JPH03194487A - Detecting device for buried body - Google Patents

Abstract

PURPOSE:To cancel a sent magnetic field which generates an error in the detection of a magnetic field with an induced current and to performs detection with high accuracy by providing a magnetic sensor with a coil which cancels a magnetic field opposite in phase to a sent magnetic field. CONSTITUTION:A lock-in amplifier 6 extracts an in-phase component and a 90 deg. out-of-phase component from a magnetic field detected by the magnetic sensor 5 by using a current signal as a reference signal. The 90 deg. out-of-phase component, i.e. component corresponding to the magnetic field by the induced current is displayed on an output means 7 such as a level meter to detect the specific underground buried body. At this time, the in-phase component output of the lock-in amplifier 6 is inputted to the gain control input part 12b of a variable gain amplifier 12 to vary the gain of the variable gain amplifier 12 and thus a cancel magnetic field is generated to cancel the sent magnetic field. Consequently, the influence of the sent magnetic field upon the magnetic field 5 is completely removed to perform detection with high accuracy.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention detects the location of conductive objects buried underground, such as gas pipes, water pipes, electric cables, telephone cables, or wires. It relates to a device for.

(Prior Art and Problems to be Solved by the Invention) Conventional methods for detecting the position of buried objects such as electrically conductive buried pipes and buried cables buried underground, that is, the position directly above them and the buried depth. Magnetic detection methods are commonly used because they are simple, have relatively high detection accuracy, and can be applied to a variety of locations. The most commonly used magnetic detection method is to pass an alternating current through the underground object and detect the distribution of the magnetic field generated around it by the alternating current using a magnetic sensor in a receiver. In this case, the methods for passing alternating current through underground objects are the direct transmission method, in which an alternating current source is directly connected to the exposed part of the ground, and the direct transmission method, in which alternating current is passed through electromagnetic induction using a transmitting magnetic field generated by a transmitter. There is a guided transmission method.

The present invention relates to the latter inductive transmission method, which has the advantage of being applicable to underground objects that do not have exposed above-ground parts at necessary locations. It is necessary to detect only the magnetic field with high precision.

However, in the inductive transmission method, in addition to the magnetic field generated by the induced current, the transmitted magnetic field generated by the transmitter is also likely to be received by the magnetic sensor of the receiver, and the transmitted magnetic field is detected by the magnetic sensor in the receiver. It distorts the magnetic field, reducing accuracy, and this tendency becomes more pronounced as the distance between the transmitter and receiver gets closer.

That is, Fig. 4 shows a vector representation of the magnetic field detected by the magnetic sensor with the transmitted magnetic field as a reference.As can be seen from the vector diagram, the magnetic field generated by the induced current has a 90'' phase with respect to the transmitted magnetic field. Therefore, the magnetic sensor detects the magnetic field in a state where this 90° phase-shifted magnetic field and the transmitting magnetic field are superimposed, so the magnetic field detected by the magnetic sensor is different from the transmitting magnetic field depending on the distance from the transmitting coil. Therefore, when it is necessary to perform detection near the transmitter, the transmitted magnetic field is a major error factor.Moreover, the magnetic field generated by the induced current and the transmitted magnetic field Of course, the frequencies are the same, so
Ordinary filters cannot distinguish between them, and it is generally difficult to remove their effects.

A device capable of removing such effects may be arranged so that the transmitting coil of the transmitter and the magnetically sensitive direction of the magnetic sensor of the receiver are perpendicular to each other, or as shown in FIG. Cancellation coil b connected in series with a
is placed in the vicinity of the magnetic sensor C, and as shown in FIG. Attempts have been made to create devices that partially reduce the magnetic field d to zero.

However, in these methods, it is essential to completely fix the relative positions of the transmitting coil a and the magnetic sensor C, and these methods cannot be applied to ordinary detection devices in which the transmitter and receiver are separated. It is not possible. Also,
Even if the transmitter and receiver are configured in a body, if the relative position of the transmitting coil a and the magnetic sensor C changes due to temperature changes or mechanical deformation, the transmitting magnetic field d cannot be completely removed even by the canceling magnetic field e. It disappears.

The present invention aims to solve the above problems.

(Means for Solving the Problems) To explain in detail the present invention for solving the above problems, firstly, the buried object detection device of the present invention detects buried objects having electrical conductivity buried in the ground. In the device for detecting the underground object by causing an induced current to flow through the object by electromagnetic induction using a transmitted magnetic field generated by a transmitter, and detecting the magnetic field generated by the induced current with a receiver, the transmitter includes a transmitting coil for generating the transmitting magnetic field, an AC power source for passing a current through the transmitting coil, a current detecting means for detecting the current flowing through the transmitting coil, and a current detected by the current detecting means. A transmission means for transmitting a signal to the receiver is provided, and the receiver includes a magnetic sensor for detecting a magnetic field, and a magnetic field detected by the magnetic sensor and the current signal transmitted from the transmitter. In phase with the current signal and 90
a component extracting means for extracting a phase-shifted component; and an output means for outputting a 90'' phase component extracted by the component extracting means;
variable gain amplification means for amplifying the current signal by changing the gain using the in-phase component extracted by the component extraction means as a gain control signal; and an output current of the variable gain amplification means to flow to the magnetic sensor. A canceling coil is provided to generate a magnetic field having a phase opposite to the transmitting magnetic field, and the variable gain amplification means is configured to perform a feedback operation so as to reduce the in-phase component to zero.

In addition, as another configuration, the buried object detection device of the present invention includes:
An induced current is caused by electromagnetic induction by a transmitting magnetic field generated by a transmitter through an electrically conductive buried object buried underground, and a receiver detects the magnetic field generated by the induced current, and the underground object is buried underground. In the device for detecting an object, the i-distribution transmitter includes a transmitting coil for generating the transmitting magnetic field, an AC power source for supplying current to the transmitting coil, and detecting the current flowing to the transmitting coil. A current detection means for detecting a magnetic field, and a transmission means for transmitting a current signal detected by the current detection means to the receiver, and the receiver includes a magnetic sensor for detecting a magnetic field, and a current signal detected by the magnetic sensor. Component extracting means for extracting components in phase with and 90' out of phase with the current signal from the magnetic field and the current signal transmitted from the transmitter, and means for outputting the 90'' phase component extracted by the component extracting means. a phase shifter for shifting the phase of the current signal by 180°; and a variable gain amplification means for amplifying the output of the phase shifter by changing the gain using the in-phase component extracted by the component extractor as a gain control signal. A canceling coil is provided for passing an output current of the variable gain amplifying means to generate a magnetic field having an opposite phase to the transmitting magnetic field with respect to the magnetic sensor, and the variable gain amplifying means is configured to reduce the in-phase component to zero. The structure is such that the feedback operation is performed.

In the above configuration, the component extracting means can be configured by a lock-in amplifier. Further, the transmission means is preferably an insulated transmission means.

(Function) With the above configuration, the detection device of the present invention sends an induced current to an underground object by electromagnetic induction using a transmitting magnetic field generated by a transmitting coil of a transmitter, and receives the magnetic field generated by this induced current. The underground object is detected using the magnetic sensor of the container, and the underground object is detected based on the result. In this case, in the receiver, a component extracting means extracts a 90° phase-shifted component corresponding to the magnetic field caused by the induced current from the detected magnetic field and the current signal corresponding to the current flowing in the transmitting coil of the transmitter. extract,
This is outputted by the output means, and the variable gain amplification means is operated as a feedback control signal using the component in phase with the current signal extracted by the component extraction means as a gain control signal to amplify the current signal and reduce the in-phase component to zero. By changing the output current flowing through the canceling coil so as to change the canceling magnetic field having the opposite phase to the transmitting magnetic field. In this way, the present invention cancels out the transmission magnetic field by adding a canceling magnetic field having the same absolute value and the opposite phase, that is, 180 degrees out of phase with the transmission magnetic field, to the magnetic sensor, thereby eliminating the influence of the transmission magnetic field. It can be completely removed, and therefore only the magnetic field due to the induced current that is 90° out of phase with the transmitted magnetic field can be detected by the magnetic sensor. Since such cancellation of the transmitted magnetic field is performed at the magnetic field stage, highly accurate underground object detection can be performed without requiring very high precision or resolution of the magnetic sensor or other components.

The above-mentioned canceling magnetic field may be generated by flowing an output current having the same phase as the current signal through a canceling coil, or may be generated by flowing an output current having the opposite phase to the current signal through a canceling coil. You can also configure
In the former and latter, the winding direction of the cancellation coil is opposite.

(Example) Next, embodiments of the present invention will be described with reference to the drawings.

First, in FIGS. 1 and 2, the symbol A corresponding to the left side of the two-dot chain line indicates a transmitter, and the symbol B corresponding to the right side of the two-dot chain line indicates a receiver.

Transmitter A includes a transmitting coil l for generating a transmitting magnetic field.
An AC power supply 2 is provided for passing current through the transmitting coil 1, and a DC resistor 3 as a current detecting means is connected in series with the transmitting coil 1, and the voltage across the DC resistor 3 causes the transmitting coil 1 to The configuration is such that the current flowing through the sensor is detected. The current signal detected by the DC resistor 3 is transmitted to the receiver B via a transformer-type insulation amplifier 4, which is an insulation type transmission means. In addition to this, a photocoupler may be used as the insulated transmission means to transmit light.

Reference numeral 5 is a magnetic sensor such as a coil, and reference numeral 6 is a lock-in amplifier as a component extraction means. This lock-in amplifier 6 inputs the current signal transmitted from the transmitter A via the isolation amplifier 4 as a reference signal, and also inputs the detected magnetic field from the magnetic sensor 5 as a detection signal, and records the information in ii'lj. The configuration is such that a current component and a component having a phase shift of 90° are extracted. The 90° phase output of the lock-in amplifier 6 is configured to be output for display etc. by an output means 7 such as a level meter.

Note that a preamplifier 8 is interposed between the magnetic sensor 5 and this lock-in amplifier 6. For example, as shown in FIG. 3, the lock-in amplifier 6 divides the reference signal into 1 part, inputs the -right side to the first multiplier 10a after passing through a 90' phase shifter 9, and inputs the other side to the first multiplier 10a. The detection signal is inputted as it is to the second multiplier 10b, and the detection signal is also divided into 1 minute parts and inputted to the first and second multipliers 10a and lOb.
, 10b perform multiplication with the reference signal, and the multiplier outputs of the respective multipliers 10a and lob are passed through low-pass filters lla, 10b.
By taking out the DC component through Ilb, it is possible to obtain a detection output that is in phase and 90° out of phase with the reference signal.

Next, reference numeral 12 denotes a variable gain amplifier as variable gain amplification means, and the variable gain amplifier 12 is configured to input the in-phase component output of the lock-in amplifier 6 to its gain control input section 12b, and output A canceling coil 13 having a portion 12c provided at an appropriate location near the magnetic sensor 5.
The configuration is such that the output current flows by connecting the and the first
In the configuration shown in the figure, the input section 12 of the variable gain amplifier 12
The current signal is directly input to a, and -
In the configuration shown in FIG. 2, the current signal is input to the input section 12a of the variable gain amplifier 12 after being phase-shifted by the phase shifter 14 of 180'. In both of the configurations shown in FIG. 1 and FIG. 2, the canceling coil 13 is configured to generate a canceling magnetic field having a phase opposite to the transmitting magnetic field using the output current of the variable gain amplifier 12. Therefore, the former and the latter cancel coil 13
The winding direction is reversed. The variable gain amplifier 12 is configured to perform a feedback operation so that the in-phase component output becomes zero.

In the above configuration, when detecting the underground buried portion described above, the current flowing from the AC power supply 2 to the transmitting coil l is as follows:
It is detected by the DC resistor 3, transmitted to the receiver B as a current signal via the isolation amplifier 4, and inputted to the reference input section 6b of the lock-in amplifier 6, as it is or 18
The signal is input to the input section 12a of the variable gain amplifier 12 in a 0° shifted state.

On the other hand, the magnetic field detected by the magnetic sensor 5 is amplified by a preamplifier 7 into a sufficiently large signal and inputted to the detection input section 6a of the lock-in amplifier 6, and the lock-in amplifier 6 converts the current signal into a reference signal. , a component in phase with it and a component out of phase by 90' are extracted. This 90° phase component, that is, the component corresponding to the magnetic field caused by the induced current, is outputted by the output means 7, such as by displaying it on a level meter, so that a predetermined underground object can be detected.

At this time, the in-phase component output of the lock-in amplifier 6 is input to the gain control input section +2b of the variable gain amplifier 12, and the gain of the variable gain amplifier 12 is changed depending on the level, and the output current corresponding to the current signal is changed. A canceling magnetic field having a phase opposite to that of the transmitting magnetic field is generated from the canceling coil 13, and the in-phase component output is made zero by its feedback operation. In this way, by canceling the transmission magnetic field with the canceling magnetic field in the magnetic sensor 5 portion, the influence of the transmission magnetic field on the magnetic sensor 5 can be completely removed. In particular, in the present invention, as described above, the transmission magnetic field is canceled at the magnetic field stage, so unlike this method, for example, after the composite magnetic field is detected by a magnetic sensor, this detected magnetic field is used as a synchronization signal of the transmission magnetic field, etc. Compared to a method in which the transmitted magnetic field is canceled by calculation, the magnetic sensor 5 and other components do not require very high precision or resolution, and highly accurate detection can be performed. Furthermore, as mentioned above, the current signal is transmitted from the transmitter to the receiver via an isolated transmission means such as the isolated amplifier 4, thereby minimizing electrical coupling such as capacitive coupling between them. If it is made smaller, the above-described canceling magnetic field can be made to have exactly the opposite phase to the transmitting magnetic field, and by completely eliminating the influence of the transmitting magnetic field, detection accuracy can be further improved.

It should be noted that the detection device of the present invention can of course be applied to a method of detecting underground objects by moving the receiver side above the part to be detected, as in the case of normal detection methods. As disclosed in the specification and drawings attached to the application of Japanese Patent Application No. 125377 of 1983, it can also be applied to a method of detecting by moving the transmitter side above the detection target area. Of course.

(Effects of the Invention) As described above, the present invention provides a transmission magnetic field that causes an error in detecting a magnetic field due to an induced current flowing in an underground object to be detected in an underground object detection device that applies the inductive transmission method. can be automatically canceled at the magnetic field stage in the vicinity of the receiver's magnetic sensor, without requiring very high precision or resolution of the magnetic sensor or its components.
This has the effect of allowing extremely high precision detection.

[Brief explanation of drawings]

1 and 2 are system explanatory diagrams showing the overall configuration of an embodiment of the present invention, FIG. 3 is a system explanatory diagram showing an example of the configuration of a lock-in amplifier as an example of component extraction means, and FIG. 5 is a vector diagram showing the detection magnetic field and the canceling operation of the transmission magnetic field by the canceling magnetic field, and FIG. 5 is a system explanatory diagram showing the overall configuration of the conventional example. Code A...Transmitter, B...Receiver, 1...Transmission coil, 2...AC power supply, 3...DC resistance (1! current detection means), 4...Isolation amplifier (transmission means), 5... magnetic sensor, 6... lock-in amplifier (component extraction means)
, 7... Output means, 8... Preamplifier, 9... Phase shifter, 10a. 10b... Multiplier, lla, llb... Low pass filter, 12... Variable gain amplifier (variable gain amplification means)
13... Cancellation coil, 14 Phase shifter (phase shifting means)
.

Claims (4)

[Claims] (1) For electrically conductive objects buried underground,
In the device for detecting the underground object by flowing an induced current by electromagnetic induction using a transmission magnetic field generated by a transmitter and detecting the magnetic field generated by the induced current with a receiver, the transmitter includes: A transmitting coil for generating the transmitting magnetic field, an AC power source for passing a current through the transmitting coil, a current detecting means for detecting the current flowing through the transmitting coil, and a current signal detected by the current detecting means. A transmission means for transmitting the signal to the receiver is provided, and the receiver includes a magnetic sensor for detecting a magnetic field, and a magnetic field detected by the magnetic sensor and the current signal transmitted from the transmitter. a component extraction means for extracting an in-phase component and a component out of phase by 90 degrees, a means for outputting a 90 degree phase component extracted by the component extraction means, and a gain control signal for the in-phase component extracted by the component extraction means. variable gain amplification means for amplifying the current signal by changing the current signal; and a canceling coil for passing an output current of the variable gain amplification means to generate a magnetic field having a phase opposite to the transmission magnetic field for the magnetic sensor. . A buried object detection device, characterized in that the variable gain amplification means is configured to perform feedback operation so as to reduce the in-phase component to zero. (2) For electrically conductive objects buried underground,
In the device for detecting the underground object by flowing an induced current by electromagnetic induction using a transmission magnetic field generated by a transmitter and detecting the magnetic field generated by the induced current with a receiver, the transmitter includes: A transmitting coil for generating the transmitting magnetic field, an AC power source for passing a current through the transmitting coil, a current detecting means for detecting the current flowing through the transmitting coil, and a current signal detected by the current detecting means. A transmission means for transmitting the signal to the receiver is provided, and the receiver includes a magnetic sensor for detecting a magnetic field, and a magnetic field detected by the magnetic sensor and the current signal transmitted from the transmitter. a component extracting means for extracting a component in phase with and 90° out of phase with the current signal; a means for outputting a 90° phase component extracted by the component extracting means; a phase shifting means for shifting the phase of the current signal by 180°; variable gain amplification means for amplifying the output of the phase shifting means by changing the gain using the in-phase component extracted by the extraction means as a gain control signal; and an output current of the variable gain amplification means to flow through the magnetic sensor. An apparatus for detecting a buried object, characterized in that a canceling coil is provided for generating a magnetic field having a phase opposite to the transmitting magnetic field, and the variable gain amplification means is configured to perform feedback operation so as to make the in-phase component zero. (3) A buried object detection device, wherein the transmission means according to claim 1 or 2 is an insulated transmission means. (4) A buried object detection device, wherein the component extracting means according to claim 1 or 2 is constituted by a lock-in amplifier.