JP3297730B2 - Electrode switching device for electrical exploration - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a direct current flowing from a pair of current electrodes provided on the ground surface and a potential difference formed between another pair of potential electrodes provided on the ground surface. The present invention relates to an electrode switching device for electric exploration.

[0002]

2. Description of the Related Art As shown in FIG. 1, in an electric prospecting method, a transmitter (DC power supply) is connected to a pair of current electrodes placed on the ground surface, and a receiver (voltmeter) is connected to another pair of potential electrodes. This is performed by measuring the value of the direct current flowing from the current electrode and the potential difference formed between the potential electrodes. When the distance between the current and potential electrodes (electrode distance) is small, the measured data reflects the resistivity of the shallow formation,
As the electrode spacing increases, the data includes the effect of the resistivity of the deep formation. Therefore, it is possible to know the specific resistance change in the depth direction of the stratum by performing measurement while changing the electrode interval in various ways.

[0006] While the center position of the entire electrode system is fixed at a certain point, measurement is performed while changing the electrode interval, and the change in resistivity in the depth direction at that point is known as vertical exploration.
In addition, while the distance between the current electrode and the potential electrode is fixed, measurement is performed by moving the position of the entire electrode system, and knowing the change in resistivity in the lateral direction at a depth according to the electrode distance is called horizontal exploration. .

[0004] Previously, these explorations were used for different purposes. However, in recent years, in order to know the precise underground structure, applications of the high-density electric prospecting method for simultaneously conducting exploration of both are increasing. In this method, a large number of electrodes are finely arranged on a measurement line or in a plane, and a large number of electrode combinations are measured while changing the electrode spacing and the position of the electrode system one after another. This is an exploration method for finding distribution. More recently, high-density electrical surveys have been repeated continuously, and resistivity monitoring that spatially grasps temporal changes in underground fluid and temperature from the temporal changes in resistivity distribution has also been implemented.

In high-density electrical prospecting, a bipolar electrode arrangement is generally used. In this electrode arrangement, one current electrode and one potential electrode are fixed as far electrodes at locations sufficiently separated from the survey area. In the measurement, the other current and potential electrodes are moved within the study area. Since only two electrodes are moved, there is an advantage that measurement efficiency is high. However, in surveys of urban areas where buildings are dense, it is often difficult to install a far electrode. Also, in the case of resistivity monitoring over a long measurement period, it is difficult to install a cable between the remote electrode located outside the study area and the study area for a long time, and the cable may be damaged by human or animal behavior. It is likely to be cut. Therefore, for high-density electric prospecting and resistivity monitoring in urban areas, it is necessary to use a quadrupole electrode arrangement that deploys electrodes only in the survey area.

In the measurement of high-density electric prospecting, it is necessary to quickly select a combination of a current electrode and a potential electrode and to efficiently acquire a large amount of data. Therefore, as shown in FIG.
An automatic electric prospecting system is often used in which a plurality of electrodes are connected at a time by a multi-core cable and an electrode combination is automatically switched. Generally, an automatic electric prospecting system is a current / potential measurement device having a transmission unit and a reception unit, a measurement control device that controls automatic measurement, a data recording device that records data,
It is composed of an electrode switching device (relay switch) for switching an electrode combination by a relay and a power supply for supplying power to each device. Conventional electrode switching devices can be roughly divided into 1) one of a pair of current electrodes and one of a pair of potential electrodes are fixed for a far electrode as shown in FIG. 3, and the other current electrode is connected to the other by a relay switch. A type for selecting potential electrodes (hereinafter, type 1), 2) A type in which a relay switch is attached to each electrode as shown in FIG. 4 and four electrodes are selected so as to be a pair of current electrodes and a pair of potential electrodes. (Less than,
Type 2). Among them, the type 1 device is basically assumed to be applied to the bipolar electrode arrangement, and therefore it is difficult to apply to the quadrupole electrode arrangement. In order to measure the arrangement of the quadrupole electrodes, it is necessary to use a type 2 apparatus.

[0007]

However, as can be seen from FIG. 4, the automatic electric prospecting system using the type 2 apparatus is based on the premise that the same electrode is used for both the current electrode and the potential electrode. . Therefore, a metal electrode or a carbon rod electrode through which a large current can flow is assumed as an electrode used for measurement. Such electrodes are easy to polarize and tend to generate noise. In the case of an exploration targeting a relatively shallow portion up to several tens of meters below the ground surface, the signal level obtained is relatively high, so that the problem of noise is small even if a metal electrode or a carbon rod electrode is used as the potential electrode. However, since the signal level becomes lower in deep exploration, a non-polarizable electrode is generally used as a potential electrode to avoid the influence of noise. In long-term monitoring, the electrodes may be subjected to chemical changes due to repetition of energization. Therefore, it is preferable to use electrodes different from the potential electrodes and the current electrodes. For this reason, the type 2 device is not suitable for measurements such as deep-hole exploration and resistivity monitoring, and a device capable of separately selecting a current electrode and a potential electrode is required.

Accordingly, an object of the present invention is to provide an electrode switching device for an automatic electric exploration system which can overcome any of the above problems, can be used for any electrode arrangement, and can be used for long-term monitoring.

[0009]

FIG. 5 is a block diagram showing the principle of the present invention. This device comprises four relay switches having n relay contacts. Connect each relay switch to the two poles of the current transmitter, C1 and C2, and the two poles of the potential measurement section, P1 and P2. Each relay switch normally turns on only one relay contact (can be energized) And only one of the n terminals can be energized. Each relay switch has an (n + 1) -th terminal which can always be energized, and is for monitoring a signal waveform of a current or a potential. Also, this terminal is not used for the measurement of the quadrupole electrode arrangement, but can be wired to the far electrode in the measurement of the bipolar electrode arrangement as described later.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 6 shows an outline of an automatic electric prospecting system using the present apparatus. As illustrated, the electrodes are divided into four groups, and each electrode group is connected using one multi-core cable and one relay switch. The first group is one potential electrode group, the second group is the other potential electrode group, the third group is one current electrode group, and the fourth group is the other current electrode group. is there.

In the measurement, the terminal of each relay contact and one electrode connected to one of the plurality of core wires of the multi-core cable are wired, and only one relay contact is turned on by each relay switch, and an arbitrary Current electrode (C1, C2) and potential electrode (P
1, P2). While the type 2 electrode switching device selects a pair of current electrodes and a pair of potential electrodes by a relay switch having four relay contacts provided for each electrode, the present device has four current switching units and a potential measurement unit. A pair of current electrodes and a pair of potential electrodes are selected by a relay switch having n relay contacts attached to the poles.

The greatest advantage of using the present apparatus is that high-precision high-density electric prospecting and resistivity monitoring can be realized. Because, in this device, the electrode group serving as the current electrode and the electrode group serving as the potential electrode can be connected by separate multi-core cables, and the metal electrode through which a large current can flow is connected to the current electrode. This is because a stable non-polarizable electrode can be used as the electrode. Also, in this device, the relay connected to the current transmitter and the relay connected to the potential measurement unit are independent, so for example, the former relay is a relay with large withstand voltage and current, and the latter is noise due to heat generation. By using a low thermal electromotive force relay with less power, it is possible to measure a larger current and higher accuracy than a conventional device. As described above, by using the present apparatus, the S / N ratio (quality) of the obtained data can be improved. Therefore, it can be said that the present apparatus is suitable for high-density electric prospecting for deep parts and resistivity monitoring for small fluctuations.

Another advantage of the present device is that it can be connected to many electrodes and many electrode combinations are possible. For example, when the number of relays used in this device is 200, a maximum of 200 electrodes can be used, and the number of electrode combinations is 781250 (50 × 50 × 50 × 50/8).
On the other hand, in the type 2 apparatus, when the number of relays used is 200, the number of usable electrodes is 50 and the number of electrode combinations is 6909.
There are 00 patterns (50 × 49 × 48 × 47/8).

If this device is incorporated in an automatic electric prospecting system having a high-speed AD converter, a plurality of potential electrodes can be sequentially switched while a current is being transmitted from a pair of current electrodes, so that a plurality of potential electrodes can be simultaneously switched. It is also possible to measure a potential difference between potential electrodes. This is equivalent to multi-channel simultaneous measurement of the potential difference using two multiplexers, and the faster the relay connected to the potential measurement unit can be switched, the more electrode combinations can be measured in a shorter time. This means that specific resistance data can be obtained. Therefore, it can be said that the present apparatus can contribute to improvement of the measurement efficiency of high-density electric prospecting, and that a rapid change is suitable for monitoring the specific resistance of a target. When selecting a relay, it is necessary to consider the dynamic range of the acquired potential value and the accuracy required for the search, so that a relay capable of high-speed switching cannot always be used.

In the present apparatus, it is possible to perform measurement using a common current electrode and potential electrode, as in an automatic electric prospecting system using a conventional type of electrode switching device. However, the numbers of the electrodes connected to the multi-core cable are 1, 2,
3,. . . n, and the terminal numbers of the respective relay switches are also 1, 2, 3,. . . Assuming that n, it is necessary to create an electrode BOX for connecting the electrode of the same number and the terminal of each relay switch. Then, Tx2 shown in FIG.
Is connected to the multi-core cable through the electrode box and the terminal of the relay switch connected to C1 and the terminal of the relay switch connected to P1 as shown in Fig. 7. The measurement of the bipolar electrode arrangement can be performed in the same manner as when using the electric prospecting system. In addition, as shown in FIG. 8, when all terminals are connected to a multi-core cable through the electrode box, measurement can be performed by the same method as in the case of using an automatic electric prospecting system using a type 2 device. As described above, this apparatus can perform the same measurement as the conventional electrode switching apparatus. Since it is possible to measure any electrode arrangement, it can be said that the versatility is extremely high.

[0016]

The electrode switching device for electric exploration of the present invention has the following features.
It can be used for any electrode arrangement and can be used for long-term monitoring.

[Brief description of the drawings]

FIG. 1 is a diagram showing a measurement example of electric prospecting.

FIG. 2 is a diagram showing a measurement example of a high-density electric prospecting using an automatic electric prospecting system.

FIG. 3 is a diagram schematically showing an automatic electric prospecting system using a conventional electrode switching device (type 1).

FIG. 4 is a diagram schematically showing an automatic electric prospecting system using a conventional electrode switching device (type 2).

FIG. 5 is a view showing the principle of an automatic switching device for an automatic electric prospecting system corresponding to all electrode arrangements.

FIG. 6 is a diagram showing an outline of an automatic electric prospecting system corresponding to all electrode arrangements.

FIG. 7 is a diagram showing the same measurement method as the type 1 system (FIG. 3) by the automatic electric prospecting system corresponding to all electrode arrangements.

FIG. 8 is a diagram showing the same measurement method as the type 2 system (FIG. 4) by the automatic electric prospecting system corresponding to all electrode arrangements.

Claims (2)

(57) [Claims] A transmitter is connected to a pair of electrodes placed on the surface of the earth, a receiver is connected to another pair of electrodes, and a value of a DC current flowing from the pair of electrodes is determined. An electrode switching device for electric exploration performed by measuring a potential difference formed between the electrodes, has a plurality of relay contacts, and includes a relay switch in which only one of them is turned on at a time, By connecting one end of each core wire of the multi-core cable to each of the relay contacts, and connecting the other end of each core wire to a plurality of electrodes arranged at predetermined intervals, and by switching the relay switch, the transmitter And a pair of electrodes connected to a receiver and another pair of electrodes connected to a receiver are selected. 2. The apparatus according to claim 1, further comprising: four relay switches and four multi-core cables, each comprising a plurality of groups of one and the other of the pair of electrodes and one and the other of the another pair of electrodes. 2. The electrode switching device for electric exploration according to claim 1, wherein the electrodes are connected to each group using one relay switch and one multi-core cable.