JP2006071348A - Geomagnetic variation sensing device and geomagnetic variation detecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a geomagnetic variation sensing device capable of detecting a change in geomagnetism in three dimensions, without any restriction of the movement of a magnet. <P>SOLUTION: When the geomagnetism does not change, a pointer 11 is arranged at a particular position. If there is a change in the geomagnetism, the magnet 12 receives a force corresponding to the change in the magnetism. When the magnet 12 receives the force corresponding to the change in the magnetism, an upward and downward rotating ring 14 and/or a left and right rotating ring 15 rotates in a direction corresponding to the force. Consequently, if the geomagnetism changes, the magnet 12 moves with the rotation of the upward and downward rotating ring and/or the left and right rotating ring 15, and the quantity of light received by a light-receiving element 18 changes according to the upward and downward rotating ring and/or the left and right rotating ring 15. Accordingly, the output of the light-receiving element 18 changes according to the change in the magnetism. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a geomagnetic variation sensing device and a geomagnetic variation detecting device, and more particularly to a geomagnetic variation sensing device and a geomagnetic variation detecting device using a magnet.

  Conventionally, various earthquake prediction methods have been tried. For example, a method of predicting an earthquake by detecting a turbulence (change) in geomagnetism occurring before a large earthquake with a magnet is known. In addition, the turbulence of geomagnetism that occurs before a large earthquake is caused by the generation of geoelectric currents associated with crustal deformation.

Japanese Patent Application No. 60-34749 (Japanese Utility Model Publication No. 61-152912) discloses a decorative compass that measures the direction of geomagnetism using a magnet. The ornamental compass described in Patent Document 1 includes a support unit that supports a magnet so as to be swingable in all directions, and a direction indicating unit that shows east, west, south, and north in a plan view.
Microfilm of Japanese Utility Model No. 60-34749 (Japanese Utility Model Application No. 61-152912)

  In the decorative compass described in Patent Document 1, the magnet is swingable but not rotatable. For this reason, a restriction | limiting arises in the motion of a magnet.

  Moreover, in the ornamental compass described in Patent Document 1, the direction indicating portion is shown in a plane. For this reason, when a magnet moves to the direction contained in the surface perpendicular | vertical with respect to the surface where the direction instruction | indication part is shown by disturbance of geomagnetism, a direction instruction | indication part cannot show the movement.

  An object of the present invention is to provide a geomagnetic fluctuation sensing device capable of detecting a change in geomagnetism in three dimensions without any restriction on the movement of a magnet.

  In order to achieve the above object, a geomagnetic variation sensing device of the present invention is a geomagnetic variation sensing device that senses a change in geomagnetism, and includes a pointer, a magnet provided with the pointer, and a first magnet to which the magnet is fixed. 1 ring, a second ring that supports the first ring so as to be rotatable about a first rotation axis, and a second ring that is rotatable about a second rotation axis that is orthogonal to the first rotation axis. And a detection unit for detecting movement of the pointer as a change in the geomagnetism.

  According to said invention, a detection part detects the movement of the pointer provided in the magnet. When there is no change in geomagnetism, the pointer points to a specific position. When a change in geomagnetism occurs, the magnet receives a force corresponding to the change in geomagnetism. When the magnet receives a force corresponding to the change in geomagnetism, the first and / or second ring rotates in a direction corresponding to the force. For this reason, when a change in geomagnetism occurs, the magnet moves in a rotatable manner with the rotation of the first and / or second ring. For this reason, the detection unit can detect a change in geomagnetism as a three-dimensional displacement of the pointer.

  In addition, the magnet moves freely with the rotation of the first and / or second ring. For this reason, there is no restriction on the movement of the magnet.

  In addition, the detection unit is preferably an optical sensor.

  According to the above invention, the movement of the pointer, that is, the change in geomagnetism can be detected without contact. For this reason, when detecting the movement of the pointer, unnecessary force is not applied to the magnet and the pointer. Therefore, it is possible to prevent malfunction caused by unnecessary force.

  The light sensor includes a light emitting element and a light receiving element, and the first and second rings have holes through which light emitted from the light emitting element passes when the pointer points to a specific position. The light receiving element is disposed at a position where the light that has passed through the hole after being emitted from the light emitting element when the pointer is pointing to the specific position can be received. It is desirable that the movement of the pointer is detected based on a change in the amount of light received from.

  According to the above invention, the movement of the magnet, that is, the change of the geomagnetism can be detected as the displacement of the first or second ring that moves in accordance with the movement of the magnet.

  Moreover, it is desirable to further include a scale portion including the specific position and a scale indicating the amount of movement from the specific position.

  According to the above invention, the user can recognize the degree of movement of the pointer, that is, the degree of change in geomagnetism, by using the scale portion. In addition, the user can easily set the direction of the pointer to a specific position by using the scale portion.

  Moreover, it is desirable that the optical sensor operates intermittently.

  According to said invention, compared with the case where an optical sensor operates continuously, the electric power which an optical sensor consumes per unit time can be decreased.

  Further, it is preferable to further include an alarm unit that generates an alarm when the detection unit detects movement of the pointer.

  According to the above invention, it is possible to notify the user of a change in geomagnetism by an alarm.

  Moreover, it is desirable that the pointer can be changed in length.

  According to the above invention, it is possible to adjust the balance (center of gravity) of the magnet by adjusting the length of the pointer. For this reason, when there is no change in geomagnetism, it is easy to set the pointer so as to face a specific position.

  Further, the geomagnetic fluctuation detecting device of the present invention is an alarm that generates an alarm only when each of the plurality of geomagnetic fluctuation sensing devices and the detection unit included in the plurality of geomagnetic fluctuation sensing devices detect movement of the pointer. Generating part.

  According to the above invention, any one of the plurality of detection units detects, for example, the movement of the pointer due to iron or a magnetic body existing around the magnet, or the movement of the pointer due to vibration. However, it is possible to prevent an alarm from being generated based on the detection. Therefore, malfunction can be prevented.

  According to the present invention, it is possible to easily detect a change in geomagnetism due to generation of a ground current accompanying a crustal movement with a magnet. The reason is as follows.

  When there is no change in geomagnetism, the pointer points to a specific position. When a change in geomagnetism occurs, the magnet receives a force corresponding to the change in geomagnetism. When the magnet receives a force corresponding to a change in geomagnetism, the first and / or second ring rotates in a direction corresponding to the force. For this reason, when a change in geomagnetism occurs, the magnet moves as the first and / or second ring rotates. For this reason, the detection unit can detect a change in geomagnetism as a displacement of the pointer. In addition, the magnet moves freely with the rotation of the first and / or second ring. For this reason, there is no restriction on the movement of the magnet.

  In addition, in order to detect changes in geomagnetism relatively, for example, even if the pointer does not accurately point to magnetic north in a reinforced-structured building such as an apartment, the direction of the pointer at that location should be a specific position. It becomes possible to capture changes in geomagnetism.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a partial cross-sectional view showing a geomagnetic fluctuation sensing device according to an embodiment of the present invention. FIG. 2 is a plan view in the direction of arrow A in FIG. FIG. 3 is a plan view in the direction of arrow B in FIG. In FIG. 3, the pointer 11, the magnet 12, the magnet support bar 13, the up / down rotating ring 14, and the left / right rotating ring 15 are omitted. FIG. 4 is a block diagram of the geomagnetic fluctuation sensing device 1.

  The geomagnetic fluctuation sensing device 1 includes a pointer 11, a magnet 12, a magnet support rod 13, a vertical rotation ring 14, a horizontal rotation ring 15, a magnet support frame 16, a light emitting element 17, a light receiving element 18, and an LED 19. And a cover 20, a scale portion 21, a control portion 22, and a power switch 23.

  The pointer 11 is provided on the magnet 12. The length of the pointer 11 can be adjusted. The pointer 11 has an instruction portion 11a at the end of the magnet 12 on the N pole side.

  The magnet 12 is fixed to the central portion of the up and down rotation ring (first ring) 14 by a magnet support bar 13.

  The vertical rotation ring 14 is provided with a convex portion 14a and a convex portion 14b that define a vertical rotation axis (first rotation axis).

  The left and right rotation ring 15 supports the vertical rotation ring 14 so as to be rotatable about the vertical rotation axis. Specifically, the left and right rotation ring 15 is provided with a rotation bearing 15a and a rotation bearing 15b that define a vertical rotation axis. A convex portion 14a is inserted into the rotary bearing 15a, and a convex portion 14b is inserted into the rotary bearing 15b.

  The left and right rotation ring 15 is provided with a convex portion 15c and a convex portion 15d that define a left and right rotation axis (second rotation axis). The left / right rotation axis is orthogonal to the up / down rotation axis.

  The magnet support frame (support part) 16 rotatably supports the left and right rotation ring 15 around the left and right rotation axis. Specifically, the magnet support frame 16 is provided with a rotation bearing 16a and a rotation bearing 16b that define left and right rotation axes. The rotary bearing 16a has a convex portion 15c, and the rotary bearing 16b has a convex portion 15d.

  A light emitting element 17 and a light receiving element 18 are disposed opposite to the magnet support frame 16. The light emitting element 17 and the light receiving element 18 constitute a detection unit (light sensor).

  For example, the light emitting element 17 may be an LD (laser diode) or an LED (for example, an infrared light emitting element). The light emitting element 17 preferably emits parallel light (for example, a light beam obtained by collimating (parallel) light emitted from the LD).

  Note that an element that emits a gas laser is preferably used as the light emitting element 17. However, when an LD is used as the light emitting element 17, the light emitting element can be made inexpensive and compact.

  As the light receiving element 18, for example, a photodiode (for example, an infrared light receiving element) is used.

  The vertical rotation ring 14 has a hole 14c and a hole 14d through which light emitted from the light emitting element 17 passes when the instruction part 11a points to the center part (specific position) 21b of the scale part 21.

  In addition, the left and right rotation ring 15 has a hole 15e and a hole 15f through which light emitted from the light emitting element 17 passes when the instruction portion 11a points to the center portion 21b.

  Moreover, the magnet support bar 13 has a hole 13a through which light emitted from the light emitting element 17 passes when the pointing portion 11a points to the central portion 21b.

  The light receiving element 18 is a position at which the light emitted from the light emitting element 17 when the pointing unit 11a points to the central portion 21b and then the light that has passed through the hole 15e, the hole 14c, the hole 13a, the hole 14d, and the hole 15f can be received. It is arranged.

  When the direction of the instruction part 11a deviates from the center part 21b, the magnet support bar 13, the vertical rotation ring 14, or the horizontal rotation ring 15 moves. For this reason, the light emitted from the light emitting element 17 is blocked by the magnet support rod 13, the up / down rotating ring 14 or the left / right rotating ring 15, and does not reach the light receiving element 18.

  The output of the light receiving element 18 changes according to the amount of light received by the light receiving element 18. For this reason, the output of the light receiving element 18 indicates the movement of the pointer 11.

  The diameter of the light beam impinging on the light receiving element 18 and the light receiving diameter of the light receiving element 18 are set to be the same, and the center of the light beam diameter and the center of the light receiving diameter are set to coincide with each other when the pointing portion 11a points to the center portion 21b. If it is, if the direction of the instruction | indication part 11a remove | deviates from the center part 21b, the light quantity of the light which the light receiving element 18 receives will reduce. For this reason, the output of the light receiving element 18 indicates the movement of the pointer 11 with high accuracy.

  If the diameter of the light beam striking the light receiving element 18 and the light receiving diameter of the light receiving element are different, a dead zone (the amount of received light does not change even if the pointer 11 moves slightly) is generated. Therefore, if this dead zone is used, it is possible to increase resistance to very weak noise.

  The LED (alarm unit) 19 blinks (alarms) when the light receiving element 18 detects the movement of the pointer 11.

  In addition, each electronic device (for example, the light emitting element 17, the light receiving element 18, LED19, and the control part 22) which the geomagnetic fluctuation sensing apparatus 1 has is driven using a battery (not shown) as a power source.

  The cover 20 is made of glass or transparent resin. The cover 20 is a transparent dome-shaped cover, and includes a pointer 11, a magnet 12, a magnet support bar 13, a vertical rotation ring 14, a left / right rotation ring 15, a part of the magnet support frame 16, and a light emitting element. 17, the light receiving element 18, and the LED 19 are covered. The cover 20 prevents the direction of the instruction unit 11a from moving due to the influence of wind.

  The scale portion 21 is fixed to the inner wall of the cover 20. The scale part 21 has a center part 21b and a scale 21a indicating the amount of movement from the center part 21b.

  The scale 21a is a line that connects points equidistant from the central portion 21b in a circular shape. Therefore, when the direction of the instruction unit 11a moves from the center portion 21b to an arbitrary position due to a change in geomagnetism, the user can recognize the displacement using the scale portion 21.

  The control unit 22 controls the light emission of the light emitting element 17. For example, the control unit 22 causes the light emitting element 17 to emit light intermittently (for example, at intervals of 1 to 30 minutes). In this case, battery consumption can be reduced as compared with the case where the light emitting element 17 continuously emits light. It is desirable that the control unit 22 can adjust the intermittent light emission timing of the light emitting element 17 in accordance with a command input from the user.

  The control unit 22 receives the output of the light receiving element 18. Further, the control unit 22 controls the operation of the LED 19 based on the output of the light receiving element 18. Furthermore, if the output of the light receiving element 18 indicates that the direction of the instruction unit 11a has moved from the central portion 21b, the control unit 22 causes the LED 19 to emit light.

  The power switch 23 controls on / off of a battery as a power source.

  Next, an example of installation of the geomagnetic fluctuation sensing device 1 will be described.

  The geomagnetic fluctuation sensing device 1 is placed on a horizontal stand. Thereafter, when the instruction unit 11a faces the magnetic north, the stationary table is rotated so that the instruction unit 11a points to the central portion 21b.

  In addition, the vertical (vertical) direction shift | offset | difference of the direction which the instruction | indication part 11a points out and the center part 21b is correct | amended by adjusting the length of the pointer 11. FIG.

  Thereafter, it is confirmed that the LED 19 does not emit light when the power switch 23 is turned on. If the cover 20 is not attached, then the cover 20 is attached to the geomagnetic fluctuation sensing device 1.

  In order to make the installation direction of the geomagnetic fluctuation sensing device 1 easy to understand, as shown in FIG. May be used to adjust the installation direction of the geomagnetic fluctuation sensing device 1.

  Next, the operation will be described.

  When there is no change in geomagnetism, the pointer portion 11a points to magnetic north by normal geomagnetism. In this case, the light receiving element 18 senses the light of the light emitting element 17 that emits light intermittently, and generates an output according to the amount of the sensed light. Therefore, the predetermined output of the light receiving element 18 synchronized with the light emission of the light emitting element 17 indicates that the magnet 12 has not moved.

  When the control unit 22 receives a predetermined output of the light receiving element 18 synchronized with the light emission of the light emitting element 17, the control unit 22 determines that the magnet 12 has not moved due to a change in geomagnetism due to a ground current. The control unit 22 prohibits the light emission of the LED 19 based on the determination result.

  When a change in geomagnetism due to earth current occurs, lines of magnetic force other than magnetic north are generated. The magnet 12 receives a force corresponding to the change in the geomagnetism. Specifically, the magnet 12 receives a force in a direction indicated by a vector obtained by synthesizing a vector of magnetic field lines generated in accordance with the geomagnetic disturbance and a vector of magnetic field lines indicating magnetic north.

  When the magnet 12 receives a force corresponding to the change in geomagnetism, the up / down rotating ring 14 and / or the left / right rotating ring 15 rotates in a direction corresponding to the force received by the magnet 12. Specifically, the left / right rotation ring 15 rotates about the left / right rotation axis, thereby enabling the movement of the magnet 12 in the horizontal plane. In addition, the vertical rotation ring 14 rotates about the vertical rotation axis to allow the magnet 12 to move on the vertical plane.

  For this reason, when a change in geomagnetism occurs, the magnet 12 moves in accordance with the rotation of the up / down rotating ring 14 and / or the left / right rotating ring 15. Therefore, the pointer portion 11a indicates a direction indicated by a vector obtained by combining a vector of magnetic lines generated according to a change in geomagnetism and a vector of magnetic lines indicating magnetic north.

  Since the up / down rotating ring 14 is installed in the left / right rotating ring 15, as a result, the magnet 12 can freely move in three dimensions in the up / down / left / right direction. For this reason, the movement of the magnet 12, more specifically, the pointer 11, the up-and-down rotation ring 14, and the left-right rotation ring 15 has a possibility of giving the user interest.

  When there is no change in geomagnetism, the light emitted from the light emitting element 17 reaches the light receiving element 18 through the holes provided in the rings 14 and 15 and the magnet support rod 13.

  However, when a change in geomagnetism occurs and the pointer portion 11a faces in a direction different from the direction indicating the center portion 21b, the relative positional relationship between the rings 14 and 15 and the magnet support rod 13 changes, and the light receiving element 18 receives light. Will not reach. Therefore, the predetermined output of the light receiving element 18 synchronized with the light emission of the light emitting element 17 is lost. The output of the light receiving element 18 indicates the movement of the pointer 11.

  When the predetermined output of the light receiving element 18 synchronized with the light emission of the light emitting element 17 is lost, the control unit 22 determines that the pointer 11 has moved and causes the LED 19 to emit light.

  The sensing range of the geomagnetic fluctuation sensing device 1 is effective for subtle movements of the pointer 11 and is related to the widths of the rings 14 and 15 and the magnet support bar 13.

  When geomagnetism fluctuates significantly, light passes through regardless of the ring frame. However, even in this case, the light irradiating the light receiving element 18 is temporarily blocked by the ring frame. Therefore, it is desirable that the control unit 22 causes the LED 19 to emit light when the output of the light receiving element 18 temporarily decreases.

   Note that the alarm unit is not limited to LEDs, but includes any of the functions of visual sensing by light emitting elements such as light bulbs and strobes, auditory sensing of chimes, buzzers, etc., and short-circuiting of no-voltage contact terminals for operating external devices. Or a combination thereof.

  Further, the significant fluctuation of the magnetic field may be determined based on the significant movement of the scale unit 21 or the pointer 11.

  The electronic device of the geomagnetic fluctuation sensing device 1 operates using a battery housed on the bottom surface of the main body as a power source. In addition, it is desirable to set the electronic device of the geomagnetic fluctuation sensing device 1 so that the battery life is one year or longer.

  According to the present embodiment, the following effects can be obtained.

  Changes in geomagnetism due to the generation of earth currents associated with crustal movements can be easily detected with magnets.

  In addition, in order to relatively sense the change in geomagnetism, even in the case where the pointing unit 11a does not accurately point to magnetic north in a building having a reinforced structure such as an apartment, the direction of the pointing unit 11a at that location is the center. The change of the geomagnetism can be caught by taking it to 21b and observing the change from the state.

  Further, by using an optical sensor as the detection unit, the movement of the pointer 11, that is, the change in geomagnetism can be detected without contact. For this reason, when detecting the movement of the pointer 11, unnecessary force is not applied to the magnet 12 and the pointer 11. Therefore, it is possible to prevent malfunction caused by unnecessary force.

  Further, the change in geomagnetism can be detected as the displacement of the first or second ring that moves in accordance with the movement of the magnet.

  In addition, the user can easily perform setting so that the direction of the pointer 11 becomes a specific position by using the scale portion 21. In addition, the user can recognize the degree of movement of the pointer 11, that is, the degree of change in geomagnetism, by using the scale unit 21.

  In addition, by intermittently operating the optical sensor, the power consumed by the optical sensor per unit time can be reduced as compared with the case where the optical sensor operates continuously.

  In addition, it is possible to notify the user of a change in geomagnetism by an alarm.

  In addition, the balance (center of gravity) of the magnet 12 can be adjusted by adjusting the length of the pointer 11. For this reason, when there is no change in geomagnetism, it is easy to set the pointer 11 to face a specific position.

  In the embodiment described above, the illustrated configuration is merely an example, and the present invention is not limited to the configuration.

  For example, three magnetic sensors may be installed in the geomagnetic fluctuation sensing device 1 in the X, Y, and Z axis directions to sense a change in magnetic field lines. In addition, when detecting a magnetic force line with a Hall element, it is desirable to provide an electronic display device that represents the amount of change so that a change in the magnetic force line can be detected visually.

  Also, connect two or more geomagnetic fluctuation sensing devices 1 wirelessly, confirm that they are synchronized in the home (short distance) (the magnetic needle points in the same direction), and iron and other magnets near the geomagnetic fluctuation sensing device 1 You may make it prevent the malfunctioning by temporary deflection of the magnet by.

  For example, as shown in FIG. 5, an alarm is given to a plurality of geomagnetic variation sensing devices 1 only when each of the optical sensors (detecting units) included in the plurality of geomagnetic variation sensing devices 1 detects the movement of the pointer portion 11a. An alarm generating unit 3 is provided.

  In FIG. 5, the alarm generation unit 3 includes a control circuit 3a and an alarm unit (for example, a sound report unit) 3b. When each light receiving element 18 generates an output indicating a change in the direction of the instruction unit 11a, each control unit 22 notifies the control circuit 3a accordingly. In FIG. 5, the same components as those shown in FIG.

  Based on the notification from each control unit, the control circuit 3a determines that a change in geomagnetism has occurred when the directions of all the instruction units 11a of the plurality of geomagnetic fluctuation sensing devices 1 change, and the alarm unit 3b To activate an alarm.

  In addition, when only one of the instruction units 11a of the plurality of geomagnetic fluctuation sensing devices 1 changes the direction based on the notification from each control unit, the control circuit 3a changes the direction to detect the geomagnetic fluctuation. The alarm unit 3b is not operated based on the judgment that it is due to iron or magnetic material around the device 1 or vibration.

1 is a partial cross-sectional view illustrating a geomagnetic fluctuation sensing device according to an embodiment of the present invention. It is a top view of the geomagnetic fluctuation sensing apparatus shown in FIG. It is a top view of the geomagnetic fluctuation sensing apparatus shown in FIG. It is a block diagram of the geomagnetic fluctuation sensing apparatus shown in FIG. It is the block diagram which showed the geomagnetic fluctuation detection apparatus of one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Geomagnetic fluctuation detection apparatus 11 Pointer 11a Instruction part 12 Magnet 13 Magnet support rod 13a Hole 14 Vertical rotation ring 14a, 14b Protrusion part 14c, 14d hole 15 Left-right rotation ring 15a, 15b Rotation bearing 15c, 15d Protrusion part 15e, 15f Hole 16 Magnet support frame 16a, 16b Rotary bearing 16c Scale 17 Light emitting element 18 Light receiving element 19 LED
20 Cover 21 Scale unit 21a Scale 22 Control unit 23 Power switch 2 Mat 2a Scale 3 Alarm generation unit 3a Control circuit 3b Alarm unit

Claims (8)

A geomagnetic fluctuation sensing device that senses changes in geomagnetism,
Guidelines,
A magnet provided with the pointer;
A first ring to which the magnet is fixed;
A second ring that rotatably supports the first ring about a first rotation axis;
A support portion that rotatably supports the second ring around a second rotation axis orthogonal to the first rotation axis;
A geomagnetism fluctuation sensing device comprising: a detection unit that detects movement of the pointer as a change in the geomagnetism. The geomagnetic fluctuation sensing device according to claim 1,
The detection unit is a geomagnetic fluctuation sensing device, which is an optical sensor. The geomagnetic fluctuation sensing device according to claim 2,
The optical sensor has a light emitting element and a light receiving element,
The first and second rings have holes through which light emitted from the light emitting element passes when the pointer points to a specific position;
The light receiving element is disposed at a position where light that has passed through the hole after being emitted from the light emitting element when the pointer points to the specific position can be received;
The said light receiving element is a geomagnetic fluctuation sensing apparatus which detects the movement of the said pointer based on the light quantity change of the light received from the said light emitting element. The geomagnetic fluctuation sensing device according to claim 3,
A geomagnetic fluctuation sensing device further comprising a scale portion including the specific position and a scale indicating a movement amount from the specific position. In the geomagnetic fluctuation sensing device according to any one of claims 2 to 4,
The optical sensor is a geomagnetic fluctuation sensing device that operates intermittently. The geomagnetic fluctuation sensing device according to any one of claims 1 to 5,
The geomagnetic fluctuation sensing device further includes an alarm unit that generates an alarm when the detection unit detects movement of the pointer. The geomagnetic fluctuation sensing device according to any one of claims 1 to 6,
The geomagnetic fluctuation sensing device, wherein the pointer can be changed in length. A plurality of geomagnetic fluctuation sensing devices according to any one of claims 1 to 7,
An earth magnetism fluctuation detecting device comprising: an alarm generating section that generates an alarm only when each of the detecting sections included in the plurality of earth magnetism fluctuation sensing devices detects movement of the pointer.

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