A time-domain electric source superconducting electromagnetic exploration primary magnetic field compensation method and system

Abstract

The present application relates to a kind of time-domain electric source superconducting electromagnetic detection primary magnetic field compensation method and system, eliminate the influence of primary magnetic field on superconducting sensor observation, improve secondary magnetic field measurement accuracy.First, the primary magnetic field distribution of electric source emission current on ground is calculated, to design secondary field measuring line with primary magnetic field contour line;The compensation current of measuring line is calculated, and compensation transmitter and electric source transmitter are synchronized using GPS, and compensation current is emitted at measuring point to offset primary magnetic field, with the same characteristics of compensation current on the same contour line;By adjusting the load RL parameter of compensation system, the turn-off time of compensation current and electric source emission current is consistent, and the primary magnetic field generated by electric source emission current is completely offset.The present application can solve the problem that superconducting sensor loses lock and magnetic saturation due to the large change rate and range of primary magnetic field in the near-source area of electric source, realize effective observation of superconducting sensor in the near-source area, and expand the measurement area and detection area.

Description

Technical Field

[0001] This invention relates to the field of time-domain electromagnetic detection technology for electrical sources, and particularly to a primary magnetic field compensation method and system for superconducting electromagnetic detection of time-domain electrical sources. Background Technology

[0002] The electric source time-domain electromagnetic detection system is a time-domain artificial field source electromagnetic detection method based on electromagnetic induction. It is one of the important means to detect electrically low resistivity anomalies in mineral bodies, especially metallic minerals. A bipolar pulse current is passed through a long grounding conductor of the electric source using a high-power electric source transmitter, exciting a primary magnetic field into the ground. The underground medium induces a secondary magnetic field due to the eddy current effect generated by the primary magnetic field. The secondary magnetic field signal is measured by the receiving system, and the conductivity information of the underground medium is obtained through data processing and inversion interpretation.

[0003] Because the transmitting current has a fall time, the signal received by the receiving system includes the fall phase of the primary magnetic field and the secondary magnetic field. In the near-source region, the primary magnetic field signal is much stronger than the secondary magnetic field signal. This causes the received secondary magnetic field signal to be distorted to varying degrees in the early stage, reducing the data quality of the early signal and making it impossible to obtain relatively accurate shallow information.

[0004] Currently, the magnetic sensors used in time-domain electromagnetic methods are generally coils, magnetic rods, and squids. Among them, squids have advantages such as high sensitivity, high bandwidth, low noise, and direct measurement of magnetic fields, making them ideal receiving sensors for time-domain electromagnetic systems. When the rate of change of the external magnetic field exceeds the slew rate of the squid system, the squid will experience lock-up and malfunction; if the range of external magnetic field changes exceeds the output capability of the readout circuit, the squid output will saturate and malfunction. In the near-source region of the electrical source time-domain electromagnetic method, if the rate of change and range of the primary magnetic field are too large, exceeding the slew rate and output range of the squid, the squid will experience lock-up and saturation. Therefore, using a compensation system to offset the primary magnetic field can both enable the squid to function normally in the near-source region and improve data quality.

[0005] Furthermore, unlike the time-domain electromagnetic field detection of magnetic sources, the primary magnetic field distribution in the time-domain electromagnetic field detection of electrical sources is uneven, the compensation current amplitude is inconsistent on the traditional straight measuring line, and the turn-off time of the electrical source emission current varies with the length of the conductor, the grounding resistance, and other conditions. Therefore, it is necessary to design a primary magnetic field compensation method and system specifically for the characteristics of the time-domain electromagnetic field detection of electrical sources.

[0006] Patent application CN202011019393.2, entitled "Airborne Transient Electromagnetic Eccentric Dual-Compensation Transmitting Coil System," discloses an eccentric dual-compensation transmitting coil system for canceling primary magnetic fields. However, this system uses coils as receiving sensors, and compared to SQUIDs, it cannot directly measure magnetic fields, has lower sensitivity and bandwidth, and is unsuitable for transient electromagnetic systems using SQUIDs as receiving sensors. Furthermore, the placement and structure of this compensation method are designed for magnetic source time-domain electromagnetic systems and are not applicable to electrical source time-domain electromagnetic systems.

[0007] Patent application CN201910608318.0, entitled "A Separate Transient Electromagnetic Measurement Compensation System and Control Method Based on SQUID," discloses a time-domain electromagnetic compensation system and control method using SQUID as a sensor. However, this system and method only consider the SQUID's unlocking and saturation problems, without considering that the compensation system load also needs to be changed when the transmitter load changes, and it does not solve the problem of completely canceling the primary magnetic field. Furthermore, the placement and structure of this compensation system and method are designed for magnetic source time-domain electromagnetic systems and are not suitable for electrical source time-domain electromagnetic systems. Summary of the Invention

[0008] This invention provides a method and system for primary magnetic field compensation in superconducting electromagnetic detection of time-domain electric sources, which solves the problem of superconducting sensor loss of lock and magnetic saturation caused by excessive change rate and range of primary magnetic field in the near-source region of the electric source.

[0009] To address the above problems, the present invention provides the following technical solution:

[0010] A primary magnetic field compensation system for superconducting electromagnetic detection using a time-domain electric source includes:

[0011] An electric source transmitting system includes an electric source grounding long conductor and a high-power electric source transmitter; the electric source grounding long conductor is connected to the ground through a grounding electrode, and the electric source transmitter transmits a bipolar trapezoidal wave current to the ground through the grounding long conductor as an excitation field source;

[0012] The receiving system uses a SQUID magnetic field sensor to collect data and reads the collected data to the receiver through a readout circuit.

[0013] The compensation system includes a compensation coil, the SQUID magnetic field sensor is placed on the central axis of the compensation coil, and the compensation transmitting coil is connected to the compensation transmitter via an adjustable RL load.

[0014] The electrical source transmitting system, compensation system, and receiving system are synchronized using GPS.

[0015] A compensation method for a primary magnetic field compensation system employing a time-domain electric source superconducting electromagnetic detection includes:

[0016] Calculate the primary magnetic field distribution of the electric source's emitted current on the ground, design the secondary field measurement line based on the primary magnetic field contour lines, and calculate the compensation current on the measurement line; place the compensation system and the receiving system at the measurement points on the measurement line, place the compensation transmitting coil and the SQUID magnetic field sensor concentrically with a certain relative height, and pass a bipolar trapezoidal wave compensation current through the compensation transmitter to the compensation transmitting coil. The compensation current has the opposite polarity to the electric source's emitted current, and the same period and duty cycle.

[0017] Adjust the load RL parameter of the compensation system so that the turn-off time of the compensation current is consistent with that of the electric source emission current. The magnetic field excited by the compensation current can completely cancel the primary magnetic field at the receiving position, so that the SQUID magnetic field sensor can receive the pure secondary magnetic field signal at the measurement position and record it using the receiver.

[0018] Furthermore, the primary magnetic field excited by the emitted current of the electric source on the ground is calculated, and the secondary magnetic field measurement line is planned based on the contour lines of the primary magnetic field, including:

[0019] The primary magnetic field value B generated by the amplitude of the emitted current from the electric source in the measurement area. 1max for:

[0020]

[0021] Where, μ0=4π×10 -7 H / m; I 1max y is the amplitude of the emitted current of the electrical source; L is the half-conduct length of the grounding conductor of the electrical source; x is the longitudinal offset distance at the measuring point; y is the lateral offset distance at the measuring point.

[0022] Furthermore, based on the radius of the compensation transmitting coil, the number of turns of the compensation transmitting coil, the relative height between the compensation transmitting coil and the SQUID magnetic field sensor, and the magnitude parameters of the primary magnetic field on the contour line, the magnitude of the compensation current I is calculated and adjusted. 2max for:

[0023]

[0024] Where r is the radius of the compensation transmitting coil; N is the number of turns of the compensation transmitting coil; z is the height difference between the center point of the compensation transmitting coil and the SQUID; B 1max This represents the amplitude of a single magnetic field along the isoline.

[0025] Furthermore, the grounding resistance after the long grounding conductor of the electrical source is laid and the turn-off time of the electrical source's emission current are measured to calculate the inductance value L1 in the load of the electrical source emission system.

[0026]

[0027] Where R1 is the grounding resistance of the electrical source; t off The turn-off time of the electrical source's emission current;

[0028] Based on the load value of the electrical source emission system, adjust the load RL parameter of the compensation device to make it so that... R2 is the load resistance value of the compensation system, and L2 is the load inductance value of the compensation system. (III) Beneficial Effects

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) The present invention designs a compensation transmitting device for electromagnetic detection of time-domain electrical sources to cancel the primary magnetic field and directly measure the pure secondary magnetic field;

[0031] (2) The present invention plans the secondary magnetic field measurement line based on the primary magnetic field contour line, which solves the problem of uneven distribution of the primary magnetic field excited by the electric source emission current. The primary magnetic field value is the same on the same contour line, and the compensation current is the same.

[0032] (3) In view of the fact that the turn-off time of the electric source emission current varies with the length of the conductor and the grounding resistance, the present invention adjusts the load RL parameter of the compensation system so that the compensation current is consistent with the turn-off time of the electric source emission current, and completely cancels the primary magnetic field.

[0033] (4) This invention cancels the primary magnetic field, solves the problem of SQUID lockout and saturation caused by the excessive rate and range of change of the primary magnetic field in the near-source region of the electric source, and expands the range of the measurement area. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall system structure used in the first example of the magnetic field compensation method of the present invention;

[0035] Figure 2 This is a schematic diagram showing the specific positional relationship between the compensation transmission system and the receiving system of the present invention;

[0036] Figure 3 A diagram showing the relationship between the radius of the transmitting coil, its relative height to the SQUID, and the compensation current;

[0037] Figure 4 A survey line map planned with reference to the contour lines of the primary magnetic field of the electric source emission excitation;

[0038] Figure 5 A schematic diagram of the load adjustment structure for the compensation launch system;

[0039] Figure 6 The graph shows the secondary magnetic field data measured by SQUID with and without a compensation system. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0041] Please see Figure 1 , Figure 1 This is a schematic diagram of the overall structure of a primary magnetic field compensation system for time-domain electric source superconducting electromagnetic detection according to an embodiment of the present invention. It mainly includes a high-power electric source transmitter, a long grounding wire for the electric source, a grounding electrode, a compensation transmitting coil, a compensation transmitter, an adjustable RL load for the compensation transmitter, a receiver, and a SQUID magnetic field sensor. The system comprises:

[0042] An electric source transmitting system includes an electric source grounding long conductor and a high-power electric source transmitter; the electric source grounding long conductor is connected to the ground through a grounding electrode, and the electric source transmitter transmits a bipolar trapezoidal wave current to the ground through the grounding long conductor as an excitation field source;

[0043] The receiving system uses a SQUID magnetic field sensor to collect data and reads the collected data to the receiver through a readout circuit.

[0044] The compensation system includes a compensation coil that is concentric with the SQUID magnetic field sensor and has a larger diameter than the SQUID magnetic field sensor. The compensation transmitting coil is connected to the compensation transmitter via an adjustable RL load.

[0045] The electrical source transmitting system, compensation system, and receiving system are synchronized using GPS.

[0046] The electrical source grounding conductor is connected to the ground via a grounding electrode. A high-power electrical source transmitter supplies a bipolar trapezoidal wave current to the electrical source grounding conductor, exciting the primary magnetic field. The compensation system and the receiving system are installed on the measuring line. The compensation system supplies a reverse bipolar current to the compensation transmitting coil through an adjustable load to cancel the primary magnetic field at the measuring point. The receiving system receives the secondary magnetic field data.

[0047] Please see Figure 2 , Figure 2 This diagram illustrates the positional relationship between the compensation transmitting and receiving systems. The compensation transmitting and receiving systems are not connected. The radius of the compensation transmitting coil is 0.3m, and the number of turns is 1. The SQUID magnetic field sensor is placed on the central axis of the compensation transmitting coil, at a horizontal height of 0.5m above the coil plane. The electrical source emits a current of 100A, with a longitudinal offset of 0m and a lateral offset of 100m from the source. The relationship between the radius, relative height, and compensation current of the compensation transmitting coil is as follows: Figure 3 As shown, refer to Figure 3 The range of the compensation current is 0 to 0.7A.

[0048] This invention provides a compensation method for a primary magnetic field compensation system employing a time-domain electric source superconducting electromagnetic detection, comprising:

[0049] Calculate the primary magnetic field distribution of the electric source's emitted current on the ground, design the secondary field measurement line based on the primary magnetic field contour lines, and calculate the compensation current on the measurement line; place the compensation system and the receiving system at the measurement points on the measurement line, place the compensation transmitting coil and the SQUID magnetic field sensor concentrically with a certain relative height, and pass a bipolar trapezoidal wave compensation current through the compensation transmitter to the compensation transmitting coil. The compensation current has the opposite polarity to the electric source's emitted current, and the same period and duty cycle.

[0050] Adjust the load RL parameter of the compensation system so that the turn-off time of the compensation current is consistent with that of the electric source emission current. The magnetic field excited by the compensation current can completely cancel the primary magnetic field at the receiving position, so that the SQUID magnetic field sensor can receive the pure secondary magnetic field signal at the measurement position and record it using the receiver.

[0051] Please see Figure 4 , Figure 4 This is a survey line map planned with reference to the contour lines of the primary magnetic field of an electric source emission excitation. The survey lines for the transient electromagnetic method using an electric source are generally straight lines. However, when using straight lines as survey lines in the measurement area, the required compensation current value differs at each measuring point along the same line due to the different amplitudes of the primary magnetic field. Conducting experiments using straight survey lines is labor-intensive and complex to debug. Based on the formula for the magnetic field generated by the amplitude of the electric source emission current in the measurement area, the primary magnetic field value generated by the amplitude of the electric source emission current in the measurement area is...

[0052]

[0053] Where, μ0=4π×10 -7 H / m, I 1max y is the amplitude of the emitted current of the electrical source; L is the length of the half-conductor of the electrical source; x is the longitudinal offset at the measuring point; y is the lateral offset at the measuring point.

[0054] Let the length of the transmitting wire be 3km and the amplitude of the transmitting current be 100A. Using Matlab, the magnetic field is calculated once in the measurement area according to the formula and the contour lines are planned. The amplitude of the magnetic field at each measuring point on the same contour line is the same, so the compensation transmitting current does not need to be changed, reducing the experimental implementation steps and improving efficiency.

[0055] Please see Figure 5 , Figure 5This invention provides a load adjustment device for compensating for the transmission system load in an embodiment of the invention. The load parameters of the transmission system are adjusted based on the actual local load of the electrical source transmission system, including the grounding resistance and the inductance of the long conductor. The electrical source grounding resistance R1 is measured with a multimeter after the electrical source grounding long conductor is laid, and the electrical source transmission current drop time t is... off Recorded using an oscilloscope. The inductance value of the load in the electric source transmitting system is determined. After obtaining the load value of the electric source transmitting system, adjust the load impedance ratio of the compensation transmitting system to make R2 is the load resistance value of the compensation transmitter system, and L2 is the load inductance value of the compensation transmitter system.

[0056] After adjusting the load parameters of the compensated transmission system, the compensation current amplitude is calculated and adjusted based on parameters such as the radius of the compensated transmission coil, the number of turns of the compensated transmission coil, the relative height between the compensated transmission coil and the SQUID, the load of the compensation system, and the amplitude of the primary magnetic field on the equipotential line.

[0057]

[0058] Where, μ0=4π×10 -7 H / m; r is the radius of the compensation transmitting coil; N is the number of turns of the compensation transmitting coil; z is the height difference between the center point of the compensation transmitting coil and the SQUID; R2 is the load of the compensation system; B 1max This represents the amplitude of a single magnetic field along an equipotential line.

[0059] The parameters of the compensation transmitter are set, including the compensation current period and duty cycle, which are consistent with the electric source's transmission current. Synchronization is achieved via GPS so that the electric source's transmission current and the compensation transmission current generate magnetic fields of equal magnitude but opposite polarity at the receiving point, completely canceling out one magnetic field.

[0060] Please see Figure 6 , Figure 6 The graphs show the secondary magnetic field data measured by SQUID with and without a compensation system. By comparing the magnetic field data quality of the compensated and uncompensated systems, B1 represents the primary magnetic field data, and B2 represents the secondary magnetic field data. By comparing the data in B1 and B1+B2, it can be seen that the compensation system can significantly reduce the rate and range of magnetic field change at the measurement location, thus meeting the normal operating conditions of SQUID. This expands the measurement area and improves the data quality of the early time-domain electromagnetic signal, thereby enhancing the performance of the electrical source's time-domain electromagnetic system.

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A compensation method for a primary magnetic field compensation system of a time-domain electric source superconducting electromagnetic detection, characterized in that, The primary magnetic field compensation system for the superconducting electromagnetic detection of the time-domain electric source includes: Includes: an electrical source transmitting system, including a long grounding conductor for the electrical source and a high-power electrical source transmitter; the long grounding conductor for the electrical source is connected to the ground through a grounding electrode, and the electrical source transmitter transmits a bipolar trapezoidal wave current to the ground through the long grounding conductor as an excitation field source; The receiving system uses a SQUID magnetic field sensor to collect data and reads the collected data to the receiver through a readout circuit. The compensation system includes a compensation coil, the SQUID magnetic field sensor is placed on the central axis of the compensation coil, and the compensation transmitting coil is connected to the compensation transmitter via an adjustable RL load. The electrical source transmitting system, compensation system, and receiving system are synchronized using GPS. The compensation method includes: Calculate the primary magnetic field distribution of the electric source's emitted current on the ground, design the secondary field measurement line based on the primary magnetic field contour lines, and calculate the compensation current on the measurement line; place the compensation system and the receiving system at the measurement points on the measurement line, place the compensation transmitting coil and the SQUID magnetic field sensor concentrically with a certain relative height, and pass a bipolar trapezoidal wave compensation current through the compensation transmitter to the compensation transmitting coil. The compensation current has the opposite polarity to the electric source's emitted current, and the same period and duty cycle. Adjust the load RL parameter of the compensation system so that the turn-off time of the compensation current is consistent with that of the electric source emission current. The magnetic field excited by the compensation current can completely cancel the primary magnetic field at the receiving position, so that the SQUID magnetic field sensor can receive the pure secondary magnetic field signal at the measurement position and record it using the receiver.

2. The compensation method according to claim 1, characterized in that, Calculate the primary magnetic field excited on the ground by the emitted current of the electric source, and plan the secondary magnetic field measurement line based on the contour lines of the primary magnetic field, including: The primary magnetic field value generated by the amplitude of the emitted current of the electric source in the measurement area for: ， in, ; y is the amplitude of the emitted current of the electrical source; L is the half-conduct length of the grounding conductor of the electrical source; x is the longitudinal offset distance at the measuring point; y is the lateral offset distance at the measuring point.

3. The compensation method according to claim 2, characterized in that, Based on the radius of the compensation transmitting coil, the number of turns of the compensation transmitting coil, the relative height between the compensation transmitting coil and the SQUID magnetic field sensor, and the magnitude parameters of the primary magnetic field on the contour line, the compensation current amplitude is calculated and adjusted. for: ， Where r is the radius of the compensation transmitting coil; N is the number of turns of the compensation transmitting coil; and z is the height difference between the center point of the compensation transmitting coil and the SQUID magnetic field sensor. This represents the amplitude of a single magnetic field along the isoline.

4. According to the compensation method of claim 2, the grounding resistance after the laying of the long grounding conductor of the electric source and the turn-off time of the electric source emission current are measured to calculate the inductance value in the load of the electric source emission system. for ， in, For electrical source grounding resistance; The turn-off time of the electrical source's emission current; Based on the load value of the electrical source emission system, adjust the load RL parameter of the compensation device to make it so that... , To compensate for the system load resistance, To compensate for the inductance of the system load.

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