified in patent claim 1 offers the advantage over the prior art of a high measuring accuracy and immediately after the gas measuring device has been put into operation, that is to say after it has been switched on. was switched. This is achieved in that the gas measuring device with interference compensation comprises a gas sensor for generating a gas concentration-dependent measurement signal, which may have an interference component. A high-pass filter with an adjustable cut-off frequency is connected downstream of the gas sensor. The limit frequency can be specified by means of a selection unit depending on the interference component.

Das erfindungsgemäße Verfahren zur Gasmessung mit Störkompensation mit den in Patentanspruch 10 angegebenen Merkmalen hat gegenüber dem Stand der Technik den Vorteil, dass die Messung bereits unmittelbar nach dem Einschalten der Gasmesseinrichtung mit hoher Genauigkeit erfolgen kann. Das Verfahren weist dazu folgende Schritte auf. Mittels eines Gassensors wird ein von der Gaskonzentration abhängiges Messsignal erzeugt, welches einen Störanteil aufweisen kann. Anschließend wird das Messsignal mittels eines Hochpassfilters mit einstellbarer Grenzfrequenz gefiltert, wobei die Grenzfrequenz von einer Auswahleinheit abhängig vom Störanteil vorgegeben wird.The method according to the invention for gas measurement with interference compensation with the features specified in claim 10 has the advantage over the prior art that the measurement can be carried out with high accuracy as soon as the gas measuring device is switched on. The method has the following steps. By means of a gas sensor, a measurement signal that is dependent on the gas concentration is generated, which may have an interference component. The measurement signal is then filtered by means of a high-pass filter with an adjustable cut-off frequency, the cut-off frequency being specified by a selection unit as a function of the interference component.

Vorteilhafte Weiterbildungen der Erfindung ergeben sich aus den in den abhängigen Patentansprüchen angegebenen Merkmalen.Advantageous developments of the invention result from the features specified in the dependent patent claims.

So ist in einer Weiterbildung der Erfindung ein Tiefpassfilter vorgesehen, das zwischen die Auswerteeinheit und den Gassensor geschaltet ist.In a further development of the invention, a low-pass filter is provided, which is connected between the evaluation unit and the gas sensor.

In einer Weiterbildung der Erfindung ist eine Recheneinheit zwischen die Auswerteeinheit und das Tiefpassfilter geschaltet. Die Recheneinheit ist zur Berechnung der Steigung eines vom Tiefpassfilter stammenden Filterausgangssignals vorgesehen.In a development of the invention, a computing unit is between the evaluation unit and the Low pass filter switched. The computing unit is provided for calculating the slope of a filter output signal originating from the low-pass filter.

In einer zusätzlichen Weiterbildung der Erfindung ist die Auswahleinheit ausgangsseitig mit einem Steuereingang des Hochpassfilters verbunden und derart ausgebildet, dass damit anhand der Steigung des Filterausgangssignals ein Wert auswählbar ist, mittels welchem die Grenzfrequenz des Hochpassfilters einstellbar ist.In an additional development of the invention, the selection unit is connected on the output side to a control input of the high-pass filter and is designed such that a value can be selected based on the slope of the filter output signal by means of which the cut-off frequency of the high-pass filter can be set.

In einer Ausführungsform der erfindungsgemäßen Gasmessvorrichtung ist die Auswahleinheit derart aus- gebildet, dass damit ein erster Filterwert vorgebbar ist, wenn die Differenz zwischen dem Sensorwert und einem Sollwert einen Grenzwert überschreitet. Zudem ist ein zweiter Filterwert vorgebbar, wenn die Differenz zwischen dem Sensorwert und dem Soll- wert innerhalb eines bestimmten Bereichs liegt. Schließlich ist ein dritter Filterwert vorgebbar, wenn der Sensorwert dem Sollwert entspricht.In one embodiment of the gas measuring device according to the invention, the selection unit is designed in such a way that a first filter value can be specified if the difference between the sensor value and a target value exceeds a limit value. In addition, a second filter value can be specified if the difference between the sensor value and the target value lies within a certain range. Finally, a third filter value can be specified if the sensor value corresponds to the target value.

In einer weiteren Ausführungsform der erfindungsge- mäßen Gasmessvorrichtung sind der erste, der zweite und der dritte Filterwert Zeitkonstanten.In a further embodiment of the gas measuring device according to the invention, the first, the second and the third filter value are time constants.

Vorteilhafter Weise ist bei der erfindungsgemäßen Gasmessvorrichtung dem Hochpässfilter ein Kompara- tor nachgeschaltet. Damit kann das gefilterte Signal mit einem Schwellenwert verglichen werden. Bei einer Weiterbildung der erfindungsgemäßen Gas- messvorrichtung ist der Gassensor ein Sn02- Gassensor .In the gas measuring device according to the invention, a comparator is advantageously connected to the high-pass filter. This allows the filtered signal to be compared to a threshold value. In a further development of the gas measuring device according to the invention, the gas sensor is an Sn02 gas sensor.

Schließlich kann bei einer weiteren Ausführungsfor- men der erfindungsgemäßen Gasmessvorrichtung der Gassensor derart ausgebildet sein, dass damit Stickoxid messbar ist.Finally, in a further embodiment of the gas measuring device according to the invention, the gas sensor can be designed such that nitrogen oxide can be measured with it.

Kurze Beschreibung der ZeichnungenBrief description of the drawings

Im folgenden wird die Erfindung anhand von drei Figuren weiter erläutert.The invention is explained in more detail below with reference to three figures.

Figur 1 zeigt in Form eines Signalflussdiagramm.es die prinzipielle Vorgehensweise zur Kompensation der Störung.FIG. 1 shows the basic procedure for compensating for the disturbance in the form of a signal flow diagram.

Figur 2 zeigt in Form eines Blockdiagramms den prinzipiellen Aufbau der erfindungsgemäßen Gasmessvorrichtung .Figure 2 shows in the form of a block diagram the basic structure of the gas measuring device according to the invention.

Figur 3 zeigt den Verlauf mehrerer Signale, wie sie bei der erfindungsgemäßen Gasmessvorrichtung auftreten können.FIG. 3 shows the course of several signals as they can occur in the gas measuring device according to the invention.

Wege zur Ausführung der ErfindungWays of Carrying Out the Invention

In Figur 1 ist der prinzipielle Verlauf des Signalflusses der Gasmessvorrichtung gezeigt. Ein NO- Sensor 1 liefert an seinem Ausgang 1.1, im folgenden auch als Ξensorausgang bezeichnet, ein Sensor- signal Sl, welches neben der gemessenen Gaskonzentration auch einen Störanteil, bedingt durch eine Verschiebung des Sättigungsgleichgewichts, aufweisen kann. Das Sensorsignal Sl wird mittels einer Einlaufkompensation 2 dahingehend ausgewertet, ob ein durch Desorbtion bedingter Störsignalanteil vorhanden und gegebenenfalls wie hoch dieser ist. Gegebenenfalls wird der Störsignalanteil im Sensorsignal Sl kompensiert. Am Ausgang der Einlaufkom- pensation 2.2 liegt ein vom Störsignalanteil befreites Sensorsignal S2 an, welches mit einem Schwellenwert verglichen wird. Dazu ist die Schwellenwert-Auswertung 3 vorgesehen. Am Ende liegt ein Steuersignal in Form eines Schaltsignals 4 vor, das eine, in den Figuren' nicht dargestellte Umluftklappe steuert.The basic course of the signal flow of the gas measuring device is shown in FIG. A NO sensor 1 supplies a sensor sensor at its output 1.1, also referred to below as a sensor output. signal Sl, which in addition to the measured gas concentration can also have an interference component due to a shift in the saturation equilibrium. The sensor signal S1 is evaluated by means of a run-in compensation 2 to determine whether an interference signal component caused by desorption is present and, if appropriate, how high it is. If necessary, the interference signal component in the sensor signal S1 is compensated. A sensor signal S2 which has been freed from the interference signal component is present at the output of the inlet compensation 2.2 and is compared with a threshold value. For this purpose, the threshold value evaluation 3 is provided. At the end there is a control signal in the form of a switching signal 4 which controls a recirculating air flap, not shown in the figures.

Der Aufbau der Einlaufkompensation 2 wird in Figur 2 in Form eines weiteren Blockdiagramms gezeigt. Der NO-Sensor 1 ist ausgangsseitig mit einem Tief- pass 5 verbunden, welcher das Sensorsignal Sl filtert. Das Tiefpassfilter 5 weist eine Zeitkonstante tv auf. Am Ausgang des Tiefpasses 5 liegt das gefilterte Sensorsignal S5 an. Das gefilterte Sensor- signal S5 wird mittels einer Recheneinheit 6 weiterverarbeitet. Dazu wird aus dem gefilterten Sen- sorsignal S5 die Steigung S' berechnet. Anschließend wird die Steigung S' einer Einheit 12 zur Vorgabe einer Zeitkonstante TH zugeführt. Die Einheit 12 zur Vorgabe der Zeitkonstante TH berechnet aus derer Steigung S' und einem Parameter a die Zeit¬ konstante TH. Falls sich aus dem Sensorsignal Sl des NO-Sensors 1 eine Zeitkonstante TH berechnet, welche, derjenigen Zeitkonstante im Normalbetrieb entspricht, wird diese dem Hochpassfilter 13 über dessen Steuereingang 13.1 zugeführt. Das ist der Fall, wenn der Leitwert NO-S des Sensors 1 zwischen p2*NO-Grenz und NO-Grenz liegt. Dies wird mittels einer Entscheidungseinheit 7. festgestellt .The structure of the inlet compensation 2 is shown in FIG. 2 in the form of a further block diagram. On the output side, the NO sensor 1 is connected to a low-pass filter 5, which filters the sensor signal S1. The low-pass filter 5 has a time constant tv. The filtered sensor signal S5 is present at the output of the low pass 5. The filtered sensor signal S5 is processed further by means of a computing unit 6. For this purpose, the slope S 'is calculated from the filtered sensor signal S5. Then the slope S 'is fed to a unit 12 for specifying a time constant TH. The unit 12 for setting the time constant TH calculated from those pitch S 'and a parameter a is the time constant TH ¬. If a time constant TH is calculated from the sensor signal S1 of the NO sensor 1, that time constant in normal operation corresponds, this is fed to the high-pass filter 13 via its control input 13.1. This is the case if the conductance NO-S of sensor 1 lies between p2 * NO limit and NO limit. This is determined by means of a decision unit 7.

Falls mittels der Entscheidungseinheit 7 jedoch festgestellt wird, dass die Differenz des aktuellen Leitwerts des NO-Sensors 1 gegenüber einem Grenz- wert NO-Grenz zu groß ist, das heißt der Leitwert NO-S des Sensors 1 ist kleiner als pl*NO-Grenz, wird auf den Steuereingang 13.1 des Hochpasses 13 die Zeitkonstante TH = Tl geschaltet. Dies ist ausschließlich zu Beginn des Einlaufvorgangs des Sen- sors 1 der Fall. In diesem Fall ist mit einer großen Steigung S' des Sensorsignals Sl zu rechnen. Da bei der Inbetriebnahme des Sensors 1 noch keine Daten über den Verlauf des Signals Sl bis zum Erreichen des Sättigungsgleichgewichts vorliegen, • wird abhängig von der Differenz zwischen dem Leitwert des NO-Sensors 1 und dem Grenzwert NO-Grenz mit einer festen, aus der Erfahrung gewonnen Grenzfrequenz gestartet. Die Werte sind in einer Tabelle, im folgenden auch als Look-up-Tabelle bezeichnet, hinterlegt. Sie werden abhängig von der aktuellen Differenz während des Einlaufvorgangs aktualisiert. Tl und T2 werden systembedingt angepasst.However, if it is determined by the decision unit 7 that the difference between the current conductance of the NO sensor 1 and a limit value NO limit is too large, that is, the conductance NO-S of the sensor 1 is smaller than p1 * NO limit , the time constant TH = Tl is switched to the control input 13.1 of the high pass 13. This is only the case at the start of the running-in process of sensor 1. In this case, a large slope S 'of the sensor signal S1 is to be expected. Since no data is available on the start-up of sensor 1 regarding the course of signal S1 until the saturation equilibrium is reached, • based on experience, the difference between the conductance of NO sensor 1 and the limit value NO limit is fixed won cutoff frequency started. The values are stored in a table, hereinafter also referred to as the look-up table. They are updated depending on the current difference during the running-in process. Tl and T2 are adjusted due to the system.

Falls die Differenz des aktuellen Leitwerts des NO- Sensors 1 gegenüber dem Grenzwert NO-Grenz klein ist, das heißt der Leitwert NO-S des Sensors 1 ist kleiner als p2*NO-Grenz, wird die Zeitkonstante TH = T2 auf den Steuereingang 13.1 des Hochpasses 13 gelegt. Aus der Steigung S' des gefilterten Sensor- signals S5 kann die Störamplitude des Signals S2 nach dem Hochpassfilter 13 abgeschätzt werden. Die Zeitkonstante TH für den Hochpass 13 wird so eingestellt, dass eine definierte begrenzte Störamplitu- de des Signals S2 am Ausgang des Hochpassfilters 13 auftritt. Die Störamplitude wird so gewählt, dass eine mit dem Signal S2 steuerbare Umluftklappe nicht unbeabsichtigt geschlossen wird.If the difference between the current conductance of NO sensor 1 and the limit value NO limit is small, that is, the conductance NO-S of sensor 1 is less than p2 * NO limit, the time constant TH = T2 is applied to control input 13.1 of the High pass 13 placed. From the slope S 'of the filtered sensor signal S5, the interference amplitude of the signal S2 can be estimated after the high-pass filter 13. The time constant TH for the high pass 13 is set such that a defined limited interference amplitude of the signal S2 occurs at the output of the high pass filter 13. The interference amplitude is selected so that a recirculation damper that can be controlled with signal S2 is not inadvertently closed.

Der Einlaufvorgang des Sensors 1 ist ein monotoner Vorgang, der dann beendet ist, wenn das Sättigungsgleichgewicht, also das Gleichgewicht zwischen Adsorption und Desorbtion des Wassers durch den NO- Sensor 1 erreicht ist.The running-in process of the sensor 1 is a monotonous process, which ends when the saturation equilibrium, that is to say the balance between adsorption and desorption of the water, has been reached by the NO sensor 1.

Die Signalform des logarith ierten Widerstands Ine lässt sich ab dem Einschaltzeitpunkt in erster Näherung durch die FunktionThe signal form of the logarith ized resistance Ine can be approximated by the function from the time of switching on

Ine = a • (1 - eτ) + bIne = a • (1 - e τ ) + b

darstellen, wobei t die Zeit, a ein experimenteller Parameter und der Übertra- gungsfaktor zwischen der Steigung S' und der Grenzfrequenz, b ein experimenteller Parameter und T ein experimenteller Parameter ist.represent, where t is time, a is an experimental parameter and the transmission factor between the slope S 'and the cutoff frequency, b is an experimental parameter and T is an experimental parameter.

Das Messsignal weist einen Nutzsignalanteil und einen Störsignalanteil auf, wobei letzterer, bedingt durch die Desorbtion von Wasser, die Charakteristik einer PTl-Sprungfunktion hat. Unter PT1 wird ein Verzögerungsglied erster Ordnung verstanden. Im Frequenzspektrum dieser Sprungfunktion herrschen zu Beginn hohe Frequenzanteile vor, die mit zunehmender Zeit abnehmen und verschwinden.The measurement signal has a useful signal component and an interference signal component, the latter, due to the desorption of water, having the characteristic of a PTI step function. Under PT1 a First order delay element understood. In the frequency spectrum of this step function, there are high frequency components at the beginning, which decrease and disappear with increasing time.

Der Störsignalanteil, im Folgenden auch als Störsignal bezeichnet, welcher durch die Desorbtion von Wasser bedingt ist, lässt sich daher zu Beginn durch das Hochpassfilter 13 mit einer geeignet hoch gewählten Grenzfrequenz für eine bestimmte Zeitdauer unterdrücken. Bei fortschreitendem EinlaufVorgang nehmen die hohen Frequenzanteile im Störsignal ab. Dem wird durch eine kontinuierliche Absenkung der Grenzfrequenz des Hochpassfilters 13 Rechnung getragen. Sobald ein Gleichgewicht zwischen Adsorption und Desorbtion erreicht ist, bleibt die Grenzfrequenz des Hochpassfilters 13 konstant und das anfangs gedämpfte Messsignal, welches nun ein reines Nutzsignal ist, kommt voll zur Geltung. Das am Ausgang des Hochpasses 13 abgreifbare Signal dient zur Steuerung der Umluftklappe.The interference signal component, hereinafter also referred to as interference signal, which is caused by the desorption of water, can therefore be suppressed at the beginning by the high-pass filter 13 with a suitably high selected cutoff frequency for a certain period of time. As the running-in process progresses, the high frequency components in the interference signal decrease. This is taken into account by continuously lowering the cut-off frequency of the high-pass filter 13. As soon as a balance between adsorption and desorption is reached, the cut-off frequency of the high-pass filter 13 remains constant and the initially attenuated measurement signal, which is now a pure useful signal, comes into its own. The signal that can be tapped at the output of the high pass 13 is used to control the recirculation flap.

Um die Grenzfrequenz für den Hochpass 13 dynamisch anpassen zu können, wird die näherungsweise Kennt- nis über das Einlaufen des NO-Sensors 1 herangezogen.In order to be able to dynamically adapt the cut-off frequency for the high-pass filter 13, the approximate knowledge about the running-in of the NO sensor 1 is used.

Nach längerem Betrieb des NO-Sensors 1, ohne dass dieser dem zu messenden Gas ausgesetzt ist, stellt sich eine Leitfähigkeit ein, die mit NO-Grenz bezeichnet wird. Die Leitfähigkeit NO-Grenz stellt sich somit bei einem Gleichgewicht zwischen Desorbtion und Adsorption bei der Betriebstemperatur des NO-Sensors ' 1 ein. In der Praxis tritt jedoch der Fall, daß der NO-Sensor 1 dem zu messenden Gas nicht ausgesetzt ist, kaum auf. Daher muss der Wert der Leitfähigkeit bei Erreichen des Gleichgewichts dadurch näherungsweise bestimmt werden, indem das Sensorsignal Sl mittels eines Tiefpasses 5 gefiltert wird. Die Zeitkonstante tv liegt dabei bei ca. 30 min. Der so gewonnene Wert für die Leitfähigkeit wird im Betrieb ständig in einem nichtflüchtigen Speicher abgelegt.After prolonged operation of the NO sensor 1 without exposing it to the gas to be measured, a conductivity is established which is referred to as the NO limit. The conductivity of the NO limit thus occurs when there is a balance between desorption and adsorption at the operating temperature of the NO sensor ' 1. In practice, however, the Case that the NO sensor 1 is not exposed to the gas to be measured, hardly. Therefore, when the equilibrium is reached, the value of the conductivity must be approximately determined by filtering the sensor signal S1 using a low-pass filter 5. The time constant tv is about 30 minutes. The conductivity value obtained in this way is constantly stored in a non-volatile memory during operation.

Die Steigung S' des Sensorsignals Sl ist kurz nach Inbetriebnahme des NO-Sensors 1, wie erwähnt, stark abhängig von der Lagerdauer des NO-Sensors 1. Die Lagerdauer kann in der Steuereinheit allerdings nur mit hohem Aufwand bereitgestellt werden., Ersatzweise kann man das Sensorsignal Sl für eine bestimmte Zeit nach dem Einschalten des Sensors 1 beobachten und dann auf den weiteren Verlauf des Sensorsignals Sl schließen. Um den Einfluss von kurzzeitig hohen Gaskonzentrationen zu minimieren, wird das Sensorsignal Sl zuerst mittels des Tiefpasses 5 gefiltert und dann dessen Steigung S1 bestimmt.The slope S 'of the sensor signal S1 is shortly after startup of the NO sensor 1, as mentioned, strongly dependent on the storage period of the NO sensor 1. However, the storage period can be provided in the control unit only with great effort Observe the sensor signal Sl for a certain time after switching on the sensor 1 and then conclude that the sensor signal Sl continues. In order to minimize the influence of briefly high gas concentrations, the sensor signal S1 is first filtered by means of the low pass 5 and then its slope S 1 is determined.

Die Amplitude des Störsignalanteils, bedingt durch die Verschiebung des Gleichgewichts, fällt monoton im Verlauf des EinlaufVorgangs .The amplitude of the interference signal component, due to the shift in equilibrium, drops monotonously in the course of the running-in process.

Die experimentellen Parameter a, b und T hängen von der Lagerdauer des Sensors 1 "und dem Sensor selbst ab. Diese Parameter können daher nicht in Versuchen bestimmt und bei der Einlaufkompensation vorgehalten werden. Bei der Erfindung wird die unterschiedliche Signal- dynamik zwischen einer durch das zu messende Gas erzeugten Ξignaländerung und einer durch die Desorbtion von Wasser erzeugten Signaländerung ausge- nutzt. Eine Änderung in der Konzentration des zu messenden Gases hat üblicherweise eine Zeitkonstante zwischen 2 und 30 s. Das durch die Desorbtion von- Wasser bedingte Störsignal hat, je nach vorheriger Lagerdauer des Sensors, eine Zeitkonstante zwischen einigen Minuten und mehreren Stunden.The experimental parameters a, b and T depend on the storage period of the sensor 1 ″ and the sensor itself. These parameters can therefore not be determined in experiments and kept in the run-in compensation. In the invention, the different signal dynamics between a signal change generated by the gas to be measured and a signal change generated by the desorption of water are used. A change in the concentration of the gas to be measured usually has a time constant between 2 and 30 s. The interference signal caused by the desorption of water has a time constant between a few minutes and several hours, depending on the previous storage period of the sensor.

In Figur 3 sind mittels eines Zeitdiagramms mehrere Signalverläufe gezeigt. Auf der x-Achse des Diagramms ist die Zeit und auf der y-Achse des Dia- gramms die Amplitude aufgetragen. Es ist zu erkennen, daß die Amplitude des -nicht kompensierten NO- Sensorsignals Sl anfänglich stark und später nur mehr geringfügig zunimmt. Der Verlauf des kompensierten Sensorsignals ist auch in Figur 3 gezeigt und mit dem Bezugszeichen S2 versehen. Der Schwellenwert SW, das gefilterte Signal 23, das Steuersignal 24 für die Umluftklappe und die Zeitkonstante 26 sind ebenfalls in Figur 3 gezeigt. An der wachsenden Zeitkonstante 26 ist erkennbar, wie die Grenzfrequenz des Hochpassfilters in Pachtung niedrigerer Werte verstellt wird und damit das System für Gaspulse empfindlicher wird. FIG. 3 shows a number of signal curves using a time diagram. The time is plotted on the x-axis of the diagram and the amplitude on the y-axis of the diagram. It can be seen that the amplitude of the —not compensated NO sensor signal S1 initially increases strongly and only slightly increases later. The course of the compensated sensor signal is also shown in FIG. 3 and provided with the reference symbol S2. The threshold value SW, the filtered signal 23, the control signal 24 for the air recirculation flap and the time constant 26 are also shown in FIG. 3. The growing time constant 26 shows how the cut-off frequency of the high-pass filter is adjusted by leasing lower values and thus the system becomes more sensitive to gas pulses.

Claims

Patentansprüche claims 1. Gasmessvorrichtung mit Störkompensation, mit einem Gassensor (1) zum Erzeugen eines gaskonzentra- tionsabhängigen Messsignals (Sl), welches einen Störanteil aufweisen kann, dadurch gekennzeichnet, dass dem Gassensor (1) ein Hochpassfilter (13) mit einstellbarer Grenzfrequenz nachgeschaltet ist, wobei die Grenzfrequenz mittels einer Auswahleinheit abhängig vom Störanteil vorgebbar ist.1. Gas measuring device with interference compensation, with a gas sensor (1) for generating a gas concentration-dependent measurement signal (Sl), which may have an interference component, characterized in that the gas sensor (1) is followed by a high-pass filter (13) with an adjustable cut-off frequency, whereby the limit frequency can be specified by means of a selection unit depending on the interference component. 2. Gasmessvorrichtung nach Patentanspruch 1, dadurch gekennzeichnet, dass ein Tiefpassfilter (5) vorgesehen ist, das zwischen die Auswerteeinheit und den Gassensor (1) geschaltet ist.2. Gas measuring device according to claim 1, characterized in that a low-pass filter (5) is provided, which is connected between the evaluation unit and the gas sensor (1). 3. Gasmess~vorrichtung nach Patentanspruch 2, dadurch gekennzeichnet, dass eine Recheneinheit (6) zwischen die Auswerteeinheit und das Tiefpassfilter (5) geschaltet ist und zur Berechnung der Steigung (S') eines vom Tiefpassfilter (5) stammenden Fil- terausgangssignals (S5) vorgesehen ist.3. Gas measurement ~ device according to claim 2, characterized in that a computing unit (6) is connected between the evaluation unit and the low-pass filter (5) and for calculating the slope (S ') of an originating from the low-pass filter (5) FIL terausgangssignals (S5 ) is provided. 4. Gasmessvorrichtung nach Patentanspruch 1, 2 oder 3, dadurch gekennzeichnet, dass die Auswahleinheit ausgangsseitig mit einem Steuereingang (13.1) des Hochpassfilters (13) verbunden ist und derart aus¬ gebildet ist, dass damit anhand der Steigung (S' ) des Filterausgangssignals (S5) ein Wert auswählbar ist, mittels welchem die Grenzfrequenz des Hochpassfilters (13) einstellbar ist. 4. The gas measuring device according to claim 1, 2 or 3, characterized in that the selection unit having a control input (13.1) of the high-pass filter (13) is connected on the output side, and is so formed from ¬ that so that the pitch (S ') on the basis of the filter output signal ( S5) a value can be selected by means of which the cut-off frequency of the high-pass filter (13) can be set. 5. Gasmessvorrichtung nach einem der Patentansprüche 1 bis 4, dadurch gekennzeichnet, dass die Auswahleinheit derart ausgebildet ist, dass damit ein erster Filterwert vorgebbar ist, wenn die Differenz zwischen dem Sensorwert und einem Sollwert ein Grenzwert überschreitet, dass ein zweiter Filterwert vorgebbar ist, wenn die Differenz zwischen dem Ξensorwert und dem Sollwert innerhalb eines be- stimmten Bereichs liegt und ein dritter Filterwert vorgebbar ist, wenn der Sensorwert dem Sollwert entspricht .5. Gas measuring device according to one of claims 1 to 4, characterized in that the selection unit is designed such that a first filter value can be specified if the difference between the sensor value and a target value exceeds a limit value that a second filter value can be specified if the difference between the sensor value and the target value lies within a certain range and a third filter value can be specified if the sensor value corresponds to the target value. 6. Gasmessvorrichtung nach Patentanspruch 5, da- durch gekennzeichnet, dass der erste, der zweite und der dritte Filterwert Zeitkonstanten (TH) sind.6. Gas measuring device according to claim 5, characterized in that the first, the second and the third filter value are time constants (TH). 7. Gasmessvorrichtung nach einem der Patentansprüche 1 bis 6, dadurch gekennzeichnet, dass dem Hoch- passfilter (13) ein Komparator (3) nachgeschaltet ist .7. Gas measuring device according to one of claims 1 to 6, characterized in that the high-pass filter (13) is followed by a comparator (3). 8. Gasmessvorrichtung nach einem der Patentansprüche 1 bis 7, dadurch gekennzeichnet, dass der Gas- sensor (1) ein Sn02-Gassensor ist.8. Gas measuring device according to one of the claims 1 to 7, characterized in that the gas sensor (1) is a Sn02 gas sensor. 9. Gas essvorrichtung nach einem der Patentansprüche 1 bis 8, dadurch gekennzeichnet, dass der Gassensor (1) derart ausgebildet ist, dass damit Stickoxid messbar ist.9. Gas eating device according to one of claims 1 to 8, characterized in that the gas sensor (1) is designed such that nitrogen oxide can be measured therewith. 10. Verfahren zur Gasmessung mit Störkompensation, wobei mittels eines Gassensors (1) ein gaskonzent- rationsabhängiges Messsignals (Sl) erzeugt wird, welches einen Störanteil aufweisen kann, dadurch gekennzeichnet, dass das Messsignal (Sl) mittels eines Hochpassfilters (13) mit einstellbarer Grenzfrequenz gefiltert wird, wobei die Grenzfrequenz von einer Auswahleinheit abhängig vom Störanteil vorgegeben wird. 10. Method for gas measurement with interference compensation, a gas concentration-dependent measurement signal (S1) being generated by means of a gas sensor (1), which may have an interference component, characterized in that the measurement signal (S1) is filtered by means of a high-pass filter (13) with an adjustable cutoff frequency, the cutoff frequency being specified by a selection unit as a function of the interference component.
EP03785546A 2002-11-29 2003-11-28 Gas measuring device and method for measuring gas with compensation of disturbances Withdrawn EP1565733A2 (en)

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