JPH1184022A - Automatically probing method of conductivity of ground - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the continuous display of the conductivity of ground in horizontal and vertical directions at the site of measurement by applying a high-speed signal processing circuit in automatically and continuously measuring the conductivity of ground through the use of artificial electromagnetic waves. SOLUTION: A transmitter 17 transmits electromagnetic waves of transmission frequencies divided into 14 frequency bands between a lower limit of 1.4 kHz and a upper limit of 125.44 kHz at a power of approximately 100 W. A magnetic field detecting coil 24 and an earthed electrode 23 are placed on ground at an interval of approximately 2 m at a receiving point for probing. The magnetic field detecting coil 24 guides a detection signal detected by a coil wound around a ferrite rod to a receiver 21 and transmits it to a personal computer 20 over a cable 22. The receiver 21 and the magnetic field detecting coil 24 are portable on a carriage, perform measurement while moving at a constant speed, and display the continuous conductivity distribution of ground in real time. The results of the probing of conductivity can be directly viewed on the display screen of the receiver 21 and are stored in the personal computer 20 for later geological review.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for automatically detecting the conductivity of a ground, and more particularly to a method for measuring the conductivity of a ground using artificial electromagnetic waves. In addition, the present invention relates to an automatic conductivity exploration method or a specific resistance automatic exploration method suitable for ground surveys often performed in the field of civil engineering construction of about 5 meters to about 100 meters underground based on measurement results obtained by the measurement method.

[0002]

2. Description of the Related Art Conventionally, methods for measuring the conductivity of the ground by means of an electromagnetic sounding method are classified according to the frequency of an electromagnetic wave to be used. One is an MT method (referred to as a geomagnetic-geocurrent method or a magnetotelluric method) utilizing an extremely low-frequency natural electromagnetic wave generated by the Schumann resonance phenomenon caused by geomagnetic activity or lightning discharge, and the second is an application of the present invention. The MT method (referred to as CSMT method) using an electromagnetic wave of several Hz to several KHz artificially transmitted, which is also disclosed in Japanese Patent No. 1610493, and the third is an extremely high frequency of several tens MHz. This is a method of detecting a conductor inside the ground by irradiating the ground with electromagnetic waves in the band of several to several GHz and measuring the electromagnetic waves reflected inside the ground, which are classified into these three types. . However, the third method is considered for the purpose of detecting iron pipes and cavities buried underground, and is also called an underground radar method. It does not measure the electrical conductivity, which is the physical property value of the geology itself (the reciprocal is also called resistivity, but the same physical quantity). In any of the electromagnetic exploration methods, the frequency to be used and the searchable depth are in a relative relationship, and the lower the frequency is, the deeper the search can be. However, the resolution of the search generally decreases. The above-mentioned underground radar method can detect only a surface portion less than about 5 meters below the ground due to the frequency used. In addition, the MT method and the CSMT method are suitable for exploring deep underground (the MT method is used at a depth of several hundred meters or more, and the CSMT method is about 50 to several km). And these two methods are not suitable for conductivity surveys in the range of about 5 to 50 meters underground. All of these conventional methods do not automatically and continuously measure the conductivity, but are vertical exploration methods for each point. In the electromagnetic survey,
It is necessary to maintain the frequency of the electromagnetic wave used as accurately as possible, but the frequency of the transmitter and the receiver often shift during measurement due to temperature changes and errors in electronic circuit elements. Lack of accuracy. Further, an error occurs in the measurement result due to noise other than the measurement frequency.

[0003]

The MT method and the CSMT method usually measure outdoors, and sometimes even in mountainous areas. Therefore, it is desirable that the measurement be as light as possible and that the measurement be possible in a short time. It is also required that the result be seen immediately at the measurement site. Conventional methods have not attempted to address these issues. In addition, since the conventional measuring device can see the result only at one point of the measurement, it is a fact that the analysis is performed indoors after the measurement.
An object of the present invention is to solve the above problems. In particular, an object of the present invention is to continuously display the electric conductivity in the horizontal direction and the vertical direction of the ground at the measurement site.
Further, the target depth of surveys and works in the field of civil engineering is often in a range of about 50 meters from the surface of the earth. However, any of the above-described methods cannot accurately search this range. The present invention is intended to be realized by utilizing an electromagnetic wave having a frequency suitable for such a search range and increasing the speed of an electronic circuit for which signal processing in this range is generally difficult. Further, in the electromagnetic survey method of the CSMT method as in the present invention, it is necessary to accurately measure the electric field and magnetic field voltages and the phase difference between the two. However, conventionally, it has been difficult to measure these quantities as the frequency increases, and the present invention is intended to solve this problem.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a method for measuring ground conductivity utilizing an artificial electromagnetic wave, which is capable of automatically and continuously outputting a measurement result of the ground as a continuous measurement result by applying a high-speed signal processing circuit. This is an automatic conductivity detection method.

[0005]

According to the present invention, the transmitter of the electromagnetic wave used for the measurement is of an automatic frequency variable type, and is of a digital control type by a computer in order to ensure the accuracy of the transmission frequency. In addition, a precision timer and a program processing method using a computer are used so that the frequency can be automatically transmitted at a fixed time interval. Next, in the receiver, the same transmitter as the measuring electromagnetic wave transmitter is incorporated in the receiver, a calibration signal having the same frequency as the frequency to be measured is taken out from the transmitter, and this signal is detected by an electric field and a magnetic field. It leads to the circuit, compares the calibration coefficient at this time with the standard calibration coefficient set in advance, corrects the calibration coefficient so as to match the difference between the two, and then measures, maintaining the accuracy of the measurement result I am trying to do it. Next, in order to speed up signal processing in the receiver, the electronic circuit uses a computer-controlled analog method, which converts the analog signal output into a digital signal and calculates the electric field necessary to calculate the conductivity. The phase difference between the electric field and the magnetic field voltage necessary to know the voltage and the magnetic field voltage and the geological structure of the ground can be output as a digital signal voltage. Then, these output voltages are guided to a high-speed personal computer through a wired or wireless communication line, and the conductivity is obtained by a pre-installed program, and in accordance with the movement of the receiver to be measured, the conductivity in the horizontal and vertical directions is measured. The distribution map is displayed on the screen in a two-dimensional cross section. Here, the operation of the automatic ground conductivity surveying method of the present invention will be described in more detail. The measuring device is composed of the transmitter shown in FIG. 1 and the receiver shown in FIG. Since the transmitter and the receiver need to perform signal processing and accurate frequency counting in accordance with real time, each has a built-in precision timer 1. The transmission of the frequency to be measured is automatically transmitted at a fixed measurement time interval by the transmitter 2 in FIG. The transmission signal is raised to a required voltage by the amplifier 4 and the transmission antenna 6 radiates an electromagnetic wave so as to reach a point to be searched. In the receiver shown in FIG. 2, before the measurement, a signal for calibration is transmitted from a transmitter synchronized with the transmitter shown in FIG. 1 (which is composed of 1, 2, 3, and 4 in FIG. 2) to a magnetic field. It is led to the detection coil 9 and the ground electrode 7 for electric field detection, and is subjected to automatic calibration processing to determine an appropriate measurement coefficient. The magnetic field calibration voltage is guided to a coil wound around the magnetic field detection coil 9. Since the response signal at the measurement point caused by the electromagnetic wave radiated from the transmitter is usually weak, it is amplified by the preamplifiers 11 and 11 'to a voltage at which the signal can be easily processed. The sensitivity of the receiver is adjusted by the automatic gain control circuits 12 and 12 '. The signals processed so far are further amplified by the main amplifiers 13 and 13 'to a required voltage. Then, the amplified electric field voltage and magnetic field voltage are output by the phase detector 15 as a voltage value based on the phase difference between the two.
The electric field, the magnetic field voltage, and the phase difference voltage detected by the above-described processing are AC, 14, 14 ", and 14 ', respectively.
The analog / digital converter converts the analog signal into a digital signal, and these signals are transmitted to a high-speed personal computer by wire or wireless communication, and the high-speed personal computer outputs and displays the ground conductivity and phase difference by program processing.

[0005]

Embodiment 1 An embodiment of the present invention will be described with reference to FIG. In FIG. 3, reference numeral 17 denotes a transmitter for measuring electromagnetic waves, and 19 denotes a circular or rectangular outer shape of about 10 mm.
A loop antenna wound around a meter, 18 is
It is a battery supplied to the transmitter. The transmitter has an output of about 100W and the power supply voltage is ± 24V
Since it requires a certain degree, it is supplied from four small batteries of 12V. Transmission frequency is 1.4K at the lower limit
Hz, and the frequency is raised to a higher frequency side at a pitch of a square root of two. The upper limit is up to 125.44 KHz, and the interval is divided into 14 frequency bands for transmission. At the receiving point to be searched, the magnetic field detecting coil 24 and a metal ground electrode for detecting the magnetic field are brought into contact with the ground at intervals of about 2 meters. The magnetic field detection coil 24 detects a signal by a coil wound around a ferrite rod having a length of about 18 cm. These detection signals are guided to the receiver 21 by a cable, and transmitted to the personal computer 20 by a cable 22. Note that, instead of the cable 22, a transmission method using wireless communication is also possible. Also, receiver 2
1 and the magnetic field detection coil 24 are portable with a small truck, and when moving and measuring at a constant speed, a continuous conductivity distribution of the ground along the moving direction can be displayed in real time to know the measurement result. . However, in this case, the ground electrode can detect the electric field by using a device in which a metal rod fixed to the lower part of the bogie is slidably contacted with the ground by a spring or the like, or a metal electrode wheel. The conductivity search results can be viewed directly from the display screen installed on the receiver at the site, but can also be easily stored in the personal computer 20 later for use in various geological studies indoors. It is. If the maximum search depth is, for example, 50 m, the interval between the transmitter 17 and the receiver 21 is as follows.
According to the search theory of the MT method, the transmitter 17 is set at a point of 150 m because it is sufficient that the distance is at least about three times the search depth. That is, since the distance between the transmitting and receiving points is short, the output of the transmitter is not increased and the above-described 100 W
Only a small transmitter is required, and the CSMT method is lightweight, making it easy to measure even in mountainous areas.

[0006]

According to the present invention, the conductivity of the ground is automatically detected by utilizing a measurement method capable of automatically and continuously measuring the conductivity of the ground using artificial electromagnetic waves as a continuous measurement result by applying a high-speed signal processing circuit. It is a method, and the above-mentioned configuration is used, so that it is possible to accurately probe the conductivity in a range of about 5 to 50 meters underground, which cannot be searched by the conventional MT method, CSMT method, or underground radar method. There is an effect that can be. Since this depth is the target depth for investigation and construction in the field of civil engineering, being able to accurately explore this depth is an important effect of the present invention. Also, while the conventional method is a vertical exploration method for each point, the method of the present invention can automatically and continuously measure the conductivity, and furthermore, at the measurement site In addition, the horizontal and vertical conductivities of the ground can be displayed continuously. Therefore, there is no need to perform analysis processing indoors after measurement as in the related art.

[Brief description of the drawings]

FIG. 1 shows a block diagram of a transmitter according to the invention.

FIG. 2 shows a block diagram of the receiver of the invention.

FIG. 3 is a perspective view showing a specific structure of the transmitter according to the present invention.

FIG. 4 is a perspective view showing a specific structure of a receiver according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Precision timer 2 Automatic variable frequency transmitter 3 Small computer 4 Output amplifier 5 Frequency display part 6 Transmission antenna 7 Ground electrode for electric field detection 9 Magnetic field detection coil 10 Calibration voltage input coil 11 Preamplifier 11 'Preamplifier 12 Automatic gain control Circuit 12 'Automatic gain control circuit 13 Main amplifier 13' Main amplifier 14 AC / DC converter 14 'AC / D
C converter 14 "AC / DC converter 15 Phase detector 17 Transmitter 18 Battery box 19 Loop antenna 20 Personal computer 21 Receiver 22 Communication cable 23 Ground electrode 24 Magnetic field detection coil

Claims (4)

[Claims] 1. An automatic ground conductivity exploration method utilizing a measurement method capable of automatically and continuously outputting a ground conductivity measurement using artificial electromagnetic waves as a continuous measurement result by applying a high-speed signal processing circuit. 2. An automatic ground conductivity exploration according to claim 1, wherein the deviation of the transmission frequency of the artificial electromagnetic wave due to a temperature change or an error of a circuit element is automatically calibrated to improve the accuracy of the measurement result. Law. 3. An automatic ground conductivity exploration method comprising a device capable of continuously displaying horizontal and vertical changes in ground conductivity while moving a receiving device. 4. An automatic conductivity surveying method suitable for ground surveys often carried out in the field of civil engineering construction of about 5 meters to about 100 meters underground where it is difficult to measure with a conventional electromagnetic surveying device.