EP1370853A2 - Sensor for detecting gas - Google Patents

Sensor for detecting gas

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Publication number
EP1370853A2
EP1370853A2 EP02727198A EP02727198A EP1370853A2 EP 1370853 A2 EP1370853 A2 EP 1370853A2 EP 02727198 A EP02727198 A EP 02727198A EP 02727198 A EP02727198 A EP 02727198A EP 1370853 A2 EP1370853 A2 EP 1370853A2
Authority
EP
European Patent Office
Prior art keywords
sensor
signal
sensor element
sensor according
gas
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Withdrawn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
EP02727198A
Other languages
German (de)
French (fr)
Inventor
Michael Bauer
Isolde Simon
Christian Krummel
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
Robert Bosch GmbH
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 Robert Bosch GmbH, Paragon AG filed Critical Robert Bosch GmbH
Publication of EP1370853A2 publication Critical patent/EP1370853A2/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Withdrawn legal-status Critical Current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
    • G01N27/122—Circuits particularly adapted therefor, e.g. linearising circuits
    • G01N27/123—Circuits particularly adapted therefor, e.g. linearising circuits for controlling the temperature
    • G01N27/124—Circuits particularly adapted therefor, e.g. linearising circuits for controlling the temperature varying the temperature, e.g. in a cyclic manner

Definitions

  • the invention is based on a sensor for detecting gases according to the category of the independent claim.
  • a gas sensor realized in micromechanical technology has become known, which is used for targeted Development of a selectivity to a given type of gas is heated to different operating temperatures.
  • the micromechanical sensor is heated in pulsed operation, the sensor element being at least approximately in thermal equilibrium at all times due to its low heat capacity.
  • the sensor signal is obtained from a measurement of the conductivity of the sensor element, which takes place during heating breaks.
  • the duration of the heating pulses varies, for example, from 6 to 300 milliseconds.
  • a complete detection cycle for example in the minute range, contains numerous heating pulses, the operating temperature being increased either from heating pulse to heating pulse or from heating pulse packet to heating pulse packet.
  • the signals recorded in the pulse pauses are put together to form a curve, the one has different course depending on the temperature, which is characteristic of the type of gas to be detected.
  • the invention has for its object a sensor for
  • Specify detection of gases in which a weighting factor can be specified when the sensor element is exposed to at least two different types of gas.
  • the sensor according to the invention for the detection of gases provides that in an evaluation circuit for the sensor signal emitted by a sensor element, an evaluation of the temporal signal curve after a temperature change is provided, the sensor signal being at least in a time interval in which the chemical equilibrium in the sensor element not available. Based on tests, it was found that after a temperature change in the sensor element, the sensor element being at least approximately in thermal equilibrium, the concentrations of more than one type of gas are inferred from the signal curve, which lies at least partially before chemical equilibrium is reached in the sensor element can be applied to the sensor element. If more than one gas type is applied to the sensor element, the signal curve therefore depends on the ratio of the concentrations of the least two gas types involved.
  • the sensor according to the invention for the detection of gases therefore makes it possible, by specifying special operating conditions of the sensor element, to provide a sensor signal in which the at least two gas types involved are provided with a predetermined ratio of their concentrations influence the sensor signal.
  • a particularly simple evaluation of the sensor signal curve results if at least a first and then at least a second signal value are recorded, the information being contained in the difference or quotient of the least two signal values.
  • An advantageous embodiment provides that the second signal value is detected when the sensor element has at least approximately reached its chemical equilibrium.
  • the evaluation of the signal curve extends from an area in which the chemical equilibrium has not been reached to an area in which this is the case.
  • the expected signal changes are maximum and, due to the higher signal swing, enable a simplified technical implementation in the evaluation circuit.
  • a particularly simple setting of the weighting factor of the at least two predetermined types of gas with which the sensor element is acted on is achieved by specifying the amount of the temperature changes.
  • the weighting factor can also be influenced by a suitable definition of the starting temperature before the temperature change.
  • the weighting factor can also be specified by specifying the evaluation of the time interval and by specifying the time of detection of the first and / or the second signal value.
  • the sensor according to the invention can advantageously be used for the simultaneous detection of existing nitrogen oxides and carbon monoxide in the breathing air. Such a sensor is more advantageous than air sensor in a force
  • switching signals for an air conditioning system are determined from the sensor signal curve in the evaluation circuit, which can include these switching signals for controlling the ventilation flap, fans or air filters.
  • FIG. 1 shows a block diagram of a sensor according to the invention for detecting gases
  • FIGS. 2a-2c show signal curves as a function of the time that occur in the sensor according to the invention according to FIG.
  • FIG. 1 shows a signal generator 10 which outputs a heating control signal 11 both to a heating controller 12 and to a time control 13.
  • the heating controller 12 outputs 35 a heating signal 14 to a heating element 15, which a sensor heated element 16.
  • the raw sensor signal 17 provided by the sensor element 16 is processed in a sensor signal processing 18 to the sensor signal S.
  • the sensor signal S reaches both a first and a second sample / hold memory 19, 20.
  • the heating control signal 11 causes the heating controller 12 to change the heating signal 14 from the first heating signal level Hl to the second heating signal level H2 at a first time Tl.
  • the temperature in the heating element 15 and accordingly in the sensor element 16 then drops from the first temperature Tempi to the second temperature Temp2.
  • a thermal time constant is achieved which can be in the range of a few milliseconds, for example 10-30 milliseconds.
  • the temperature change from the first temperature Tempi to the second temperature Temp2 takes place correspondingly quickly.
  • the first time interval II is followed by the second time interval 12, within which a thermal equilibrium has been reached in the sensor element 16, but no chemical equilibrium has been reached by the gas acting on the sensor element 16.
  • an evaluation of the course of the sensor signal S shown in FIG. 2a is provided as a function of the time t, the sensor signal S being at least partially in the second time interval II, in which the chemical equilibrium is not present.
  • the sensor signal S provides the sensor signal processing 18, which converts the raw sensor signal 17 into a signal suitable for further signal processing.
  • the sensor rest signal 17 lies, for example, as a signal element 16 flowing current, the amount of which depends on the electrical resistance or conductance of the sensor element 16 at a predetermined operating voltage.
  • a pulsed operation of the sensor element 16 can be provided.
  • the sensor signal S provided by the sensor signal conditioning unit 18 according to FIG. 2a should be a measure of the time course of the electrical resistance of the sensor element 16.
  • the sensor signal S Starting from an output signal level S1, the sensor signal S increases in the first time interval II during the temperature reduction of the sensor element 16 to a final value which is not specified in more detail, from which a signal drop can be determined at constant temperature Temp2 while the chemical balance is being divided.
  • the two sample / hold memories 19, 20 are provided, which are controlled by the sample signals 21, 22, which the time control 13 determines from the heating control signal 11.
  • the / Hold signal 21 is generated at the second time TA1 and causes the first sample / hold memory 19 to take over the first signal value S2 of the sensor signal S present at the second time TAl and stores it.
  • an evaluation of the signal curve of the sensor signal S is provided, which lies at least partially in the second time interval 12.
  • the evaluation of the signal curve is possible, for example, by forming a difference between signal levels.
  • the sampling is therefore provided at the third point in time TA3 of the sensor signal S at which S has a second signal value S3.
  • the sampling can be, for example, towards the end of the second time interval 12.
  • the third point in time TA2 is at which the second sampling / Hold memory 20, caused by the second sample / hold signal 22, takes over and stores the second signal value S3 in a third time interval 14, in which the chemical equilibrium in sensor element 16 is at least approximately established or has already approximately been set.
  • the determination of the evaluation in the third time interval 13 enables the greatest possible level change in the sensor signal S to be detected and simplifies the requirements for the signal evaluation 23, which include, for example, the difference between the first and second signal values S2, S3 of the sensor signal S or other computing operations described in more detail below performs.
  • the determination of the beginning of the third time interval 13, at which it is assumed that the chemical equilibrium in the sensor element 16 is at least approximately adjusted, can be carried out on the basis of experiments and is determined at a point in time after which the sensor signal S changes until a saturation level S4 is reached only changes a predetermined percentage of, for example, 10 or 5%.
  • the time duration of the second and third time intervals 12, 13 is, for example, in the range of 100-200 milliseconds, it being possible for the two time intervals 12, 13 to be at least approximately the same length, for example.
  • the heating signal level changes, starting from the second heating signal level H3, back to the first heating signal level H1, which leads to an increase in temperature from the second temperature Temp2 to the first temperature Tempi in the sensor element 16.
  • the renewed temperature change takes place in the fourth time interval 14, the duration of which corresponds to that of the first time interval II.
  • the sensor signal S falls from the saturation level S4 to a return level S5 during the fourth interval 14.
  • the amount of change in sensor signal S during First time interval II, on the one hand, and during fourth time interval 14, depending on the concentration of the different types of gas with which sensor element 16 is acted upon, can differ considerably in some cases.
  • a further signal evaluation in the further signal course after the fourth time interval 14 can be provided, since at this point in time there is a thermal equilibrium in the sensor element 16 and on the other hand the chemical equilibrium has not been reached.
  • the signal evaluation 23 can provide an output signal 24 which reflects more detailed information about the curve shape of the signal S, which lies at least partially in the second subinterval 12. For example, considerably more signal values S2, S3 can be recorded than shown in the exemplary embodiment. In addition or as an alternative to the determination of signal differences, the determination of quotients can be provided.
  • the signal evaluation 23 determines a mathematical function that describes the signal curve of the sensor signal S as at least approximately.
  • An evaluation by interpolation of several signal values S2, S3 can provide parameters of the underlying functional relationships. For example, it can be determined whether there is at least approximately a linear course or an exponential signal course. In the case of an exponential signal curve, the signal offset and the exponent can be specified. It has been demonstrated experimentally that a gradual change from an exponential course to a linear signal course of the sensor signal S is based on an aging process of the sensor element 16. It is therefore possible to set a threshold give that indicates that the sensor element 16 should be replaced if necessary. The thresholds can be given by the parameters of the exponential or linear curve shape.
  • a further advantageous embodiment provides for the sensor element 16 to be initially exposed to a gas type or a gas mixture to be detected and then to be exposed to air. By evaluating a relative signal change in both cases, a statement can be made about the sensitivity of the sensor element 16 to the type of gas or the gas mixture.
  • the sensor according to the invention for the detection of gases can be used, for example, as an air quality sensor in a motor vehicle, in which at least one output signal 24 is passed on to an air conditioning system (not shown in more detail).
  • the air conditioning system can take into account the switching signal 24 when actuating an air flap, when operating fans or, for example, when operating air filters.
  • the sensor element 16 for example a tin oxide semiconductor gas sensor, is provided, for example, for determining the concentration of
  • the weighting factor can preferably take place by determining the amount of the temperature change from the first temperature Tempi to the second temperature Temp2. Another possibility is given by specifying the initial temperature, in the exemplary embodiment shown the first temperature tempi. Another way to add the weighting factor influence, lies in the determination of the duration of the second time interval 12, during which the chemical equilibrium is not present in the sensor element 16.
  • a further possibility for influencing the weighting factor lies in the determination of the temporal position of the scanning signals 21, 22 at the second and third times TAl, TA2.
  • the influence of the parameters mentioned on the sensitivity to individual types of gas and in particular to the weighting factor when the sensor element 16 is exposed to different types of gas can preferably be determined experimentally.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

Abstract

The invention relates to a sensor for detecting gas. According to the invention, a signal evaluation (23) emits an output signal (24) whereby a predetermined weighting factor for at least two types of gas is set in the sensor element (16). A sensor heater (15) is provided and alters the temperature (Temp1, Temp2) of the sensor element (16) in a first time interval (I1) which is shorter than the time required for the sensor element (16) to create a chemical equilibrium, the sensor element (16) being at least approximately in a state of thermal equilibrium. The signal evaluation (23) evaluates the temporal sensor signal response after the temperature has been altered (Temp1, Temp2). The sensor signal (S) is at least partially located in a second time interval (I2), wherein the chemical equilibrium of the sensor element (16) is not created.

Description

Sensor zur Detektion von GasenGas detection sensor
Stand der TechnikState of the art
Die Erfindung geht aus von einem Sensor zur Detektion von Gasen nach der Gattung des unabhängigen Patentanspruchs. Aus dem Fachzeitschriftenbeitrag von Cavicchi et. al . : "Fast Temperature Programmed Sensing for Micro-Hotplate Gas Sensors", IEEE Electron Device Letrers, Vol.16, No.6, June 1995, S. 286-288 ist ein in mikromechanischer Technik reali- sierter Gassensor bekannt geworden, der zur gezielten Herausbildung einer Selektivität gegenüber einer vorgegebenen Gasart auf unterschiedliche Betriebstemperaturen geheizt wird. Die Beheizung des mikromechanischen Sensors erfolgt im Impulsbetrieb, wobei das Sensorelement aufgrund seiner ge- ringen Wärmekapazität jederzeit wenigstens näherungsweise im thermischen Gleichgewicht ist. Das Sensorsignal wird gewonnen aus einer Messung der Leitfähigkeit des Sensorelements, die in Heizungspausen erfolgt. Die Dauer der Heizimpulse variiert beispielsweise von 6 bis 300 Millisekunden. Ein vollständiger Erfassungszyklus, der beispielsweise im Minutenbereich liegt, enthält zahlreiche Heizungsimpulse, wobei die Betriebstemperatur entweder von Heizungsimpuls zu Heizungsimpuls oder von Heizungsimpulspaket zu Heizungsimpulspaket erhöht wird. Die in den Impulsenpausen erfaßten Si- gnale werden zu einem Kurvenzug zusammengesetzt, der einen unterschiedlichen Verlauf in Abhängigkeit von der Temperatur aufweist, der charakteristisch ist für die zu detektierende Gasart.The invention is based on a sensor for detecting gases according to the category of the independent claim. From the journal article by Cavicchi et. al. : "Fast Temperature Programmed Sensing for Micro-Hotplate Gas Sensors", IEEE Electron Device Letrers, Vol.16, No.6, June 1995, pp. 286-288, a gas sensor realized in micromechanical technology has become known, which is used for targeted Development of a selectivity to a given type of gas is heated to different operating temperatures. The micromechanical sensor is heated in pulsed operation, the sensor element being at least approximately in thermal equilibrium at all times due to its low heat capacity. The sensor signal is obtained from a measurement of the conductivity of the sensor element, which takes place during heating breaks. The duration of the heating pulses varies, for example, from 6 to 300 milliseconds. A complete detection cycle, for example in the minute range, contains numerous heating pulses, the operating temperature being increased either from heating pulse to heating pulse or from heating pulse packet to heating pulse packet. The signals recorded in the pulse pauses are put together to form a curve, the one has different course depending on the temperature, which is characteristic of the type of gas to be detected.
Der Erfindung liegt die Aufgabe zugrunde, einen Sensor zurThe invention has for its object a sensor for
Detektion von Gasen anzugeben, bei dem ein Gewichtungsfaktor bei der Beaufschlagung des Sensorelements mit wenigstens zwei unterschiedlichen Gasarten vorgebbar ist.Specify detection of gases, in which a weighting factor can be specified when the sensor element is exposed to at least two different types of gas.
Die Aufgabe wird durch die in die im unabhängigen Anspruch angegebenen Merkmale gelost.The problem is solved by the features specified in the independent claim.
Vorteile der ErfindungAdvantages of the invention
Der erfindungsgemaße Sensor zur Detektion von Gasen sieht vor, dass in einer Auswerteschaltung für das von einen Sensorelement abgegebene Sensorsignal eine Bewertung des zeitlichen Signalverlaufs nach einer Temperaturanderung vorgesehen ist, wobei das Sensorsignal zumindest in einem Zeitin- tervall liegt, in welchem das chemische Gleichgewicht im Sensorelement nicht vorliegt. Anhand von Versuchen wurde festgestellt, dass nach einer Temperaturanderung des Sensorelements, wobei das Sensorelement wenigstens naherungsweise im thermischen Gleichgewicht ist, aus dem Signalverlauf, der zumindest teilweise vor dem Erreichen des chemischen Gleichgewichts im Sensorelement liegt, auf die Konzentrationen von mehr als einer Gasart geschlossen werden kann, mit denen das Sensorelement beaufschlagt ist. Bei der Beaufschlagung des Sensorelements mit mehr als einer Gasart hangt der Signal- verlauf demnach vom Verhältnis der Konzentrationen der wenigsten zwei beteiligten Gasarten ab. Der erfindungsgemaße Sensor zur Detektion von Gasen ermöglicht deshalb mit der Vorgabe von speziellen Betriebsbedingungen des Sensorelements die Bereitstellung eines Sensorsignals, bei dem die wenigstens beiden beteiligten Gasarten mit einem vorgegebe- nen Verhältnis ihrer Konzentrationen das Sensorsignal beeinflussen.The sensor according to the invention for the detection of gases provides that in an evaluation circuit for the sensor signal emitted by a sensor element, an evaluation of the temporal signal curve after a temperature change is provided, the sensor signal being at least in a time interval in which the chemical equilibrium in the sensor element not available. Based on tests, it was found that after a temperature change in the sensor element, the sensor element being at least approximately in thermal equilibrium, the concentrations of more than one type of gas are inferred from the signal curve, which lies at least partially before chemical equilibrium is reached in the sensor element can be applied to the sensor element. If more than one gas type is applied to the sensor element, the signal curve therefore depends on the ratio of the concentrations of the least two gas types involved. The sensor according to the invention for the detection of gases therefore makes it possible, by specifying special operating conditions of the sensor element, to provide a sensor signal in which the at least two gas types involved are provided with a predetermined ratio of their concentrations influence the sensor signal.
Vorteilhafte Weiterbildungen und Ausgestaltungen des erfin- dungsgemäßen Sensors ergeben sich aus abhängigen Ansprüchen.Advantageous further developments and refinements of the sensor according to the invention result from the dependent claims.
Eine besonders einfache Bewertung des Sensorsignalverlaufs ergibt sich, wenn wenigstens ein erster und danach wenigstens ein zweiter Signalwert erfaßt werden, wobei die Infor- mation in der Differenz oder im Quotienten der wenigsten beiden Signalwerte enthalten ist.A particularly simple evaluation of the sensor signal curve results if at least a first and then at least a second signal value are recorded, the information being contained in the difference or quotient of the least two signal values.
Eine vorteilhafte Ausgestaltung sieht vor, dass der zweite Signalwert erfaßt wird, wenn das Sensorelement zumindest näherungsweise sein chemisches Gleichgewicht erreicht hat. Mit dieser Maßnahme erstreckt sich die Auswertung des Signalverlaufs von einem Bereich, in welchem das chemische Gleichgewicht nicht erreicht ist bis zu einem Bereich, in welchem dieses der Fall ist. Die erwarteten Signaländerungen sind mit dieser Maßnahme maximal und ermöglichen durch den höheren Signalhub eine vereinfachte technische Realisierung in der Auswerteschaltung.An advantageous embodiment provides that the second signal value is detected when the sensor element has at least approximately reached its chemical equilibrium. With this measure, the evaluation of the signal curve extends from an area in which the chemical equilibrium has not been reached to an area in which this is the case. With this measure, the expected signal changes are maximum and, due to the higher signal swing, enable a simplified technical implementation in the evaluation circuit.
Eine besonders einfache Einstellung des Gewichtungsfaktors der wenigstens zwei vorgegebenen Gasarten, mit denen das Sensorelement beaufschlagt ist, wird durch die Festlegung des Betrags der Temperaturänderungen erreicht. Der Gewichtungsfaktor kann weiterhin beeinflußt werden durch eine geeignete Festlegung der Ausgangstemperatur vor der Tempera- turänderung. Der Gewichtungsfaktor kann weiterhin vorgegeben werden durch eine Festlegung der Auswertung des Zeitintervalls sowie durch eine Festlegung des Zeitpunktes der Erfassung des ersten und/oder des zweiten Signalwerts. Eine vorteilhafte Weiterbildung des erfmdungsgemaßen Sensors sieht vor, dass der Sensorsignalverlauf daraufhin untersucht wird, welcher mathematische Kurvenverlauf vorliegt. So kann beispielsweise festgestellt werden, ob ein wenigstens naherungsweise linearer Verlauf oder ein exponentiel- ler Verlauf vorliegt. Aus dem Ergebnis kann auf den Zustand des Sensorelements geschlossen werden. Beispielsweise kann ein linearer Kurvenverlauf auf ein gealtertes Sensorelement hinweisen, das gegebenenfalls zu ersetzen ist.A particularly simple setting of the weighting factor of the at least two predetermined types of gas with which the sensor element is acted on is achieved by specifying the amount of the temperature changes. The weighting factor can also be influenced by a suitable definition of the starting temperature before the temperature change. The weighting factor can also be specified by specifying the evaluation of the time interval and by specifying the time of detection of the first and / or the second signal value. An advantageous development of the sensor according to the invention provides that the sensor signal profile is examined to determine which mathematical curve profile is present. For example, it can be determined whether there is an at least approximately linear course or an exponential course. The state of the sensor element can be concluded from the result. For example, a linear curve shape can indicate an aged sensor element that may need to be replaced.
L0L0
Der erfindungsgemaße Sensor kann vorteilhaft zur gleichzeitigen Detektion von vorhandenen Stickoxyden und Kohlenmon- oxid m der Atemluft eingesetzt werden. Ein derartiger Sensor wird vorteilhafter als Luftgutesensor m einem Kraft-The sensor according to the invention can advantageously be used for the simultaneous detection of existing nitrogen oxides and carbon monoxide in the breathing air. Such a sensor is more advantageous than air sensor in a force
15 fahrzeug eingesetzt, wobei aus dem Sensorsignalverlauf in der Auswerteschaltung Schaltsignale für eine Klimaanlage ermittelt werden, die diese Schaltsignale zur Steuerung von Luftungsklappe, Ventilatoren oder Luftfiltern mit einbeziehen kann.15 vehicle used, switching signals for an air conditioning system are determined from the sensor signal curve in the evaluation circuit, which can include these switching signals for controlling the ventilation flap, fans or air filters.
2020
Vorteilhafte weitere Ausgestaltungen und Weiterbildungen des erfmdungsgemaßen Sensors ergeben sich aus aus der folgenden Beschreibung.Advantageous further refinements and developments of the sensor according to the invention result from the following description.
25 Zeichnung25 drawing
Figur 1 zeigt ein Blockschaltbild eines erfmdungsgemaßen Sensors zur Detektion von Gasen und die Figuren 2a-2c zeigen Signalverlaufe Abhängigkeit von der Zeit, die in dem 30 erf dungsgemaßen Sensor gemass Figur 1 auftreten.FIG. 1 shows a block diagram of a sensor according to the invention for detecting gases, and FIGS. 2a-2c show signal curves as a function of the time that occur in the sensor according to the invention according to FIG.
Figur 1 zeigt einen Signalgenerator 10, der e n Heizungs- steuersignal 11 sowohl an einen Heizungsregler 12 als auch an eine Zeitsteuerung 13 abgibt. Der Heizungsregler 12 gibt 35 ein Heizsignal 14 an ein Heizelement 15 ab, das ein Senso- relement 16 beheizt. Das vom Sensorelement 16 bereitgestellte Sensorrohsignal 17 wird in einer Sensorsignalaufbereitung 18 zum Sensorsignal S aufbereitet. Das Sensorsignal S gelangt sowohl in einen ersten als auch in einen zweiten Ab- tast-/Haltespeicher 19, 20.FIG. 1 shows a signal generator 10 which outputs a heating control signal 11 both to a heating controller 12 and to a time control 13. The heating controller 12 outputs 35 a heating signal 14 to a heating element 15, which a sensor heated element 16. The raw sensor signal 17 provided by the sensor element 16 is processed in a sensor signal processing 18 to the sensor signal S. The sensor signal S reaches both a first and a second sample / hold memory 19, 20.
Das Heizungssteuersignal 11 veranlaßt den Heizungsregler 12 zu einem ersten Zeitpunkt Tl zu einer Änderung des Heizsignals 14 von dem ersten Heizsignalpegel Hl zum zweiten Heiz- signalpegel H2. Im anschließenden ersten Zeitintervall II fällt daraufhin die Temperatur in Heizelement 15 und entsprechend im Sensorelement 16 von der ersten Temperatur Tempi auf die zweite Temperatur Temp2 ab. In Abhängigkeit von den Wärmekapazitäten des Heizelements und des Sensorele- ments 16, die im Rahmen einer mikromechanischen Realisierung gering sind, wird eine thermische Zeitkonstante erreicht, die im Bereich von wenigen Millisekunden, beispielsweise 10 - 30 Millisenkunden liegen kann. Entsprechend rasch erfolgt die Temperaturänderung von der ersten Temperatur Tempi auf die zweite Temperatur Temp2.The heating control signal 11 causes the heating controller 12 to change the heating signal 14 from the first heating signal level Hl to the second heating signal level H2 at a first time Tl. In the subsequent first time interval II, the temperature in the heating element 15 and accordingly in the sensor element 16 then drops from the first temperature Tempi to the second temperature Temp2. Depending on the heat capacities of the heating element and the sensor element 16, which are low in the context of a micromechanical implementation, a thermal time constant is achieved which can be in the range of a few milliseconds, for example 10-30 milliseconds. The temperature change from the first temperature Tempi to the second temperature Temp2 takes place correspondingly quickly.
An das erste Zeitintervall II schließt sich das zweite Zeitintervall 12 an, innerhalb dem im Sensorelement 16 zwar ein thermisches Gleichgewicht, aber kein chemisches Gleichge- wicht durch das das Sensorelement 16 beaufschlagende Gas erreicht ist. Erfindungsgemäß ist eine Bewertung des in Figur 2a gezeigten Verlaufs des Sensorsignals S in Abhängigkeit von der Zeit t vorgesehen, wobei das Sensorsignal S zumindest teilweise im zweiten Zeitintervall II liegt, in welchem das chemische Gleichgewicht nicht vorliegt.The first time interval II is followed by the second time interval 12, within which a thermal equilibrium has been reached in the sensor element 16, but no chemical equilibrium has been reached by the gas acting on the sensor element 16. According to the invention, an evaluation of the course of the sensor signal S shown in FIG. 2a is provided as a function of the time t, the sensor signal S being at least partially in the second time interval II, in which the chemical equilibrium is not present.
Das Sensorsignal S stellt die Sensorsignalaufbereitung 18 bereit, die das Sensorrohsignal 17 in ein zur weiteren Signalverarbeitung geeignetes Signal umsetzt. Das Sensorruhe- signal 17 liegt beispielsweise als ein durch das Sensorele- ment 16 fließender Strom vor, dessen Betrag vom elektrischen Widerstand bzw. Leitwert des Sensorelements 16 bei einer vorgegebenen Betriebsspannung abhangt. Gegebenenfalls kann ein nicht naher gezeigtes zeitlich impulsformiges Betreiben des Sensorelements 16 vorgesehen sein. Im gezeigten Ausfuhrungsbeispiel soll das von der Sensorsignalaufbereitung 18 bereit gestellte Sensorsignal S gemass Figur 2a ein Maß den zeitlichen Verlauf des elektrischen Widerstands des Sensorelements 16 sein. Ausgehend von einem Ausgangssignalpegel Sl steigt im ersten Zeitintervall II wahrend der Temperaturreduzierung des Sensorelements 16 das Sensorsignal S an auf einen nicht naher spezifizierten Endwert, von dem aus bei konstanter Temperatur Temp2 während des Einsteilens des chemischen Gleichgewichts ein Signalabfall festgestellt werden kann.The sensor signal S provides the sensor signal processing 18, which converts the raw sensor signal 17 into a signal suitable for further signal processing. The sensor rest signal 17 lies, for example, as a signal element 16 flowing current, the amount of which depends on the electrical resistance or conductance of the sensor element 16 at a predetermined operating voltage. Optionally, a pulsed operation of the sensor element 16, not shown in detail, can be provided. In the exemplary embodiment shown, the sensor signal S provided by the sensor signal conditioning unit 18 according to FIG. 2a should be a measure of the time course of the electrical resistance of the sensor element 16. Starting from an output signal level S1, the sensor signal S increases in the first time interval II during the temperature reduction of the sensor element 16 to a final value which is not specified in more detail, from which a signal drop can be determined at constant temperature Temp2 while the chemical balance is being divided.
Zur Auswertung des Sensorsignals S sind die beiden Abtast- /Haltespeicher 19, 20 vorgesehen, die von den Abtastsignalen 21, 22 gesteuert werden, welche die Zeitsteuerung 13 aus dem Heizungssteuersignal 11 ermittelt. Das erste Abtast-For the evaluation of the sensor signal S, the two sample / hold memories 19, 20 are provided, which are controlled by the sample signals 21, 22, which the time control 13 determines from the heating control signal 11. The first sampling
/Haltesignal 21 wird zum zweiten Zeitpunkt TA1 erzeugt und veranlaßt den ersten Abtast-/Haltespeicher 19 zur Übernahme des zum zweiten Zeitpunkt TAl vorliegenden ersten Signalwerts S2 des Sensorsignals S und speichert diesem. An Stelle lediglich der Bewertung des Signalpegels des ersten Signalwerts S2 ist eine Bewertung des Signalverlaufs des Sensorsignals S vorgesehen, der wenigstens teilweise im zweiten Zeitintervall 12 liegt. Die Bewertung des Signalverlaufs ist beispielsweise durch eine Differenzbildung von Signalpegeln möglich. Im gezeigten Ausfuhrungsbeispiel ist deshalb die Abtastung zum dritten Zeitpunkt TA3 des Sensorsignals S vorgesehen, bei dem S einen zweiten Signalwert S3 aufweist. Die Abtastung kann beispielsweise gegen Ende des zweiten Zeitintervalls 12 liegen. Im gezeigten Ausfuhrungsbeispiel liegt der dritte Zeitpunkt TA2, bei dem der zweite Abtast- /Haltespeicher 20, veranlaßt durch das zweite Abtast- /Haltesignal 22 den zweiten Signalwert S3 übernimmt und speichert, in einem dritten Zeitmtervall 14, in welchem sich wenigsten naherungsweise das chemische Gleichgewicht im Sensorelement 16 einstellt bzw. bereits naherungsweise eingestellt hat. Die Festlegung der Auswertung im dritten Zeitmtervall 13 ermöglicht die Erfassung einer größtmöglichen Pegelanderung des Sensorsignals S und vereinfacht die Anforderungen an die Signalbewertung 23, die beispielsweise die Differenz zwischen dem ersten und zweiten Signalwert S2, S3 des Sensorsignals S oder andere, weiter unten naher beschriebene Rechenoperationen vornimmt./ Hold signal 21 is generated at the second time TA1 and causes the first sample / hold memory 19 to take over the first signal value S2 of the sensor signal S present at the second time TAl and stores it. Instead of merely evaluating the signal level of the first signal value S2, an evaluation of the signal curve of the sensor signal S is provided, which lies at least partially in the second time interval 12. The evaluation of the signal curve is possible, for example, by forming a difference between signal levels. In the exemplary embodiment shown, the sampling is therefore provided at the third point in time TA3 of the sensor signal S at which S has a second signal value S3. The sampling can be, for example, towards the end of the second time interval 12. In the exemplary embodiment shown, the third point in time TA2 is at which the second sampling / Hold memory 20, caused by the second sample / hold signal 22, takes over and stores the second signal value S3 in a third time interval 14, in which the chemical equilibrium in sensor element 16 is at least approximately established or has already approximately been set. The determination of the evaluation in the third time interval 13 enables the greatest possible level change in the sensor signal S to be detected and simplifies the requirements for the signal evaluation 23, which include, for example, the difference between the first and second signal values S2, S3 of the sensor signal S or other computing operations described in more detail below performs.
Die Festlegung des Beginns des dritten Zeitmtervalls 13, bei dem von einer wenigstens nanerungsweise Einstellung des chemischen Gleichgewichts im Sensorelement 16 ausgegangen wird, kann anhand von Versuchen erfolgen und wird auf einen Zeitpunkt festgelegt, nach dem sich das Sensorsignal S bis zum Erreichen eines Sattigungspegels S4 um lediglich noch einen vorgegebenen Prozentsatz von beispielsweise 10 oder 5% ändert. Die zeitliche Dauer des zweiten und dritten Zeitintervalls 12, 13 liegt beispielsweise im Bereich von 100-200 Millisekunden, wobei die beiden Zeitintervalle 12, 13 beispielsweise wenigstens naherungsweise gleich lang sein kon- nen. Nach Ablauf des dritten Zeitintervalls 13 ändert sich der Heizsignalpegel, ausgehend vom zweiten Heizsignalpegel H3 zurück auf den ersten Heizsignalpegel Hl, der zu einem Temperaturanstieg von der zweiten Temperatur Temp2 zur ersten Temperatur Tempi im Sensorelement 16 fuhrt.The determination of the beginning of the third time interval 13, at which it is assumed that the chemical equilibrium in the sensor element 16 is at least approximately adjusted, can be carried out on the basis of experiments and is determined at a point in time after which the sensor signal S changes until a saturation level S4 is reached only changes a predetermined percentage of, for example, 10 or 5%. The time duration of the second and third time intervals 12, 13 is, for example, in the range of 100-200 milliseconds, it being possible for the two time intervals 12, 13 to be at least approximately the same length, for example. After the third time interval 13 has elapsed, the heating signal level changes, starting from the second heating signal level H3, back to the first heating signal level H1, which leads to an increase in temperature from the second temperature Temp2 to the first temperature Tempi in the sensor element 16.
Die erneute Temperaturanderung erfolgt im vierten Zeitmtervall 14, dessen Dauer der des ersten Zeitmtervalls II entspricht. Das Sensorsignal S fallt wahrend des vierten Intervalls 14 vom Sattigungspegel S4 auf einen Ruckkehrpegel S5 ab. Der Betrag der Änderung des Sensorsignals S wahrend des ersten Zeitintervalls II einerseits und wahrend des vierten Zeitintervalls 14 können sich in Abhängigkeit von der Konzentration der unterschiedlichen Gasarten, mit denen das Sensorelement 16 beaufschlagt ist, zum Teil erheblich unterscheiden. Eine weitergehende Signalbewertung im weiteren Signalverlauf nach dem vierten Zeitintervall 14 kann vorgesehen sein, da auch zu diesem Zeitpunkt einerseits ein thermisches Gleichgewicht im Sensorelement 16 vorliegt und andererseits das chemische Gleichgewicht nicht erreicht ist.The renewed temperature change takes place in the fourth time interval 14, the duration of which corresponds to that of the first time interval II. The sensor signal S falls from the saturation level S4 to a return level S5 during the fourth interval 14. The amount of change in sensor signal S during First time interval II, on the one hand, and during fourth time interval 14, depending on the concentration of the different types of gas with which sensor element 16 is acted upon, can differ considerably in some cases. A further signal evaluation in the further signal course after the fourth time interval 14 can be provided, since at this point in time there is a thermal equilibrium in the sensor element 16 and on the other hand the chemical equilibrium has not been reached.
Die Signalbewertung 23 kann zusatzlich zur Differenz der Signalwerte S2, S3 ein Ausgangssignal 24 bereitstellen, das nähere Informationen über den Kurvenverlauf des Signals S, der zumindest teilweise im zweiten Teilintervall 12 liegt, widerspiegelt. Beispielsweise können erheblich mehr Signalwerte S2, S3, erfaßt werden als im Ausfuhrungsbeispiel gezeigt. Zusatzlich oder alternativ zur Ermittlung von Signaldifferenzen kann die Ermittlung von Quotienten vorgesehen sein .In addition to the difference between the signal values S2, S3, the signal evaluation 23 can provide an output signal 24 which reflects more detailed information about the curve shape of the signal S, which lies at least partially in the second subinterval 12. For example, considerably more signal values S2, S3 can be recorded than shown in the exemplary embodiment. In addition or as an alternative to the determination of signal differences, the determination of quotients can be provided.
Eine besonders vorteilhafte Weiterbildung sieht vor, dass die Signalbewertung 23 eine mathematische Funktion ermittelt, die den Signalverlauf des Sensorsignals S als wenigstens n herungsweise beschreibt. Eine Auswertung durch eine Interpolation von mehreren Signalwerten S2, S3 kann Kenngroßen der zugrunde liegenden funktionalen Zusammenhange bereitstellen. Beispielsweise kann festgestellt werden, ob wenigstens naherungsweise ein linearer Verlauf oder ein exponentieller Signalverlauf vorliegt. Bei einem exponenti- ellem Signalverlauf können der Signal-Offset und der Exponent angegeben werden. Experimentell konnte nachgewiesen werden, dass einem allmähliches Andern von einem exponenti- ellem Verlauf hin zu einem linearen Signalverlauf des Sensorssignals S ein Alterungsprozeß des Sensorelements 16 zugrunde liegt. Es ist deshalb möglich, eine Schwelle vorzu- geben, die anzeigt, dass das Sensorelement 16 gegebenenfalls ausgetauscht werden sollte. Die Schwellen können durch die Kenngroßen des exponentiellen oder linearen Kurvenverlaufs gegeben sein.A particularly advantageous development provides that the signal evaluation 23 determines a mathematical function that describes the signal curve of the sensor signal S as at least approximately. An evaluation by interpolation of several signal values S2, S3 can provide parameters of the underlying functional relationships. For example, it can be determined whether there is at least approximately a linear course or an exponential signal course. In the case of an exponential signal curve, the signal offset and the exponent can be specified. It has been demonstrated experimentally that a gradual change from an exponential course to a linear signal course of the sensor signal S is based on an aging process of the sensor element 16. It is therefore possible to set a threshold give that indicates that the sensor element 16 should be replaced if necessary. The thresholds can be given by the parameters of the exponential or linear curve shape.
Eine weitere vorteilhafte Ausgestaltung sieht die Beaufschlagung des Sensorelements 16 zunächst mit einer zu detektierenden Gasart oder einem zu detektierenden Gasgemisch und anschließend die Beaufschlagung mit Luft vor. Über eine Bewertung einer relativen Signalanderung in beiden Fallen kann eine Aussage zur Empfindlichkeit des Sensorelements 16 gegenüber der Gasart oder des Gasgemisches gemacht werden.A further advantageous embodiment provides for the sensor element 16 to be initially exposed to a gas type or a gas mixture to be detected and then to be exposed to air. By evaluating a relative signal change in both cases, a statement can be made about the sensitivity of the sensor element 16 to the type of gas or the gas mixture.
Der erfindungsgemaße Sensor zur Detektion von Gasen kann beispielsweise als Luftgutesensor einem Kraftfahrzeug verwendet werden, bei dem wenigstens ein Ausgangssignal 24 an eine nicht naher gezeigte Klimaanlage weitergegeben wird. Die Klimaanlage kann das Schaltsignal 24 bei der Betätigung einer Luftklappe, beim Betreiben von Ventilatoren oder bei- spielsweise beim Betreiben von Luftfiltern in Betracht ziehen.The sensor according to the invention for the detection of gases can be used, for example, as an air quality sensor in a motor vehicle, in which at least one output signal 24 is passed on to an air conditioning system (not shown in more detail). The air conditioning system can take into account the switching signal 24 when actuating an air flap, when operating fans or, for example, when operating air filters.
Das Sensorelement 16, beispielsweise ein Zinnoxyd- Halbleitergassensor ist in einer solchen Anwendung bei- spielsweise vorgesehen zur Konzentrationsbestimmung vonIn such an application, the sensor element 16, for example a tin oxide semiconductor gas sensor, is provided, for example, for determining the concentration of
Gasgemischen wie beispielsweise CO/CH4, CO/NOx, CH4/C2H6. 'Gas mixtures such as CO / CH4, CO / NOx, CH4 / C2H6. '
Beispielsweise sollen eine Konzentration von 50 ppm CO und 5 ppm NOx den gleichen Einfluß auf das Sensorsignal S haben. Der Gewichtungsfaktor kann vorzugsweise durch Festlegung des Betrags der Temperaturanderung von der ersten Temperatur Tempi auf die zweite Temperatur Temp2 erfolgen. Eine andere Möglichkeit ist gegeben durch Festlegung der Ausgangstemperatur, im gezeigten Ausfuhrungsbeispiel der ersten Tempera- tur Tempi. Eine andere Möglichkeit, den Gewichtungsfaktor zu beeinflussen, liegt in der Festlegung der Dauer des zweiten Zeitintervalls 12, wahrend dem das chemische Gleichgewicht im Sensorelement 16 nicht vorliegt.For example, a concentration of 50 ppm CO and 5 ppm NOx should have the same influence on the sensor signal S. The weighting factor can preferably take place by determining the amount of the temperature change from the first temperature Tempi to the second temperature Temp2. Another possibility is given by specifying the initial temperature, in the exemplary embodiment shown the first temperature tempi. Another way to add the weighting factor influence, lies in the determination of the duration of the second time interval 12, during which the chemical equilibrium is not present in the sensor element 16.
Eine weitere Möglichkeit, den Gewichtungsfaktor zu beeinflussen liegt in der Festlegung der zeitlichen Lage der Abtastsignale 21, 22 zum zweiten und dritten Zeitpunkt TAl, TA2.A further possibility for influencing the weighting factor lies in the determination of the temporal position of the scanning signals 21, 22 at the second and third times TAl, TA2.
Der Einfluß der genannten Kenngroßen auf die Empfindlichkeit gegenüber einzelner Gasarten und insbesondere gegenüber dem Gewichtungsfaktor bei der Beaufschlagung des Sensorelements 16 mit unterschiedlichen Gasarten kann vorzugsweise experimentell ermittelt werden. The influence of the parameters mentioned on the sensitivity to individual types of gas and in particular to the weighting factor when the sensor element 16 is exposed to different types of gas can preferably be determined experimentally.

Claims

Ansprüche Expectations
1. Sensor zur Detektion von Gasen, mit einer Signalbewer- tung (23) für ein Sensorsignal (S) , das wenigstens ein1. Sensor for the detection of gases, with a signal evaluation (23) for a sensor signal (S), which is at least one
Sensorelement (16) bereitstellt, mit einer Sensorheizung (15) , die eine Temperaturanderung (Tempi, Temp2) in einem ersten Zeitintervall (II) vornimmt, das kurzer ist als die Zeit, die das Sensorelement (16) zur Einstellung eines chemischen Gleichgewichts benotigt, wobei das Sensorelement (16) wenigstens naherungsweise im thermischen Gleichgewicht ist, dadurch gekennzeichnet, dass eine Signalbewertung (23) des zeitlichen Sensorsignalverlaufs (S) nach der Temperaturanderung (Tempi, Temp2) vorgese- hen ist, wobei das Sensorsignal (S) zumindest teilweise in einem zweiten Zeitintervall (12) liegt, in welchem das chemische Gleichgewicht im Sensorelement (16) nicht vorliegt .Provides sensor element (16) with a sensor heater (15) which changes the temperature (Tempi, Temp2) in a first time interval (II) which is shorter than the time required for sensor element (16) to establish a chemical equilibrium, wherein the sensor element (16) is at least approximately in thermal equilibrium, characterized in that a signal evaluation (23) of the temporal sensor signal profile (S) is provided after the temperature change (Tempi, Temp2), the sensor signal (S) at least partially in a second time interval (12) in which the chemical equilibrium is not present in the sensor element (16).
2. Sensor nach Anspruch 1, dadurch gekennzeichnet, dass die Signalbewertung (23) wenigstens einen ersten und wenigstens einen zweiten Signalwert (S2, S3) erfaßt und wenigstens einen Differenzbetrag oder einen Quotienten ermittelt.2. Sensor according to claim 1, characterized in that the signal evaluation (23) detects at least a first and at least a second signal value (S2, S3) and determines at least one difference or a quotient.
3. Sensor nach Anspruch 1, dadurch gekennzeichnet, dass die Signalbewertung (23) aus mehreren Signalwerten (S2, S3) Kenngroßen für wenigstens naherungsweise einen linearen oder exponentiellen Kurvenverlauf ermittelt. 3. Sensor according to claim 1, characterized in that the signal evaluation (23) determines from several signal values (S2, S3) parameters for at least approximately a linear or exponential curve.
4. Sensor nach Anspruch 3, dadurch gekennzeichnet, daß durch Vergleich des Kurvenverlaufs mit wenigstens einem vorgegebenen Kurvenverlauf auf den Sensorzustand geschlossen wird.4. Sensor according to claim 3, characterized in that the sensor state is inferred by comparing the curve with at least one predetermined curve.
5. Sensor nach Anspruch 4, dadurch gekennzeichnet, daß wenigstens eine Kenngröße des Kurvenverlaufs mit einem vor- gebenen Schwellenwert verglichen wird.5. Sensor according to claim 4, characterized in that at least one parameter of the curve profile is compared with a predetermined threshold value.
6. Sensor nach Anspruch 4, dadurch gekennzeichnet, dass ein wenigstens näherungsweise linearer Kurvenverlauf als ein gealtertes Sensorelement (16) gewertet ist.6. Sensor according to claim 4, characterized in that an at least approximately linear curve shape is evaluated as an aged sensor element (16).
7. Sensor nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass wenigstens der zweite Signalwert7. Sensor according to any one of the preceding claims, characterized in that at least the second signal value
(S3) erfaßt wird in einem dritten Zeitintervall (13), in welchem das chemische Gleichgewicht des Sensorelements (16) wenigstens naherungsweise vorliegt.(S3) is detected in a third time interval (13) in which the chemical equilibrium of the sensor element (16) is at least approximately present.
8. Sensor nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass ein Gewichtungsfaktor von wenigstens zwei vorgegebenen Gasarten, mit denen das Sensorelement (Iβ) beaufschlagt ist, durch Festlegung des Betrags der Temperaturänderung (Tempi, Temp2) , festgelegt ist.8. Sensor according to one of the preceding claims, characterized in that a weighting factor of at least two predetermined gas types with which the sensor element (Iβ) is acted upon is determined by specifying the amount of the temperature change (tempi, temp2).
9. Sensor nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass ein Gewichtungsfaktor von wenigstens zwei vorgegebenen Gasarten, mit denen das Senso- relement (16) beaufschlagt ist, durch Festlegung der9. Sensor according to one of the preceding claims, characterized in that a weighting factor of at least two predetermined gas types with which the sensor element (16) is acted upon by determining the
Ausgangstemperatur (Tempi) , vor einer Temperaturänderung (Tempi, Temp2) festgelegt ist.Initial temperature (tempi), before a temperature change (tempi, temp2) is set.
10. Sensor nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass ein Gewichtungsfaktor von wenig- stens zwei vorgegebenen Gasarten, mit denen das Sensorelement (16) beaufschlagt ist, durch Festlegung der Dauer des zweiten Zeitintervalls (12) eingestellt ist.10. Sensor according to one of the preceding claims, characterized in that a weighting factor of little at least two predetermined types of gas with which the sensor element (16) is acted upon by setting the duration of the second time interval (12).
11. Sensor nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass ein Gewichtungsfaktor von wenigsten zwei vorgegebenen Gasarten, mit denen das Sensorelement (16) beaufschlagt ist, durch Festlegung des Zeitpunkts der Erfassung des wenigstens ersten und/oder des wenig- stens zweiten Signalwerts (S2, S3) eingestellt;ist . »11. Sensor according to one of the preceding claims, characterized in that a weighting factor of at least two predetermined gas types with which the sensor element (16) is acted upon by determining the time of detection of the at least first and / or the at least second signal value ( S2, S3) set ; is. »
12. Sensor nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass als Gasarten Stickoxyde (NOx) und Kohlenmonoxid (CO) vorgesehen sind.12. Sensor according to one of the preceding claims, characterized in that nitrogen oxides (NOx) and carbon monoxide (CO) are provided as gas types.
13. Sensor nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass der Sensor in einem Kraftfahrzeug eingesetzt ist und daß ein Ausgangssignal (24) der Signalbewertung (23) wenigstens ein an eine Klimaanlage des Kraftfahrzeugs abgegebenen Signal ist.13. Sensor according to one of the preceding claims, characterized in that the sensor is used in a motor vehicle and that an output signal (24) of the signal evaluation (23) is at least one signal given to an air conditioning system of the motor vehicle.
14. Sensor nach Anspruch 2, dadurch gekennzeichnet, daß aus einem Vergleich einer relativen Signaländerung bei einer Beaufschlagung des Sensorelements (16) mit einer zu^ de- tektierenden Gasart oder einem zu detektierenden Gasgemisch und einer Beaufschlagung mit Luft auf die Empfindlichkeit des Sensorelements (16) geschlossen wird. 14. The sensor according to claim 2, characterized in that from a comparison of relative signal change when a load of the sensor element (16) with a to ^ detected type of gas or a gas to be detected mixture and is acted upon with air on the sensitivity of the sensor element (16 ) is closed.
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