JPH0249676B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to the use of buried long bodies such as submarine cables and pipelines buried under the seabed or cables buried under the ground on land. The present invention relates to a method and apparatus for measuring the depth of burial of a buried elongated object.

[Prior art] In recent years, when long bodies such as submarine cables and pipelines are installed on the seabed, they are buried at a depth of about 1 to 2 meters below the seabed to prevent damage from anchors, fishing gear, etc. It is becoming common to do so. However, the seabed surface is affected by tidal currents, and the initial burial depth changes due to the movement of bottom sediment. Therefore, for maintenance of buried long bodies, the buried depth is periodically measured, and if the buried depth is insufficient, protective measures such as re-burying the part are taken.

Conventionally, to measure the buried depth of submarine cables, an alternating current of about 5 to 10 A is passed through the buried cable's conductor or a dedicated conductor for measurement, and a magnetic field is generated around the conductor according to Ampere's law. In a cold state, a buried depth measuring device with multiple search coils fixed at predetermined intervals in the front and back direction is moved in a direction perpendicular to the cable, and the voltage induced in a certain search coil by the magnetic field is maximized. The depth of burial was measured by the magnitude of the voltage induced in other search coils at the same time.

However, with this method of measuring burial depth, it is necessary to actively create a leakage magnetic field to the outside by passing a measuring current through the cable's conductor, so generally the cable's power transmission must be stopped. In addition, in the case of buried long objects that do not have conductors that can carry large currents for measurement, such as pipelines such as water pipes and communication cables, there is a drawback that the depth of burial cannot be measured. .

[Object of the Invention] An object of the present invention is to provide a method and apparatus for measuring the depth of burial of a buried elongated object, which can measure the depth of burial without passing a current through the elongated object.

[Principle of the Invention] The present invention focuses on the fact that the buried long body is equipped with a magnetic material such as armored iron wire or iron pipe, and that this magnetic material is weakly magnetized to several Gauss by the earth's magnetic field. The depth of the buried long object can be measured by efficiently detecting the weak magnetic field of the object using a magnetic sensor.

When a magnetic sensor is brought close to a buried elongated body having a magnetic material that is magnetized by the earth's magnetic field, the electromotive force E appearing on the magnetic sensor is expressed by the following equation.

E=dX/dt=dX/dx×dx/dt Here, X=horizontal component of detected magnetism dX/dx=change in magnetic force depending on location dx/dt=moving speed of magnetic sensor From the above equation, increase the electromotive force E In order to achieve this, it is effective to increase the total magnetic flux passing through the magnetic sensor or to increase the moving speed (towing speed) of the magnetic sensor.

However, increasing the moving speed of the magnetic sensor means that, for example, when the magnetic sensor is mounted on a sensor carrier running on the seabed and the sensor carrier is towed by a ship, the speed of the ship increases. There is a limit to that. The same can be said for track and field.

Therefore, in the present invention, regardless of the speed of the sensor carrier, the magnetic sensor is moved faster to increase the electromotive force E, thereby increasing measurement accuracy and measurable depth.

Possible methods of moving the magnetic sensor quickly regardless of the speed of the sensor carrier include reciprocating the magnetic sensor or rotating the magnetic sensor.

[Structure of the Invention] The first invention of the present application is to run a sensor carrier carrying a magnetic sensor over the surface to be explored, and use the magnetic sensor to detect a magnetic field emitted by a long body buried under the surface to be explored. In the method for measuring the depth of burial of a buried elongated object, the magnetic sensor is moved on the sensor carrier to measure the depth of the buried elongated object that is magnetized by the earth's magnetic field. Obtain an electromotive force waveform signal due to a magnetic field, and when the time width between the starting point and the end point where the electromotive force waveform signal intersects the time axis is the sensing width T, from the sensing width T and the moving speed V of the magnetic sensor. This method is characterized in that the buried depth D of the buried elongated body is determined from the following formula: D=1/α·TV (where α is a proportionality constant).

The second invention of the present application is to detect the magnetic field emitted by the buried elongated body under the surface to be surveyed by running a sensor carrier carrying a magnetic sensor over the surface to be surveyed, and detect the magnetic field emitted by the long body buried under the surface to be surveyed. In the buried depth measuring device for a buried elongated body that measures the buried depth of a long body, the sensor carrier is formed mainly of a non-magnetic material, and the magnetic sensor is mounted on the sensor carrier so that the sensor carrier moves forward. A sensor reciprocating mechanism for reciprocating the sensor in a direction is mounted on the tower, a control and data processing unit is provided at a position away from the sensor carrier, and the control and data processing unit sends a control signal to the sensor reciprocating mechanism via a cable. a speed controller for controlling the speed of movement of the magnetic sensor; and a speed controller for controlling the speed of movement of the magnetic sensor; and a speed controller based on the movement of the magnetic sensor at a speed controlled by the speed controller of the output output from the magnetic sensor via a cable. A tuning amplifier that obtains an electromotive force waveform signal due to the magnetic field of the buried elongated body by selectively amplifying only the frequency component of the signal generated by the magnetic sensor by controlling the tuning frequency using the control signal from the speed controller. With the electromotive voltage waveform signal as an input signal, the time width between the start point and the end point where the electromotive voltage waveform signal intersects the time axis is defined as a sensing width T.
and an arithmetic unit that calculates the buried depth D of the buried elongated body from the sensing width T and the moving speed V of the magnetic sensor as follows: D=1/α・TV (where α is a proportionality constant) It is characterized by

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. As shown in FIGS. 1 and 2, the buried elongated object buried depth measuring device 1 of this embodiment is used to measure the depth of a buried elongated object such as a submarine cable, which is buried under a seabed surface 2 as a surface to be investigated. 3, which is placed on the seabed 2 and towed by a research vessel 5 via a towline 4, and runs on the seabed 2, with a length of about 5 m and a width, for example. It has a sensor carrier 6 mainly made of non-magnetic material and has a size of about 4 m. This sensor carrier 6
An elevator 7 made of a vane-like non-magnetic material is provided before and after the device 1 to prevent the device 1 from floating up while traveling.
is installed at the required angle. As the non-magnetic material forming the sensor carrier 6 and the elevator 7,
For example, aluminum, duralumin, wood,
FRP etc. can be used. Sensor coils 8 ₁ , 8 ₂ , 8 ₃ , and 8 ₄ as magnetic sensors are mounted on the sensor carrier 6 at the front and rear of one side in the width direction and at the front and rear of the other side, respectively. . These sensor coils 8 ₁ to 8 ₄ are connected to the cable 9
It is connected to the control and data processing section 10 on the research vessel 5 through the , so that data processing for buried depth measurement can be performed. Further, on the sensor carrier 6, there is a sensor reciprocating mechanism 11 ₁ that reciprocates each of the sensor coils 8 ₁ to 8 ₄ in the traveling direction of the sensor carrier 6 at a high speed independently of the travel of the sensor carrier 6. ~11 ₄ are listed.

3 and 4 show the sensor reciprocating mechanism 1
Specific examples of 1 ₁ to 11 ₄ are shown. Since they all have the same structure, the sensor coil is represented by 8, and the sensor reciprocating mechanism is represented by 11.
I will explain it as a representative. This sensor reciprocating mechanism 11 includes a watertight cylindrical case 12 made of a non-magnetic material, and a sensor coil 8 is housed within the case 12 and arranged within a sensor case 13 made of a non-magnetic material. Sur case 13
is supported in the middle of the reciprocating drive shaft 14. This reciprocating drive shaft 14 is connected to a
The sensor carrier 6 is
It is supported so that it can freely move back and forth in the direction of movement. One end of a connecting rod 17 is connected to the end of the reciprocating drive shaft 14 by a joint pin 16, and the other end of this connecting rod 17 is connected to a crank mechanism 18. The crank mechanism 18 includes a crank disk 2 integrated with a crankshaft 19.
0 and a crank pin 21 eccentrically attached to the crank disk 20. The other end of the connecting rod 17 is rotatably connected to the crank pin 21. A bevel gear 22 is fixed to the crankshaft 19, and this bevel gear 22 is connected to the motor 2.
It is meshed with the bevel gear 25 of the output shaft 24 of No. 3. The output shaft 24 is supported by a bearing 26. A bracket 27 is protruded from the sensor case 13, and a buffer spring 28 is interposed between the bracket 27 and the left and right guide frames 15 to provide a buffering effect when the sensor case 13 moves back and forth. It's getting old.

FIG. 5 shows an electrical system diagram of the device of this embodiment. In the figure, 29 is a sensor section provided on the sensor carrier 6, and 10 is the aforementioned control and data processing section provided on the ship. The sensor section 29 includes a sensor reciprocating mechanism 11 that reciprocates the sensor coil 8 and a preamplifier 30 that amplifies the output of the sensor coil 8.
It is made up of. Control and data processing section 10
A speed controller 31 sends a control signal to the sensor reciprocating mechanism 11 to control the moving speed of the sensor coil 8, a main amplifier 32 voltage amplifies the output signal of the preamplifier 30, and a signal outputted by the main amplifier 32. Based on the movement of the sensor coil 8 at a speed controlled by the speed controller 31, only the frequency component of the signal generated by the sensor coil 8 is subjected to tuning frequency control using a control signal from the speed controller 31. Therefore, a tuning amplifier 33 obtains an electromotive voltage waveform signal due to the magnetic field of the buried elongated body 3 by selectively amplifying it, and an absolute value amplifier 34 and this absolute value amplifier 3
The sensing width T and the moving speed of the sensor coil 8 when the DC induced voltage waveform signal No. 4 is an input signal and the sensing width T is the time width between the starting point and the ending point where the DC induced voltage waveform signal intersects the time axis. It consists of a calculator 35 that calculates the burial depth D of the buried long body 3 from There is. The sensor section 29 is provided for each of the sensor coils 8 ₁ to 8 ₄ , and the onboard control and data processing section 10 is shared by each sensor section 29 .

Next, a method of measuring the buried depth of the buried elongated body 3 using such a buried depth measuring device 1 will be explained. As described above, this device 1 is towed by the research vessel 5 and made to travel on the seabed surface 2. In addition, each sensor reciprocating mechanism 11 can be controlled by operating the speed controller 31.
is driven to reciprocate each sensor coil 8 ₁ to 8 ₄ on the sensor carrier 6 . Since the operations of these sensor coils 8 ₁ to 8 ₄ are the same, the sensor coil 8 will be described as a representative. In the sensor coil 8, no electromotive force is generated when there is only a parallel magnetic field such as the earth's magnetic field, but when the earth's magnetic field magnetizes armored iron wire, etc., and a weak spiral magnetic field is generated, an electromotive force is generated in the vicinity of the buried long body 3. When this occurs, the electromotive force is increased due to the fast reciprocating motion of the sensor coil 8, and as the sensor coil 8 reciprocates, an AC waveform of exactly one cycle is generated in the reciprocating motion. This AC waveform signal is amplified by a preamplifier 31, guided to a main amplifier 32 on the ship for voltage amplification, and then sent to a tuning amplifier 33 to provide an S/N ratio.
improve. The number of reciprocating movements per time can be adjusted within a certain range by the speed controller 31, and thereby the frequency of the alternating current voltage generated in the sensor coil 8 is also changed. Tuned amplifier 33
The frequency component generated by the sensor coil 8 based on the movement of the sensor coil 8 at a speed controlled by the speed controller 31 is controlled by tuning frequency using the speed control signal from the speed controller 31. When selectively amplified, for example, Fig. 6 a, b,
An AC electromotive force waveform signal as shown in c is obtained. Such an AC electromotive voltage waveform signal is then input to an absolute value amplifier 34 and rectified to produce a DC electromotive force waveform signal as shown in FIGS. 7a, b, and c. The reason why the waveform changes in this way is that the position of the magnetic pole changes depending on the direction in which the buried elongated body 3 is installed or the position on the earth. This is due to the three elements of geomagnetism: inclination, declination, and horizontal component; in this case, the inclination has a particularly large effect. When the buried long body 3 is laid in the east-west direction, N and S magnetic poles are formed on the cross section of the buried long body 3 at an angle of about 45° to 50°, as shown in Figure 8a. Conceivable. Furthermore, when the buried elongated body 3 is laid in the north-south direction, the N and S poles are considered to be located above and below the buried elongated body 3, as shown in FIG. 8c. However, the above is a story in the vicinity of Japan, and even if the cables are laid in the same east-west direction, it is thought that near the equator, for example, N and S magnetic poles will be formed at almost horizontal positions as shown in Figure 8b. . Figure 9a,
The electromotive force waveforms shown in b and c are obtained when the sensor carrier 6 is moved above the buried elongated body 3 having magnetic poles in the directions shown in FIG. This is a waveform obtained by rectifying the resulting electromotive voltage waveform. If the time width between the start point and the end point where both ends of these electromotive voltage waveforms intersect with the time axis is defined as the sensing width T of the electromotive voltage waveforms, the buried elongated body 3 itself has a small diameter circular shape, and the magnetic pole spacing is also Because it is small, the magnetic field it generates is almost circular. Therefore, the influence of the position of the magnetic pole on the sensing width T is considered to be extremely small. Therefore, looking at the electromotive force waveform shown in FIG. 9b as a typical example, the relationship between the magnetic field generated from the buried elongated body 3, the position of the sensor coil 8, and the electromotive force at that point is shown. It will look like Figure 10. If the moving direction of the sensor coil 8 is the direction of the arrow, and the temporally different positions of the sensor coil 8 on each route are , or , the sensor coil 8 is moved from outside the magnetic field to a position where the magnetic flux density is sparse. It enters, gradually advances to a denser area, passes through a point directly above the buried elongated body 3 where the magnetic flux density is highest, and gradually passes through to a position where the magnetic flux density is sparse. At this time, the electromotive force generated in the sensor coil 8 changes depending on the magnetic flux density passing through the sensor coil 8, and reaches its maximum value just above the magnetic pole. Further, at the position shown by the dotted line where the sensor coil 8 is approximately perpendicular to this magnetic flux, the electromotive force becomes almost zero, resulting in an electromotive force waveform as shown in FIG. In the figure, D ₁ shows the electromotive force waveform when the buried depth from the buried long body 3 to the sensor coil 8 is shallow and D ₁ , and D ₂ shows the electromotive force waveform when the buried depth from the buried long body 3 to the sensor coil 8 is shallow. It shows the electromotive force waveform when D ₂ is deeper than D ₁ . That is, the buried elongated body 3
When the buried depth from the sensor coil 8 to the sensor coil 8 is D ₁ (shallow), the width of the magnetic field emitted by the buried elongated body 3 is small, so the sensing width of the electromotive voltage waveform D ₁ is T ₁ . On the other hand, from the buried long body 3 to the sensor coil 8
When the buried depth reaches _D2 (deep), the spread width of the magnetic field emitted by the buried elongated body 3 increases, so the sensing width increases to _T2 , which is larger than _T1 .

Furthermore, as the traveling speed V of the sensor coil 8 increases, the time it takes to cross the location where the magnetic field exists becomes shorter, so the sensing width T becomes narrower. Conversely, when the running speed V of the sensor coil 8 becomes slower, the time it takes to cross the location where the magnetic field exists becomes longer, so the sensing width T becomes wider.

Therefore, the burial depth D and the sensing width T are almost proportional, and the burial depth D and the running speed V of the sensor coil 8 are almost inversely proportional, T=D/V・α...(1 ). Here, α is a proportionality constant.

Furthermore, in Figure 11, the maximum value of the electromotive force is larger in D ₁ , which is buried at a shallower depth, than in D ₂ , which is buried at a deeper depth. This is because the strength of the magnetic field is large.

Using the electromotive voltage waveform signal output from the absolute value amplifier 34 as input, the arithmetic unit 35 calculates the following: D=1/α・TV (2) to obtain the burial depth D of the buried elongated body 3, This is displayed on the display 36.

Next, if four sensor coils are used in this embodiment, the following three effects can be obtained.

(b) The moving speed of the sensor coil can be accurately measured.

In this example, sensor coils 8 ₁ , 8 ₂ and 8 ₃
The interval between and 8 ₄ is predetermined to be a certain distance. When the sensor carrier 6 is towed almost perpendicularly to the buried elongated body 3 as shown in FIG. 2, it is first detected by the sensor coils 8 ₁ and 8 ₃ , and then An electromotive force waveform as shown _{in FIG} . By measuring the time t between them, the moving speed V of the sensor coil can be easily obtained from V=/t (3). In this way, equation (1) becomes T=D・t/×α...(4) Since is a known constant value determined in advance, if we set /α=K, D=T/t・K...(5) Therefore, if the value of K is obtained through experiments in advance, the burial depth D can be easily calculated.
Further, even if the value of K is determined and a graph as shown in FIG. 13 is created, the burial depth D can be easily determined from T/t.

(b) It is possible to determine whether the object is a buried long object or another magnetic object.

In reality, there are many discarded magnetic materials scattered on the seabed, which hinders the work of measuring the depth of buried long objects such as submarine cables. However, as in this embodiment, the sensor coils 8 ₁ , 8 ₃ and 8 ₂
and 8 ₄ respectively at a distance of S (for example, 4 m
In the case of the buried long body 3, the output waveforms of the sensor coils 8 ₁ and 8 ₃ and 8 ₂ and 8 ₄ should have almost the same amplitude and the same waveform. If the waveforms or waveforms are different, or if output is obtained from only one of the sensor coils, it can be determined by using a logic circuit or the like that it is not the object of measurement.

(c) It is possible to measure the intersection angle between the buried long body and the sensor carrier.

In order to accurately measure the burial depth of the buried elongated body 3, it is important to tow the sensor carrier 6 substantially at right angles to the buried elongated body 3. As shown in FIG. 2, when the angle between the buried elongated body 3 (indicated by a broken line) and the sensor carrier 6 is a right angle, the detected waveform (output waveform of the absolute value amplifier 34) is as shown in a solid line in FIG. However, in reality, it is not possible to tow the sensor carrier 6 at right angles to the buried elongated body 3, and for example, as shown by the dashed line in FIG. 6, the detected waveform becomes as shown by the broken line in FIG. 12, and the detected waveforms of sensor coils ₈₃ and ₈₄ are earlier than the detected waveforms of sensor coils ₈₁ and ₈₂ by Δt. appear. From this, it can be seen that the towing direction of the sensor carrier 6 is not perpendicular to the buried elongated body 3, and it is possible to determine the direction of correction so that it is perpendicular to the buried elongated body 3. Further, at this time, the buried direction of the buried elongated body 3 can also be determined from the navigation direction of the research vessel 5.

Note that, as described above, the present invention can measure the burial depth not only of a long body buried on the seabed, but also of a long body buried on land.

[Effects of the Invention] As explained above, in the method for measuring the depth of buried elongated objects according to the present invention, the detection sensitivity is increased by moving the magnetic sensor on the sensor carrier. The depth of burial can be measured by efficiently detecting the weak magnetic field emitted by the buried long body when it is magnetized by the earth's magnetic field, without passing any current through the body. Therefore, according to the present invention, it is possible to easily measure pipelines, water pipes, etc. at buried depths, which have been difficult to measure in the past. Further, in the method of the present invention, the burial depth is determined from the sensing width T of the electromotive voltage waveform signal and the moving speed V of the magnetic sensor, so the burial depth can be easily measured using the electromotive voltage waveform signal.

On the other hand, in the buried depth measuring device for a buried elongated body of the present invention, the magnetic sensor is moved by the sensor reciprocating mechanism, so that the magnetic sensor can be easily moved on the sensor carrier. In addition, such a reciprocating type mechanism allows the magnetic sensor to be easily moved in a direction parallel to the surface to be investigated, which is suitable for investigating the burial depth. Furthermore, in the device of the present invention,
Since the tuning frequency of the tuning amplifier that amplifies the output of the magnetic sensor is controlled by the control signal from the speed controller that controls the moving speed of the sensor reciprocating mechanism, the speed controlled by the speed controller The advantage is that only the frequency component of the signal generated by the magnetic sensor can be easily selectively amplified based on the movement of the magnetic sensor, and the electromotive force waveform signal due to the magnetic field of the buried elongated body can be easily extracted. There is. Furthermore, if the tuning frequency of the tuned amplifier is controlled by the control signal of the speed controller that controls the moving speed of the sensor reciprocating mechanism in this way, when the moving speed of the magnetic sensor is changed, the tuning frequency of the tuned amplifier is automatically changed. The tuning frequency also changes, and there is an advantage that the electromotive voltage waveform signal can be easily extracted. Furthermore, since the sensor carrier is made of a non-magnetic material, it does not interfere with the detection of weak magnetic fields, which is preferable.

[Brief explanation of drawings]

FIGS. 1 and 2 are a side view and a plan view of an embodiment of the buried depth measuring device of the present invention in use, and FIG.
4 and 4 are a longitudinal sectional plan view and a longitudinal sectional side view of the sensor reciprocating mechanism used in this embodiment, FIG. 5 is a block diagram showing an example of the electrical configuration of the device of the present invention, and FIG. b, c are output waveform diagrams of the sensor coil, Fig. 7 a, b, c are rectified waveform diagrams of the waveforms in Fig. 6 a, b, c, and Fig. 8 a, b, c are magnetization of the buried long body. Explanatory diagram showing the state of Figure 9 a, b, c
are the magnetic field detection waveform diagrams in Figures 8a, b, and c, and Figure 10.
Figures 11 and 11 are diagrams showing the relationship between a buried long body, magnetic field, and sensor coil to explain the principle of measuring buried depth, and diagrams showing differences in buried depth and changes in waveform. Figure 12 is a diagram showing each sensor coil. FIG. 13 is a diagram showing the relationship between the buried depth and T/t. 1... Buried depth measuring device, 2... Surface to be explored, 3
... Buried long body, 4 ... Towing, 5 ... Research vessel, 6
...sensor carrier, 8 ₁ - 8 ₄ ... sensor coil, 9 ... cable, 10 ... control and data processing section, 11 ₁ - 11 ₄ ... sensor reciprocating mechanism,
30... Preamplifier, 32... Main amplifier, 33...
... Tuned amplifier, 34 ... Absolute value amplifier, 35 ...
Arithmetic unit, 36...display unit.

Claims (1)

[Scope of Claims] 1. A sensor carrying body carrying a magnetic sensor is run over a surface to be investigated, and the magnetic field emitted by the buried long body under the surface to be surveyed is detected by the magnetic sensor, and the long body buried under the surface to be surveyed is detected. In the method for measuring the depth of burial of a buried elongated body, the magnetic sensor is moved on the sensor carrier to generate an electromotive force waveform signal due to the magnetic field of the buried elongated body that is magnetized by the earth's magnetic field. and the time width between the starting point and the ending point where the electromotive voltage waveform signal intersects the time axis is the sensing width T. From the sensing width T and the moving speed V of the magnetic sensor, the length of the buried elongated body is calculated. A method for measuring the depth of burial of a buried long object, characterized in that the depth of burial D is determined from D=1/α·TV (where α is a proportionality constant). 2. A sensor carrier carrying a magnetic sensor is run over the surface to be explored, and the magnetic sensor detects the magnetic field emitted by the buried elongated object below the surface to be explored, thereby measuring the burial depth of the buried elongated object. In the buried depth measuring device for a buried elongated object, the sensor carrier is formed mainly of a non-magnetic material, and a sensor reciprocating device is provided on the sensor carrier to reciprocate the magnetic sensor in the traveling direction of the sensor carrier. A moving mechanism is mounted on the tower, and a control and data processing unit is provided at a position remote from the sensor carrier, and the control and data processing unit sends a control signal to the sensor reciprocating mechanism via a cable to control the magnetic field. a speed controller that controls the speed of movement of the sensor; and a signal generated by the magnetic sensor based on the movement of the magnetic sensor at a speed controlled by the speed controller among the outputs output from the magnetic sensor via a cable. a tuning amplifier that obtains an electromotive force waveform signal due to the magnetic field of the buried elongated body by selectively amplifying only the frequency component of by controlling a tuning frequency using the control signal from the speed controller; As an input signal, the time width between the start point and the end point where the electromotive voltage waveform signal intersects the time axis is defined as the sensing width T.
and an arithmetic unit that calculates the buried depth D of the buried elongated body from the sensing width T and the moving speed V of the magnetic sensor as follows: D=1/α・TV (where α is a proportionality constant) A device for measuring the depth of buried elongated objects.