A time-difference type current sensor and a signal processing method thereof
By designing a time-difference current sensor, utilizing an oscillation time difference measurement and control circuit and amorphous wire materials, the problems of low measurement accuracy, high power consumption, and complex parameter adjustment of fluxgate current sensors are solved, achieving miniaturized and high-precision current measurement.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- YICHANG TESTING TECHNIQUE RESEARCH INSTITUTE
- Filing Date
- 2023-11-09
- Publication Date
- 2026-07-31
AI Technical Summary
Existing fluxgate current sensors have a small measurement range, low accuracy, large size, high power consumption, and complex parameter adjustment, and are easily affected by temperature.
A time-difference current sensor is used, which utilizes an oscillation time difference measurement and control circuit, a bias resistor, an analog switch and a hysteresis comparator, combined with an amorphous wire as the sensitive material. The current is measured by switching between forward and reverse bias, which simplifies the electronic circuit and reduces power consumption.
It reduces power consumption while minimizing size, improves measurement accuracy, simplifies parameter adjustment processes, is suitable for mass production, and can assist in the design of dedicated ASIC chips.
Smart Images
Figure CN117572067B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of current sensor technology, and in particular to a time-difference current sensor and its signal processing method. Background Technology
[0002] Current sensors play a crucial role in the new energy vehicle industry. Current parameters are often core parameters for energy transmission and automatic control. New energy vehicles primarily rely on electric power systems for power. Current sensors are vital for battery charging and discharging management, motor condition monitoring, fault diagnosis, and safety protection. Therefore, current sensors are needed to accurately measure the charging and discharging status of battery packs. With the continuous development of new energy vehicle technology, new requirements are being placed on the measurement accuracy and power consumption of current sensors.
[0003] Currently, most fluxgate current sensors use permalloy or cobalt-based amorphous alloys as sensing materials. However, due to limitations in the properties of these magnetic materials, the current sensors suffer from limited measurement range, low accuracy, large size, and high power consumption. Furthermore, traditional fluxgate current sensors often employ analog signal processing circuits, where the parameter adjustment of the amplification and filtering circuits is complex, requiring individual adjustment for each sensor. Additionally, the zero bias of the current sensor is easily affected by temperature. Summary of the Invention
[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a time-difference current sensor and its signal processing method, which can solve the problems of large temperature drift, complex parameter adjustment, low accuracy and high power consumption of current sensors.
[0005] To achieve the above and other related objectives, the present invention provides a time-difference current sensor, comprising:
[0006] The oscillation time difference measurement and control circuit is used to output positive bias drive signal, negative bias drive signal, and bias switching signal.
[0007] The first bias resistor has its input terminal used to receive the positive bias drive signal, and its output terminal is connected to one end of the current sensor probe, forming a first node.
[0008] The second bias resistor has its input terminal used to receive the negative bias drive signal, and its output terminal is connected to the other end of the current sensor probe, forming a second node.
[0009] An analog switch has its first input terminal connected to the other end of the first bias resistor and receiving the negative analog signal output by the first bias resistor; its second input terminal is connected to the other end of the second bias resistor and receiving the positive analog signal output by the second bias resistor; and its third input terminal receives the bias switching signal output by the oscillation time difference measurement and control circuit.
[0010] The hysteresis comparator has a positive input terminal for receiving a reference voltage, a negative input terminal for receiving an analog signal from the analog switch, and an output terminal for outputting a square wave signal.
[0011] In one embodiment of the present invention, the current sensor probe includes:
[0012] A magnetic core with grooves on the outside, and amorphous wire wound around the magnetic core;
[0013] A supporting framework is disposed on the outside of the amorphous filament;
[0014] An induction coil is wound around the outside of the support frame, and the induction coil and the magnetic core are equivalent to a variable inductor;
[0015] A current-carrying conductor is positioned at the center of the magnetic core.
[0016] In one embodiment of the present invention, the oscillation time difference measurement and control circuit includes:
[0017] A logic control module, the input of which is used to receive a square wave signal, and the output of which is used to output a bias switching signal;
[0018] An increment / decrement counter, the input terminals of which are respectively connected to the logic control module and the output terminal of the reference clock;
[0019] The data latch has its input terminals connected to the logic control module and the output terminal of the increment / decrement counter, respectively.
[0020] A communication module, the input of which is connected to the output of the data latch, and the output of the communication module is used for data output.
[0021] In one embodiment of the present invention, the magnetic core is made of polytetrafluoroethylene.
[0022] In one embodiment of the present invention, the diameter of the magnetic core is 50-150 μm.
[0023] In one embodiment of the present invention, the magnetic core is ring-shaped, and the current-carrying wire is disposed at the center of the ring formed by the magnetic core.
[0024] In one embodiment of the present invention, when the bias switching signal is high, the positive analog signal of the second node enters the hysteresis comparator through the analog switch; when the bias switching signal is low, the negative analog signal of the first node enters the hysteresis comparator through the analog switch.
[0025] In one embodiment of the present invention, when the square wave signal is high, the voltage of the analog signal rises. When it exceeds the upper limit voltage of the hysteresis comparator, the square wave signal output by the hysteresis comparator reverses and outputs a low level. The positive bias drive signal and the negative bias drive signal both become low, and the voltage of the analog signal drops. When it falls below the lower limit voltage of the hysteresis comparator, the square wave signal output by the hysteresis comparator reverses and outputs a high level, starting a new oscillation cycle.
[0026] The present invention also provides a signal processing method for a time-difference current sensor, comprising:
[0027] S1. Output positive bias drive signal, negative bias drive signal, and bias switching signal through the oscillation time difference measurement and control circuit;
[0028] S2. The positive bias drive signal is received through the input terminal of the first bias resistor, and the output terminal of the first bias resistor is connected to one end of the current sensor probe, forming a first node.
[0029] S3. The negative bias drive signal is received through the input terminal of the second bias resistor, and the output terminal of the second bias resistor is connected to the other end of the current sensor probe, forming a second node.
[0030] S4. The negative analog signal output by the first bias resistor is received through the first input terminal of the analog switch, the positive analog signal output by the second bias resistor is received through the second input terminal of the analog switch, and the bias switching signal output by the oscillation time difference measurement and control circuit is received through the third input terminal of the analog switch.
[0031] S5. Receive the reference voltage through the positive input terminal of the hysteresis comparator, receive the analog signal from the analog switch through the negative input terminal of the hysteresis comparator, and output a square wave signal through the output terminal of the hysteresis comparator.
[0032] As described above, the time-difference current sensor and its signal processing method of the present invention have the following beneficial effects:
[0033] (1) The time difference current sensor of the present invention includes an oscillation time difference measurement and control circuit, a first bias resistor, a second bias resistor, a current sensor probe, an analog switch, a hysteresis comparator, and a sampling amorphous wire as the sensitive material, replacing commonly used magnetic materials such as permalloy and cobalt-based amorphous alloy. Compared with fluxgate current sensors, it reduces the size and power consumption of the current sensor, and improves the measurement accuracy compared with Hall current sensors.
[0034] (2) The time difference current sensor of the present invention uses the time difference signal of the probe with forward and reverse bias to measure the current magnitude, which greatly simplifies the complexity of electronic circuits and the parameter adjustment process, making it suitable for mass production. The present invention can significantly improve the temperature drift of electronic circuit systems.
[0035] (3) The time difference current sensor of the present invention can be used as a circuit prototype and can assist in the design of a dedicated ASIC chip to realize the chip-based current sensor. Attached Figure Description
[0036] Figure 1 This is a schematic diagram of the structure of a time-difference current sensor provided in an embodiment of this application.
[0037] Figure 2 This is a schematic diagram of the current sensor probe of the time difference current sensor provided in the embodiments of this application.
[0038] Figure 3 Magnetization curve of the amorphous wire core of the time difference current sensor provided in this application embodiment.
[0039] Figure 4 The sensor probe response curve of the time difference current sensor provided in this application embodiment under external current excitation.
[0040] Figure 5 This is a schematic diagram of the forward and reverse biasing circuit of the time difference current sensor provided in the embodiments of this application.
[0041] Figure 6 This is a block diagram of the oscillation time difference measurement and control circuit of the time difference current sensor provided in the embodiments of this application.
[0042] Figure 7 A flowchart illustrating the signal processing method for a time-difference current sensor provided in this application embodiment.
[0043] Component designation explanation
[0044] 1. Oscillation Time Difference Measurement and Control Circuit
[0045] 21 First bias resistor
[0046] 22 Second bias resistor
[0047] 3 Current sensor probe
[0048] 4. Analog Switch
[0049] 5 Hysteresis Comparator
[0050] 31 magnetic core
[0051] 32 Current-carrying conductors
[0052] 33 Supporting skeleton
[0053] 34 Induction coil Detailed Implementation
[0054] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.
[0055] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.
[0056] Please see Figure 1 , Figure 1This is a schematic diagram of the structure of a time-difference current sensor provided in an embodiment of this application. The present invention provides a time-difference current sensor, including an oscillation time difference measurement and control circuit 1, a first bias resistor 21, a second bias resistor 22, a current sensor probe 3, an analog switch 4, and a hysteresis comparator 5. The oscillation time difference measurement and control circuit 1 is used to output a positive bias drive signal, a negative bias drive signal, and a bias switching signal. The input terminal of the first bias resistor 21 is used to receive the positive bias drive signal, and the output terminal of the first bias resistor 21 is connected to one end of the current sensor probe 3, forming a first node. The input terminal of the second bias resistor 22 is used to receive the negative bias drive signal, and the output terminal of the second bias resistor 22 is connected to the current sensor probe. The other end of 3 forms a second node; the first input terminal of analog switch 4 is connected to the other end of the first bias resistor 21 and receives the negative analog signal output by the first bias resistor 21; the second input terminal of analog switch 4 is connected to the other end of the second bias resistor 22 and receives the positive analog signal output by the second bias resistor 22; the third input terminal of analog switch 4 receives the bias switching signal output by the oscillation time difference measurement and control circuit 1; the positive input terminal of hysteresis comparator 5 is used to receive the reference voltage, its negative input terminal is used to receive the analog signal of analog switch 4, and the output terminal of hysteresis comparator 5 is used to output a square wave signal.
[0057] Please see Figure 2 , Figure 2 This is a schematic diagram of the current sensor probe of the time-difference current sensor provided in this application embodiment. The current sensor probe 3 includes a magnetic core 31, a support frame 33, an induction coil 34, and a current-carrying wire 32. The magnetic core 31 has a groove on its outside, and an amorphous wire is wound around the magnetic core 31. The support frame 33 is disposed on the outside of the amorphous wire. The induction coil 34 is wound on the outside of the support frame 33, and the induction coil 34 and the magnetic core 31 are equivalent to a variable inductor. The current-carrying wire 32 is disposed at the center of the magnetic core 31.
[0058] Specifically, the current sensor probe 3 comprises a magnetic core 31, a current-carrying wire 32, a support frame 33, and an induction coil 34. An external magnetic field affects the differential permeability of the amorphous wire; therefore, the induction coil 34 and the magnetic core 31 constitute a variable inductor affected by the external magnetic field. Currents of different magnitudes and directions flowing through the current-carrying wire 32 will cause changes in the variable inductance.
[0059] The current sensor probe 3 itself does not output any signal. It needs to be combined with the oscillation time difference measurement and control circuit 1, bias resistor, analog switch 4, hysteresis comparator 5, and other devices to form a Schmitt trigger circuit with forward and reverse bias switching function in order to achieve LR resonant output. By switching between forward and reverse bias, the forward bias and reverse bias output resonant signals of different periods are made, and the difference between the two is linearly related to the external magnetic field.
[0060] The positive and negative bias switching circuit consists of an analog switch 4, a current sensor probe 3, a bias resistor, etc. Its switching function is controlled by three control signals output by the oscillation time difference measurement and control circuit, namely the positive bias drive signal, the negative bias drive signal, and the bias switching signal.
[0061] The Schmitt oscillator circuit with forward and reverse bias switching function mainly consists of a forward and reverse bias switching circuit and a hysteresis comparator 5. The square wave signal output by the hysteresis comparator 5 is fed back to the oscillation time difference measurement and control circuit 1, and the forward bias drive and negative bias drive signals are controlled according to the high and low levels of the square wave signal.
[0062] When the bias switching signal is high, the positive analog signal of the second node enters the hysteresis comparator 5 through the analog switch 4. When the bias switching signal is low, the negative analog signal of the first node enters the hysteresis comparator 5 through the analog switch 4. When the square wave signal is high, the voltage of the analog signal rises. When it exceeds the upper limit voltage of the hysteresis comparator 5, the square wave signal output by the hysteresis comparator 5 inverts and outputs a low level. Both the positive bias drive signal and the negative bias drive signal become low, and the voltage of the analog signal drops. When it falls below the lower limit voltage of the hysteresis comparator 5, the square wave signal output by the hysteresis comparator 5 inverts and outputs a high level, starting a new oscillation cycle.
[0063] The functional logic table of the Schmitt trigger oscillator circuit with forward / reverse bias switching function is as follows:
[0064] high level high level high level low level Positive bias analog signal at node 2 high level low level low level high level Negative bias analog signal at node 1 low level remain unchanged low level low level remain unchanged
[0065] As shown in the table above, when the bias switching signal is high, the analog signal of the second node enters the hysteresis comparator through the analog switch; when the bias switching signal is low, the analog signal of the first node enters the hysteresis comparator through the analog switch, determining whether the circuit is positively or negatively biased. The square wave signal is the output of the hysteresis comparator and is fed back to the control circuit. With the bias switching signal unchanged, the level of the square wave signal affects the charging and discharging process of LR. When the square wave signal is high, LR charges, and the bias analog signal voltage rises. When it exceeds the upper limit voltage of the hysteresis comparator, the square wave signal output by the hysteresis comparator reverses, outputting a low level. At this time, both the positive bias drive and the negative bias drive become low, LR begins to discharge, and the bias analog signal voltage drops. When this voltage exceeds the lower limit voltage of the hysteresis comparator, the square wave signal output by the hysteresis comparator reverses, outputting a high level, and then a new oscillation cycle begins.
[0066] The logic control module 11 of the oscillation time difference measurement and control circuit 1 controls the forward and reverse bias switching circuit on one hand, and participates in the resonance process through the feedback square wave signal on the other. Simultaneously, the logic control module 11 outputs an increment / decrement control signal, which is determined by the bias switching signal. When forward biased, the increment / decrement counter increments (or decrements); when negative biased, it decrements (or increments). The increment / decrement counter is a signed counter that uses a high-frequency reference clock for counting. The same number of square wave periods are measured for both forward and reverse biases. Although the number of measurements is the same, the square wave signal periods are different under forward and reverse biases. Therefore, the final result of the increment / decrement counter is the time difference between the two, and this data enters the data latch module under the control of the latch signal. The SPI or I2C communication module is mainly used for external communication. An external microprocessor can read the latched result through this module and can also bias internal registers, such as setting the sampling frequency and the number of square wave counts.
[0067] The current sensor probe 3 is made of magnetic core material. In this embodiment, amorphous wire is selected, which is characterized by high magnetic permeability, low coercivity, and a diameter of 50-150 μm.
[0068] Please see Figure 3 , Figure 3 The magnetization curve of the amorphous wire core of the time-difference current sensor provided in this application embodiment is shown. The core 31 is supported by polytetrafluoroethylene and is made into a ring with grooves on the outside, with the amorphous wire wound around it. An induction coil 34 with a certain number of turns is wound around the outside of the support frame 33 and the amorphous wire. The induction coil 34 and the core 31 are equivalent to a variable inductor.
[0069] Please see Figure 4 , Figure 4This is the sensor probe response curve of the time-difference current sensor provided in this application embodiment under external current excitation. The magnetic core 31 operates in the linear range of differential permeability. In the case of zero current, the oscillation period generated by forward bias and reverse bias is the same. When the current is not zero, the oscillation period generated by forward bias and reverse bias is different, and the difference between the two is linearly related to the magnitude of the current.
[0070] Please see Figure 5 , Figure 5 This is a schematic diagram of the forward and reverse biasing circuit of the time-difference current sensor probe provided in this application embodiment. One operating cycle of the current sensor probe 3 includes two processes: forward and reverse biasing. During forward biasing, the current in the induction coil 34 generates a magnetic field, the direction of which is the same as the magnetic field generated by the current in the current-carrying wire. During reverse biasing, the direction of this magnetic field is opposite to the direction of the magnetic field generated by the current in the current-carrying wire. Therefore, the magnitude of the synthesized magnetic field differs during forward and reverse biasing, resulting in different probe inductances for forward and reverse biasing. The probe inductance, bias resistor, and Schmitt trigger constitute an oscillation circuit. Forward and reverse biasing cause the output oscillation signal period to be different; therefore, measuring the same number of oscillation signals requires different time intervals. The time difference signal between forward and reverse biasing is linearly related to the current value.
[0071] Please see Figure 6 , Figure 6 This is a block diagram of the oscillation time difference measurement and control circuit of the time difference current sensor provided in this application embodiment. The oscillation time difference measurement and control circuit 1 includes a logic control module 11, an increment / decrement counter 12, a data latch 13, and a communication module 14. The input terminal of the logic control module 11 is used to receive a square wave signal, and the output terminal of the logic control module 11 is used to output a bias switching signal. The input terminal of the increment / decrement counter 12 is connected to the output terminal of the logic control module 11 and the reference clock, respectively. The input terminal of the data latch 13 is connected to the output terminal of the logic control module 11 and the increment / decrement counter 12, respectively. The input terminal of the communication module 14 is connected to the output terminal of the data latch 13, and the output terminal of the communication module 14 is used for data output.
[0072] The oscillation time difference measurement and control circuit 1 is implemented by a programmable logic device or a dedicated ASIC circuit. Under the action of the logic control circuit, the current sensor is in both forward bias and reverse bias processes. During forward bias, several forward bias oscillation cycles are measured, for example, 100 cycles. At this time, the counter increments its count with a higher frequency reference clock as input. During reverse bias, the count is also repeated for a number of cycles (the same number as in forward bias, i.e., 100 cycles), but the counter decrements its count. Finally, the counter obtains the difference between the two counts. Because a fixed frequency reference clock is used as the counting source, the time difference can be easily obtained from the difference and the reference clock frequency. This difference is proportional to the current magnitude. It is particularly noteworthy that the counter here is a signed counter, which can obtain negative count values.
[0073] Similar to the principle of the time-difference current sensor of the present invention, the present invention also provides a signal processing method for a time-difference current sensor, comprising:
[0074] Step S1: Output positive bias drive signal, negative bias drive signal, and bias switching signal through oscillation time difference measurement and control circuit 1.
[0075] Step S2: Receive the positive bias drive signal through the input terminal of the first bias resistor 21. The output terminal of the first bias resistor 21 is connected to one end of the current sensor probe 3 and forms the first node.
[0076] Step S3: Receive the negative bias drive signal through the input terminal of the second bias resistor 22. The output terminal of the second bias resistor 22 is connected to the other end of the current sensor probe 3, and forms a second node.
[0077] Step S4: Receive the negative analog signal output by the first bias resistor 21 through the first input terminal of the analog switch 4, receive the positive analog signal output by the second bias resistor 22 through the second input terminal of the analog switch 4, and receive the bias switching signal output by the oscillation time difference measurement and control circuit 1 through the third input terminal of the analog switch 4.
[0078] Step S5: Receive the reference voltage through the positive input terminal of the hysteresis comparator 5, receive the analog signal from the analog switch 4 through the negative input terminal of the hysteresis comparator 5, and output a square wave signal through the output terminal of the hysteresis comparator 5.
[0079] In summary, the time difference current sensor of the present invention includes an oscillation time difference measurement and control circuit 1, a first bias resistor 21, a second bias resistor 22, an analog switch 4, and a hysteresis comparator 5. It uses a sampling amorphous wire as the sensitive material, replacing commonly used magnetic materials such as permalloy and cobalt-based amorphous alloy. Compared with fluxgate current sensors, it reduces the size and power consumption of the current sensor. Compared with Hall current sensors, it improves the measurement accuracy.
[0080] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.
Claims
1. A time-difference type current sensor characterized by, include: Oscillation time difference measurement and control circuit (1) is used to output positive bias drive signal, negative bias drive signal and bias switching signal; The first bias resistor (21) has its input terminal used to receive the positive bias drive signal, and its output terminal is connected to one end of the current sensor probe (3) and forms the first node. The second bias resistor (22) has its input terminal used to receive the negative bias drive signal, and its output terminal is connected to the other end of the current sensor probe (3) and forms a second node. The analog switch (4) has its first input terminal connected to the output terminal of the first bias resistor (21) and receives the negative analog signal output by the first bias resistor (21). The second input terminal of the analog switch (4) is connected to the output terminal of the second bias resistor (22) and receives the positive analog signal output by the second bias resistor (22). The third input terminal of the analog switch (4) receives the bias switching signal output by the oscillation time difference measurement and control circuit (1). The hysteresis comparator (5) has a positive input terminal for receiving a reference voltage and a negative input terminal for receiving an analog signal from the analog switch (4). The output terminal of the hysteresis comparator (5) is used to output a square wave signal.
2. A time-difference current sensor according to claim 1, characterized in that The current sensor probe (3) includes: The magnetic core (31) has grooves on its outside, and amorphous wire is wound around the magnetic core (31); A support frame (33) is disposed on the outside of the amorphous filament; An induction coil (34) is wound around the outside of the support frame (33), and the induction coil (34) and the magnetic core (31) are equivalent to a variable inductor; A current-carrying conductor (32) is disposed at the center of the magnetic core (31).
3. A time-difference current sensor according to claim 2, characterized in that The oscillation time difference measurement and control circuit (1) includes: The logic control module (11) has an input terminal for receiving square wave signals and an output terminal for outputting bias switching signals. The increment / decrement counter (12) has its input terminals connected to the logic control module (11) and the output terminal of the reference clock, respectively. The data latch (13) has its input terminals connected to the output terminals of the logic control module (11) and the increment / decrement counter (12), respectively. The communication module (14) has its input end connected to the output end of the data latch (13), and the output end of the communication module (14) is used for data output.
4. A time-difference current sensor according to claim 2, characterized in that: The magnetic core (31) is made of polytetrafluoroethylene.
5. A time-difference current sensor according to claim 2, characterized in that: The diameter of the magnetic core (31) is 50~150um.
6. A time-difference current sensor according to claim 2, characterized in that: The magnetic core (31) is ring-shaped, and the current-carrying wire (32) is located at the center of the ring formed by the magnetic core (31).
7. A time-difference current sensor according to claim 3, characterized in that: When the bias switching signal is high, the positive analog signal of the second node enters the hysteresis comparator (5) through the analog switch (4). When the bias switching signal is low, the negative analog signal of the first node enters the hysteresis comparator (5) through the analog switch (4).
8. A time-difference current sensor according to claim 7, characterized in that: When the square wave signal is high, the voltage of the analog signal rises. When it exceeds the upper limit voltage of the hysteresis comparator (5), the square wave signal output by the hysteresis comparator (5) reverses and outputs a low level. The positive bias drive signal and the negative bias drive signal both become low, and the voltage of the analog signal drops. When it falls below the lower limit voltage of the hysteresis comparator (5), the square wave signal output by the hysteresis comparator (5) reverses and outputs a high level, starting a new oscillation cycle.
9. A signal processing method for a time-difference current sensor, characterized in that, include: S1. The positive bias drive signal, negative bias drive signal, and bias switching signal are output through the oscillation time difference measurement and control circuit (1); S2. The positive bias drive signal is received through the input terminal of the first bias resistor (21), and the output terminal of the first bias resistor (21) is connected to one end of the current sensor probe (3) and forms the first node. S3. The negative bias drive signal is received through the input terminal of the second bias resistor (22), and the output terminal of the second bias resistor (22) is connected to the other end of the current sensor probe (3) to form a second node. S4. The negative analog signal output by the first bias resistor (21) is received through the first input terminal of the analog switch (4), the positive analog signal output by the second bias resistor (22) is received through the second input terminal of the analog switch (4), and the bias switching signal output by the oscillation time difference measurement and control circuit (1) is received through the third input terminal of the analog switch (4). S5. Receive the reference voltage through the positive input terminal of the hysteresis comparator (5), receive the analog signal of the analog switch (4) through the negative input terminal of the hysteresis comparator (5), and output a square wave signal through the output terminal of the hysteresis comparator (5).