Apparatus and method for monitoring contamination on discharge electrodes

Abstract

An exemplary disclosed apparatus for monitoring contamination on discharge electrodes 3, 4, 5, 6, 7, 8 having at least one emission tip 32 useful for contactless discharge of an electrically charged surface includes a ground terminal 21 connected or connectable to the discharge electrode 3, 4, 5, 6, 7, 8, and a control device 27 configured to detect partial currents coupled from the at least one emission tip to the ground terminal, determine active powers based on the partial currents i1(t), i2(t), i3(t), and generate a status signal based on the calculated active powers i1(t), i2(t), i3(t).

Description

[Technical Field]

[0001] [Related Applications] This international application claims priority to German Patent Application No. 102023103041.8, filed February 8, 2023, which is hereby incorporated by reference in its entirety.

[0002] The present disclosure relates to an apparatus for monitoring contamination on a discharge electrode. According to a further aspect, the present disclosure relates to a method for monitoring contamination on a discharge electrode. [Background technology]

[0003] Passive and active discharge or charging electrodes are known in various embodiments and variants. Often, such electrodes have several emission peaks, arranged in a single or two rows with different grid widths, or as a laminated array of emission peaks, similar to a fakir board, for example. Very often, such emission peaks are embedded in an elongated U-profile with an insulating casting compound together with a current-limiting resistor. This electrical resistor is associated with either each single peak or n peaks. Passively operating discharge electrodes are frequently used even when they do not actually have a current-limiting resistor.

[0004] In the presence of an electric field, the highest possible field strength is effective at the emitting tips of the active and passive high-voltage electrodes where they are located. Each tip must protrude far enough away from the insulating recess, in addition to being subject to further boundary conditions. This is certainly similar to the necessarily free-standing end of a lightning rod on the object being protected.

[0005] By applying a high voltage and the associated high electric field strength, a corona discharge is generated at the emission tip. Corona discharge is an electrical discharge that occurs in a non-conductive medium, such as air. Such corona discharge can be used in a variety of applications. As an example, mention is made here of the electrical surface treatment of plastic foil, paper, and aluminum foil, in which the insulating surface is uniformly electrically charged. On the other hand, the electrostatically charged surface of an insulating material can be discharged without contact, in that the emission tip of the discharge electrode emits bipolar gas ions and electrons through corona discharge.

[0006] One example of a discharge electrode with an emission tip known from the prior art can be found in Patent Document 1. According to the discharge electrode shown in this document, a plurality of emission tips are arranged in an insulated manner on a metal carrier profile, which is connected to a ground terminal. In an alternative design variant, the emission tips are arranged on a plastic profile with embedded metal conductors, which are also connected to a ground terminal.

[0007] In fact, when such discharge electrodes are used, one or more of the emitting tips of the discharge electrodes inevitably become contaminated. The contamination can be, for example, dry particles such as dust that accumulate on the emitting tip. For example, these particles can be called insulating contamination, since they reduce the amount of free bipolar ions required for functioning until all function is lost. This also applies to passively acting parts of such discharge electrodes.

[0008] Conversely, so-called conductive contamination of the surface of the discharge electrode also occurs when a creepage current path exists from the high-voltage-operated emission tip to the nearest machine ground. This can occur, for example, when moisture deposits connect the emission tip to a conductive part of the discharge electrode housing. Such a creepage current path can result in significant power loss on the one hand and the destruction of the entire discharge electrode on the other hand, often with serious consequences for the respective production process in which the electrode is used. Even if a single emission tip has the ground potential of the machine ground, the low-impedance connection caused by the creepage current path of that emission tip can lead to the malfunction of the entire discharge electrode. In extreme cases, a fire of the discharge electrode may occur. Creepage current-related destruction of the carrier profile can be prevented if the carrier profile is made of a conductive material or has a high-ohmic surface coating, but temporary local malfunction of the affected emission tip still occurs until the required cleaning is performed. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] European Patent No. 3248254 Summary of the Invention [Problem to be solved by the invention]

[0010] Based on the aforementioned problems, industry increasingly needs both the occurrence and type of contamination to be detected with the highest possible sensitivity. Industry 4.0 and the associated intelligent networking of industrial machines and processes increasingly benefit from such fault detection systems that allow automatic fault removal. For example, each discharge electrode can be switched off from time to time to avoid fire accidents or total system failure.

[0011] One problem addressed by the present disclosure is to provide an apparatus for monitoring contamination on discharge electrodes that can detect required maintenance in time, and in particular before anticipated failure of the discharge electrodes. [Means for solving the problem]

[0012] According to the present disclosure, the aforementioned problem is solved by an apparatus according to independent claim 1. A corresponding method is specified in independent claim 15. Advantageous further developments of the solution according to the present disclosure are recited in the dependent claims.

[0013] The present disclosure therefore relates to an apparatus for monitoring contamination on a discharge electrode having at least one emission tip, useful for contactless discharge of an electrically charged surface, said apparatus comprising:

[0014] a ground terminal connected or connectable to said discharge electrode;

[0015] - a control device configured to achieve the following objectives:

[0016] detecting a partial current coupled from the at least one emitting tip to the ground terminal; and

[0017] generating a status signal based on the detected partial current; a control device configured to: Equipped with.

[0018] The present disclosure will be explained in more detail below with reference to embodiments shown in the drawings. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic diagram of an apparatus for monitoring contamination on a discharge electrode according to the invention for a discharge electrode having a metal profile;

[0020] [Figure 2] 2 is a schematic, idealized diagram of current, voltage, and instantaneous power curves, as well as active power calculated as the average of the instantaneous power over a period of time;

[0021] [Figure 3] 10 is a schematic diagram of an apparatus for monitoring contamination on a discharge electrode according to a further embodiment for monitoring the discharge electrode using an insulatedly embedded conductor; DETAILED DESCRIPTION OF THE INVENTION

[0022] The disclosed method and apparatus for monitoring contamination on discharge electrodes is based on the idea that the active power received by each discharge electrode can change due to contamination. Therefore, based on the change in active power, inferences can be drawn regarding the contamination of the discharge electrodes and the associated emission tips. However, there are several issues that make such monitoring of active power seem undesirable. In particular, active power is only minimally affected by insulating contamination, such as dusting of the emission tips. Below the noise level of the currents resulting from passive and active discharges, this is therefore virtually undetectable, or by the time it can be detected, it is too late. Furthermore, detecting the total active power of multiple discharge electrodes in an ionization system requires providing a separate transformer for each discharge electrode so that the active power of each individual discharge electrode can be determined.

[0023] The present invention avoids the above-mentioned problem in that only the partial current flowing between the emitting tip of the discharge electrode and the ground terminal of the device is measured. During normal operation, i.e., when there is no conductive contamination or excessive insulating contamination, such partial current arises due to capacitive coupling between the emitting tip and the metal profile carrier or between the emitting tip and the insulated buried conductor, as will be explained in more detail with reference to the drawings. The partial current generated by capacitive coupling is based solely on the AC current caused by the AC voltage. This is because passive discharge through the emitting tip causes DC current, which cannot affect the capacitive coupling. Therefore, the partial current does not include the relatively high current fraction generated by passive discharge. The resulting partial current signal has high resolution and can therefore be used to detect even the smallest contamination, i.e., an active power drop of less than about 1% of the maximum possible useful signal.

[0024] Those skilled in the art know that when the emitting tip is insulatingly contaminated, there is a slow (often over weeks and months) decrease in active power, which can be used to draw conclusions about contamination, as will be explained in more detail below.

[0025] It should be noted that partial currents flowing between the emitting tip and the ground terminal of the device can occur in some situations, regardless of capacitive coupling. For example, these partial currents may be creepage currents that occur when conductive contamination exists between the emitting tip and the ground terminal. For example, moisture adhesion between the tip and the metal profile carrier can cause creepage currents between the tip and the carrier, which rapidly increase the detected partial currents and the associated active power. Based on the aforementioned partial currents, not only insulating contamination but also conductive contamination such as moisture can be inferred in this way.

[0026] To detect the partial current, the control device can be configured to receive / request different data / parameters. For example, this data can include the voltage drop across a reference resistor placed between the emitting tip and the ground terminal. It should be noted that the present invention is not limited to the way in which the partial current is detected. On the contrary, the idea behind the present invention is to use the partial current in this way as a parameter for contamination of the discharge electrode.

[0027] According to a further embodiment, the control device comprises:

[0028] calculating an active power based on the partial currents;

[0029] generating a status signal based on the calculated active power; The device is configured to:

[0030] To calculate the active power, the control device according to one embodiment is configured to determine the average value of the product of the instantaneous value of the partial current and the instantaneous value of the supply voltage measured on the secondary side of the transformer, i.e., the average value of the instantaneous power. On the one hand, the control device can be configured to determine the product of the secondary voltage and the partial current in an analog manner. On the other hand, it is of course also possible for the control device to determine the product of the voltage and current digitally.

[0031] According to a further embodiment, the control device comprises:

[0032] comparing the calculated active power with a first active power reference value;

[0033] generating a status signal based on a comparison between the calculated active power and a first active power reference value; The device is configured to:

[0034] The active power reference value can be the expected active power achieved when the discharge electrode is clean, i.e., without significant contamination. Of course, this value is a parameter that depends on many factors, such as the number of discharge tips and the material and condition of the discharge electrode. Therefore, the active power reference value of each discharge electrode can be calibrated at the factory or even by the user.

[0035] In a further embodiment, the active power reference value can also be changed automatically or manually to account for wear of the discharge electrode over time. In other words, over time, the current flowing between the emission tip and ground can change (e.g., decrease) even without the cause of contamination of the discharge electrode. For example, to account for this change in the expected active power value over time, the user can perform an active power calibration measurement after each cleaning of the electrode system and define the resulting value as the new active power reference value. Of course, this can also be done automatically.

[0036] In a further embodiment, the control device comprises:

[0037] generating a first status signal indicative of insulation contamination if the calculated active power is below a first active power reference value; and / or

[0038] generating a second status signal indicative of conductive contamination if the calculated active power exceeds the first active power reference value; The device is configured to:

[0039] As noted above, a decrease in the active power relative to the active power reference value can indicate insulating contamination, which also reduces the capacitive coupling between the discharge tip and the ground connection of the discharge electrode. Consequently, the partial current also changes, which is detected by the control device and ultimately leads to a decrease in the determined active power. In this case, i.e., if the determined active power is below the first active power reference value, indicating insulating contamination, the control device can output a status signal. This status signal can be output to the user, for example, via an optical or audible warning signal. On the other hand, the status signal can additionally or alternatively be used to automatically clean the discharge electrode. This also applies when the determined active power exceeds the first active power reference value. This can indicate conductive contamination, such as excessive moisture, on the discharge electrode. A second status signal can be used to notify the user accordingly or to automatically take countermeasures.

[0040] In a further embodiment, the control device can be configured to output a first status signal when a first active power reference value is exceeded and a second status signal when a second active power reference value is exceeded. The second active power reference value can be significantly higher than the first active power reference value. This is particularly justified because the determined active power increases predictably and rapidly in the event of conductive contamination. The use of two active power reference values ​​prevents small changes in active power above the active power reference value from causing undesired error messages.

[0041] According to a further embodiment, the apparatus comprises at least one discharge electrode resistor through which the metal profile or the insulated buried conductor is connected to the ground terminal, the apparatus being configured to measure a voltage drop across the discharge electrode resistor, and the control device being further configured to determine the partial current based on the voltage drop across the discharge electrode resistor. If the apparatus is used to monitor multiple discharge electrodes, the apparatus comprises at least one discharge electrode resistor for each discharge electrode, one of which is connected to the metal profile or buried conductor of the discharge electrode and the other of which is connected to the ground terminal. Thus, the partial current flowing through the capacitive coupling or the creepage current between the emitting tip and the ground terminal can be determined in a simple manner by the discharge electrode resistor.

[0042] According to a further embodiment, the apparatus includes a transformer, the secondary of which can be connected to the discharge electrode, and the control device is connected to the secondary of the transformer, particularly via a voltage divider, and configured to determine the secondary voltage of the transformer. The voltage divider can be configured so that the voltage value output to the control device is within a preferred operating range of the control device. To determine the active power, the control device can determine the secondary voltage of the transformer based on the voltage output via the voltage divider, as described above, and multiply this secondary voltage by the determined partial current. By connecting the control device to the secondary of the transformer, time-varying voltages can also be taken into account by the control device. Therefore, fluctuations in the power supply voltage cannot distort the measurement result, i.e., the determination of the active power.

[0043] According to a further embodiment, the apparatus is configured to simultaneously monitor multiple discharge electrodes, and the control device is configured to detect, for each discharge electrode, a partial current coupled from at least one emission tip of the respective discharge electrode to the ground terminal. In other words, the apparatus is configured to detect a number of different partial currents corresponding to the number of discharge electrodes being monitored. On the hardware side, whether more or fewer discharge electrodes are monitored, only one discharge electrode resistor per discharge electrode is required to configure the apparatus.

[0044] According to a further embodiment, the control device is configured to detect a partial current that is capacitively coupled from the emitting tip to the metal profile or to the insulated buried conductor and, as a result, to the ground terminal.

[0045] According to further embodiments, the detection of partial currents and thus the generation and evaluation of signals for contamination detection can be performed selectively and independently for any number of discharge electrodes.

[0046] According to a further embodiment, the control device is further configured to determine the pollution-dependent effective resistance by dividing the square of the secondary voltage of the transformer by the pollution-dependent active power, the pollution-dependent effective resistance thus determined being in particular independent of possible mains voltage fluctuations.

[0047] According to a further embodiment, the detected partial current for generating the status signal is independent of the DC component that necessarily flows to ground when a highly charged surface discharges through the emitting tip and the secondary coil of the transformer.

[0048] According to a further embodiment, the device comprises a display for showing the status signal in analog or digital form. For example, if the above-mentioned active power criteria are not met, the user can be notified via the display that insulating contamination may be present on the discharge electrodes. As already mentioned above, by independently evaluating the individual partial currents, the device can also inform the user as to which discharge electrodes appear to be contaminated. The device can also output further information via the display, for example, to prompt the user to clean a particular discharge electrode.

[0049] According to a further embodiment, the apparatus comprises a plurality of discharge electrodes and the status signal includes individual status data for each discharge electrode.

[0050] According to a further aspect, the present disclosure relates to a method for monitoring contamination on a discharge electrode useful for contactless discharge of an electrically charged surface, the discharge electrode comprising at least one emission tip, the method comprising:

[0051] detecting a partial current coupled from at least one emission tip to a ground terminal connected to the discharge electrode;

[0052] generating a status signal based on the detected partial current; Includes.

[0053] According to a further aspect, the present invention relates to a method for monitoring contamination on discharge electrodes 3, 4, 5, 6, 7, 8 serving for contactless discharge of electrically charged surfaces, the discharge electrodes 3, 4, 5, 6, 7, 8 comprising at least one emission tip 32, the method comprising:

[0054] detecting partial currents i1(t), i2(t), i3(t) coupled from at least one emission tip 32 to a ground 21 connected to the discharge electrode;

[0055] determining active power based on the partial currents i1(t), i2(t), i3(t);

[0056] generating a status signal based on the calculated active powers i1(t), i2(t), i3(t); Includes.

[0057] Figure 1 shows a schematic diagram of an apparatus according to the invention for detecting contamination on discharge electrodes. In the example of Figure 1, the apparatus 100 is connected to three discharge electrodes 3, 4, 5. However, it should already be mentioned at this point that the apparatus 100 according to the invention can also be applied to any number of discharge electrodes 3, 4, 5.

[0058] The device comprises a high-voltage transformer 10 and a measurement or evaluation assembly 20. The high-voltage transformer 10 is connected to the power grid by means of its primary windings 11, 12 or to a variable frequency variable voltage power unit (not shown). A first end of the secondary winding 13 is connected via a high-voltage cable 2 to three discharge electrodes 3, 4, 5. The discharge electrodes 3, 4, 5 are typically AC voltage discharge electrodes or high-voltage ionizers.

[0059] The second end of the secondary winding 14 is connected to a ground terminal 21. The AC high voltage delivered to the high-voltage cable 2 via the secondary winding is typically in the range of 4 kV to 10 kV. Such a high voltage is required to achieve a high electric field strength that accompanies a corona discharge at the discharge tips of the discharge electrodes 3, 4, and 5. This corona discharge generates bipolar gas ions and free electrons via impact ionization. Such free charge carriers can neutralize or discharge positively or negatively charged surfaces.

[0060] A portion of the AC high voltage of the transformer 10 provided to the secondary side is provided as an input signal to the control device 27 via voltage dividers 22, 23. The voltage signal u(t) provided to the control device 27 is therefore proportional to the AC high voltage prevailing in the high voltage cable 2. As will be explained in more detail below, the voltage signal u(t) can be used by the control device 27 to determine the active power.

[0061] The control device 27 of the evaluation assembly 20 is further connected to the metal parts of each of the discharge electrodes 3, 4, 5. In other words, the control device 27 is used to collect parameters and data that provide information about the partial currents of the discharge electrodes 3, 4, 5 flowing in the direction of the ground terminal 21. The partial current of the discharge electrode 3 is shown schematically in FIG. 1 as "i1(t)". ​​The partial current of the second discharge electrode 4 is shown schematically as "i2(t)". ​​Finally, the partial current of the third discharge electrode 5 is shown schematically as "i3(t)". ​​However, it should be mentioned at this point that it is not necessary to provide the control device 27 with direct measurements of the partial currents i1(t), i2(t), i3(t). Instead, any parameter or data that provides information about the partial currents flowing in the direction of the ground terminal 21 can be provided to the control device 27.

[0062] 1, the control device can for this purpose multiply the voltage signal u(t) by the partial currents i1(t), i2(t), i3(t), respectively, and form an average value to determine the active power of the partial currents i1(t), i2(t), i3(t) resulting from the coupling of the emitting tip to the ground terminal 21. Expressed in mathematical terms, the control unit can calculate the active power resulting from the capacitive coupling or creepage current as:

number

[0063] The capacitive coupling shown above will be explained in more detail below. The discharge electrodes 3, 4, and 5 shown in Figure 1 are substantially identical. However, it should be noted that the arrangement and number of emission tips may vary significantly between discharge electrodes. Therefore, the schematic arrangement according to Figure 1 should be considered as an overview only. As an example, only discharge electrode 3 of Figure 1 will be explained below.

[0064] The discharge electrode 3 has one or more emission tips 32, each associated with a current-limiting resistor 31. The emission tips 32 and the current-limiting resistors are embedded in a metal profile 33 by an insulating casting material that serves as a carrier profile for the emission tips. Preferably, this metal profile 33 has an insulating, stress-resistant surface. One end of the current-limiting resistor 31 is connected to the high-voltage cable 2 of the device 100, and the other end is connected to the corresponding emission tip 32. Thus, the AC high voltage provided by the transformer 10 can generate a high electric field intensity accompanied by a corona discharge at the emission tip 32. This corona discharge generates bipolar gas ions and free electrons via impact ionization. A portion of these charge carriers generated by the ionization current, and consequently a portion of the active power emitted by the emission tip 32, is transmitted from the emission tip 32 to the metal profile 33 via a capacitive coupling 34, shown schematically in dashed lines.

[0065] The metal profile 33 of the discharge electrode 3 is connected to the ground terminal 21 of the device 100 via an electrical terminal 35. A first discharge electrode resistor 24 is arranged between the electrical terminal 35 and the ground terminal 21, i.e., ground. The same applies to a second discharge electrode resistor 25 arranged between the second discharge electrode 4 and the ground terminal 21 and a third discharge electrode resistor 26 arranged between the third discharge electrode 5 and the ground terminal 21.

[0066] The voltage drop across the first discharge electrode resistor 24 is proportional to the ion-generating active current i1(t) of the first discharge electrode 3. This also applies to current measurements via voltage drops across the discharge electrodes 4, 5 and the discharge electrode resistors 25, 26. Any number of discharge electrodes can therefore be monitored (not shown) as required. In summary, it should be noted here that the discharge electrode resistors 24, 25, 26 serve to determine (for example, by determining the voltage drop) the respective partial currents coupled to the metal profile 33 via the capacitive coupling 34 of the emission tip 32 and further to the ground terminal 21.

[0067] It has been found that the capacitively coupled currents of the discharge electrodes 3, 4, 5 depend on contamination of the discharge electrodes. For example, in the case of insulating contamination, i.e. dusting of the emission tip, a change in the partial currents i1(t), i2(t), i3(t) or the active power associated with these partial currents can be detected. The individually provided discharge electrode resistors 24, 25, 26 therefore make it possible to individually detect insulating contamination on each individual discharge electrode 3, 4, 5.

[0068] However, the apparatus 100 is not only capable of detecting the partial current generated via the aforementioned capacitive coupling 34. Rather, it can also determine the creepage current between the emitting tip 32 and the metal profile 33. Such creepage current is generated, for example, by an undesirable low-impedance material between the emitting tip and the metal profile 33, which may be generated, in particular, by moisture adhesion at the emitting tip. Such creepage current is typically several times larger than the partial current generated by the capacitive coupling 34. In other words, in the case of conductive contamination (e.g., excessive moisture at the emitting tip), partial currents i1(t), i2(t), i3(t) exist toward the ground terminal 21, whose effective current percentages are significantly higher than the partial currents i1(t), i2(t), i3(t) generated by the capacitive coupling 34. As will be described in more detail below, the control device 27 can accordingly infer conductive contamination of one or more of the discharge electrodes 3, 4, 5 upon a sudden change in one or more of the partial currents i1(t), i2(t), i3(t).

[0069] The high sensitivity of the partial currents allows early detection and indication of contamination conditions, even when there are minor changes in the emission performance of the discharge electrodes. Therefore, the status signal generated by the control device 27 based on the partial currents i1(t), i2(t), i3(t) allows reliable planning of preventive maintenance without undesired machine downtime. This signal is unique and assigned only to electrodes with insulating or conductive contamination.

[0070] The apparatus 100 further comprises a fieldbus terminal 28 to which the control device 27 is connected with a bidirectional operational connection. Status signals generated by the control device 27 can therefore be output to any process environment for higher levels of quality assurance or general provision of data within the meaning of Industry Standard 4.0. For this purpose, the apparatus 100 can have interfaces (not further discussed).

[0071] In the embodiment of the apparatus 100 shown in FIG. 1 , a display 29 is further provided that can output data from the control device 27. For example, the display 29 can visualize the degree of contamination numerically or graphically. For example, the status signal of the control device 27 can be used to issue a warning to the user via the display if conductive or insulating contamination is detected by the control device 27. This output can further inform the user which of the discharge electrodes 3, 4, 5 is affected. In a further embodiment, the status signal of the control device 27 can also include information or suggestions for correcting the contamination. Alternatively or additionally, the status signal generated by the control device 27 can be used to initiate automatic cleaning of the respective discharge electrodes 3, 4, 5.

[0072] Below, a method for generating a status signal indicative of the contamination state of the discharge electrodes is described in more detail.

[0073] As already mentioned above, the AC high voltage provided in the high-voltage cable 2 generates a high electric field strength at the emitting tip, with an associated corona discharge. A portion of the emitted electronic charge carriers, and consequently a portion of the emitted active power, is transferred from the emitting tip 32 to the metal profile 33 via the capacitive coupling 34. Such charge carriers are dissipated in the form of a partial current i1(t) towards the ground terminal 21. The resulting current flow / partial current i1(t) can be detected by the voltage drop across the discharge electrode resistor 24.

[0074] The control device 27 is configured to multiply the current intensity of the partial current i1(t) detected as described above by the voltage signal u(t) and form the average value of this product in order to determine the portion of the emitted active power that is transmitted to the metal profile via the capacitive coupling.

[0075] In this regard, reference is also made to Figure 2, which shows a schematic, idealized graph of the current signal, the voltage signal, and the instantaneous power signal, as well as the active power curve. In the schematic representation according to Figure 2, the voltage signal (u(t)) and the current signal (i(t)) are shown in the form of pure sinusoids. In reality, only the voltage signal approximately corresponds to the sinusoid shown in Figure 2. On the other hand, the current signal of the partial current 202 has a very high harmonic content, so that there is no sinusoid. Therefore, the illustration according to Figure 2 should only be referred to schematically.

[0076] The instantaneous power 206 signal resulting from the multiplication of the voltage signal 204 and the current signal 202 is also shown schematically in Figure 2. The control device

number

[0077] Contamination of the discharge electrode results in a phase shift of the current signal relative to the voltage signal 204. This phase shift is shown diagrammatically by an arrow in FIG. 2. Thus, in the case of conductive contamination, which can generate creepage currents, there is a phase shift of the current signal relative to the voltage signal, which often results in a sudden spike in the active power 208. In the case of insulating contamination, the phase difference between the partial current voltage signal 204 and the current signal 202 increases, and thus the active power 208 gradually decreases. It should be noted at this point that monitoring the active power (i.e., the change in the active power), i.e., calculating the product of the current and voltage and forming an average value, is a particularly fast and reliable method for detecting a change in the phase shift between the current signal and the voltage signal and thereby drawing a conclusion about contamination of the discharge electrode. However, it is also conceivable that only the phase shift can be detected based on the current signal 202. This can be achieved, for example, by Fourier analysis of the current signal; calculating the active power is not absolutely necessary. In this case, the control unit can instead be configured to directly draw a conclusion about insulating or conductive contamination of the discharge electrode based on the phase shift.

[0078] 2, it should be further noted that in the case of conductive or insulating contamination of the discharge electrode, the amplitude of the current signal 202 does not change substantially, and therefore no meaningful conclusions can be drawn about the contamination of the discharge electrode by simply observing the amplitude of the current signal 202. This is especially true in the case of low insulating contamination.

[0079] The control device 27 may be provided with an active power reference value, which is determined, for example, at the factory. The active power reference value is a value for the active power generated due to the capacitive coupling 34 that would be expected in the case of an uncontaminated discharge electrode. This may be determined at the factory, for example, by measuring an uncontaminated discharge electrode, and may be stored in the memory of the control device 27. On the other hand, the active power reference value may also be changeable / adjustable by the user, as will be explained in more detail below.

[0080] The control device is configured to compare the active power based on the partial current i1(t) with an active power reference value. A calculated active power below the active power reference value can then be an indication of the presence of insulating contamination, as described above. The active power reference value can be several percentage points lower than the actual expected active power for a clean discharge electrode in order to generate an alert signal, i.e., a change in the status signal of the control device, only when a certain degree of contamination has already occurred. This can be provided, inter alia, to compensate for natural fluctuations in the calculated active power.

[0081] The control device can be configured to generate a first status signal indicative of insulation contamination if the calculated active power is below a first active power reference value. By way of example, Figure 2 shows a first active power reference value 210 that is below the active power 208 in an uncontaminated state.

[0082] The control device may generate a second status signal indicative of conductive contamination when the calculated active power exceeds the first active power reference value.

[0083] Since the expected active power is fundamentally different in the case of conductive or insulating contamination, the control device can be provided with a second active power reference value in addition to the first active power reference value. Thus, the control device can compare the calculated active power with the first active power reference value and the second active power reference value, respectively, continuously or at intervals. If the calculated active power is below the first active power reference value, the control device generates a first status signal indicating insulating contamination. If the calculated active power is above the second active power reference value, the control device outputs a second status signal indicating conductive contamination. The second active power reference value is preferably several times higher than the first active power reference value. Typically, the difference can be about 100 times.

[0084] According to a further design variant, the control device 27 can be configured to generate a difference between the active power and the first and second active power reference values, respectively. Based on the difference between the active power reference value and the calculated active power, the control device 27 can generate a status signal. For example, an active power below the first active power reference value results in a negative difference. This negative difference can be used by the control device to output a first status signal. Alternatively or additionally, the control device 27 can be configured to check whether the difference exceeds a certain threshold. For example, it can ensure that the first status signal is not generated until the calculated active power falls below the first active power reference value by a certain value or percentage. This is advantageous because the calculation of active power according to the present invention is very sensitive and can already detect very slight contamination of the discharge electrodes. Therefore, the threshold can be set by the user to avoid unnecessary notification of minimal contamination. This can be set, for example, as a percentage via the display, so that the first status signal is generated only if the calculated active power deviates significantly (e.g., by more than 10%) from the first active power reference value.

[0085] The control device can be configured to accordingly determine the difference between the calculated active power and a second active power reference value and use this difference to generate a second status signal, as described above with respect to the first active power reference value. An exemplary second active power reference value 212 can also be seen in FIG. 2 and is above the active power P for an uncontaminated discharge electrode.

[0086] If insulating contamination and conductive contamination occur simultaneously (e.g., from water dripping onto the electrode), a clearly high active power will always occur, so the control unit will only output the second status signal for the conductive contamination. Conductive contamination generally has the highest priority and is therefore the first priority. Only when the discharge electrode is dry again and the insulating contamination is still present will the control unit output the first status signal for the insulating contamination once the conductive contamination has disappeared.

[0087] It should be mentioned at this point that the expected active power achieved, particularly via the capacitive coupling 34, may change over time due to wear of the discharge electrodes 3, 4, and 5. Therefore, it may be practical to occasionally readjust the first active power reference value. For this purpose, the apparatus 100 may have an interface for the user to input a new reference value. For example, the display 29 may be configured as a touch screen for inputting the desired active power reference value. The display may be equipped with a corresponding input mask for this purpose. Alternatively or additionally, the control device may be configured to automatically adjust the active power reference value periodically. All that is required to ensure that the discharge electrode in question is free of contamination is a user input. The control device may then perform a test operation on each discharge electrode to determine the corresponding active power of the currently clean discharge electrodes. This average active power may then be stored as the new first active power reference value.

[0088] Since the sizes and arrangements of the different discharge assemblies 3, 4, 5 may differ substantially from one another, it is generally considered that the control device has a corresponding first and / or second active power reference value for each monitored discharge electrode. The status signals generated by the control device can therefore be respectively adjusted to the situation of the different discharge electrodes 3, 4, 5. Thus, generation and evaluation of signals for contamination detection is possible selectively and independently for any number of discharge electrodes.

[0089] When the discharge electrode is operated with the device 100 according to the invention against a moving substrate that is highly electrically charged, a DC discharge current flow across the discharge tip 32 and the secondary windings 13, 14 of the transformer occurs depending on the polarity of the substrate charge. However, such a DC discharge current flow does not result in capacitive coupling and is therefore not detected by the control device 27. Therefore, the calculation of the active power according to the invention is not dependent on very high DC discharge current flows, which can further increase the sensitivity of the proposed contamination detection.

[0090] FIG. 3 is a schematic circuit diagram of a device 100 according to the present invention, which includes second-type discharge electrodes 6, 7, and 8. In other words, the device 100 is identical to the device 100 according to FIG. 1. Only the discharge electrodes 6, 7, and 8 of FIG. 3, which are monitored using the device 100, differ from those of FIG. 1. In particular, the discharge electrodes 6, 7, and 8 of FIG. 3 are discharge electrodes having a carrier profile made of an insulating material 63, which has at least one embedded conductor 65 connected via an electrical terminal point 66 to the ground terminal 21 of the device 100 via a conductor. The function of the discharge electrodes 6, 7, and 8 shown in FIG. 3, which have a carrier profile made of an insulating material 63, is disclosed in detail in EP 096862881.

[0091] In the case of a discharge electrode having a carrier profile made of an insulating material, a portion of the ionization current and charge carriers generated by the emission tip 62, and thus a portion of the released active power, is transferred via a capacitive coupling 64 to a conductor 65 embedded in the insulating material 63 and is consequently discharged towards the ground terminal 21. The electrical connection of the conductor 65 to the ground terminal 21 is made via a resistor 24. The voltage drop across the resistor 24 is therefore proportional to the ion-generating active current of the discharge electrode 6 and, consequently, to the active power. This applies equally to the discharge electrodes 7, 8 and also to the current measurement via the voltage drop across the discharge electrode resistors 25, 26.

[0092] The operation of the control device 27 to determine the status signal is substantially identical to that already described with reference to Figure 1. Therefore, the use of the apparatus for different discharge electrodes does not require any further modifications to the apparatus 100. Only the active power reference values ​​of the discharge electrodes 6, 7, 8 differ substantially from the active power reference values ​​of the discharge electrodes 3, 4, 5 according to Figure 1.

[0093] The present disclosure is not limited to the embodiments shown in the figures, but rather results from all combinations of features disclosed herein.

Claims

1. 1. A device (100) for monitoring contamination on a discharge electrode (3, 4, 5, 6, 7, 8) having at least one emission tip (32) serving for said non-contact discharge of an electrically charged surface, comprising: a ground terminal (21) connected or connectable to the discharge electrodes (3, 4, 5, 6, 7, 8); A control device (27) comprising: detecting partial currents (i1(t), i2(t), i3(t)) coupled from said at least one emitting tip (32) to said ground terminal (21); determining active power based on the partial currents (i1(t), i2(t), i3(t); generating a status signal based on the calculated active powers (i1(t), i2(t), i3(t)); a control device (27) configured to: An apparatus (100) comprising:

2. The control device (27) comparing the determined active power with a first active power reference value; generating the status signal based on the comparison between the determined active power and the first active power reference value; The apparatus (100) of claim 1, further configured to:

3. The control device (27) generating a first status signal indicative of insulation contamination if the calculated active power is below the first active power reference value; and / or generating a second status signal indicative of conductive contamination if the calculated active power exceeds the first active power reference value; The apparatus (100) of claim 2, further configured to:

4. 4. The apparatus (100) of claim 2 or 3, wherein the first active power reference value is set at the factory or is adjustable by the user.

5. The apparatus (100) according to any one of claims 1 to 4, comprising at least one discharge electrode resistor through which a metal profile (33) or an insulated buried conductor (67) is connected to the ground terminal (21), the apparatus (100) being configured to measure a voltage drop across the discharge electrode resistor, and the control device (27) being configured to determine the partial current based on the voltage drop across the discharge electrode resistor.

6. The apparatus (100) according to any one of claims 1 to 5, wherein the apparatus (100) comprises a transformer (10), the secondary side of which can be connected to the electrode assembly, and the control device is connected to the secondary side of the transformer (10), in particular via a voltage divider, and is configured to determine the secondary voltage of the transformer (10).

7. The apparatus (100) according to any one of claims 1 to 6, wherein the apparatus (100) is configured to simultaneously monitor a plurality of discharge electrodes (3, 4, 5, 6, 7, 8), and the control device is configured to detect, for each discharge electrode, a partial current coupled from the at least one discharge tip (32) of the respective discharge electrode to the ground terminal (21).

8. The apparatus (100) according to any one of claims 1 to 7, wherein the control device (27) is configured to detect the partial current capacitively coupled from the emission tip (32) to the metal profile (33) or the insulated buried conductor (67) and, as a result, to the ground terminal (21).

9. 9. The device (100) according to claim 1, wherein the detection of the partial currents (i1(t), i2(t), i3(t)) is performed selectively for any number of discharge electrodes (3, 4, 5, 6, 7, 8) and is performed independently from the generation and evaluation of the signals for contamination detection.

10. The apparatus (100) according to any one of claims 1 to 9, wherein the control device is further configured to determine an effective resistance due to pollution by dividing the square of the secondary voltage of the transformer (10) by an effective power due to pollution.

11. The device (100) according to any one of claims 1 to 10, wherein the detected partial currents (i1(t), i2(t), i3(t)) for generating the status signals are independent of a DC component that necessarily flows to the ground when a highly charged surface discharges through the emitting tip and the secondary coil of the transformer (10).

12. The device (100) of any one of claims 1 to 11, wherein the device (100) comprises a display (29) for showing the status signal in analog or digital form.

13. The apparatus (100) of any one of claims 1 to 12, wherein the apparatus (100) comprises a plurality of electrode assemblies, and the status signal includes individual status data for each electrode assembly.

14. A method for monitoring contamination on a discharge electrode (3, 4, 5, 6, 7, 8) serving for contactless discharge of an electrically charged surface, said discharge electrode (3, 4, 5, 6, 7, 8) comprising at least one emission tip (32), said method comprising the steps of: detecting partial currents (i1(t), i2(t), i3(t)) coupled from the at least one emission tip (32) to the ground (21) connected to the discharge electrode; determining active power based on the partial currents (i1(t), i2(t), i3(t); generating a status signal based on the calculated active powers (i1(t), i2(t), i3(t)); A method comprising:

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