Method for measuring circumferential alternating current loop of magnetic microfilament based on LabVIEW

Abstract

The invention discloses a method for measuring a circumferential alternating current loop of a magnetic microwire based on LabVIEW. The method realizes loop measurement based on LabVIEW program control, and comprises the following steps of: connecting a magnetic microfilament and a resistor in series and then connecting the magnetic microfilament and the resistor into a signal generator, and simultaneously connecting another channel of the signal generator into an oscilloscope. The other two channels of the oscilloscope measure voltage signals at the two ends of the magnetic microfilament and the resistor at the same time and are connected to a computer to achieve control. The LabVIEW program reads a voltage signal measured by the oscilloscope, and carries out digital filtering processing, numerical integration processing, image display processing, and data recording and storage. Through the two steps, the circumferential alternating-current hysteresis loop of the magnetic microfilament can be measured. According to the method, the use of an induction coil is avoided, an indirect measurement method is obtained and demonstrated through physical derivation, the annular alternating-current hysteresis loop of the material is obtained, the measurement mode is simple enough, and only two common devices, namely a signal generator and an oscilloscope, are needed.

Description

Technical Field

[0001] The invention relates to the technical field of sensors, and in particular to a method for measuring a magnetic micro-wire toroidal AC loop based on LabVIEW. Background Art

[0002] Giant magneto-impedance effect (GMI) refers to the phenomenon that the impedance of soft magnetic materials changes greatly under the influence of external magnetic fields. Taking advantage of this characteristic, these materials have been widely used in the field of magnetic sensor technology. For example, fluxgate sensors, GMI sensors, etc. Taking the fundamental wave orthogonal fluxgate sensor as an example, its core structure includes a magnetic core and a pickup coil wrapped around the magnetic core, and the magnetic core is a magnetic micro-wire with a strong GMI effect. When the probe is excited by AC, the magnetic micro-wire will generate an alternating magnetic field in the annular direction, which will cause the magnetic core to be magnetized in the annular direction, which is the main reason for the sensor to generate magnetic noise. This is a dynamic magnetization process. Within a cycle of AC excitation, the projection of the magnetization intensity of the magnetic micro-wire in the annular direction has a periodic change, and the process will produce hysteresis, which will cause an energy loss, namely hysteresis loss, and AC excitation will also generate eddy current loss. The energy loss will be dissipated in the form of heat, which will produce a thermal disturbance to the magnetic moment, which will be reflected on the pickup coil and produce a large noise. The hysteresis loop measured by the dynamic excitation field is called the AC loop, which includes hysteresis loss and eddy current loss. Therefore, measuring the toroidal AC loop of the microfilamentary magnetic core is helpful for evaluating the performance of magnetic materials and sensors, and also for selecting related magnetic materials. Summary of the invention

[0003] The technical problem to be solved by the present invention is a method for measuring the toroidal AC loop of a magnetic microwire based on LabVIEW, which is invented for studying the source mechanism of sensor probe noise. The present invention can obtain the toroidal AC hysteresis loop of the magnetic microwire according to theory by only measuring the voltage at both ends of the magnetic microwire and the current in the loop.

[0004] In order to solve the technical problem of the present invention, the following technical solution is adopted: A method for measuring a magnetic microwire loop AC loop based on LabVIEW comprises: connecting the magnetic microwire and a resistor in series and then connecting them to the first channel of a signal generator, connecting the second channel of the signal generator to the channel I of an oscilloscope, the first channel and the second channel of the signal generator generating completely identical excitation signals, the oscilloscope collecting voltage signals, the channels II and III of the oscilloscope measuring the voltage signals at both ends of the magnetic microwire and the resistor at the same time, the three channels of the oscilloscope are respectively channel I receiving the excitation signal of the signal generator itself, channel II receiving the voltage signals at both ends of the magnetic microwire, and channel III receiving the voltage signals at both ends of the series resistor. Voltage signal, and then use LabVIEW program to control the oscilloscope and read and process the collected voltage signal, process the voltage signals of channel I and channel II to get the induced voltage, and integrate the induced voltage to get the waveform Φ(t) of the magnetic microwire's annular magnetic flux changing with time, and then divide the voltage signal of channel III by the resistance value of the series resistor to get the current waveform I(t) flowing through the magnetic microwire, and use the current waveform I(t) flowing through the magnetic microwire and the waveform Φ(t) of the magnetic microwire's annular magnetic flux changing with time as X and Y axes respectively to get the magnetic microwire annular AC loop.

[0005] In the LabVIEW program, the DC resistance value of the magnetic microwire is input in advance, and then the excitation signal read by the oscilloscope channel I is used to calculate the theoretical DC voltage division value of the magnetic microwire through the voltage division theory; then the data of channel II is subtracted from this DC voltage division to obtain the induced voltage data. The product of the current waveform I(t) flowing through the magnetic microwire and the waveform Φ(t) of the magnetic flux in the magnetic microwire changing with time is the energy dimension, which can be used to evaluate the energy loss of the magnetic microwire.

[0006] The excitation signal of the signal generator is a sine wave with a frequency of 10 kHz and an amplitude of 5V.

[0007] The resistance value of the resistor is 5 ohms. The function of the series resistor is to obtain the current size in the excitation circuit and convert the current signal into a voltage signal. In order not to reduce the current in the circuit, a small resistor is used as much as possible.

[0008] The changing magnetic field in the magnetic microfilament will induce a changing electric field, which will generate an induced voltage at both ends of the magnetic microfilament. V i , let the annular magnetic flux be Φ , then we can get the following approximate relationship: , t represents time, and this formula represents magnetic flux Φ The differential with respect to time t is approximately the induced voltage V i .

[0009] The signal generator has two channels, and the two channels are coupled together to make the frequency, amplitude and phase of the voltage signals in the channels consistent. The first channel is used for excitation, and the voltage signal of the second channel is passed to the oscilloscope to calculate the theoretical DC voltage division.

[0010] The LabVIEW program performs digital filtering on the data read from the oscilloscope and reads waveforms of multiple cycles.

[0011] The excitation signal of the signal generator can be adjusted into the form of AC plus DC bias, and is used to measure the magnetic micro-wire toroidal AC loop with DC bias.

[0012] The magnetic micro-wire is an amorphous wire or a composite wire and is used for the magnetic core of a fundamental wave orthogonal fluxgate sensor.

[0013] Principle of the present invention: Considering the columnar structure of magnetic microwires, a circular cross-section wire can be used as a model. When the wire is excited by a known sinusoidal current, at any given moment, the electric field on the surface of the wire is a certain value, that is, (1), where E represents the electric field strength, and const represents a constant, which is determined by the instantaneous current flowing through the wire.

[0014] Under quasi-static conditions, there is (2), in formula (2), represents the vector differential operator, the two formulas are the dot product and cross product of the vector respectively; There is (3), in formula (3) μ represents the magnetic permeability of the transmission medium, σ represents the conductivity of the transmission medium, c represents the speed of light, and t represents time; The cylindrical coordinates are established with the axial direction of the wire as the z direction. Then the electric field in the wire has only a z component and is related to the position in the radial direction r. Then, by introducing the time factor, the above formula can be written as: (4), in formula (4) r represents the radial position in cylindrical coordinates, k Defined as the propagation coefficient of electromagnetic waves in the medium, δ represents the skin depth, i represents an imaginary number; Expand the above formula and rewrite it as: (5); This formula satisfies the Bessel equation: (6), where x, y, and m represent the independent variables in the Bessel equation; Then the finite solution of the electric field at r=0 is: (7), where E z represents the electric field in the wire in the z direction, J 0 represents the zero-order Bessel function, i represents an imaginary number, ω represents the frequency of the sinusoidal current, t represents the time, e represents a natural constant; And by (8), where B represents the magnetic induction intensity, c represents the speed of light, and t represents time; Can get (9), in formula (9), A corner mark indicating the circumferential direction, Indicates the magnetic field strength in the circular direction of the conductor; Also because (10), where J 1 represents the first-order Bessel function, x represents the independent variable of the Bessel function; get (11), in formula (11), H Indicates the magnetic field strength within the conductor; Through the above deduction, the specific distribution of the electric field and magnetic field inside the magnetic microwire under the excitation state is determined, but in fact the properties of the magnetic material itself are ignored, and the entire derivation process is based on quasi-static conditions. Therefore, there is definitely a deviation between the final result and the actual result, but this approximate result will be reflected in the test principle of the loop.

[0015] as follows Figure 1 As shown, consider a cylindrical conductor with a radius of R and a length of L. When current passes through it, the magnetic flux inside it can be deduced from formula (11): (12), where Φ represents the annular magnetic flux inside the conductor, R represents the conductor radius, L Indicates the length of the conductor; The partial derivative of magnetic flux with respect to time is: (13); The voltage V across the conductor can be approximated by equation (7): (14); Under quasi-static conditions, considering only the DC resistance of the material, the voltage drop across it is: (15), where R i It represents the voltage drop across the conductor under quasi-static conditions; Then, the following approximate relationship can be obtained from equations (13), (14), and (15): (16).

[0016] The above derivation proves the feasibility of the measurement method. The physical mechanism behind it is correct. The magnetic flux obtained by integrating the induced voltage differs from the actual magnetic flux by a coefficient. By omitting the coefficient, equation (16) can be obtained.

[0017] The above is the theoretical basis for measuring the toroidal AC loop of the magnetic microwire. The toroidal AC hysteresis loop of the magnetic microwire can be obtained according to the theory by only measuring the voltage at both ends of the magnetic microwire and the current in the loop.

[0018] Therefore, as long as the voltage across the amorphous wire in the loop is measured and the theoretical DC voltage divider is subtracted, the induced voltage can be obtained, and the magnetic flux can be obtained by integrating the induced voltage over time. Since the voltage signal collected by the oscilloscope is discrete, integration is actually an accumulation process. The magnetic flux obtained by integration is an array that changes with time and is used as the vertical coordinate. Regarding the horizontal coordinate, according to Ampere's loop theorem, the toroidal excitation field is proportional to the instantaneous value of the current flowing through the amorphous wire. Therefore, it is only necessary to simultaneously obtain the waveform of the current changing with time, and the two are plotted as Lissajous figures to obtain the final toroidal AC hysteresis loop. Figure 2 In the circuit, the function of resistor R is to convert the current signal into a voltage signal, which is then collected and read by the oscilloscope.

[0019] The testing method of the toroidal AC hysteresis loop of the present invention is to serve the research on the performance of the probe material of the orthogonal fluxgate sensor. At present, composite wire and amorphous wire are both materials used as the magnetic core of the sensor probe. When the sensor is working, the alternating current passing through the magnetic core will magnetize the magnetic core in the toroidal direction. Corresponding energy loss will be generated during the magnetization process, and this energy loss will affect the noise of the sensor. Therefore, in the process of studying the sensor probe material, we found that the toroidal AC hysteresis loop is more important. However, the existing equipment for measuring hysteresis loops, such as VSM and BH-loop, cannot meet the demand, because the magnetic lines of force are closed in the material, and the induction coil cannot be used to directly detect the magnetic signal. The advantage of the present invention is that it avoids the use of induction coils, and an indirect measurement method is obtained and demonstrated through physical deduction, so as to obtain the toroidal AC hysteresis loop of the material, and the measurement method is simple enough, and only two common devices, a signal generator and an oscilloscope, are needed. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of magnetic field distribution inside a cylindrical conductor; Figure 2 This is a schematic diagram of an experiment for measuring the toroidal AC loop of a magnetic microwire based on LabVIEW in the present invention; Figure 3 It is a circular loop of the amorphous wire of the present invention at the same excitation amplitude and different frequencies; Figure 4 The toroidal loops of the amorphous wire of the present invention are measured at 30 kHz and different sinusoidal excitation amplitudes; Figure 5 It is the toroidal loop of the amorphous wire of the present invention measured under the condition of direct current bias; Figure 6 It is the circular loop measured for the composite wire of the present invention at a sinusoidal excitation amplitude of 10 kHz and 5 V. DETAILED DESCRIPTION

[0021] Example 1 A method for measuring a magnetic microwire toroidal AC loop based on LabVIEW, wherein the magnetic microwire is an amorphous wire, and the specific steps are as follows: (1) Take a piece of amorphous wire and use a multimeter to measure the DC resistance of the amorphous wire, which is 10.6 ohms; (2) Connect the amorphous wire and a 5-ohm resistor in series and connect them to the first channel of the signal generator. Connect the second channel of the signal generator to channel I of the oscilloscope and set the excitation condition to a sine wave with a frequency of 10 kHz and an amplitude of 5 V. (3) Couple the first channel and the second channel of the signal generator together to ensure that the voltage signals in the two channels are exactly the same and have no phase difference; (4) Connect the voltage signals at both ends of the amorphous wire and the resistor to channel II and channel III of the oscilloscope respectively. Channel II of the oscilloscope receives the voltage signals at both ends of the amorphous wire, and channel III receives the voltage signals at both ends of the series resistor. (5) Connect the oscilloscope to the upper computer and implement program control through serial port communication of LabVIEW program; (6) Turn on the two channels of the signal generator and start excitation. At this time, three voltage waveforms will be displayed in the oscilloscope. Run the LabVIEW program, input the DC resistance value of the amorphous wire, and then use the excitation signal read by oscilloscope channel I in the program to calculate the theoretical DC voltage divider value of the amorphous wire through voltage divider theory. Then subtract this DC voltage divider from the voltage signal data in channel II to obtain the induced voltage data. Finally, integrate the induced voltage to obtain the waveform Φ(t) of the amorphous wire's annular magnetic flux changing with time. For the voltage signal read by channel III, divide it by the resistance value of the series resistor to obtain the current waveform I(t) flowing through the amorphous wire in the loop. Finally, use the current waveform I(t) flowing through the amorphous wire and the waveform Φ(t) of the amorphous wire's annular magnetic flux changing with time as the X and Y axes respectively to obtain the amorphous wire annular AC loop.

[0022] like Figure 2As shown, the signal generator has two signal output terminals, which can generate the required excitation signal. The oscilloscope shown has 4 channels, which mainly collects voltage signals in loop measurement. The amorphous wire is connected in series with a 5-ohm resistor and connected to the signal generator to form an excitation loop. The signal generator in the loop has a 50-ohm impedance. The sinusoidal excitation signal in the signal generator is set to: (17), where V 0 represents the amplitude of the sinusoidal excitation signal, represents a sinusoidal excitation signal; The voltage across the amorphous wire is: (18), where V i represents the induced voltage, V represents the voltage across the amorphous wire, R 0 represents the DC resistance of the amorphous wire, R1 represents the resistance connected in series with the amorphous wire, Represents the theoretical DC voltage divider under quasi-static conditions.

[0023] like Figure 3 It is the toroidal AC hysteresis loop of different frequencies measured by amorphous wire under a sinusoidal excitation signal with an amplitude of 5 V. The hysteresis loop meets the general law of dynamic hysteresis loop. As the frequency increases, the shape of the loop changes from narrow and long to wide and rounded. This is because the dynamic hysteresis loop contains hysteresis loss and eddy current loss. As the frequency increases, the eddy current loss will dominate, resulting in deformation of the loop. Therefore, as long as the test frequency is low enough, the test result can be close to the static hysteresis loop. Figure 4 The graph shows the loops of amorphous wire at different excitation amplitudes under the same excitation frequency of 30 kHz. It can be seen from the graph that as the excitation amplitude increases, the shape of the loop approaches saturation. From the measurement results, the measured results basically meet the characteristics of the AC hysteresis loop, so the feasibility of the measurement method can be explained. Figure 5 This is the measured toroidal loop of amorphous wire at 300 kHz, 5V AC plus 4.4V DC bias excitation conditions. Because of the DC bias, the toroidal AC loop is deformed, but the excitation conditions are more consistent with the working mode in the sensor.

[0024] Example 2 A method for measuring a magnetic microwire toroidal AC loop based on LabVIEW, wherein the magnetic microwire is a composite wire, and the specific steps are as follows: (1) Take a piece of composite wire and use a multimeter to measure the DC resistance of the composite wire, which is 0.5 ohms; (2) Connect the composite wire and a resistor with a resistance of 5 ohms in series and connect them to the first channel of the signal generator. Connect the second channel of the signal generator to channel I of the oscilloscope and set the excitation condition to a sine wave with a frequency of 10 kHz and an amplitude of 5 V. (3) Couple the first channel and the second channel of the signal generator together to ensure that the voltage signals in the two channels are exactly the same and have no phase difference; (4) Connect the voltage signals at both ends of the composite wire and the resistor to channel II and channel III of the oscilloscope respectively. Channel II of the oscilloscope receives the voltage signals at both ends of the composite wire, and channel III receives the voltage signals at both ends of the series resistor. (5) Connect the oscilloscope to the upper computer and implement program control through serial port communication of LabVIEW program; (6) Turn on the two channels of the signal generator and start excitation. At this time, three voltage waveforms will be displayed in the oscilloscope. Run the LabVIEW program, input the DC resistance value of the composite wire, and then use the excitation signal read by oscilloscope channel I in the program to calculate the theoretical DC voltage divider value of the composite wire through voltage divider theory; then subtract this DC voltage divider from the voltage signal data in channel II to obtain the induced voltage data. Finally, integrate the induced voltage to obtain the waveform Φ(t) of the composite wire's annular magnetic flux changing with time. For the voltage signal read by channel III, divide it by the resistance value of the series resistor to obtain the current waveform I(t) flowing through the composite wire in the loop. Finally, use the current waveform I(t) flowing through the composite wire and the waveform Φ(t) of the composite wire's annular magnetic flux changing with time as the X and Y axes respectively to obtain the annular AC loop of the composite wire. The measurement results are as follows: Figure 6 shown.

[0025] During the measurement process, the following steps should be noted: 1. The signal generator needs to use two channels, and the two channels need to be coupled together to ensure that the frequency, amplitude, and phase are consistent. The first channel is used for excitation, and the signal of the second channel is passed to the oscilloscope, which is then used to calculate the theoretical DC voltage divider.

[0026] 2. The oscilloscope uses three channels. The signal received by Channel I is the excitation signal of the signal generator itself, Channel II receives the voltage signal at both ends of the magnetic microwire, and Channel III receives the voltage signal at both ends of the series resistor.

[0027] 3. In order to realize the automation of the measurement process, the LabView program is used to program the oscilloscope and process the data. After the test loop is connected, the signals of the three channels of the oscilloscope are read through the LabView program, and the signals of channels I and II are numerically calculated to obtain the induced voltage, which is then integrated to obtain the waveform Φ(t) of the magnetic flux of the magnetic microwire changing with time. Then the data of channel III is divided by the DC resistance to obtain the current waveform I(t) flowing through the magnetic microwire. The waveform Φ(t) of the magnetic flux of the magnetic microwire changing with time and the current waveform I(t) flowing through the magnetic microwire are drawn as a Lissajous figure to obtain the corresponding AC loop.

[0028] 4. The LabView program needs to perform digital filtering on the data read from the oscilloscope to remove high-frequency noise, so that the final loop is clear. At the same time, multiple cycles of waveforms can be read to ensure the accuracy of the loop.

Claims

1. A method for measuring the magnetic microwire toroidal AC loop based on LabVIEW. Features include: After the magnetic microwire and the resistor are connected in series, they are connected to the first channel of the signal generator. The second channel of the signal generator is connected to the channel I of the oscilloscope. The first channel and the second channel of the signal generator generate exactly the same excitation signal. The function of the oscilloscope is to collect voltage signals. The channels II and III of the oscilloscope simultaneously measure the voltage signals at both ends of the magnetic microwire and the resistor. The three channels of the oscilloscope are channel I receiving the excitation signal of the signal generator itself, channel II receiving the voltage signals on both sides of the magnetic microwire, and channel III receiving the voltage signals at both ends of the series resistor. Then, through LabVI The EW program is used to control the oscilloscope and read and process the collected voltage signals. The voltage signals of channel I and channel II are processed to obtain the induced voltage, and the induced voltage is integrated to obtain the waveform Φ(t) of the magnetic flux of the magnetic microwire changing with time. Then, the voltage signal of channel III is divided by the resistance value to obtain the current waveform I(t) flowing through the magnetic microwire. The current waveform I(t) flowing through the magnetic microwire and the waveform Φ(t) of the magnetic flux of the magnetic microwire changing with time are used as the X and Y axes respectively to obtain the magnetic microwire annular AC loop.

2. A method for measuring a magnetic microwire toroidal AC loop based on LabVIEW according to claim 1, Features: In the LabVIEW program, the DC resistance value of the magnetic microwire is input in advance, and then the excitation signal read from the oscilloscope channel I is used to calculate the theoretical DC voltage division value of the magnetic microwire through voltage division theory; then the data of channel II is subtracted from this DC voltage division to obtain the induced voltage data.

3. A method for measuring a magnetic microwire toroidal AC loop based on LabVIEW according to claim 1 or 2, Features: The excitation signal of the signal generator is a sine wave with a frequency of 10 kHz and an amplitude of 5V.

4. A method for measuring a magnetic microwire toroidal AC loop based on LabVIEW according to claim 3, Features: The resistance value of the resistor is 5 ohms.

5. A method for measuring a magnetic microwire toroidal AC loop based on LabVIEW according to claim 1 or 4, Features include: The changing magnetic field in the magnetic microfilament will induce a changing electric field, which will generate an induced voltage at both ends of the magnetic microfilament. V i , let the annular magnetic flux be Φ , then we can get the following approximate relationship: , t represents time, and this formula represents magnetic flux Φ Differentiate with respect to time t.

6. The method for measuring a magnetic microwire toroidal AC loop based on LabVIEW according to claim 1, Features: The LabVIEW program performs digital filtering on the data read from the oscilloscope and reads waveforms of multiple cycles.

7. A method for measuring a magnetic microwire toroidal AC loop based on LabVIEW according to claim 6, Features: The excitation signal of the signal generator can be adjusted into the form of AC plus DC bias, and is used to measure the magnetic micro-wire toroidal AC loop with DC bias.

8. A method for measuring a magnetic microwire toroidal AC loop based on LabVIEW according to claim 1 or 7, Features: The magnetic micro-wire is an amorphous wire or a composite wire and is used for the magnetic core of a fundamental wave orthogonal fluxgate sensor.

Images