Fluxgate-based weak current signal detection system and method thereof

Abstract

The invention relates to a weak current signal detection system and method based on a fluxgate, and the system comprises an excitation module, a range selection module, a power amplification module, a fluxgate magnetic core coil, a sampling resistor, a differential amplification module and a data processing module which are connected in sequence, the magnetic core current reaches saturation current; the range selection module is used for adjusting the gain of the power amplification module; the power amplification module is used for amplifying the excitation signal; the fluxgate magnetic core coil is used for sensing current to be measured; the sampling resistor is used for sampling saturation current of a magnetic core coil of the fluxgate; the differential amplification module is used for amplifying saturation current of a magnetic core coil of the fluxgate; and the data processing module performs time difference calculation on the amplified saturation current through resampling, and outputs a weak current detection result. Compared with the prior art, the hardware cost can be reduced while the measurement precision is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of weak signal detection, and in particular to a weak current signal detection system and method based on a fluxgate. Background Art

[0002] The polarization / depolarization current (PDC) measurement method is based on the time domain dielectric response theory. It analyzes and evaluates the insulation status of the motor from the perspective of electrical characteristics. It is a non-destructive insulation aging assessment method and is therefore widely used in motor insulation testing.

[0003] The fluxgate sensor has the characteristics of strong anti-interference ability and high detection accuracy, and is often used in weak current detection. For the fluxgate sensor, the traditional second harmonic amplitude method technology is relatively mature, and further in-depth research is too costly and has little effect. The time difference method needs to achieve high-precision detection, and the hardware cost is too high.

[0004] The prior art mainly uses fluxgate sensors or spectrum methods to measure current for weak current signal detection. For fluxgate sensors, the second harmonic component is extracted, and the magnitude of the measured current is indirectly measured by measuring the amplitude of the second harmonic. For time-difference fluxgate sensors, the measured magnetic field is obtained by measuring the difference in the saturation current time of the core in the first half cycle and the second half cycle of the excitation signal. The spectrum method is to decompose the collected signal into multiple frequency components through Fourier transform. In the spectrum diagram, the magnitude of the measured current can be indirectly measured according to the amplitude of the second harmonic peak.

[0005] In practical applications, a dual-core structure design is usually used to improve the signal-to-noise ratio of the sensor. Ideally, only when the position, structural parameters, number of turns and density of the dual cores of the fluxgate are exactly the same, the odd harmonic noise generated by the transformer effect will cancel each other out. However, this ideal condition is difficult to achieve in practical applications. The detection of the second harmonic is relatively complex and cannot effectively avoid the probe symmetry error of the traditional even-harmonic fluxgate. The accuracy of the time-difference fluxgate in detecting the measured current depends on the accuracy of the time-difference detection. Higher-precision measurements will lead to excessively high hardware costs, while lower-precision measurements will lead to inaccurate measurements.

[0006] The spectrum value method has resolution limitations, that is, in some cases it cannot obtain high time and frequency resolution, and may also cause spectrum leakage. The Fourier transform and spectrum analysis are computationally intensive and require a lot of time.

[0007] In summary, the above methods have high hardware requirements or strict restrictions on core structure and materials, and the production design is relatively complex. In addition, the detection methods are mostly hardware-based and software-assisted, which cannot give full play to the characteristics of digital signal processing technology. Summary of the invention

[0008] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a weak current signal detection system and method based on fluxgate, which can improve the measurement accuracy and reduce the hardware cost.

[0009] The purpose of the present invention can be achieved by the following technical solutions: A weak current signal detection system based on fluxgate, comprising an excitation module, a range selection module, a power amplification module, a fluxgate core coil, a sampling resistor, a differential amplification module and a data processing module connected in sequence, wherein the excitation module is used to generate an excitation signal to the fluxgate core coil so that the core current reaches a saturation current;

[0010] The range selection module is used to adjust the gain of the power amplification module;

[0011] The power amplifier module is used to amplify the excitation signal;

[0012] The fluxgate core coil is used to sense the current to be measured;

[0013] The sampling resistor is used to sample the saturation current of the fluxgate core coil;

[0014] The differential amplifier module is used to amplify the saturation current of the fluxgate core coil;

[0015] The data processing module performs time difference calculation on the amplified saturation current through resampling, and outputs a weak current detection result.

[0016] Furthermore, the excitation signal is specifically a triangular wave signal.

[0017] Furthermore, the excitation module is specifically a triangle wave excitation circuit, including an integration unit, a hysteresis comparison unit and a positive feedback unit.

[0018] Furthermore, the range selection module is specifically an inverted T-type resistor network, which obtains voltage at different nodes of the inverted T-type resistor network to control the input voltage of the power amplifier to adjust the gain, while also ensuring automatic impedance matching between input and output.

[0019] Furthermore, the sampling resistor is connected in series to the fluxgate core coil, and the measurement of the core saturation current is achieved through the STC single chip microcomputer.

[0020] Furthermore, the ground terminal of the differential circuit in the differential amplifier module is connected to the ground.

[0021] Furthermore, the fluxgate core coil is wrapped with a shielding cover on the outside.

[0022] A method for detecting weak current signals based on fluxgate, comprising the following steps:

[0023] S1, the excitation module outputs a triangular wave excitation signal, the range selection module adjusts the gain of the power amplifier module, and the power amplifier module amplifies the triangular wave excitation signal;

[0024] S2. Under the excitation of the amplified triangle wave excitation signal, the fluxgate core coil senses the current signal to be measured, and the core current of the fluxgate core coil reaches saturation;

[0025] S3, measuring the core saturation current through a sampling resistor, and amplifying it through a differential amplifier module;

[0026] S4. Through the resampling technology, the data processing module processes the amplified core saturation current sampling signal, calculates the time difference, and outputs the weak signal detection result.

[0027] Furthermore, the step S4 specifically adopts the optimal resampling parameters to resample the amplified core saturation current sampling signal, fits the measured time difference with the measured magnetic field, obtains the functional relationship between the time difference and the measured magnetic field, and obtains the weak current detection result.

[0028] Furthermore, the optimal resampling parameter is a sampling rate of 2 Mbps.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] The present invention designs an excitation module, a range selection module, a power amplifier module, a fluxgate core coil, a sampling resistor, a differential amplifier module and a data processing module that are connected in sequence, and uses the excitation module to generate an excitation signal to the fluxgate core coil so that the core current reaches the saturation current, uses the range selection module to adjust the gain of the power amplifier module, uses the power amplifier module to amplify the excitation signal, uses the fluxgate core coil to sense the current to be measured, uses the sampling resistor to sample the saturation current of the fluxgate core coil, uses the differential amplifier module to amplify the saturation current of the fluxgate core coil, and uses the data processing module to calculate the time difference of the amplified saturation current through resampling, and outputs a weak current detection result. Thus, a time difference reading scheme based on resampling technology is realized, which can effectively avoid the probe symmetry error that cannot be avoided by the traditional even harmonic fluxgate, has the characteristics of simple structure, low power consumption, low hardware cost, etc., designs the hardware circuit to minimize the error caused by the hardware part, and uses the resampling technology to process the collected signal, which can effectively improve the detection accuracy.

[0031] The present invention designs a triangular wave generating circuit to generate a signal for exciting a fluxgate sensor, so that its core current quickly reaches saturation. After the differential amplifier circuit amplifies the core saturation current of the time difference type fluxgate sensor, it is collected and transmitted to the data processing module, and the time difference is calculated after processing by a resampling method. The effect of a high sampling rate is achieved through a low sampling rate, which effectively improves the accuracy of the collected data and reduces the cost of hardware. Among them, the selection of a triangular wave as an excitation signal can ensure the linearity of the obtained time difference; the use of an inverted T-type network and a power amplifier circuit can achieve the selection of different ranges; in addition, considering that resampling has low signal requirements, a low sampling circuit is designed, and resampling is selected in data processing, which can improve the accuracy of the measured time difference.

[0032] The present invention uses a shielding cover to wrap the time difference type fluxgate sensor to significantly improve the sensor's anti-interference ability and measurement accuracy; the ground terminal of the differential amplifier circuit is connected to the earth to greatly reduce the impact of external interference on the circuit. This can effectively isolate external noise interference and improve measurement accuracy.

[0033] The present invention samples the optimal resampling parameters for resampling processing, adopts a digital method in fluxgate detection technology, and combines it with the resampling technology. It can improve the accuracy of the time difference fluxgate sensor without high hardware cost, thereby better realizing the detection of weak currents, and effectively realizing the method of low-speed acquisition to achieve the accuracy requirements similar to high-speed acquisition. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the system structure of the present invention;

[0035] Figure 2 This is a schematic diagram of a triangle wave excitation circuit in the present invention;

[0036] Figure 3 It is a schematic diagram of a power amplifier circuit in the present invention;

[0037] Figure 4 It is a schematic diagram of an inverted T-type resistor network in the present invention;

[0038] Figure 5 Schematic diagram of the differential amplifier circuit in the present invention;

[0039] Figure 6 It is a schematic diagram of the method flow of the present invention;

[0040] Figure 7 It is a schematic diagram of the numerical analysis calculation process in the present invention;

[0041] Explanation of the markings in the figure: 1. Excitation module, 2. Range selection module, 3. Power amplifier module, 4. Fluxgate core coil, 5. Sampling resistor, 6. Differential amplifier module, 7. Data processing module. DETAILED DESCRIPTION

[0042] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] Example

[0044] like Figure 1 As shown, a weak current signal detection system based on fluxgate includes an excitation module 1, a range selection module 2, a power amplification module 3, a fluxgate core coil 4, a sampling resistor 5, a differential amplification module 6 and a data processing module 7 connected in sequence, wherein the excitation module 1 is used to generate an excitation signal to the fluxgate core coil 4 so that the core current reaches a saturation current;

[0045] The range selection module 3 is used to adjust the gain of the power amplifier module 3;

[0046] The power amplifier module 3 is used to amplify the excitation signal;

[0047] The fluxgate core coil 4 is used to sense the current to be measured;

[0048] The sampling resistor 5 is used to sample the saturation current of the fluxgate core coil 4;

[0049] The differential amplifier module 6 is used to amplify the saturation current of the fluxgate core coil 4;

[0050] The data processing module 7 performs time difference calculation on the amplified saturation current through resampling, and outputs a weak current detection result.

[0051] In order to ensure the linearity of the obtained time difference, this scheme selects a triangular wave as an excitation signal, and uses an inverted T-type network and a power circuit to achieve the selection of different ranges. Since resampling has low signal requirements, a low sampling circuit is designed, and resampling is selected in data processing to improve the accuracy of the measured time difference. The signal generated by the triangular wave generating circuit of this embodiment is used to excite the fluxgate sensor through the driving circuit, so that its core current quickly reaches saturation. After the differential amplifier circuit amplifies the saturation current of the core of the time difference type fluxgate sensor, it is collected by an oscilloscope and transmitted to LabVIEW. The time difference is calculated after processing using the resampling method, and the effect of high sampling rate is achieved through low sampling rate, which effectively improves the accuracy of the collected data and reduces the cost of hardware.

[0052] Specifically include the following:

[0053] 1. Design of the excitation circuit. Since the rising and falling edges of the triangular wave are linear, the changes of the magnetic core during saturation and desaturation are more uniform. In addition, the time difference obtained by triangular wave excitation is fitted with the measured current curve, and its linearity is better than that under sine wave excitation. The rapid rise and fall characteristics of the triangular wave signal make the sensor more sensitive to changes in the magnetic field, thereby enhancing its adaptability to dynamically changing environments. The frequency component of the triangular wave signal is single and easy to generate and process. The triangular wave excitation circuit is as follows: Figure 2 As shown in the figure (R3 and C form an integration circuit, R1 and R4 form a hysteresis comparison circuit, and R2 forms a positive feedback), a periodic square wave signal is generated by a square wave generator, and then converted into a triangle wave signal by an integration circuit. The output U0 is not only used to generate a triangle wave, but also serves as the input of the in-phase input hysteresis comparator in the rectangular wave generator, limiting U0 within the threshold range of the hysteresis comparator. This design effectively avoids the output saturation problem caused by poor quality of the square wave signal, thereby improving the stability and reliability of the signal.

[0054] In this embodiment, the design index of the triangle wave generating circuit is:

[0055] Voltage output type: triangle wave signal;

[0056] Rated output voltage: 5V;

[0057] Rated output current: 1mA;

[0058] Frequency: 40hz;

[0059] Rated output power: 5W.

[0060] Second, a power amplifier circuit with adjustable gain is used. In order to drive the load more effectively, a power amplifier circuit is designed, such as Figure 3As shown, the purpose is to amplify the power of the triangular wave signal to a sufficiently high level while ensuring the quality of the triangular wave signal, so that the time difference fluxgate core can quickly reach saturation. In addition, by obtaining voltages at different nodes of the inverted T-type resistor network, the input voltage of the power amplifier is controlled to adjust the gain, while also ensuring that the input and output impedances are automatically matched. The inverted T-type resistor network is as shown in FIG. Figure 4 shown.

[0061] 3. Use differential circuit to design the circuit, such as Figure 5 As shown in the figure, the sampling process uses differential signals throughout, and the ground in the differential circuit is connected to the earth. The differential signal uses a numerical value to represent the difference between two physical quantities, which is the voltage difference between two points in the circuit. The circuit uses differential signals for the following two advantages:

[0062] 1) Differential signals can be used to identify small signals. In single-ended signal measurement circuits, the system usually uses "ground" as the reference voltage, and the measurement accuracy depends on the consistency of the "ground" in the system. In the weak current and voltage test, the difference in the "ground" at each point is greater than the weak current being measured, which will greatly interfere with the measurement circuit. The differential source used in this weak current measurement circuit is the voltage difference across the four-pin sampling resistor. In the differential circuit, the "reference" voltage is controlled to avoid interference caused by inconsistent "ground".

[0063] 2) Use differential signals to minimize EMI. Since the collected signal value is the voltage difference between the two ends, the same interference has almost the same impact on the two ports of the differential signal, so the use of differential signals can ignore the same interference signals on the two ports and effectively shield electromagnetic interference.

[0064] 4. Sampling circuit, connect a resistor in series with the fluxgate core coil, and measure the core saturation current through the STC microcontroller.

[0065] 5. Anti-interference processing: For external noise interference, the main isolation method is adopted, and two solutions are proposed:

[0066] 1) Using a shielding cover to wrap the time difference type fluxgate sensor can significantly improve the sensor's anti-interference ability and measurement accuracy.

[0067] 2) The "ground" of the test circuit board is connected to the earth, which can greatly reduce the impact of external interference on the circuit.

[0068] 6. Data processing, combined with digital signal processing technology, processes the signals collected by the microcontroller through resampling, improves the time resolution, and calculates the time difference.

[0069] In this embodiment, the design index of the low sampling rate sampling circuit (same as NI-USB6001) is:

[0070] Sampling frequency: 20k;

[0071] Input impedance: 1MΩ;

[0072] Data depth: 4kByte

[0073] Resolution: 14 bits;

[0074] During the digital processing, the collected signal is resampled so that the resampling effect under the sampling rate of 10k is the same as that under the sampling rate of 500k; the measured time difference is fitted with the measured magnetic field to obtain the functional relationship between the time difference and the measured magnetic field.

[0075] Based on the above hardware system, a weak current signal detection method based on fluxgate is implemented, such as Figure 6 As shown, the following steps are included:

[0076] S1, the excitation module outputs a triangular wave excitation signal, the range selection module adjusts the gain of the power amplifier module, and the power amplifier module amplifies the triangular wave excitation signal;

[0077] S2. Under the excitation of the amplified triangle wave excitation signal, the fluxgate core coil senses the current signal to be measured, and the core current of the fluxgate core coil reaches saturation;

[0078] S3, measuring the core saturation current through a sampling resistor, and amplifying it through a differential amplifier module;

[0079] S4. Through the resampling technology, the data processing module processes the amplified core saturation current sampling signal, calculates the time difference, and outputs the weak signal detection result.

[0080] For the measurement of weak current of time-difference fluxgate sensor, high-precision detection is required, but the hardware cost is too high and it is not easy to expand. Therefore, this solution adopts a digital method in fluxgate detection technology and combines it with resampling technology. It can improve the accuracy of time-difference fluxgate sensor without high hardware cost, thereby better realizing the detection of weak current, and can effectively realize the method of low-speed acquisition to achieve the accuracy requirements similar to high-speed acquisition.

[0081] This embodiment optimizes the model and parameters by numerical values ​​based on the model. In order to ensure that the algorithm can perform well in practical applications and achieve results comparable to those of high-speed acquisition systems, numerical analysis and calculations are performed to find the optimal resampling parameters, fitting parameters, and resampling methods. The specific process is as follows: Figure 7As shown in the figure, the computational analysis shows that different parameters have a significant impact on the results of the resampling algorithm, and choosing appropriate parameters can ensure sufficient accuracy.

[0082] Secondly, the oscilloscope was used to measure and record the time accuracy under the conditions of sampling rates of 200kps, 400kps, 800kps, 1Mbps, and 2Mbps. When the sampling rate is above 2Mbps, the error between the measured result and the actual result is the smallest.

[0083] Finally, the parameters obtained by calculation optimization were actually tested using a USB-6001 data acquisition card. After resampling the time measured by the data acquisition card, the time accuracy obtained was the smallest error compared to the time value obtained by the oscilloscope at a sampling rate of 2Mbps.

[0084] In summary, the fluxgate coil in this solution combines the advantages of the magnetic amplifier, can realize accurate magnetic field induction and signal amplification in the circuit, has high gain and strong anti-interference ability, and in data processing, combines digital processing technology to convert analog signals into digital signals, reducing hardware costs. Applying this solution in practice can effectively avoid the probe symmetry error that cannot be avoided by traditional even-order harmonic fluxgates. It has the characteristics of simple structure, low power consumption, low hardware cost, etc., which is convenient for on-site testing and is an ideal choice for on-site testing of motor intelligent operation and maintenance.

Claims

1. A weak current signal detection system based on fluxgate, characterized in that: The invention comprises an excitation module (1), a range selection module (2), a power amplification module (3), a fluxgate core coil (4), a sampling resistor (5), a differential amplification module (6) and a data processing module (7) which are connected in sequence, wherein the excitation module (1) is used to generate an excitation signal to the fluxgate core coil (4) so ​​that the core current reaches a saturation current; The range selection module (2) is used to adjust the gain of the power amplification module (3); The power amplification module (3) is used to amplify the excitation signal; The fluxgate core coil (4) is used to induce a current to be measured; The sampling resistor (5) is used to sample the saturation current of the fluxgate core coil (4); The differential amplification module (6) is used to amplify the saturation current of the fluxgate core coil (4); The data processing module (7) performs time difference calculation on the amplified saturation current through resampling, and outputs a weak current detection result.

2. A weak current signal detection system based on fluxgate according to claim 1, characterized in that: The excitation signal is specifically a triangular wave signal.

3. A weak current signal detection system based on fluxgate according to claim 2, characterized in that: The excitation module (1) is specifically a triangular wave excitation circuit, comprising an integration unit, a hysteresis comparison unit and a positive feedback unit.

4. A weak current signal detection system based on fluxgate according to claim 1, characterized in that: The range selection module (2) is specifically an inverted T-type resistor network, which obtains voltages at different nodes of the inverted T-type resistor network, thereby controlling the input voltage of the power amplifier to adjust the gain, while also ensuring automatic impedance matching between input and output.

5. The weak current signal detection system based on fluxgate according to claim 1, characterized in that: The sampling resistor (5) is connected in series to the fluxgate core coil (4), and the measurement of the core saturation current is achieved through the STC single chip microcomputer.

6. A weak current signal detection system based on fluxgate according to claim 1, characterized in that: The grounding terminal of the differential circuit in the differential amplification module (6) is connected to the ground.

7. The weak current signal detection system based on fluxgate according to claim 1, characterized in that: The fluxgate core coil (4) is externally wrapped with a shielding cover.

8. A method for detecting weak current signals based on fluxgate, applied to a weak current signal detection system based on fluxgate as claimed in claim 1, characterized in that: The following steps are involved: S1, the excitation module (1) outputs a triangular wave excitation signal, the range selection module (2) adjusts the gain of the power amplifier module (3), and the power amplifier module (3) amplifies the triangular wave excitation signal; S2. Under the excitation of the amplified triangular wave excitation signal, the fluxgate core coil (4) induces the current signal to be measured, and the core current of the fluxgate core coil (4) reaches saturation; S3, measuring the core saturation current through a sampling resistor (5), and amplifying it through a differential amplifier module (6); S4. The data processing module (7) processes the amplified magnetic core saturation current sampling signal through a resampling technique, calculates the time difference, and outputs a weak signal detection result.

9. The method for detecting weak current signals based on fluxgate according to claim 8, characterized in that: The step S4 specifically adopts the optimal resampling parameter to resample the amplified core saturation current sampling signal, fits the measured time difference with the measured magnetic field, obtains the functional relationship between the time difference and the measured magnetic field, and obtains the weak current detection result.

10. A method for detecting weak current signals based on fluxgate according to claim 9, characterized in that: The optimal resampling parameter is a sampling rate of 2 Mbps.

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