Ionization apparatus

Abstract

 The invention is directed to a ionization apparatus comprising a housing (1) and at least partly within in the housing (1) a high voltage power supply arrangement (2) with at least one ion emitting electrode (3-5) connected thereto. It is proposed that a measuring arrangement (6) with at least one measuring electrode (7, 8) connected thereto is provided for detecting an indication for housing surface pollution (P) based on a change in complex resistance (Z') between at least one said ion emitting electrode (3-5) and at least one said measuring electrode (7, 8).

Description

[0001] The invention is directed to a ionization apparatus according to the general part of claim 1 and to a method for detecting an indication for surface housing pollution on the housing surface of an ionization apparatus according to the general part of claim 12.

[0002] The ionization apparatus in question has its application in controlling the charge of a target area. In particular, this includes the neutralisation of a target area which is often required when plastic films are being processed in the bag-making industry or the like.

[0003] A known ionization apparatus (EP 2 061 124 A2), which is to be considered the starting point of the invention, comprises a high voltage power supply arrangement with a ion emitting electrode connected thereto. The voltage power supply arrangement supplies a bipolar voltage against ground potential to a so called ionizer bar. Such a ionizer bar normally comprises a number of ion emitting electrodes that are supplied with the voltage of the high voltage power supply arrangement.

[0004] One problem of the ionization apparatus in question is the fact that the ionizer bar may not be focused exactly onto the target area, for example the plastic film to be processed. This is why dust particles as well as housing components of the ionization apparatus are being charged or at least being influenced by the ionizer bar as well. In the end a considerable amount of dust and dust-like particles are being attracted to various housing parts such that housing surface pollution is building up during operation.

[0005] The above noted hosing surface pollution may, depending on its composition, provide a layer of conducting material on the housing surface which can lead to decrease in performance or even a shortcut situation.

[0006] The problem underling the invention is to improve the known ionization apparatus such that the buildup of housing surface pollution can be detected in a reproducible manner.

[0007] The above noted problem is solved by a ionization apparatus according to the characterizing part of claim 1.

[0008] The proposed solution is based on the finding that the electrical properties of housing surface pollution may be used for an easy detection of the buildup of such housing surface pollution.

[0009] In detail a measuring arrangement with at least one measuring electrode connected thereto is provided for detecting an indication for housing surface pollution, which detecting is based on a change in complex resistance between at least one said ion emitting electrode and at least one said measuring electrode.

[0010] The at least one ion emitting electrode is coupled to ground potential via a complex resistance that depending on the installation may be composed of a large number of ohmic devices, capacitive devices and, if so, even inductive devices. What is important for the present invention is the fact that at least a part of the complex resistance between ion emitting electrode and the measuring electrode is influence by housing surface pollution as long as the measuring electrode is positioned correctly.

[0011] The positioning of the measuring electrode is correct in the above noted sense if the buildup of housing surface pollution leads to a change in voltage measured at the measuring electrode against ground. In this situation the complex resistance between the ion emitting electrode and ground may be seen as two complex resistances that are serially coupled. In this sense one complex resistance corresponds to the path between the ion emitting electrode and the measuring electrode and the other complex resistance corresponds to the path between the measuring electrode and the ground potential.

[0012] The proposed measurement only works with AC-voltages and AC-currents as the measurement is based on the change of complex resistances due to the buildup of housing surface pollution. Accordingly, for performing measuring cycles by the measuring arrangement an AC-voltage at the ion emitting electrode is necessary. The expression "AC-voltage" is to be widely understood. For example, it includes a pulsed DC-voltage as will be explained further down.

[0013] In the preferred embodiments according to claims 2 to 5 such an AC-voltage is provided anyhow for the ionization process. In the further preferred embodiment according to claim 6 it is proposed to evaluate the voltage against ground at at least one said measuring electrode during ionization. Accordingly the voltage which is supplied to at least one said ion emitting electrode is being used not only for ionization but also for detecting an indication for housing surface pollution by the measuring arrangement. This leads to a cost saving apparatus altogether.

[0014] According to claim 9 it has been found that for particularly good measurement results at least one said ion emitting electrode and at least one said measuring electrode are to be located on opposite sides of a housing wall which surface pollution is to be detected. This has been proven successful especially when the respective housing wall is made of a plastic material.

[0015] According to claim 11 the housing comprises at least one rib like wall segment that mechanically protects the at least one ion emitting electrode which protrude from a housing wall and that the at least one rib like wall segment is detachably connected to the rest of the housing. This rib like wall segment is preferably, connected to the rest of the housing via a snap fit connection.

[0016] According to claim 11 it has been found that in some areas of operation it is more efficient to exchange certain housing components instead of cleaning them after having detected the buildup of housing surface pollution. In order to make this possible it is proposed to have the above noted rib like wall segments connected detachably to the housing, preferably via a snap fit connection as noted above.

[0017] The idea described above with respect to claim 11 is to be considered a reaching which does not necessarily require the above noted measuring arrangement. Therefore a ionization apparatus comprising a housing and at least partly within the housing a high voltage power supply arrangement with a ion emitting electrode connected thereto, wherein the housing comprises at least one rib like wall segment that mechanically protects the ion emitting electrodes protruding from a housing wall and that the at least one rib like wall segment is detachably connected to the rest of the housing, preferably, wherein the rib like wall segment is connected to the rest of the housing via a snap fit connection, shall be claimable as such as well.

[0018] According to the teaching of claim 12 a method for detecting the above noted indication for surface housing pollution on the housing surface of an ionization apparatus is claimed independently.

[0019] According to the method it is proposed that an above noted measuring arrangement with at least one measuring electrode connected thereto is provided and that an indication for housing surface pollution is being detected by the measuring arrangement based on a change in complex resistance between at least one said ion emitting electrode and at least one said measuring electrode.

[0020] The method according to claim 12 is directed to the operation of the ionization apparatus according to claim 1. All explanations and advantageous variants explained with reference to claim 1 are fully applicable to the teaching of claim 12.

[0021] In the following the invention is explained referring to only one embodiment shown in the drawings. The drawings show in

Fig. 1

a ionization apparatus according to the invention in a perspective view,

Fig. 2

the ionization apparatus according to Fig. 1 in a sectional view along the line II-II and

Fig. 3

a schematical circuit diagram with only those components of the ionization apparatus that are relevant for the present invention.

[0022] The ionization apparatus shown in Fig. 1 may be applied in various areas as explained in the general part of the specification. The main area of application for the displayed ionization apparatus is the neutralization which is not to be understood as a restriction.

[0023] The ionization apparatus comprises a housing 1. The expression "housing" is to be understood in a broad sense. Accordingly the housing includes all components that are depicted with reference numbers 1a, 1b, 1c and 1d, 1e and 1f. Those components 1a-f will be explained in detail later on.

[0024] At least partly within the housing 1 a high voltage power supply arrangement 2 with at least one ion emitting electrode 3-5 is provided. In the preferred embodiment altogether three ion emitting electrodes 3-5 are realized. Depending from the application more or fewer ion emitting electrodes 3-5 may be necessary.

[0025] It is of major importance for the proposed solution that a measuring arrangement 6 with at least one measuring electrode 7, 8 connected thereto is provided for detecting an indication for housing surface pollution based on a change in complex resistance Z' between at least one said ion emitting electrode 3-5 and at least one said measuring electrode 7, 8. For this measurement the at least one said ion emitting electrode 3-5 builds one common measurement port and the at least one said measuring electrode 7, 8 builds the other common measurement port.

[0026] It will be explained later that preferably a measuring electrode 7, 8 is assigned to a particular ion emitting electrode 3-5, such that the detection of the indication for housing surface pollution is based on a change in complex resistance Z' between the ion emitting electrode 3-5 and the measuring electrode 7, 8 assigned thereto.

[0027] The complex resistance Z' is shown in Fig. 2 in the sense of an equivalent circuit. As this is only the display of a theoretical approach to explain the real electric arrangement the complex resistance Z' is only displayed in dotted lines.

[0028] According to Fig. 2 between the ion emitting electrode 5 and ground potential 9 a complex resistance Z is present according to the equivalent circuit. The complex resistance Z is composed of a serious of the two complex resistances Z' and Z". According to this model the measuring electrode 8 is measuring exactly between the complex resistances Z' and. Z".

[0029] Accordingly the complex resistance Z' describes the path between the ion emitting electrode 5 and the measuring electrode 8, comprising the sub-path between the ion emitting electrode 5 and the housing 1, which is mainly an air capacity and the path through the housing 1 itself. In addition the path between the ion emitting electrode 5 and the measuring electrode 8 may comprise a layer of housing surface pollution P which influences at least the value of the complex resistance Z'.

[0030] If now the housing surface pollution P is building up it is to be expected that due to the electric and ohmic effects the value of the complex resistance Z' will decrease. For the present evaluation only the value of the vectorial variable of the complex resistance is of interest such that the direction of the complex resistance will not be discussed at that point.

[0031] The above noted decrease of the value of the complex resistance Z' has the effect that the value of the voltage at the point between the two complex resistances Z' Z" against ground potential will increase, if the voltage supplied to the ion emitting electrode 5 against ground potential is kept constant. As noted above "voltage" in this respect is understood as an AC-voltage, as the underlying model is based on complex resistances.

[0032] It may be pointed out that the above noted model is applicable to all of the ion emitting electrodes 3-5 shown in the drawings. Just for an easy understanding the equivalent circuit comprising the complex resistances is only shown for the ion emitting electrode 5, which is assigned the measuring electrode 8.

[0033] Interesting now is the fact that the AC-voltage which is necessary for detecting the above noted indication for housing surface pollution is provided for ionization anyhow according to a preferred embodiment. Here, for ionization, the high voltage power supply arrangement 2 supplies high voltage with an AC-component to the ion emitting electrode 3-5 against ground. Preferably the high voltage power supply arrangement 2 in this respect supplies a modulated, further preferably a pulsed, DC-voltage to the ion emitting electrode 3-5 against ground. The supplied voltage is nothing else but a PWM-voltage with a certain duty-cycle.

[0034] The preferred value of the modulated, here and preferably pulsed, DC-voltage preferably lies between 2 kV and 60 kV, preferably between 20 kV and 40 kV. In addition or alternatively the pulse frequency lies between 0,5 Hz and 100 Hz, preferably between 1 Hz and 10 Hz.

[0035] It has been pointed out already that for the shown, preferred embodiment multiple ion emitting electrodes 3-5 are provided and that at least some of the ion emitting electrodes 3-5 are each assigned at least one said measuring electrode 7, 8, here and preferably exactly one measuring electrode 7, 8, for detecting an indication for housing surface pollution based on a change in complex resistance Z' between the respective ion emitting electrode 3, 5 and the respective measuring electrode 7, 8. As noted above, the measuring electrode 7 is assigned to the ion emitting electrode 3 and the measuring electrode 8 is assigned to the ion emitting electrode 5. Generally it can also be advantageous if at least some of the ion emitting electrodes 3-5 are as an electrode-group assigned to a measuring electrode 7, 8 or to multiple measuring electrodes 7, 8.

[0036] For ionization the high voltage power supply arrangement 2 supplies modulated, here and preferably pulsed, positive high DC-voltage to a first electrode-group of ion emitting electrodes 3, 4 against ground and modulated, preferably pulsed, negative high DC-voltage to a second electrode-group of ion emitting electrodes 5 against ground. The expression "electrode-group" is to be understood in a broad sense such that only one electrode can compose such an electrode-group. This is applicable for electrode 5 as noted above.

[0037] It is particularly important for the shown embodiment that the high voltage power supply arrangement 2 synchronizes the voltages supplied to the ion emitting electrodes 3, 4 and 5 such that during operation, in an alternating manner, the a first electrode-group consisting of electrodes 3, 4 is supplied with a reference voltage and the second electrode-group consisting of electrode 5 is provided with high positive DC-voltage and then the first electrode-group consisting of electrodes 3, 4 is supplied with high negative DC-voltage and the second electrode-group consisting of electrode 5 is supplied with the reference voltage. Here and preferably, the supply with the reference voltage generally corresponds to the supply with ground potential. In another embodiment the reference voltage is a relatively low voltage against ground potential, for example a voltage in the area of 1 kV and 5 kV against ground potential.

[0038] The above noted high positive DC-voltage and high negative DC-voltage may be of the same value against ground potential. In another embodiment, however, those positive and negative voltages may be of different value against ground such that an unsymmetrically voltage supply will result.

[0039] The above noted alternating supply of DC-voltages leads to the situation that during the positive voltage pulse on the electrode 3, 4 the electrode 5 is supplied with ground potential and that during the negative pulse on the electrode 5 in turn the electrodes 3, 4 are supplied with ground potential. This leads to the fact that at all the times the full DC-voltage is present between the electrodes 3, 4 and the electrode 5. Only the polarity of the voltage periodically changes. With this arrangement, in an alternating manner, positive ions are being generated at the electrodes 3, 4 and negative ions are being generated at the electrode 5.

[0040] Is has been found in a particularly preferred embodiment that the above noted voltage supply at the electrodes 3-5 may be used for detecting an indication for housing surface pollution as noted above. In further detail it is provided that the measuring arrangement 6 evaluates the voltage against ground 9 at the measuring electrodes 7, 8 during ionization by the ion emitting electrodes 3-5. This leads to a very simple measuring arrangement as the measurement is reduced to detecting a voltage at the measuring electrode 7, 8 against ground 9.

[0041] In a cost effective embodiment a measurement arrangement 6 comprises a comparator unit 10 which compares the voltage against ground 9 at the measuring electrode 7, 8 to a threshold value V_ref and outputs a signal CLB (cleanbar) depending on the result of the comparison. If the voltage against ground at the measuring electrode exceeds the threshold value V_ref the output signal CLB is set to a high level. If the voltage against ground at the measuring electrode 7, 8 stays below the threshold value the output signal CLB is set to a low level. The comparator unit 10 may be an electronic part like an operational amplifier, a microcontroller or the like.

[0042] The value of the above noted voltage at the measuring electrode 7, 8 may also be transferred to other components via a serial data interface and/or a data bus system. For this, preferably, a analog/digital conversion is being performed on the measured voltage.

[0043] In order to reduce the influence of one electrode-group on the other electrode group during detection an indication for housing surface pollution in the above noted sense a rectifier 11 is preferably provided between the measuring electrode 7, 8 and the comparator unit 10. This rectifier 11 in this sense is designed to pass through only the positive half-waves for the electrodes 3,4 and the negative half-waves for the electrode 5.

[0044] Further preferably, between the measuring electrode 7, 8 and the comparator unit 10 at least one filter, preferably a low-pass filter 12, is provided for smoothening out the measured signal.

[0045] As shown in Fig. 2 the measuring electrodes 7, 8 are provided in addition to the ion emitting electrodes 3-5. This makes the electric circuit of the measuring arrangement 6 simple and cost efficient. However, it may be advantageous to use at least one ion emitting electrode 3-5 as a measuring electrode. This can reduce the complexity on the side of the measuring electrode.

[0046] It has been pointed out already that the optimal location of the measuring electrodes 7, 8 is essential for the proposed solution. Here and preferably the ion emitting electrodes 3-5 and the measuring electrodes 7, 8 are located on opposite sides of a housing wall 13 which surface pollution is to be detected. Here it becomes clear that the expression "housing wall" is to be understood in a broad sense. For example, according to Fig. 2 the housing wall 13 is at least a double wall consisting of housing components 1a, 1b and 1d. All of those housing components are here and preferably non-conductive components. The housing components 1a and 1d are made of plastics, in particular PVC, while housing component 1b is a casting resin.

[0047] Further preferably it is proposed that the ion emitting electrode 3-5 and the measuring electrode 7, 8 assigned to the respective ion emitting electrode 3-5 are located offset from one another along the housing wall 13, 14 which surface pollution is to be detected. The above noted offset is indicated in Fig. 1 with the reference number 15.

[0048] As noted above the housing wall 13, 14 which surface pollution is to be detected is made of a plastic material, preferably of PVC. It is generally possible, however, that for such housing walls 13, 14 coated metal or the like is being used.

[0049] Fig. 2 shows that the measuring electrode 7, 8 is located close to the respective side of the housing wall 13, 14 which surface pollution is to be detected. In the shown embodiment according to Fig. 2 the measuring electrode 7, 8 is even in contact to the respective side of the housing wall 13, 14, here to the lower side of the respective housing wall 13, 14. In order to guarantee the contact it is further preferably so, that the measuring electrode 7, 8 is spring tensioned against the respective side of the housing wall 13, 14. Accordingly a spring is coupled to the measuring electrode 7, 8 as is shown in Fig. 2 as well.

[0050] The measuring electrode 7, 8 is preferably of spherical design. With this it is possible to provide a punctual contact to the respective housing wall 13, 14 such that this contact in electrical terms, in particular in view of the capacity between the measuring electrode 7, 8 and the respective housing wall 13, 14, stays exactly constant even if a certain deformation of the housing 1 due to temperature changes occur.

[0051] The structure of the housing 1 is simple for the shown embodiment. The housing 1 comprises the housing component 1a which carries the ion emitting electrodes 3-5 as well as a PCB 16 for the high voltage power supply arrangement 2 as well as for the measuring arrangement 6. On the upper side of this housing component 1a the electrodes 3-5 together with electrode resistances and the like are being embedded in a casting resin, depicted with reference number 1 b.

[0052] The measuring electrodes 7, 8 are fixed on the PCB 16 and press against the lower side of the housing component 1a, The housing 1a is closed to the bottom side by the housing component 1c which may be of plastics material as well or of metal material.

[0053] The ion emitting electrodes 3-5 are constructed in an interesting manner, as may be seen from Fig. 2. The electrodes 3-5 comprise a non conducting sheathing 3a, 5a which may be exchanged if the surface pollution on the sheathing 3a, 5a has built up to a certain level. The exchange may be easily done after screwing off the conductive ion emitting head portions 3b, 5b. The sheathing 3a, 5a may be of hose like structure made of silicone or the like.

[0054] Interesting is also the fact that the housing 1 further comprises two rib like wall segments 1d that mechanically protect the ion emitting electrodes 3-5 which are protruding from the housing wall 13, 14. In Fig. 2 those rib like wall segments 1d extend along the electrodes 3-5 such that the electrodes 3-5 are not being damaged by any components moving by the ionization apparatus during industrial operation.

[0055] The two rib like wall segments 1d are each detachably connected to the rest of the housing 1. For easy attachment and detachment the rib like wall segments 1d are connected to the rest of the housing 1 via a snap fit connection. For this snap fit connection the rib like wall segments 1d comprise mounting flaps 1e and 1f that engage the rest of the housing 1 on an upper side and on a lower side.

[0056] It has been noted already that the ionization apparatus with the at least one above noted rib like wall segment 1d shall be claimable as such without the measuring arrangement 6 being necessary.

[0057] According to another teaching a method for detecting an indication for surface housing pollution P on the housing surface of an above noted ionization apparatus is claimed. According to this teaching it is of considerable importance that an above noted measuring arrangement 6 is provided with a measuring electrode 7, 8 connected thereto and that an indication for housing surface pollution P is being detected by the measuring arrangement 6 based on a change in complex resistance Z' between the ion emitting electrode 3-5 and the assigned measuring electrode 7, 8. As this is the normal operation of the above noted ionization apparatus regarding the teaching and regarding preferred embodiments reference may be made to all explanations given for the proposed ionization apparatus.

Claims

1. Ionization apparatus comprising a housing (1) and at least partly within in the housing (1) a high voltage power supply arrangement (2) with at least one ion emitting electrode (3-5) connected thereto,
characterized in
that a measuring arrangement (6) with at least one measuring electrode (7, 8) connected thereto is provided for detecting an indication for housing surface pollution (P) based on a change in complex resistance (Z') between at least one said ion emitting electrode (3-5) and at least one said measuring electrode (7, 8).

2. Ionization apparatus according to claim 1, characterized in that for ionization the high voltage power supply arrangement (2) supplies high voltage with an AC-component to at least one said ion emitting electrode (3-5) against ground potential (9), preferably, that the high voltage power supply arrangement (2) supplies a modulate, preferably pulsed DC-voltage to at least one said ion emitting electrode (3-5) against ground potential (9).

3. Ionization apparatus according to claim 2, characterized in that the value of the modulated, preferably pulsed, DC-voltage lies between 2 kV and 60 kV, preferably between 20 kV and 40 kV, and/or, wherein the pulse frequency lies between 0,5 Hz and 100 Hz, preferably between 1 Hz and 10 Hz.

4. Ionization apparatus according to one of the preceding claims, characterized in that multiple ion emitting electrodes (3-5) are provided and that at least some of the ion emitting electrodes (3-5) are each or as an electrode-group assigned at least one said measuring electrode (7, 8) for detecting an indication for housing surface pollution (P) based on a change in complex resistance (Z') between the respective ion emitting electrode (3-5) or electrodes (3-5) and the respective measuring electrode (7, 8) or electrodes (7, 8), preferably, that for ionization the high voltage power supply arrangement (2) supplies modulated, preferably pulsed, positive high DC-voltage to a first electrode-group of ion emitting electrodes (3, 4) against ground potential and modulated, preferably pulsed, negative high DC-voltage to a second electrode-group of ion emitting electrodes (5) against ground potential (9).

5. Ionization apparatus according to claim 4, characterized in that the high voltage power supply arrangement (2) synchronizes the voltages supplied to the ion emitting electrodes (3-5) such that during operation, in an alternating manner, the first electrode-group is supplied with a preferably low reference voltage, preferably with ground potential (9), and the second electrode-group is provided with high positive DC-voltage and then the first electrode-group is supplied with high negative DC-voltage and the second electrode-group is supplied with the reference voltage, preferably with ground potential (9).

6. Ionization apparatus according to one of the preceding claims, characterized in that the measuring arrangement (2) evaluates the voltage against ground potential (9) at at least one said measuring electrode (7, 8) during ionization.

7. Ionization apparatus according to one of the preceding claims, characterized in that the measuring arrangement (2) comprises a comparator unit (10) which compares the voltage against ground potential (9) at at least one said measuring electrode (7, 8) to a threshold value (V_ref) and outputs a signal (CLB) depending on the result of the comparison, preferably, that the measuring arrangement (6) comprises a rectifier (11) and/or a filter (12), preferably a lowpass filter, between at least one said measuring electrode (7, 8) and the comparator unit (10).

8. Ionization apparatus according to one of the preceding claims, characterised in that at least one said measuring electrode (7, 8) is provided in addition to the ion emitting electrode (3-5) or ion emitting electrodes (3-5), or, that a ion emitting electrode (3-5) is used as a measuring electrode (7, 8).

9. Ionization apparatus according to one of the preceding claims, characterized in that at least one said ion emitting electrode (3-5) and at least one said measuring electrode (7, 8) are located on opposite sides of a housing wall (13, 14) which surface pollution is to be detected, preferably, that at least one said ion emitting electrode (3-5) and at least one said measuring electrode (7, 8) are located offset from one another along the housing wall (13, 14) which surface pollution is to be detected, further preferably, that the housing wall (13, 14) which surface pollution is to be detected is made of a plastic material, preferably of PVC.

10. Ionization apparatus according to one of the preceding claims, characterized in that at least one said measuring electrode (7, 8) is located close to the respective side of the housing wall (13, 14) which surface pollution (P) is to be detected, preferably that at least one said measuring electrode (7, 8) is in contact to the respective side of the housing wall (13, 14), further preferably, that at least one said measuring electrode (7, 8) is spring tensioned against the respective side of the housing wall (13, 14).

11. Ionization apparatus according to one of the preceding claims, characterized in that the housing (1) comprises at least one rib like wall segment (1a) that mechanically protects at least one said ion emitting electrode (3-5) protruding from a housing wall (13, 14) and that the at least one rib like wall segment (1d) is detachably connected to the rest of the housing (1), preferably, that the rib like wall segment (1d) is connected to the rest of the housing (1) via a snap fit connection.

12. A method for detecting an indication for surface housing pollution (P) on the housing surface of an ionization apparatus with a high voltage power supply arrangement (2) with at least one ion emitting electrode (3-5) connected thereto, characterized in
that a measuring arrangement (6) with at least one measuring electrode (7, 8) connected thereto is provided and that an indication for housing surface pollution (P) is being detected by the measuring arrangement (6) based on a change in complex resistance (Z') between at least one said ion emitting electrode (3-5) and at least one said measuring electrode (7, 8).

13. Method according to claim 12, characterized in that via the high voltage power supply arrangement (2) a modulated, preferably pulsed, positive high DC-voltage is being supplied to a a first electrode-group of ion emitting electrodes (3, 4) against ground potential (9) and a modulated, preferably pulsed, negative high DC-voltage is being supplied to a second electrode-group of ion emitting electrodes (5) against ground potential (9), preferably, that via the high voltage power supply arrangement (2) the voltages supplied to the ion emitting electrodes (3-5) are being synchronized such that during operation, in an alternating manner, the first electrode-group is supplied with a preferably low reference voltage, preferably with ground potential (9), and the second electrode-group is provided with high positive DC-voltage and then the first electrode-group is supplied with high negative DC-voltage and the second electrode-group is supplied with the reference voltage, preferably with ground potential (9).

14. Method according to claim 12 or 13, characterized in that via the measuring arrangement (6) the voltage against ground potential (9) at at least one said measuring electrode (7, 8) is being evaluated during ionization.

15. Method according to one of the claims 12 to 14, characterized in that via the measuring arrangement (6) the voltage against ground potential (9) at at least one said measuring electrode (7, 8) is being compared to a threshold value (V_ref) and depending on the result of the comparison a signal (CLB) is being output.

Drawing