JPS6279347A - Detection of hidden conductor - Google Patents

Abstract

PURPOSE:To detect a hidden conductor of the like accurately, by propagating a square wave outputted from a first oscillation circuit between an underground buried steel pipe and the ground to detect and display it with a portable detector containing a second oscillation circuit with the oscillation frequency and phase equal to those of the first oscillation circuit. CONSTITUTION:One output terminal of an oscillation circuit 4 is electrically connected to a steel pipe 1 through a line 5 while the other output terminal is grounded 2 with an electrode 6. A square wave oscillation signal outputted from the circuit 4 is detected with a detection coil 9 of a detector 8 carried by a worker. An output of the coil 9 is amplified 10 and introduced to multiplication circuits 14 and 22 of synchronous detection circuits 13 and 21. On the other hand, an oscillation circuit 11 in the unit 8 has an oscillation frequency and phase equal to those of the circuit 4 and an output thereof is shifted 20 by 90 deg. to be applied to the circuit 22. Output signals of the circuits 13 and 21 are inputted into a computing circuit 19 as X and Y axis components respectively in an X-Y coordinate system and displayed on a display circuit 27. Thus, a worker can detect damage to a coating layer of an underground buried steel pipe and a hidden conductor accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a method for detecting conductors located in hidden locations, such as underground metal pipes.

Background technology Coating for corrosion protection! ii of underground steel pipe with LJω
In order to detect the damaged part of the J coating layer from the ground, the output of the oscillation circuit is applied to the steel pipe, and the electromagnetic waves passing through the steel pipe are detected by a detection coil on the ground. The output level of the detection coil is weak, and therefore it is necessary to remove noise contained in the output of the detection coil.

In the prior art, the output from the detection coil is given to one input of the synchronous detection circuit, and the output from the oscillation circuit is led to Ikekata's power of the synchronous detection circuit via a cable, thereby /N ratio is modified to obtain a signal corresponding to the output from the detection coil.

Problems to be Solved by the Invention In such prior art, it is necessary to run a good cable along the underground steel pipe to detect damage to the coating layer, which is a cumbersome process. be. This problem is particularly important when steel pipes are buried under roads.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for detecting a hidden conductor, which allows a conductor provided at a hidden location to be detected accurately with simple work.

In the present invention, a first oscillation circuit is connected to a conductor provided in a hidden place, and the phase of the detection coil, the second oscillation circuit, and the output of the second oscillation circuit is adjusted to 90°. The phase shift circuit and the output from the detection coil! a first synchronous detection circuit that receives the output from the m2 oscillation circuit and performs synchronous detection; a second synchronous detection circuit that receives the output from the detection coil and the output from the phase shift circuit and performs synchronous detection; preparing a detection device including an arithmetic circuit that calculates the magnitude of the output from the detection coil based on the output from the second synchronous detection circuit, and detecting the conductor by the output of the arithmetic circuit of the detection VC device. This is a method for detecting hidden conductors with the following characteristics.

In a preferred embodiment, the oscillation frequencies of the first and tjS2 oscillation detection circuits are similar values.

According to the present invention, the output from the first synchronous detection circuit is X-Y.
This is the X-axis component in the rectangular coordinate system, and the output from the second synchronous detection circuit is the Y-axis component of the output of the detection filter. Therefore, the magnitude of the output of the detection coil can be determined from the X-axis component and Y-axis component of the detection coil using the arithmetic circuit. Therefore, it becomes possible to detect the conductor provided at the hidden location based on the output from the arithmetic circuit of the detection device.

Example FIG. 1 is a system diagram of one embodiment of the present invention.

A steel pipe 1 coated with a coating layer is buried in the ground 2.

The present invention is implemented in order to detect damaged locations 3 in the coating layer of this underground steel pipe 1 above ground. One output terminal of the first oscillation circuit 4 is electrically connected to the steel pipe 1 through a line 5 . The northern output terminal of the first oscillator circuit 4 rises to the electrode 6 and is grounded to the ground 2. First oscillation circuit 4
The oscillation frequency is, for example, from 100 Ilz to several hundred kllz, and the oscillation frequency is stabilized using a crystal or ceramic oscillator 7 or the like.

The worker carries the detection device 8 with him or her. This detection device 8 includes a detection coil 9. As shown in FIG. 1, the output level from the detection coil 9 is higher at the connection point 5a between the line 5 and the steel pipe 1 than at the damaged location 3, and the loss is 1vJ at the location 3. is at a low level on the opposite side from the connection point 5a. By detecting such a change in the output level of the detection filter 9, it becomes possible to detect the damaged location 3 of the coating layer on the ground.

FIG. 2 is a block diagram showing the specific electrical configuration of the detection device 8. As shown in FIG. The output from the detection coil 9 is sent to the amplifier circuit 1.
amplified by 0. This detection device rI18 includes a second oscillation circuit 11. The riS2 oscillation circuit 11 includes a crystal or ceramic oscillator 12, which stabilizes the oscillation frequency. The oscillation frequency of the second oscillation circuit 11 is selected to be close to the oscillation frequency of the first oscillation circuit 4, and may be the same value. The output from the amplifier circuit 1o and the output from the second oscillation circuit 11 are applied to a multiplier 14 provided in the first synchronous detection circuit 13 and are multiplied. The output from the multiplier 14 is connected to the resistor 15 and capacitor 1.
6, and its output is led to an arithmetic circuit 19 through a line 18.

The phase of the output from the oscillation circuit 11 is delayed by 90 degrees by the 90 degree phase shift circuit 20, and the phase is delayed by 90 degrees by the 90 degree phase shift circuit 20.
The output from the amplifier circuit 10 is also applied to the a multiplier 22 .

In the second synchronous detection circuit 21, the output of the multiplier 22 is filtered through a low-pass filter 25 including a resistor 23 and a capacitor 24.
given to. The output from the low-pass filter 25 is provided to the arithmetic circuit 19 via a line 26.

The operation of the detection circuit 8 will be explained with reference to FIG. The output from the detection filter is shown in FIG. 3(1). Assuming that the oscillation frequencies of the first and V second oscillation circuits 4 and 11 are the same and in phase, the second oscillation circuit 11 derives the waveform shown in FIG. 20 is shown in Figure 3 (
3) Derive the signal shown in . First synchronous detection circuit 13
The multiplier 14 receives the signal shown in FIG. 3 (1) from the detection coil 9 and the f:lS3 diagram (
2) and derive a signal having the waveform shown in FIG. 3 (4). Low pass filter 17
The output of is also shown by line E1 in FIG. 3(4). The multiplier 22 in the second synchronous detection circuit 21 is
The signal shown in FIG. 3 (1) from the amplifier circuit 10 and the signal 9
By multiplying by the signal shown in FIG. 3 (3) from the 0 degree phase shift circuit 20, Q't shown in FIG. 3 (5) is derived. When the signal detected by the detection coil 9 is in phase with the output of the 22nd oscillating circuit 11 as described above, the signal derived from the low-pass filter 25 to the line 26 is shown in FIG. As shown, it is zero. In addition,
The input signals to the multipliers 141 and 22 are rectangular; as shown above, even if they are sine waves, the same operation will occur.

From the detection filter to the amplifier circuit 10 as shown in FIG.
If the signal amplified and derived by The signal derived from circuit 21 on line 26 is the Y-axis component E2. First and second oscillation circuit 4
, 11 have the same oscillation frequency, and the above E and 12 oscillation circuit 1
When the outputs of 1 are in phase, the angle θ in FIG. 4 is zero. When the frequencies of the first and second oscillation circuits 4 and 11 are the same and the phase between E and the output of the second oscillation circuit 11 is shifted, θ≠0.

When the frequencies of the first and second oscillation circuits 4 and 11 are different, the vector E rotates in the XY orthogonal coordinate system.

At this time, the frequencies of the first and second oscillation circuits 4.11 are similar, and the difference in frequency is determined by the low-pass filter 17.
and if it is below the cutoff frequency of 25, the first and second
Each output of the synchronous detection circuit 13.21 becomes a projection E1 and E2 of E onto the X-axis and Y-axis, respectively.

Enichi circuit 19 receives values E1, E2 from line 18.26.
Receive a signal with , and calculate the first equation as ↑
cormorant .

1El=~rr lower 7th lower 2' ・ (
1) The output Il thus obtained by the arithmetic circuit 19
l is displayed by the display circuit 27. Therefore, by looking at the change in the output of the display circuit 27, it is possible to
Damaged locations 3 of the coating layer of 4W1 can be known.

The arithmetic circuit 19 may have a structure in which the arithmetic operation shown in formula f51 is directly performed by an analog arithmetic element or the like, or it may have a structure in which the arithmetic operation in the first formula is performed in any number of places. .

The present invention can be implemented not only for detecting damaged locations 3 in the coating layer of underground steel pipes 1, but also widely for detecting conductors installed in concealed locations.

Effects As described above, according to the present invention, there is no need to run long cables as described in connection with the prior art described above, and a conductor installed in a concealed place can be detected accurately with a simple operation. Things become 'nJ Noh.

[Brief explanation of drawings]

FIG. 1 is a system diagram of an embodiment of the present invention, FIG. 2 is a block diagram showing a specific electrical configuration of the detection device 8, and FIG. 3 is a waveform diagram for explaining the operation of the detection device 8. FIG. 4 is a diagram for explaining the principle of the detection device 8. 1... Underground steel pipe, 4... First oscillation circuit, 8...
- Detection 'Vc position, 9... Detection coil, 10... Amplifier circuit, 11... Second oscillation circuit, 13... First synchronous detection circuit, 14°22... Multiplier, 17. 25...Low pass filter, 19...Arithmetic circuit, 20...90
degree phase shift circuit, 21... second synchronous detection circuit, 27...
Display circuit agent Patent attorney Number of strokes Keiichi Figure 1

Claims (2)

[Claims] (1) A first oscillation circuit is connected to a conductor provided in a concealed place, and a detection coil, a second oscillation circuit, a phase shift circuit that shifts the phase of the output of the second oscillation circuit by 90 degrees, and a detection coil are connected to the conductor. a first synchronous detection circuit that receives the output from the detection coil and the output from the second oscillation circuit and performs synchronous detection, and a second synchronous detection circuit that receives the output from the detection coil and the output from the phase shift circuit and performs synchronous detection. , and an arithmetic circuit that determines the magnitude of the output from the detection coil based on the outputs from the first and second synchronous detection circuits; A method for detecting a hidden conductor, the method comprising: detecting a hidden conductor. (2) The method for detecting a hidden conductor according to claim 1, wherein the oscillation frequencies of the first and second oscillation circuits are approximate values.