JP2006145441A - Thunder-approach detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thunder-approach detector capable of reducing detection omission and erroneous detection, and capable of finding a distance up to a thunder. <P>SOLUTION: This thunder-approach detector is provided with an antenna 11 for receiving a thunder electric wave emitted from the thunder, a tank circuit 12 for holding the thunder electric wave of a prescribed frequency band received by the antenna, a rectifying circuit 13 for rectifying the thunder electric wave held in the tank circuit, an integration circuit 14 for integrating the rectified thunder electric wave, and an approach determination circuit 15 for outputting an approach signal when the integrated thunder electric waves of specified intensity or more are detected at a fixed frequency or more per a prescribed time. The thunder-approach detector is able to reduce the erroneous detection of the thunder by the tank circuit and the integration circuit. The thunder-approach detector may be provided further with an electrostatic filed intensity measuring circuit for finding an electrostatic filed intensity variation, and a distance calculation circuit for calculating the distance of the thunder, based on the electrostatic filed intensity variation when determined as the approach of the thunder and a ratio of the thunder electric wave intensities held in the tank circuit. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lightning approach detection device capable of detecting the approach of lightning. More specifically, the present invention relates to a lightning approach detection device that can detect the distance to lightning with few detection omissions and false detections. This lightning approach detection device is a computer used for temperature management of agricultural greenhouses, computers used in offices and general households, wireless relay stations such as mobile phones, broadcasting facilities and communication facilities, NC machine tool control devices In addition, it can be used for a protection device for disconnecting external devices such as various electric devices of consumers from the electric circuit or switching to a lightning surge protection circuit. Further, it can be used for alarm devices using light, sound, etc. used in outdoor facilities such as athletic fields, campgrounds, and golf courses.

There is a demand for a means for detecting that a lightning is approaching in order to turn off the power of an electronic device such as a computer or close a window in preparation for a failure caused by a thunderstorm or lightning.
As a means for detecting the approach of lightning, there is known a method for detecting a change in lightning radio wave or electric field intensity generated with lightning (see Patent Documents 1 and 2).

JP 60-42680 A (2nd page) JP 2003-28968 A (page 4)

However, since detection of lightning of different conditions such as lightning that is small and frequently generated, and lightning that is large but rarely occurs is not taken into consideration, there is a possibility of detection omission and false detection.
The present invention solves such problems, and an object thereof is to provide a lightning approach detection device that can detect the distance to lightning with few detection omissions and false detections.

The present invention is as follows.
1. An antenna for receiving a lightning radio wave generated by lightning, a tank circuit for holding a lightning radio wave of a predetermined frequency band received by the antenna, a rectifying circuit for rectifying the lightning electromagnetic wave held in the tank circuit, and the rectified An integration circuit that integrates lightning radio waves, and an approach determination circuit that outputs an approach signal when the integrated lightning radio waves with an intensity greater than a specified level are detected more than a predetermined number of times per predetermined time. Thunder approach detector.
2. The predetermined frequency band is 10 to 200 kHz. The described lightning approach detection device.
3. The approach determination circuit includes two or more determination circuits that detect lightning approach under different conditions of the intensity and the number of times, and an approach output circuit that outputs an approach signal when at least one of the determination circuits detects a lightning approach The above 1. comprising. Or 2. The described lightning approach detection device.
4). Electrostatic field strength measurement circuit that determines the amount of change in electrostatic field strength, and distance calculation that calculates the distance of lightning from the ratio of the amount of change in electrostatic field strength when it is determined that lightning is approaching and the intensity of the lightning radio wave held in the tank circuit. The above-described 1. further comprising a circuit. To 3. The lightning approach detection apparatus in any one of.
5. 3. A lightning protection circuit comprising a lightning protection switch that opens a power line of an external device when the lightning distance is shorter than a predetermined value. The described lightning approach detection device.
6). A timer circuit that outputs a lightning protection signal after a predetermined time from the reception of the approach signal; and a lightning protection circuit that includes a lightning protection switch that opens a power line of an external device when the lightning protection signal is received. 1. To 5. The lightning approach detection apparatus in any one of.
7). 3. A lightning protection circuit for further inserting a lightning protection transformer into a power line of an external device when the distance of the lightning becomes shorter than a predetermined value. The described lightning approach detection device.
8). A timer circuit for outputting a lightning protection signal after a predetermined time from the reception of the approach signal; and a lightning protection circuit for inserting a lightning protection transformer into a power line of an external device when the lightning protection signal is received. 2. 3. 4. And 7. The lightning approach detection apparatus in any one of.

According to the lightning approach detection device of the present invention, the approach of lightning can be easily detected by detecting lightning radio waves. Further, since the frequency band of lightning radio waves detected by the tank circuit is limited and noise countermeasures are taken by the integration circuit, lightning detection errors can be reduced.
Furthermore, when the frequency band to be detected is 10 to 200 kHz, lightning can be easily detected. Moreover, when the approach determination circuit includes a plurality of determination circuits and an approach output circuit, lightning under various conditions can be detected, and detection omissions and erroneous detections can be prevented.
When equipped with a distance calculation circuit that calculates the distance of lightning from the ratio of the change in electrostatic field intensity and the lightning radio wave intensity, the distance of lightning can be obtained, and detailed lightning can be detected by an external device connected to the lightning proximity detector. Information can be provided.
When a lightning protection circuit that performs control according to the distance of lightning is provided, a lightning protection state can be achieved when lightning approaches, and erroneous detection of the approaching state can be reduced. In addition, when the timer circuit and the lightning protection circuit are provided, the external device can be protected after the external device prepares for lightning protection.
When equipped with a lightning protection circuit using a lightning protection switch, the external device is disconnected from the power line before a lightning strike, preventing lightning surges from reaching the external device via the power line even if there is a lightning strike. can do.
When equipped with a lightning protection circuit that inserts a lightning-proof transformer, the lightning-proof transformer is disconnected from the power line during normal times, and the lightning-proof transformer is inserted into the power line before a lightning strike. be able to.

Hereinafter, an embodiment of a lightning approach detection device according to the present invention will be described with reference to FIGS.
The “frequency band” is preferably a band in which it is easy to distinguish radio waves caused by lightning and other noises. Although this frequency band can be selected in various ways, it is preferably 10 to 200 kHz (more preferably 12 to 100 kHz, particularly 15 to 50 kHz). The frequency in such a range is (1) The electric field intensity of the lightning radio wave emitted by lightning is 10 to 100 kHz because the electric field intensity is higher than other frequencies, so the SN ratio can be increased. (2) Received by the antenna Lightning radio waves are integrated in the tank circuit, but the Q of this tank circuit can be higher at higher frequencies. (3) Noise generated from electronic equipment such as radio and television, automobiles, etc. is about 200 kHz. This is because there are many.

The “tank circuit” is a resonance circuit using a capacitor and a coil, and is used to selectively output to the rectifier circuit a frequency band used for detection out of lightning radio waves detected by the lightning proximity detection device.
The Q of the tank circuit is preferably 0.5 ≦ Q ≦ 100 (particularly preferably 10 ≦ Q ≦ 90). This is because if it is 0.5 or less, it will not vibrate, and if it is 100 or more, it will be difficult to distinguish lightning that occurs continuously.
The “rectifier circuit” is a circuit that rectifies lightning radio waves for an integrating circuit in the subsequent stage.
As shown in FIG. 2, the “integration circuit” is a circuit for shaping a lightning radio wave so that it can be easily detected by an approach determination circuit at a later stage and preventing erroneous detection due to steep pulse noise other than the lightning radio wave. . Further, in this integrating circuit, the number of lightning radio wave cycles necessary for the integrated lightning radio wave signal to be a potential that can be detected by the approach determination circuit in the subsequent stage is 2 to 20 (preferably 2 to 10). It is preferable to do so. This is because when the number of cycles is 1, steep pulse noise may be erroneously detected. Further, if the number of cycles exceeds 20, the lightning radio wave held in the tank circuit is attenuated and cannot be detected.

The “approach determination circuit” is a circuit that determines whether or not lightning is approaching by determining whether or not the lightning radio wave shaped by the integrating circuit satisfies the approach condition. As this “approach condition”, the intensity of lightning radio waves, the number of times of lightning radio wave detection per predetermined time, or the like can be used. Among these, it is preferable that a lightning radio wave with a certain intensity or more is detected a certain number of times or more per predetermined time.
The “strength” can be arbitrarily selected, but usually the air field intensity is 3 to 15 kV / m (preferably 3.5 to 14 kV / m, particularly preferably 4 to 13 kV / m) and / or above. The voltage output from the integrating circuit can be set to an intensity at which lightning radio waves of 0.5 to 20 V (preferably 1 to 15 V, particularly preferably 2 to 10 V) can be detected. In addition, the “predetermined time” can be arbitrarily selected, and can be an arbitrary time of usually 2 to 30 minutes (preferably 3 to 20 minutes, particularly preferably 5 to 20 minutes). Furthermore, the above “fixed number of times” can also be arbitrarily selected, and can usually be 1 to 50 times (preferably 1 to 30 times, particularly preferably 1 to 20 times).

Further, the approach determination circuit may include two or more determination circuits that are different approach conditions and an approach output circuit that determines whether or not to output an approach signal based on the determination results. . By determining whether to output an approach signal based on a plurality of approach conditions, it is possible to detect various lightnings with different lightning wave waveforms.
As an example of this, the number of times that the signal voltage output from the integration circuit exceeds a low level value (for example, the air field intensity is 3 to 7 kV / m or more and / or the output of the integration circuit is 0.5 to 5 V or more). The first determination circuit that determines the approach of lightning when there are two or more times in 10 minutes, and the signal voltage output from the integration circuit is a high level value (for example, the air field intensity is 7 to 15 kV / m or more and / or the above When the number of times that the output of the integration circuit exceeds 5 to 20 V or more is one or more times in 10 minutes, and when at least one of the determination circuits detects the approach of lightning An approach determination circuit including an approach output circuit that outputs an approach signal can be provided.
Such an approach determination circuit can detect lightning that is small and frequently generated by the first determination circuit, and can detect lightning that is large but rarely generated by the second determination circuit. Lightning that cannot be detected by the circuit can be detected by the other determination circuit, and detection omission can be reduced.
Note that the number of determination circuits and the signal voltage and number of times of each determination circuit can be arbitrarily selected within the range of the air field intensity and a fixed number of times.

The “approach signal” is a signal indicating that the lightning approach detection device has detected the approach of lightning. The approach signal may be output to a timer circuit, a distance calculation circuit, or the like, or can be transmitted to any external device.
Moreover, the output method of an approach signal can be selected arbitrarily, and an optical fiber, a radio | wireless, etc. can be used other than a wire. In particular, the use of an optical fiber is preferable because insulation between devices can be performed, and a lightning surge caused by a lightning strike is not transmitted.

The “timer circuit” is a circuit that outputs a lightning protection signal after a predetermined time from the time when the approach signal is received from the approach determination circuit. The certain time can be arbitrarily selected. For example, the time required for protection after lightning detection can be obtained and used in advance.
As shown in FIG. 3, the “lightning protection circuit” includes a lightning protection switch 24 that switches between a normal state in which the power supply line 33 of the external device is connected to the power supply 32, or a lightning protection state in which the power supply line 33 is disconnected from the power supply. It is a circuit provided. According to such a lightning protection circuit, the external device is disconnected from the power line before the lightning strike, so that it is possible to prevent a lightning surge from reaching the external device via the power line even if there is a lightning strike. it can. Such a lightning-resistant switch is preferably one that can interrupt a lightning surge in a lightning-resistant state. Further, the lightning protection switch 24 is switched by the operation control means 26.
Furthermore, as illustrated in FIG. 7, the lightning protection circuit includes a lightning protection transformer 21, a bypass line 22, a normal state in which the bypass line 22 is inserted into a power supply line 33 of a power supply 32 of an external device, or the lightning protection transformer 21. Can be a circuit comprising state changeover switches 231 and 232 for switching lightning protection states inserted into the power line 33. According to such a lightning protection circuit, the lightning protection transformer is disconnected from the power line during normal operation, and the lightning protection transformer is inserted into the power supply line before a lightning strike, so power loss due to the lightning protection transformer during normal operation can be eliminated. . The state changeover switches 231 and 232 are changed over by the operation control means 26.
The operation control means is means for receiving the lightning protection signal and switching the lightning protection switch 24 or the state changeover switches 231 and 232. The received lightning protection signal can be received from at least one of the timer circuit 16 and the distance calculation circuit 19. Furthermore, each switch may be switched by receiving a lightning protection signal output from an external device.

The “electrostatic field strength measuring circuit” is a circuit that measures the amount of change in electrostatic field strength caused by lightning. This circuit is not particularly limited as long as it is an electrostatic field strength measuring circuit.
The “distance calculation circuit” is a circuit that calculates the distance of lightning from the ratio of the change in electrostatic field intensity and the lightning intensity.
As illustrated in FIG. 5, the electrostatic field strength changes with the occurrence of lightning. A graph of Δs / E, which is a ratio of the electrostatic field intensity change amount Δs (usually 10 to 100 kV / m) and the intensity E of the lightning electric wave held in the tank circuit, and the lightning generation distance Then, as illustrated in FIG. 6, a substantially constant curve is obtained at a certain distance or more.
For example, when the location of lightning is 3 km away from the detection position and the magnitude of the main discharge current of lightning is 20 kAh, the output voltage of the tank circuit, which is the intensity E of the lightning radio wave, is 2 V, and the amount of change in electrostatic field strength Δs is 5 kV / m, and Δs / E is 2.5. When the main discharge current of lightning of the same distance is 40 kAh, the output voltage of the tank circuit, which is the intensity E of the lightning radio wave, is 2.5 V, and the electrostatic field strength change Δs is 5.4 kV / m. , Δs / E is 2.16, and it can be seen that the value is substantially the same as that when the magnitude of the main discharge current is 20 kAh. Thus, Δs / E becomes a substantially constant straight line at a certain distance or more (3 km or more in FIG. 6) regardless of the magnitude of the main discharge. For this reason, it can be found that the lightning generation distance is obtained from the ratio Δs / E.
The lightning detection distance can be arbitrarily selected, but is preferably within a radius of 6 km (more preferably within 4 km, particularly preferably within 2 km) from the antenna of the lightning proximity detector. This is because if the distance that can be detected is too close, lightning may occur before making preparations for lightning protection.

The lightning approach detection device according to the first embodiment is a lightning protection device that detects the approach of lightning from a distance of a radius of about 2 km and notifies an external device, and turns off the power supply of the external device after a certain time.
As shown in FIG. 1, the lightning approach detection device includes an antenna 11, a tank circuit 12, a rectifier circuit 13, an integration circuit 14, an approach determination circuit 15, a timer circuit 16, and a lightning protection circuit 2. Further, the lightning approach detection device 1 is used by being connected to an external device 3. The type of the external device 3 is not particularly limited, and examples thereof include industrial and agricultural computers, power distribution facilities, wireless communication devices, and the like. These external devices 3 can input the approach signal output from the approach determination circuit 15 and can perform any operation for lightning protection when the approach signal is input.

The tank circuit 12 is an LC resonance circuit having a resonance frequency of about 20 kHz. Q is 25.
The integration circuit 14 integrates with a constant exceeding the detection level value of the first determination circuit 151 by a 20 kHz lightning radio wave having a cycle number of 3 (see FIG. 2).
The approach determination circuit 15 includes a first determination circuit 151, a second determination circuit 152, and an approach determination circuit 153. The first determination circuit 151 determines the approach of lightning when the number of times that the signal voltage output from the integration circuit 14 exceeds the low level value (the air field intensity is 4 kV / m or more) is twice or more in 10 minutes. , Notify the approach determination circuit 153. The second determination circuit 152 determines the approach of lightning when the number of times that the signal voltage output from the integration circuit 14 exceeds the high level value (the air field intensity is 8 kV / m or more) is once or more in 10 minutes. , Notify the approach determination circuit 153.

The timer circuit 16 outputs an instruction signal for setting a lightning protection state to the lightning protection circuit 2 when an arbitrarily set number of seconds from 0 to 60 seconds elapses after the approach signal output from the approach determination circuit 15 is input. To do. In addition, when 900 seconds have passed since the last approach signal, an instruction signal for making the lightning protection circuit 2 in a normal state is output.
As shown in FIG. 3, the lightning protection circuit 2 includes a lightning protection switch 24 that switches between a normal state in which the power supply line 33 of the external device is connected to the power supply 32, or a lightning protection state in which the power supply line 33 is disconnected from the power supply 32. The circuit includes an operation control means 26 for controlling 24 switching operations. The lightning protection switch 24 is a mechanical contact switch that is operated by the operation control means 26 and switches the connection state between the power supply line 33 and the power supply 32.
The operation control means 26 switches the lightning protection switch 24 according to the lightning protection signal output from the timer circuit 16. The operation control means 26 may be manually switched by providing a manual switch, or may be switched by receiving a lightning protection signal from the external device 3.

In such a lightning approach detection device, when a lightning radio wave reaches the antenna 11, it is held by the tank circuit 12, rectified by the rectifier circuit 13, and then integrated by the integration circuit. The integrated lightning radio wave is determined by the first determination circuit 151 and the second determination circuit 152 of the approach determination circuit 15, and when the determination condition of one of the determination circuits 151 and 152 is satisfied, the approach determination circuit 153. To the external device 3 and the timer circuit 16.
After receiving the approach signal, the timer circuit 16 outputs a lightning protection signal to the lightning protection circuit 2 so that the power line 33 is disconnected after a lapse of a certain time so that the external device 3 can be protected from the lightning surge. The external device 3 can receive the approach signal and perform arbitrary processing.

Since this thunder approach detection device limits the frequency band of the lightning radio wave detected by the tank circuit and takes noise countermeasures by the integration circuit, it can reduce false detection of lightning.
Furthermore, the detection of lightning can be facilitated by setting the frequency band to be detected to 10 to 200 kHz. In addition, since the approach determination circuit includes a plurality of determination circuits and an approach output circuit, lightning under various conditions can be detected, and detection omission and erroneous detection can be prevented.
In addition, by providing the timer circuit and the lightning protection circuit, it is possible to protect the device from lightning surge by cutting off the power supply after waiting for termination processing of the external device.

The lightning approach detection device according to the second embodiment notifies the external device of the approach of lightning and its distance, and after a certain time and / or when the lightning distance is within a certain range, the lightning transformer is connected to the power supply of the external device. A lightning protection device to be inserted into the wire.
As shown in FIG. 4, the lightning approach detection device includes an antenna 11, a tank circuit 12, a rectifier circuit 13, an integration circuit 14, an approach determination circuit 15, a timer circuit 16, an electrostatic field antenna 17, an electrostatic field strength measurement circuit 18, A distance calculation circuit 19 and a lightning protection circuit 2 ′ are provided. Further, the lightning approach detection device 1 is used by being connected to an external device 3.
Since the antenna 11, the tank circuit 12, the rectifier circuit 13, the integration circuit 14, the approach determination circuit 15, and the timer circuit 16 are the same as those in the first embodiment, description thereof is omitted.

The electrostatic field strength measurement circuit 18 is a circuit that measures the electrostatic field strength using the electrostatic field antenna 17.
The distance calculation circuit 19 acquires the intensity of the lightning radio wave from the tank circuit 12, obtains the ratio between the lightning radio wave intensity and the electrostatic field intensity obtained from the electrostatic field intensity measurement circuit 18, and uses the distance calculation curve shown in FIG. , A circuit for obtaining a distance corresponding to the ratio. Further, the obtained distance is output to the external device 3. Furthermore, when the distance is within 2 km, a lightning protection signal is output to the lightning protection circuit 2.
As shown in FIG. 3, the lightning protection circuit 2 ′ includes a lightning protection transformer 21, a bypass line 22, a normal state where the bypass line 22 is inserted into a power supply line 33 of an external device, or the lightning protection transformer 21 is connected to the power supply. The circuit includes state changeover switches 231 and 232 for switching the lightning protection state inserted in the line 33 and operation control means 26 for controlling the changeover operation of the state changeover switches 231 and 232.
The lightning resistant transformer 21 is a transformer that insulates between the primary and secondary sides of the transformer and can absorb lightning surges and the like.
The bypass line 22 is a wiring connected to the power supply line 33 in a normal state where the lightning proof transformer is not inserted into the power supply line 33.
The state changeover switches 231 and 232 are mechanical contact switches that are operated by the operation control means 26 and switch the lightning resistant transformer 21 or the bypass line 22 to connect to the power supply line 33. The state changeover switch 231 includes two sets of a state changeover switch 231 on the power supply side and a state changeover switch 232 on the external device side.
The operation control means 26 switches the state changeover switches 231 and 232 in accordance with the lightning protection signal output from the timer circuit 16. The operation control means 26 can also switch the state changeover switches 231 and 232 according to the lightning protection signal output from the distance calculation circuit 19. Moreover, a manual switch may be provided and switched manually, or a lightning protection signal from the external device 3 may be switched upon reception.
When a lightning protection signal is received from at least one of the timer circuit 16 and the distance calculation circuit 19, the state changeover switches 231 and 232 are operated to switch the lightning protection transformer 21 or the bypass line 22 to the power line 33.

In addition to the effect of the lightning approach detection device of the first embodiment, the lightning approach detection device of the second embodiment includes a distance calculation circuit 19 that calculates the distance of lightning from the ratio of the change in electrostatic field intensity and the lightning radio wave intensity. The distance of lightning can be obtained, and finer lightning information can be provided to the external device 3 connected to the lightning proximity detection device.
Furthermore, since the lightning protection circuit 2 'that controls according to the distance of lightning is provided, it is possible to disconnect the lightning protection transformer from the power line during normal operation and to insert the lightning protection transformer into the power supply line before lightning strike. It is possible to eliminate the power loss due to the lightning-resistant transformer.

In the present invention, the present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention depending on the purpose and application. That is, the first and second embodiments include the lightning protection circuits 2 and 2 ′, but may not be provided. Further, the lightning protection circuit 2 ′ using the lightning protection transformer of the second embodiment may be provided in the first embodiment, or the lightning protection circuit 2 using the lightning protection switch of the first embodiment may be provided in the second embodiment. Furthermore, the number of determination circuits may be only one, or three or more.
In addition, a lightning protection signal can be output from the external device 3 to the lightning protection circuit 2. When the lightning protection preparation of the external device 3 is completed before the lightning protection signal is output from the timer circuit 16, the lightning surge can be supported by inserting the lightning transformer directly from the external device 3 into the lightning protection circuit 2. Thus, the external device 3 can be protected.

It is a block diagram for demonstrating the lightning approach detection apparatus of Example 1. FIG. (1) It is a graph for demonstrating the waveform of the lightning electromagnetic wave output from a tank circuit, and (2) the waveform of the lightning electromagnetic wave output from an integration circuit. It is a circuit diagram for demonstrating the structure of the lightning protection circuit of Example 1. FIG. It is a block diagram for demonstrating the lightning approach detection apparatus of Example 2. FIG. It is a graph for demonstrating the change of an electrostatic field when the distance from a lightning is about 2 km. It is a graph for demonstrating the relationship between k * (DELTA) s / E and distance. It is a circuit diagram for demonstrating the structure of the lightning protection circuit of Example 2. FIG.

Explanation of symbols

11; Antenna, 12; Tank circuit, 13; Rectifier circuit, 14; Integration circuit, 15; Access determination circuit, 151; First determination circuit, 152; Second determination circuit, 153; Access determination circuit, 16; 17; Electrostatic field antenna; 18; Electrostatic field strength measurement circuit; 19; Distance calculation circuit;
2, 2 '; lightning protection circuit, 21; lightning protection transformer, 22; bypass line, 231 and 232; state changeover switch, 24; lightning protection switch, 26; operation control means, 3; external device, 32; .

Claims (8)

An antenna that receives thunder-generated lightning,
A tank circuit that holds lightning radio waves of a predetermined frequency band received by the antenna;
A rectifier circuit for rectifying lightning radio waves held in the tank circuit;
An integrating circuit for integrating the rectified lightning radio wave;
A lightning approach detection device, comprising: an approach determination circuit that outputs an approach signal when the integrated lightning radio wave having an intensity higher than a specified value is detected a predetermined number of times or more per predetermined time.   The lightning approach detection device according to claim 1, wherein the predetermined frequency band is 10 to 200 kHz.   The approach determination circuit includes two or more determination circuits that detect lightning approach under different conditions of the intensity and the number of times, and an approach output circuit that outputs an approach signal when at least one of the determination circuits detects a lightning approach The thunder approach detection device according to claim 1 or 2, further comprising:   Electrostatic field strength measurement circuit that determines the amount of change in electrostatic field strength, and distance calculation that calculates the distance of lightning from the ratio of the amount of change in electrostatic field strength when it is determined that lightning is approaching and the intensity of the lightning radio wave held in the tank circuit. The lightning approach detection device according to any one of claims 1 to 3, further comprising a circuit.   The lightning approach detection device according to claim 4, further comprising: a lightning protection circuit including a lightning protection switch that opens a power line of an external device when the lightning distance is shorter than a predetermined value.   A timer circuit that outputs a lightning protection signal after a predetermined time from the reception of the approach signal, and a lightning protection circuit that includes a lightning protection switch that opens a power line of an external device when the lightning protection signal is received. Item 6. The lightning approach detection device according to any one of Items 1 to 5.   The lightning approach detection device according to claim 4, further comprising a lightning protection circuit that inserts a lightning protection transformer into a power line of an external device when the lightning distance is shorter than a predetermined value.   A timer circuit that outputs a lightning protection signal after a predetermined time from the reception of the approach signal, and a lightning protection circuit that inserts a lightning protection transformer into a power line of an external device when the lightning protection signal is received. The lightning approach detection device according to any one of 3, 4, and 7.

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