JPH10197648A - Position survey device for underground pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exactly survey the position of an underground pipe with a pipe locator by reducing magnetic noise effects. SOLUTION: In a gas pipe 12 buried underground, alternating current is supplied from an oscillator 13 via a cable 14. Around the gas pipe 12, a magnetic field 16 formed by magnetic line of force 12a of concentric circle is supplied in accordance with the alternating current signal generates. A detection coil 17 for detecting the magnetic field 16 on the ground 11 is covered with a cylindrical magnetic shield 20. Thus, the magnetic line of force 14a generated around the cable 14 and the like cannot easily invade inside the detection coil 17 due to the magnetic shield 20. As the detection coil 17 detects only the magnetic field 16 from the gas pipe 12 and so exact buried position can be surveyed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for exploring a pipe such as a gas pipe buried underground from the surface of the ground.

[0002]

2. Description of the Related Art Metal pipes such as gas pipes buried underground and synthetic resin pipes having electrical insulation are often buried in public lands such as roads. Since the work is performed by another entity, it is necessary to accurately search the buried position from the ground surface to avoid damage.

FIG. 5 shows a conventional structure for exploring an underground pipe. An AC signal is sent from the transmitter 3 to the gas pipe 2 in the direction of the center axis of the gas pipe 2 to search the gas pipe 2 buried underground from the ground surface 1. The frequency of the AC signal is, for example, about 2 kHz to 100 kHz. In order to supply the output of the transmitter 3 to the gas pipe 2, cables 4, 5 and the like are used. When an AC signal current flows through the gas pipe 2 via the cables 4 and 5, a magnetic field 6 formed by concentric magnetic force lines around the central axis of the gas pipe 2.
Occurs. In order to search the position of the gas pipe 2 underground on the ground surface 1, a detection coil 7 for detecting the magnetic field 6 is used. The change in the magnetic field 6 detected by the detection coil 7 is
A cathode ray tube (abbreviated as "CRT") or a liquid crystal display (abbreviated as "L
CD "). When the worker moves the detection coil 7 while walking on the ground surface 1 and searches for a position where the strength of the magnetic field 6 is highest, it is found that the gas pipe 2 is buried in the ground below that position. Such a position detecting device is also called a pipe locator or the like and is widely used.

When the gas pipe 2 is a metal pipe such as a steel pipe having conductivity, an alternating current is directly passed from the transmitter 3. When the gas pipe 2 is an electrically insulating synthetic resin pipe such as polyethylene, the pipe may be buried together with the pipe with a conducting wire such as a locating wire attached when the gas pipe 2 is laid in advance.

[0005]

In a configuration for exploring an underground pipe as shown in FIG. 5, a magnetic field 6 is generated in a gas pipe 2 buried underground, and a magnetic field 6 is generated by a detection coil 7. The position search of the gas pipe 2 is performed by detecting the intensity distribution and detecting the peak. However, the magnetic field 6
, It is necessary to guide an alternating current from the transmitter 3 to the gas pipe 2 via, for example, the cables 4 and 5.
Since a magnetic field is generated in the surrounding space also in the cables 4 and 5 used to guide the alternating current, the detection coil 7 is connected to the gas pipe 2.
There is a possibility that not only the magnetic field 6 from the outside but also the magnetic field generated around the cables 4 and 5 may be detected. Also,
If a guardrail or the like is provided on a road on which the gas pipe 2 is searched, an induced magnetic field is generated by the magnetic field 6 around the gas pipe 2 and the magnetic field generated around the cables 4 and 5. The detection coil 7 includes not only a magnetic field 6 from the gas pipe 2 but also a magnetic field generated around the cables 4 and 5,
It is affected by the induced magnetic field generated from guardrails. If the detection coil 7 detects not only the magnetic field 6 around the gas pipe 2 but also other magnetic fields, it causes magnetic noise and the inspection accuracy of the position of the gas pipe 2 is deteriorated.

An object of the present invention is to reduce the influence of magnetic noise from the surroundings when detecting a magnetic field generated from an underground pipe to be searched, and to accurately detect the position of the underground pipe. It is an object of the present invention to provide a device for locating underground pipes which can be buried underground.

[0007]

SUMMARY OF THE INVENTION The present invention is directed to an apparatus for conducting an AC current to an underground pipe or the like, detecting a generated magnetic field on the surface of the earth, and performing a position search, having a central axis, A magnetic field detection winding includes a coil wound around a central axis, and a magnetic shield surrounding the coil while releasing both ends of the central axis. is there. According to the present invention, if a magnetic field exists such that lines of magnetic force pass alternately in the direction of the center axis of the coil, a signal of the frequency of the magnetic field is induced in the coil. If the coil is surrounded by a magnetic shield while releasing both ends of the center axis, the magnetic shield prevents magnetic lines of force that pass in a direction different from the center axis direction of the coil whose ends are released from passing through the coil. Then, only the lines of magnetic force from the underground pipe can pass through the coil. Therefore, even if there is a magnetic noise source around the surface of the ground where the position of the underground pipe or the like is to be searched, an accurate position search of the underground pipe can be performed.

[0008]

FIG. 1 shows a schematic configuration of an apparatus for locating an underground pipe according to an embodiment of the present invention.
An alternating current is supplied from a transmitter 13 via a cable 14 to search for a gas pipe 12 buried underground from the ground surface 11. The frequency of the alternating current is 2 kHz to 100
It is about kHz. If a means for discriminating from commercial AC is provided, a lower frequency can be used. Gas pipe 1
Reference numeral 2 denotes a steel pipe, and when an alternating current flows in the axial direction, a magnetic field 16 is formed by concentric lines of magnetic force 12a. When the magnetic field 16 is detected by the detection coil 17 on the surface 11, the gas pipe 12
It can be seen that is buried. The detection coil 17 supplies the detected signal to the display device 18 to display the detected intensity of the magnetic field 16. The detection coil 17 is provided at the tip of the rod-shaped receiving antenna 19 as in FIG. 5, and is configured so as to facilitate the exploration of the position of the gas pipe 12 while the operator moves on the ground surface 11.

In the search for the position of the gas pipe 12 by the pipe locator, a magnetic field is generated around the cable 14 for supplying an AC signal from the transmitter 13 to the gas pipe 12 by the concentric magnetic field lines 14 a, and the detection coil 17. Easy to enter as magnetic noise. In the present embodiment, the periphery of the detection coil 17 is covered with a cylindrical magnetic shield 20 so that magnetic noise from a direction different from the direction of the magnetic field 16 from the gas pipe 12 hardly enters the inside of the detection coil 17. ing. The shapes of the magnetic shield 20 and the detection coil 17 are determined so that magnetic noise is reduced and detection sensitivity of a target magnetic field is improved.

FIG. 2 shows a schematic electrical configuration of the position locating device of the embodiment of FIG. Inside the display device 18,
An amplifier 21 for amplifying a detection signal from the detection coil 17;
From the signals amplified by the amplifier 21, the transmitter 13
And a display 23 for displaying the intensity of the signal selected by the filter 22. The AC signal from the transmitter 13 is electrically connected to the pipe system of the gas pipe 12 via the cables 14 and 15, for example, to a pipe or the like that is exposed to a gas meter or the like on the ground surface to be supplied to an end user. Connected.

FIG. 3 shows the effect of using the magnetic shield 20 in this embodiment. If the magnetic shield 20 is not used, the intensity of the magnetic field detected by the detection coil 17 peaks at a position shifted from a position immediately above the gas pipe 12 as indicated by a virtual line due to a magnetic field from the cable 14. By covering the detection coil 17 with the magnetic shield 20, the detection intensity is maximized immediately above the buried position of the gas pipe 12 as shown by the solid line, and the buried position can be accurately searched.

FIG. 4 shows the shapes of the detection coil 17 and the magnetic shield 20. The detection coil 17 is a solenoid wound cylindrically around the center axis, and the magnetic shield 20 has a cylindrical shape that covers the outside of the detection coil 17. The magnetic shield 20 is formed of, for example, a ferromagnetic material having electric insulation such as ferrite. Magnetic shield 2
Since 0 is cylindrical, both ends in the axial direction are open. Therefore, the magnetic field lines in the axial direction can penetrate inside. The lines of magnetic force in the direction intersecting with the axial direction pass through the material of the magnetic shield, and do not easily enter the inside. Therefore, if the detection coil 17 is arranged inside the magnetic shield 20,
Although the magnetic field through which the magnetic field lines pass in the direction of the central axis can be detected, the magnetic field in which the magnetic field lines pass through in a direction intersecting with the central axis direction is hardly detected. By using such a magnetic shield 20, the influence of magnetic noise other than the magnetic field 16 from the gas pipe 12 to be located can be reduced, and more accurate location of the gas pipe 12 can be performed. . The ferrite of the magnetic shield may be a hard ferrite formed by sintering, or a soft ferrite mixed into a powder of synthetic resin or rubber. Instead of ferrite, a magnetic shield can be formed by winding another ferromagnetic material such as an iron plate.

In the above description of the embodiment, a case is described in which the gas pipe 12 is made of metal and can be supplied with an AC signal. However, in the case where the gas pipe 12 is made of synthetic resin and is electrically insulating. By providing a locating wire along the gas pipe 12 in advance, an accurate position search can be performed as in the case of the metal gas pipe 12. Further, not only the gas pipe 12 but also other types of underground pipes such as water pipes can be accurately searched.

[0014]

As described above, according to the present invention, by covering the periphery of a coil for detecting the magnetic field for detecting the position of an underground pipe with a magnetic shield, magnetic noise around the location where the search is performed is obtained. Even if there is a source, the position of the underground pipe can be accurately probed.

[Brief description of the drawings]

FIG. 1 is a simplified cross-sectional view showing a schematic configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic electrical configuration of the embodiment of FIG.

FIG. 3 is a graph showing the effect of the embodiment of FIG.

FIG. 4 is an exploded perspective view of the detection coil 17 and the magnetic shield 20 of the embodiment of FIG.

FIG. 5 is a simplified cross-sectional view showing a conventional method for detecting the position of an underground pipe.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Ground surface 12 Gas pipe 12a Magnetic field line 13 Transmitter 14, 15 Cable 16 Magnetic field 17 Detection coil 20 Magnetic shield

Claims (1)

[Claims] 1. An apparatus for conducting an AC current to an underground pipe or the like and detecting a generated magnetic field on the surface of the earth to perform position exploration, wherein the apparatus has a central axis, and a magnetic field detecting winding has a central axis. An underground pipe position locating device comprising: a coil wound around the coil; and a magnetic shield surrounding the coil while releasing both ends of a central axis.