JP2014185962A - Static electricity discharge detection device and static electricity discharge detection system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a static electricity discharge detection device capable of actually and reliably detect the static electricity discharge even at the site such as a factory without needing a high sensitive camera.SOLUTION: On the assumption of a static electricity discharge detection device for detecting the static electricity discharge generated from an electrically-charged object, there are provided an optical sensor 2 for outputting electric signals in accordance with inputted light, and a filter 4 for limiting a wavelength area of light taken in the optical sensor 2. In the filter 4, an upper limit value in a pass wavelength area is made to be 410 [nm] or less.

Description

  The present invention relates to, for example, an electrostatic discharge detection device that detects electrostatic discharge generated inside an apparatus that transports a granular material.

Electrostatic discharge may occur due to frictional charging between the powder transported in the apparatus and the transport tube wall. In order to detect such discharge, a method of photographing discharge light has been conventionally known.
The intensity of the light generated by the discharge is weak compared to sunlight, so a high-sensitivity camera must be used to accurately capture the light, and external light such as sunlight should not enter the monitoring area inside the device. I must. In this way, in order to prevent external light from entering the monitoring area, the entire room is darkened, or the powder transportation device and the camera are covered with a black curtain.

  On the other hand, an apparatus that captures a U-VC ultraviolet image to detect discharge as in Patent Document 1 has also been known. This device performs ultraviolet image capturing using a filter while repeatedly irradiating and blocking ultraviolet rays on the insulator portion that may be discharged, and compares the captured images to determine the presence or absence of discharge light. Is.

JP 2005-241623 A

As described above, in the conventional detection method using a camera, in order to photograph discharge light due to electrostatic discharge, it is necessary to focus on a light emitting portion to be monitored. However, it is impossible to focus in a dark state. In addition, when monitoring a specific location such as a specific insulator as in the device of the above-mentioned Patent Document 1, the camera can be kept in focus, but a discharge site such as powder during transportation is specified in advance. In addition, it is difficult to specify the position to be focused because the powder surface also moves during powder transportation. In particular, focusing may be impossible when the powder transport device is enlarged.
In addition, the high-sensitivity camera is expensive, and there is a problem in that the use of this camera increases the cost. In particular, in order to roughen the focusing, using a lens capable of photographing a wide range at the same time further increases the cost.

Further, in an apparatus for transporting powder, it may be necessary to apply vibration to the entire apparatus in order to prevent stagnation of the powder. If the apparatus is vibrated in this way, the expensive camera may be damaged, or the camera position may be shifted and the focus may be lost.
As described above, it has not been practical to continuously detect electrostatic discharge using camera images in the field of powder transportation.
An object of the present invention is to provide an electrostatic discharge detection device that does not require a high-sensitivity camera and that can detect electrostatic discharge realistically and accurately even at a site such as a factory where a charged object moves.

  A first aspect of the present invention is an electrostatic discharge detection device for detecting electrostatic discharge generated from a charged object, an optical sensor that outputs an electrical signal in accordance with input light, and a wavelength region of light to be captured by the optical sensor The filter is characterized in that the upper limit value of the pass wavelength region is 410 [nm] or less.

The second invention is characterized in that the optical sensor detects discharge light and noise light due to the electrostatic discharge in the atmosphere.
The third invention is characterized in that a lower limit value of a pass wavelength region of the filter is 250 [nm] or more.

According to a fourth aspect of the present invention, the light sensor and the filter are incorporated in a case provided with a light introduction window in the process of guiding the light to the light sensor, and the pressure in the case is maintained higher than the pressure outside the case. It is characterized by.
In order to maintain the pressure in the case higher than the external pressure, the pre-pressurized case may be prevented from leaking to maintain the internal pressure, or from the case to the outside. You may make it continue supplying compressed gas in a case, accept | permitting some leaks.

According to a fifth aspect of the present invention, a gas is supplied into the case, and the case is provided with a spout for ejecting the gas supplied into the case along the outer surface of the light introduction window. .
The sixth invention is characterized in that the case is made of metal and the case is grounded.

  According to a seventh aspect of the present invention, there is provided an electrostatic discharge detection system comprising a plurality of the electrostatic discharge detection devices according to any one of the first to sixth aspects provided in a monitoring target area.

According to the first to sixth inventions, electrostatic discharge can be detected without using an expensive camera, and the cost of the detection apparatus can be reduced. In addition, the use of a filter eliminates the need for a device or a trouble to block external light.
In particular, since the wavelength range of light guided to the optical sensor by the filter is set to 410 [nm] or less, strong light exceeding 410 [nm] among noise light such as sunlight is blocked, and a signal including discharge light is blocked. It can be detected stably and efficiently.

  In the second invention, since the discharge light and the noise light are detected by the optical sensor, it is not necessary to completely block the noise light by the filter. If you try to detect a discharge in a wavelength region that does not include noise light such as sunlight, the discharge light will also be weak, and you may not be able to detect the discharge unless the photosensor sensitivity is very high. By taking discharge light and noise light simultaneously in an area where they can be distinguished, more efficient detection becomes possible.

  According to the third aspect of the invention, noise light can be efficiently blocked by preventing light having a wavelength of less than 250 [nm], which is a wavelength region where the intensity of discharge light is small, from passing therethrough. As a result, the discharge can be detected more accurately.

In the fourth and fifth inventions, foreign matter can be prevented from entering the case by maintaining the pressure inside the case higher than the external pressure.
If a foreign substance enters the case, the detection sensitivity of the optical sensor will decrease, but the sensitivity of the optical sensor can be maintained by these inventions.
In addition, the pressure inside the case is detected and the pressure difference between the internal pressure and the external pressure is kept at a predetermined pressure or more. When the internal pressure decreases and the pressure difference becomes small, the optical sensor is turned on. If it is configured to stop, it can be used as an explosion-proof electrostatic discharge detection device.
In particular, according to the fifth aspect of the invention, it is possible to prevent the detection sensitivity of the optical sensor from being lowered due to powder or the like adhering to the surface of the light introduction window.
In addition, according to the sixth aspect of the invention, it is possible to prevent the influence of electrical noise outside the case on the optical sensor and to detect electrostatic discharge more accurately.

In the seventh invention, since a plurality of electrostatic discharge detection devices are provided, it is possible to detect a wider range of electrostatic discharges than in the case of only one electrostatic discharge detection device. In addition, a discharge at a position that cannot be detected by a specific electrostatic discharge device can be detected by another electrostatic discharge detection device, and the discharge in the monitoring target area can be reliably detected.
Furthermore, the discharge generation position can be specified from the positions of the plurality of electrostatic discharge detection devices. As a result, it is possible to identify a location where discharge is likely to occur, and to take measures to prevent discharge.

FIG. 1 is a configuration diagram of the electrostatic discharge detection device of the first embodiment. FIG. 2 is a schematic diagram of an experimental apparatus in which an experiment using the electrostatic discharge detection apparatus of the first embodiment was performed. FIG. 3 is a table showing the pass wavelengths of the filters used in Experiments 1 and 2. FIG. 4 is a graph showing the results of Experiment 1 with the fluorescent lamp in the laboratory turned on. FIG. 5 is a table showing the results of Experiment 1. FIG. 6 is a graph showing the results of Experiment 2 with the fluorescent lamp in the laboratory turned off. FIG. 7 is a partial cross-sectional view of the second embodiment.

A first embodiment of the present invention will be described with reference to FIGS.
In the electrostatic discharge detection device according to the first embodiment, as shown in FIG. 1, an optical sensor 2 is incorporated in a cylindrical case 1.
The case 1 is made of metal, and the case 1 is connected to the ground when the electrostatic discharge detection device is used. Thus, since the metal case 1 is grounded, it is possible to prevent electrical noise outside the case 1 from affecting the optical sensor 2.
A light introduction window 1c is opened at one end of the case body 1a, and the light introduction window 1c is closed with a transparent cover 3 made of quartz glass. A band pass filter 4 which will be described in detail later is provided inside the transparent cover 3.
The detection window 2a of the optical sensor 2 is opposed to the bandpass filter 4. When the light sensor 2 receives light that has passed through the transparent cover and the bandpass filter 4 through the detection window 2a, the light sensor 2 outputs an electrical signal corresponding to the intensity.

In the first embodiment, the diameter of the light introduction window 1c is made smaller than the inner diameter of the case main body 1a, and a convex portion 1d toward the center of the light introduction window 1c is provided at the tip of the case main body 1a. The light introduction window 1c is closed by adhering the periphery of the transparent cover 3 to the convex portion 1d, but the method of attaching the transparent cover 3 is not limited to the above. For example, the transparent cover 3 may be adhered to the outside of the case body 1 or may be fixed using screws or the like. However, in order to prevent foreign matter from entering the case main body 1a from the light introduction window 1c, it is preferable to attach the transparent cover 3 and the light introduction window 1c so that there is no gap.
The bandpass filter 4 and the optical sensor 2 are provided inside the transparent cover 3, and a sponge-like filling member (not shown) is pushed into the case body 1a to fix the optical sensor 2 and the bandpass filter 4. ing.

The other end of the case body 1a is closed with a cap 1b. A seal member (not shown) is interposed between the cap 1b and the case body 1a. Further, a power cord 5 for supplying power to the optical sensor 2 and a signal line 6 for outputting a signal from the optical sensor 2 are drawn out from the cap 1b.
A power source 7 is connected to the power cord 5, and an oscilloscope 9 is connected to the signal line 6 via an amplifier 8.
The signal output from the optical sensor 2 that has detected the light is amplified by an amplifier 8 and can be confirmed by an oscilloscope 9.

The band-pass filter 4 is used to reduce the passage of noise light such as sunlight other than the discharge light due to electrostatic discharge and to facilitate detection of the discharge light.
For this reason, in the electrostatic discharge detection device of the first embodiment, the upper limit of the passing wavelength of the bandpass filter 4 is set to 410 [nm] or less.
The filter of the present invention for reducing the amount of noise light passing is not limited to a bandpass filter, but a combination of a shortpass filter and a longpass filter, a shortpass filter alone, or various filters. May be used in combination.
A plurality of band pass filters having an upper limit of the pass wavelength of 410 [nm] or less may be used.

  In the first embodiment, the upper limit of the passing wavelength region of the band-pass filter 4 is set to 410 [nm] or less because when light in a wavelength region exceeding 410 [nm] is passed through the following confirmation experiment, noise is passed. This is because it has been confirmed that the intensity of light is so strong that discharge light cannot be detected accurately.

Hereinafter, Experiment 1 for determining the wavelength of the band-pass filter 4 in the electrostatic discharge detection device of the first embodiment will be described.
In this experiment, polypropylene (PP) particles having a diameter of about 2 to 3 [mm] are charged and the discharge light is detected. And in this experiment 1, the apparatus shown in FIG. 2 was used in the laboratory where sunlight entered through the window and the fluorescent lamp illumination was turned on.

The experimental apparatus of FIG. 2 includes a silo 10, a transport pipe 11 that transports the PP particles continuously from the bottom discharge port 10 a of the silo 10 to the input port 10 c of the ceiling surface 10 b, and the ceiling surface 10 b of the silo 10. And a gas pipe 12 that continuously supplies gas from the exhaust port 10d to the transport pipe 11. A blower 13 for supplying gas is connected to the gas pipe 12, and a bag filter 14 is provided between the blower 13 and the exhaust port 10 d of the silo 10. This bag filter 14 is for preventing PP particles in the silo from being drawn into the gas pipe 12.
In the figure, the movement path of PP particles is indicated by solid arrows, and the gas flow is indicated by broken arrows.

Further, the silo 10 is provided with a plurality of observation windows 10e on its side surface so that the state inside the silo can be visually observed.
In the figure, reference numeral 15 denotes a rotary valve, which opens and closes the bottom discharge port 10a of the silo 10. Reference numeral 16 denotes an air conditioner that adjusts the temperature and humidity of the gas supplied to the gas passage and the transport pipe 11.
And although not shown in figure, the transparent cover 3 of the electrostatic discharge detection apparatus shown in FIG.

  The PP particles are charged into the silo 10, and the PP particles are supplied from the transport pipe 11 into the silo 10 by gas. The discharge light generated when PP particles charged by friction with the transport tube 11 while moving in the transport tube 11 are discharged in the silo 10 is detected by an electrostatic discharge detection device attached to the ceiling surface 10b. To do.

The specific experimental method of Experiment 1 is as follows.
As the band-pass filter 4, nine types of filters shown in FIG. 3 are used.
FIG. 3 shows the center wavelength and the full width at half maximum of each bandpass filter 4, but when it is necessary to distinguish the filters below, they are distinguished by the center wavelength. . Specifically, an experiment was performed on nine bandpass filters having a center wavelength of 240 [nm] to 600 [nm].

Then, the detection signal when the PP particles that passed through the transport pipe 11 were supplied into the silo 10 was measured by the oscilloscope 8 for each detection device to which each bandpass filter 4 was attached.
When supplying PP particles, the gas from the blower 13 is supplied to the transport pipe 11 and the rotary valve 15 is opened. At this time, the gas supplied to the transport pipe 11 by the air conditioner 16 was adjusted to 30 ° C. and 30% RH, and the gas flow rate was adjusted so that the PP particle flow rate was 0.38 [kg / s].

Then, with the PP particles supplied, the oscilloscope 9 measured the peak voltage value when the peak was detected as a discharge signal and the other base portion voltage value as a noise signal.
The results of Experiment 1 detected by the oscilloscope 9 are as shown in FIGS.
In the graph of FIG. 4, the horizontal axis indicates the center wavelength of the bandpass filter 4, and the vertical axis indicates the voltage detected by the oscilloscope 9 at that time. In addition, the vertical axis | shaft of this graph is a logarithmic scale.

In this graph, the voltage value of the discharge signal is indicated by a white circle ◯, and the voltage value of the noise signal which is the base portion is indicated by a black circle ●. The value of the white circle ◯ is an average value of the detected three peak voltage values.
FIG. 5 is a table showing voltage values of the discharge signal and noise signal when each bandpass filter 4 of Experiment 1 is used. In this table, S is the discharge signal, N is the noise signal, and the ratio S / N is shown. It can be said that the larger the S / N value, the greater the difference between the discharge signal and the noise signal, and the easier it is to detect the discharge signal.

It is confirmed that the voltage value detected by the oscilloscope 9 is at the same level as the base voltage with the supply of the PP particles stopped.
Also, in an experiment different from the experiment 1, a peak voltage is output from the electrostatic discharge detection device of the first embodiment at the timing when a high-sensitivity camera is attached to the silo 10, the discharge is photographed, and the discharge is confirmed. I have also confirmed that. In the experiment using this camera, the surroundings of the camera and the viewing window 10e of the silo 10 were covered with a dark screen so that external light did not enter the silo 10.
When the noise light is cut off using the dark curtain in this way, the voltage based on the noise light is not detected in a state where no discharge light is generated.

On the other hand, when the discharge light is generated without blocking the noise light as in Experiment 1, the optical sensor 2 detects both the discharge light and the noise light. That is, the discharge signal indicated by white circles in FIG. 4 is an output signal based on both the discharge light and the noise light, and the peak voltage is detected by the oscilloscope 9 when the signal based on the discharge light is included.
Therefore, if the above discharge signal and noise signal can be distinguished, the occurrence of discharge can be detected.
In other words, in the graph of FIG. 4, there is a difference between the discharge signal indicated by the white circle ◯ and the noise signal indicated by the black circle ●, and in the wavelength region where the S / N value in FIG. This means that a discharge can be detected by a signal.

From the results of Experiment 1 shown in FIGS. 4 and 5, it can be seen that the bandpass filter 4 having a wavelength of 270 [nm] to 400 [nm] has a larger discharge signal than the noise signal, and can distinguish these signals. It was. That is, the filter of 270 [nm] to 400 [nm] is appropriate as the band-pass filter 4 of the electrostatic discharge detection device of the first embodiment.
In the graph of FIG. 4, the difference between the discharge signal and the noise signal appears to be small at 400 [nm]. However, since this graph is a semilogarithmic graph, the difference between the two signals is sufficient, and the peak voltage is actually detected by the oscilloscope 9. it can. The ratio S / N when the band pass filter 4 of 400 [nm] was used was 3.2 (see FIG. 5).

On the other hand, in the case of 240 [nm], 450 [nm], 500 [nm] and 600 [nm] bandpass filters, the discharge signal was buried in the noise signal and could not be distinguished. The reason why a clear discharge signal could not be obtained in this way is considered that the discharge light hardly contains light in these wavelength regions.
In consideration of the full width at half maximum of the bandpass filter 4 of 400 [nm], it is appropriate that the upper limit of the pass region of the filter that can detect discharge efficiently is 410 [nm] or less.

FIG. 6 is a graph showing the results of Experiment 2 in which the laboratory fluorescent lamp was turned off and the other conditions were the same as in Experiment 1 above. In FIG. 6, black triangles ▲ are noise signals, and white triangles △ are discharge signals.
In Experiment 2, since the fluorescent lamp in the laboratory was turned off, the noise light was only sunlight. Therefore, compared with the result of FIG. 4, the noise signal is particularly small at 350 [nm] or more.

In Experiment 2, since the noise light was small as described above, the discharge signal and the noise signal could be distinguished even when the band filter 4 of 450 [nm] was used as shown in FIG. In other words, it was found that the light passing area of the filter that enables discharge detection is somewhat different depending on the presence or absence of a fluorescent lamp in a laboratory where sunlight enters.
It has been found that it is appropriate to set the upper limit of the pass region of the filter to 410 [nm] or less in order to always perform stable and accurate discharge detection regardless of the presence or absence of a fluorescent lamp in the laboratory.

Also, from the above experimental results shown in FIGS. 4 to 6, in order to realize more stable discharge detection, the bandpass filter 4 has a wavelength 300 [nm] at which the S / N value shown in FIG. ] To 360 [nm] are preferably used, and it can be seen that the band-pass filter 4 of 330 [nm] is particularly optimal. The full width at half maximum of the 330 [nm] band-pass filter is 315 [nm] to 345 [nm]. That is, the most stable and accurate discharge detection can be performed by using a filter having a pass region in the vicinity of 315 [nm] to 345 [nm].
Furthermore, from the results of the above experiments 1 and 2, it was found that the lower limit value of the pass region of the filter is preferably 250 [nm] or more.

As described above, if the electrostatic discharge detection device of this embodiment provided with a filter having an appropriate pass wavelength region, noise light such as sunlight or fluorescent light can be used without the cost of using a high-sensitivity camera. Even under, electrostatic discharge can be detected accurately.
In the experiments 1 and 2, the detection signal of the optical sensor 2 is measured by the oscilloscope 9, but the electrostatic discharge detection device used in the field is not expensive but is not so accurate in place of the expensive oscilloscope 9. A data logger may be used.

FIG. 6 is a cross-sectional view of a second embodiment in which compressed gas is supplied into the case 1 so that the inside can be kept at a higher pressure than the outside.
This electrostatic discharge detection device is different in the structure of the case 1, but the other configuration is the same as that of the first embodiment. Therefore, the same reference numerals are used for the same components as those in the first embodiment, and descriptions of the individual components are omitted. And it demonstrates centering on a different part from 1st Embodiment.

In the case 1 of the second embodiment, a compressed gas supply pipe 20 is connected to the cap 1b so that compressed gas is supplied into the case 1 from a supply source (not shown).
A plurality of gas passages 21 are formed within the thickness of the side wall of the case body 1a. The gas passage 21 communicates from the inlet 21a in the case main body 1a to the jet outlet 21b outside the case main body 1a. And this jet nozzle 21b faces the said light introduction window 1c, and the compressed gas supplied in case 1 spouts along the surface of the transparent cover 3 which is the outer surface of the light introduction window 1c from the said jet nozzle 21b. Like to do. By ejecting the gas from the ejection port 21b, it is possible to prevent foreign matters such as PP particles and powder from adhering to the surface of the transparent cover 3, and foreign matters stagnating on the front surface of the transparent cover 3 can be prevented. Can be blown away.

If foreign matter or the like adheres to the surface of the transparent cover 3 or is stagnant, the intensity of light reaching the optical sensor 2 becomes weak, so that the output signal from the optical sensor 2 becomes small and discharge occurs. It becomes difficult to detect. However, if the case 1 as in the second embodiment is used, the foreign matter on the surface can be blown away with the compressed gas, so the discharge detection accuracy does not drop.
Moreover, in this 2nd Embodiment, since the compressed gas is supplied in the case 1, the inside of the case 1 is a pressure higher than the exterior. Therefore, it is possible to prevent foreign matter from entering the case 1 through the minute gap. Intrusion of foreign matter also lowers the detection accuracy of the optical sensor 2, but can be prevented.

In addition, if the inside of the case 1 can be maintained at a higher pressure than the outside, it is possible to prevent the entry of foreign matter from the outside. Therefore, in order to achieve the purpose of preventing the entry of foreign matter, compressed gas is supplied into the case 1. You don't have to keep doing it. However, if the compressed gas for blowing off the foreign matter on the surface of the transparent cover 3 is continuously supplied as in the second embodiment, more accurate discharge detection can be performed.
Further, if the pressure inside the case 1 is detected and the power supply to the optical sensor 2 is stopped when the difference from the external pressure becomes a predetermined pressure difference or less, the explosion-proof electrostatic discharge It can also be used as a detection device.

In the first and second embodiments, the transparent cover 3 made of quartz glass is provided in the light introduction window 1c of the case 1, but the material of the transparent cover 3 is not limited to quartz glass if the light transmittance is high. . For example, other glass or acrylic resin can be used.
Further, although the transparent cover 3 exhibits the function of protecting the bandpass filter 4, it may be omitted and the bandpass filter 4 may be directly exposed outside the case 1.

  In addition, although the example of detecting electrostatic discharge of PP particles in the silo 10 has been described above, it is natural that the electrostatic discharge detection devices of the first and second embodiments can detect electrostatic discharge other than PP particles. If discharge light is generated regardless of the material or form, it can be detected by the electrostatic discharge detection device of the above embodiment. Moreover, the electrostatic discharge detection apparatus of the said embodiment can detect similarly to the above also about discharge outside silos 10, such as a laboratory.

In the first and second embodiments, the example in which one static electricity detection device is installed in the silo 10 has been described. However, a plurality of static electricity detection devices are installed in the monitoring target area such as the silo to provide static electricity. A discharge detection system can also be configured.
If multiple electrostatic discharge detection devices are installed and operated at the same time, it may be difficult to detect the discharge because one electrostatic discharge detection device is separated from the discharge location or light is blocked by dust. Even in this case, the discharge can be detected by another electrostatic discharge detection device. Therefore, a wider range can be monitored, and electrostatic discharge in the monitored area can be reliably detected.

Furthermore, it is also possible to specify the position where electrostatic discharge occurs based on the presence or absence of an output signal from each electrostatic discharge detection device installed at a different position and the signal intensity. Thus, if the position where electrostatic discharge is generated can be specified, the position where discharge is likely to occur can be specified. For example, when it is found that electrostatic discharge is likely to occur in a specific part in the silo 10, the electrostatic discharge is generated by changing the shape or material of the part or changing the powder transport conditions. You can also take measures to make it harder to do.
And if it is the electrostatic discharge detection apparatus of the said embodiment which does not use an expensive high-precision camera, since the price of 1 unit | set can be suppressed, it is also realistic to install several units | sets simultaneously.

  It can be used for discharge detection at various sites that handle charged objects such as powder transportation sites.

DESCRIPTION OF SYMBOLS 1 Case 1a Main body 1b Cap 1c Light introduction window 2 Optical sensor 3 Transparent cover 4 Band pass filter 20 Compressed gas supply pipe 21 Gas passage 21a Inlet 21b Spout

Claims (7)

An electrostatic discharge detection device for detecting electrostatic discharge generated from a charged object,
An optical sensor that outputs an electrical signal in accordance with the input light;
A filter that restricts the wavelength region of the light taken into the optical sensor;
The said filter is an electrostatic discharge detection apparatus which sets the upper limit of a passage wavelength area to 410 [nm] or less.   The electrostatic discharge detection device according to claim 1, wherein the optical sensor detects discharge light and noise light due to the electrostatic discharge in the atmosphere.   The electrostatic discharge detection device according to claim 1 or 2, wherein a lower limit value of a passing wavelength region of the filter is 250 [nm] or more. While incorporating the light sensor and the filter in a case provided with a light introduction window in the process of guiding the light to the light sensor,
The electrostatic discharge detection device according to claim 1, wherein the pressure inside the case is maintained higher than the pressure outside the case.   The electrostatic discharge detection device according to claim 4, wherein a gas is supplied into the case, and the case is provided with a jet outlet that jets the gas supplied into the case along an outer surface of the light introduction window.   6. The electrostatic discharge detection device according to claim 4, wherein the case is made of metal and the case is grounded.   An electrostatic discharge detection system provided with a plurality of electrostatic discharge detection devices according to any one of claims 1 to 6 for an area to be monitored.

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