EP1530487A1

EP1530487A1 - Air purification device

Info

Publication number: EP1530487A1
Application number: EP03784198A
Authority: EP
Inventors: Werner Schröder
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-08-07
Filing date: 2003-08-07
Publication date: 2005-05-18
Also published as: CA2494917A1; AU2003258584A1; AU2003258584A2; JP2006500976A; DE10236196A1; WO2004014442A1; CN1681537A; DE10236196B4

Abstract

The invention relates to an air purification device for reducing pollutants in the air. Said device comprises an ioniser (904), which is exposed to an air flow (906) and impinged upon by an ionisation power from a driver stage (903) for ionising the air that is supplied by the air flow, and a gas sensor (905) for measuring pollutant concentrations. To provide an air purification device, which purifies the air according to requirements even if the pollutant concentrations change rapidly and/or have extreme values, the driver stage (903), ioniser (904) and gas sensor (905) co-operate with a controller (902) in a closed loop control circuit, in such a way that the output signal of the gas sensor (905) essentially corresponds to a predetermined target value.

Description

Air cleaning device

The invention relates to an air purification device for reducing pollutants in the air with an ionizer which is exposed to an air flow and which can be acted upon by a driver stage with ionization power, the air supplied by the air flow being ionizable depending on the ionization performance, and with "a Gas sensor for measuring pollutant concentrations.

It is known in principle to treat room air or breathing air with so-called ionizers to reduce pollutants. Pollutants or odorous substances usually form complex and large molecules, which are broken down into small-molecule fragments by the ionizer. At the same time, the ionization forms radicals and here in particular oxygen adicals, which can then oxidize with the split fragments. The ionizer is based on a controlled gas discharge that takes place between two electrodes and a dielectric in between. The gas discharge represents a barrier discharge, with the dielectric acting as a dielectric barrier. In this way, time-limited individual discharges are achieved, which are preferably distributed homogeneously over the entire electrode area. It is characteristic of these barrier discharges that the transition to a thermal arc discharge is prevented by the dielectric barrier. The discharge stops before the ignition occurs high-energy electrons (1 - 10 eV)

Thermalization release their energy to the surrounding gas.

For the household sector in particular, there are already various applications for such

Air purifier has been proposed. For example, it is known from DE 198 10 497 AI to provide such an air cleaning device in a toilet for removing odors. For this purpose, suitable suction devices with air ducts on the upper rinsing edge of the toilet bowl or in a hollow channel in the toilet seat direct the contaminated air to the ionizer in order to reduce the odor nuisance.

One problem with operating the ionizer is that

Control of the ionizer with a needs-based ionization performance. If too little ionization power is applied to the ionizer, the ionization is unsatisfactorily low, while if the ionization is too high, too much ions and radicals are released, which leave the user with the impression of the smell of a harsh caustic or cleaning agent. In this operating state, in addition to the formation of ions, ozone is also produced, the overproduction of which is also undesirable.

To solve this problem, WO 98/26482 describes an air cleaning device with an ionizer, the supply voltage of which is controlled by a gas sensor. The gas sensor is one

Metal oxide semiconductor sensor, the resistance of which decreases with increasing concentration of certain gases (usually oxidizable gases or vapors, for example hydrogen sulfide, hydrogen, ammonia, ethanol or carbon monoxide). The change in resistance is thus a measure of the air pollution with certain pollutants. According to WO 98/26482, the ionization power with which the ionizer is acted upon is increased in a sensor-controlled manner with increasing pollutant concentration up to a maximum value. This means that if the gas sensor has a low pollutant concentration, a correspondingly low ionization power is applied to the ionizer, while if the gas pollutant concentration is high, the ionizer is also driven with a correspondingly high ionization power. To supplement this sensor control, WO 98/26482 also describes the use of an additional ionization sensor and / or ozone sensor. Since the air quality sensor measures the pollutant concentration of the air supplied and is thus arranged in terms of flow technology in front of the ionizer, the additional ionization sensor and / or ozone sensor serve to determine a still undesirable ozone concentration in the cleaned air in order to then possibly correspond to the ionization output correct.

A sensor control corresponding to WO 98/26482 is also described in DE 43 34 956 AI. In DE 43 34 956 AI a tin dioxide gas sensor is proposed, which detects the oxidizable indoor air components. If this gas sensor detects a larger space load, then the ionizer is also controlled with a higher ionization power. In addition, the use of a moisture sensor and a flow sensor is proposed in order to increase the ionization capacity even when a larger amount of air or a higher humidity is measured. A disadvantage of the known control methods from WO 98/26482 and DE 43 34 956 AI is the fact that the gas sensors used have a limited measuring range and additionally a relatively slow response time. The limited measuring range means that sensor control of the ionization power in the edge regions of the measuring range is not possible. If the pollutant concentration is below the lowest measured value of the gas sensor, for example, the ionizer is either switched off or continues to be operated at a predetermined minimum value of the ionization power. When things change quickly

Pollutant concentrations, the slow response time of the sensor also means that the ionizer only needs to be activated after a certain time

Delay occurs. This delay is disadvantageous, for example, in the removal of odors in a toilet, since an immediate removal of the odorants by the ionizer is desirable, especially in the event of a sudden increase in the odorants.

It is therefore an object of the invention to provide an air purification device which enables air purification to meet requirements even when pollutant concentrations change rapidly and / or assume extreme values.

This object is achieved by an air cleaning device with the features of claim 1 and a method for reducing pollutants with the features of claim 18.

An essential feature of the invention is that the driver stage, the ionizer and the gas sensor interact with a controller in a closed control loop in such a way that the output signal of the gas sensor essentially corresponds to a predetermined target value. Thus, while a sensor control is proposed according to the prior art, in which the sensor characteristic is traversed as a function of the measured pollutant concentration, the invention describes a fundamentally different route. According to the invention, the gas sensor is operated only at a certain operating point, which is predetermined by the setpoint of the control loop. The gas sensor therefore always delivers as the output signal a value which essentially corresponds to the target value, while the controller is responsible for setting the ionization power at the ionizer which keeps the output of the gas sensor at the said target value.

To achieve this goal, however, there must be some feedback between the gas sensor and the ionizer. The necessity of this feedback and the connection between the feedback and the arrangement of the gas sensor in relation to the air flow and in relation to the ionizer have not yet been recognized in the prior art either. The arrangements of the gas sensor described in the prior art only relate to arrangements which are upstream of the ionizer in terms of flow technology, so that the control loop effect according to the invention cannot occur.

In contrast, the invention is based further on the recognition that the gas sensor is arranged in relation to the air flow and with respect to the ionizer such that a change in the ^'output signal supplied during open loop control of the gas sensor due to an abrupt change in the concentration of pollutants in the air flow Air can be compensated for by a change in the ionization energy, so that Output signal of the gas sensor can be traced back to its original value. The feedback between the ionizer and the gas sensor must be brought about by the arrangement of the gas sensor in relation to the air flow and in relation to the ionizer so that the effect of the ionizer and the effect of the pollutant concentrations contained in the air flow can overlap at the gas sensor.

An open control loop in the sense of the invention is present when there is an electrical feedback between the

Output signal of the gas sensor and the controller is interrupted.

A step change in the pollutant concentration as a test function for the open control loop is present in the sense of the invention when the pollutant concentration in the air supplied to the ionizer by the air flow changes from a first constant value by a certain step height to a second constant value at a certain point in time changes. With a practical

Experimental arrangement, this means that a possibly provided air circulation of the air flow has to be interrupted so that the pollutant concentration in the air flow supplied to the ionizer is required before and after the abrupt change in the air flow

Pollutant concentration remains constant and is not additionally influenced by the air flow discharged by the ionizer.

The jump amplitude of the sudden change in the pollutant concentration is preferably based on typical changes in the pollutant concentration. Typical changes in the pollutant concentration in the air flow can be determined for the respective application by the expected changes in the Pollutant concentration according to their expected frequency are plotted in a histogram. For example, all cases that lie within +/- 10% of a frequency maximum can be assumed to be typical. If, for example, the air purification device in a room is to reduce the smell of cigarette smoke, the expected change in the concentration of pollutants is based on the expected air pollution from cigarette smoke compared to normal air pollution. According to the invention, the gas sensor must now be arranged in relation to the air flow and in relation to the ionizer in such a way that said change in the pollutant concentration in the air flow can be compensated for by a change in the ionization energy, so that the output signal of the gas sensor is on it

The original value can be traced back, which in the example corresponds to the original value of the normal air pollution. The greater the expected influence of the change in the pollutant concentration, the closer the gas sensor must be to the ionizer. If, on the other hand, only small changes in the pollutant concentration are to be expected, the gas sensor should not be arranged too close to the ionizer, since otherwise the output signal of the gas sensor can easily be limited. In any case, however, the gas sensor must maintain a certain minimum distance from the ionizer so that the feedback between the ionizer and the gas sensor is not sufficient in order to compensate for the changes in the pollutant concentration that occur and thus to keep the output signal in the range of a predetermined target value according to the invention.

Another finding of the invention is that commercially available gas sensors can be used as the measuring element of the control loop for measuring pollutant concentrations. It has already been shown that way An overproduction of ozone which is disruptive to humans can be avoided by the ionizer, so that the ionization sensors or ozone sensors which are otherwise used for this purpose are not absolutely necessary.

In the method according to the invention for reducing pollutants in the air, the setpoint is set to a certain pollutant concentration with the air purification device according to the invention, polluted air is fed to the ionizer and pollutant-reduced air is removed from the ionizer. According to a preferred embodiment, it is provided that all or part of the air removed is recirculated to the ionizer in the recirculation mode in order to increase the efficiency of the air purification.

An important advantage of the invention is that the mode of operation of the air cleaning device is not fundamentally limited by the measuring range of the gas sensor. Since the gas sensor is operated in accordance with the operating point specified by the setpoint, changes in the pollutant concentration can also be treated by the air purification device that go beyond the measuring range of the gas sensor. In the case of a conventional sensor control, on the other hand, the output signal of the gas sensor would be limited and would therefore also limit the activation of the ionizer or the driver stage. The limits of the air purification device are therefore in principle only due to the limitation of the ionization power. Appropriate measures can, however, additionally increase the ionization output, for example by connecting additional ionizers and / or fans to increase the flow velocity of the air flow. The air cleaning device according to the invention This opens up a wide range of possible applications, from the household sector to industrial cleaning of large air spaces.

Another advantage of the invention is that an appropriate design of the controller enables a settling behavior of the closed control loop, the settling time of which is below the time constant of the gas sensor. This can be achieved, for example, by means of a differential component in the controller, which causes large manipulated variables at the driver stage even with small changes in the output signal of the gas sensor.

According to a preferred embodiment, it is provided that the driver stage comprises a high-voltage transformer, on the secondary side of which an oscillating high voltage can be generated. The ionization power supplied to the ionizer can be influenced primarily by the peak value of the oscillating high voltage and / or by pulsing the oscillating high voltage. The driver stage preferably comprises a circuit for pulse width modulation with which the

High-voltage transformer can be controlled on the primary side and the peak value and / or the pulse ratio of the high-voltage oscillating on the secondary side can be set. In the case of a series circuit consisting of a high-voltage transformer and a resonator, which is supplied with a DC voltage on the input side, the pulse-width-modulated signal can be rectified and fed to the input of the resonator. The resonator in turn supplies an oscillating voltage to the primary side of the

High-voltage transformer, so that the peak value on the secondary side of the high-voltage transformer is therefore proportional to the pulse width ratio. Additionally or alternatively, it can be provided that the on the Secondary side delivered high voltage is pulsed. This means that the ionizer is only subjected to a certain number of full waves before the oscillating high voltage is interrupted again. The ionization power thus supplied on average is also proportional to the pulse width ratio. The pulse width ratio can be the same

Pulse width modulation signal are obtained, which is present at the input of the resonator, or a further pulse width modulation signal is generated for this purpose.

According to a further preferred embodiment, it is provided that the high voltage oscillating on the secondary side can be set with a peak value in the range from 1 kV to 10 kV and with a frequency in the range from 10 kHz to 50 kHz.

According to a preferred embodiment, the ionizer consists of a glass tube, the inner wall of which is lined with a perforated plate as the first electrode and the outer wall of which is surrounded by a wire mesh as the second electrode, the oscillating high voltage of the driver stage being present between the first electrode and the second electrode. In order to achieve disinfection or purification of the gas flowing around the ionization tube, the high-voltage transformer is controlled in such a way that radicals, preferably oxygen radicals, are generated in the event of a gas discharge. The high-voltage transformer is usually supplied with an AC voltage in the range of -ca; 10 kHz to 50 kHz, preferably in the range from 15 kHz to 30 kHz, operated at a peak value of 1 to 10 kV. If a gas flows around such an ionization tube, a gas discharge thus takes place, which results in ionization of the gas flowing around. The gas discharge represents one Barrier discharge, which takes place through the glass tube acting as a dielectric barrier. In this way, time-limited individual discharges are achieved, which are distributed homogeneously over the entire electrode area. It is characteristic of these barrier discharges that the transition to a thermal arc discharge is prevented by the dielectric barrier. The discharge stops before the high-energy electrons (1 - 10 eV) generated during ignition release their energy to the surrounding gas through thermalization. Alternatively, of course, any other form of ionizer is conceivable, such as, for example, a plate-shaped arrangement or combinations of tube arrangement and plate-shaped arrangement.

According to a preferred embodiment, it is further provided that the gas sensor consists of a metal oxide sensor, the resistance of which changes during reactions with gases. The metal oxide is applied to a substrate which is kept at a predetermined temperature with a heating element. A gas sensor is preferably used which shows no change in resistance to changing oxygen concentration in the air. It has been shown that a particularly reliable control of the pollutant concentration is possible with such gas sensors. The metal oxide can consist of tin dioxide, for example.

According to a further preferred embodiment, it is provided that the air inlet opening of the gas sensor is at a distance of approximately 0.5 cm to 5.0 cm, preferably approximately 1.0 cm to 2.0 cm, from the air in relation to the air flowing around the ionizer Has surface of the ionizer. It has been shown that at these distances the Adjustment range of the gas sensor can be reconciled with the adjustment range of the ionizer and the range of values for usual pollutant concentrations.

According to a further preferred embodiment, it is provided that the setpoint on the device can be set manually. The operator thus has the option of specifying a mode of operation of the device which is pleasant for him, given the normal concentration of pollutants in the air. The arrangement of the gas sensor is particularly preferably selected in such a way that the predefined setpoint value corresponds to a middle range in relation to the entire modulation range of the output signal of the gas sensor. Since, according to the invention, the control loop ensures that the pollutant concentration measured by the gas sensor essentially corresponds to the desired value, the gas sensor is thus operated in a range which enables maximum controllability during the transient process of the closed control loop.

According to a further preferred embodiment, it is provided that the air flow is generated by convection, which in the case of small domestic appliances can, for example, result from the air supplied to the electrical components of the appliance being heated.

According to another preferred embodiment, a fan is provided for generating the air flow. It was recognized that the air flow can also influence the way the control loop works. If the gas sensor is located, for example, on the flow side in front of the ionizer, the coupling between the ionizer and the gas sensor is smaller compared to one with the same distance between the gas sensor and the surface of the ionizer Arrangement in which the gas sensor is arranged on the flow side behind the ionizer.

According to a further preferred embodiment it is therefore provided that an additional controller

Also regulates the flow speed of the air flow in such a way that the output signal of the gas sensor essentially corresponds to a predetermined setpoint. In particular, it has proven to be expedient that the additional controller is switched on as soon as in the

Control circuit consisting of ionizer, driver stage, gas sensor and controller a limitation occurs. In this case, the additional controller must act in such a way that the limitation that occurs can be sensibly compensated for.

The mode of operation of the control loop naturally depends to a large extent on the type of controller used. If the transmission behavior of the other control loop elements, i.e. the ionizer, the driver stage and the gas sensor, has been determined by suitable identification methods, the controller can basically be designed according to the available control engineering methods. A P controller, a PI controller or a PID controller can be used as classic control loop elements. The simplest case is the P controller, which in principle, however, requires a control difference between the specified setpoint and the pollutant concentration measured by the gas sensor in order to be able to output a manipulated variable. However, if the gain factor of the P controller is chosen high enough, the control difference can be neglected. However, a high gain factor of the P-controller is only permissible if there is still a sufficient signal / noise ratio at the output signal of the gas sensor. Should the signal / noise ratio at the output signal of the gas sensor If, on the other hand, you are no longer sufficient to use a P controller, the use of a PI controller is recommended. Thanks to its integrative behavior, the PI controller is able to deliver a permanent manipulated variable even if the control difference disappears. Thus, when using a PI controller, the disappearance of the control difference can basically be achieved when the control loop is steady. In order to accelerate the settling behavior of the control loop, a di ferential element is usually added to the PI controller, creating a PID controller. The differential behavior of the PID controller can lead to limits appearing in the control loop elements when there are rapid changes in the pollutant concentration or the setpoint. In this case, it is advantageous to add a

To provide additional controller for the flow rate. If the ionizer reaches its upper limit with its ionization capacity, the additional controller can instead provide for an increase in the flow velocity of the air flow.

In addition to the classic controller types P controller, PI controller and PID controller, other controllers can of course also be provided, such as a rule-based fuzzy controller or a state controller. A rule-based fuzzy controller or also a state controller are particularly suitable if the controller is to process further measured variables in addition to the measured pollutant concentration. Basically, it is conceivable that the control behavior by additional

To improve sensors, such as a moisture sensor and / or an ionization sensor and / or an ozone sensor. According to a further preferred embodiment, it is provided that a calibration element calibrates the gas sensor to the desired value when the gas sensor is supplied with a pollutant concentration corresponding to the desired value. The ionizer is preferably supplied

Ionization energy switched off during the calibration of the gas sensor in order to avoid disturbing effects of the ionizer in calibration operation. As an alternative to this, the ionizer can also be controlled in calibration operation with a predetermined continuous ionization power with which the ionizer is to be operated at least in order to maintain a pleasant room climate at all times.

The manufacturing-related tolerances of a gas sensor can be compensated for by calibrating the gas sensor. When using the tin dioxide gas sensors mentioned above, it was observed that the. Tolerances essentially affect an absolute shift in the characteristic curve, while the relative change in the sensor signal as a function of

Gas concentration remains approximately the same for all gas sensors. In this case, the calibration element can consist of a simple adder, which adds a corresponding voltage to the output voltage of the gas sensor in calibration operation. In this case, it is additionally necessary that a pollutant concentration is supplied to the gas sensor during the calibration operation, which the user presupposes as "clean air". Goal is _. it is to determine in the calibration operation by the calibration element that additional voltage which is necessary to make the control deviation approximately zero. The invention is explained in more detail below on the basis of various exemplary embodiments with reference to the accompanying drawings. These show:

1: a block diagram for the transmission behavior of a gas sensor with a step function as an input,

Fig. Lb: the response function at output 150 with a step amplitude of 1,

Fig. Lc: the response function at output 150 with a step amplitude of 2.5,

2a: a block diagram for the transmission behavior of a sensor control with a step function as input,

2b: the response function at output 250 with a step amplitude of 1,

2c: the response function at output 250 with a step amplitude of 2.5,

3a: a block diagram for the transmission behavior of an open control loop with a step function of the pollutant concentration,

3b: the response function at output 350 with a jump amplitude 1,

4a: a block diagram for the transmission behavior of an open control loop with a step function of the ionization power, 4b: the response function at output 450 with a step amplitude of 1,

4c: the response function at output 450 with a step amplitude of -1,

5a: a block diagram for the signal flow of a closed control loop,

5b: a block diagram for the transmission behavior of a closed control loop with a step function of the pollutant concentration,

5c: the response functions at the outputs 550 and 551 with a step amplitude of 1,

Fig. 6a: a block diagram for the transmission behavior of a closed control loop with a step function of the setpoint and a subsequent step function of the

Pollutant concentration,

6b: the response functions at outputs 650 and 651 with step amplitudes of 1,

7: the sensitivity characteristic of a tin dioxide gas sensor,

8 is a perspective view of an air cleaning device according to the invention,

9: a block diagram of the air cleaning device according to the invention according to FIGS. 8 and 10: a flowchart of the control algorithm of the controller from FIG. 9.

Fig. La shows a block diagram for the transmission behavior of a gas sensor with a step function as an input. The series connection of two PTI elements 111, 112 and a limiting element 113 was therefore adopted as a model for the transmission behavior of a gas sensor 110. An abrupt increase in pollutant concentration 101 is present as an input function, and the corresponding response function can be tapped at output 150. The following parameters were used:

PTI elements 111.112: time constant = 10.0s, transmission value = 1.0.

Limitation 113: upper limit = 2.0, lower limit = - 2.0.

It was thus assumed that the output signal of the

Gas sensor can be controlled in a range from -2.0 volts to 2.0 volts.

1b shows the response function at output 150 with a step amplitude of 1. To a step function of

The gas sensor responds with a delayed pollutant concentration as expected and approaches the jump amplitude of 1 exponentially-1 after approx. 60 seconds.

1c shows the response function at output 150 with a step amplitude of 2.5. When the value 2.0 is reached, the limit 113 becomes effective, so that the response function remains constant at the value 2.0 after approx. 30 seconds and the jump amplitude of 2.5 cannot approach any further. 2a shows a block diagram for the transmission behavior of a sensor controller with a step function as an input. A sensor control according to the state of the art, such as, for example, according to WO 98/26482 or DE 43 34 956 AI, basically consists of a gas sensor 210 with a subsequent driver stage 220. The gas sensor 210 consists, as in FIG. 1 a, of two PTI elements 211, 212 and a limitation 213, the parameters likewise corresponding to those from FIG. As a model for driver stage 220, a P-link 221 with a downstream limit 222 was used. The following were assumed as parameters:

P-link 221: transfer coefficient = 250.0

Limiter 222: upper limit = 500 V, lower limit -500.0 V.

This means that, according to FIG. 2a, the output voltage of the gas sensor 210 is converted by the driver stage 220 into a high voltage by a factor of 250, although the offsets that occur in practice were not taken into account for simplification. Usual output voltages of a gas sensor connected in a voltage divider are, for example, in the range from 1 V to 5 V and are translated into a high voltage of, for example, 1000 V to 2000 V by the driver stage. However, these offsets are of no further importance for the control loop model and can be easily added at any time if necessary.

To investigate the transmission behavior of the sensor controller according to FIG. 2a, it was again assumed that a sudden increase in the Pollutant concentration 201 acts, which is recorded at the output 250 of the driver stage 220.

Fig. 2b shows the response function at the output 250 with a step amplitude of 1. In order to be able to also represent the step amplitude in Fig. 2b, this was enlarged by a factor of 250. As expected, the same response function as in FIG. 1b is shown in FIG. 2b, but now stretched by a factor of 250 due to the downstream driver stage 220.

2c finally shows the response function at output 250 with a jump amplitude of 2.5, the jump amplitude again being increased by a factor of 250 for reasons of illustration. Because of the increased

Jump amplitude of 2.5, the limits 213 or

222 effective, so that after approx. 30 seconds the

Response function according to FIG. 2c remains constant at 500 V.

The transmission behavior shown in accordance with FIGS. 2a, 2b and 2c essentially corresponds to the known sensor controls for air cleaning devices with ionizers. In contrast to this, the invention proposes the construction of a closed control loop in which the effects of the pollutant concentration and air ionization on the part of the ionizer are appropriately superimposed and compensated for on the pollutant sensor. A block diagram for the signal flow of a control loop closed in this way is shown in FIG. 5a and is explained further below. In order to analyze individual components of the control loop, a block diagram for the transmission behavior of an open control loop with a step function of the pollutant concentration is first shown in FIG. 3a. According to its basic structure, the open control circuit according to FIG. 3a consists of a controller 340, a subsequent driver stage 320 and the following ionizer 330. According to the invention, the effects of the ionizer 330 and the pollutants contained in the air flow should now overlap at the entrance of the gas sensor 310 , This circumstance is modeled in the block diagram according to FIG. 3a by the summation point 303, to which both a step function of the pollutant concentration 301 and via the

Transmission path 332 acts on the ionizer 330. The parameters of the gas sensor 310 are identical to the parameters given in FIG. Since only the behavior of the gas sensor in the case of a step function of the pollutant concentration is initially to be considered in isolation according to FIG.

3b shows the response function at output 350 with a step amplitude 1. Since an open control loop was assumed in accordance with FIG. 3a, the response function in accordance with FIG. 3b results exclusively from the abrupt change in the pollutant concentration and thus corresponds to the response function in accordance with FIG.

Fig. 4a shows a block diagram for the

Transmission behavior of an open control loop with a step function of the ionization power. As in FIG. 3a, the open control loop again consists of a controller 440, a driver stage 420, an ionizer 430 and a gas sensor 410. In this case, only the ionizer 430 acts at the summation point 403 without any additional influence on the part of the Pollutant concentration, which is now kept constant in the air flow supplied to the ionizer.

In order to investigate a step function of the ionization power in the block diagram according to FIG. 4a, the summation point 405, on which the step function 404 acts, was inserted between the controller 440 and the driver stage 420. The parameters of the blocks 411, 412, 413 of the gas sensor 410 are identical to the parameters of the gas sensor 110 according to FIG. Furthermore, the parameters of blocks 421, 422 of driver stage 420 are identical to the parameters of driver stage 220 according to FIG. 2a. The ionizer 430 was modeled by a simple P-link 431 with the following parameter:

P-term 431: transfer coefficient = -0.004

The output of the ionizer acts directly on the summation point 403 via the path 432 without any delay. It was assumed here that the gas sensor 410 is arranged in the immediate vicinity of the ionizer 430. If there is a greater distance between ionizer 430 and gas sensor 410, a dead time element must be inserted on route 432, for example. The transmission behavior of the P-element of the 431 thus corresponds to a translation of the change in high voltage present at the output of the driver stage 420 into a change in the pollutant concentration to be measured by the gas sensor 410.

4b shows the response function at output 450 with a step amplitude of 1. An increase in the input voltage at driver stage 420 by 1 volt thus results in a decrease in the output voltage of the gas sensor of likewise 1 volt, the time function again here results from the transmission behavior of the two PTI elements 412, 413. The opposite behavior can be explained by the fact that an increase in the ionization capacity is accompanied by a decrease in pollutants in the air flow. Accordingly, Fig. 4c shows the

Response function at output 450 with a step amplitude of -1. The opposite behavior can also be found here, since a reduction in the ionization capacity results in an increase in the concentration of pollutants in the air flow.

The measurements on the open control loop according to FIGS. 3a, 3b and 4a, 4b, 4c show how the arrangement of the gas sensor according to the invention in relation to the air flow and in relation to the ionizer can be determined in a simple manner can be. 3b shows the output signal of the gas sensor with an open control loop due to a change in the pollutant concentration in the air flow. Due to this change, the output signal at the gas sensor increases from 0 V to 1 V.

According to the invention now, the gas sensor must be arranged on the ionizer in such a way with respect to the air flow, and ^■ in respect that this change by a change of ionization _at. Open control loop can be compensated so that the output signal of the gas sensor can be returned to its original value. FIG. 4b shows the output signal of the gas sensor with an open control loop when there is a change in the ionization energy and at the same time a constant pollutant concentration in the air flow supplied to the ionizer. The output signal of the gas sensor 450 changes in this case from 0 V to -1 V when the voltage at the input of the driver stage is increased by 1 V. The arrangement of the gas sensor simulated in this case in relation to the air flow and in relation to the ionizer corresponds exactly to the desired effect that the change in the output signal of the gas sensor shown in FIG. 3b can be compensated for by a corresponding change in the ionization energy according to FIG. 4b. In practice, corresponding tests to FIGS. 3a and 4a can be carried out in order to verify the said compensation effect on the open control loop.

The behavior of the closed control loop is now explained in more detail below. 5a shows a block diagram for the basic signal flow of the closed control loop. The closed control loop consists of the control loop elements already described above, i.e. a gas sensor 510, a controller 540, a driver stage 520 and an ionizer 530. The driver stage 520 in turn consists of a voltage source 525, a pulse width modulator 526, a resonator 527 and a high voltage transformer 528.

A DC voltage supplied by the voltage source 525 is converted by the pulse width modulator 526 into pulses with a pulse width ratio specified by the controller 540 and one by a clock generator (not shown further) with a specified clock rate. When these pulses are smoothed, a direct voltage which is proportional to the pulse width ratio results and is fed to a resonator 527. The resonator 527 is connected to the subsequent high-voltage transformer 528 in such a way that, on the one hand, it vibrates automatically when a DC voltage is fed in at a working frequency in the range from approx. 25 kHz to 35 kHz, and on the other hand supplies a high-voltage oscillating on the secondary side, the peak value of which is approximately proportional the input voltage of the resonator 527 or the set pulse width of the pulse width modulator 526. The one from that High voltage transformer 528 supplied oscillating high voltage with peak values in the range of, for example, 1.0 kV to 2.0 kV is applied to the two electrodes of ionizer 530.

The air 500 to be cleaned flows around the ionizer 530, the gas sensor 510 being arranged on the flow side behind the ionization tube 530. In the case of a closed control loop, the air flow can optionally be partially or completely returned by recirculation mode. The gas sensor 510 supplies its output signal to the controller 540, which performs a setpoint / actual value comparison on the basis of the setpoint 547 and sets the pulse width ratio of the pulse width modulator 526 in accordance with the underlying control algorithm.

Fig. 5b shows a block diagram for the

Transmission behavior of a closed control loop with a step function of the pollutant concentration. The closed control loop according to Fig. 5b goes from the open loop shown in FIG. 3a characterized ^'indicates that the output signal of the gas sensor 550 is fed back via branch 514 to the controller 540th The blocks of the gas sensor 510, the driver stage 520 and the ionizer 530 with the associated parameters are identical to the specified parameters of the gas sensor 310 according to FIG. 3a or the driver stage 420 and the ionizer 430 according to FIG. 4a, so that in this respect to the Description can be made according to FIG. 3a and FIG. 4a.

The structure of controller 540 will now be described in detail. The setpoint 547 is fed to the subtraction point 546 in the controller. The control difference determined in this way reaches the subsequent PID controller via P-element 541. The PID controller in turn consists of a P-element 542, a DTI-element 543 and an I-element 544, the outputs of which are combined with the summation point 545 to form the output 551. Output 551 provides the manipulated variable that serves as the input for driver stage 520. The parameters of controller 540 were defined as follows:

Setpoint 547: setpoint = 0

P-element 541: transfer coefficient = -1

P-element 542: transfer coefficient = 2

DTI element 543: transmission coefficient = 8, time constant = 2 s

I controller 544: transfer coefficient = 0.2 l / second, corresponding to an integration constant of 5 s.

The closed control loop behavior is now examined using the step function 501, which corresponds to a step change in the pollutant concentration in the air flow. The time signals at the output of gas sensor 550 and at the output of controller 551 are shown.

5c shows the response functions at the outputs 550 and 551 with a step amplitude of 1.

On the basis of the output signal of the gas sensor 550, it becomes clear that, despite an abrupt change in the pollutant concentration, the control loop is able to return the output signal 550 to the setpoint 547. After increasing the output signal to approx. 0.25, the output signal reaches after approx. 40 seconds back to its original value and then approaches the setpoint again with a small overshoot within a further 40 seconds. The output variable 551 of the controller 540, on the other hand, ensures that the driver stage 520 is supplied with a sufficient input value so that the change in the pollutant concentration that has occurred can be compensated for at the summation point 503. After approx. 25 seconds, the manipulated variable 551 has reached its maximum value and from there approaches the final value of 1.0 / what an input voltage of 1.0 V at the input of

Driver level 520 corresponds. It can be seen from FIG. 5c that the settling behavior of the closed control loop is essentially determined by the time behavior of the gas sensor 510, provided there are no additional ones on the path 532 between the ionizer 530 and the gas sensor 510

Delays occur. The time constant of the gas sensor can be determined using an arrangement as shown in FIG. The time constant of the recorded step function 150 corresponds approximately to the time in which the step function 150 has reached the value (1 - 1 / e) if it is assumed that the entire transmission behavior of the gas sensor is approximated by a single PTI element.

If, on the other hand, the path 532 between the ionizer 530 and the gas sensor 510 has a delay (for example due to the flow velocity of the air flow when the gas sensor is arranged away from the ionizer), a secondary condition can be set up for this delay time in order to

Do not unnecessarily slow settling behavior of the closed control loop. As a secondary condition, it can be formulated that the delay time of the output signal of the gas sensor with an open control loop and with a constant pollutant concentration changes the ionization energy should be below the time constant of the gas sensor defined above. In the present case, the time constant of the gas sensor 510 can be determined from the time function according to FIG. 1b to be approximately 20 seconds. To optimize the timing of the

Transient response of the closed control loop, the gas sensor should therefore meet the additional constraint with regard to the air flow and with regard to the ionizer, that the delay time of the section 532 is also less than 20 seconds. As a rule, this secondary condition can be easily met by arranging the gas sensor appropriately close to the ionizer.

Fig. 6a shows a block diagram for the transmission behavior of a closed control loop with a step function of the setpoint and a subsequent step function of the pollutant concentration. The block diagram according to FIG. 6a differs from the block diagram according to FIG. 5b only in that a step function 648 is now present as the setpoint and that the abrupt change in the pollutant concentration 601 only takes place after a certain dead time 602. 100 s were assumed as parameters for the dead time. Otherwise, the block diagram according to FIG. 6a corresponds to the block diagram according to FIG. 5b, so that reference can be made to the description there with regard to the other components.

The closed control circuit according to FIG. 6a is therefore initially subjected to a change in the setpoint 648 and is additionally subjected to a change in the pollutant concentration 601 after the dead time 602. 6b shows the corresponding response functions at outputs 650 and 651. The dashed line at value 2 also indicates the limit that the Limitation of driver stage 620, taking into account the transfer coefficient of P-element 621.

The sudden increase in the setpoint 648 initially causes a large manipulated variable 651 due to the differential component 643 of the controller 640. After 60 seconds, the control loop has then settled to the new setpoint, so that the output signal with the value -1.0 at the output 650 of the gas sensor is applied. After 100 seconds there is then an additional activation of the abrupt change in the pollutant concentration, whereupon the manipulated variable 651 rises again in order to keep the output signal 650 of the gas sensor at the value -1 this time. The interpretation of areas 623 and 624 is instructive here

This is because driver stage 620 cannot pass the controlled variables above the value 2.0 or below the value -2.0 to the ionizer 630. As already mentioned above, it therefore makes sense to provide additional measures in these areas in order to provide a higher ionization capacity, for example by switching on an additional blower and / or by switching on further ionizers.

Fig. 7 shows the sensitivity characteristic of a tin dioxide gas sensor. The relative air resistance-related change in resistance of the tin dioxide element is plotted as a function of the pollutant concentration of various pollutants. As line 701 shows, the tin dioxide gas sensor is insensitive to air or

Oxygen. In contrast, there are pronounced sensitivities for H ₂ S, hydrogen, ammonia, ethanol and CO with increasing concentrations of pollutants. For the household sector, it has been found that a stable regulation can be achieved especially if the Regulation is set to the sensitivity curve 702 of CO.

8 shows a perspective view of an air cleaning device according to the invention. The

Air cleaning device 801 is designed as a tabletop device with a base 802 and a cover 803. An ionization tube 804, which is constructed in the manner described above, is attached to the base as an ionizer. Also attached to the base is a gas sensor 805, which according to the invention is arranged in relation to the ionizer 804 in such a way that, with an open control loop, a change in the output signal of the gas sensor due to a sudden change in the pollutant concentration in the air supplied by the air flow due to a change in the ionization energy is compensable. The air flow enters and exits the housing through the air slots 806 embedded in the cover 803. To support the air flow, a suitable fan can additionally be provided on the base 802 or outside the device. An LED display 807, an operating potentiometer 808 and an electrical supply line 809 are provided on the edge of the base for operating the device.

The function of the air cleaning device 801 is explained with reference to FIG. 9, which shows a block diagram of the air cleaning device according to the invention according to FIG. 8. First, the calibration operation is described in which the gas sensor is calibrated to a predetermined pollutant concentration. This calibration is generally necessary because standard gas sensors have different characteristics and would cause different control loop behavior. When using tin dioxide gas sensors, however, it was observed that the relative change in the output signal of the gas sensor is approximately constant when the gas concentration changes and that only an absolute shift in the output signal can be observed between different gas sensors for a given gas concentration. In addition, the fact that the sensor is only operated in a small working area in the control according to the invention can be exploited, so that the sensor characteristic curve can be linearized around this working area once the working point has been calibrated.

For the calibration operation, the changeover switch 901 is first set to position 1, so that the ionization tube 904 is not subjected to ionization power. Instead, the control deviation is fed to the calibration element 912. A constant pollutant concentration is then introduced into the air flow 906, which concentration corresponds to "clean air" and thus to the desired setpoint as a function of the respective application. On the device, the operating potentiometer 808 is brought into the desired setpoint position, so that the setpoint 908 set thereby is applied to the comparison point 909. If the calibration has not yet taken place, a control deviation 910 will then be observed at the output of the comparison element. The addition element 911 and the calibration element 912 are now additionally provided for calibration. The calibration element 912 receives the control deviation 910 as input from the changeover switch 901 and thereupon increases or decreases the output voltage 913 in such a way that the control deviation 910 becomes zero. The voltage value 913 determined in this way can, for example, be stored in a memory so that it is still available even after a power failure. This type of calibration can be repeated several times, if necessary changing pollutant concentrations 906 can be taken into account.

The current operation is now described, for which purpose the changeover switch 901 is switched to position 2, so that the controller 902 receives the control deviation 910 as an input variable. Depending on the output of the controller 902, the driver stage 903 supplies the ionization tube 904 with ionization power. The control algorithm of controller 902 corresponds to one

Integration controller, the function of which is represented by the flow diagram according to FIG. 10. First of all, it is assumed that the controller delivers a previously stored initialization variable at the output, which corresponds to a low ionization power. So far the

If the pollutant concentration 906 corresponds to the preset setpoint, the control deviation 910 remains unchanged at zero, so that the controller does not take any action. If the pollutant concentration 906 now increases, this increase in the pollutant concentration is detected by the gas sensor 905, which results in an increase in the control difference 910. Depending on the control algorithm, the controller 902 then increases the manipulated variable 914, so that a greater ionization power is applied to the ionization tube 904 via the driver stage 903. This process continues until, according to the invention, the output signal of the gas sensor 905 is returned to its original value due to the increased ionization power and the control difference 910 thus becomes zero again. The corresponding mode of operation is obtained if, conversely, the pollutant concentration 906 is reduced again.

The display 907 is used by the user to check the manipulated variable 914. Large manipulated variables indicate a large one Ionization performance and thus to a highly polluted air, while low manipulated variables correspond to the pollutant loads specified during the calibration operation. In the air cleaning device according to FIG. 8, the display 907 has been realized by an LED display 807. In this case, it is expedient to adaptively adapt the current value range of manipulated variable 914 to the display range of LED display 807. This can be done by capturing the value range between the smallest and the largest manipulated variable in a given time window and in between the values of the manipulated variable are divided linearly or appropriately scaled (ie logarithmically) on the LED display 807.

The control algorithm is explained in detail with reference to FIG. 10, which shows a flow diagram of the control algorithm of the controller from FIG. 9. In step 1001 there is first a comparison between the setpoint value and the delivered measured value of the gas sensor, which, if necessary, has been corrected by a calibration value as explained above. In steps 1002 and 1003, it is then first checked whether there is a positive or a negative control difference. If this is the case, a wait timer is started in steps 1004 and 1005, which is used to suppress

Disturbance serves. In step 1006 or 1007, it is then checked whether the control difference is still present. If this is the case, the manipulated variable 914 is increased or decreased.

Claims

claims

Air purification device to reduce pollutants in the air,

with an ionizer which is exposed to an air flow and which can be acted upon by a driver stage with ionization power for ionizing the air supplied by the air flow, and

with a gas sensor for measuring pollutant concentrations,

characterized,

that the driver stage, the ionizer and the gas sensor interact with a controller in a closed control loop in such a way that the output signal of the gas sensor essentially corresponds to a predetermined setpoint,

wherein the gas sensor is arranged in relation to the air flow and in relation to the ionizer such that a change in the output signal of the gas sensor due to a sudden change in the pollutant concentration in the air supplied by the air flow can be compensated for by a change in the ionization energy when the control loop is open, so that the output signal of the gas sensor can be traced back to its original value.

2. Air cleaning device according to claim 1, characterized in that the driver stage comprises a high-voltage transformer, at the An oscillating high voltage can be generated on the secondary side.

3. Air cleaning device according to claim 2, characterized in that the driver stage comprises a circuit for pulse width modulation with which the high-voltage transformer can be controlled on the primary side and the peak value and / or the pulse ratio of the high-voltage oscillating on the secondary side can be set.

4. Air cleaning device according to claim 3, characterized in that the secondary side oscillating high voltage is adjustable with a peak value in the range from 1 kV to 10 kV and with a frequency in the range from 10 kHz to 50 kHz.

5. Air purification device according to one of claims 2-4, characterized in that the ionizer consists of a glass tube, the inner wall of which with a

Perforated sheet is lined as the first electrode and the outer wall of which is surrounded by a wire mesh as the second electrode, the oscillating high voltage of the driver stage being present between the first electrode and the second electrode.

6. The air cleaning apparatus according to any one of claims 1-5, characterized in that the gas sensor consists of a metal oxide sensor, whose resistance changes in ^'■ depending on the concentration of certain gases.

7. Air cleaning device according to claim 6, characterized in that the metal oxide consists of tin dioxide.

8. Air cleaning device according to one of claims 1-7, characterized in that the air inlet opening of the gas sensor with respect to the air flowing around the ionizer on the exhaust air side a distance of about 0.5 cm to 2 cm, preferably about 1 cm from the surface of the Has ionizer.

9. Air cleaning device according to one of claims 1-8, characterized in that the setpoint on the device is manually adjustable.

10. Air cleaning device according to one of claims 1-9, characterized in that a fan is provided for generating the air flow.

11. Air cleaning device according to claim 10, characterized in that an additional controller additionally controls the speed of the fan such that the

Output signal of the gas sensor essentially corresponds to a predetermined setpoint.

12. Air cleaning device according to claim 11, characterized in that the additional controller is switched on as soon as a limitation occurs in the control loop consisting of ionizer, driver stage, gas sensor and controller.

13. Air cleaning device according to one of claims 1-12, characterized in that the controller consists of a P controller or a PI controller or a PID controller.

14. Air cleaning device according to one of claims 1-12, characterized in that in addition to the controller of the measured pollutant concentration, further measured variables can be processed.

15. Air cleaning device according to claim 14, characterized in that a flow sensor and / or a moisture sensor and / or an ionization sensor and / or an ozone sensor for processing further measured variables is connected to the controller.

16. Air cleaning device according to one of claims 14 - 15, characterized in that the controller consists of a rule-based fuzzy controller.

17. Air cleaning device according to one of claims 14 - 15, characterized in that the controller from one

State controller exists.

18. Air cleaning device according to one of claims 1-17, characterized in that a calibration element calibrates the gas sensor to the target value when the gas sensor is supplied with a pollutant concentration corresponding to the target value.

19. Air cleaning device according to claim 18, characterized in that the ionization energy supplied to the ionizer is switched off during the calibration of the gas sensor.

20. .Procedure to reduce pollutants in the air with an air purification device according to one of the

Claims 1-17, in which the setpoint is set to a certain pollutant concentration, in which pollutant-containing air is fed to the ionizer and in which pollutant-reduced air is removed.