JP3500515B2 - Pressure sensitive cable - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure-sensitive cable suitable for a method of detecting the depth of a landslide surface in a landslide area.

[0002]

2. Description of the Related Art Conventionally, when carrying out landslide countermeasure work, the site selection and scale of the countermeasure work are determined by measuring the depth of the slip surface in the landslide area. There are the following two methods for measuring the depth of the slip surface.
The first method is to dig a boring hole vertically in the landslide area, insert a coaxial cable in the boring hole,
We use the fact that the cable length is shortened due to disconnection due to the occurrence of landslides by packing the area around the cable with mortar. In this first method, a pulse is injected from the cable end on the ground side, and the time until the reflected signal from the disconnection part is detected is measured to measure the cable length from the cable end to the disconnection part. The depth of the landslide surface is obtained by subtracting the length of the cable on the ground from the calculated cable length.

In the second method, a coaxial pressure-sensitive cable is inserted and arranged in the boring hole, the circumference of the pressure-sensitive cable is packed with sand or the like, and a short circuit occurs in the pressure-sensitive cable due to compression due to occurrence of landslide. I'm taking advantage of that. Also in this second method, a pulse is injected from the ground end of the pressure-sensitive cable, and the time from when the reflected wave having a polarity different from that of the incident wave is detected to measure the length from the ground end to the compression generation position. Then, the depth of the landslide surface is obtained by subtracting the length of the pressure-sensitive cable on the ground from the measured length.

A pressure-sensitive cable structure based on the second method is as shown in FIG. In FIG. 7, the center conductor 7
1 is covered with a conductive rubber 72, and a nylon thread braid 73 is provided on the outside thereof. A conductive rubber 74 is wound around the nylon thread braid 73, and the metal shield 7 is wound around the conductive rubber 74.
5 is arranged, and the outside thereof is covered with a sheath 76. When the pressure-sensitive cable configured as described above is compressed, the pressure-sensitive cable is deformed and the conductive rubber 72 enters the gap between the nylon thread braids 73, and the center conductor 71 and the metal shield 75 are short-circuited with a resistance of about 10Ω. To be done. as a result,
When a pulse is made incident from the incident end, a reflected wave having a polarity opposite to that of the incident wave is obtained at the incident end. The electric resistance between the central conductor 71 and the metal shield 75 is in inverse proportion to the contact area of the conductive rubber 72, and the electric resistance decreases as the external pressure increases.

[0005]

However, in the above-mentioned conventional method, when the pressure-sensitive cable is installed in the ground for a long period of time, moisture is introduced into the nylon yarn braid through the sheath, so that insulation between the center conductor and the metal shield is caused. It showed a tendency to deteriorate. Therefore, when the pressure-sensitive cable is long, there is a drawback that the attenuation becomes large and the reflected wave cannot be obtained.

Therefore, an object of the present invention is to detect a landslide surface which solves the problems of the conventional pressure-sensitive cable as described above, has good water resistance, and enables detection of a plurality of compression points at different positions. To provide a pressure sensitive cable.

[0007]

According to the present invention, a resistance layer is provided around a center conductor, spacers made of an insulator are arranged at intervals outside the resistance layer, and a metal is provided outside the spacer. A tube is arranged, an insulating sheath is provided on the outside of the metal tube , the resistance layer is provided , and a conductive paint is applied around the center conductor.
A pressure-sensitive cable characterized by being formed by coating is obtained.

[0008]

The spacers are formed by arranging ring-shaped insulators on the outer side of the resistance layer at intervals in the lengthwise direction.

The spacer may be formed by spirally winding a linear body made of an insulating material on the outside of the resistance layer.

[0011]

In the above pressure-sensitive cable for detecting the landslide surface, when the pressure-sensitive cable is compressed on the slip surface due to the occurrence of landslide, the center conductor and the metal pipe contact each other while sandwiching the resistance layer. The characteristic impedance of the cable itself changes. Therefore, when a pulse is incident from the cable end, the reflected wave from the compression point is observed at the incident end of the cable, and by measuring the time from the incident wave to the reflected wave, the length from the incident end to the compression point can be measured. The depth of the landslide surface can be obtained by knowing the depth.

In particular, in this method, the presence of the resistance layer does not directly short-circuit the central conductor and the metal tube, and the effect of preventing water from entering is enhanced, so that reflected waves from a plurality of compression points at different positions are generated. There is a feature that it can be observed at the pulse incident end.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a diagram showing the configuration of the first embodiment of the present invention. A resistor is applied around the center conductor 11 to form a resistor layer 12. The material of the resistive layer 12 is preferably a conductive material rather than a material having a high resistivity. Resistance layer 12
The ring-shaped spacers 13 made of an insulating material are arranged on the outer side of the with an interval in the length direction to form an insulating layer. The pressure sensitive cable is formed by arranging the metal tube 14 on the outer side and applying the sheath 15 of the insulating material on the outer side. When a strong compressive force acts on this cable, the central conductor 11 and the metal tube 14 sandwich the resistance layer 12 at the compression point and come into contact with each other. Therefore, the resistance between the central conductor 11 and the metal tube 14 does not become 0Ω, and the cable It is possible to keep the resistance value at about ½ of its own characteristic impedance.

FIG. 2 is a diagram showing the configuration of the second embodiment of the present invention. A conductive paint is applied as a resistor around the center conductor 11 to form a resistance layer 21. A linear body 22 made of an insulating material is spirally wound around the central conductor 11 on the outer side of the resistance layer 21 to form an insulating layer. A metal tube 14 is arranged on the outer side of this, and a sheath 15 of an insulating material is arranged on the outer side thereof.
A pressure-sensitive cable is formed by applying. When a strong compressive force acts on this cable, the center conductor 11 and the metal tube 1
No. 4 sandwiches the resistance layer 21 at the compression point and makes contact therewith,
The resistance between the central conductor 11 and the metal tube 14 does not become 0Ω, and it is possible to maintain the resistance value of about 1/2 of the characteristic impedance of the cable itself.

FIG. 3 is a diagram showing the configuration of the third embodiment of the present invention. A conductive rubber is applied as a resistor around the center conductor 11 to form a resistance layer 31. A linear body 22 made of an insulating material is wound around the resistance layer 31 around the center conductor 11 to form an insulating layer. Metal tube 14 on the outside
Is arranged, and a sheath 15 made of an insulating material is applied to the outside thereof to form a pressure-sensitive cable. Even when a strong compressive force acts on this cable, the central conductor 11 and the metal tube 14 sandwich the resistance layer 31 at the compression point and come into contact with each other. Therefore, the resistance between the central conductor 11 and the metal tube 14 does not become 0Ω. It is possible to keep the resistance value at about 1/2 of the characteristic impedance of the cable itself.

FIG. 4 is a diagram showing the configuration of the fourth embodiment of the present invention. A conductive plastic is applied as a resistor around the center conductor 11 to form a resistance layer 41. Resistance layer 4
A linear member 22 made of an insulating material is provided on the outer side of the center conductor 1.
The insulating layer is formed by spirally winding it around 1.
The pressure sensitive cable is formed by arranging the metal tube 14 on the outer side and applying the sheath 15 of the insulating material on the outer side. When a strong compressive force acts on this cable, the central conductor 11 and the metal tube 14 sandwich the resistance layer 41 and come into contact with each other. Therefore, the resistance between the central conductor 11 and the metal tube 14 does not become 0Ω, and the characteristic of the cable itself. It is possible to maintain the resistance value at about ½ of the impedance.

FIG. 5 is a diagram showing an example of an apparatus for measuring the depth of the landslide surface using the pressure-sensitive cable according to the present invention. Boring hole 1 was dug vertically in the landslide area,
A pressure sensitive cable 10 is inserted and arranged in the bore hole 1. The circumference of the pressure-sensitive cable 10 is filled with mortar 2 or the like.

Referring also to FIG. 6, the oscillation circuit 51 generates the trigger pulse (FIG. 6a) at a constant cycle, and the amplification circuit 52
The trigger pulse is amplified by and is incident from the incident end of the pressure-sensitive cable 10 through the central conductor 11. The metal tube 14 of the pressure sensitive cable 10 is grounded. Incident wave (Fig. 6)
In b), since the characteristic impedance of the cable is significantly reduced at the compression point, a reflected wave of opposite polarity is generated. As a result, in the reflected wave detection circuit 57 connected to the incident end, a reflected wave having a polarity different from that of the incident wave (Fig. 6c) is detected.
The RS flip-flop 5 is triggered by the trigger pulse of the oscillation circuit 51.
3 is set, and the RS flip-flop 53 is reset by the reflected wave (FIG. 6e) that has passed through the gate circuit 55, the output of the RS flip-flop 53 (FIG. 6f) outputs a high level for the pulse propagation time. .

When reflected waves from a plurality of compression points are assumed, a delay circuit 54 and a gate circuit 55 are used to detect from reflected waves from a compression point (sliding surface 2) farther from the incident end. Use the method. This output is low pass filter 5
A DC output (FIG. 6g) is obtained by passing through 6, and the value is proportional to the distance from the incident end of the pressure-sensitive cable 10 to the reflection point, that is, the compression point. Next, the delay circuit 54
6D is shifted by shortening the time setting and the RS flip-flop 53 is reset by the reflected wave near the incident end that has passed through the gate circuit 55, and the compression point (slip surface) near the incident end It is possible to obtain the length up to 1).

[0020]

As is apparent from the above description, according to the present invention, it is possible to measure a pulse by forming a transmission line with a central conductor and an outer metal tube, and to perform cable measurement on a slip surface due to occurrence of a landslide. The structure is such that the characteristic impedance changes due to compression, and the resistance between the central conductor and the metal tube at the compression point does not decrease to 0Ω. With this structure, it is possible to prevent a 0Ω short circuit, which is a problem when detecting multiple slip surface depths, and it is possible to prevent water from entering by using a metal tube. By installing it, it is possible to detect slip planes at multiple depths over a long period of time, which is very effective.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a third exemplary embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a fourth exemplary embodiment of the present invention.

FIG. 5 is a diagram showing an example of a measuring circuit according to the present invention.

FIG. 6 is a diagram showing signal waveforms of respective parts shown in FIG.

FIG. 7 is a diagram showing an example of a conventional cable.

[Explanation of symbols]

1 boring hole 2 mortar 10 Pressure-sensitive cable 11 center conductor 12, 21, 31, 41 Resistance layer 13 Spacer 14 metal tubes 15 sheath 22 linear objects

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01L 1/20

Claims (3)

(57) [Claims] 1. A resistance layer is provided around a central conductor, spacers made of an insulating material are arranged outside the resistance layer at intervals, a metal pipe is arranged outside the spacer, and a metal pipe is arranged outside the metal pipe. An insulating sheath is applied to the
A pressure-sensitive cable characterized by being formed by applying a conductive paint to the surrounding area . 2. The spacer is attached to the outside of the resistance layer.
Formed with ring-shaped insulators at intervals in the length direction
The pressure-sensitive cable according to claim 1, wherein the pressure-sensitive cable is formed. 3. The spacer is provided outside the resistance layer.
The pressure-sensitive cable according to claim 1, wherein the linear body formed of an edge body is spirally wound and formed .