A wide-range signal acquisition device for high-density electrical method in frozen soil exploration

Abstract

The present invention discloses a wide-range signal acquisition device for high-density electrical method in frozen soil exploration. This device can ensure the simultaneous measurement of weak voltage signals and strong voltage signals, broaden the voltage measurement range in frozen soil exploration, achieve the one-time measurement of wide-range signals to be measured, and avoid problems such as slow response, long time, and low stability caused by multiple feedbacks in traditional methods; the voltage range automatic switching circuit directly judges the signals and selects channels, effectively avoiding the problem of circuit failure caused by too high signal voltage, can control the measured signal to a preset range and send it to the corresponding conversion channel, further increasing the stability and efficiency of the measurement.

Description

Technical Field

[0001] The present invention relates to the field of exploration, and particularly to a wide - range signal acquisition device for high - density electrical method in frozen soil exploration. Background Art

[0002] As Figure 2 shown, the high - density electrical method device mainly includes three parts: a current emission system, an electrode management system, and a signal acquisition system. The current emission system injects a stable and controllable current into the ground; the electrode management system is responsible for the automatic control, connection, and switching of electrodes; the signal acquisition system is responsible for collecting the potential difference between electrodes. The measurement principle and process are as follows:

[0003] First, the electrode management system sets electrodes A, B, M, and N. Secondly, a current signal with a known waveform is applied to electrodes A and B through the current emission system. I Finally, the voltage difference between the two ends of electrodes M and N is collected by the signal acquisition system, and a single - point measurement is completed. After the management settings of several arranged electrodes are completed and all required combined measurements are carried out, an electrical method measurement is completed. According to the basic theoretical formula of the point - source electric field, when an electric field is applied between AB, the voltage difference between any two points MN in the middle is expressed as:

[0004]

[0005] where AM, AN, BM, and BN respectively represent the distance from electrode A to electrode M, the distance from electrode A to electrode N, the distance from electrode B to electrode M, and the distance from electrode B to electrode N; represents the voltage of electrode M; represents the voltage of electrode N; is the resistivity; is the pi.

[0006] By transforming the above formula, the resistivity expression between MN can be obtained as:

[0007]

[0008] Let , then the resistivity can be expressed as . I is the known supply current, and K is a value related to the electrode layout spacing. It can be seen that the resistivity of points M and N is mainly measured by the voltage difference between M and N. By using the scanning measurement of multiple electrode permutations and combinations, geological information in different regions and at different depths can be obtained. It can be seen that the signal acquisition system in the electrical method device is crucial.

[0009] In the existing electrical method signal acquisition system, the acquisition of the voltage difference between M and N electrodes mainly adopts the acquisition scheme of voltage range switching, voltage pre-amplification, voltage programmable amplification, and ADC (analog-to-digital conversion). For example, in the M and N voltage acquisition system of Patent CN201110433062.8 (High-density electrical method instrument receiver device), the voltage is adjusted to the range that can be measured by the ADC through range switching and a programmable gain amplifier circuit (PGA) and then sent to the ADC for measurement. This process requires multiple feedback judgments and adjustments of the PGA and ADC to obtain the voltage value. The amplification factor of the PGA needs to be set by programming, and the amplification factor is limited and depends on the number of PGA hardware.

[0010] In Patent CN202211557176.8 (A method, device, and system for constructing a seismic ground resistivity acquisition module), the measured signal of ground resistivity is connected to a signal conditioning circuit for impedance transformation and signal limiting, and then the signal is transmitted to an ADC analog-to-digital conversion circuit to obtain the voltage value, which limits the measurement range of the input voltage and cannot achieve precise measurement within a large range.

[0011] Patent CN201610387113.0 (An adaptive data acquisition system for a mine-used ultra-high-density electrical method instrument) uses a two-stage dual-voltage comparator network to judge the range of the input voltage, and then amplifies or attenuates the signal by a fixed multiple to meet the ADC sampling standard. This method can only meet the voltage conditioning in some interval ranges (such as 1 mV - 10 V), and it is difficult to amplify and effectively identify weaker or stronger signals, with limited application scenarios. If it is lower than the minimum value of the range, multiple feedback judgments and adjustments are required, increasing the time and links of acquisition and processing, and possibly introducing more interference signals and measurement errors. If it is higher than the maximum value of the range, it is limited by the maximum input voltage of the comparator (such as 15 V), and the allowable measurement voltage range is limited. Moreover, this voltage comparison network also needs to provide multiple precise reference voltage sources, increasing the complexity of circuit design.

[0012] When the above acquisition method is used to measure a dynamically changing voltage, the programmable gain amplifier (PGA) circuit needs to continuously receive feedback signals for adjustment to bring the signal within the range acceptable to the analog-to-digital converter (ADC) before a voltage measurement can be made. To complete a full electrical resistivity tomography (ERT) measurement, thousands of voltage measurements are required. The entire process is time-consuming and the control process is complex. If a comparator is used to divide the voltage into multiple ranges and then amplify the voltages in different ranges by corresponding multiples respectively, for example, the voltages in the range of 0 - 200 mV are uniformly amplified 100 times and then input to the ADC circuit for acquisition, the determination range is too rough. There is still a situation where the voltage is too small to meet the ADC sampling standard or exceeds the ADC sampling amplitude. If the determination range is refined, multiple reference comparison voltages or multiple feedback determinations are required, which will increase the circuit design cost and complexity. Moreover, conventional comparators can generally only perform voltage comparisons above the mV level, and for voltages below the mV level, the circuit design is more difficult.

[0013] In frozen soil exploration, the high-density electrical resistivity tomography (ERT) injects current into the ground through a surface electrode array and measures the resistivity differences of different strata, which is widely used in investigations of permafrost, seasonal frozen soil, and underground ice structures. Different from non-frozen soil exploration, the internal structure of frozen soil undergoes periodic phase transitions with changes in the external air temperature, resulting in a large dynamic range of resistivity signals (the resistivity of frozen soil varies from a few Ω·m to hundreds of thousands of Ω·m, resulting in a voltage difference amplitude between the acquisition signals of electrodes M and N ranging from a few μV to dozens of volts, with a variation range of 10 7 and above). Due to the above special properties of frozen soil, the following problems exist when the existing high-density electrical resistivity tomography is applied to frozen soil exploration:

[0014] (1) The measurement voltage range is limited (such as 1 mV - 5 V), which is not suitable for the range of a few μV to dozens of volts in the frozen soil environment, and there is no way to simultaneously process strong and weak voltage signals and high-dynamic-range voltage signals.

[0015] (2)When measuring weak voltage signals (in the range of μV to mV, and voltage signals less than μV level), for example, there are still 6 orders of magnitude from nV to mV, and it is impossible to determine which order of magnitude the input voltage is in. The existing solution uses a PGA programmable amplifier, and determining the amplification factor is a difficult problem. It is necessary to perform a small multiple amplification in advance, and then perform ADC detection after amplification. If the detected voltage is appropriate, it can be measured. If the detected voltage is too small, the amplification factor needs to be increased, and then the above steps are repeated for measurement. The existing weak voltage detection solutions often involve multiple judgments, multiple feedback amplifications, and multiple feedback adjustments of the current emission system power supply. In a system with hundreds of electrode combinations for acquisition, the overall acquisition time of the system will be very long, which is not suitable for the fast and accurate measurement requirements of frozen soil exploration in high-cold and high-altitude regions, and is not conducive to the long-term exploration work of staff in extreme environments. Moreover, for the solution using programmable amplification (PGA) and analog-to-digital conversion (ADC), to achieve high multiple amplification, multiple PGA amplifiers need to be cascaded, and the hardware design requirements for high-digit ADC acquisition circuits are high. Overall, it consumes a large amount of hardware resources, increases the circuit design cost, and has high complexity.

[0016] (3)When measuring strong voltage signals (such as those higher than 10V), the voltage between electrodes M and N exceeds the maximum acquisition voltage of the ADC, and the circuit cannot process information and is extremely likely to burn out the chip. The traditional electrical method instrument processing method is to feedback and adjust the input current and input voltage, but there is still a situation where even after adjusting the power supply, the measured voltage still does not meet the standard measurement requirements (for example: 1mV - 5V); if the method of first judging through a comparator and then attenuating the voltage is used, the range of the measured input voltage is limited by the maximum input voltage standard of the comparator, and the judgment upper limit is restricted.

[0017] In summary, the existing conventional equipment has a limited measurement range and cannot process strong and weak voltage signals simultaneously; in the measurement of weak voltage signals, multiple judgments and feedback amplifications are required, resulting in long measurement time, low accuracy, and poor response, making it difficult to meet the requirements of rapid exploration and fine measurement of frozen soil in high-cold regions. Summary of the Invention

[0018] In view of the above deficiencies in the prior art, a high-density electrical method wide-range signal acquisition device for frozen soil exploration provided by the present invention solves the problem that the signal acquisition system of the existing high-density electrical method device cannot process strong and weak voltage signals simultaneously and is difficult to meet the requirements of frozen soil exploration.

[0019] To achieve the above invention purpose, the technical solution adopted by the present invention is as follows:

[0020] Provide a high-density electrical method wide-range signal acquisition device for frozen soil exploration, which includes a signal preprocessing component, a voltage range automatic switching circuit, a logarithmic conversion circuit, an adaptive filtering circuit, and a voltage-frequency conversion circuit; where:

[0021] A signal preprocessing component, which is used to extract differential-mode voltage signals from the high-density electrical method signals in frozen soil exploration, filter out power frequency interference, convert the positive and negative alternating differential-mode voltage signals after filtering out power frequency interference into positive voltage signals, and obtain the positive and negative polarities of the differential-mode voltage signals after filtering out power frequency interference;

[0022] A voltage gear automatic switching circuit, which is used to attenuate the voltage of the positive voltage signal output by the signal preprocessing component. When the attenuated voltage is greater than or equal to the first threshold voltage, the attenuated voltage is directly sent to the adaptive filtering circuit; when the attenuated voltage is less than the first threshold voltage, the positive voltage signal output by the signal preprocessing component is compared with the second threshold voltage. When the positive voltage signal output by the signal preprocessing component is greater than or equal to the second threshold voltage, the positive voltage signal output by the signal preprocessing component is directly sent to the adaptive filtering circuit; when the positive voltage signal output by the signal preprocessing component is less than the second threshold voltage, the positive voltage signal output by the signal preprocessing component is sent to the logarithmic conversion circuit;

[0023] A logarithmic conversion circuit, which is used to logarithmically amplify the signal input into it and send the amplified signal to the adaptive filtering circuit;

[0024] An adaptive filtering circuit, which is used to filter out noise from the signal input into it and send the signal after noise filtering to the voltage-frequency conversion circuit;

[0025] A voltage-frequency conversion circuit, which is used to perform voltage-frequency conversion on the signal input into it to complete the acquisition of the high-density electrical method signals in frozen soil exploration in the form of frequency.

[0026] The beneficial effects of the present invention are as follows: This device can ensure the simultaneous measurement of weak voltage signals and strong voltage signals, broaden the voltage measurement range in frozen soil exploration, realize the one-time measurement of wide-range signals to be measured, avoid problems such as slow response, long time, and low stability caused by multiple feedbacks in traditional methods, improve the acquisition and exploration efficiency, and shorten the working time of exploration personnel in extreme environments; the voltage gear automatic switching circuit directly judges the signal and selects the channel, effectively avoiding the problem of circuit failure caused by too high signal voltage, and can control the measured signal to the preset range and send it to the corresponding conversion channel, further increasing the stability and efficiency of the measurement.

[0027] Further, the signal preprocessing component includes an impedance matching circuit, a differential amplification circuit, a filtering circuit, and a zero-crossing analysis and processing circuit connected in sequence; among them:

[0028] The impedance matching circuit is used for impedance matching;

[0029] The differential amplification circuit is used to extract the differential-mode voltage signal between the signal acquisition electrodes;

[0030] A filtering circuit for filtering out power frequency interference;

[0031] A zero-crossing analysis and processing circuit for converting the differential-mode voltage signal with positive and negative alternation after filtering out power frequency interference into a positive voltage signal and obtaining the positive and negative polarities of the differential-mode voltage signal with positive and negative alternation after filtering out power frequency interference.

[0032] The beneficial effects of the above further solution are as follows: Through the impedance matching circuit, the filtering circuit, and the zero-crossing analysis and processing circuit, the differential-mode voltage signal between the acquisition electrodes M and N can be accurately extracted, and the common (50 Hz) power frequency noise can be removed. The voltage signal with positive and negative alternation is converted into a positive voltage signal, and the positive and negative polarities of the differential-mode voltage signal with positive and negative alternation after filtering out power frequency interference are obtained, so that the subsequent circuit can directly perform the processing and measurement of the positive voltage, and the subsequent devices can be powered by a single power supply, thereby reducing the complexity of the circuit design and facilitating the subsequent signal conversion and processing.

[0033] Further, the voltage range automatic switching circuit includes a follower A1, a comparator A2, a comparator A3, an NPN transistor Q1, an NPN transistor Q2, a first relay, and a second relay; where:

[0034] The positive input terminal of the follower A1 is respectively connected to one end of a resistor R1 and a grounding resistor R2; the other end of the resistor R1 is connected to the first static contact of the first relay and serves as the input terminal of the voltage range automatic switching circuit; the negative input terminal of the follower A1 is respectively connected to the output terminal of the follower A1, the positive input terminal of the comparator A2, and the second static contact of the first relay; the negative input terminal of the comparator A2 is connected to a first threshold voltage; the output terminal of the comparator A2 is connected to the base of the NPN transistor Q1 through a resistor R3;

[0035] The collector of the NPN transistor Q1 is connected to an external power supply; the emitter of the NPN transistor Q1 is connected to one end of the coil of the first relay; the other end of the coil of the first relay is grounded; the moving contact of the first relay is respectively connected to the positive input terminal of the comparator A3 and the moving contact of the second relay;

[0036] The negative input terminal of the comparator A3 is connected to a second threshold voltage; the output terminal of the comparator A3 is connected to the base of the NPN transistor Q2 through a resistor R4; the collector of the NPN transistor Q2 is connected to an external power supply; the emitter of the NPN transistor Q2 is connected to one end of the coil of the second relay; the other end of the coil of the second relay is grounded; the first static contact of the second relay is connected to the input terminal of the logarithmic conversion circuit; the second static contact of the second relay is connected to the input terminal of the adaptive filtering circuit;

[0037] When the voltage at the positive input terminal of the comparator A2 is greater than or equal to the voltage at the negative input terminal, the comparator A2 outputs a high level, the NPN transistor Q1 conducts, and the moving contact of the first relay is connected to the second static contact of the first relay;

[0038] When the voltage at the positive input terminal of comparator A2 is less than the voltage at the negative input terminal, comparator A2 outputs a low level, the NPN transistor Q1 is turned off, and the moving contact of the first relay is connected to the first stationary contact of the first relay;

[0039] When the voltage at the positive input terminal of comparator A3 is greater than or equal to the voltage at the negative input terminal, comparator A3 outputs a high level, the NPN transistor Q2 is turned on, and the moving contact of the second relay is connected to the second stationary contact of the second relay;

[0040] When the voltage at the positive input terminal of comparator A3 is less than the voltage at the negative input terminal, comparator A3 outputs a low level, the NPN transistor Q2 is turned off, and the moving contact of the second relay is connected to the first stationary contact of the second relay.

[0041] Furthermore, the first threshold voltage and the second threshold voltage are 1V and 0.5V respectively.

[0042] The beneficial effects of the above further solution are as follows: The voltage range automatic switching circuit directly performs signal judgment and channel selection. It first attenuates through resistor R1 and resistor R2 and then makes a judgment, which can effectively avoid the problem of circuit failure caused by too high a signal; the measured signal is controlled within a preset range and then sent to the corresponding conversion channel. Only one judgment process is required to quickly divide the wide-range voltage signal. There is no need for feedback judgment and adjustment. The number of reference levels of the comparator is small (only 2), and there is no need for a high-precision reference voltage. Moreover, the reference voltage (threshold voltage) is extremely easy to obtain (such as 1V and 0.5V), which further increases the stability and efficiency of the measurement and reduces the design complexity. At the same time, the method of attenuating first and then making a judgment can effectively avoid the problem of circuit failure caused by too high a signal and expand the upper and lower limits of the voltage detection range.

[0043] Furthermore, the logarithmic conversion circuit includes a chip U1 of model LOG114; pin 3 of chip U1 is connected to one end of resistor R5, and the other end of resistor R5 is the input terminal of the logarithmic conversion circuit; pin 4 of chip U1 is connected to the reference voltage through resistor R6; pin 5 and pin 7 of chip U1 are connected to the reference voltage; pin 6 of chip U1 is respectively connected to one end of capacitor C1, one end of capacitor C2, and -5V voltage; the other end of capacitor C1 is connected to the other end of capacitor C2 and grounded; pin 8 of chip U1 is respectively connected to one end of capacitor C3, one end of capacitor C4, and 5V voltage; the other end of capacitor C3 is connected to the other end of capacitor C4 and grounded;

[0044] Pin 9 of chip U1 is connected to one end of resistor R10 and pin 11 of chip U1 through resistor R9 respectively; pin 10 of chip U1 is connected to one end of resistor R7 and grounding resistor R8 respectively; pin 12 of chip U1 is connected to pin 13 of chip U1 and the other end of resistor R10 respectively; pin 15 of chip U1 is connected to pin 14 of chip U1 and serves as the output end of the logarithmic conversion circuit; pin 16 of chip U1 is connected to the other end of resistor R7 and the reference voltage respectively.

[0045] The beneficial effects of the above further scheme are as follows: The logarithmic conversion circuit is used for the measurement of small-amplitude signals. Through logarithmic operation, a signal with a low amplitude and a high dynamic range (nV-V level) is compressed into a voltage value with a low dynamic range (V level), avoiding the amplification process of signal feedback, improving the signal processing efficiency, and at the same time avoiding the problems of increased measurement time due to feedback and the consumption of more PGA / AGC hardware resources caused by insufficient amplification factor.

[0046] Further, the adaptive filtering circuit is a programmable band-pass filter, including operational amplifier U2; the non-inverting input terminal of operational amplifier U2 is connected to the negative electrode of polarized capacitor C5 and one end of programmable potentiometer Rs2 respectively; the positive electrode of polarized capacitor C5 is connected to the positive electrode of polarized capacitor C6, one end of resistor R11 and one end of programmable potentiometer Rs1 respectively; the other end of programmable potentiometer Rs1 is the input end of the adaptive filtering circuit; the negative electrode of polarized capacitor C6 is connected to the other end of programmable potentiometer Rs2 and one end of resistor R13 and grounded;

[0047] The inverting input terminal of operational amplifier U2 is connected to the other end of resistor R13 and one end of resistor R12 respectively; the output terminal of operational amplifier U2 is connected to the other end of resistor R11 and the other end of resistor R12 respectively and serves as the output end of the adaptive filtering circuit.

[0048] The beneficial effects of the above further scheme are as follows: Since the output frequency of the voltage-frequency conversion circuit is prone to error and difficult to separate when there is a large amount of white noise and other noises in the input signal, according to the characteristics of the current emission system in the electrical method system, the frequency of the input current signal between electrodes A and B is known and controllable, and the signal frequency between electrodes M and N is the same as the A and B power supply frequencies. Therefore, a programmable band-pass filter is added before the voltage-frequency conversion circuit in this device. The narrow-bandwidth adaptive band-pass filter is used to reduce noise and extract the effective signal between electrodes M and N, which can eliminate the influence of noise to the greatest extent, ensure the measurement accuracy and measurement dynamic range, and improve the measurement accuracy.

[0049] Further, the voltage-to-frequency conversion circuit includes a chip U3 of model VFC110; pin 2 of the chip U3 is the input terminal of the voltage-to-frequency conversion circuit; pin 4 of the chip U3 is respectively connected to the grounding capacitor C7 and the negative pole of the external power supply; pin 7 of the chip U3 is connected to the grounding resistor R15; pin 8 of the chip U3 is connected to one end of the resistor R14 and serves as the output terminal of the voltage-to-frequency conversion circuit; the other end of the resistor R14 is connected to a 5V voltage; pin 10 of the chip U3 is respectively connected to one end of the capacitor C8 and the positive pole of the external power supply; pins 11 and 12 of the chip U3 are connected; pin 13 of the chip U3 is respectively connected to pin 14 of the chip U3 and the other end of the capacitor C8 and grounded.

[0050] The beneficial effects of the above further solution are as follows: The device converts the voltage signal into a frequency signal through the voltage-to-frequency conversion circuit, which not only has strong anti-interference ability, but also is convenient for long-distance transmission and processing, and is convenient for the remote end to receive the signal acquisition result. And this voltage-to-frequency conversion method can restore the voltage signal without a high-precision ADC, reducing the complexity and cost of instrument design.

[0051] Further, it also includes a host computer, which is respectively connected to the signal preprocessing component, the voltage range automatic switching circuit, the adaptive filtering circuit and the voltage-to-frequency conversion circuit, and is used to obtain the positive and negative polarities of the differential mode voltage signal that alternates between positive and negative after filtering the power frequency interference, the output channel of the voltage range automatic switching circuit, control the center frequency of the adaptive filtering circuit, and calculate the output frequency of the voltage-to-frequency conversion circuit to obtain the electrophysical measurement result.

[0052] The beneficial effects of the above further solution are as follows: Obtaining the positive and negative polarities of the differential mode voltage signal that alternates between positive and negative after filtering the power frequency interference and the output channel of the voltage range automatic switching circuit is convenient for subsequent data calculation to obtain the actual voltage data and resistivity; the center frequency of the adaptive filtering circuit can be controlled according to the known and controllable current emission frequency, and then the effective signal can pass through the adaptive filtering circuit to the greatest extent, filtering out the interference signal to ensure the accuracy of signal acquisition. At the same time, the host computer can process multi-channel data in parallel, can easily increase the number of measurement channels of the electrophysical method without increasing the cost, can further improve the acquisition efficiency and save the acquisition time. Description of the Drawings

[0053] Figure 1 is a schematic structural diagram of the device;

[0054] Figure 2 is a schematic structural diagram of the high-density electrophysical method device;

[0055] Figure 3 is a working logic diagram of the voltage range automatic switching circuit;

[0056] Figure 4 is a circuit diagram of the voltage range automatic switching circuit;

[0057] Figure 5 is a logarithmic conversion circuit diagram;

[0058] Figure 6 is a test diagram of the logarithmic conversion circuit;

[0059] Figure 7 is an adaptive filtering circuit diagram;

[0060] Figure 8 is a voltage-frequency conversion circuit diagram;

[0061] Figure 9 is a test diagram of the voltage-frequency conversion circuit. Specific embodiments

[0062] The following describes the specific embodiments of the present invention to facilitate those skilled in the art of this technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art of this technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

[0063] As Figure 1 shown, the high-density electrical method wide-range signal acquisition device for frozen soil exploration includes a signal preprocessing component, a voltage range automatic switching circuit, a logarithmic conversion circuit, an adaptive filtering circuit, and a voltage-frequency conversion circuit; wherein:

[0064] The signal preprocessing component is used to extract a differential-mode voltage signal from the high-density electrical method signal for frozen soil exploration, filter out power frequency interference, convert the differential-mode voltage signal with positive and negative alternation after filtering out power frequency interference into a positive voltage signal, and obtain the positive and negative polarities of the differential-mode voltage signal with positive and negative alternation after filtering out power frequency interference;

[0065] As Figure 3 shown, the voltage range automatic switching circuit is used to attenuate the voltage of the positive voltage signal output by the signal preprocessing component. When the attenuated voltage is greater than or equal to the first threshold voltage, the attenuated voltage is directly sent to the adaptive filtering circuit; when the attenuated voltage is less than the first threshold voltage, the positive voltage signal output by the signal preprocessing component is compared with the second threshold voltage. When the positive voltage signal output by the signal preprocessing component is greater than or equal to the second threshold voltage, the positive voltage signal output by the signal preprocessing component is directly sent to the adaptive filtering circuit; when the positive voltage signal output by the signal preprocessing component is less than the second threshold voltage, the positive voltage signal output by the signal preprocessing component is sent to the logarithmic conversion circuit;

[0066] The logarithmic conversion circuit is used to logarithmically amplify the signal input therein and send the amplified signal to the adaptive filtering circuit;

[0067] An adaptive filtering circuit is used to filter the noise of the signal input into it and send the signal after noise filtering into a voltage-frequency conversion circuit;

[0068] A voltage-frequency conversion circuit is used to perform voltage-frequency conversion on the signal input into it and complete the acquisition of high-density electrical method signals for frozen soil exploration in the form of frequency.

[0069] The signal preprocessing component includes an impedance matching circuit, a differential amplification circuit, a filtering circuit, and a zero-crossing analysis and processing circuit connected in sequence; among them:

[0070] The impedance matching circuit is used to perform impedance matching;

[0071] The differential amplification circuit is used to extract the differential-mode voltage signal between the signal acquisition electrodes;

[0072] The filtering circuit is used to filter out power frequency interference;

[0073] The zero-crossing analysis and processing circuit is used to change the differential-mode voltage signal that alternates between positive and negative after filtering out power frequency interference into a positive voltage signal and obtain the positive and negative polarities of the differential-mode voltage signal that alternates between positive and negative after filtering out power frequency interference.

[0074] As Figure 4 shown, the voltage range automatic switching circuit includes a follower A1, a comparator A2, a comparator A3, an NPN transistor Q1, an NPN transistor Q2, a first relay (i.e., relay 1) and a second relay (i.e., relay 2); among them:

[0075] The positive input terminal of the follower A1 is respectively connected to one end of a resistor R1 and a grounding resistor R2; the other end of the resistor R1 is connected to the first static contact of the first relay and serves as the input terminal of the voltage range automatic switching circuit; the negative input terminal of the follower A1 is respectively connected to the output terminal of the follower A1, the positive input terminal of the comparator A2, and the second static contact of the first relay; the negative input terminal of the comparator A2 is connected to a first threshold voltage; the output terminal of the comparator A2 is connected to the base of the NPN transistor Q1 through a resistor R3;

[0076] The collector of the NPN transistor Q1 is connected to an external power supply; the emitter of the NPN transistor Q1 is connected to one end of the coil of the first relay; the other end of the coil of the first relay is grounded; the moving contact of the first relay is respectively connected to the positive input terminal of the comparator A3 and the moving contact of the second relay;

[0077] The negative input terminal of comparator A3 is connected to the second threshold voltage; the output terminal of comparator A3 is connected to the base of NPN transistor Q2 through resistor R4; the collector of NPN transistor Q2 is connected to the external power supply; the emitter of NPN transistor Q2 is connected to one end of the coil of the second relay; the other end of the coil of the second relay is grounded; the first static contact of the second relay is connected to the input terminal of the logarithmic conversion circuit; the second static contact of the second relay is connected to the input terminal of the adaptive filtering circuit;

[0078] When the positive input terminal of comparator A2 is greater than or equal to the voltage of the negative input terminal, comparator A2 outputs a high level, NPN transistor Q1 conducts, and the moving contact of the first relay is connected to the second static contact of the first relay;

[0079] When the positive input terminal of comparator A2 is less than the voltage of the negative input terminal, comparator A2 outputs a low level, NPN transistor Q1 is turned off, and the moving contact of the first relay is connected to the first static contact of the first relay;

[0080] When the positive input terminal of comparator A3 is greater than or equal to the voltage of the negative input terminal, comparator A3 outputs a high level, NPN transistor Q2 conducts, and the moving contact of the second relay is connected to the second static contact of the second relay;

[0081] When the positive input terminal of comparator A3 is less than the voltage of the negative input terminal, comparator A3 outputs a low level, NPN transistor Q2 is turned off, and the moving contact of the second relay is connected to the first static contact of the second relay.

[0082] In this embodiment, the first relay is defaultly connected to the attenuated voltage, and the relay 2 is defaultly connected to the adaptive filtering circuit. The input voltage Vin1 of the voltage gear automatic switching circuit is first attenuated in proportion through the resistor R1 and the resistor R2 (for example: R1 = 9kΩ, R2 = 1kΩ, that is, attenuated to 1 / 10 of the original voltage), so that the input voltage of the follower A1 is Vin2. After impedance matching adjustment by the follower A1, the output voltage V1 of the follower A1 = Vin2. The comparator A2 compares the attenuated voltage V1 with the first threshold voltage Vf1 (such as 1V). If V1≥Vf1, the signal (ctr1 signal) output to the host computer is high level, and the NPN transistor Q1 is turned on, and the relay 1 switches to the attenuated V1 voltage channel; if V1<Vf1, the signal output to the host computer is low level, and the NPN transistor Q1 is turned off, and the relay 1 switches to the original Vin1 voltage channel. The comparator A3 compares the signal V2 after the previous stage range adjustment with the second threshold voltage Vf2 (such as 0.5V). If V2≥Vf2, the output signal V3 of the comparator A3 is high level, and the NPN transistor Q2 is turned on, and the relay 2 switches to the V / F voltage-frequency conversion channel (the output of the voltage gear automatic switching circuit is directly sent into the adaptive filtering circuit, and then output through the voltage-frequency conversion circuit); if V2<Vf2, the output signal V3 of the comparator A3 is low level, and the NPN transistor Q2 is turned off, and the relay 2 switches to the logarithmic conversion channel (the output of the voltage gear automatic switching circuit is first sent into the logarithmic conversion circuit, and then output through the adaptive filtering circuit and the voltage-frequency conversion circuit).

[0083] As Figure 5 shown, the logarithmic conversion circuit includes a chip U1 of model LOG114; one end of the resistor R5 is connected to the pin 3 of the chip U1, and the other end of the resistor R5 is the input end of the logarithmic conversion circuit; the pin 4 of the chip U1 is connected to the reference voltage through the resistor R6; the pins 5 and 7 of the chip U1 are connected to the reference voltage; the pin 6 of the chip U1 is respectively connected to one end of the capacitor C1, one end of the capacitor C2 and the -5V voltage; the other end of the capacitor C1 is connected to the other end of the capacitor C2 and grounded; the pin 8 of the chip U1 is respectively connected to one end of the capacitor C3, one end of the capacitor C4 and the 5V voltage; the other end of the capacitor C3 is connected to the other end of the capacitor C4 and grounded;

[0084] one end of the resistor R10 and the pin 11 of the chip U1 are respectively connected to the pin 9 of the chip U1 through the resistor R9; one end of the resistor R7 and the grounding resistor R8 are respectively connected to the pin 10 of the chip U1; the pin 13 of the chip U1 and the other end of the resistor R10 are respectively connected to the pin 12 of the chip U1; the pin 15 of the chip U1 is connected to the pin 14 of the chip U1 and serves as the output end of the logarithmic conversion circuit; the other end of the resistor R7 and the reference voltage are respectively connected to the pin 16 of the chip U1.

[0085] In the specific implementation process, according to the operating ambient temperature of the electrical method, which may range from dozens of degrees below zero to dozens of degrees above zero, in order to enable the logarithmic conversion circuit to adapt to temperature changes, chip U1 is selected as LOG114, which has a built-in temperature compensation circuit. Other chips with the same functions as the LOG114 chip can also be used as chip U1 of the logarithmic conversion circuit.

[0086] LOG114 is originally a current-input type chip. In the implementation, the input voltage VLOGIN is converted into a current signal through a known precision resistor R5. , , and a reference input current is obtained through resistor R6 (2.5 MΩ) and the on-chip reference voltage source (2.5 V). , = 2.5 V / 2.5 MΩ = 1 μA. Then the output voltage after logarithmic conversion is Voutlog = -0.249 * lg(I1 / I2) + 1.5. The input voltage VLOGIN of the logarithmic conversion circuit can be calculated inversely from the magnitude of Voutlog.

[0087] If R5 = 1 kΩ is selected, during exploration, if the signal to be measured is 1 μV, I2 = 1 nA is calculated, and Voutlog = 0.753 V; if the signal to be measured is 100 mV, I2 = 100 μA is calculated, and VLOGOUT = 1.998 V. It can be seen that after logarithmic conversion, the voltage with an input range of 1 μV - 100 mV can be compressed into an output voltage in the range of 0.753 V - 1.998 V, which is convenient for subsequent circuit signal processing. More test data of the logarithmic conversion circuit are shown in Table 1 and Figure 6 as shown.

[0088] Table 1

[0089]

[0090] Since the resistance value of the resistor in actual life will have a certain deviation, during the test of the logarithmic conversion circuit, the actual resistance value of resistor R5 is 1003.7 Ω. In Figure 6 , a high coincidence rate of the two curves indicates a small error. It can be seen that this logarithmic conversion circuit can measure weak voltage signals well, and the error is very small under voltages of different magnitudes.

[0091] Such as Figure 7As shown, the adaptive filtering circuit is a programmable band-pass filter, including an operational amplifier U2; the non-inverting input terminal of the operational amplifier U2 is respectively connected to the negative electrode of a polarized capacitor C5 and one end of a programmable potentiometer Rs2; the positive electrode of the polarized capacitor C5 is respectively connected to the positive electrode of a polarized capacitor C6, one end of a resistor R11, and one end of a programmable potentiometer Rs1; the other end of the programmable potentiometer Rs1 is the input terminal of the adaptive filtering circuit; the negative electrode of the polarized capacitor C6 is respectively connected to the other end of the programmable potentiometer Rs2 and one end of a resistor R13 and grounded.

[0092] The inverting input terminal of the operational amplifier U2 is respectively connected to the other end of the resistor R13 and one end of a resistor R12; the output terminal of the operational amplifier U2 is respectively connected to the other end of the resistor R11 and the other end of the resistor R12 and serves as the output terminal of the adaptive filtering circuit.

[0093] In this programmable band-pass filter, the programmable potentiometer Rs1 and the capacitor C6 form a low-pass filter, the programmable potentiometer Rs2 and the capacitor C5 form a high-pass filter, and the sizes of Rs1 and Rs2 are controlled by the host computer. The values of Rs1 and Rs2 are feedback-controlled by the waveform frequency of the excitation signal generated by the current emission system, thereby adjusting the center frequency of the band-pass filter, and the effective measurement signal can be passed through to the greatest extent while filtering out interference signals. The calculation formula for the center frequency of the programmable band-pass filter is:

[0094]

[0095] where is the center frequency of the programmable band-pass filter, is the cut-off frequency of the low-pass filter, is the cut-off frequency of the high-pass filter.

[0096] As Figure 8 shown, the voltage-frequency conversion circuit includes a chip U3 of model VFC110; pin 2 of the chip U3 is the input terminal of the voltage-frequency conversion circuit; pin 4 of the chip U3 is respectively connected to a grounded capacitor C7 and the negative electrode of an external power supply; pin 7 of the chip U3 is connected to a grounded resistor R15; pin 8 of the chip U3 is connected to one end of a resistor R14 and serves as the output terminal of the voltage-frequency conversion circuit; the other end of the resistor R14 is connected to a 5V voltage; pin 10 of the chip U3 is respectively connected to one end of a capacitor C8 and the positive electrode of the external power supply; pins 11 and 12 of the chip U3 are connected; pin 13 of the chip U3 is respectively connected to pin 14 of the chip U3 and the other end of the capacitor C8 and grounded.

[0097] In this embodiment, the calculation expression for the voltage resolution S of the chip U3 of model VFC110 is , is the maximum value of the input voltage, is the minimum value of the input voltage, is the maximum value of the output voltage, is the minimum value of the output voltage. When the input is 0V - 10V, the output can be set to 0MHz - 4MHz, which is approximately 2.5uV / Hz after conversion. The voltage value is measured through frequency, and its resolution can be restored without an ADC. Based on voltage-to-frequency conversion, the higher the input voltage, the higher the converted output frequency, the faster the recognition speed, and it has the characteristic of a relatively smaller relative error. After a large number of practical data tests, the voltage resolution requirements can also be met without using a high-precision ADC. In this embodiment, the voltage range preferably entering the voltage-to-frequency conversion circuit is 1~10V.

[0098] To enable the voltage-to-frequency conversion circuit to achieve the highest resolution, configure the voltage-to-frequency conversion circuit to operate at the highest frequency of 4MHz full-scale output frequency. In this mode configuration, 5V is used for the voltage, R14 is a pull-up resistor, and bypass capacitors are not used for this port because it will cause a slow, arc-shaped rising edge at the end of the output pulse, affecting frequency counting; C7 and C8 are decoupling capacitors, which can reduce power supply noise, and R15 is used to isolate the analog ground and the digital ground. The test data of the voltage-to-frequency conversion circuit in this embodiment is shown in Table 2 and Figure 9 as follows.

[0099] Table 2

[0100]

[0101] It can be seen from Table 2 that this voltage-to-frequency conversion circuit has high conversion accuracy and small error for voltages above 0.5V, meeting the requirements for accurately testing a wide range of voltages. In Figure 9 , a high coincidence rate of the two curves indicates a small error. Thus, it can be seen that this voltage-to-frequency conversion circuit can measure voltage signals above 0.5V well, and the frequency errors converted from voltages of different magnitudes are all very small.

[0102] In the specific implementation process, it also includes a host computer, which is respectively connected to a signal preprocessing component (specifically a zero-crossing analysis and processing circuit), a voltage range automatic switching circuit, an adaptive filtering circuit, and a voltage-to-frequency conversion circuit, and is used to obtain the positive and negative polarities of the differential-mode voltage signal that alternates between positive and negative after filtering the power frequency interference, the output channels of the voltage range automatic switching circuit (the output channels include a V / F voltage-to-frequency conversion channel and a logarithmic conversion channel, specifically by Figure 4The ctrl signal and V3 signal in it are used to determine the output channel), control the center frequency of the adaptive filter circuit, and calculate the output frequency of the voltage-frequency conversion circuit to obtain the electrical method measurement result. The host computer can use FPGA, that is, the frequency converted by the voltage-frequency conversion circuit is measured by FPGA. FPGA is a hardware-level processor device with low delay in frequency measurement and high frequency measurement accuracy, which can ensure the accuracy and efficiency of data acquisition. Since the internal output triode of the used voltage-frequency conversion chip is an open-collector device, the negative edge provides the fastest logic transition and can provide the best measurement effect in a noisy environment. And FPGA is a parallel processor device that can process multi-channel data in parallel. This feature can easily increase the number of measurement channels of the electrical method without adding too much cost.

[0103] In summary, the present invention does not use the voltage measurement method of PGA (programmable gain amplification) or AGC (automatic gain control) + ADC feedback regulation. The present invention adopts the method of automatic voltage range switching + logarithmic conversion + voltage-frequency conversion to achieve the rapid measurement of the voltage between the MN electrodes, ensuring that weak voltage signals (microvolt level) and strong voltage signals (>10V) can be measured with only one judgment, increasing the measurement dynamic range of the electrical method instrument and improving the measurement efficiency.

Claims

1. A wide-band signal acquisition device for high-density electrical method in frozen soil exploration, characterized in that, It includes a signal preprocessing component, an automatic voltage range switching circuit, a logarithmic conversion circuit, an adaptive filtering circuit, and a voltage-frequency conversion circuit; among which: The signal preprocessing component is used to extract a differential-mode voltage signal from the high-density electrical method signal for frozen soil exploration, filter out power frequency interference, convert the positive and negative alternating differential-mode voltage signal after filtering out power frequency interference into a positive voltage signal, and obtain the positive and negative polarities of the positive and negative alternating differential-mode voltage signal after filtering out power frequency interference; The automatic voltage range switching circuit is used to attenuate the voltage of the positive voltage signal output by the signal preprocessing component. When the attenuated voltage is greater than or equal to the first threshold voltage, the attenuated voltage is directly sent to the adaptive filtering circuit; when the attenuated voltage is less than the first threshold voltage, the positive voltage signal output by the signal preprocessing component is compared with the second threshold voltage. When the positive voltage signal output by the signal preprocessing component is greater than or equal to the second threshold voltage, the positive voltage signal output by the signal preprocessing component is directly sent to the adaptive filtering circuit; when the positive voltage signal output by the signal preprocessing component is less than the second threshold voltage, the positive voltage signal output by the signal preprocessing component is sent to the logarithmic conversion circuit; The logarithmic conversion circuit is used to logarithmically amplify the signal input into it and send the amplified signal to the adaptive filtering circuit; The adaptive filtering circuit is used to filter out noise from the signal input into it and send the signal after noise filtering to the voltage-frequency conversion circuit; The voltage-frequency conversion circuit is used to perform voltage-frequency conversion on the signal input into it to complete the acquisition of the high-density electrical method signal for frozen soil exploration in the form of frequency.

2. The wide-band signal acquisition device for frozen soil exploration according to claim 1, wherein The signal preprocessing component includes an impedance matching circuit, a differential amplifier circuit, a filtering circuit, and a zero-crossing analysis and processing circuit connected in sequence; among which: The impedance matching circuit is used for impedance matching; The differential amplifier circuit is used to extract the differential-mode voltage signal between the signal acquisition electrodes; The filtering circuit is used to filter out power frequency interference; The zero-crossing analysis and processing circuit is used to convert the positive and negative alternating differential-mode voltage signal after filtering out power frequency interference into a positive voltage signal and obtain the positive and negative polarities of the positive and negative alternating differential-mode voltage signal after filtering out power frequency interference.

3. The wide - amplitude signal acquisition device for frozen soil exploration according to claim 1, characterized in that, The automatic voltage range switching circuit includes a follower A1, a comparator A2, a comparator A3, an NPN transistor Q1, an NPN transistor Q2, a first relay, and a second relay; among which: The positive input terminal of the follower A1 is respectively connected to one end of a resistor R1 and a grounding resistor R2; the other end of the resistor R1 is connected to the first static contact of the first relay and serves as the input terminal of the automatic voltage range switching circuit; the negative input terminal of the follower A1 is respectively connected to the output terminal of the follower A1, the positive input terminal of the comparator A2, and the second static contact of the first relay; the negative input terminal of the comparator A2 is connected to the first threshold voltage; the output terminal of the comparator A2 is connected to the base of the NPN transistor Q1 through a resistor R3; The collector of the NPN transistor Q1 is connected to an external power supply; the emitter of the NPN transistor Q1 is connected to one end of the coil of the first relay; the other end of the coil of the first relay is grounded; the moving contact of the first relay is respectively connected to the positive input terminal of the comparator A3 and the moving contact of the second relay; The negative input terminal of comparator A3 is connected to the second threshold voltage; the output terminal of comparator A3 is connected to the base of NPN transistor Q2 through resistor R4; the collector of NPN transistor Q2 is connected to an external power supply; the emitter of NPN transistor Q2 is connected to one end of the coil of the second relay; the other end of the coil of the second relay is grounded; the first static contact of the second relay is connected to the input terminal of the logarithmic conversion circuit; the second static contact of the second relay is connected to the input terminal of the adaptive filtering circuit; When the voltage at the positive input terminal of comparator A2 is greater than or equal to the voltage at the negative input terminal, comparator A2 outputs a high level, NPN transistor Q1 conducts, and the moving contact of the first relay is connected to the second static contact of the first relay; When the voltage at the positive input terminal of comparator A2 is less than the voltage at the negative input terminal, comparator A2 outputs a low level, NPN transistor Q1 is turned off, and the moving contact of the first relay is connected to the first static contact of the first relay; When the voltage at the positive input terminal of comparator A3 is greater than or equal to the voltage at the negative input terminal, comparator A3 outputs a high level, NPN transistor Q2 conducts, and the moving contact of the second relay is connected to the second static contact of the second relay; When the voltage at the positive input terminal of comparator A3 is less than the voltage at the negative input terminal, comparator A3 outputs a low level, NPN transistor Q2 is turned off, and the moving contact of the second relay is connected to the first static contact of the second relay.

4. The wide-band signal acquisition device for frozen soil exploration according to claim 1 or 3, characterized in that, The first threshold voltage and the second threshold voltage are 1V and 0.5V respectively.

5. The wide - range signal acquisition device for frozen soil exploration according to claim 1, characterized in that, The logarithmic conversion circuit includes a chip U1 of model LOG114; pin 3 of chip U1 is connected to one end of resistor R5, and the other end of resistor R5 is the input terminal of the logarithmic conversion circuit; pin 4 of chip U1 is connected to the reference voltage through resistor R6; pins 5 and 7 of chip U1 are connected to the reference voltage; pin 6 of chip U1 is respectively connected to one end of capacitor C1, one end of capacitor C2 and -5V voltage; the other end of capacitor C1 is connected to the other end of capacitor C2 and grounded; pin 8 of chip U1 is respectively connected to one end of capacitor C3, one end of capacitor C4 and 5V voltage; the other end of capacitor C3 is connected to the other end of capacitor C4 and grounded; Pin 9 of chip U1 is connected to one end of resistor R10 and pin 11 of chip U1 through resistor R9; pin 10 of chip U1 is respectively connected to one end of resistor R7 and grounding resistor R8; pin 12 of chip U1 is respectively connected to pin 13 of chip U1 and the other end of resistor R10; pin 15 of chip U1 is connected to pin 14 of chip U1 and serves as the output terminal of the logarithmic conversion circuit; pin 16 of chip U1 is respectively connected to the other end of resistor R7 and the reference voltage.

6. The wide-band signal acquisition device for frozen soil exploration according to claim 1, characterized in that The adaptive filtering circuit is a programmable band-pass filter, including an operational amplifier U2; the non-inverting input terminal of the operational amplifier U2 is respectively connected to the negative electrode of the polarized capacitor C5 and one end of the programmable potentiometer Rs2; the positive electrode of the polarized capacitor C5 is respectively connected to the positive electrode of the polarized capacitor C6, one end of the resistor R11, and one end of the programmable potentiometer Rs1; the other end of the programmable potentiometer Rs1 is the input terminal of the adaptive filtering circuit; the negative electrode of the polarized capacitor C6 is respectively connected to the other end of the programmable potentiometer Rs2 and one end of the resistor R13 and grounded. The inverting input terminal of the operational amplifier U2 is respectively connected to the other end of the resistor R13 and one end of the resistor R12; the output terminal of the operational amplifier U2 is respectively connected to the other end of the resistor R11 and the other end of the resistor R12 and serves as the output terminal of the adaptive filtering circuit.

7. The wide - band signal acquisition device for frozen soil exploration according to claim 1, characterized in that, The voltage-frequency conversion circuit includes a chip U3 of model VFC110; pin 2 of the chip U3 is the input terminal of the voltage-frequency conversion circuit; pin 4 of the chip U3 is respectively connected to the grounded capacitor C7 and the negative electrode of the external power supply; pin 7 of the chip U3 is connected to the grounded resistor R15; pin 8 of the chip U3 is connected to one end of the resistor R14 and serves as the output terminal of the voltage-frequency conversion circuit; the other end of the resistor R14 is connected to a 5V voltage; pin 10 of the chip U3 is respectively connected to one end of the capacitor C8 and the positive electrode of the external power supply; pins 11 and 12 of the chip U3 are connected; pin 13 of the chip U3 is respectively connected to pin 14 of the chip U3 and the other end of the capacitor C8 and grounded.

8. The wide-band signal acquisition device for frozen soil exploration according to claim 1, characterized in that, It also includes a host computer, which is respectively connected to the signal preprocessing component, the automatic voltage range switching circuit, the adaptive filtering circuit, and the voltage-frequency conversion circuit, and is used to obtain the positive and negative polarities of the differential mode voltage signal with positive and negative alternation after filtering the power frequency interference, the output channel of the automatic voltage range switching circuit, control the center frequency of the adaptive filtering circuit, and calculate the output frequency of the voltage-frequency conversion circuit to obtain the electrical method measurement result.

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