JPH09101373A - Method for searching buried object - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately search a buried object by eliminating such influence as direct magnetic field from an oscillator by arranging a specific number of detection coils horizontally with a space in the up-and-down direction inside a transmitter. SOLUTION: Three detection coils C1 , C2 , and C3 are horizontally arranged in a receiver R being installed on the ground with spaces L1 and L2 in the vertical direction. By positioning the receiver R directly above a buried cable K so that an axial line ϕ is in the vertical direction to the cable K, the synthetic magnetic field between magnetic fields H1 , H2 , and H3 formed by a current I flowing to the cable K and a direct magnetic field H from an oscillator cross each other, and hence detection voltages V1 , V2 , and V3 in proportional to magnetic fields H1 +H, H2 +H, and H3 are induced at coils C1 , C2 , and C3 , respectively. Two sets of differential voltages are obtained from the detection voltages V1 , V2 , and V3 and a burial depth D is calculated under conditions where magnetic field constituents are canceled from the transmitter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for exploring buried objects using electromagnetic induction, and conductors such as telephone cables, power cables, gas pipes and water pipes buried in the ground (hereinafter simply referred to as cables). ) Related to the improvement of the electromagnetic induction type buried object exploration method used for exploration.

[0002]

2. Description of the Related Art An electromagnetic induction type buried object search method generally involves passing an alternating current through a buried conductor such as a cable, and detecting the magnetic field generated by this alternating current with a receiving device to detect the position directly above the cable or its buried position. It detects depth, can be operated easily, and has relatively good measurement accuracy.
Moreover, it is an extremely excellent exploration method that can be easily applied to any place.

In the method of exploring the buried object, the following three methods are often used as a method of passing an alternating current through a buried conductor such as a buried cable. A method in which the output side of the oscillator is connected to the exposed part of the buried cable above the ground, and an alternating current is passed directly to the cable. An outer magnet clamp formed by winding a ring-shaped magnetic material is clamped on the embedded cable, and the winding of the outer magnet clamp is used as the primary winding to generate an induced current in the embedded cable that is the secondary conductor. The clamp method that was used. An induction method in which an oscillator installed on the ground emits an alternating magnetic field, and this alternating magnetic field causes an induced current in the buried cable.

By the way, the above-mentioned methods and methods require a part of the buried cable to be exposed, which is troublesome and restricts the construction site. On the other hand, the above-mentioned induction method can be easily applied only by installing an oscillator on the ground surface,
It has high practicality.

However, the following problems are inherent in the induction method. Since the induced current induced in the buried cable is small,
Requires a large oscillator output. Applicable only when the distance between the oscillator and the receiver is sufficient, because a part of the transmitted magnetic field from the oscillator is easily received directly by the receiver.

FIG. 5 shows an example of the basic principle of a conventional buried object search by the electromagnetic induction method. In the figure, K is a buried cable, I is a current flowing through the buried cable,
C ₁ and C ₂ are detection coils, H ₁ and H ₂ are alternating magnetic fields due to the current I, H is a direct magnetic field (or external noise magnetic field) emitted from an oscillator, L is a detection coil interval, and D is a buried depth (lower). Of the detection coil C ₂ and the cable K).

Two coils C as shown in FIG.₁, C_TwoBuried
Arranged directly above the installation cable K at a distance of L, and
Coil with C parallel to the ground₁, C_TwoDetection voltage
To V ₁, V_TwoThen, the depth D is D = LV₁/ (V
_Two-V₁) Can be requested. Where V₁Is an invitation
Magnetic field H due to conductive current I₁And the direct magnetic field H from the oscillator
Proportional to the composite magnetic field, and similarly V_TwoIs the magnetic field H₁And the direct magnetic field H
Proportional to the combined magnetic field of and. Also, the denominator of the above formula (1) is
V_TwoAnd V₁The differential voltage of
Be erased. On the other hand, L ・ V₁Becomes a direct magnet
The influence of the field H exists as it is, and therefore the depth D
There is an error factor in the calculation formula of. as a result,
In the depth measurement in the induction method, the depth D is often
It will give a deeper measurement.

On the other hand, in order to avoid a measurement error caused by the direct magnetic field H when the above-mentioned induction method is used, FIG. 6 is shown between the transmission magnetic field (direct magnetic field H) and the induction magnetic fields H ₁ and H ₂ . Paying attention to the theoretical phase difference of 90 ° as shown, the oscillator and the receiver are connected by wire or wirelessly, and the phase of the transmission magnetic field H is transmitted to the receiver side, and the detection magnetic field is transmitted based on this. Magnetic field component H and magnetic field component H due to induced current I
A method has been attempted in which the depth D is decomposed into ₁ (or H ₂ ) and then the magnetic field component H ₁ (or H ₂ ) due to the induced current I is used to calculate the depth D.

However, in this method as well, it is necessary to connect the oscillator and the receiver in a wired or wireless manner, which complicates the device, and when the distance between the transmitter and the receiver changes, the electrical characteristics of the buried cable may cause a problem. There is a possibility that it will change from the phase difference of °, and a phase shift will occur even if there is a conductor other than the probe cable in the surroundings. (It becomes impossible to decompose into magnetic field components).

[0010]

SUMMARY OF THE INVENTION The invention of the present application is mainly due to the above-mentioned problem in the electromagnetic induction type buried object search using the conventional induction method, that is, due to the direct magnetic field from the oscillator. To reduce the detection accuracy and the detection error due to the direct magnetic field from the oscillator,
Since it is necessary to separate the oscillator and the receiver greatly, it becomes difficult to carry out the detection work, and the method of correcting the detection error due to the direct magnetic field from the oscillator increases the manufacturing cost of the buried object exploration device itself and It is intended to solve problems such as difficulty in sufficiently and stably increasing accuracy, and three detection coils C ₁ and C on the receiver side.
₂ and C ₃ are provided, and each detection coil C ₁ , C ₂ , C
_The structure is simple and the exploration device is obtained by calculating two sets of differential voltages from the detection voltages V ₁ , V ₂ and V _{3 of 3} and calculating the burial depth D under the condition in which the direct magnetic field component from the oscillator is canceled. The present invention provides an electromagnetic induction type buried object exploration method capable of performing extremely accurate exploration of an embedded object without causing a significant increase in manufacturing cost.

[0011]

The invention according to claim 1 of the present invention is a method for exploring a buried object by passing a current through the buried object and detecting an alternating magnetic field due to the current with a receiver on the ground. , Three detection coils are horizontally arranged inside the receiver at intervals in the vertical direction, and a differential voltage between the detection coils is obtained for a combination of two sets of detection coils. By amplifying each differential voltage and adjusting each amplification factor, the product of differential voltage x amplification factor is made equal, and each amplification factor at that time and the upper and lower intervals of each detection coil The calculation of the buried depth of the buried object is the basic configuration of the invention.

Further, the invention according to claim 3 is a method for exploring an embedded object by causing an electric current to flow through the embedded object and detecting an alternating magnetic field due to the current with a receiver on the ground. The three detection coils are horizontally arranged at intervals in the vertical direction, and the detection coil in the middle is movably supported in the vertical direction, and the vertical position of the detection coil in the middle is determined. The differential voltage (V ₃ −V ₂ ) between the detection coil located below and the detection coil located in the middle, and the differential voltage between the detection coil located in the middle and the detection coil located above (V ₃ −V ₂ ). V ₂ −V ₁ ) is minimized, and the buried depth of the buried object is calculated from the distance between the detection coils when the difference between the two differential voltages is the minimum. It has a basic configuration.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment will be described. FIG. 1 shows the base of the first embodiment of the present invention.
It is explanatory drawing of this principle. Above the receiver R installed on the ground
Space L downward₁, L_TwoPut three detector coils
C₁, C_Two, C_ThreeAre on the same axis φ and perpendicular to the axis φ (immediately
It is arranged horizontally with the ground E). Now in Figure 1
As shown, place the receiver R directly above the buried cable K
Position the axis φ so that it is perpendicular to the cable K.
Then, each detection coil C₁, C_Two, C _ThreeThe buried cave
Magnetic field H created by current I flowing through₁, H_Two, H_ThreeAnd oscillation
Magnetic field combined with direct magnetic field H from the container (not shown)
As a result, each detection coil C₁, C_Two, C_ThreeIn the magnetic field
H₁+ H, H_Two+ H, H_ThreeDetection voltage proportional to + H
V ₁, V_Two, V_ThreeWill be induced respectively. The above
Each detection coil C₁, C_Two, C_ThreeHave the same electrical characteristics
It is desirable to be formed to have.

Now, the detection coil C ₃ and the detection coil C
₂ differential voltage V ₃ -V ₂ and a detection coil C ₂ of the differential voltage V ₂ -V ₁ and the detection coils C _1, or a differential circuit, or the winding direction of the detection coil C ₂ When it is detected by making the detection coil C ₁ and C ₃ reversely wound, V
₃ The value of -V ₂ and V ₂ -V ₁ is made shall voltage component directly proportional to the magnetic field H from the oscillator is countered, only the voltage component proportional to the magnetic field H _1, H _2, H ₃ due to the current I Becomes

By the way, each of the detection coils C ₁ , C ₂ ,
Magnetic field H ₁ due to current I generated at the installation position of C ₃ ,
H ₂ and H ₃ are given by the following equations (1), (2) and (3), where i is the magnitude of the current I. H ₁ = i / 2π (D + L ₁ + L ₂ ) (1) H ₂ = i / 2π (D + L ₂ ) (2) H ₃ = i / 2πD (3) And the differential voltage V The values of _3- V ₂ and V ₂ -V ₁ are amplified by using programmable voltage amplifiers respectively, and the amplification degree is adjusted to A ₁ and A _{2 so} that the relation of the following equation (4) is established. To A ₁ · (V ₃ −V ₂ ) = A ₂ · (V ₂ −V ₁ ) ... (4)

On the other hand, as described above, the differential voltage V_Three-V_TwoIs H
_Three-H_TwoAnd the differential voltage V_Two-V ₁Is H_Two-H₁Husband
Since they are proportional to each other, the above steps (1) to (4)
When the burial depth D of the cable K is obtained, the burial depth D is
It is given by the equation (5). D = (L₁+ L_Two) / (A₁/ A_Two) ・ (L₁/ L_Two) -1 (5) That is, the buried depth D of the buried cable K satisfies the formula (4).
Amplification A₁, A_TwoBy calculating
It can be calculated using.

In FIG. 1, a programmable voltage amplifier is used, and the amplification degree A ₁ , A ₂ is adjusted to satisfy the equation (4). As described above, the detection coil C ₂ located at the center is configured to be movable in the vertical direction along the axis φ while being held in the horizontal posture. When the detection coil C ₂ is moved, the differential voltage V ₃ −
A position where V ₂ and the differential voltage V ₂ −V ₁ are equal (or the difference between them is minimized) may be obtained. now,
In FIG. 2, the positions of the detection coils C ₁ , C ₂ and C ₂ , C ₃ when V ₃ −V ₂ = V ₂ −V ₁ (6) are established are L ₁ ′, L Assuming ₂ ', the depth D is (1) ~
From the expressions (3) and (6), it is given by the following expression (7). D = (L ₁ + L ₂ ) / (L ₁ ′ / L ₂ ′) −1 (7)

That is, the above equations (5) and (7) show that the depth D of the buried cable K can be calculated under the condition that the component of the magnetic field H directly from the oscillator is canceled, and the measurement accuracy is improved. The exploration by the guidance method, which was previously applicable only when the distance between the oscillator and the receiver R was sufficiently large,
It is possible near the oscillator. Also, because the noise magnetic field component can be canceled by the coil part that is the sensor,
The electronic circuit that follows can be simplified.

The embodiment of the present invention shown in FIGS. 1 and 2 is not limited to the so-called inductive method for exploring the buried object in which the induced current is generated in the buried cable K by the magnetic field emitted from the oscillator. Even in the case where the electric current is directly supplied to the buried cable K, the effect of the external noise magnetic field is eliminated, so that the excellent effect is achieved.

(Embodiment 1) FIG. 3 is a block diagram of a receiver R of the buried object exploration apparatus used for implementing the present invention shown in FIG. In FIG. 3, C ₁ , C ₂ , C ₃
Is a detection coil, 4a, 4b and 4c are amplifiers, 5a and 5b
Is a differential amplifier, 6a and 6b are filters, and 7a and 7b are A
C / DC converter, 8 DA converter, 9 comparator, 10 clock oscillator, 11 logic gate, 12 counter,
Reference numeral 13 is a calculation counter, and 14 is a display unit.

An outline of the operation will be described with reference to FIG. _3. The output signals of the detection coils C ₁ , C ₂ and C ₃ are output from the amplifier 4.
The voltage is amplified by a, 4b, and 4c, and the differential amplifier 5
a and 5b are coils C ₂ and C ₁ , and coils C ₃ and C, respectively.
_Get the differential voltage of ₂ . The outputs of the differential amplifiers 5a and 5b are
After the signal components are separated through the filters 6a and 6b, the AC / DC converters 7a and 7b convert the AC to DC. The DA converter 8, the comparator 9, the clock oscillator 10, the logic gate 11, and the counter 12 form a programmable amplifier. The output of the D / A converter 8 and the output of the AC / DC converter 7b are compared by the comparator 9, and when the output values of the D / A converter 8 and the AC / DC converter 7b are different, the logic gate 11 is opened. Clock generator 10
Is input to the counter 12. The output of the counter 12 controls the output of the D / A converter 8, and the output of the AC / DC converter 7
When the output of b matches, the logic gate is closed and the counter 1
The operation of 2 is stopped. At this time, the output of the counter 12 gives the value of (A ₁ / A ₂ ) in the equation (5), the arithmetic circuit 13 calculates the depth, and the display unit 14 displays the depth.

(Embodiment 2) FIG. 4 is a block diagram of a receiver of the buried object exploration apparatus used for implementing the present invention shown in FIG. In FIG. 4, 4a, 4b and 4c are amplifiers, 5a, 5b and 5c are differential amplifiers, 6a and 6b are filters, 7a and 7b are AC / DC converters, 14 is a display unit, and 15 is a depth scale plate. is there.

Thus, the output signals of the detection coils C ₁ , C ₂ , C ₃ are voltage-amplified by the amplifiers 4a, 4b, 4c, and are differential amplifiers 5a, 5b between the coils C ₂ and C ₁ and the coil C, respectively. Obtain the differential voltage between ₃ and C ₂ . The outputs of the differential amplifiers 5a and 5b are separated into signal components through filters 6a and 6b, and then the AC / DC converter 7
AC is converted to DC by a and 7b. AC
The outputs of the / DC converters 7a and 7b are differentially amplified by the differential amplifier 5c, and the differential voltage is displayed by the display unit 14. The operator looks at the display unit 14 and looks at the central coil C.
₂ is moved up and down, and the coil C ₂ is fixed at the place where the indicated value displayed on the display unit 14 becomes the minimum. Depth scale 1
A scale indicating depth is marked on the coil 5, and the coil C ₂
The depth D is directly read from the fixed position of the depth scale plate 15.

[0024]

According to the inventions of claims 1 to 3, the voltage between the detection coils is obtained for each of the combinations of the two coils, and the buried depth of the buried object is based on both differential voltages. Is calculated. That is, since the buried depth D is calculated by using the detection value in which the effects of the direct magnetic field H from the oscillator and the external magnetic field of the nozzle are all canceled, the calculation accuracy is significantly improved and the oscillator and the receiver Even if the distance between the vessels R is short, the buried object can be searched with high accuracy. Further, in the invention of claim 2, the buried depth D can be easily obtained only by adjusting the amplification degree of the amplifier that amplifies both differential voltages, and the automatic buried object search excellent in handleability can be realized. It will be possible. Further, in the invention of claim 3, the buried depth D can be directly read only by adjusting the upper and lower positions of the detection coil positioned in the middle, and the electronic circuit of the receiver can be greatly simplified. It will be possible. As described above, the present invention has excellent practical utility.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a basic principle of buried object exploration according to the invention of claim 1.

FIG. 2 is an explanatory view of the basic principle of exploration of a buried object in the invention of claim 3;

FIG. 3 is a block diagram of a receiver used to implement the invention of claim 1.

FIG. 4 is a block diagram of a receiver used to implement the invention of claim 3;

FIG. 5 is an explanatory diagram of a basic principle of a buried object search using a conventional electromagnetic induction type buried object search apparatus.

FIG. 6 is an explanatory diagram showing a relationship between a transmission magnetic field, an induction magnetic field, and a detection magnetic field when the induction method is used.

[Explanation of symbols]

K is the buried cable I is the current (alternating current) R is the receiver C ₁ , C ₂ , C ₃ is the detection coil H ₁ , H ₂ , H ₃ is the magnetic field due to the current I H is the direct magnetic field from the oscillator V ₁ , V ₂ , V ₃ is the detection voltage of each detection coil L ₁ , L ₂ is the distance between each detection coil C ₁ , C ₂ , C ₃ D is the distance between the detection coil C ₂ and the cable (buried depth) φ is the receiver Vertical axis E is the ground plane 4a, 4b, 4c is an amplifier 5a, 5b is a differential amplifier 6a, 6b is a filter 7a, 7b is an AC / DC converter 8 is a DA converter 9 is a comparator 10 is a clock oscillator 11 is A logic gate 12, a counter 13, an arithmetic circuit 14, a display unit 15, and a depth scale plate.

Claims (3)

[Claims] 1. A method for exploring a buried object by passing an electric current through the buried object and detecting an alternating magnetic field due to the current with a receiver on the ground, wherein three spaces are vertically provided inside the receiver. The detection coils are arranged horizontally, the differential voltage between the detection coils is obtained for each combination of the two detection coils, and then the two differential voltages are amplified respectively to adjust each amplification degree. By doing so, the product of differential voltage × amplification is made equal, and the buried depth of the buried object is calculated from each amplification at that time and the spacing between the detection coils in the up / down direction. How to search for things. 2. A differential voltage (V ₃ between a detection coil located below and a detection coil located in the middle)
-V ₂ ) and the differential voltage (V ₂ -V ₁ ) between the detection coil positioned in the middle and the detection coil positioned above, and the amplification degree A ₁ and the amplification degree A ₂ of the amplifiers of the both differential voltages are By adjusting, A ₁ (V ₃ −V ₂ ) = A ₂ (V ₂ −
The buried object exploration method according to claim 1, wherein the relationship of V ₁ ) is established. 3. A method for exploring a buried object by causing an electric current to flow through the buried object and detecting an alternating magnetic field due to the current with a receiver on the ground. While arranging the individual detection coils horizontally,
A differential voltage between the detection coil located below and the detection coil located in the middle is supported by movably supporting the detection coil located in the middle in the vertical direction and adjusting the vertical position of the detection coil located in the middle. The difference between (V ₃ −V ₂ ) and the differential voltage (V ₂ −V ₁ ) between the detection coil located in the middle and the detection coil located above is minimized, and A method for exploring a buried object, which comprises calculating a buried depth of a buried object from a distance between respective detection coils in a state where the difference is minimum.