JPS6238370A - Metal contact detection device in the wall of steel pipes - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is applicable to a steel pipe that electrically contacts the reinforcing steel inside the wall when a coated steel pipe or the like penetrates a reinforced wall of a building or the like. This invention relates to a metal contact detection device within the wall of a steel pipe.

[Conventional technology] When bringing coated steel pipes such as gas pipes into a building from the outside, or when piping them to each room within the building, the coated steel pipes are passed through reinforced walls. need to be piped. In this case, if the coated steel pipe comes into electrical contact with the internal reinforcing steel at the part that penetrates the wall, the grounding resistance of the building itself is low, so even if the coated steel pipe is given cathodic protection, the contact area will be Corrosive current flows into the ground through the reinforcing steel. Therefore, the corrosion rate of the coated steel pipe increases, the durability of the coated steel pipe becomes shorter, and in the worst case, there is a concern that gas leakage may occur. 5 In order to avoid such problems, when constructing a new building, the piping work must be done with great care so that the steel pipes do not come into direct electrical contact with the reinforcing bars, but in existing buildings, It is necessary to detect from the outside whether or not the wall penetration part is electrically in contact with the internal reinforcing steel.

One method of detecting the presence or absence of contact within the walls of an existing building is to measure the ground resistance of steel pipes. The method for measuring this ground resistance is as shown in FIG. That is, a coated steel pipe 1 such as a gas pipe buried underground is led indoors by penetrating the wall 3 of a building whose lower end is also buried below the ground surface 2. 1 and the ground using a resistance measuring device 4.

If the coated steel pipe 1 is not in electrical contact with the reinforcing bars 5 disposed within the wall 3, the resistance value is a large value, and the coating of the coated steel pipe 1 is If it is in electrical contact with the bare iron M5, the reinforcing bar 5 is generally grounded, and the coating replacement 1 is grounded via the reinforcing bar 5, so the resistance value becomes small. Therefore, it is possible to detect whether the coated steel pipe 1 is in electrical contact with the reinforcing bars 5 or not.

Furthermore, as shown in FIG. 9, there is a detection method that detects electrical contact between the coated steel pipe 1 and the reinforcing bars 5 by measuring the potential distribution on the ground surface 2.

That is, a voltage is applied between the coating replacement 1 and the ground surface 2 using the voltage application device 7. If the coated steel @1 is in electrical contact with the reinforcing bar 5, changes such as a "dent" or "protrusion" will occur in the potential distribution of the ground surface 2 near the contact point.

[Problems to be Solved by the Invention] However, each of the above-mentioned detection methods also has the following problems. In other words, in the first method of measuring ground resistance, in the case of an existing building, the coated steel pipe 1 may be artificially grounded at a place other than the part where it penetrates the wall 3, so the measured resistance value is small. The coated steel pipe 1 is reinforced with reinforcing bar 5
There is a problem in that it cannot necessarily be determined that there is electrical contact with the

Therefore, the detection results are not reliable.

In addition, in the method of measuring the potential distribution on the ground surface 2,
Since the value of the grounding resistance of the reinforcing bars 5 is very small compared to the value of contact resistance when the coated steel pipe 1 contacts the reinforcing bars 5, Changes in potential distribution are minute and therefore very difficult to detect. Furthermore, since the ground surface 2 is often paved with asphalt, it is even more difficult to accurately measure changes in potential distribution.

In addition to the above two detection methods, there is also a method using a vibrocator, but it is easily affected by induced current and has not yet been put into practical use.

The present invention was made based on these circumstances, and its purpose is to detect the magnetic field formed by the current flowing through the reinforcing bars when a steel pipe makes electrical contact with the reinforcing bars, thereby improving the wall surface. An object of the present invention is to provide a metal contact detection device in the wall of a steel pipe that can easily and reliably detect contact of a steel pipe with a reinforcing bar in a non-contact manner and improve reliability.

Means for Solving Problem E] The metal contact detection device in the wall of a steel pipe of the present invention installs a current source between the steel pipe and the ground, and uses the steel pipe that penetrates the wall containing reinforcing bars as an outgoing current path to connect to the ground. A pair of magnetic sensors, which are controlled to move along the wall while maintaining a fixed positional relationship with each other, detect the magnetic field perpendicular to the wall, and a differential amplifier is used to detect the magnetic field. The difference between the magnetic fields detected by the pair of magnetic sensors is thereby amplified, and the output signal of the differential amplifier is further recorded by the recorder.

[Function] - In the metal contact detection device in the wall of a steel pipe configured as described above, a current circuit is formed in which the steel pipe that penetrates the wall is used as an outgoing current path, and the earth is used as a current return path.

When the steel pipe electrically contacts the reinforcing bars in the wall, a grounding current 'flows through the contact portion to the reinforcing bars, and a magnetic field is formed around the reinforcing bars due to this grounding current. Since the direction of the magnetic field around the reinforcing bars is perpendicular to the wall surface, it is detected by a pair of magnetic sensors whose movement is controlled along the wall surface. Incidentally, since the direction of the magnetic field formed around the steel pipe forming the current circuit is parallel to the wall surface, it is not detected by each of the magnetic sensors. Furthermore, the reason why two magnetic sensors are provided and the difference between the detected magnetic fields is amplified is to eliminate the influence of earth's magnetism. Therefore, while moving the pair of magnetic sensors along the wall surface while maintaining a constant positional relationship, the output signal of the differential amplifier is monitored, and if this output signal changes significantly, the steel pipe is is in electrical contact with.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing a schematic configuration of a metal contact detection device in the wall of a steel pipe according to an embodiment. In the figure, 11 is a concrete wall of a building, for example, and although not shown, the lower end of this wall 11 is buried under the ground surface. Further, a plurality of reinforcing bars 12 are arranged in the vertical direction at the center of the wall 11 as reinforcing members. A steel pipe 13 made of a coated steel pipe, such as a gas pipe, passes through the wall 11 at a substantially right angle to the wall surface 14. A current source 15 consisting of a battery is connected between the uncoated metal surface of the near side of the wall 11 of the steel pipe 13 and the ground in the polarity shown.

Further, the rear portion of the wall 11 in the steel pipe 13 is directly grounded to the earth. Therefore, the current source 15° steel pipe 13.
A current circuit is formed in which the steel pipe 13 penetrating the wall 11 is used as an outgoing current path and the earth is used as a return path.

Further, a pair of magnetic sensors 16a and 16b are disposed on the wall surface 14 of the wall 11 and are manually controlled to move along the wall surface 14 in the Y-axis direction. These pair of magnetic sensors 16a, 16b are fixed to a spacer 17 in order to maintain a constant mutual positional relationship. Furthermore, each magnetic sensor 16a.

16b is configured to detect only the magnetic field in the longitudinal direction, that is, in the direction orthogonal to the wall surface 14, and the detection signal of each magnetic sensor 16a, 16b is sent to the differential amplifier 1.
It is input to the (+) side input terminal and the (-) side input terminal of 8. The output signal of the differential amplifier 18 is input to a recorder 19 and recorded on recording paper. During measurement, while moving the pair of magnetic sensors 16a and 16b whose mutual spacing distance is fixed to L by the spacer 17 in the Y-axis direction, changes in the output signal level of the differential amplifier 18 recorded on the recorder 19 are measured. Observe. If the signal level changes significantly, it is determined that the steel pipe 13 is in electrical contact with the reinforcing bar 12.

FIG. 2 is a perspective view for explaining the operating principle of the detection device of the embodiment. That is, there are vertical reinforcing bars 1 in the wall 11.
In addition to the reinforcing bars 2a-e, horizontal reinforcing bars 2Qa-6 are arranged, and the reinforcing bars 12.degree. 20 in both directions are arranged in a mesh shape. Now, suppose the steel pipe 13 is the central reinforcing bar 1
Assume that it is in electrical contact with 2C. And electric 111
15 voltage is E, the grounding resistance on the current source 15 side of the steel pipe 13 is R1, and the grounding resistance on the anti-il flow WA15 side of the steel pipe 13 is R2.
, the contact resistance between the steel pipe 13 and the reinforcing bar 12C is Rp.

Let the grounding resistance of the wall 11 be Re. Then, the current supplied from the M flow source 15 to the steel pipe 13 in the direction of the arrow is 11, and the current supplied to the steel pipe 13 is
If the current flowing from the opposite end of 3 to the ground via the grounding resistor R2 is I2, the current flowing to the ground via the reinforcing bar 12a is (I''1t-12).Then, the current 11
A magnetic field HYI! is formed around the axis (X-axis) of the steel pipe 13 due to HYI! is a plane parallel to the wall surface 14 (Y-
Spreads within two planes. In addition, the magnetic field Hx formed around the axis (Z axis) of the reinforcing bar 12c due to the current (1-11-12)
r extends in a plane perpendicular to wall surface 14 (X-Y plane) as shown. Therefore, each magnetic sensor 16a, 16
b is the iron WJ12 without detecting the magnetic field HYZ due to the steel pipe 13.
Only the magnetic field Hxy caused by c is detected.

The flow of each current in FIG. 2 can be represented by the equivalent circuit in FIG. 3. That is, in this equivalent circuit, the ground resistance Rs on both sides of the steel pipe 13.

Assuming that R2 is equal, by simple consideration, reinforcing bar 12c
The current I flowing through is determined by equation (1).

1-1 heavy-12 -E/ (2(Rp +Ra) +R1) River (1
) Next, consider how the current ■ flows inside the wall 11.

That is, inside the concrete wall 11, a plurality of reinforcing bars 12a-e and 20a-e are assembled in a mesh shape as described above. However, if the mesh is uniform as shown in FIG. 4(a), the total current flowing in the wall 11 is as shown in FIG.
As shown in b), it flows uniformly in the vertical direction (Z-axis direction). Therefore, if there are n reinforcing bars 12 extending in the vertical direction, the current 1 flowing through each reinforcing bar is I/n, and <2
It is shown in equation 1.

i-E/n (2(RP +RO) +Rt
) ・A23 Next, find the magnetic field formed around this reinforcing bar 12G by the current i flowing through one reinforcing bar 12C. As shown in Figure 5, this current I is at the origin (0) of the X-Y coordinate system.
, 0) and flows downward perpendicular to the paper surface, then 8
The magnitude of the magnetic field HXY at the point (X, 'l/) is (3
The direction is clockwise.

Hx-i/)π What is necessary is to measure the X-axis direction component Hx of HxY. That is, as is clear from FIG. 5, this magnetic field Hx is expressed by equation (4).

Hx-HX'rCO3θ -1'j i/2π(x2+y2) -144(4
) is a value when only one reinforcing bar 12 exists in the wall 11, but in reality, as shown in FIG. 2, a large number of reinforcing bars 12 are arranged in the wall 11. Therefore, it is necessary to superimpose equation (4).

In Figure 6, the thickness 2d of the wall 11 is 12 cm, and each reinforcing bar is 1;)
When the mutual spacing S between a and d is 1Qcl, the number n is 5, and each current value i is 0.3A, one magnetic sensor is moved from the leftward position of the reinforcing bar 12a to the rightward position of the reinforcing bar 12d. It is an output characteristic diagram of a magnetic sensor when it is moved. As is clear from this characteristic diagram, the polarity of the magnetic field Hx is reversed when the magnetic sensor is located at the center of each reinforcing bar 12a to 12d (reinforcing bar 12C). Therefore, if the magnetic field characteristics shown in FIG. 6 are obtained, it means that current is flowing through the reinforcing bar 12,
is detected to be in electrical contact with the reinforcing bar 12 within the wall 11.

However, in reality, the ground resistance R1, R2 of the steel pipe 13
Since the value of is small compared to the value of contact resistance Rp when this steel pipe 13 contacts the reinforcing bar 12, the value of the grounding current ■ flowing from this contact part to the ground via the reinforcing bar 12 is very small. , susceptible to the effects of magnetic fields from the Earth's magnetism. For example, even if the output of the current source 15 is adjusted to set the value of the current 1 flowing through the steel pipe 13 to 2A, the number of reinforcing bars 12a to d
Since a ground current flows at the same time, the value of the current i flowing through one reinforcing bar 12 is approximately several hundred mA.

Therefore, for example, if the thickness 2d of 111 is 12C■, the value of the magnetic field Hx on the wall surface 14 due to this current i will be approximately several + Oe (Oersteds), which is 0.7 to 0. 208).

In order to eliminate the influence of the earth's magnetic field, as shown in FIG.
6b is installed. And each magnetic sensor i5a, 1
A differential amplifier 18 amplifies the difference between the magnetic fields obtained by the magnetic field 5b. Then, with the spacer 17, the distance Ltll
If the magnetic sensors 16a and 16b are moved along the wall surface 14 in the Y-axis direction while keeping the same distance, each magnetic sensor 16a, 16b will have the characteristics shown in FIG. The characteristic diagram shown in FIG. 7 is obtained by taking the difference in characteristics. That is, in a place where no current flows through the reinforcing bars 12, the magnetic fields detected by the magnetic sensors IEA and 16b are only the magnetic fields due to the earth's magnetism, so they have the same value, and the difference therebetween is a very small value. However, at a position where a current is flowing through the reinforcing bar 12, the magnetic field detected by each magnetic sensor 16a, 16b differs greatly depending on the position in the Y-axis direction, as shown in FIG. Therefore, the difference is a very large value. Therefore, when the output signal of the differential amplifier 18 is recorded by the recorder 19, the position where a large change in signal level occurs as shown in FIG. Can be identified.

In the steel pipe wall metal contact detection device configured in this way, the steel pipe 13 electrically contacts the reinforcing bar 12 within the wall 11, and the magnetic field Hx1 due to the ground current I flowing through the reinforcing bar 12 is detected.
Since the magnetic field Hx perpendicular to the wall surface 14 of the steel pipe 13 is detected, the influence of the magnetic field HYZ caused by the electric current FE I1 flowing through the steel pipe 13 can be eliminated, and it is possible to ensure that the ground current ■ has flowed through the reinforcing bar 2. Can be detected.

Further, a pair of magnetic sensors 1 are arranged at a correspondingly constant interval.
6a and 16b are used to detect the grounding current of the reinforcing bars 12, so that measurement can be performed while completely eliminating the influence of earth's magnetism. Therefore, it is possible to reliably detect that the steel pipe 13 is in electrical contact with the reinforcing bar 12 within the wall 11.

[Effects of the Invention] As described above, according to the present invention, when a steel pipe comes into electrical contact with a reinforcing bar, the magnetic field formed by the current flowing through the reinforcing bar is detected.

Therefore, contact of the steel pipe with the reinforcing bar can be easily and reliably detected from the wall surface without contact. In addition, by using a pair of magnetic sensors, the influence of geomagnetism can be removed.
Measurement accuracy and reliability can be further improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the general configuration of a metal contact detection device in the wall of a steel pipe according to an embodiment of the present invention, FIG. 2 is a perspective view for explaining the operating principle of the embodiment, and FIG. An equivalent circuit diagram for explaining the principle of operation, Fig. 4 is a diagram showing the current flow in the reinforcing bars of the same example, Fig. 5 is a diagram showing the magnetic field formed by the M flow, Figs. FIG. 7 is a magnetic field characteristic diagram of the same embodiment, and FIGS. 8 and 9 are diagrams showing a conventional method for detecting metal contact within the wall of a steel pipe. 11...Wall, 12.20...Reinforcing bar, 13...Steel pipe, 14...Wall surface, 15 ・L flow source, 16a, 16
b-... Magnetic sensor, 17... Spacer, 18...
Differential amplifier, 19...recorder. Applicant's representative Patent attorney Takehiko Suzue Figure 3 (a) (b) Figure 5 I standing f (Y axis I-1'fl) Figure 7 Figure 8 Figure 9 Figure 1 Display of the case No. 60-178724 2, name of the invention! Person who performs correction of metal contact detection device 3 in the wall of I pipe. Relationship to the case Patent applicant (412> Nippon Kokan Co., Ltd. 4, agent No. 17 Mori Building, 1-26-5 Toranomon, Minato-ku, Tokyo) (2)
Figures 2, 3, 6, and 7 of the drawings are corrected as shown in the attached sheet. Method Description: 1. Name of the invention: Device for detecting metal contact in a wall of a steel pipe 2. Claims: A steel pipe that penetrates the wall of a building containing reinforcing bars at a substantially right angle to the wall surface is in electrical contact with the reinforcing bars. In the metal contact detection device in the wall of a steel pipe, the current source is provided between the steel pipe and the ground, and forms a current circuit with the steel pipe penetrating the wall as the current return path and the ground as the current outgoing path. , a pair of magnetic sensors that each detect a magnetic field perpendicular to the wall surface and are controlled to move along the wall surface while maintaining a fixed positional relationship with each other; A metal contact detection device in the wall of a steel pipe, characterized by comprising a differential amplifier that amplifies the difference, and a recorder that records the output signal of the differential amplifier. 3. Detailed Description of the Invention [Field of Industrial Application] The present invention provides a method for preventing electrical contact between the steel pipe and the reinforcing steel inside the wall when a coated steel pipe or the like penetrates a reinforced wall of a building or the like. This invention relates to a metal contact detection device within the wall of a steel pipe. [Conventional technology] When bringing coated steel pipes such as gas pipes into a building from the outside, or when piping them to each room within the building, the coated steel pipes are passed through reinforced walls. need to be piped. In this case, if the coated steel pipe comes into electrical contact with the internal reinforcing steel at the part that penetrates the wall, the grounding resistance of the building itself is low, so even if the coated steel pipe is given cathodic protection, the contact area will be Corrosive current flows into the ground through the reinforcing steel. Therefore, the corrosion rate of the coated steel pipe increases, the durability of the coated steel pipe becomes shorter, and in the worst case, there is a concern that gas leakage may occur. To avoid such problems, when constructing a new building, the piping work must be done with great care to ensure that the steel pipes do not come into direct electrical contact with the reinforcing bars, but in existing buildings, steel pipes are It is necessary to detect from the outside whether or not the penetration part is electrically in contact with the internal reinforcing steel. One method of detecting the presence or absence of contact within the walls of an existing building is to measure the ground resistance of steel pipes. The method for measuring this ground resistance is as shown in FIG. That is, a coated steel pipe 1 such as a gas pipe buried underground is led indoors by penetrating the wall 3 of a building whose lower end is also buried below the ground surface 2. 1 and the ground using a resistance measuring device 4. If the coated steel pipe 1 is not in electrical contact with the reinforcing bars 5 disposed within the wall 3, the resistance value is a large value, and the coating of the coated steel pipe 1 is If it is in electrical contact with the stripped reinforcing bar 5, the reinforcing bar 5 is grounded at -@ □, and the coated steel pipe 1 is grounded via the reinforcing bar 5, so the resistance value is becomes smaller. Therefore, it is possible to detect whether the coated steel pipe 1 is in electrical contact with the reinforcing bars 5 or not. Furthermore, as shown in FIG. 9, there is a detection method that detects electrical contact between the coated steel pipe 1 and the reinforcing bars 5 by measuring the potential distribution on the ground surface 2. That is, a voltage is applied between the coated steel pipe 1 and the ground surface 2 using the voltage application device 7. If the coated steel pipe 1 is in electrical contact with the reinforcing bar 5, a change such as a depression or a protrusion will occur in the potential distribution on the ground surface 2 near the contact point. [Problems to be Solved by the Invention] However, each of the above-mentioned detection methods also has the following problems. In other words, in the first method of measuring ground resistance, in the case of an existing building, the coated steel pipe 1 may be artificially grounded at a place other than the part where it penetrates the wall 3, so the measured resistance value is small. There is a problem in that it cannot necessarily be determined that the coated steel pipe 1 is in electrical contact with the reinforcing bar 5. Therefore, the detection results are not reliable. In addition, in the method of measuring the potential distribution on the ground surface 2,
Since the value of the grounding resistance of the reinforcing bars 5 is very small compared to the value of contact resistance when the coated AM pipe 1 contacts the reinforcing bars 5, Changes in potential distribution are minute and therefore very difficult to detect. Furthermore, since the ground surface 2 is often paved with asphalt, it is even more difficult to accurately measure changes in potential distribution. In addition to the above two detection methods, there is also a method using a vibrocator, but it is easily affected by induced current and has not yet been put into practical use. The present invention was made based on these circumstances, and its purpose is to detect the magnetic field formed by the current flowing through the reinforcing bars when a steel pipe makes electrical contact with the reinforcing bars, thereby improving the wall surface. An object of the present invention is to provide a metal contact detection device in the wall of a steel pipe that can easily and reliably detect contact of a steel pipe with a reinforcing bar in a non-contact manner and improve reliability. [Means for Solving the Problems] The metal contact detection device in the wall of a steel pipe according to the present invention installs a current source between the steel pipe and the ground, and uses the steel pipe that penetrates the wall in which reinforcing bars are present as a current return path to connect to the ground. A pair of magnetic sensors that are controlled to move along the wall surface while maintaining a fixed positional relationship with each other detect the magnetic field perpendicular to the wall surface, and a differential amplifier detects the magnetic field. The difference between the magnetic fields detected by an equal pair of magnetic sensors is amplified, and the output signal of the differential amplifier is recorded by a recorder. [Function] In the w4Ilt in-wall metal contact detection device configured as described above, a current circuit is formed in which the steel pipe penetrating the wall serves as a current return path and the ground serves as a current outgoing path. Then, when the steel pipe electrically contacts the reinforcing bars in the wall, a grounding current flows through the contacted reinforcing bars through this contact portion, and a magnetic field is formed around the reinforcing bars due to this grounding current. Since the direction of the magnetic field around the reinforcing bars is perpendicular to the wall surface, it is detected by a pair of magnetic sensors whose movement is controlled along the wall surface. Note that since the direction of the magnetic field formed in the steel pipe layer forming the 'Ii flow circuit is parallel to the wall surface, it is not detected by each of the magnetic sensors. Furthermore, the reason why two magnetic sensors are provided and the difference between the detected magnetic fields is amplified is to eliminate the influence of earth's magnetism. Therefore, while moving the pair of magnetic sensors along the wall surface while maintaining a fixed positional relationship, the output signal of the differential amplifier is monitored, and if this output signal changes significantly, the steel pipe becomes a reinforcing bar. There will be electrical contact. [Example] An example of the present invention will be described below with reference to the drawings. The first factor is a schematic diagram showing a schematic configuration of a metal contact detection device in the wall of a steel pipe according to an embodiment. In the figure, reference numeral 11 is a concrete wall of, for example, a pill house, and although not shown, the lower end of this wall 11 is buried under the ground surface. Further, a plurality of reinforcing bars 12 are arranged in the vertical direction at the center of the wall 11 as reinforcing materials. A steel pipe 13 made of a coated steel pipe, such as a gas pipe, passes through the wall 11 at a substantially right angle to the wall surface 14. A current 11i15 from a battery is connected between the uncoated metal surface of the front part of the wall 11 of the steel pipe 13 and the ground with the polarity shown. Further, the rear portion of the wall 11 in the steel pipe 13 is directly grounded to the earth. Therefore, - current source 15. Steel pipe 13. A current circuit is formed in which the steel pipe 13 penetrating the wall 11 is used as a current return path, and the earth is used as an outgoing current path. Further, on the wall surface 14 of the wall 11, a pair of magnetic sensors 16a, 1 are provided which are controlled to move along the wall surface 14 in the Y-axis direction.
6b is arranged. These pair of magnetic sensors 16a, 1
6b are fixed to both ends of the spacer 17 in order to maintain a constant mutual positional relationship. Furthermore, each magnetic sensor 16a. 16b is configured to detect only the magnetic field in the longitudinal direction of the ll tube 13, that is, in the direction orthogonal to the wall surface 14, and the detection signal of each magnetic sensor 16a, 16b is the (+) sub-field of the differential amplifier 18. Input to the input terminal and (-) sub-input terminal. Furthermore, the output signal of the differential amplifier 18 is input to a recorder 19 and recorded on recording paper. During measurement, while moving the pair of magnetic sensors 16a and 16b whose mutual spacing distance is fixed to L by the spacer 17 in the Y-axis direction, changes in the output signal level of the differential amplifier 18 recorded on the recorder 19 are measured. Observe. If the signal level changes significantly, it is determined that the steel pipe 13 is in electrical contact with the reinforcing bar 12. FIG. 2 is a perspective view for explaining the operating principle of the detection device of the embodiment. That is, there are vertical reinforcing bars 1 in the wall 11.
In addition to the reinforcing bars 2a to 12e, horizontal reinforcing bars 20a to 20e are arranged, and the reinforcing bars 12 and 20 in both directions are arranged in a mesh shape. Assume now that the steel pipe 13 is in electrical contact with the central reinforcing bar 12C. and,
The voltage of the current source 15 is E, and the grounding resistance on the current source 15 side of the Ill tube 13 is R1,! R2 is the grounding resistance on the counter current source 15 side of the $4 pipe 13, and Rp is the contact resistance between the m pipe 13 and the reinforcing bar 12C.
, the ground resistance of the wall 11 is Ro. And the current aN
``If the current supplied from 15 to the earth l\ in the direction of the arrow through the earthing resistor R1 is 11, and the current flowing from the earth to the opposite side of the steel pipe 13 through the earthing resistor R2 is 12, then the earthing resistance Ro from the earth is 11. The current I flowing into the reinforcing bar 12a through the reinforcing bar 12a is (1=11-12).Then, the magnetic field Hyz formed around the axis (X axis) of the steel pipe 13 due to the current 1 is
extends in a plane parallel to the wall surface 14 (YZ plane) as shown. In addition, the magnetic field HXY formed around the axis (two axes) of the reinforcing bar 12G due to the current (1=1*-12) is generated in the plane (X-Y plane) perpendicular to the wall surface 14 as shown in the figure. spread. Therefore, each magnetic sensor 16a, 16b does not detect the magnetic field HYZ caused by the steel pipe 13, but only detects the magnetic field Hxy caused by the reinforcing bar 12G. The flow of each current in FIG. 2 can be represented by the equivalent circuit in FIG. 3. That is, in this equivalent circuit, the ground resistance Rt on both sides of the m tube 13. Assuming that R2 is equal, by simple consideration, reinforcing bar 12c
'R flow I flowing through is determined by equation (1). 1-It-I2 = E/ (2(Rp +Ro) +Rt) -[
1) Next, consider how the current I flows inside the wall 11. In other words, the g of concrete! Inside 11, a plurality of reinforcing bars 12a to i2e and 20a to 20e are arranged in a mesh shape as described above. However, if the mesh is uniform as shown in FIG. 4(a), the total current flowing in 111 will flow uniformly in the vertical direction (Z-axis direction) as shown in FIG. 4(b). Therefore, if there are n reinforcing bars 12 extending in the vertical direction, the current i flowing through each reinforcing bar is I/n, (2)
It is shown by the formula. i = E/n (2(RP +RO) +Rt) ・
(2) Next, find the magnetic field formed around this reinforcing bar 12G by the current i flowing through one reinforcing bar 12C. As shown in Figure 5, this current i is the origin of the X-Y coordinate system (0,0
), if the flow is perpendicularly downward to the plane of the paper, then the point P (
The magnitude of the magnetic field Hx at (x, y) is shown by equation 3, and the direction is clockwise.
Here, the magnetic field HYJ? formed around the axis of the steel pipe 13 by the current ■1 flowing through the steel pipe 13? iron 112 without the influence of
To detect only -1xy (magnetic field of C), this magnetic field HX
What is necessary is to measure the X-axis direction component Hx of Y. That is, as is clear from FIG. 5, this magnetic field Hx is expressed by equation (4). Hx=HxiCOSθ=yi/2π (x2 +y2)...
(4) Equation (4) is the value when only one reinforcing bar 12 exists in the wall 11, but in reality, as shown in FIG.
A large number of reinforcing bars 12 are arranged inside. therefore,
It is necessary to superimpose equations (4). In Fig. 6, the thickness 2d of the wall 11 is 120 m, and each reinforcing bar 128
When the mutual spacing S between ~12e is 10CIll2, the number n is 5, and each current 1i11i is 0.3 A, one magnetic sensor is moved from the leftward position of the reinforcing bar 12a to the rightward position of the reinforcing bar 12e. FIG. 3 is an output characteristic diagram of a magnetic sensor when As is clear from this characteristic diagram, the magnetic sensor is located at the center position of each reinforcing bar 128 to 12e (reinforcing bar 12
In C), the polarity of the magnetic field Hx is reversed. Therefore, if the magnetic field characteristics shown in FIG. 6 are obtained, it means that a current is flowing through the reinforcing bars 12, and it is detected that the steel pipe 13 is in electrical contact with the reinforcing bars 12 within the wall 11. However, in reality, the ground resistance Rs, R of the steel pipe 13
Since the value of 2 is small compared to the value of the contact resistance Rp when this steel pipe 13 contacts the reinforcing bar 12, the value of the grounding current I flowing from the ground to the reinforcing bar 12 through this contact part is very large. Because it is small, it is easily affected by the magnetic field caused by the Earth's magnetism. For example, even if the value of the current 11 flowing through the steel pipe 13 is set to 2A by adjusting the output of the current source 15, the number of reinforcing bars 12a
12e simultaneously, the value of the current i flowing through one reinforcing bar 12 is approximately several hundred mA. Therefore, for example, if the thickness 2d of the wall 11 is 12CI11, the value of the magnetic field Hx on the wall surface 14 due to this current i will be about several tens of mG (Gauss), and the magnitude of the magnetic field due to normal geomagnetism (0.7~ 0.2mG). In order to eliminate the influence of the earth's magnetic field, as shown in FIG.
6b is installed. And each magnetic sensor 16a, 1
A differential amplifier 18 amplifies the difference between the respective magnetic fields obtained in the magnetic field 6b. Then, if it is moved along the wall surface 14 in the Y-axis direction while keeping the distance fixed with the spacer 17,
Each of the magnetic sensors 16a and 16b, excluding the earth's magnetism, has characteristics shown in FIG. 6 that are shifted in parallel in the Y-axis direction by a distance wIL, so even when there is earth's magnetism, the differential amplifier 1
By using 8, the difference between the two characteristics of a simple substance will be the same value as here, and the characteristic diagram shown in FIG. 7 will be obtained. That is, in places where no current flows through the reinforcing bars 12, each magnetic sensor 16a
, 16b are only magnetic fields due to the earth's magnetism, so they have the same value, and the difference between them is a very small value. However, at a position where a current is flowing through the reinforcing bar 12, the magnetic field detected by each magnetic sensor 16a, 16b differs greatly depending on the position in the Y-axis direction, as shown in FIG. Therefore, the difference is a very large value. Therefore, when the output signal of the differential amplifier 18 is recorded by the recorder 19, the position where a large change in signal level occurs as shown in FIG. Can be identified. With the metal contact detection device in the wall of a steel pipe configured as described above, the steel pipe 13 electrically contacts the reinforcing bar 12 within the wall 11, and the magnetic field Hx due to the ground current I flowing through the reinforcing bar 12 is generated on the wall surface 14. Since the magnetic field Hx orthogonal to the magnetic field Hx caused by the current 11 flowing through the steel pipe 13
z can be eliminated, and it is possible to reliably detect that the grounding 'R flow I has flowed through the reinforcing bar 2. Further, a pair of magnetic sensors 1 are arranged at a constant distance from each other.
6a and 16b are used to detect the grounding current of the reinforcing bars 12, so that measurement can be performed while completely eliminating the influence of earth's magnetism. Therefore, it is possible to reliably detect that the steel pipe 13 is in electrical contact with the reinforcing bar 12 within the wall 11. [Effects of the Invention] As described above, according to the present invention, when a steel pipe comes into electrical contact with a reinforcing bar, the magnetic field formed by the current flowing through the reinforcing bar is detected. Therefore, contact of the steel pipe with the reinforcing bar can be easily and reliably detected from the wall surface without contact. In addition, by using a pair of magnetic sensors, the influence of geomagnetism can be removed.
This improves measurement accuracy and further improves reliability. 4. Brief description of the drawings Fig. 1 is a schematic diagram showing a schematic configuration of a metal contact detection device in the wall of a steel pipe according to an embodiment of the present invention, and Fig. 2 is a diagram for explaining the operating principle of the same embodiment. Fig. 3 is an equivalent circuit diagram for explaining the principle of operation of the same example, Fig. 4 is a diagram showing the flow of current in the reinforcing bars of the same example, and Fig. 5 shows the magnetic field formed by the same current. 6 and 7 are magnetic field characteristic diagrams of the same embodiment, and FIGS. 8 and 9 are diagrams showing a conventional method for detecting metal contact within the wall of a steel pipe. 11...Wall, 12.20...Reinforcing bar, 13...Steel pipe, 14...Wall surface, 15...Current source, 16a, 16
b...Magnetic sensor, 17...Spacer, 18...
Differential amplifier, 19...° recorder. Applicant's agent Patent attorney Takehiko Suzue Figure 3

Claims (1)

[Claims] In a steel pipe wall metal contact detection device for detecting that a steel pipe that penetrates a wall of a building containing reinforcing bars at a substantially right angle to the wall surface is in electrical contact with the reinforcing bars, the steel pipe is installed between the steel pipe and the ground. , a current source forming a current circuit with the steel pipe penetrating the wall as the forward current path and the earth as the current return path; A pair of magnetic sensors whose movement is controlled along the magnetic field, a differential amplifier that amplifies the difference between the magnetic fields detected by the pair of magnetic sensors, and a recorder that records the output signal of the differential amplifier. A device for detecting metal contact within the wall of a steel pipe.