DE102007052689A1 - Sensor system for influencing ventilation system of e.g. vehicle, has measuring and controlling device producing signal for influencing ventilation system during deviations of output signals of low pass and high pass-frequency filters - Google Patents

Abstract

The system has a sensor (S) e.g. heatable metal oxide-sensor, for detection of oxidisable and/or reducible gases or vapors and providing output signals. An electronic measuring and controlling device is provided for measuring and evaluating the output signals. A high pass-frequency filter and a low pass-frequency filter are supplied with the output signals, where output signals of the filters are compared with one another in the controlling device. The controlling device produces a signal for influencing a ventilation system during deviations of the output signals of the filters. An independent claim is also included for a sensor system for influencing a ventilation system.

Description

Technical area:

The The invention relates to a sensor system for the purpose of influencing of ventilation systems of all kinds, consisting of at least a sensor, preferably heatable metal oxide sensor, for detection oxidizable and / or reducible gases or vapors whose / their Output signal / e representing air quality, an electronic measuring and control device for measurement and evaluation of the gas-dependent signals of the sensor as well for influencing the ventilation system, according to the The preamble of claim 1. Likewise, the invention relates to a method for the purpose of influencing ventilation systems of all Type by means of a sensor system consisting of at least one Sensor, preferably heatable metal oxide sensor, the oxidizable and / or reducible gases or vapors detected, the / Output signal / e representing air quality, and using an electronic measuring and control device, which the gas-dependent signals of the sensor for influencing the ventilation system measures and evaluates according to the Preamble of claim 7.

State of the art:

The Air quality is in accordance with the prior art measured with metal oxide semiconductor gas sensors (MOX-S). It will in general, the fact that gases use the electrical resistance in ohms of the semiconducting metal oxide active layer. The resistance of the gas sensor follows the gas concentration on one strongly curved characteristic, oxidizable gases (VOC, TVOC) reduce the sensor resistance and reducible gases (ozone, Nitrogen oxides) increase the sensor resistance.

The Interruption of air supply and switching to recirculation mode According to the state of the art, it does not correspond to a specific, absolute air quality value coupled. Rather, the air supply is dependent from the outside air quality then stopped when either a health-threatening absolute gas level measured or one compared to the average quality the sudden and relatively rapid deterioration of the air Air quality occurs.

In the DE-A1 33 04 324 For example, the sensor signal obtained by the resistance change of the sensor is differentially conducted via an electrical high-pass filter. Slow changes of the sensor signal, which z. B. by changing the humidity or regionally very different air quality can be caused are not forwarded. Rapid changes in the sensor signal indicate that the vehicle has entered a zone of greatly increased air pollution. Fast signals, on the other hand, are evaluated and generate a signal switching the ventilation.

It Systems are known in which by the resistance change the signal obtained over a period of time averaged and compared with the currently measured signal. Slow changes in air quality go into the mean value. Fast changes compared to averaging the air quality generate a ventilation switching Signal.

Both the subject of DE-A1 39 34 532 and related systems disadvantageously fail to recognize air quality reduced by diesel exhaust.

From the DE-C2 40 20 133 a two-sensor system is known, in which two semiconductor gas sensors are used in principle, wherein a sensor preferably reduces its resistance under the influence of oxidizable gases. These gases are preferred in exhaust gases of gasoline engines. The other sensor increases its resistance preferably under the influence of reducible gases, such as. B. nitrogen oxides. These gases are common in exhaust gases from diesel engines. The signals generated due to the resistance changes of the gas sensors are brought to suitable levels by electronic measures and effectively linked together. A system designed in this way advantageously detects both exhaust gases from diesel engines and from gasoline engines.

Of Furthermore, a system is known that works with a single sensor. The active layer of the sensor element is designed so that it both in the presence of gasoline exhaust gases as well as in the presence of diesel exhaust gases to typical changes in the resistance of the gas-sensitive Active layer of the gas sensor comes. Typically, the sensor resistance decreases in the presence of oxidizable gases (gasoline exhaust gases) and increases in the presence of reducible gases (diesel exhaust gases). The by the Resistance change of the gas sensor generated sensor signals are evaluated with a suitable method. Does it come to one fast signal change - independent from the direction of the signal change - becomes Switching signal generated.

A systematic disadvantage of this prior art is that the characteristic curve of the resistance characteristic of a gas sensor as a function of the gas concentration is extremely non-linear (see 1 ) runs. The amount of change in the resistance of the gas sensor is low when impulsively offered Gas concentrations very high. However, if the sensor is operated in an atmosphere where there is already a relatively high base level of gas (typical city air or air on a busy highway), additional pulsed gas offers only low signal amplitudes. Such gas sensors run at gas concentrations of z. B.> 500-2000 ppm increasingly asymptotic in the saturation. Higher gas concentrations no longer produce any evaluable resistance change and thus no change in the sensor signal.

Known Measure sensor systems for influencing ventilation systems non-permanent gas levels, but react preferentially on rapid changes in gas concentration or air quality. If z. B. a vehicle in a highly polluted by exhaust gas parking garage started, known systems have difficulties, this circumstance detect.

It can not be excluded that outside air in the Vehicle arrives. In other situations (eg traffic jam in a tunnel or passage through a very long tunnel) the resistance of the semiconductor sensor (s) in the saturation region be so that change amounts no longer take place. Disadvantageously, a malfunction of the system can not be safely ruled out become.

Known Furthermore, systems do not provide information about how the found ones influencing the air quality Compose gas mixtures. Rather, by MOX-S is a weighted Sum signal won. This changes the resistance of the sensor more or less pronounced in dependence from the chemical affinity of the gas to the gas sensor. are Several gases are present, resulting in traffic exhausts and indoor air with reduced quality always the case, sum up the influences of the individual gases become a sum signal, which allows no further conclusions.

In the DE-A1 10 2005 009 246.2 and the PCT / EP2006 / 001785 is further described that depending on gas offers the electrical charge / amount of electrons in the active layer of the sensor changed and can be measured directly with a suitable method. The electrical resistance of the active layer of the sensor is measured neither directly nor indirectly, because here the physical quantities current / voltage / resistance at both AC voltage and DC voltage play no role. It is advantageous that the characteristic of the sensor when measuring the amount of electrons is much more linear than the known characteristic of the resistance profile in gas supply. It is also advantageous that the saturation of the sensor begins only at significantly higher gas concentrations. When operating sensors in higher gas concentrations, this is an important advantage. In contrast to the prior art, therefore, the electrical resistance of the active layer of the semiconducting metal oxide sensor is not measured, but the gas-dependent electron quantity or the gas-dependent electrical charge of the active layer of the gas sensor.

Purpose of the invention:

At a sensor system for the purpose of influencing ventilation systems In general, the requirement is made that the system up a rapid increase even of small gas concentrations or quantities should react. Likewise, the system should respond appropriately, if in the long term higher gas concentrations or quantities deteriorate the air quality.

Technical task:

Of the Invention is based on the object, the ventilation of buildings, Rooms or vehicles of all kinds due to the current in the measured air quality Meaning of a situational influenced ventilation, both the outside air as well as the inside air as influencing variable should be usable.

Disclosure of the invention and its advantages:

at a sensor system of the type mentioned is the solution the task is that the sensor system both a high-pass frequency filter and a low-pass frequency filter over which the sensor signal supplied by the sensor is in each case conductive, wherein the output signals of both the high-pass frequency filter and the low-pass frequency filter on the electronic measuring and control device and comparable there, with deviations the two output signals from each other the electronic measuring and Control device of the ventilation system triggers a signal, which is capable of influencing the ventilation system.

In a further advantageous embodiment of the invention are the The signals supplied by the sensor can be evaluated so that the measured best air qualities and the worst measured Air qualities can be determined electronically, with the measured values the air qualities over a certain, longer Period and where these benchmarks are weighted Update consideration of new metrics.

In a further advantageous embodiment of the invention, the electronic measuring and control device of the ventilation system is capable of form the difference between the signals or values of the measured best air qualities and the measured worst air qualities, wherein the difference between the respective value for the best and the worst air quality is subdivided into a plurality of stages, and the actual signal of the transducer or the sensor signal source directly the measuring and control device is supplied, wherein a switching system influencing the ventilation system is then triggered by the measuring and control device, if the currently measured air quality, represented by the current signal of the transducer or the sensor signal source, worse than a predetermined value or outside above mentioned values of "best air quality" and "worst air quality".

In Another advantageous embodiment of the invention are after Claim 1 generated output signals of the high-pass frequency filter and the low-pass frequency filter with the signals of the measured best air qualities and measured worst Air qualities according to claim 2 in one OR link can be linked to one another in this way, that the electronic measuring and control device a the ventilation system influencing new signal then is able to trigger if one of the input signals is present.

In Another advantageous embodiment of the invention provides the sensor system the quality of the indoor air firm and is capable of the ventilation system in the sense that the ventilation used Air quantity increases when the air quality in accordance with Criteria according to one of the preceding claims bad is.

In Another advantageous embodiment of the invention provides the sensor system the quality of the outside air and is able to to influence the ventilation system in the sense that the for ventilation used air volume decreases or is persistent or stopped when the air quality according to the criteria of any of the preceding Claims 1 to 4 is bad.

Procedurally, The solution to the problem is that both a High-pass frequency filter as well as a low-pass frequency filter used via which the sensor signal (S) supplied by the sensor is passed, wherein the output signals of both the high-pass frequency filter as well as the low-pass frequency filter on the electronic measuring and control device abandoned and compared there, wherein in case of deviations of the two output signals from each other the electronic measuring and control device of the ventilation system a signal triggers the ventilation system affected.

• • Wird die gemessene Luftqualität schlechter als ein vorgegebenes Normal, wird die zur Lüftung eingesetzte Luftmenge erhöht.
• • Wird die gemessene Luftqualität besser als ein vorgegebenes Normal, wird die zur Lüftung eingesetzte Luftmenge vermindert oder ausgesetzt.

According to the invention, the procedure is thus as follows: measurement of the air quality in interiors or inside vehicles:

• • If the measured air quality is worse than a specified normal, the air volume used for ventilation is increased.
• • If the measured air quality is better than a specified normal, the air volume used for ventilation is reduced or suspended.

• • Wird die Außenluft schlechter als ein vorgegebener Wert, wird die Luftzufuhr unterbrochen und das Lüftungssystem wird z. B. auf Umluftbetrieb geschaltet.
• • Ist die Qualität der Außenluft wieder akzeptabel geworden, wird von Umluftbetrieb auf Normalbetrieb umgeschaltet.

Measurement of the air quality of outside air, which is introduced into rooms or cabins for ventilation:

• • If the outside air is worse than a preset value, the air supply is interrupted and the ventilation system is z. B. switched to recirculation mode.
• • If the quality of the outside air has become acceptable again, the air recirculation mode switches to normal operation.

In this case, in the embodiment of the invention, the subjects of the inventions DE-A1 10 2005 009 246.2 or the PCT / EP2006 / 001785 be used. An inexpensive sensor system for controlling the ventilation system of preferably vehicles is ideally based on a single sensor element. The sensor element supplies gas-dependent sensor signals, which are advantageously obtained from the measurement of the gas-dependent amount of electrons or the electrical charge in the gas-sensitive active layer of the sensor.

at Higher requirements, the sensor system can have multiple sensor elements exhibit. The sensor elements each deliver specific Signals which are generated by different methods and which are further processed by different methods can.

Of the The invention basically has the advantage on that with him the ventilation of buildings, rooms or of all types of vehicles due to the currently measured air quality can be favorably influenced in the sense of a situational influenced ventilation. It can be done in an advantageous manner both the outside air and the inside air as an influence be used.

Short name of the drawing, in the demonstrate:

1 the characteristic of the resistance curve of a gas sensor of the prior art as a function of the gas concentration, it being apparent that this is extremely non-linear,

2 1 is a block diagram of the circuit structure of a sensor system with only one sensor element,

3 a block diagram of a sensor system for the consideration of dynamic, constantly changing sensor signals and

4 the time course of two thresholds "good air" and "bad air".

preferred Solving the problem "Sensor-controlled influencing of ventilation systems ":

a) system with a single sensor element according to the 2 :

The Sensor system consists of a sensor S, wherein preferably a MOX sensor element used which is based on both oxidizable and reducible gases or vapors with a change in the amount of electrons / charge reacts in the active layer of the sensor. The gas-dependent Charge the active layer of the sensor with a suitable circuit measured, which is referred to as a transducer. Its output signal is hereinafter referred to as "signal".

• • Frequenzfilter einer Frequenz zwischen vorzugsweise cirka 0,0001–0,001 Hz oder einem Tiefpassfrequenzfilter der gleichen Grenzfrequenz = Tiefpass
• • Frequenzhochpass bzw. Differenzierer einer Grenzfrequenz von vorzugsweise cirka 0,1–10 Hz = Hochpass.

The sensor signals of the transducer are pre-processed for the purpose of obtaining a switching signal via two separate paths:

• • Frequency filter of a frequency between preferably about 0.0001-0.001 Hz or a low pass frequency filter of the same cutoff frequency = low pass
• • Frequency high pass or differentiator of a cutoff frequency of preferably approximately 0.1-10 Hz = high pass.

Either the output of the high pass as well as the output of the Low-pass filters are used on an electronic measuring and control device abandoned, preferably a microcontroller, which measuring and control device compare both supplied waveforms.

If in this comparison of the two output signals that of the high pass supplied output signal by a certain, specifiable value deviates from the output signal supplied by the low pass generated the measuring and control device generates a switching signal because It is precisely the gas concentration or air quality detected by the sensor has changed significantly. The switching signal can, for example be placed on an actuator in the ventilation system for example, a mechanical adjustment of a ventilation member, like ventilation flaps, performs.

The The aforementioned method takes into account dynamic, ie itself constantly changing sensor signals. Static sensor signals or those sensor signals that change only slowly, can not directly or not with the above method readily used to influence ventilation equipment become.

Therefore, according to the invention further according to the 3 Suggested: As in 1 The sensor system may consist of a sensor S, for example MOX sensor element, which sensor S reacts to both oxidizable and reducible gases or vapors with a change in the amount of electrons / charge in the active layer of the sensor. The gas-dependent charge of the active layer of the sensor is again measured with a suitable circuit, which is referred to as a sensor signal source or as a transducer. Its output signal is also referred to below as "signal".

The measured signals always fluctuate between a value which represents the best air quality and one second value representing the worst air quality. It is thus in at least one electronic circuit, both the one Value representing the best air quality, as well as the value which gives the worst air quality represented, stored in a dynamic way. These Saving the mentioned best and bad values can of course also by means of the electronic measuring and control device for measurement and evaluation of the gas-dependent signals of the sensor as well to influence the ventilation system. The measuring and Control device or its microcontroller stores each measured best and worst value, with constantly incoming signal values be considered, so one for a given Period, for. For 1 h or 10 h or 100 h or 1,000 h or 10.00 h, a representative minimum and maximum value is detected. At the same time the current signal of the transducer is displayed or the sensor signal source of the electronic measuring and control device fed.

• Beste Luftqualität = 0
• Schlechteste Luftqualität = 100

The amount between the minimum and maximum values is divided into a plurality of levels, which is in 4 is shown, for example:

• Best air quality = 0
• Worst air quality = 100

Whenever the current signal of the transducer or the sensor signal source within the electronic measuring and control device falls below or exceeds an arbitrarily defined threshold between the long-term tracked and stored minimum and maximum values, the measuring and control device generates a switching signal which the ventilation system affected. For example, the switching signal is applied to an actuator, which in the ventilation system, for example, a mechanical adjustment of a Ventilation member, such as ventilation flaps, makes. The absolute value of the measured gas concentration is stored.

The described absolute value measurement of air quality is continuous continued. If the air quality of the outside air has improved by a freely specified amount and considered harmless can apply, the air supply is released.

If On the other hand, for example, ammonia is in the outside air and this has been determined by the system, the air supply is only released if no evidence of the presence of ammonia exist more.

additionally It is proposed, in addition, a freely defined time to wait with the release because ammonia for humans even in low concentrations extremely unpleasant is and because ammonia-enriched air is in the air could be (harassment).

The System can also be applied to the detection of irritating gases, such as CN or CS, be aligned and recognize early, when irritating gases are in the outside air. The same applies to anesthetic gases or other highly toxic Substances. In this case, the supply air remains permanently locked. The ventilation will be after detecting a dangerous situation only released again when the sensor system no Gases in the air can determine more.

alternative the ventilation system can be designed so that the release by staff has to do after this the situation as safe has judged. This may be the case in applications with increased security requirements be appropriate.

Certainly the sensor system the quality of indoor air, can be supplied Air quantity can then be increased if the air quality in the interior deteriorates. For example, a fan automatically switched on or off or the air flow can be automatically lowered or raised.

The Invention ensures that occurs in case of sudden onset of gases or vapors (eg in the air of kitchens, Kitchen hoods, toilets or in other private, commercially or industrially used rooms or cabins of vehicles of all kinds) the ventilation makes sense very quickly is influenced by inappropriate and unpleasant gas or vapor concentrations to prevent in the interiors. At the same time, the Invention sure that with creeping, very slow changes the ventilation is reliably activated when the Air quality falls below a specified size.

Advantageous is always that the sensor system automatically on each prevailing situation and no calibration or Adjustment with changing air quality requires.

• • Einsatz von halbleitenden Metalloxid-Sensoren (MOX-S), Sensor S,
• • Erzeugen eines gasabhängigen Sensorsignals durch Messung der Elektronenmenge bzw. der elektrischen Ladung in der Wirkschicht des/der Sensorelement/e, mittels eines Messwertwandlers bzw. einer Sensorsignalquelle (gemäß der DE-A1 10 2005 009 246.2 und der PCT/EP2006/001785 )
• • Schnelle Sperrung der Luftzufuhr dann, wenn sich die Luftqualität der Außenluft in kurzer Zeit um festgelegte Beträge verschlechtert,
• • Schnelle Erhöhung der Luftzufuhr dann, wenn sich die Luftqualität der Innenluft in kurzer Zeit um festgelegte Beträge verschlechtert.
• • Sinnvolle Beeinflussung der Luftzufuhr dann, wenn die Luftqualität auf einer Skala zwischen einer statistisch langfristig ermittelten besten und schlechtesten Luftqualität unter einen festgelegten Luftqualitätswert sinkt,
• • Bei dieser Messung wird die Anwesenheit von Ammoniak festgestellt oder ausgeschlossen,
• • Verwertung der Messdaten zu Steuerungszwecken der Lüftungsanlage oder zum Zwecke der Warnung vor Gefahren.

The essential elements of this invention for the purpose of controlling ventilation systems are:

• • Use of semiconducting metal oxide sensors (MOX-S), sensor S,
• Generating a gas-dependent sensor signal by measuring the quantity of electrons or the electric charge in the active layer of the sensor element (s), by means of a measured value converter or a sensor signal source (according to FIG DE-A1 10 2005 009 246.2 and the PCT / EP2006 / 001785 )
• • Quick shut-off of the air supply when the air quality of the outside air deteriorates in a short time by predetermined amounts,
• • Rapid increase in air supply when the indoor air quality deteriorates by a specified amount in a short time.
• • Sensible effect on air supply when air quality falls below a set air quality value on a scale between a statistically long-term best and worst air quality,
• • In this measurement, the presence of ammonia is detected or excluded,
• • Utilization of the measured data for control purposes of the ventilation system or for the purpose of warning against dangers.

• • Sensor zur Detektion oxidierbarer und/oder reduzierbarer Gase oder Dämpfe, die die Luftqualität repräsentieren, vorzugsweise beheizter Metalloxid-Sensor,
• • elektronische Schaltung zur Messung gasabhängiger Sensorsignale,
• • elektronische Schaltung zur Auswertung der gemessenen Sensorsignale,
• • elektronische Steuerung zur Beeinflussung der Lüftungsanlagen,

wobei das vom Sensor gelieferte Sensorsignal über einen Hochpass-Frequenzfilter geleitet wird, das vom Sensor gelieferte Sensorsignal über einen Tiefpass-Frequenzfilter geleitet wird, und dass bei Abweichungen dieser beiden Sensorsignale voneinander ein die Lüftungsanlage beeinflussendes Signal ausgelöst wird.The invention is thus a sensor system for the purpose of influencing ventilation systems of all kinds, consisting of

• Sensor for detecting oxidizable and / or reducible gases or vapors, which represent the air quality, preferably heated metal oxide sensor,
• Electronic circuit for measuring gas-dependent sensor signals,
• Electronic circuit for evaluating the measured sensor signals,
• • electronic control for influencing the ventilation systems,

wherein the sensor signal supplied by the sensor is passed through a high-pass frequency filter, the sensor signal supplied by the sensor is passed through a low-pass frequency filter, and that in case of deviations of these two sensor signals from each other a signal influencing the ventilation system is triggered.

The signals supplied by the sensor are evaluated so that the measured best air quality and the measured worst air quality are determined electronically, taking measurements over a certain, longer period of time and updating these benchmarks by weighting new measurements. The difference between the value for the best and the worst air quality is divided into a plurality of stages. A signal influencing the ventilation system is triggered when the currently measured air quality is worse than a certain value located between the aforementioned basic values.

The to page 12, lines 1-12, generated output signals and page 12, lines 14-22, are generated output signals so interconnected that one the ventilation system influencing new signal is then triggered when one of the input signals is present (OR operation).

The Sensor system determines the quality of indoor air and influences the ventilation system in the sense that the Ventilation used air volume is increased when the air quality according to the above criteria page 12, lines 1 to 27 is bad.

equally the sensor system represents the quality of the outside air firmly and affects the ventilation system in the sense that the amount of air used for ventilation is reduced or stopped if the air quality is according to the criteria page 12, Lines 1 to 27, is bad.

Industrial Applicability:

Of the Subject matter of the invention, both the invention Sensor system and the method according to the invention, is advantageous for influencing ventilation systems of all kinds used.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 3304324 A1 [0004]
• - DE 3934532 A1 [0006]
• - DE 4020133 C2 [0007]
• - DE 102005009246 A1 [0013, 0025, 0050]
• - EP 2006/001785 [0013, 0025, 0050]

Claims (8)

Sensor system for the purpose of influencing ventilation systems of all kinds, consisting of at least one sensor (S), preferably heatable metal oxide sensor, for the detection of oxidizable and / or reducible gases or vapors, whose / their output signal / e represented the air quality, and an electronic Mess - And control device for measuring and evaluating the gas-dependent signals of the sensor and for influencing the ventilation system, characterized in that the sensor system comprises both a high-pass frequency filter and a low-pass frequency filter, via which the sensor (S) supplied sensor signal is in each case conductive , Wherein the output signals of both the high-pass frequency filter and the low-pass frequency filter on the electronic measuring and control device can be aufgebbar and there comparable with each other, wherein in case of deviations of the two output signals from each other, the electronic measuring and control device of the Lüf system triggers a signal which is capable of influencing the ventilation system. Sensor system according to claim 1, characterized that the signals supplied by the sensor (S) are evaluable that measured best air qualities and measured worst air quality can be determined electronically, with the measured values of the air qualities over a certain, longer period are available and where these are Basic values through weighted consideration of new measured values To update. Sensor system according to claim 1 or 2, characterized that the electronic measuring and control device of the ventilation system is able to choose from the signals or values of the best measured Air qualities and the measured worst air qualities to form the difference, with the difference between the respective Value for the best and the worst air quality is subdivided into a plurality of stages, and the current signal of the transducer or sensor signal source directly to the and control means is supplied, wherein one The ventilation system then influences the switching signal the measuring and control device is triggered, if the currently measured air quality, represents by the current signal of the transducer or the sensor signal source, worse than a given value or an outside the above-mentioned benchmarks "best air quality" and "worst air quality" Air quality "value is. Sensor system according to one of the preceding claims, characterized in that the output signals generated according to claim 1 the high-pass frequency filter and the low-pass frequency filter with the signals of the measured best air qualities and the measured worst air quality according to claim 2 in an OR link so mutually linked are that the electronic measuring and control device a the Ventilation system influencing new signal then trigger is capable of, if one of the input signals is present. Sensor system according to at least one of the preceding Claims, characterized in that the sensor system the quality of the indoor air determines and the ventilation system in the sense of being able to influence that for ventilation used air volume increases when the air quality in accordance with Criteria according to one of the preceding claims bad is. Sensor system according to at least one of the preceding Claims, characterized in that the sensor system the quality of the outside air determines and the Ventilation system in the sense of being able to influence that the amount of air used for ventilation decreases or is sustainable if the air quality is in accordance with the Criteria according to one of the preceding claims 1 to 4 bad is. Method for the purpose of influencing ventilation systems of all kinds by means of a sensor system consisting of at least a sensor (S), preferably heatable metal oxide sensor, the oxidizable and / or reducible gases or vapors detected, the / Output signal / e representing air quality, and using an electronic measuring and control device, which the gas-dependent signals of the sensor for influencing the ventilation system measures and evaluates, characterized that both a high-pass frequency filter and a low-pass frequency filter are used, over which the sensor (S) supplied Sensor signal is passed, the output signals both the high-pass frequency filter as well as the low-pass frequency filter abandoned on the electronic measuring and control device and be compared there with each other, with deviations of Both output signals from each other, the electronic measuring and control device the ventilation system triggers a signal which the ventilation system influences. A method according to claim 7, characterized in that the signals supplied by the sensor are evaluated so that the measured best air qualities and the measured worst air quality are determined electronically, whereby measured values are used over a certain, longer period of time and these Update benchmarks by weighting new measurements, dividing the difference between the best and worst air quality values into a plurality of stages, and triggering a signal affecting the ventilation system when the currently measured air quality is worse than a certain one and between the above Value is.