JPH0435798Y2 - - Google Patents

Description

[Detailed explanation of the invention] [Background and purpose of the invention] The invention monitors abnormalities caused by ground subsidence, damage caused by excavation of underground cables and their conduits, gas pipes, water pipes, etc. This relates to an underground object monitoring device.

Conventionally, there are few methods for detecting abnormalities in underground objects due to excavation and ground subsidence, and in the case of power cables, it is often unknown until insulation breaks down after inspection due to deterioration due to damage, and power outages due to insulation breakdown. It has been difficult to implement preventive measures immediately after receiving an injury. In addition, it is only when gas or water leaks occur in gas pipes, water pipes, etc. that it becomes clear that the cause was trauma sustained in the past. In addition, there is a method of burying important buried objects with a sensor attached, but this is a local detection method and is not a linear sensor.However, if an insulated wire such as a pilot cable is used as a sensor, cutting it This is a method that detects trauma for the first time, and it is impossible to detect external forces such as trauma or local abnormal tension or lateral pressure on the pilot cable before it is severed.

Furthermore, the sensitivity of detection using a pilot cable buried underground may be significantly limited by underground stray currents and electromagnetic induction of the underground cable.

Furthermore, when detecting in the longitudinal direction when buried underground, countermeasures against corrosion of the sensor are required.

An object of the present invention is to provide an underground object abnormality monitoring device that eliminates the drawbacks of the prior art and includes a line sensor using optical fiber that easily detects abnormalities of underground objects and generates an alarm. There is a particular thing.

[Summary of the invention] A line sensor equipped with an optical fiber, a light emitting element provided at one end of the optical fiber, a light receiving element provided at the other end of the optical fiber, and a time sensor connected to the light receiving element. The line sensor is composed of a differential circuit and an alarm circuit connected to the time differential circuit, and the line sensor has the optical fiber attached to a spiral metal tube, and a flexible coating layer is applied to the outer periphery of the optical fiber. It is characterized by its structure.

[Example] Hereinafter, the present invention will be specifically described based on an illustrated example.

FIG. 1 shows an embodiment of the line sensor 4 in the device of the present invention. An optical fiber 2 is linearly attached to the spiral metal tube 1 in the longitudinal direction.
A flexible coating layer 3 is applied to its outer periphery. The spiral metal tube 1 may be, for example, an Al sheath of an OF cable, and there are no restrictions on the type.

The cladding tube 3 is provided to an extent to prevent the optical fiber 2 from being deformed and causing transmission loss during the manufacture of the line sensor 4. However, in order for the optical fiber 2 to be easily deformed when the line sensor 4 is buried underground and external force such as lateral pressure is generated, the coating layer 3 is required to be flexible. Ru.

FIG. 2 is an explanatory diagram showing another embodiment of the line sensor 14 in the device of the present invention, in which the optical fiber 12 is attached to the helical and reverse pitch of the spiral metal tube 11, and a flexible A covering layer 13 is applied.

FIG. 3 is an explanatory diagram showing an embodiment of the underground buried object monitoring device according to the present invention, in which a light emitting element 26 is provided at one end of the optical fiber 22 of the line sensor 24,
A light receiving element 27 is installed on the other end, and lateral pressure P or tension Q is
When this occurs, the light receiving element captures the transmission loss of the optical fiber, the time differentiation circuit 28 detects the abnormality, and the alarm circuit 29 issues an alarm.

For reference, if an optical pulse measuring device is installed at one end of the optical fiber, the location of the abnormality can be determined.

This detection method utilizes the phenomenon that scattered light is generated in the optical fiber when the optical pulse signal propagates through the optical fiber. By measuring the intensity change of the incoming scattered light over time, it is possible to detect the point where an abnormality has occurred in the optical fiber.

In other words, when a pulse signal is transmitted with no external pressure applied to the optical fiber, the scattered light that returns to the pulse measuring instrument decays smoothly over time, but when external pressure is applied to the optical fiber, that part Since the amount of transmission loss in the optical fiber increases, the intensity change of the scattered light returning to the pulse measuring device becomes a waveform that rapidly attenuates at a certain time when the intensity of the scattered light is viewed in time series.

Therefore, by reading the time at which the sudden change occurs, it is possible to detect the location of optical loss in the optical fiber, that is, the location where external pressure is applied.

[Effects of the Invention] As explained in detail above, the present invention provides the following remarkable effects.

(1) By attaching an optical fiber to a spiral metal tube, transmission loss in the optical fiber easily occurs due to external forces such as compression, and the occurrence of an abnormality can be easily detected.

(2) Optical fiber has no electrical induction, so it is not affected by underground stray currents, power cables, or lightning.

(3) Since it uses optical fiber, it is corrosion resistant as an underground object.

[Brief explanation of drawings]

1 and 2 are explanatory diagrams showing an embodiment of the line sensor in the device of the present invention, and FIG. 3 is an explanatory diagram showing an embodiment of the device of the present invention. 1,11...Spiral metal tube, 1,12...Optical fiber, 3,13...Coating layer, 4,14,24...
...Line sensor, 26...Light emitting element, 27...
Light receiving element, 28... time differentiation circuit, 29... alarm circuit.

Claims (1)

[Scope of utility model registration request] A line sensor equipped with an optical fiber, a light emitting element provided at one end of the optical fiber, a light receiving element provided at the other end of the optical fiber, a time differentiation circuit connected to the light receiving element, and an alarm circuit connected to a time differentiation circuit, wherein the line sensor has a structure in which the optical fiber is attached to a spiral metal tube and a flexible coating layer is applied to the outer periphery of the optical fiber. Features: Abnormality monitoring device for underground objects.