Electrostatic field measurement method and system based on variable capacitance diode

Abstract

The invention discloses a variable capacitance diode-based electrostatic field measurement method and system. The system comprises an electrostatic field sensor, an alternating current driving module, a capacitance measurement loop, a voltage measurement module and a power supply module. The electrostatic field sensor applies induced voltage in an electrostatic field to the two ends of the variable capacitance diode so as to change capacitance of the variable capacitance diode, and the alternating current driving module provides stable sine wave alternating current signals to drive the whole capacitance measurement loop. The capacitance measurement loop measures the capacitance change of the variable capacitance diode and converts a current signal into a voltage signal. The voltage measurement module carries out amplification, filtering, detection and sampling holding processing on the signal, and capacitance change is converted into electrostatic field intensity through the processor. According to the invention, the corresponding relation between the capacitance change and the electrostatic field intensity is determined through the calibration experiment, so that the accurate measurement of the external electrostatic field is realized. The device has the advantages of being high in sensitivity, simple in structure, easy to miniaturize and low in cost, and is suitable for realizing large-range electrostatic field monitoring through multi-point installation.

Description

Technical Field

[0001] The invention relates to an electrostatic field measurement method and a measurement system based on a varactor diode, belonging to the technical field of electrostatic field measurement. Background Art

[0002] At present, electrostatic field measurement technology is widely used in many fields. The mainstream sensors widely used in electrostatic field measurement are optical electric field sensors, vibration capacitive electric field sensors and field mill sensors. However, there are many limitations in existing electrostatic field measurement methods and instruments. For example, optical measuring instruments based on Kerr effect or Pockels effect often have complex optical path structures, and electrical vibration capacitive electric field sensors and field mill electric field instruments face the problem of needing reliable grounding and mechanical structures that are prone to mechanical failures. These devices are usually complex in structure and expensive, which limits their popularity in practical applications.

[0003] The electrostatic field sensor based on the varactor diode provides a new possibility for measuring the electrostatic field. Taking advantage of the small size, simple structure and voltage-controlled capacitance change characteristics of the varactor diode, the present invention designs an electrostatic field measurement system based on the varactor diode, which can achieve accurate measurement of the electrostatic field, has the advantages of high sensitivity, large measurement range, simple structure and easy miniaturization suitable for multi-point arrangement, and can effectively overcome the problems existing in the above-mentioned methods. Summary of the invention

[0004] To solve the above problems, the purpose of the present invention is to propose an electrostatic field measurement method and system based on a varactor diode, so as to solve the above-mentioned problems of field grinding electrostatic field sensors, vibration capacitive electric field sensors having movable mechanical parts and optical electric field sensors having complex structures and high prices.

[0005] To achieve the above object, the following technical solution is provided: an electrostatic field measurement system based on a varactor diode, comprising an electrostatic field sensor, a capacitance measurement circuit, an AC drive module, a voltage measurement module and a power supply module;

[0006] The electrostatic field sensor is composed of a pair of induction plates made of metal conductors, an insulating medium and a varactor diode. The induction plates are respectively connected to the cathode and anode of the varactor diode through wires to form an electrostatic field sensor port. The electrostatic field generates a potential difference through the induction plates, which acts on the two ends of the varactor diode to cause a change in capacitance.

[0007] The capacitance measurement circuit includes a varactor diode, a standard capacitor, a sampling resistor and an AC drive module, and its main function is to measure the capacitance change of the varactor diode and convert the current signal into a voltage signal;

[0008] The AC drive module is used to provide a voltage excitation signal with constant amplitude and frequency to the measurement circuit;

[0009] The voltage measurement module obtains the capacitance change signal through the voltage drop on the sampling resistor, and amplifies, filters, detects, samples and holds the signal, and performs digital-to-analog conversion processing, and converts the measured capacitance change into the field strength value of the electrostatic field through the processor, and outputs the result through the communication interface;

[0010] The power supply module is used to provide stable electric energy for the system to ensure the normal operation of each functional module.

[0011] Another object of the present invention is to provide: a method for measuring an electrostatic field based on a varactor diode, using the above system, and performing the following steps:

[0012] The electric field to be measured is converted into the capacitance value of the varactor diode through the electrostatic field sensor, and then the capacitance of the varactor diode is measured through the capacitance measurement circuit. The current signal of the capacitance measurement circuit is converted into a voltage signal using a sampling resistor. The output voltage value of the circuit is measured by the voltage measurement module, and the corresponding relationship between the field strength and the output voltage is measured through experimental calibration. The corresponding relationship between the field strength and the output voltage is measured based on the output voltage of the measurement system and the calibration experiment, that is, the value of the electrostatic field is measured.

[0013] The principle of the present invention is as follows:

[0014] (1) Installation and positioning: The electrostatic field sensor is placed in the electrostatic field to be measured, ensuring that the normal direction of the sensing plate is parallel to the field strength direction of the external electrostatic field; at this time, the electrostatic field will induce a potential difference between the two plates, which is applied to the two ends of the varactor diode, causing a change in the diode capacitance;

[0015] (2) Applying an excitation signal: applying an AC signal with a constant frequency and amplitude to the capacitance measurement circuit through an AC drive module. The signal is usually a sine wave signal, which is used to drive the capacitance measurement circuit to work;

[0016] Function of the signal: Under the influence of the external electrostatic field, the induced potential difference is applied to the two ends of the varactor diode as a reverse bias, causing its junction capacitance to change. At this time, the applied AC signal and the electrostatic field induced voltage work together to cause the current in the capacitance measurement circuit to change;

[0017] (3) Operation of capacitance measurement circuit:

[0018] Acquisition of current signal: The AC excitation signal works through the varactor diode, standard capacitor and sampling resistor to generate loop current. As the strength of the electrostatic field changes, the capacitance of the varactor diode changes accordingly, causing the current signal in the loop to change accordingly. The sampling resistor converts the current signal into a voltage signal, and the size of the voltage signal is directly related to the capacitance change of the varactor diode.

[0019] (4) Signal processing and measurement:

[0020] Function of the voltage measurement module: The voltage measurement module obtains the voltage signal reflecting the change of the capacitance of the varactor diode by detecting the voltage drop on the sampling resistor, and indirectly measures the electric field.

[0021] Signal processing steps:

[0022] Signal amplification: First, amplify the weak voltage signal to ensure measurement accuracy.

[0023] Filtering: Filter out noise in the signal to ensure the stability of the effective signal.

[0024] Detection and sample-and-hold: Convert the AC signal to a DC signal and perform sample-and-hold at a specific time point to capture and stabilize the signal generated by the capacitance change.

[0025] Analog-to-digital conversion: The processed analog signal is converted into a digital signal through an ADC (analog-to-digital converter) and sent to the processor for further analysis.

[0026] (5) Calibration of field strength and capacitance change:

[0027] Calibration process: In order to obtain accurate measurement results, system calibration is required. The sensor is calibrated in a standard electrostatic field with known field strength. Under different field strengths, the sensor outputs different capacitance changes and the voltage measurement module collects different voltage values. The system fits the corresponding relationship curve or formula between field strength and collected voltage value based on these data.

[0028] Repeat calibration: By measuring the collected voltage values ​​of the sensor under different electrostatic field strengths multiple times, multiple sets of data on field strength and voltage changes are obtained to ensure the measurement accuracy of the system.

[0029] (6) Electrostatic field measurement and result output:

[0030] Measurement process: During actual measurement, the sensor is placed in the electrostatic field to be measured, and the voltage value collected by the voltage measurement module is converted into electrostatic field strength in combination with the calibration curve.

[0031] Calculation and output: The processor converts the measured voltage signal into the current electrostatic field strength value according to the calibrated field strength-voltage change relationship. The result can be displayed in real time through the display unit, or output to an external system through the communication interface for further recording or analysis.

[0032] The advantages and effects of the present invention are as follows: The present invention uses the characteristic that the junction capacitance of the varactor diode changes with the reverse bias voltage as the sensing principle, and the method is unique and the sensing principle is simple. The measuring probe of the present invention is composed of a medium filled between two plates, and the structure is simple, stable and reliable. The present invention increases the input capacitance of the circuit by adding a standard capacitor, reduces the potential difference of the sensing plate, and expands the measurement range of the electrostatic field measurement system. The invention does not contain movable mechanical parts, and overcomes the defects of the vibration capacitive electric field sensor and the field grinding electric field sensor that the mechanical structure will be mechanically worn and mechanically failed. Compared with the complex optical path structure of the optical electric field sensor, which needs to be converted to the photoelectric signal and has a large volume, the circuit structure of this method is simple and easy to implement, and the existing varactor diode is used as the sensor device, which is low in cost and easy to obtain. The measurement system is small in size, light in weight and easy to carry. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the structural block diagram of the electrostatic field measurement system based on varactor diode;

[0034] Figure 2 The circuit diagram of the electrostatic field measurement system based on the varactor diode;

[0035] Figure 3 The capacitance-voltage characteristic curve of the 1SV149 varactor diode;

[0036] Figure 4 Schematic diagram of the calibration experiment of the electrostatic field measurement system based on varactor diode;

[0037] Figure 5 It is the structural block diagram of the measurement module;

[0038] Figure 6 is a circuit diagram of a controllable multi-standard capacitor;

[0039] Figure 7 is the electric field voltage calibration curve in the embodiment;

[0040] Figure 8 This is a schematic diagram of the capacitance connection of the measurement system. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with the embodiments and drawings.

[0042] Example 1

[0043] The electrostatic field measurement system based on varactor diode includes an electrostatic field sensor 100, a capacitance measurement circuit 200, an AC drive module 204, a voltage measurement module 300 and a power supply module 400; the electrostatic field sensor 100 is composed of an induction plate 101, an induction plate 202, an insulating medium 103 and a varactor diode 201.

[0044] The first induction plate 101 and the second induction plate 102 are conductors, and the insulating medium 103 is air or other materials with a high dielectric constant.

[0045] The sensing plate 1 101, the sensing plate 2 102 and the insulating medium 103 form a sandwich structure. The two sensing plates are thin-layer structures with equal areas and are parallel to each other. The insulating medium is filled between the two plates to form a parallel plate capacitor device. The sensing plate 1 101, the sensing plate 2 102 and the insulating medium 103 constitute the sensing probe of the entire sensor system.

[0046] The varactor diode 201 is connected to two sensing plates through wires, and the two sensing plates are respectively connected to the cathode and anode of the varactor diode.

[0047] When the electrostatic field sensor 100 is in use, the two sensing plates and the insulating medium form a sandwich-like structure and are placed in an electrostatic field to sense the electrostatic field and generate an induced voltage. The two sensing plates are placed perpendicular to the field strength direction in the electric field, so there is an induced voltage. Different field strengths will generate different induced voltages between the two plates.

[0048] The varactor diode 201 has the characteristic that the junction capacitance changes with the reverse voltage. After the two sensing plates are connected to the varactor diode through a wire, the induced voltage between the two sensing plates is applied to the two ends of the varactor diode through the wire, causing the junction capacitance value of the varactor diode to change. Different field strengths can produce different induced voltages, and different induced voltages correspond to different capacitance values. Therefore, by measuring the junction capacitance value of the diode, the magnitude of the electrostatic field can be measured.

[0049] The capacitance value of the varactor diode 201 is measured by the capacitance measurement circuit 200 .

[0050] The capacitance measurement circuit 200 is composed of a varactor diode 201 , a standard capacitor 202 , a sampling resistor 203 and an AC drive module 204 .

[0051] The standard capacitor 202 is connected in series in the capacitance measurement loop 200 and is a large capacitor with a certain capacitance value, which is used to increase the input capacitance of the system circuit and reduce the value of the induced voltage.

[0052] The sampling resistor 203 is a resistor of known resistance, which is connected in series in the capacitance measurement loop 200 and is used to measure the current passing through the circuit. By measuring the voltage drop across the resistor, the capacitance change can be indirectly calculated.

[0053] The AC drive module 204 is used to provide a drive signal for the entire loop, and its output is usually a sine waveform, which can provide a stable and continuous AC voltage signal for the measurement loop.

[0054] The AC driving module 204 may be directly connected in series to the capacitance measurement loop 200 , or may be coupled to the capacitance measurement loop 200 via a transformer.

[0055] The voltage measurement module 300 is used to measure the voltage difference between two ends of the sampling resistor 203 .

[0056] The voltage measurement module 300 is composed of a follower circuit 301 , a signal amplifying circuit 302 , a filtering circuit 303 , a peak detection circuit 304 , a sampling and holding circuit 305 , a digital-to-analog conversion circuit 306 , a microprocessor 307 , and an output communication interface 308 .

[0057] The follower circuit is connected to the sampling resistor to provide high input impedance and low output impedance, so as to isolate the front and rear stage circuits and prevent the measurement module from generating a load effect on the capacitance measurement loop, thereby maintaining the accuracy of the measurement signal.

[0058] The signal amplification circuit amplifies the weak voltage signal across the sampling resistor for subsequent processing and measurement.

[0059] The filter circuit is used to suppress unnecessary frequency components in the measurement signal to ensure that the measurement signal is clean and stable.

[0060] The peak detection circuit is used to convert the AC signal into a DC signal, which is convenient for subsequent measurement and analysis.

[0061] The sample-and-hold circuit is used to sample a measurement signal at a specific time point and hold the voltage value for subsequent stable measurement.

[0062] The digital-to-analog conversion circuit converts the analog signal of the sampling and holding circuit into a digital signal so that the back-end microcontroller can perform digital processing.

[0063] The microprocessor is used to analyze and process the digital signal, and output the measured voltage through communication with the display device.

[0064] In one embodiment, the microprocessor can be used to control the controllable switch to control the number of standard capacitors connected to the capacitance measurement loop so as to change the input capacitance of the circuit.

[0065] The output communication interface is used for transmitting the processed data and communicating with the display device for displaying the results.

[0066] The power module 400 is connected to each module via a power line to provide stable power to each functional module to ensure the normal operation of the circuit and the accuracy of the measurement result.

[0067] Using the above system:

[0068] (1) The sensor consists of a pair of sensing electrodes, an insulating medium and a varactor diode. The electrodes are two conductor plates placed in parallel. The electrodes are connected to the cathode and anode of the varactor diode to form the port of the sensor;

[0069] (2) The sensor probe consists of a pair of sensing electrodes and an insulating medium and is placed in the electrostatic field to be measured;

[0070] (3) The external electrostatic field to be measured changes the induced voltage between the induction plates, thereby changing the junction capacitance of the varactor diode, forming a coupling relationship between the electrostatic field strength and the capacitance change;

[0071] (4) The capacitance measurement circuit includes a varactor diode, a standard capacitor, a sampling resistor, and an AC drive module. Due to the capacitance measurement of the varactor diode;

[0072] (5) Standard capacitors are used to construct capacitance measurement loops and to increase circuit input capacitance and reduce induced voltage values;

[0073] (6) The AC drive module provides a sinusoidal AC voltage drive signal with constant amplitude and frequency to the capacitance measurement circuit;

[0074] (7) Under the excitation of the constant voltage signal of the AC drive module, the current generated by the capacitance measurement circuit will change when the capacitance of the varactor diode changes, and the sampling resistor is used to convert the current signal in the circuit into a voltage signal;

[0075] (8) The voltage measurement module is used to measure the voltage across the sampling resistor;

[0076] (9) Calibrate the sensor: Calibrate the sensor in a known standard electrostatic field, measure the change in the output voltage of the sensor voltage measurement module under different field strengths, and obtain a curve or fitting equation for the relationship between the field strength and the output voltage change;

[0077] (10) Measuring the electrostatic field strength: Based on the relationship curve obtained from the calibration experiment, the voltage change value measured by the sensor is used to convert the current electrostatic field strength to achieve electrostatic field measurement.

[0078] The electrostatic field measurement system needs to be calibrated before use to determine the corresponding relationship between the measured electric field and the output voltage value. The measurement system can be calibrated by curve fitting or polynomial fitting to obtain U = f (E 外 ), in actual measurement, the corresponding electric field size to be measured can be measured by combining the measured voltage value U with the above fitting function relationship.

[0079] The calibration experiment process is as follows: the electrostatic field sensor of the electrostatic field measurement system 1 is placed in a standard electrostatic field source, electric fields of different field strengths are applied to the electric field sensor, and then the output voltage values ​​corresponding to the different field strengths are measured to obtain a one-to-one correspondence between the output voltage and the standard field strength. The measured data are subjected to curve fitting to obtain U=f(E 外 ) is a functional relationship.

[0080] The corresponding relationship can not only be described by a curve, but also recorded in a diagram.

[0081] The voltage-electric field correspondence obtained from the calibration experiment, whether in the form of a function expression, a data table or a curve diagram, can be stored in a storage unit of a processor, and the conversion from voltage to electric field value is performed in the microprocessor, and the result is output through an output communication interface.

[0082] In some embodiments, the system may be connected to an external display unit for displaying the results.

[0083] In some embodiments, the system can transmit the measurement results to other systems, such as a host computer, through an output communication interface.

[0084] The electrostatic field measurement method using the above system includes the following steps:

[0085] (1) Construct an electrostatic field sensor based on a varactor diode, the structure of which is as follows: Figure 2 As shown, the first sensing plate 101 is connected to the cathode of the varactor diode 201 through a wire, and the second sensing plate 102 is connected to the anode of the varactor diode 201 through a wire. The two sensing plates are of equal facing area and placed in parallel, and an insulating medium is used to fill the internal space of the two plates.

[0086] (2) Place the induction probe consisting of two electrodes and an insulating medium in the electrostatic field to be measured, with the normal direction of the electrodes parallel to the direction of the field strength.

[0087] (3) When the varactor diode and the capacitance measurement circuit are not connected, the induced voltage between the two plates can be calculated by the following steps:

[0088] When the induction plate is in the electrostatic field E 外When the external electric field is in the state of being, it will generate induced charge Q on two parallel conductor plates (induction plates).

[0089] The induced charge Q can be calculated by formula (1):

[0090] Q=ε0ε r1 AE 外 (1)

[0091] ε0 is the dielectric constant of vacuum, which is about 8.854×10-12F / m;

[0092] ε r1 is the relative dielectric constant of the insulating medium in the presence of an external electric field distribution;

[0093] A is the area of ​​the induction plate;

[0094] E 外 is the field strength of the external electrostatic field to be measured.

[0095] Because the measured electric field is a spatial electric field, the electric field is distributed in the air and the insulating medium is air, ε r1 The value is 1, so the induced charge Q = ε0AE 外 .

[0096] The structure of the induction plate is similar to that of a parallel plate capacitor. The capacitance C of the induction plate A It can be calculated by formula (2):

[0097]

[0098] ε0 is the dielectric constant of vacuum, which is about 8.854×10-12F / m

[0099] ε r2 is the relative dielectric constant of the medium between the plates;

[0100] A is the area of ​​the induction plate;

[0101] d is the distance between the two plates;

[0102] When the insulating medium between the sensing plates is air, ε r2 The value is 1.

[0103] At this time, the induced voltage U between the two plates can be calculated by formula (3):

[0104]

[0105] Substituting equation (1) and equation (2) into equation (3), we get:

[0106]

[0107] After simplification, the voltage between the induction levels is:

[0108]

[0109] The external electric field E in the space to be measured 外 Distributed in the air, the relative dielectric constant of air is ε r1 The value is 1,

[0110]

[0111] When the medium between the plates is air, the relative dielectric constant ε r2 When the value is 1, the induced voltage U between the two plates Air for:

[0112] U Air =E 外 d (7)

[0113] U Air The induced voltage of the plates in the external electric field when the medium between the induction plates is air;

[0114] (4) When the sensing probe is connected to the varactor diode through a wire, the induced voltage acts as a reverse bias voltage on both ends of the varactor diode, causing the capacitance of the varactor diode to change. The corresponding relationship between the reverse bias voltage of the varactor diode and the junction capacitance of the diode can be expressed as:

[0115]

[0116] c j represents the diode junction capacitance;

[0117] V R represents the applied bias voltage;

[0118] c j0 represents the zero bias junction capacitance, i.e. V R = Junction capacitance when 0;

[0119] V j Represents the threshold voltage of the PN junction;

[0120] M Indicates the capacitance variation coefficient of the diode;

[0121] c j0 、V j , M The characteristic parameters of the varactor diode are related to the varactor diode model. When the diode model is determined and the parameters are determined, a curve graph can be drawn to represent the relationship between junction capacitance and reverse bias voltage.

[0122] (5) In one embodiment, the varactor diode used is 1SV149, and its capacitance-voltage relationship is represented by a curve diagram as follows: Figure 3 From the figure, it can be seen that the capacitance value of the varactor diode gradually decreases with the increase of the reverse bias voltage, and when the voltage increases to a certain level, the change speed gradually slows down and finally basically stops changing.

[0123] The varactor diode works under reverse bias, but the varactor diode has a maximum reverse voltage, which is usually between 5V and 30V. When the reverse bias voltage exceeds the maximum reverse voltage, the diode will be broken down and damaged, which will greatly limit the measurement range of the measurement system.

[0124] (6) The capacitance value of the varactor diode 201 is measured by the capacitance measurement circuit 200 , wherein the capacitance measurement circuit 200 is composed of the varactor diode 201 , the standard capacitor 202 , the sampling resistor 203 , and the AC drive module 204 .

[0125] (7) The AC drive module 204 is an AC power source that provides a drive signal for the entire circuit. The power source is usually a sine wave and can provide a stable voltage excitation signal for measurement.

[0126] In an implementation such as Figure 4 In the embodiment, the AC drive module 204 is connected to the capacitance measurement circuit 200 through a transformer. Figure 4 In the illustrated embodiment, the AC driving module 204 provides a sinusoidal AC voltage excitation signal with an amplitude of 200 mV and a frequency of 1 MHz to the capacitance measurement circuit 200 through an isolation transformer.

[0127] Under the action of the excitation signal output by the AC drive module 204, a loop current is generated in the capacitance measurement loop 200. When the external electric field remains unchanged, the induced voltage is a certain value, the capacitance of the varactor is also a certain value, and a current of corresponding magnitude will be generated in the capacitance measurement loop 200.

[0128] When the external electric field changes, the induced voltage changes, the capacitance of the varactor changes, and the current in the capacitance measurement loop 200 changes.

[0129] (8) The sampling resistor 203 is used to convert the current signal in the capacitance measurement circuit 200 into a voltage signal for subsequent voltage measurement circuit measurement. The sampling resistor 203 is a resistor with a known resistance value, which is connected in series in the capacitance measurement circuit 200 and is used to measure the circuit current. By measuring the voltage drop across the sampling resistor 203, the electric field can be indirectly measured.

[0130] (9) The voltage measurement module 300 measures the voltage across the sampling resistor 203 .

[0131] The voltage measurement module 300 is composed of a follower circuit 301 , a signal amplifying circuit 302 , a filtering circuit 303 , a peak detection circuit 304 , a sampling and holding circuit 305 , a digital-to-analog conversion circuit 306 , a microprocessor 307 , and an output communication interface 308 .

[0132] The follower circuit is connected to the sampling resistor to provide high input impedance and low output impedance, so as to isolate the front and rear stage circuits to prevent the measurement module from generating a load effect on the signal source, thereby maintaining the accuracy of the measurement signal.

[0133] The signal amplification circuit amplifies the weak voltage signal across the sampling resistor for subsequent processing and measurement.

[0134] The filter circuit is used to suppress unnecessary frequency components in the measurement signal to ensure that the measurement signal is clean and stable.

[0135] The peak detection circuit is used to convert the AC signal into a DC signal, which is convenient for subsequent measurement and analysis.

[0136] The sample-and-hold circuit is used to sample a measurement signal at a specific time point and hold the voltage value for subsequent stable measurement.

[0137] The digital-to-analog conversion circuit converts the analog signal of the sampling and holding circuit into a digital signal so that the back-end microcontroller can perform digital processing.

[0138] The microprocessor is used to analyze and process the measured voltage, and convert the measured voltage into a corresponding field strength value through function calculation, table lookup, etc.

[0139] In a Figure 6 In an embodiment of the present invention, the microprocessor can be used to control the controllable switch to control the value of the standard capacitor connected to the capacitance measurement loop, thereby changing the input capacitance of the circuit to flexibly adjust the measurement range of the system.

[0140] The output communication interface is used for transmitting the processed data and communicating with the display device for displaying the results.

[0141] (10) For different electrostatic field strength inputs, the measurement system will collect and output different voltage values. The corresponding relationship between the field strength and the output voltage can be measured through experimental calibration. The value of the electric field to be measured can be obtained by measuring the output voltage of the measurement system and the corresponding relationship between the field strength and the output voltage measured through the calibration experiment.

[0142] In one embodiment, a schematic diagram of a calibration experiment is shown in FIG. Figure 4As shown in the figure, the key to calibrating an electric field sensor is to build a numerically controllable uniform electric field environment. According to theory, a uniform electric field can be formed between two infinitely large, parallel conductive metal plates at different potentials in free space. This principle can be used to construct a uniform electric field for calibration.

[0143] The calibration device 500 is composed of a high-voltage DC power supply 501, an upper metal plate 502, a lower metal plate 503, connecting wires and an insulating support frame. Both metal plates are square aluminum plates with a thickness of 2 mm and a side length of 1 meter.

[0144] The positive pole of the high voltage power supply 501 is connected to the upper metal plate 502 through a wire, and the negative pole of the high voltage power supply 501 is connected to the lower metal plate 503 and the ground through a wire. The insulating support frame keeps the two metal plates facing each other and parallel and placed 40 cm apart.

[0145] When performing a calibration experiment, the sensor Figure 4 As shown, it is placed in the middle of the two metal plates, and different high-voltage DC voltages are connected to the upper and lower metal plates respectively using a high-voltage DC source. By changing the value of the high-voltage source, the electric field generated between the metal plates can be calculated by the following formula:

[0146]

[0147] EUse the uniform electric field generated by the calibration device

[0148] U AB is the voltage value output by the high voltage DC source,

[0149] D is the distance between the two metal plates of the calibration device.

[0150] In a Figure 4 In the embodiment shown in FIG. AB The value is 0V to 2000V, the D value is 40cm, the varactor diode model is 1SV149, the standard capacitor value is 820pF, the sampling resistor value is 20 ohms, and the AC drive module provides a sinusoidal voltage excitation signal with a frequency of 1MHz and an amplitude of 200mv for the capacitance measurement circuit through an isolation transformer.

[0151] The corresponding relationship between the electric field strength generated by the device and the output voltage of the measurement system is shown in Table 1, and is represented by a curve graph as Figure 7 :

[0152] Table 1

[0153]

[0154]

[0155] (11) Whether it is static electricity in daily life, static electricity in industrial environments, or static electricity in high-voltage DC transmission lines, the field strength they generate can often reach several thousand volts per meter to tens of kilovolts per meter or even hundreds of kilovolts per meter. The induced voltage generated by the sensor's inductive probe in these electric fields has far exceeded the normal operating range of the varactor diode.

[0156] (12) Principle of the method to expand the measurement range by changing the capacitance of the standard capacitor connected to the circuit

[0157] In order to improve the measurement range of the system, this method mainly increases the input capacitance of the measurement system by incorporating a large-capacity standard capacitor to reduce the induced voltage, so that when the system is used to measure a strong electric field, the induced voltage will not exceed the normal working range of the varactor diode.

[0158] The induction probe is placed in the electric field to be measured. Without changing the probe structure, the capacitance of the parallel plate capacitor is C. A is a constant value, the electric field to be measured is an electrostatic field, and its field strength value E is constant. From formula (1), it can be known that the induced charge Q is also constant.

[0159] After connecting to the capacitance measurement circuit, the total capacitance C of the system total By C A , Cj, C B , C C The composition is expressed as:

[0160] C total =C A +Cj+C B +C C (10)

[0161] C A is the structural capacitance of the probe, Cj is the junction capacitance of the diode, C B is the capacitance value of the standard capacitor, C C is the stray capacitance value (mainly composed of wires, usually small and negligible);

[0162] When the electrostatic balance of the measuring system reaches a stable state in the electric field, no current flows in the DC path of the probe and the capacitance measurement loop, and the charge induced by the induction plate is stored in the capacitor C. A , Cj, C B , C C Upper, C A , Cj, C B , C C In parallel, such as Figure 8 shown.

[0163] When capacitors are connected in parallel, the voltage across all capacitors is equal, that is,

[0164]

[0165] This is the induced voltage on the probe, U Cj is the voltage on the varactor diode, is the voltage on the standard capacitor, is the voltage between the connecting wires, U total is the voltage of the equivalent capacitor.

[0166] According to the capacitance formula (12)

[0167]

[0168] The voltage depends on the charge Q and the total capacitance C total ,From formula (1), we can know that the induction plate will induce a certain amount of induced charge Q in a constant electrostatic field. When the electric field is constant, the induced charge is a certain value. At this time, U total By C total Decide.

[0169] Comparing equation (12) with equation (3), we find that the induced charge Q is the same in both equations, C total >C A , so U total <U,U total The contrast U is reduced. In this way, the induced voltage of the strong electric field can be reduced to the normal operating range of the varactor diode.

[0170] In C total In the structure, the capacitance of the parallel plate capacitor formed by the inductive probe is determined by its own structure to be a fixed value. The junction capacitance of the varactor diode capacitor can vary within a limited range, usually between a few picofarads and several hundred picofarads. The circuit stray capacitance C C Determined by the circuit structure, usually a few picofarads.

[0171] Standard capacitor C B You can make flexible choices based on measurement needs.

[0172] Standard capacitors can be connected in parallel via controllable switches, such as Figure 6 In the illustrated embodiment, capacitors CB1, CB2, and CB3 are connected in parallel to a capacitance measurement loop via controllable switches S1, S2, and S3, respectively. By connecting multiple standard capacitors to the circuit, the measurement range of the system can be flexibly adjusted.

Claims

1. An electrostatic field measurement system based on a varactor diode, characterized in that: It includes an electrostatic field sensor, a capacitance measurement circuit, an AC drive module, a voltage measurement module and a power supply module; The electrostatic field sensor is composed of a pair of metal conductor sensing plates, an insulating medium and a varactor diode, and the sensing plates are respectively connected to the cathode and anode of the varactor diode through wires to form an electrostatic field sensor port; The capacitance measurement circuit includes a varactor diode, a standard capacitor, a sampling resistor and an AC drive module; The standard capacitor is used to increase the input capacitance of the measurement system and reduce the induced voltage; The AC drive module is used to provide a voltage excitation signal with constant amplitude and frequency to the measurement circuit; The voltage measurement module obtains the capacitance change signal through the voltage drop on the sampling resistor, and amplifies, filters, detects, samples and holds the signal, and performs digital-to-analog conversion processing, and converts the measured capacitance change into the field strength value of the electrostatic field through the processor, and outputs the result through the communication interface; The power supply module is used to provide stable electric energy for the system to ensure the normal operation of each functional module.

2. A method for measuring electrostatic field based on a varactor diode, using the system described in claim 1, characterized in that After the following steps: The electric field to be measured is converted into the capacitance value of the varactor diode through the electrostatic field sensor, and then the capacitance of the varactor diode is measured through the capacitance measurement circuit. The current signal of the capacitance measurement circuit is converted into a voltage signal using a sampling resistor. The output voltage value of the circuit is measured by the voltage measurement module, and the corresponding relationship between the field strength and the output voltage is measured through experimental calibration. The corresponding relationship between the field strength and the output voltage is measured based on the output voltage of the measurement system and the calibration experiment, that is, the value of the electrostatic field is measured.

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