Current sensor and preparation method thereof, and current acquisition circuit and device

Abstract

The invention discloses a current sensor and a preparation method thereof, and a current acquisition circuit and equipment. The current sensor comprises an inductor and a TMR sensor which are connected in parallel; and controlling the optimal working frequency of the TMR sensor to be at the preset resonant frequency through the inductance value of the inductor. The inductor and the TMR sensor which are connected in parallel are adopted to construct the current sensor, and the optimal working frequency of the TMR sensor is controlled to be located at the preset resonant frequency by controlling the inductance value of the inductor, so that the sensitivity is improved, the signal-to-noise ratio is higher, the minimum current resolution is better, and the current sensor is more adaptive to weak partial discharge signals.

Description

Technical Field

[0001] The present invention relates to a current sensor and a preparation method thereof, a current acquisition circuit and equipment, and belongs to the technical field of current measurement. Background Art

[0002] The perception layer is the lowest level of the IoT system, primarily responsible for information collection and signal processing. Current sensors can transform measured current information into electrical signals or other required information outputs that meet certain standards. They are detection devices that can meet the requirements of information transmission, processing, storage, display, recording, and control, and serve as the device terminal in the perception layer.

[0003] High-frequency partial discharge current sensors are now widely recognized and adopted internationally as a diagnostic technology for equipment insulation conditions. They are primarily used for routine inspections or on-site testing of high-voltage equipment in substations. They monitor and analyze partial discharge signals within gas-insulated switchgear (GIS) equipment. Data analysis systems centrally analyze, display, and issue alarms, thereby monitoring and evaluating the operating status of GIS equipment and effectively preventing unexpected accidents involving GIS high-voltage equipment. However, existing partial discharge current sensors suffer from insufficient sensitivity, making them difficult to detect weak partial discharge signals. Summary of the Invention

[0004] The present invention provides a current sensor and a preparation method thereof, a current acquisition circuit and a device, which solve the problems disclosed in the background technology.

[0005] According to one aspect of the present disclosure, a current sensor is provided, comprising an inductor and a TMR sensor connected in parallel; the optimal operating frequency of the TMR sensor is controlled to be at a preset resonant frequency by the inductance value of the inductor.

[0006] Furthermore, the inductor is a variable inductor, and the optimal operating frequency of the TMR sensor is controlled to be located at different preset resonant frequencies by adjusting the inductance value of the inductor.

[0007] Furthermore, it also includes a transmission line, the connection between the inductor and the TMR sensor is connected to the transmission line, the transmission line includes a metal sleeve and a shielding wire passing through the metal sleeve, and a gap is left between the inner wall of the metal sleeve and the outer wall of the shielding wire.

[0008] Furthermore, an end of the metal sleeve is grounded, and one end of the shielding layer of the shielding wire is grounded.

[0009] According to another aspect of the present disclosure, a method for preparing a current sensor is provided, wherein the current sensor is the above-mentioned current sensor; The method comprises: Measuring the capacitance value of the TMR sensor when it operates at a preset resonant frequency; wherein the capacitance value is the capacitance value of the capacitor in the equivalent structure of the TMR sensor; Calculate the inductance value that controls the optimal operating frequency of the TMR sensor based on the capacitance value and the preset resonant frequency; Connect an inductor that matches the inductance value in parallel with the TMR sensor.

[0010] Furthermore, the inductance value that controls the optimal operating frequency of the TMR sensor is calculated using the following formula: L=1 / (ω 2 *C); Where ω is the resonant frequency, L is the inductance of the inductor, and C is the capacitance of the capacitor in the equivalent structure of the TMR sensor.

[0011] According to another aspect of the present disclosure, a current acquisition circuit is provided, comprising an impedance network and the above-mentioned current sensor, wherein the output end of the current sensor is connected to the input end of the impedance network; wherein the impedance network is used to correct the non-flat amplitude-frequency curve output by the current sensor into a flat amplitude-frequency curve.

[0012] Furthermore, it also includes an operational amplifier circuit, wherein the input end of the operational amplifier circuit is connected to the output end of the impedance network.

[0013] Furthermore, the impedance network is an RLC network.

[0014] According to another aspect of the present disclosure, a current acquisition device is provided, characterized in that it includes the above-mentioned current acquisition circuit.

[0015] The beneficial effects achieved by the present invention are as follows: 1. The present invention uses a parallel inductor and a TMR sensor to construct a current sensor. By controlling the inductance value of the inductor, the optimal operating frequency of the TMR sensor is controlled to be located at a preset resonant frequency, thereby improving sensitivity, enhancing the signal-to-noise ratio, and improving the minimum current resolution, and being more adaptable to weak partial discharge signals; 2. The present invention connects an impedance network to the output end of the current sensor, thereby improving the consistency of the sensor output through the impedance network. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the equivalent structure of the current sensor; Figure 2 The voltage of the TMR sensor changes with the magnetic field strength at different operating frequencies; Figure 3 is a cross-sectional view of the transmission line; Figure 4 is a flow chart of a method for preparing a current sensor; Figure 5 is the relationship between the impedance of the current sensor and the frequency; Figure 6 A comparison chart of the sensitivity of the current sensor and the single TMR structure; Figure 7 This is the block diagram of the current acquisition circuit; Figure 8 This is the actual spectrum response effect of the impedance matching network. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present disclosure to clearly and completely describe the technical solutions in the embodiments of the present disclosure. It is obvious that the embodiments described are only part of the embodiments of the present disclosure, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present disclosure and its application or use. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present disclosure.

[0018] Unless specifically stated otherwise, the relative arrangement of components and steps, the numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present disclosure.

[0019] At the same time, it should be understood that for the convenience of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship.

[0020] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0021] In all examples shown and discussed herein, any specific values should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0022] It should be noted that like symbols and letters refer to like items in the following figures, so once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0023] See also Figure 1 , Figure 1 This is a schematic diagram of the equivalent structure of a current sensor provided in an embodiment of the present application. The current sensor may include at least an inductor and a TMR sensor. The inductor and the TMR sensor are connected in parallel, and the optimal operating frequency of the TMR sensor is controlled to be at a preset resonant frequency by adjusting the inductance value of the inductor. In this way, by adjusting the operating frequency of the TMR sensor, the sensitivity of the current sensor in the frequency band corresponding to the preset resonant frequency is improved.

[0024] It should be noted that in Figure 1In the current sensor, the inductance value of the inductor corresponds to the preset resonant frequency. To determine this relationship, a low-frequency TMR sensor with an operating bandwidth of DC-30kHz can be selected as the analysis object. The specific analysis can be as follows: We can first study the relationship between the magnetic field strength and the output signal amplitude (i.e. voltage) of the TMR sensor. Through experimental testing, we can get the output of the TMR sensor at different frequencies. Figure 2 As can be seen from the figure, the TMR sensor has the maximum response characteristic at 2 kHz.

[0025] Usually, the magnetic field to be measured is below the uT level. In high-frequency partial discharge sensors, even nT-level magnetic field measurement accuracy is required. Therefore, the sensitivity of the sensor should be defined as the maximum value of the sensor response within the small magnetic field amplitude fluctuation range. The formula is as follows: ζ = ΔV / ΔB; Where ζ is the sensitivity, ΔB is the change in magnetic field, and ΔV is the change in voltage. The formula describes that at a specific frequency, when the magnetic field changes by ΔB, the output voltage change of the TMR sensor is ΔV. At this time, the sensitivity of the TMR sensor should be ζ.

[0026] If we assume that the TMR sensor needs to operate at 5 kHz, then Figure 2 From the sensitivity formula, we can see that its sensitivity will inevitably decrease. This is because the TMR sensor is equivalent to a capacitor and resistor in parallel. As the frequency increases, the addition of the capacitor causes the TMR sensor to deviate from its optimal operating point (i.e., optimal operating frequency). To reduce the impact of the capacitor, a parallel inductor can be used to shift the sensor's resonance point, bringing the optimal operating frequency to 5 kHz.

[0027] The impedance model of the parallel inductor of the TMR sensor can be expressed as: Z=(1 / jωL+1 / R+jwC)-1; Where Z is the impedance of the TMR sensor's parallel inductor, ω is the resonant frequency, L is the inductance of the inductor, and C is the capacitance of the capacitor in the TMR sensor's equivalent structure.

[0028] Then the resonant frequency can be expressed as: ω=1 / sqrt(L*C); Here, sqrt is the square root function. This formula shows the relationship between inductance and resonant frequency. Since C is measurable, the inductance value of the inductor can be obtained after determining the resonant frequency.

[0029] It should be noted that the inductor can be a common wire-wound inductor, a multilayer chip inductor, a thin film inductor, or the like. For example, if a coil inductor is used, the inductor type is not particularly important, as the inductor's value is the only concern here. Of course, in some embodiments, a variable inductor may be used to adapt the current sensor to different resonant frequencies. By adjusting the inductor's value, the optimal operating frequency of the TMR sensor can be controlled to lie at different preset resonant frequencies.

[0030] To prevent the influence of external magnetic fields, in some embodiments, the parallel structure of the inductor and the TMR sensor can be installed in a metal housing and configured with a transmission line with shielding capability, which is mainly connected to the connection between the inductor and the TMR sensor.

[0031] See also Figure 3 The transmission line at least includes a metal casing and a shielded wire passed through the metal casing; the metal casing can be a metal corrugated tube as shown in the figure, and the shielded wire is wrapped with a signal wire, a plastic filling layer and a shielding layer from the inside to the outside. There is a gap between the inner wall of the metal casing and the outer wall of the shielded wire (i.e., the shielding layer). There is no strict requirement for the gap, as long as the diameter of the metal casing is larger than the shielded wire, preferably more than 3 times. This double-layer shielding reduces external magnetic and electric field interference.

[0032] In some embodiments, the ends of the metal sleeve are also grounded, specifically, both ends are grounded, and one end of the shielding layer of the shielding wire is grounded. This design is beneficial to improving the shielding ability of the sensor transmission line against the external magnetic field, and the effect is far better than the ordinary double-layer shielding effect.

[0033] This application uses a parallel inductor and TMR sensor to construct a current sensor, that is, combining two magnetic sensitive elements. By controlling the inductance value of the inductor, the optimal operating frequency of the TMR sensor can be controlled to be at a preset resonant frequency, thereby improving sensitivity, enhancing the signal-to-noise ratio, and improving the minimum current resolution, making it more adaptable to weak partial discharge signals.

[0034] See also Figure 4 , Figure 4 This is a flow chart of a method for preparing a current sensor provided in an embodiment of the present application. The current sensor is specifically the above-mentioned current sensor. The process of preparing the current sensor may at least include: Step 1: Measure the capacitance value of the TMR sensor when it operates at a preset resonant frequency; wherein the capacitance value is the capacitance value of the capacitor in the equivalent structure of the TMR sensor.

[0035] It should be noted that, taking 5 kHz as an example, when the TMR sensor operates at a frequency of 5 kHz, its impedance is measured using an LCR meter Keysight E4980A, see Figure 5,The resistance value of the TMR sensor is measured to be approximately 10.5 kΩ and the capacitance value is approximately 180 pF.

[0036] Step 2: Calculate the inductance value for controlling the optimal operating frequency of the TMR sensor based on the capacitance value and the preset resonant frequency.

[0037] It should be noted that the formula for calculating the inductance value that controls the optimal operating frequency of the TMR sensor is a variation of the above resonant frequency formula, as follows: L=1 / (ω 2 *C); Where ω is the resonant frequency, L is the inductance of the inductor, and C is the capacitance of the capacitor in the equivalent structure of the TMR sensor. Based on this formula, the required inductance can be calculated to be approximately 2.7 H.

[0038] Step 3: Connect an inductor that matches the inductance value in parallel with the TMR sensor.

[0039] It should be noted that, taking the coil inductance as an example, after determining the inductance value, the coil can be wound around the magnetic core to complete the inductor winding. This inductor can then be connected in parallel with the TMR sensor. Testing the resulting current sensor with an LCR meter reveals that the resonant frequency of the current sensor is approximately 5 kHz, shifting the optimal operating point to 5 kHz.

[0040] See also Figure 6 Further, according to the sensitivity formula, it can be calculated that the sensitivity of the current sensor formed in parallel is 165.2 mV / mT. The sensitivity before adjusting the resonant frequency (that is, without parallel inductance) is 136.8 mV / mT, which is an increase of about 21%. It can be seen that the sensitivity of the sensor at the resonance point has been significantly improved.

[0041] It should be noted that, based on the realization of the parallel structure, the parallel structure is encapsulated in a metal housing, and the output end of the parallel structure is extended through a transmission line. These processes are relatively conventional and will not be described in detail here.

[0042] The current sensor prepared by the above method can control the inductance value of the inductor to control the optimal operating frequency of the TMR sensor to be at a preset resonant frequency, thereby improving sensitivity, enhancing the signal-to-noise ratio, and improving the minimum current resolution, making it more adaptable to weak partial discharge signals.

[0043] Since the frequency response of the TMR sensor is non-uniform after matching with the inductor, the data output amplitude at different frequency points will be inconsistent during measurement, which leads to serious data errors. It is often necessary to perform a lot of spectrum response correction work on the digital end, which will sacrifice a lot of digital resources and increase the cost of digital circuits. Based on this, see Figure 7 , Figure 7 This is a block diagram of a current acquisition circuit provided in an embodiment of the present application, which includes at least an impedance network and the above-mentioned current sensor, wherein the output end of the current sensor is connected to the input end of the impedance network; wherein the impedance network is used to correct the non-flat amplitude-frequency curve output by the current sensor into a flat amplitude-frequency curve.

[0044] from Figure 7 It can be seen that the spectrum response of the sensor input is non-flat, and the spectrum characteristics of the impedance network are opposite to the trend of the sensor input curve, making the spectrum response curve of the sensor input multiplied by the impedance network approximately flat.

[0045] It should be noted that the current acquisition circuit also includes an operational amplifier circuit. Specifically, the input end of the operational amplifier circuit is connected to the output end of the impedance network. It mainly amplifies the output end of the impedance network and finally sends the data after operational amplifier to the digital end, such as a smart terminal.

[0046] The current acquisition circuit corrects the non-flat amplitude-frequency curve into a flat amplitude-frequency curve through an impedance network, without requiring a large amount of spectrum response correction work. It can be directly output at the digital end by averaging a small number of data points.

[0047] The present application also discloses a current acquisition device, which at least includes the above-mentioned current acquisition circuit, and the circuit can cooperate with a smart terminal, etc. to realize current acquisition.

[0048] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A current sensor, characterized in that: The invention comprises an inductor and a TMR sensor connected in parallel; and the optimal operating frequency of the TMR sensor is controlled to be located at a preset resonant frequency by adjusting the inductance value of the inductor.

2. The current sensor according to claim 1, wherein The inductor is a variable inductor. By adjusting the inductance value of the inductor, the optimal operating frequency of the TMR sensor is controlled to be located at different preset resonant frequencies.

3. The current sensor according to claim 1, wherein: It also includes a transmission line, a connection point between the inductor and the TMR sensor is connected to the transmission line, the transmission line includes a metal sleeve and a shielding wire passed through the metal sleeve, and a gap is left between the inner wall of the metal sleeve and the outer wall of the shielding wire.

4. The current sensor according to claim 3, characterized in that The end of the metal sleeve is grounded, and one end of the shielding layer of the shielded cable is grounded.

5. A method for preparing a current sensor, characterized in that: The current sensor is the current sensor according to any one of claims 1 to 4; The method comprises: Measuring the capacitance value of the TMR sensor when it operates at a preset resonant frequency; wherein the capacitance value is the capacitance value of the capacitor in the equivalent structure of the TMR sensor; Calculate the inductance value that controls the optimal operating frequency of the TMR sensor based on the capacitance value and the preset resonant frequency; Connect an inductor that matches the inductance value in parallel with the TMR sensor.

6. The method according to claim 5, characterized in that Calculate the inductance value that controls the optimal operating frequency of the TMR sensor. The formula is: L=1 / (ω 2 *C); Where ω is the resonant frequency, L is the inductance of the inductor, and C is the capacitance of the capacitor in the equivalent structure of the TMR sensor.

7. A current acquisition circuit, characterized in that: The invention comprises an impedance network and the current sensor according to any one of claims 1 to 4, wherein the output end of the current sensor is connected to the input end of the impedance network; wherein the impedance network is used to correct the non-flat amplitude-frequency curve output by the current sensor into a flat amplitude-frequency curve.

8. The circuit according to claim 7, characterized in that The utility model further includes an operational amplifier circuit, wherein the input end of the operational amplifier circuit is connected to the output end of the impedance network.

9. The circuit according to claim 7 or 8, characterized in that The impedance network is an RLC network.

10. A current acquisition device, characterized in that: The invention comprises the circuit according to any one of claims 7 to 9.

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