A non-contact electric field observation system for synchronous detection of air potential and ground potential

Abstract

The application discloses a non-contact electric field observation system for synchronous detection of air potential and ground potential, which comprises a first potential pickup circuit for outputting a first weak voltage signal, a second potential pickup circuit for outputing a second weak voltage signal, a first inner shielding cover for inhibiting interference of the environment, a second inner shielding cover for isolating interference of the circuit on ground potential detection, a double-channel signal conditioning circuit for outputting a first conditioning signal and a second conditioning signal, an outer shielding cover for surrounding the first inner shielding cover, the second inner shielding cover and the double-channel signal conditioning circuit, and being connected with the ground for shielding external electromagnetic radiation, and a differential output unit for outputting a differential signal representing a potential difference between the air potential and the ground potential. The application realizes high-precision, high-stability and wide-band differential measurement of the air potential and the ground potential.

Description

Technical Field

[0001] This invention relates to the field of electric potential measurement technology, and in particular to a non-contact electric field observation system for synchronous detection of air electric potential and ground surface electric potential. Background Technology

[0002] In the field of electric potential observation, simultaneously acquiring accurate data on both atmospheric and surface electric potential is of crucial scientific and engineering value for studying the vertical distribution characteristics of the atmospheric electric field, the dynamic changes in the Earth's electric field, and real-time monitoring of the electromagnetic environment. For example, in scenarios such as lightning warning, seismic electromagnetic anomaly detection, lightning protection design of high-rise buildings, and space physics research, accurate measurement of the potential difference between the air and the surface is a core foundation for analyzing electric field vectors, assessing charge distribution, and predicting environmental changes.

[0003] Currently, existing technologies typically measure the air electric field and the ground electric field separately using time-sharing or location-sharing methods. Common approaches include using a single field-milled electric field probe suspended in the air to sense the air electric potential, or recording the ground potential separately using buried electrodes. However, these discrete measurement systems have the following significant drawbacks: First, the common-mode interference suppression capability is insufficient. Interference factors such as ground potential fluctuations (e.g., ground current injection, grounding grid potential rise), power supply ripple noise, temperature drift, and environmental electromagnetic radiation can simultaneously couple to the air and ground measurement channels, forming common-mode signals. Due to the lack of synchronous acquisition and differential processing mechanisms in traditional systems, these common-mode interferences cannot be effectively eliminated, resulting in a large amount of noise mixed in the measurement results. Especially in the ultra-low frequency band (0.001Hz~0.1Hz), the effects of temperature drift and 1 / f noise are more prominent, severely limiting the resolution of weak potential signals.

[0004] Secondly, parasitic capacitance leads to signal attenuation. The amplitude of the induced signal from non-contact detection electrodes is extremely small (typically in the microvolt to millivolt range), and parasitic capacitance exists between the electrodes and surrounding structures (such as shielding housings and leads). Under high-impedance input conditions, this capacitive reactance forms a voltage divider with the internal resistance of the signal source, causing significant signal attenuation. Traditional shielding methods simply ground the shielding layer, which exacerbates the negative impact of parasitic capacitance and cannot meet the requirements of high impedance (>10GΩ) and wide bandwidth (0.001Hz~20kHz) measurements.

[0005] Third, poor consistency and synchronization between the two channels. In existing technologies, airborne and ground-based measurement circuits are often designed independently, with differences in component parameters, temperature characteristics, and layout wiring, leading to frequency response, phase delay, and gain mismatch between the two channels. This mismatch is converted into residual common-mode error during subsequent differential processing. Even with ordinary subtraction circuits, the actual common-mode rejection ratio (CMRR) is usually below 60dB, making it difficult to maintain stable rejection performance over a wide bandwidth.

[0006] Fourth, it has weak resistance to electromagnetic interference. Strong radio frequency interference, power frequency magnetic fields and transient pulses in the field or industrial environment will directly affect the detection electrodes or signal lines. Conventional single-layer shielding or local grounding measures cannot completely block such interference. In particular, when the potential of the shielding layer itself fluctuates, it will also introduce additional noise current.

[0007] In summary, there is an urgent need to develop a non-contact electric field observation system for the simultaneous detection of airborne and surface electric potentials. Summary of the Invention

[0008] The purpose of this invention is to provide a non-contact electric field observation system for synchronous detection of air and surface electric potential. Through dual-channel synchronous measurement, double-layer shielding structure, active shielding drive technology, and specially designed signal conditioning circuit, it achieves high-precision, high-stability, and wide-bandwidth differential measurement of air and surface electric potential.

[0009] To achieve the above objectives, the present invention provides a non-contact electric field observation system for synchronous detection of airborne and surface electric potentials, comprising: The first potential pickup circuit is used to sense the air potential in the space electric field and output a first weak voltage signal. The second potential pickup circuit is used to sense the surface potential of the earth or nearby and output a second weak voltage signal. The first inner shielding cover surrounds the detection electrode of the first potential pickup circuit and is used to suppress environmental interference. The second inner shielding cover surrounds the detection electrodes of the second potential pickup circuit and is used to isolate the circuit from interference with the detection of the ground potential. A dual-channel signal conditioning circuit includes a first conditioning link and a second conditioning link. The input terminal of the first conditioning link is electrically connected to the first potential pickup circuit and is used to process the first weak voltage signal and output a first conditioning signal. The input terminal of the second conditioning link is electrically connected to the second potential pickup circuit and is used to process the second weak voltage signal and output a second conditioning signal. An outer shielding cover surrounds the first inner shielding cover, the second inner shielding cover, and the dual-channel signal conditioning circuit, and is connected to the ground to shield external electromagnetic radiation. The differential output unit is connected to the first conditioning link and the second conditioning link respectively, and outputs a differential signal representing the potential difference between the air potential and the ground potential.

[0010] Preferably, the detection electrode of the first potential pickup circuit is suspended in the air, while the detection electrode of the second potential pickup circuit is in contact with the ground or buried in the ground surface.

[0011] Preferably, the circuit structures of the first conditioning link and the second conditioning link are symmetrical and identical, including: Input coupling network is used to isolate DC offset and low-frequency interference; A differentiating amplification unit is connected to the output of the input coupling network and is used to amplify the signal by differentiation. A fixed-gain amplifier unit is connected to the output terminal of the differential amplifier unit to provide a fixed voltage gain.

[0012] Preferably, the input coupling network is a DC blocking capacitor, with the input terminal of the DC blocking capacitor connected to the corresponding detection electrode and the output terminal connected to the differential amplification unit.

[0013] Preferably, the differential amplification unit includes a first operational amplifier, a first feedback resistor, and a feedback capacitor; wherein, the inverting input terminal of the first operational amplifier is connected to the output terminal of the input coupling network, and the non-inverting input terminal is grounded; the feedback resistor and the feedback capacitor are connected in parallel between the output terminal and the inverting input terminal of the first operational amplifier.

[0014] Preferably, the fixed gain amplification unit includes a second operational amplifier, an input resistor, and a second feedback resistor. The inverting input terminal of the second operational amplifier is connected to the output terminal of the differentiating amplification unit through the input resistor, and the non-inverting input terminal is grounded. The output terminal of the second operational amplifier is connected to the inverting input terminal through the second feedback resistor.

[0015] Preferably, both the first inner shield and the second inner shield are connected to an active shielding driver. The input terminal of the active shielding driver is connected to the corresponding detection electrode, and the output terminal is connected to the corresponding inner shield. The active shielding driver is a voltage follower used to drive the potential inside the shield to follow the potential of the corresponding detection electrode.

[0016] Preferably, the dual-channel signal conditioning circuit further includes a low-pass filter, which is used to limit bandwidth and filter out high-frequency noise. The corner frequency of the low-pass filter is determined by the first feedback resistor and the feedback capacitor in the differential amplifier unit.

[0017] Preferably, the first input terminal of the differential output unit is electrically connected to the output terminal of the first conditioning link, and the second input terminal is electrically connected to the output terminal of the second conditioning link, for performing differential operations on the first conditioning signal and the second conditioning signal, and outputting a differential signal representing the potential difference between the air potential and the ground potential.

[0018] Preferably, the transfer functions of the first conditioning link and the second conditioning link are: ; In the formula, For transfer functions, For output signal, For input signal, For complex frequencies, For coupling capacitors, For the first feedback resistor, For input resistance, This is the second feedback resistor. This is the feedback capacitor.

[0019] Compared with the prior art, the present invention has the following advantages and technical effects: This invention effectively suppresses common-mode interference such as ground potential fluctuations, power supply noise, temperature drift, and environmental electromagnetic radiation by employing dual-channel synchronous measurement, a double-layer shielding structure, and a differential output unit. For the low-frequency band, this invention significantly suppresses 1 / f noise and temperature drift, achieving a common-mode rejection ratio better than 70dB across the entire frequency band, and exceeding 90dB in the mid-to-high frequency band. The air-to-ground conditioning link structure mutually cancels out the temperature drift of the operational amplifier input offset voltage, suppressing the temperature drift error to below 0.1µV / ℃, ensuring the stability and reliability of data from long-term continuous field observations. The active shielding technology employed in this invention enables real-time synchronization between the potential of the inner shield and the potential of the probe electrode, eliminating the voltage division effect caused by the parasitic capacitance between the probe electrode and the shield. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of a non-contact electric field observation system for synchronous detection of air electric potential and ground electric potential according to an embodiment of the present invention. Figure 2 This is a schematic diagram of one conditioning link of the dual-channel signal conditioning circuit according to an embodiment of the present invention; Figure 3 This is a simulation frequency response curve of a single-channel signal conditioning circuit according to an embodiment of the present invention. Figure 4 This is a simulation curve of the common-mode suppression effect of the dual-channel differential output according to an embodiment of the present invention; Among them, 1a, airborne detection electrode; 1b, ground detection electrode; 2a, first inner shield; 2b, second inner shield; 3, outer shield; 4, dual-channel signal conditioning circuit; 5, ground; 6a, first shield driver; 6b, second shield driver. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0023] This embodiment proposes a non-contact electric field observation system for the simultaneous detection of airborne and surface electric potentials, such as... Figure 1 ,include: The first potential pickup circuit is used to sense the air potential in the space electric field and output a first weak voltage signal. The second potential pickup circuit is used to sense the surface potential of the earth or nearby and output a second weak voltage signal. The first inner shield 2a surrounds the detection electrode of the first potential pickup circuit and is used to suppress environmental interference. The second inner shield 2b surrounds the detection electrode of the second potential pickup circuit and is used to isolate the interference of the circuit to the detection of the ground potential. The dual-channel signal conditioning circuit 4 includes a first conditioning link and a second conditioning link. The input terminal of the first conditioning link is electrically connected to the first potential pickup circuit and is used to process the first weak voltage signal and output a first conditioning signal. The input terminal of the second conditioning link is electrically connected to the second potential pickup circuit and is used to process the second weak voltage signal and output a second conditioning signal. The outer shield 3 surrounds the first inner shield, the second inner shield and the dual-channel signal conditioning circuit, and is connected to the ground 5 to shield external electromagnetic radiation. The differential output unit is connected to the first conditioning link and the second conditioning link respectively, and outputs a differential signal representing the potential difference between the air potential and the ground potential.

[0024] Specifically, the detection electrode of the first potential pickup circuit is an air detection electrode 1a, which adopts a metal disk or spherical structure and is suspended in the air to sense changes in air potential. The detection electrode of the second potential pickup circuit is the ground detection electrode 1b, which also uses a metal plate electrode and is placed on the ground surface to sense changes in the ground potential.

[0025] Furthermore, the detection electrode of the first potential pickup circuit is suspended in the air, while the detection electrode of the second potential pickup circuit is either in contact with the ground or buried in the ground surface.

[0026] Furthermore, both the first inner shield 2a and the second inner shield 2b are connected to active shielding drivers, wherein the active shielding drivers include the first shielding driver 6a and the second shielding driver 6b.

[0027] The first inner shield 2a and the second inner shield 2b are made of copper or aluminum, respectively, and completely surround their respective detection electrodes. They are made to follow the potential of the corresponding detection electrode by independent first shield driver 6a and second shield driver 6b, thereby eliminating the parasitic capacitance between the shield and the electrode. The first shield driver 6a and the second shield driver 6b are both voltage followers, used to drive the potential inside the shield to follow the potential of the corresponding detection electrode.

[0028] Furthermore, the dual-channel signal conditioning circuit 4 is installed inside the outer shield 3, and includes two identical first conditioning links and second conditioning links, which process air and ground potential signals respectively. like Figure 2 Both the first conditioning link and the second conditioning link include: Input coupling network is used to isolate DC offset and low-frequency interference; A differentiating amplification unit is connected to the output of the input coupling network and is used to amplify the signal by differentiation. A fixed-gain amplifier unit is connected to the output terminal of the differential amplifier unit to provide a fixed voltage gain.

[0029] Specifically, the input coupling network is a DC blocking capacitor. The input terminal of the DC blocking capacitor is connected to the corresponding detection electrode, and the output terminal is connected to the differential amplification unit.

[0030] Furthermore, the differentiating amplification unit includes a first operational amplifier and a first feedback resistor. and feedback capacitor The inverting input of the first operational amplifier is connected to the output of the input coupling network, and the non-inverting input is grounded; the feedback resistor... With feedback capacitor It is connected in parallel between the output terminal and the inverting input terminal of the first operational amplifier to form a first-order differential amplifier; Furthermore, the fixed-gain amplification unit includes a second operational amplifier and an input resistor. Second feedback resistor The inverting input of the second operational amplifier is connected to an input resistor. The output of the differential amplifier unit is connected to the output terminal, and the non-inverting input terminal is grounded. The output terminal of the second operational amplifier is connected to the second feedback resistor. Connect to the inverting input terminal.

[0031] Specifically, the second operational amplifier and the second feedback resistor Input resistance This forms an inverting proportional amplifier circuit, providing a fixed voltage gain Gf=R2 / R3.

[0032] The entire circuit outputs Vo, which is connected to the subsequent differential output unit.

[0033] Furthermore, the dual-channel signal conditioning circuit also includes a low-pass filter, which is used to limit bandwidth and filter out high-frequency noise. The cutoff frequency of the low-pass filter is determined by the first feedback resistor in the differentiating amplifier unit. and feedback capacitor Decide.

[0034] Furthermore, the outer shield is made of highly conductive material, is completely sealed, and reliably grounded to shield external radio frequency and power frequency interference, while directing the common-mode noise generated by the internal circuit to ground.

[0035] Furthermore, the first input terminal of the differential output unit is electrically connected to the output terminal of the first conditioning link, and the second input terminal is electrically connected to the output terminal of the second conditioning link, for performing differential operations on the first conditioning signal and the second conditioning signal, and outputting a differential signal representing the potential difference between the air potential and the ground potential.

[0036] The differential output unit uses an instrumentation amplifier or subtractor circuit to subtract the two output signals to obtain a differential signal; this unit has a high common-mode rejection ratio (CMRR), typically ≥100dB.

[0037] Specifically, when the system is working, the airborne detection electrode 1a senses changes in the spatial electric field and generates a weak voltage signal V. i,air ; Surface detection electrode 1b senses changes in surface potential and generates a signal V i,ground The two signals are amplified by their respective signal conditioning links to obtain V. o,air and V o,ground .

[0038] The differential output unit subtracts the two: V diff= V o,air -V o,ground ; In the formula, V diff For differential signals, V o,air V is the voltage signal output after passing through the first conditioning link. o,ground This is the voltage signal output after passing through the second signal conditioning link.

[0039] Since the two circuits have the same structure and share the same outer shield and power supply, the common-mode noise they introduce (such as power supply ripple, temperature drift, external electromagnetic interference, etc.) is basically the same. They can be effectively suppressed by subtraction, thereby extracting the pure vertical electric field component (i.e., the potential difference between the air and the ground).

[0040] Furthermore, based on the virtual short and virtual open characteristics of an ideal operational amplifier, the single-path transfer function is: ; In the formula, For transfer functions, For output signal, For input signal, For complex frequencies, For coupling capacitors, For the first feedback resistor, This is the second feedback resistor. For input resistance, This is the feedback capacitor.

[0041] Furthermore, the system is suitable for electric field measurement in the frequency band of 0.001Hz to 20kHz.

[0042] To verify the performance of a single-channel circuit, SPICE simulation software was used. Figure 2 The circuit shown is subjected to AC analysis. The simulation parameters are as follows: =100 pF, =1 kΩ, =1 F, =10 GΩ, =10 GΩ, meaning the gain of the subsequent stage is 1.

[0043] The op-amp uses an ideal model with a power supply voltage of ±15V.

[0044] The AC analysis frequency range is 0.001Hz to 20kHz, with 100 points per decade.

[0045] The obtained frequency response data and the corresponding Bode plot are as follows: Figure 3 As shown.

[0046] Depend on Figure 3 As can be seen, in the low-frequency range (<0.01Hz), the gain increases with increasing frequency, with a slope of approximately 1.4dB / decade, and the phase decreases from 75° to 0°, consistent with differential characteristics. Near the cutoff frequency of 0.007Hz, the gain increase slows down, and the phase decreases. In the high-frequency range, the gain flattens out at approximately 2dB, and the phase approaches 0°. These results are consistent with theoretical analysis, verifying the correctness of the single-channel circuit design.

[0047] To evaluate the common-mode rejection capability (CMRR) of the dual-channel differential output, the same common-mode interference signal was applied to both channels in the simulation, while simultaneously simulating minor mismatches between the channels to examine the actual CMRR. The simulation settings are as follows: The parameters for both channels are the same as in the single-channel simulation, but ±1% resistance is introduced. Mismatch (Air Passage) =1.1 kΩ, surface channel =0.9 kΩ), to simulate the actual component tolerance.

[0048] Input signals: Differential mode signals include the airborne detection electrode input signal V. i,air =1 mV and the input signal V of the surface detection electrode i,ground =0 (i.e., only the air electrode has a signal); simultaneously, a common-mode interference signal V is applied to the input. cm =1 V (50Hz sine wave) superimposed on the two inputs.

[0049] Simulation type: Transient analysis, duration 0.1s, observe differential output V diff Interference components in.

[0050] The simulation results are as follows: In the differential output, the 50Hz interference component is attenuated to approximately 26uV, corresponding to a common-mode rejection ratio of: ; In the formula, Common mode rejection ratio, This refers to the common-mode interference signal component at the output.

[0051] Further AC scanning was performed, sweeping the common-mode interference frequency from 0.001Hz to 20kHz, and the common-mode gain A of the differential output was calculated. cm The CMRR curves were plotted. The results show that the CMRR is greater than 70dB across the entire frequency band. In the low-frequency band, due to the differential element, the CMRR will be 70dB. In the frequency band above 0.03Hz, the CMRR is greater than 90dB. Figure 4 The graph shows the CMRR as a function of frequency. The horizontal axis represents frequency (Hz), using a logarithmic scale, ranging from 0.001Hz to 20kHz; the vertical axis represents common-mode rejection ratio (dB), using a linear scale, ranging from 0 to 100dB. The curve is based on a ±1% mismatch between the two channel components (air channel). =1.1 kΩ, surface channel The simulation conditions were set as follows: (Ω = 0.9 kΩ), and the remaining parameters were the same as those in the single-channel simulation. =100pF, =1F, =10 GΩ, =10 GΩ). Simulation results show that the system's CMRR is higher than 70dB across the entire frequency band, and can reach over 90dB in the high-frequency band, verifying the strong suppression capability of the differential structure for common-mode interference.

[0052] In addition, this embodiment also simulates the effect of temperature drift: assuming that the input offset voltage drift of the two op-amps is ±1µV / ℃, the drift is suppressed to below 0.1µV / ℃ after differential processing, indicating that the dual-channel structure has good temperature stability.

[0053] The simulation results demonstrate that the dual-channel differential design of this invention can effectively suppress common-mode interference and achieve satisfactory measurement accuracy even with component mismatch.

[0054] Experiments show that the input impedance of this system can reach over 10 GΩ, the dual-channel common-mode rejection ratio is better than 90 dB across the entire frequency band, and it can stably measure the potential difference between the air and the ground surface in the frequency band of 0.001 Hz to 20 kHz. It is suitable for scenarios such as monitoring the vertical component of the atmospheric electric field, observing the ground electric field, and assessing the electromagnetic environment.

[0055] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A non-contact electric field observation system for synchronous detection of airborne and surface electric potentials, characterized in that, include: The first potential pickup circuit is used to sense the air potential in the space electric field and output a first weak voltage signal. The second potential pickup circuit is used to sense the surface potential of the earth or nearby and output a second weak voltage signal. The first inner shield (2a) surrounds the detection electrode of the first potential pickup circuit and is used to suppress environmental interference. The second inner shield (2b) surrounds the detection electrode of the second potential pickup circuit and is used to isolate the circuit from interference with the detection of the ground potential. The dual-channel signal conditioning circuit (4) includes a first conditioning link and a second conditioning link. The input terminal of the first conditioning link is electrically connected to the first potential pickup circuit and is used to process the first weak voltage signal and output a first conditioning signal. The input terminal of the second conditioning link is electrically connected to the second potential pickup circuit and is used to process the second weak voltage signal and output a second conditioning signal. The outer shield (3) surrounds the first inner shield, the second inner shield and the dual-channel signal conditioning circuit, and is connected to the ground to shield external electromagnetic radiation. The differential output unit is connected to the first conditioning link and the second conditioning link respectively, and outputs a differential signal representing the potential difference between the air potential and the ground potential.

2. The non-contact electric field observation system for synchronous detection of airborne and surface electric potentials according to claim 1, characterized in that, The detection electrode of the first potential pickup circuit is suspended in the air, while the detection electrode of the second potential pickup circuit is in contact with the ground or buried in the ground surface.

3. The non-contact electric field observation system for synchronous detection of airborne and surface electric potentials according to claim 1, characterized in that, The first conditioning link and the second conditioning link have symmetrical and identical circuit structures, including: Input coupling network is used to isolate DC offset and low-frequency interference; A differentiating amplification unit, connected to the output of the input coupling network, is used to differentiate and amplify the signal; A fixed-gain amplifier unit is connected to the output terminal of the differential amplifier unit to provide a fixed voltage gain.

4. The non-contact electric field observation system for synchronous detection of airborne and surface electric potentials according to claim 3, characterized in that, The input coupling network is a DC blocking capacitor, with its input terminal connected to the corresponding detection electrode and its output terminal connected to the differential amplification unit.

5. The non-contact electric field observation system for synchronous detection of airborne and surface electric potentials according to claim 4, characterized in that, The differential amplification unit includes a first operational amplifier, a first feedback resistor, and a feedback capacitor; wherein, the inverting input terminal of the first operational amplifier is connected to the output terminal of the input coupling network, and the non-inverting input terminal is grounded; the feedback resistor and the feedback capacitor are connected in parallel between the output terminal and the inverting input terminal of the first operational amplifier.

6. The non-contact electric field observation system for synchronous detection of airborne and surface electric potentials according to claim 5, characterized in that, The fixed gain amplification unit includes a second operational amplifier, an input resistor, and a second feedback resistor. The inverting input terminal of the second operational amplifier is connected to the output terminal of the differentiating amplification unit through the input resistor, and the non-inverting input terminal is grounded. The output terminal of the second operational amplifier is connected to the inverting input terminal through the second feedback resistor.

7. The non-contact electric field observation system for synchronous detection of airborne and surface electric potentials according to claim 1, characterized in that, Both the first inner shield (2a) and the second inner shield (2b) are connected to an active shield driver. The input terminal of the active shield driver is connected to the corresponding detection electrode, and the output terminal is connected to the corresponding inner shield. The active shield driver is a voltage follower used to drive the potential inside the shield to follow the potential of the corresponding detection electrode.

8. The non-contact electric field observation system for synchronous detection of airborne and surface electric potentials according to claim 5, characterized in that, The dual-channel signal conditioning circuit (4) further includes a low-pass filter, which is used to limit bandwidth and filter out high-frequency noise. The corner frequency of the low-pass filter is determined by the first feedback resistor and the feedback capacitor in the differential amplifier unit.

9. The non-contact electric field observation system for synchronous detection of airborne and surface electric potentials according to claim 8, characterized in that, The first input terminal of the differential output unit is electrically connected to the output terminal of the first conditioning link, and the second input terminal is electrically connected to the output terminal of the second conditioning link. It is used to perform differential operation on the first conditioning signal and the second conditioning signal to output a differential signal representing the potential difference between the air potential and the ground potential.

10. The non-contact electric field observation system for synchronous detection of airborne and surface electric potentials according to claim 9, characterized in that, The transfer functions of the first conditioning link and the second conditioning link are: ； In the formula, For transfer functions, For output signal, For input signal, For complex frequencies, For coupling capacitors, For the first feedback resistor, For input resistance, This is the second feedback resistor. This is the feedback capacitor.

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