JPH0980132A - Differential type ac magnetic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an AC magnetic sensor for detecting a high-sensitivity submarine cable which can be easily handled. SOLUTION: Coils 11 and 12 for detecting AC magnet are stored in a stainless steel cylindrical pressure-resistance container 13. The axes of the coils 11 and 12 match those of the pressure-resistance container 13 and are fixed to a lid 14 by a press metal fitting 15. Output signals from the coils 11 and 12 are inputted to a differential amplifier in an electronic circuit 20 and the differential signal of the output signal of the two coils 11 an d12 is outputted from an electronic circuit 20. The output signal passes through an underwater cable 22 via an underwater connector 16 and further is transmitted to a mother ship via a towing cable which is not shown in the drawing. Since the difference of the output signals of the two coils is obtained, a sensor rocks, thus eliminating a noise signal which is generated by rotation in earth magnetism.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC magnetic sensor, and more particularly to an AC magnetic sensor suitable for use in a submarine cable exploration system for detecting the presence of a submarine cable by towing by a mother ship.

[0002]

2. Description of the Related Art In order to repair a fault that has occurred in a submarine cable, it is first necessary to search the laying position of the submarine cable and to specify the position where the fault has occurred. Among the methods for exploring the submarine cable, the method that uses the AC magnetic sensor mounted on the underwater robot is the most sensitive and easy to handle. According to this method, an alternating current of about 16 to 25 Hz is made to flow from a submarine cable relay station on land to a conductor in the submarine cable in advance, and an alternating magnetic field generated from this alternating current is detected by an alternating magnetic sensor to detect the submarine cable. Is to detect the position of. However, there is a possibility that the underwater robot has a failure or there is no underwater robot that can be used. In such a case, a sensor that can search the submarine cable is required.

Conventionally, in such a case, a towed type DC magnetic sensor has been used. This DC magnetic sensor detects a DC current flowing through a submarine cable and a DC magnetic field generated from a magnetic material such as iron that constitutes the submarine cable. In this case, since it is necessary to detect a minute fluctuation of the DC magnetic field from the large geomagnetism, a very sensitive proton magnetometer is used as the DC magnetic sensor.
It is also conceivable that an alternating current is made to flow in the conductor in the submarine cable in advance as described above, and the alternating magnetic sensor is connected to the tow cable to tow the tow.

[0004]

However, in the method using the towed DC magnetic sensor, since the proton magnetometer used is very sensitive, it is sensitive only to a magnetic substance such as iron nearby. Will react to. In addition, it has a drawback that it is very difficult to handle such as the operation cannot be confirmed on a repair ship.

On the other hand, when the AC magnetic sensor is connected to the tow cable and towed, a large noise is generated when the sensor sways, and it is difficult to distinguish the signal from the signal due to the AC magnetic field generated from the cable. That is, since the AC magnetic sensor usually has sensitivity directivity, if the sensor fluctuates, a change in the DC earth magnetic field will be felt. Since the AC component of the fluctuation is detected as noise and this noise is large, it has been difficult to adopt a method of towing an AC magnetic sensor in the past.

An object of the present invention is to solve the above problems and provide an AC magnetic sensor for detecting a submarine cable which is easy to handle and has high sensitivity.

[0007]

In order to achieve the above object, the differential AC magnetic sensor of the present invention comprises two or more AC magnetic sensors having directivity of sensitivity and outputs from the AC magnetic sensors. And a means for outputting a signal difference, and the AC magnetic sensors are arranged so that their respective axes are parallel to each other. Further, each of the AC magnetic sensors is composed of a coil and is housed in a pressure resistant container. Further, it has means for correcting the sensitivity of each of the AC magnetic sensors.

Furthermore, the differential AC magnetic sensor of the present invention is towed by a mother ship using a tow cable having a transmission line for transmitting electric power and a signal and a tension member. Furthermore, it is covered with a cushioning material so that noise caused by impact due to contact with the sea bottom during towing can be reduced. Furthermore, a buoyancy member and a wing for stabilizing the posture are attached so that the buoyancy member can be stably floated in the water during towing, and the tip of the towing cable is connected by using a rope with a light underwater weight. ,
A weight is attached to the tip of the tow cable so that the tip of the tow cable comes into contact with the seabed.

[0009]

1 is a diagram for explaining the principle of a differential AC magnetic sensor of the present invention. As shown in this figure, the differential AC magnetic sensor of the present invention is composed of two left and right coils having the same structure and characteristics. The orthogonal coordinate system xyz is defined as shown in the figure. As shown, the two coils are arranged such that their axes are parallel to the y-axis and are aligned, and Δy is the distance between the centers of the two coils. The two coils arranged in this way are sensitive only to the y component of the magnetic field.

The cable is arranged so as to be perpendicular to the plane of the drawing and pass through the origin of the Cartesian coordinate system xyz, and an alternating current of low frequency (25 Hz) is flowing through this cable. I shall. In this case, the output voltage V generated in each coil is expressed by the following equation.

[Equation 1] Here, N is the number of turns of the coil, S is a representative value of the area for one turn of the coil, and By is the y component of the magnetic field. Therefore, by finding the difference in the output of each coil,
The difference between the alternating magnetic fields at the two points where the two coils are placed can be obtained.

Generally, when a single coil is rotated in the earth's magnetic field, the coil feels the rotating magnetic field, and an output voltage proportional to the angular velocity of rotation and the magnitude of the earth's magnetic field appears. Of this output voltage, the AC component having the same frequency as the current flowing through the cable becomes noise and hinders the detection of the cable. FIG. 2 shows an example of theoretically obtained frequency components of 25 Hz of output when a single coil is randomly rotated in the earth's magnetic field. Normally, the magnitude of the alternating magnetic field generated from a submarine cable is several tens nT (nano T
esla), the magnitude of the noise appearing in Fig. 2 is considerably larger than this, and it is difficult to detect the submarine cable under this condition.

In order to solve this problem, in the present invention,
The two coils are fixed so that they move as a unit, and the difference between their outputs is determined. By doing this,
The output due to the rotation of the coil can be canceled and only the alternating magnetic field generated from the submarine cable can be detected.

FIG. 3 shows an example of calculating the relationship between the difference ΔBy in the y component of the magnetic field at the positions of the two coils and the horizontal distance Ly from the cable when the sensor of FIG. 1 is moved parallel to the y axis. In this calculation example, the distance Δy between the two coils is 1 [m], and the vertical distance from the cable is 1 [m].
And In this way, by appropriately setting the distance between the two coils, the presence of the cable can be detected from the signal of the difference between the output voltages. For reference,
The magnitude By of the AC magnetic field before the difference is taken is shown in the same drawing.

FIG. 4 is a diagram showing an embodiment of the differential AC magnetic sensor 10 of the present invention constructed on the basis of the above-described principle. In this figure, 11 and 12 are coils for detecting an alternating magnetic field, 13 is a cylindrical pressure-resistant container made of stainless steel or the like, 14 is a lid of the pressure-resistant container 13, and 15 is a coil 11 or a coil 12 for fixing the coil 11 to the lid 14. Is a submersible connector, 17 is a protective frame for the underwater connector 16, 18 and 19 are winding frames for the coils 11 and 12, respectively, 20 is an electronic circuit, 21 is an O-ring, and 22 is an underwater cord.

In this embodiment, two coils 11 and 12 are provided in a cylindrical pressure resistant container 13 made of stainless steel.
Has been fixed. The axes of these coils are aligned with the axis of the cylindrical pressure-resistant container 13. And coil 1
Each of 1 and 12 is fixed to the lid 14 of the pressure-resistant container 13 by using a pressing fitting 15. An O-ring 21 is inserted between the lid 14 and the pressure-resistant container 13 so that the container is kept watertight.

A substrate on which an electronic circuit 20 is mounted is fixed in the pressure resistant container 13, and a circuit for outputting a difference between output signals from two coils 11 and 12, which will be described later, is provided to the electronic circuit 20. Is provided. This sensor 10
The output signal from the electric power source and the electric power supplied to the electronic circuit 20 are transmitted to the mother ship (not shown) via the underwater cord 22, the underwater connector 16 fixed to the lid 14 and the tow cable (not shown). The underwater connector 16 is protected from external force by the protective frame 17. The external dimensions of this differential AC magnetic sensor are about 1 to 1.5 in length.
[M] and the diameter is about 10 to 15 [cm]. The influence of the magnetic field disturbance due to the use of the stainless steel container is almost negligible.

FIG. 5 shows an example of the structure of the electronic circuit 20 housed in the pressure resistant container of FIG. In the figure, 11 and 12 are the above-mentioned coils, 201 and 202 are variable gain amplifiers to which the output signals of the coils 11 and 12 are input, respectively, and 203 is an output signal from the variable gain amplifiers 201 and 202. A differential amplifier that outputs a difference signal, and 204 is a band-pass filter that passes a signal having a frequency of an alternating current flowing through the cable.

In the electronic circuit 20 configured as described above, the signals from the coils 11 and 12 can be adjusted in gain, respectively, and the variable gain amplifiers 201 and 20 can be adjusted.
After being amplified by 2, it is input to the differential amplifier 203,
The signal of the difference is output from the differential amplifier 203. The output signal is passed through the bandpass filter 204, so that a signal having the same frequency as the alternating current flowing through the submarine cable is extracted. The first stage variable gain amplifier 201
Alternatively, by controlling the gain of 202 individually, when there is a difference in sensitivity between the coils 11 and 12, the difference in sensitivity can be compensated.

FIG. 6 shows the differential AC magnetic sensor 1 described above.
An example of a towing method of 0 is shown. In this example, the sensor 10 is towed while in contact with the seabed. When towing while contacting the seabed in this way, the shock of contact with the seabed causes the axes of the two coils to relatively vibrate, and the output S
/ N (signal noise ratio) may deteriorate.

Therefore, in this example, in order to prevent such deterioration, a cushioning material 23 such as rubber, sponge or vinyl hose is arranged around the pressure resistant container 13,
The periphery thereof is covered with, for example, a plastic cylindrical cover 24. In addition, the outside of the bag 25 such as a hemp bag or net
The towing rope 26 is fastened to the bag. The other end of the rope 26 is the towing cable 2
Retained at 7. Although the structure of the towing cable 27 is not shown, a composite cable composed of power and signal transmission lines and a tensile strength material is used. As described above, the power line and the signal line in the tow cable 27 are connected to the electronic circuit 20 in the pressure vessel 13 via the underwater cord 22 and the underwater connector 16. The other end of the tow cable 27 is towed by the mother ship.

Furthermore, by attaching a weight such as a metal chain to the tail of the sensor 10 (the side not connected to the towing cable 27), it is possible to prevent the tail from rising due to the unevenness of the sea bottom. With the above configuration, it is possible to reduce the level of noise caused by the impact due to contact with the seabed.

Although not shown in the drawings on the display device on the mother ship, the signal output from the sensor 10 is, for example, passed through a bandpass filter, rectified by a rectifier, and recorded in an XT recorder or the like. Will be done. As described above, the differential AC magnetic sensor 1 of the present invention
When 0 crosses over the submarine cable, a waveform like ΔBy in FIG. 3 appears on the XT recorder. By observing this waveform, the position of the submarine cable can be detected.

Usually, the laying position and the laying direction of the submarine cable can be roughly estimated from the construction record. Then, the sensor 10 is towed by the mother ship so as to be orthogonal to the cable. An AC current for exploration is supplied to the submarine cable from the terminal station on land. More specifically, the submarine cable is provided with a power supply line for supplying DC power to the repeater outside the signal line group arranged at the center thereof. When a failure occurs in the submarine cable, the land-based terminal station superimposes an AC signal for exploration having a frequency of about 16 to 25 Hz on the power supply line and sends it out. Since the power supply line is in contact with seawater at the fault occurrence point of the submarine cable, the AC signal for exploration sent from the terminal station on land is in the submarine cable from the terminal station to the fault point of the submarine cable. It flows through, but is grounded to seawater before the point of failure. Therefore, an AC magnetic field is generated from the submarine cable up to the fault point, but no AC magnetic field is generated from the submarine cable beyond that point.

Therefore, the AC magnetic sensor 10 of the present invention is towed so as to be orthogonal to the submarine cable, and as described above, the position of the submarine cable is detected by observing the waveform appearing on the XT recorder. Next, the towing position is shifted in a direction farther from the terminal station that is sending the search AC signal, and the position of the submarine cable is searched again.
By repeating the search in this manner, it is possible to specify the point where the alternating magnetic field does not occur, that is, the failure position. After specifying the fault position, cut the submarine cable in the vicinity of the fault position, pull up the submarine cables at both ends of the cut position on the mother ship, cut out the fault point, and connect the repair cable. , By laying on the seabed again, the faulty part will be repaired

FIG. 7 is a diagram showing another example of the towing method of the differential type sensor. FIG. 7A shows a plan view thereof,
(B) shows a front view. In this example, in order to prevent S / N deterioration due to impact caused by contact with the sea bottom,
This is an example in which the sensor 10 is floated from the sea bottom and towed.

In order to give buoyancy to the sensor 10, a buoyancy member 30 is fixed on the upper part of the sensor. Further, in order to adjust the height between the sensor and the sea bottom, a weight 29 is hung from the sensor 10 via a rope 26. By adjusting the weight of the weight 29 and the buoyancy of the buoyancy member 30, the weight 2
It is possible to tow the sensor in a situation where the 9 is always grounded. That is, the rope 26 for hanging the weight 29
It is possible to adjust the height of the sensor from the sea bottom by adjusting the length. In addition, the weight of the towing cable 27 does not affect the buoyancy of the sensor 10, so that the towing cable 27
A rope 26 connects the tip of the sensor and the sensor 10. Furthermore, a weight 28 is attached to the tip of the tow cable 27 so that the tip of the tow cable 27 bottoms. The rear part of the sensor 10 has a stable posture in water.
Horizontal stabilizers 31 and vertical stabilizers 32 are attached. The distance between the sensor 10 and the sea bottom is 0.5 to 1
It may be set to be about [m].

By floating the sensor above the sea bottom in this way, it is possible to prevent the impact due to contact with the sea bottom. The sway of the sensor's slow posture cannot be eliminated, but the fast sway can be eliminated. Since the frequency component of the output fluctuation of the sensor due to the swaying of the slow posture is low, it does not significantly affect the measurement. That is, with the configuration as in this example, it is possible to eliminate the fluctuation of the sensor in a fast cycle that greatly affects the measurement.

In the above embodiments, a sensor using two coils is assumed, but it is also possible to use two or more coils, and the coil used is not limited to an air core. , Those with magnetic core can be used.
Further, as the AC magnetic sensor, other sensors such as a fluxgate type magnetic sensor can be used in addition to the coil described above. Furthermore, in the description of FIGS. 1 to 3, the y component is used as the component of the magnetic field detected by the coil, but substantially the same result can be obtained with the z component.
Since the magnitude of the magnetic field component in the x-axis direction parallel to the cable is zero, the coil axial direction may be any direction other than the x-axis. Further, for example, two sets of differential AC magnetic sensors having sensitivities in different directions can be used in combination.

Furthermore, although an example in which the differential AC magnetic sensor is towed has been described above, the differential AC magnetic sensor of the present invention can be mounted on an underwater vehicle such as an underwater robot. Is. Furthermore, in the above description, the case of exploring a submarine cable has been described, but the present invention is not limited to this, and it is possible to detect any long object to which an alternating current is applied. Is clear.

[0030]

EFFECTS OF THE INVENTION Two or more AC magnetic sensors having sensitivity directivity are arranged so that their axes are parallel to each other.
According to the differential AC magnetic sensor of the present invention configured to output the signal of the difference in its output, it is possible to remove a noise signal generated by crossing the earth's magnetic field due to a change in the position of the sensor. Only the signal of can be detected. Further, according to the present invention in which the AC magnetic sensor is composed of a coil, the differential AC magnetic sensor can be made inexpensive.

Furthermore, according to the present invention having means for correcting the sensitivity of each AC magnetic sensor, the sensitivity difference can be compensated even when the AC magnetic sensors have different sensitivities. Furthermore, according to the present invention, which is towed by a mother ship using a tow cable having a transmission line for transmitting electric power and a signal and a strength member, an inexpensive AC magnetic sensor is used to detect a fault position of a submarine cable or the like. It becomes possible. Furthermore, according to the present invention, which is covered with the cushioning material, it is possible to prevent the axes of the two coils from relatively vibrating due to the impact due to the contact with the seabed, so that noise is not generated.

Further, a buoyancy member and a posture stabilizing wing are attached so that the buoyancy member is stably floated in the water during towing, and a weight is attached to the tip of the buoyant member so as to come into contact with the seabed. According to the present invention, in which the tip of the towed cable is connected to the underwater rope using a rope, the sensor is prevented from swaying in a fast cycle which has no contact with the sea bottom and has a great influence on the measurement. It is possible to eliminate noise.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the principle of a differential AC magnetic sensor of the present invention.

FIG. 2 is a diagram showing a calculation example of the magnitude of the 25 Hz component of the output when a single coil is randomly rotated in the earth's magnetic field.

FIG. 3 is a diagram showing a relationship between a horizontal distance y from a submarine cable and ay component By of an AC magnetic field generated from the submarine cable, and a calculation example of a difference ΔBy between AC magnetic fields By generated in two coils.

FIG. 4 is a diagram showing an example of an embodiment of a differential AC magnetic sensor of the present invention.

FIG. 5 is a diagram showing an example of a configuration of an electronic circuit 20 used in the differential AC magnetic sensor of the present invention.

FIG. 6 is a diagram showing an example of a towing method of the differential AC magnetic sensor of the present invention.

FIG. 7 is a diagram showing another example of the towing method of the differential AC magnetic sensor of the present invention.

[Explanation of symbols]

 10 Differential type AC magnetic sensor 11, 12 Coil 13 Columnar pressure resistant container 14 Lid 15 Holding fitting 16 Underwater connector 17 Protective frame 18, 19 Coil reel 20 Electronic circuit 21 O-ring 22 Underwater cord 23 Buffer material 24 Cylindrical cover 25 bag 26 rope 27 tow cable 28, 29 weight 30 buoyancy material 31 horizontal stabilizers 32 vertical stabilizer 201, 202 variable gain amplifier 203 differential amplifier 204 bandpass filter

Claims (6)

[Claims] 1. An AC magnetic sensor having two or more AC magnetic sensors having sensitivity directivity, and means for outputting a difference between output signals from the AC magnetic sensors, each axis of the AC magnetic sensors being A differential AC magnetic sensor, which is arranged so as to be parallel to each other. 2. The differential AC magnetic sensor according to claim 1, wherein each of the AC magnetic sensors includes a coil and is housed in a pressure resistant container. 3. The method according to claim 1, further comprising means for correcting the sensitivity of each AC magnetic sensor.
The differential AC magnetic sensor according to any one of 1. 4. The differential alternating current according to claim 1, wherein the towed cable is towed by a mother ship using a tow cable having a transmission line for transmitting electric power and a signal and a strength member. Magnetic sensor. 5. The differential AC according to claim 4, wherein the differential AC is covered with a cushioning material so that noise caused by impact due to contact with the seabed during towing is reduced. Magnetic sensor. 6. A buoyancy member and a posture stabilizing wing are attached so that the buoyancy member can be stably floated in the water during towing, and the tip of the towing cable is connected by using a rope with a light underwater weight. The differential AC magnetic sensor according to claim 4, wherein a weight is attached to the tip of the towing cable so that the tip of the towing cable contacts the seabed.