JPH04313097A - Measuring device for position of buried cable and measuring method - Google Patents

Abstract

PURPOSE:To obtain a measuring device for the position of a buried cable and the measuring method by which one measuring person can perform transmitting and receiving operations. CONSTITUTION:Two transmitting coils 3a and 3b having the same windings are arranged in parallel and differentially connected. A transmitting circuit 5 supplies AC signals to the transmitting signals to the transmitting coils 3a and 3b. A receiving coil 4 which forms pairs with the transmitting coils 3a and 3b is further provided. A receiving circuit 6 amplifies the transmitted signals which are received through a buried cable 1 and the transmitted coils 3a and 3b. An operating circuit 7, a display device 8 and an input part 9 are provided. Thus, the buried position of the buried cable 1 on the horizontal palne is searched, and the buried depth is measured.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention involves passing a signal current of a predetermined frequency indirectly through a buried cable or metal conduit (hereinafter simply referred to as a cable) from a transmitting coil, and generating an alternating magnetic field generated from the cable. The present invention relates to a buried cable position measuring device and measuring method that searches for the buried position of a cable and measures the buried depth by detecting the buried cable on the ground surface with a receiving coil.

0002

[Prior Art] Conventional buried cable position measuring instruments have separate transmitters and receivers, and when searching for cables,
First, the transmitter was installed on the ground directly above the buried cable to be searched for, and then the position was measured by detecting the magnetic field from the cable with a receiver at a location far from the transmitter.

0003

[Problem to be solved by the invention] However, at first,
Since the target cable location is unknown, the transmitter is temporarily installed in a position thought to be directly above it, and then the transmitter is moved to an appropriate position based on the search results by the receiver. Ta. For example, after temporarily installing the transmitter, you can search for the point where the receiver has the maximum sensitivity, and then install the transmitter there. This was done by moving the receiver and installing it in a location where the reception sensitivity would be even higher, which was essential in order to avoid accidentally searching for other buried objects. In addition, in normal cable position measurement, the route of the cable is often tracked from the ground, and the measurer is forced to move away from the transmitter, so he or she may act as a watchman for the transmitter or change the transmission output during measurement. For example, a person was required to be near the transmitter. Furthermore, buried objects parallel to the target cable,
For example, it is often necessary to check the presence and location of metal pipes such as gas pipes before excavating the ground, and it is extremely difficult to conduct searches that include these quickly and accurately unless the conditions are very good. There was a drawback.

0004

[Means for Solving the Problems] The present invention provides a buried cable position measuring device using electromagnetic induction, in which two sets of coils whose coil axes are orthogonal to the ground are arranged so that the centers of each coil are at the same height from the ground. transmitting coils disposed at predetermined intervals and differentially connected; a transmitting circuit connected to the transmitting coils and supplying an alternating current signal of a predetermined frequency to the transmitting coils; and a coil axis parallel to the ground and the transmitting coils. a set of receiving coils disposed on a straight line at the same height as the height from the ground of each center of the transmitting coils, and arranged so that the centers of the coils are equidistant from each center of the transmitting coils; a receiving circuit that amplifies the transmitted signal from the transmitting coil received via a connected underground cable buried underground; an arithmetic circuit that calculates the cable position from the receiving circuit output; and an operating circuit that operates the arithmetic circuit. and a display for displaying the results of arithmetic processing, and detects the magnetic field generated from the cable by the receiving coil due to the induced current generated in the cable by the magnetic field from the transmitting coil, thereby detecting the horizontal surface of the cable. In addition to the buried cable position measuring device that searches for the upper position, the transmitting coil and the receiving coil are rotated together by a predetermined angle around a straight line parallel to the coil axis of the receiving coil in the buried cable position measuring device, and before and after rotation. A buried cable position measuring method for measuring the buried depth of a cable from the voltage induced in a receiving coil.

[0005]

According to the buried cable position measuring device of the present invention, the magnetic field created by the differentially connected transmitting coils is a composite of magnetic fields of equal magnitude and opposite direction generated from each transmitting coil. Therefore, as a result of the magnetic fields generated from each transmitting coil canceling out each other, there is a point where the strength of the magnetic field becomes zero. By using the receiving coil to detect only the magnetic field generated from the cable due to the induced current generated in the cable by the magnetic field, it becomes possible to measure the horizontal position of the buried cable. The buried cable position measuring device configured in this way has
Because the transmitting coil and receiving coil are moved simultaneously to search, the difference in the received signal depending on whether it is directly above the cable or not is greater than with conventional measuring instruments, making it possible to search for the buried position of the cable with great accuracy. . Further, according to the buried cable position measuring method of the present invention, the transmitting coil and the receiving coil are rotated together by a predetermined angle about a straight line that is parallel to the coil axis of the receiving coil and passing through the two sets of coil axes of the transmitting coil. , it becomes possible to measure the buried depth of the buried cable from the change in voltage induced in the receiving coil before and after rotation without being affected by the direct magnetic field from the transmitting coil.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the structure of an embodiment of the present invention will be explained with reference to the drawings. The two sets of transmitting coils 3a and 3b are differentially connected to the transmitting circuit 5, and the receiving coil 4 is connected to the receiving circuit 6.
The arithmetic circuit 7 is connected to a display 8 for displaying numerical values of the calculation results, and an input section 9 for setting specific numerical values and the like required during calculation. In this case, the transmitting coils 3a, 3b are arranged perpendicularly to the ground plane 2 at a distance d apart from each other and face the cable 1 buried underground, as shown in FIG. When the output of the transmitting circuit 5 is input to the differentially connected transmitting coils 3a and 3b, the transmitting coils 3a and 3b generate magnetic fields of equal magnitude and opposite direction, and the combined magnetic field 10 causes the cable 1 to An induced current i flows through. The voltage induced in the receiving coil 4 by the magnetic field 11 generated by the induced current i is selected and amplified by the receiving circuit 6 with noise signals and the like being appropriately cut off, converted into numerical values by the arithmetic circuit 7, and displayed on the display 8.

Next, a case will be described in which the magnetic field generated by the transmitting coils 3a and 3b at one point on the cable is equal in distance from the position directly above the cable 1 to both transmitting coils 3a and 3b. FIG. 3 shows the magnetic field H generated at a point on the cable 1 by one transmitting coil 3a. The sizes of the magnetic poles generated at both ends of the transmitting coil 3a are +qm and -qm, the length of the transmitting coil 3a is l, the vertical distance between the lower surface of the transmitting coil 3a and the cable 1 is h, and the distance between the transmitting coil 3a and the cable 1 is If the horizontal distance is d/2, the magnetic field H is a combination of the magnetic field H1 generated by +qm and the magnetic field H2 generated by -qm.

[0008]

[Math 1]

[Math 2]

[Math 3]

[Math 4]

##EQU00005## FIG. 4 shows the magnetic field H' generated at a point on the cable 1 by the other transmitting coil 3b. Transmission coil 3b
The respective sizes of the magnetic poles generated at both ends of +qm, -q
m, the length of the transmitting coil 3b is l, the vertical distance between the transmitting coil 3b and cable 1 is h, the transmitting coil 3b and cable 1
The horizontal distance of is the same as that of the transmitting coil 3a, and the magnetic field H' generated by this is +qm of the transmitting coil 3b.
The magnetic field H1' generated by qm and the magnetic field H2' generated by -qm are combined.

[0009]

[Math 6]

[Math 7]

[Math. 8]

[Math. 9]

[Math. 10]

[Equation 11] Here, the magnetic field H0 generated at the point of cable 1 is the magnetic field H
and the magnetic field H', where the magnetic field H2
The y-direction components of the magnetic field H1' and H1' are equal and have opposite directions, so they cancel each other out. Similarly, since the y-direction component of the magnetic field H1 and the magnetic field H2' is canceled out, the magnetic field H0 is a magnetic field having only the X-direction component. Due to the above magnetic field H0, the magnetic flux Φ interlinks with the cable 1, so according to Faraday's law,

0010

A voltage e is induced, and a current i flows. Next, a description will be given of the magnetic field generated at point A, which is located at the same distance from each magnetic pole of the transmitting coils 3a and 3b. FIG. 5 shows the magnetic field H generated at point A by one transmitting coil 3a. Assuming that the sizes of the magnetic poles generated at both ends of the transmitting coil 3a are +qm and -qm, respectively, and the distance from each magnetic pole to point A is r, the magnetic field H is the magnetic field H1 generated by +qm and -
It is a composite of the magnetic field H2 generated by qm.

[0011]

[Math. 13]

[Math. 14]

[Formula 15] FIG. 6 shows the magnetic field H' generated at point A by the other transmitting coil 3b. The respective sizes +qm, -qm of the magnetic poles generated at both ends of the transmitting coil 3b, and the distance r from each magnetic pole to point A are the same values as in the case of the transmitting coil 3a, and the magnetic field H' generated by this is the same as that of the transmitting coil. 3b
The magnetic field H1' generated by +qm and the magnetic field H2' generated by -qm are combined.

0012

[Math. 16]

[Math. 17]

[Math. 18]

[Equation 19] Here, the magnetic field H0 generated at the point of cable 1 is the magnetic field H
and the magnetic field H', where the magnetic field H1
Since the x-direction component and the z-direction component of the magnetic field H2 are equal and opposite in direction, they are canceled out, leaving only the y-direction component. Moreover, since the same can be said of the magnetic field H1' and the magnetic field H2', the magnetic field H' has only the y-direction component. Further, since the magnetic fields H and H' are equal in magnitude and opposite in direction and cancel each other out, there is no magnetic field generated by the transmitting coils 3a and 3b at point A.

[0013] Such a point exists on a straight line on a horizontal plane that includes the centers of each of the transmitting coils 3a and 3b. Therefore, if the receiving coil 4 is arranged so that the coil axis is perpendicular to the straight line, parallel to the ground, and the center of the coil is on the straight line, the differentially connected transmitting coils 3a and 3b are connected to the cable 1.
An induced current can be passed through the receiving coil 4, and the receiving coil 4 can detect the magnetic field from the cable 1 and measure the position of the cable 1 without receiving a direct magnetic field from the transmitting coils 3a and 3b. As a result, the position directly above the cable 1 can be found by finding the point where the received signal is maximum, and in the buried cable position measuring device configured in this way, the transmitting coils 3a, 3b and the receiving coil 4 are located directly above the cable 1. Since the transmission coils 3a and 3b move simultaneously with respect to the cable 1, the magnetic field generated by the transmitting coils 3a and 3b at the cable 1 position becomes stronger at a position close to the cable 1, and as a result, the induced current flowing through the cable 1 increases and the magnetic field generated from the cable 1 also becomes stronger. In addition, in this state, the receiving coil 4 is also close to the cable 1, so the received signal also increases.The synergistic effect of transmission and reception emphasizes the magnitude of the received signal due to the movement of the measuring instrument, making position detection easy and reliable. effective.

Next, using this measuring device, the cable 1
This section explains how to measure the burial depth of. FIG. 8 is a side view. Without changing the positional relationship between the coils shown in FIG. 3, the transmitting coils 3a, 3b and the receiving coil 4 are integrated by an angle θ clockwise in the figure, with the straight line passing through the centers of both transmitting coils 3a, 3b as the axis. In this state, if the vertical distance from the bottom surface of the transmitting coils 3a, 3b to the cable 1 is h, each magnetic pole is connected to the cable 1.
The magnetic field generated at each position is

[0015]

[Math. 20]

[Math. 21]

[Math. 22]

[Math. 23]

[Math. 24]

[Math. 25]

[Math. 26]

[Formula 27] FIG. 9 shows this in a view from the cross-sectional direction of the cable. In this case, the relationship between l Sinθ and the buried depth h of cable 1 is

[0016]

[Math. 28] Then, the magnetic field H0 at the point of cable 1 is

0
017]

##EQU29## As in the case of FIG. 2, there is a magnetic field only in the X direction. An induced current i corresponding to this magnetic field H0 flows through the cable 1, and the receiving coil 4

[0018]

A voltage E1 of E1 is induced. Next, as shown in FIG. 10, the transmitting coils 3a, 3b and the receiving coil 4 are rotated by an angle of 2.theta. counterclockwise in the figure. As a result, the transmitting coil 3a
, 3b make an angle θ with a straight line perpendicular to the ground. The cross-sectional view at this time is shown in FIG. 11, and the magnetic field generated by each magnetic pole of the transmitting coils 3a and 3b at the cable 1 position is shown in FIG.
0 and Figure 11.

[0019]

[Math. 31]

[Math. 32]

[Math. 33]

[Math. 34] Therefore, the composite magnetic field H0' is also

[0020]

[Formula 35] An induced current i flows in the cable 1 due to the magnetic field H0', and as a result, an induced current i flows in the receiving coil 4.

[0021]

[Formula 36] K is induced by voltage E2, which is a proportionality constant. From E1 measured earlier and this E2, h can be determined as follows.

[0022]

##EQU00003## From this h, it is possible to calculate the burial depth up to the cable 1.

[0023]

[Effects of the Invention] According to the buried cable position measuring device of the present invention, since the transmitter and receiver, which were conventionally separated, can be integrated, the transmitting and receiving operation can be performed by one measuring person. As a result, the position of buried cables can be measured quickly and accurately, and the depth of buried cables can also be easily determined by measuring the magnetic field from the cable at two levels without changing the cable induced current. There are effects that can be measured.

[Brief explanation of drawings]

FIG. 1 is a perspective view including a block diagram showing the structure of a buried cable position measuring device according to an embodiment of the present invention.

[Fig. 2] Buried cable 1 and transmitting coil 3a of this embodiment,
3b is a sectional view illustrating the relationship between the receiving coil 3b and the receiving coil 4. FIG.

FIG. 3 is a cross-sectional view illustrating the magnetic field generated at the position of the cable 1 by each magnetic pole of the transmitting coils 3a and 3b of this embodiment.

FIG. 4 is a cross-sectional view illustrating the magnetic field generated at the position of the cable 1 by each magnetic pole of the transmitting coils 3a and 3b of this embodiment.

FIG. 5 is a perspective view illustrating magnetic fields generated at positions equal distance from the magnetic poles of each transmitting coil 3a, 3b in this embodiment.

FIG. 6 is a perspective view illustrating magnetic fields generated at positions equally distanced from the magnetic poles of each transmitting coil 3a, 3b in this embodiment.

FIG. 7 is a plan view showing the positional relationship between transmitting coils 3a, 3b and receiving coil 4 of this embodiment.

FIG. 8 is a cross-sectional view illustrating the relationship between the buried cable 1, transmitting coils 3a, 3b, and receiving coil 4 during depth measurement in this embodiment.

FIG. 9 Transmission coils 3a and 3b during depth measurement in this embodiment
FIG. 2 is a cross-sectional view illustrating the magnetic field generated by each magnetic pole at the position of the cable 1. FIG.

FIG. 10 is a cross-sectional view illustrating the relationship between the buried cable 1, transmitting coils 3a, 3b, and receiving coil 4 during depth measurement in this embodiment.

FIG. 11: Transmission coils 3a, 3 during depth measurement in this embodiment
FIG. 3 is a cross-sectional view illustrating the magnetic field generated by each magnetic pole at the position of the cable 1 in FIG.

[Explanation of symbols]

1 Cable 2　Ground 3a Transmission coil 3b Transmission coil 4 Receiving coil 5 Transmission circuit 6 Receiving circuit 7 Arithmetic circuit 8 Display circuit 9 Input section

Claims (2)

[Claims] Claim 1: Two sets of coils with the same number of turns are connected in a differential manner, separated by a predetermined period of time and arranged in parallel, and the two sets of differentially connected coils are placed at the same height from the ground surface in a state perpendicular to the ground. a transmitting coil that can be installed at a position; a transmitting circuit connected to the transmitting coil that supplies an alternating current signal of a predetermined frequency to the transmitting coil; Located perpendicularly to the two sets of the transmitting coils on orthogonal center lines, and installed at the same height from the ground surface with the two sets of transmitting coils perpendicular to the ground at the same height from the ground surface. a possible set of receiving coils, a receiving circuit connected to the receiving coil and amplifying a transmitted signal from the transmitting coil received via a buried cable buried underground, and an output from the receiving circuit. a calculation circuit for calculating the position of the buried cable buried underground in A buried cable position measuring device that searches for a buried position of a buried cable on a horizontal plane using the maximum output from the receiving coil by detecting, with the receiving coil, a magnetic field generated from the buried cable due to an induced current generated in the buried cable. 2. In a buried cable position measuring device, the transmitting coil and the receiving coil are rotated together by a predetermined angle about a straight line that is parallel to the coil axis of the receiving coil and passes through the two sets of coil axes of the transmitting coil, and 2. The buried cable position measuring method according to claim 1, wherein the buried depth of the buried cable is measured from changes in voltage induced in the transmitting coil before and after.