JPH01123185A - Method for magnetically detecting position of ground embedded object - Google Patents

Abstract

PURPOSE:To detect the position of a ground embedded object with high accuracy, by allowing an induced current to flow to the conductive ground embedded object from a transmitter by electromagnetic induction and eliminating the effect of other ground embedded object close to the ground embedded object to be detected. CONSTITUTION:A pair of coils 3a, 3b whose axes are turned in vertical and horizontal directions with respect to the surface of the ground are provided to a transmitter 2 and, by respectively changing the magnitudes of the AC currents flowing to the coils 3a, 3b, the magnetic flux interlinkage state to a ground embedded object is changed. Herein, magnetic fields are generated from the coil 3a whose axis l1 is turned in the vertical direction and the coil 3b whose axis l2 is turned in the horizontal direction. When these two magnetic fields are superposed each other, a synthetic magnetic field is formed and the axis in this synthetic magnetic field is inclined by an angle theta from the axis l1 (l2) and this angle theta can be changed by changing the currents flowing to the coils 3a, 3b. Next, in a receiver 4, a data transmitting part 7 transmits the signal from a signal processing part 8 to the data receiving control part 6 of the transmitter 2 through a medium 9 such as a radio wave or an optical fiber. A magnetic sensor 6' is constituted of a plurality of sensor parts S1-Sn.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for magnetically detecting the position of underground objects such as buried pipes, and in particular, a method of magnetically detecting the position of underground objects such as underground pipes, and in particular, a method of magnetically detecting the position of underground objects such as underground pipes, and in particular, a method for magnetically detecting the position of underground objects such as underground pipes, and in particular, a method of magnetically detecting the position of underground objects such as underground pipes, and in particular, a method of magnetically detecting the position of underground objects such as underground pipes, and in particular, a method of magnetically detecting the position of underground objects such as underground pipes, and in particular, a method of magnetically detecting the position of underground objects such as underground pipes, and in particular, a method of magnetically detecting the position of underground objects such as underground pipes, and in particular, a method of magnetically detecting the position of underground objects such as underground pipes. The present invention relates to a method for detecting the position of underground objects by detecting the magnetic field generated by this induced current.

(Prior art and its problems) As a method for detecting the position of conductive underground objects such as gas pipes and water pipes, that is, the above-ground corresponding position and depth, there is usually a method that is easy and has relatively low detection accuracy. Magnetic sensing methods are often used due to their good performance. And in such a magnetic sensing method,
The most commonly used method is to flow an alternating current through an underground object and detect it from the distribution of the magnetic field generated around it. There is a direct method in which an alternating current source is directly connected to one end to flow the current, and an induction method (or indirect method) in which the current is flown by an electric current source from a transmitter.

In general, direct methods have the advantage of higher detection accuracy than indirect methods because current can be applied only to the underground object to be detected, but on the other hand, it cannot be applied if the underground object has no exposed surface above ground. It has the disadvantage of On the other hand, the induction method has the advantage that it can be applied even when there is no exposed part of the underground object, but on the other hand, there are conductive underground objects nearby other than the underground object to be detected. In this case, induced current also flows to the other underground objects, so the distribution of the magnetic field generated by these is different from the cylindrical magnetic field distribution generated by the current flowing to a single underground object. This has the disadvantage that the detection accuracy of the underground object to be detected deteriorates. Therefore, this will be explained based on the drawings.

Figure 6 (a) shows underground object 0 from the front to the back of the page when there are no other conductive underground objects nearby than the underground object ○ to be detected. This diagram schematically represents the distribution of the magnetic field M generated by the induced current flowing in the direction, that is, the cylindrical magnetic field distribution. Figures 7 (a) and (b) show the horizontal and vertical components of the magnetic field M, respectively. The distribution is plotted in the horizontal direction with the origin at the above-ground corresponding position p of the underground object O.
(direction) expressed relative to distance. This figure 7 (
As can be seen from a) and (b), the horizontal component of the magnetic field M has a maximum value at the ground correspondence position 2 inches (x-0), and has a curved distribution that decreases as it moves away from this point. Further, the vertical component has a curved distribution that becomes zero at the position p. The slope of this curve becomes smaller as the underground object 0 becomes deeper. Therefore, by measuring these components with the receiver, it is possible to accurately detect the ground relative position I2p and depth of the underground object O from their size and inclination.

Next, in FIG. 6(b), there is another electrically conductive underground object O' in the vicinity of the underground object 0 to be detected, and this underground object O' also has underground objects O'. This diagram schematically represents the distribution of the magnetic field M' generated when an induced current equal to O is flowing, and Figures 8(a) and (b) show the horizontal distribution of this magnetic field M', respectively. An example of the distribution of direction and vertical components is
It is expressed with respect to the distance (horizontal direction x direction) from the ground corresponding position p of the underground object O to be detected as the origin.

As can be seen from this figure, the distribution of the magnetic field M' is greatly distorted from the above-mentioned cylindrical distribution of the magnetic field M, due to the influence of the induced current flowing in the nearby underground object 0'. For example, in the distributions shown in Fig. 8(a) and (b), the position where the horizontal component is maximum and the position where the vertical component is zero correspond to the ground 4 corresponding p of the underground object O to be detected. The distance from ta to fh is U, p' (x=0.5). Therefore, if the position is detected by the method described above, a detection error will occur and the accuracy will be poor.

The present invention has been devised in view of the above points, that is, as described above, when there is another electrically conductive underground object in the vicinity of the underground object to be detected. In this case, it is an object of the present invention to provide a method that can detect underground objects to be detected with high precision by applying the guidance method.

(Means for solving the problems) In order to achieve the above-mentioned object, the present invention causes an induced current to flow from a transmitter to a conductive underground object by electromagnetic induction,
This induced current generates ra around the underground object.
In the method of detecting the position of the underground object by detecting the distribution of
Measure the magnetic field distribution, change the magnetic flux linkage state while detecting the deviation between this and a predetermined cylindrical magnetic field distribution, adjust the transmitter to minimize this deviation, and perform the measurement at this time. The purpose of this method is to detect the location of underground objects based on magnetic field distribution.

(Function) Next, the function of the present invention is shown in Fig. 1(a), which shows the basic concept.
, (b), and (c). In the figure, reference numeral 1 indicates the ground, 0 indicates an underground object to be detected, and 0' indicates another underground object close to the underground object O. Also, the code 2 indicates a transmitter, and this transmitter 2
The magnetic flux linkage state with respect to the underground objects o and o' is made variable by various configurations as shown in the examples described later, but in this figure, the axis of the coil 3 shown hypothetically is 1
It is shown as a configuration in which the magnetic flux linkage state can be varied by changing the direction of the magnetic flux. Next, reference numeral 4 indicates a receiver, and this receiver 4 measures the magnitude of 1i11 at each position in the horizontal direction, and if it is possible to measure the magnetic field distribution, it can be used in various ways as shown in the examples described later. However, in this figure, the configuration is such that the magnetic field is measured at each position by moving in the horizontal direction. Therefore, as shown in FIG. 1(a), the axis 1 of the coil 3
is on the right side of the underground object 0°0' in the figure, coil 3
The magnetic flux φ from φ interlinks with both underground objects o and o' in the same direction, and at the time shown in the figure, an induced current flows from the front side to the back side of the page, and the magnetic field M' Occur. In the state shown in the figure, the induced current flowing through the underground object 0 is larger, so the distribution of the magnetic field M' becomes a distorted elliptical cylinder shape, which deviates greatly from the cylindrical magnetic field distribution, and also in the vertical direction in the figure. It is not line symmetrical with respect to the straight line.

Next, as shown in Fig. 1(b), when the axis of the coil 3 is located between the underground objects 0 and 0', the magnetic flux φ from the coil 3 is
Since the underground objects o and o' are interlinked in opposite directions, at the time shown in the figure, the underground objects O are connected from the front side to the back side of the page, and the underground object O' An induced current flows in the opposite direction. Therefore, the distribution of the magnetic field M' due to the induced current deviates greatly from the cylindrical magnetic field distribution.

Then, from the state of FIG. 1(a) to the state of FIG. 1(b), or from the state of FIG. 1(b) to the state of FIG. 1(a).
By changing the magnetic flux linkage state in the direction of the state shown in Fig. 1 (C
), when the axis l of the coil 3 is directed toward the underground object O', in this state of magnetic flux linkage, no induced current is generated in the underground object O', and no induced current is generated in the underground object O'. An induced current flows from the front side of the page to the back side. Therefore, a magnetic field M is generated only around the underground object 0, and the distribution of this magnetic field M becomes the cylindrical magnetic field distribution described above. As described above, the above-ground corresponding position p and depth of the target underground object 0 can be detected with high accuracy from this cylindrical magnetic field distribution.

Therefore, the receiver 4 measures the magnetic field distribution, and while detecting the deviation between the measured magnetic field distribution and the cylindrical magnetic field distribution, the transmitter 2 changes the magnetic flux linkage state with respect to the underground object 0°0'. , In order to minimize this deviation, the transmitter 2 is set to 111iL, . . . , in a state as shown in FIG. It can be detected with high accuracy.

In this way, the present invention requires an operation to detect the deviation between the measured magnetic field distribution and the cylindrical 1i111 distribution at location r, but such deviation can be easily detected by the following method. .

First, the second method is to measure and detect whether the ratio of the horizontal magnetic field component to the vertical magnetic field component at each horizontal position changes linearly with the position. 9th
Figure (a) shows the ratio of the horizontal magnetic field component to the vertical magnetic field component shown in Figures 7 (a) and (b), respectively, expressed with respect to position, and Figure 9 (b) ) is shown in Figure 8(a)
, (b), the value of the ratio is similarly expressed with respect to the position.

As can be seen from this figure, in a cylindrical magnetic field distribution, the value of the ratio changes linearly with position, whereas in a magnetic field distribution that deviates from this cylindrical magnetic field distribution, , it deviates from the linear change shown by the dotted line in the figure.

From this, for example, a straight line is fitted using a method such as the least squares method from the ratio of the horizontal and vertical components of the measured magnetic field distribution measured by the receiver 4, and the sum of squares of the residual between the approximated straight line and the measured value is calculated. Therefore, it is possible to set the amount corresponding to the deviation from the cylindrical magnetic field distribution, and it is easy to control the transmitter 2 so as to minimize the amount corresponding to the deviation.

Next, another method for detecting deviation is to measure and detect whether the absolute value of the horizontal or vertical magnetic field component at each horizontal position is line symmetrical with respect to a certain position. can also be applied. This is because, as mentioned above, in the state shown in Figure 1(a), the distribution of the magnetic field M' has a distorted elliptical cylinder shape, and is not symmetrical with respect to the appropriate straight line in the vertical direction in the figure. On the other hand, in a cylindrical shape, the line symmetry is utilized.

(Example) Next, the present invention will be explained in detail.

First, FIG. 2 schematically shows the configuration of an embodiment of the transmitter 2 and receiver 4 applied to the present invention. In this embodiment, a transmitter 2 is provided with a pair of coils 3a and 3b whose axes are oriented vertically and horizontally with respect to the earth's surface, and the magnitude of alternating current flowing through the pair of coils 3a and 3b is changed, respectively. This changes the state of magnetic flux linkage to underground objects. Reference numerals 5a and 5b are variable alternating current sources that can vary the magnitude of current, and this variable alternating current power source 5a.

5b is controlled by the information reception control section 6.

In this configuration, a magnetic field is generated from the coil 3a with the axis 11 directed in the vertical direction, as shown in FIG. 3(a), and a magnetic field is generated from the coil 3b with the axis J12 directed in the horizontal direction.
A magnetic field is generated as shown in b).

When these two magnetic fields are superimposed, it becomes a composite magnetic field as shown in FIG. , 3b can be changed by changing the current flowing through them, and thus the state of magnetic flux linkage to the underground object can be changed as described above.

Next, the receiver 4 includes a magnetic sensor 6 for measuring the magnitude of the magnetic field, and processes the signal of this magnetic sensor 6 to detect the deviation between the measured magnetic field distribution and a predetermined cylindrical magnetic field distribution. A signal processing section 8 is provided which transmits the information to the information transmitting section 7 and calculates the position of the underground object. The information transmitting section 7 transmits the signal from the signal processing section 8 to the information receiving control section 6 of the transmitter 2 via a medium 9 such as a radio wave or an optical fiber. In the embodiment, the magnetic sensor 6 includes a plurality of sensor sections St corresponding to a plurality of positions in the horizontal direction.

S2. ..., Sn is provided and the magnetic field distribution is measured by the plurality of sensor sections, but as mentioned above, the magnetic field distribution is measured by moving a single sensor section or a small number of sensor sections in the horizontal direction. You can also do that.

In addition, the above-mentioned energization of each coil 3a, 3b can be carried out continuously and simultaneously, or it can be carried out intermittently or in a time-sharing manner. can.

Next, FIG. 4 shows another embodiment of the transmitter 2 applied to the present invention, and in this embodiment, the transmitter 2 includes:
A coil 3 that can be rotated 5 times around a horizontal axis 10 is provided, and by rotating this coil 3, the direction of the axis A is changed and the underground J! ]! This changes the state of magnetic flux linkage to the facility.

This coil 3 is operated by a rotating device 11 controlled by the information reception control section 6. The configuration of the receiver 4 in FIG. 4 is the same as the configuration in FIG. 2, so a description thereof will be omitted.

Next, FIG. 5 shows still another embodiment of the transmitter 2 applied to the present invention, and in this embodiment, the transmitter 2
A coil 3 is provided which is movable laterally with respect to the ground surface,
By moving this coil 3 in the lateral direction, the axis A is moved, thereby changing the state of magnetic flux linkage with respect to the underground object. In the figure, only the coil 3 whose axis is oriented in the vertical direction is shown, but it goes without saying that the configuration of the above-mentioned 2* embodiment may be applied to this coil 3. In the figure, the coil 3 is installed on a base 13 that is movable along a guide member 12, and this base 1
3 is moved by a moving device 14 controlled by an information reception control section 6.

(Effects of the Invention) As described above, the present invention provides electrically conductive underground j! ! While applying the induction method, in which an induced N current is passed through the facility, a receiver detects the distribution of the magnetic field generated around the underground facility due to this induced current, and the position of the underground facility is detected. By eliminating the influence of other underground objects close to the target underground object, it is possible to detect the position of the target underground object with high precision, which was difficult with the direct method. This has the effect of allowing highly accurate position detection even for underground objects with no exposed parts above ground. Thus, the present invention can improve work efficiency, reduce costs, and ensure safety in maintenance and replacement work of gas pipes, water pipes, etc.

[Brief explanation of the drawing]

FIGS. 1(a), (b), and (c) are schematic explanatory diagrams representing the basic concept of the present invention, and FIG. 2 is a system explanation schematically representing an embodiment of the apparatus applied to the present invention. Figure, Figure 3 (
a), (b), and (c) are explanatory diagrams schematically representing the operation of the transmitter in the device of FIG. 2, and FIG. 4 and FIG. Fig. 6 (a) and (b) are system explanatory diagrams schematically representing the embodiment, and Fig. 7 are schematic explanatory diagrams of magnetic field distribution in the case of a single underground object and in the case of multiple underground objects. (a) and (b) are explanatory diagrams showing the horizontal and vertical components of the III field weight distribution of No. 6 @ (a) in correspondence to the horizontal position, and Fig. 8 (a) and (b) HaruW
Figure 6 (b) f) Magnetic jj1 distribution f) An explanatory diagram showing the horizontal and vertical components in correspondence with the horizontal position, Figures 9 (a) and (b) are similar to Figures 7 and 9, respectively. FIG. 9 is an explanatory diagram showing the ratio of the horizontal component to the vertical component of the magnetic field distribution shown in FIG. 8 with respect to position. Code 0.0'...underground object, M, M'...magnetic field,
1... Ground, 2... Transmitter, 3... Coil, 4...
... Receiver, 5... Variable AC current source, 6... Information reception control section, 7... Information transmission section, 8... Signal processing section,
9... Medium, 1o... Shaft, 11... Rotating device, 1
2... Guide member, 13... Base, 14... Moving device.

Claims (7)

[Claims] (1) An induced current is sent from a transmitter to a conductive underground object by electromagnetic induction, and a receiver detects the distribution of the magnetic field generated around the underground object due to this induced current, and the underground object is installed. In the method of detecting the position of an object, the transmitter has a variable magnetic flux linkage state with respect to the underground object, measures a magnetic field distribution with the receiver, and compares this with a predetermined cylindrical magnetic field distribution. The magnetic flux linkage state is changed while detecting the deviation, and the transmitter is adjusted to minimize this deviation, and the position of the target underground object is detected from the measured magnetic field distribution at this time. A magnetic position detection method for underground objects characterized by (2) The transmitter is equipped with a pair of coils whose axes are oriented perpendicularly and horizontally to the earth's surface, and an alternating current source that flows current through each coil, and determines the magnitude of the alternating current that flows through the pair of coils. The method for detecting the magnetic position of an underground object according to claim 1, characterized in that the state of magnetic flux linkage with respect to the underground object is changed by respectively changing the . (3) The transmitter is equipped with a coil that can be rotated around a horizontal axis and an alternating current source that supplies current to the coil, and by rotating the coil, magnetic flux linkage with underground objects can be reduced. A method for detecting the magnetic position of an underground object according to claim 1, characterized in that the magnetic position of an underground object is changed. (4) The transmitter is equipped with a coil that can be moved laterally along the ground surface and an alternating current source that supplies current to the coil, and by moving the coil laterally, magnetic flux chains to underground objects can be created. A method for detecting the magnetic position of an underground object according to claim 1, characterized in that the magnetic position of an underground object is changed. (5) The deviation between the measured magnetic field distribution and the predetermined cylindrical magnetic field distribution is
Claim 1, characterized in that the method detects by measuring whether the ratio of the horizontal magnetic field component to the vertical magnetic field component at each position in the horizontal direction changes linearly with respect to the position. Magnetic position detection method for underground objects described above (6) The deviation between the measured magnetic field distribution and the predetermined cylindrical magnetic field distribution is
Claim 1, characterized in that it is detected by measuring whether the absolute value of the horizontal or vertical magnetic field component at each position in the horizontal direction is line symmetrical with respect to a certain position. magnetic position detection method for underground objects (7) Claim 1, characterized in that the receiver comprises a magnetic sensor that detects magnetic field components in the horizontal and vertical directions with respect to the earth's surface, and a signal processing circuit that processes the output signal. Magnetic position detection method for underground objects described above