JPS63313087A - Method for detecting buried metallic pipe or the like - Google Patents

Abstract

PURPOSE:To eliminate the influence of the magnetic field of a main pipe even nearby a branch point of a duct by arranging two magnetic sensors which have equal characteristics coaxially, putting their outputs together differentially, and performing measurement so that sensitivity is high and an error is small. CONSTITUTION:A high-frequency current (10-100kHz) is supplied to a buried metallic pipe 1, etc., directly or inductively and a generated electromagnetic wave is detected by using two magnetic sensor coils L1 and L2. The sensor coils L1 and L2 which have equal characteristics are arranged coaxially at an interval (d) and connected differentially. Those sensor coils L1 and L2 are moved over the buried metallic pipe 1 to be measured and then the sensor coils L1 and L2 at respective positions on a center point O generate electromotive forces +M and -M. Therefore, it is found that the buried metallic pipe 1 is right below the point O where the composite reception output waveform is minimum. Further, when the buried metallic pipe 1 is a branch pipe, lines (p) of magnetic force by the current of the main pipe 2 are not cross-linked with the sensor coils L1 and L2, so only the lines (q) of magnetic force of the branch pipe generate electromotive force, so that a differential voltage is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for detecting buried metal pipes, cables, etc.

More specifically, the present invention applies electromagnetic waves to a buried metal body such as a buried metal pipe or a buried cable, picks up only the magnetic field of the measurement signal current, and provides a highly sensitive output to obtain measurement values with few errors. Also, near the branch point of the pipeline,
The present invention provides a method for detecting buried metal pipes, etc., which enables accurate measurement of branch pipes without being affected by the magnetic field of the main pipe.

[Prior art] Conventional methods for detecting buried metal pipes, etc. include the minimum method, in which one magnetic sensor is lowered vertically and moved perpendicular to the pipe to detect the minimum point of output, and the other is the minimum method, in which the sensor is moved horizontally. The maximum method is used, in which the point of maximum output is detected by moving perpendicularly to the pipe.

That is, Fig. 6 of the attached drawings shows a detection method using the minimum method, in which q indicates the magnetic field lines generated from the buried metal pipe 1, and Ao, A+, and A2 are the magnetic sensor coils A perpendicular to the pipe line. The respective positions are shown when moved to . FIG. 7 shows the relative relationship between the voltages induced in the sensor coil A at Ao, A+, and A2, centering on the conduit, and FIG. 8 shows the receiver output. In this method, the minimum point of output is directly above the conduit. FIG. 9 shows a detection method using the maximum method in which the sensor coil is held horizontally and moved perpendicular to the pipe. FIG. 10 shows the induced voltage (receiver output) of the sensor coil.

[Problems to be Solved by the Invention The advantage of the minimum method is that the center point can be measured relatively sharply. However, it is easily influenced by noise magnetic fields (unnecessary interfering magnetic fields other than the magnetic field caused by the signal current for measurement). As a result, a disadvantage is that errors often occur in measured values. On the other hand, the maximum method does not cause many errors due to noise magnetic fields, but the characteristics of the peak near the maximum value of the output signal are gentle, and the measurement accuracy is inferior. Generally, the minimum method and the maximum method are used together to reduce errors, but the operations are complicated and it is difficult to obtain satisfactory results.

[Means for solving the problems] The present invention aims to eliminate these drawbacks. In other words, unnecessary noise magnetic fields are canceled and only the magnetic field of the measurement signal current flowing through the buried metal body is picked up.
It also provides sharp and highly sensitive output. As a result, it is characterized in that measured values with few errors can be obtained.

Further, even near the branching point of the pipe, it is not affected by the magnetic field due to the current in the main pipe, so it is possible to accurately measure up to the branching point.

Therefore, taking only the advantages of the minimum method and maximum method,
This can be said to be a method that eliminates the disadvantages.

That is, the method for detecting buried metal pipes, etc. of the present invention involves passing a high frequency current (1 Hz from 10 KHz to 100 KHz) through the buried metal pipes, etc. directly or in a guided manner, and receiving the generated electromagnetic waves.
This method of detecting the position of buried pipes, etc. is characterized by arranging two magnetic sensors with the same characteristics on the same axis, and detecting by differentially combining their outputs.

[Example] Below, the method for detecting a buried metal pipe, etc. of the present invention will be explained in detail with reference to an example.

As shown in FIG. 1, in the present invention, two magnetic sensor coils L1 and L2 having the same characteristics are arranged on the same axis F with an interval d, and both sensor coils L
, , L2 are differentially connected and combined. This sensor coil L1. When L2 is moved left and right on the buried metal object 1 to be measured, the electromotive force of each sensor coil Ll and L2 at each position on the center point O becomes as shown in FIG. 0, they are 10M and -M, respectively. That is, the receiver output obtained by combining these becomes as shown in FIG. 3, and it can be seen that there is a buried pipe directly below the 0 point indicating the minimum point of the waveform.

Further, FIG. 4 shows the state in the vicinity of the branch pipe 1 as a buried metal pipe. That is, if the magnetic line of force due to the current in the main pipe 2 is p, the line of magnetic force p is parallel to the sensor coils L and L2 and does not interlink with each other, so no electromotive force is generated in the sensor coils L and L2. Therefore, only the magnetic lines of force 9 caused by the branch pipe 1 interlink with the sensor coils L, L2 to generate an electromotive force, and the differential voltage appears in the output.

In addition, a noise magnetic field parallel to the magnetic field lines 9 also generates an electromotive force,
Since it always produces electromotive forces in opposite directions in the differentially connected sensor coils L1 and L2, the outputs due to the noise magnetic field cancel each other out and do not appear.

Fig. 5 shows a side view of Fig. 4, and the magnetic field lines P of the main pipe 2 do not interlink with the sensor coils L, L2, but only the magnetic field lines q of the branch pipe 1 interlink with the sensor coils Ll, L2. This indicates that there is a

[Effects of the invention] As described above, two magnetic sensors with the same characteristics are placed on the same axis and their outputs are differentially combined, so only the magnetic field of the signal current of the buried metal body is picked up, and the noise magnetic field is effect is canceled out. Therefore, it is possible to obtain measured values with high sensitivity and little error, and there is no influence from the magnetic field of the woodwind even near the branching point of the pipe. Therefore, it is very effective in detecting buried metal pipes, etc.

[Brief explanation of the drawing]

1 to 5 are explanatory diagrams showing the method of detecting a buried metal pipe, etc. of the present invention. is an induced voltage diagram of the magnetic sensor coil, Figure 3 is an output diagram of the three receivers, Figure 4 is an implied explanatory diagram of the vicinity of the branch pipe, and Figure 5 is an implied longitudinal side view taken along the line V-V in Figure 4. , Fig. 6 is an implicit vertical cross-sectional view showing the conventional detection method using the minimum method, Fig. 7 is a diagram of the induced voltage of sensor coil A, Fig. 8 is a receiver output diagram of the same coil, and Fig. 9 is a diagram using the maximum method. An implicit longitudinal cross-sectional view showing the detection method, and FIG. 10 are receiver output diagrams of the same coil.

Claims (1)

[Claims] High frequency current (10KHz to 100KHz) in buried metal pipes, etc.
) is applied directly or inductively to receive the generated electromagnetic waves and detect the position of buried pipes, etc. In this method, two magnetic sensors with the same characteristics are placed coaxially and their outputs are differentially transmitted. A method for detecting buried metal pipes, etc., characterized in that the position of the buried metal pipes is detected by combining them.