An oil level detection system and method based on a software amplitude identification principle

Abstract

This invention discloses an oil level detection system and method based on software amplitude discrimination principle. Utilizing the built-in DAC and ADC functions of the MCU processor, combined with the efficient DMA and timer functions within the MCU, a complete closed-loop process from excitation signal generation to signal acquisition and processing is achieved through a perfect combination of software and hardware. This enables high-precision acquisition of capacitance signals from 20pF to 500pF, replacing complex LCR bridges and allowing for efficient and accurate measurement of the capacitance value of the capacitor under test with a simpler circuit, thereby achieving efficient and accurate measurement of oil level.

Description

Technical Field

[0001] This invention belongs to the technical field of aviation fuel level detection, specifically relating to a fuel level detection system and method based on software amplitude discrimination principle. Background Technology

[0002] There are many methods for detecting fuel level in aviation fuel tanks, such as mechanical float methods, ultrasonic level methods, radar ranging methods, and photoelectric marker methods. However, these are clearly unsuitable for aviation fuel tanks, whose attitude may change at any time. In this area, capacitance detection is commonly used for fuel level detection. From a capacitance detection perspective, there are also many methods. There is a highly accurate LCR bridge, which can achieve professional-grade capacitance monitoring. However, its functionality is complex and has high requirements for the operating environment, making it difficult to apply in the complex environments of aviation equipment. There is also a simple and crude voltage divider sampling method. This uses a standard impedance to divide the voltage with the capacitor, and the capacitive reactance is determined from the voltage obtained, thus determining the capacitance. This method is relatively crude and is greatly affected by the external environment, making it difficult to apply in the demanding environments of aviation equipment.

[0003] Therefore, in view of the problems existing in the prior art of detecting oil level by capacitance, the present invention discloses an oil level detection system and detection method based on the software amplitude discrimination principle. Summary of the Invention

[0004] This invention discloses an oil level detection system and method based on the software amplitude discrimination principle, which can replace the complex LCR bridge and perform efficient and accurate measurement of the capacitance value of the capacitor under test with a simpler circuit.

[0005] This invention is achieved through the following technical solution:

[0006] An oil level detection system based on software amplitude discrimination principle includes an MCU processor. The MCU processor includes a first ADC port, a second ADC port, and a DAC port capable of outputting a sinusoidal voltage. The DAC port is connected to a capacitor under test via a smoothing and shaping circuit. A voltage sampling circuit is provided between the capacitor under test and the first ADC port, and a current sampling circuit is provided between the capacitor under test and the second ADC port. The voltage sampling circuit is used to acquire the sinusoidal voltage across the capacitor under test, and the current sampling circuit is used to acquire the current flowing through the capacitor under test and convert the current signal into a voltage signal. The MCU processor has a built-in detection unit, which includes a time-division acquisition module and a filtering calculation module. The time-division acquisition module is used to independently acquire signals from the first ADC port or the second ADC port in a time-division manner. The filtering calculation module is used to filter out the maximum value in the signal, calculate the capacitance value of the capacitor under test based on the filtered maximum value, and calculate the output oil level based on the capacitance value of the capacitor under test.

[0007] To better realize the present invention, a current amplification circuit and a gain switching circuit are connected sequentially between the current sampling circuit and the second ADC port; the current amplification circuit is used to amplify the signal of the current sampling circuit by a factor, and the gain switching circuit is used to connect the current amplification circuit with different gain resistors to obtain different gain factors.

[0008] To better realize the present invention, the smoothing and shaping circuit further includes a resistor R1 and a capacitor C2 connected in series between the DAC port and the capacitor under test, a resistor R4 connected in parallel on one side of the resistor R1, and a resistor R5 connected in parallel on one side of the capacitor C2.

[0009] To better realize the present invention, an overcurrent protection circuit is further connected between the smoothing and shaping circuit and the capacitor under test. The overcurrent protection circuit includes an operational amplifier U2 and a resistor R2. The input terminal of the operational amplifier U2 is connected to the output terminal of the smoothing and shaping circuit, and the output terminal of the operational amplifier U2 is connected to the resistor R2 to form a voltage follower circuit.

[0010] To better realize the present invention, the voltage sampling circuit further includes an operational amplifier U3, a resistor R3, and a resistor R7. The inverting input terminal of the operational amplifier U3 is connected to the capacitor under test through the resistor R3, the non-inverting input terminal of the operational amplifier U3 is connected to the capacitor under test through the resistor R7, and the output terminal of the operational amplifier U3 is connected to the first ADC port.

[0011] To better realize the present invention, the current sampling circuit further includes an operational amplifier U4, resistors R8 and R9, and a capacitor C7. The inverting input terminal of the operational amplifier U4 is connected to the capacitor under test through resistor R8, and the non-inverting input terminal of the operational amplifier U4 is connected to resistor R9. A capacitor C7 is connected in parallel between resistor R9 and the negative power supply terminal of the operational amplifier U4. The output terminal of the operational amplifier U4 is connected to the second ADC port through a current amplification circuit and a gain switching circuit.

[0012] To better realize the present invention, the current amplification circuit further includes an operational amplifier U5, resistors R10, R12, and R14. The inverting input terminal of the operational amplifier U5 is connected to the capacitor under test through resistor R10, the non-inverting input terminal of the operational amplifier U5 is connected to the output terminal of the operational amplifier U4 through resistor R14, and the output terminal of the operational amplifier U5 is connected to the MCU processor through resistor R12.

[0013] To better realize the present invention, the gain switching circuit further includes a chip U6 and a gain resistor. The chip U6 includes several parallel switching adjustment branches, all of which are connected to the RG1 port of the operational amplifier U5. The chip U6 includes several analog switches, which are connected to the RG2 port of the operational amplifier U5 through the gain resistor. The input port of the chip U6 is connected to the MCU processor.

[0014] An oil level detection method based on software amplitude discrimination principle includes the following steps:

[0015] Step 1: Enable the DAC control module in the MCU processor and set a timing of 1μs to drive the N sinusoidal signal data generated before the DMA shift in the MCU processor to be output through the DAC port;

[0016] Step 2: Smooth and shape the signal output from the DAC port using a smoothing and shaping circuit, and increase the bias voltage of the sine wave signal;

[0017] Step 3: The MCU processor independently starts the voltage acquisition single channel and continuously acquires K sets of first voltage data from the voltage sampling circuit under the drive of the built-in timer of the MCU processor;

[0018] Step 4: The MCU processor independently starts the single channel of current acquisition and continuously acquires K sets of second voltage data from the current sampling circuit under the drive of the built-in timer of the MCU processor;

[0019] Step 5: The MCU processor extracts the first maximum voltage from the K sets of first voltage data, the MCU processor extracts the second maximum voltage from the K sets of second voltage data, calculates the second current using the second maximum voltage, and calculates the capacitance value of the capacitor under test using the first maximum voltage and the second current.

[0020] Step 6: Calculate the oil level based on the capacitance value of the capacitor under test.

[0021] To better realize the present invention, further, in step 5, the formula for calculating the capacitance value of the capacitor to be tested is as follows:

[0022] ;

[0023] Where: C represents the capacitance value of the capacitor under test; I represents the second current; V represents the first maximum voltage; and f represents the operating frequency of the capacitor under test.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] (1) This invention utilizes the large Q value of the oil level measuring capacitor and discards the ESR value to solve the capacitance value within its measurement range. This simplifies the capacitance measurement method that requires strict and accurate phase detection to be calculated into a simple software amplitude detection method. This greatly simplifies the hardware circuit design and reduces the complexity of software calculation. At the same time, it solves the problems of load LCR bridge not working and engineering application in harsh environments.

[0026] (2) This invention utilizes the built-in DAC port of the MCU processor to generate a sine wave, saving the circuit design of a dedicated DDS digital waveform generator. It utilizes the built-in 12-bit ADC function of the MCU processor to replace the design of an external ADC chip that requires a higher number of acquisitions, thereby effectively simplifying the circuit while ensuring the detection effect.

[0027] (3) This invention utilizes the advantage of generating and controlling the sinusoidal excitation signal itself to separately acquire the voltage and current signals of the capacitor under test. It realizes the parallel acquisition function of voltage and current on the MCU processor that works serially, which must be implemented by FPGA, thus omitting the use of FPGA devices.

[0028] (4) All operational amplifier circuits involved in this invention are powered by a single power supply, which reduces the complexity of power supply circuit design for positive and negative power supply. By making reasonable use of instrumentation amplifiers, the instrumentation operational amplifiers that require positive and negative power supply are powered by a single power supply. By designing an independent intermediate bias voltage, the 0-axis position of the positive line excitation signal is raised, which solves both the problem of positive and negative power supply and the problem that the signal is difficult to directly interface with the ADC acquisition circuit due to positive and negative power supply. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the principle of the present invention;

[0030] Figure 2 This is the circuit diagram of the oil level detection system. Detailed Implementation

[0031] Example 1:

[0032] This embodiment discloses an oil level detection system based on the software amplitude discrimination principle, such as... Figure 1 and Figure 2As shown, the system includes an MCU processor, which includes a first ADC port, a second ADC port, and a DAC port capable of outputting a sinusoidal voltage. The DAC port is connected to the capacitor under test (UUT) via a smoothing and shaping circuit. A voltage sampling circuit is provided between the UUT and the first ADC port, and a current sampling circuit is provided between the UUT and the second ADC port. The voltage sampling circuit is used to acquire the sinusoidal voltage across the UUT, and the current sampling circuit is used to acquire the current flowing through the UUT and convert the current signal into a voltage signal. The MCU processor has a built-in detection unit, which includes a time-division multiplexing acquisition module and a filtering and calculation module. The time-division multiplexing acquisition module is used to independently acquire signals from the first ADC port or the second ADC port in a time-division multiplexing manner. The filtering and calculation module is used to filter out the maximum value in the signal, calculate the capacitance value of the UUT based on the filtered maximum value, and calculate the output oil level based on the capacitance value of the UUT.

[0033] An oil level detection method based on software amplitude discrimination principle includes the following steps:

[0034] Step 1: Enable the DAC control module in the MCU processor and set a timing of 1μs to drive the N sinusoidal signal data generated before the DMA shift in the MCU processor to be output through the DAC port;

[0035] Step 2: Smooth and shape the signal output from the DAC port using a smoothing and shaping circuit, and increase the bias voltage of the sine wave signal;

[0036] Step 3: The MCU processor independently starts the voltage acquisition single channel and continuously acquires K sets of first voltage data from the voltage sampling circuit under the drive of the built-in timer of the MCU processor;

[0037] Step 4: The MCU processor independently starts the single channel of current acquisition and continuously acquires K sets of second voltage data from the current sampling circuit under the drive of the built-in timer of the MCU processor;

[0038] Step 5: The MCU processor extracts the first maximum voltage from the K sets of first voltage data, the MCU processor extracts the second maximum voltage from the K sets of second voltage data, calculates the second current using the second maximum voltage, and calculates the capacitance value of the capacitor under test using the first maximum voltage and the second current.

[0039] Step 6: Calculate the oil level based on the capacitance value of the capacitor under test.

[0040] Furthermore, in step 5, the formula for calculating the capacitance value of the capacitor to be tested is as follows:

[0041] ;

[0042] Where: C represents the capacitance value of the capacitor under test; I represents the second current; V represents the first maximum voltage; and f represents the operating frequency of the capacitor under test.

[0043] Example 2:

[0044] This embodiment discloses an oil level detection system based on the software amplitude discrimination principle, which is an improvement on Embodiment 1, such as... Figure 2 As shown, a current amplification circuit and a gain switching circuit are connected sequentially between the current sampling circuit and the second ADC port; the current amplification circuit is used to amplify the signal of the current sampling circuit by a factor, and the gain switching circuit is used to connect the current amplification circuit with different gain resistors to obtain different gain factors.

[0045] The current sampling circuit includes an operational amplifier U4, resistors R8 and R9, and a capacitor C7. The inverting input of the operational amplifier U4 is connected to the capacitor under test through resistor R8, and the non-inverting input of the operational amplifier U4 is connected to resistor R9. A capacitor C7 is connected in parallel between resistor R9 and the negative power supply terminal of the operational amplifier U4. The output of the operational amplifier U4 is connected to the second ADC port through a current amplification circuit and a gain switching circuit.

[0046] The current amplification circuit includes an operational amplifier U5, resistors R10, R12, and R14. The inverting input of the operational amplifier U5 is connected to the capacitor under test through resistor R10, the non-inverting input of the operational amplifier U5 is connected to the output of the operational amplifier U4 through resistor R14, and the output of the operational amplifier U5 is connected to the MCU processor through resistor R12.

[0047] The gain switching circuit includes a chip U6 and a gain resistor. The chip U6 includes several parallel switching adjustment branches, all of which are connected to the RG1 port of the operational amplifier U5. The chip U6 also includes several analog switches, which are connected to the RG2 port of the operational amplifier U5 through the gain resistor. The input port of the chip U6 is connected to the MCU processor.

[0048] The rest of this embodiment is the same as that of Embodiment 1, so it will not be described again.

[0049] Example 3:

[0050] This embodiment discloses an oil level detection system based on the software amplitude discrimination principle, which is an improvement on embodiment 1 or 2, such as... Figure 2 As shown, the voltage sampling circuit includes an operational amplifier U3, a resistor R3, and a resistor R7. The inverting input terminal of the operational amplifier U3 is connected to the capacitor under test through the resistor R3, the non-inverting input terminal of the operational amplifier U3 is connected to the capacitor under test through the resistor R7, and the output terminal of the operational amplifier U3 is connected to the first ADC port.

[0051] The rest of this embodiment is the same as that of embodiment 1 or 2, so it will not be described again.

[0052] Example 4:

[0053] This embodiment discloses an oil level detection system based on the software amplitude discrimination principle, which is an improvement on any one of embodiments 1-3. The smoothing and shaping circuit includes a resistor R1 and a capacitor C2 connected in series between the DAC port and the capacitor to be tested. A resistor R4 is connected in parallel on one side of the resistor R1, and a resistor R5 is connected in parallel on one side of the capacitor C2.

[0054] An overcurrent protection circuit is connected between the smoothing and shaping circuit and the capacitor under test. The overcurrent protection circuit includes an operational amplifier U2 and a resistor R2. The input terminal of the operational amplifier U2 is connected to the output terminal of the smoothing and shaping circuit, and the output terminal of the operational amplifier U2 is connected to the resistor R2 to form a voltage follower circuit.

[0055] The rest of this embodiment is the same as any one of embodiments 1-3, so it will not be described again.

[0056] Example 5:

[0057] This embodiment discloses an oil level detection system and method based on the software amplitude discrimination principle, which is an improvement on any one of the embodiments 1-4 above, such as... Figure 2 As shown, in the system hardware circuit required for voltage software amplitude discrimination, operational amplifier U1, capacitors C10 and C11, crystal oscillator Y1, capacitor C9, resistors R11, C13, C6, and R19 constitute the basic minimum detection unit for the MCU processor's power-on operation. Resistors R1, R4, C2, and R5 constitute a smoothing and shaping circuit, which smooths the glitches between adjacent points of the sine wave waveform generated by the voltage points of the DAC port output voltage of the MCU processor, while simultaneously increasing the bias voltage of the unipolar sine wave.

[0058] Operational amplifier U2 and resistor R2 constitute an overcurrent protection circuit with output signal impedance conversion and overcurrent protection functions. The capacitor under test is the object being tested, equivalent to the equivalent capacitance of an oil tank. Resistors R3 and R7, and operational amplifier U3 constitute a voltage sampling circuit across the capacitor under test; resistors R8 and R9, capacitor C7, and operational amplifier U4 constitute a current sampling circuit, which can collect the current value flowing through the capacitor under test and convert the current value to voltage value through I / V conversion. Capacitors R10 and R14, operational amplifier U5, and capacitor R12 constitute a current amplification circuit. Chip U6, gain resistors R15, R16, R17, and R18 are connected in parallel to form a gain switching circuit. The four sets of analog switches S1-S4 on chip U6 are connected to gain resistors R15, R16, R17, and R18 respectively to form switching circuits with different gains. With the help of the gain switching circuit, the operational amplifier U5 can amplify the current sampling signal at different rates, and can achieve adaptive detection of different capacitance values ​​by switching the rate.

[0059] Using the sine function sin(θ), where θ = 0~2π, the voltage values ​​at different points are calculated. The MCU processor's detection unit is programmed to output these voltages one by one to the internal DAC controller. Under the control of a timer and a DMA controller, the sine wave voltage is output uniformly and accurately through the DAC port repeatedly. This original sine wave signal is formed by the stepwise combination of different voltages, creating a rudimentary sine wave. However, the voltage values ​​between adjacent voltage data points are not smooth; they jump, not conforming to the sin(θ) relationship, which affects the accuracy of the data acquired by the ADC port later. By using a smoothing and shaping circuit to smooth the voltage data between adjacent voltage points, the charging and discharging of the capacitor under test ensures that the voltage between adjacent voltage points no longer jumps but changes linearly with a certain slope. This linear change approximates the change of the sin(θ) function, greatly reducing the impact on the values ​​acquired by the ADC port later. After the smoothed sine signal passes through the voltage follower formed by the operational amplifier U2 device, with the addition of a 1.65V DC bias voltage, the sine signal becomes a sine wave excitation signal with the intermediate voltage of 1.65V of the 3.3V power supply as the zero point. This allows the current amplifier circuit to achieve complete amplification of the sine wave signal at the positive terminal without the need for positive and negative power supplies.

[0060] When a sinusoidal excitation signal passes through the capacitor under test, it generates a sinusoidal voltage across the capacitor and simultaneously induces a sinusoidally changing current within the capacitor. The voltage sampling circuit converts the sampled voltage value into a single-ended signal via a differential operational amplifier (OA), which is then sent directly to the PA2 port of the MCU processor (the first ADC port) for ADC acquisition via resistor R6. The current flowing through the capacitor also passes through the current sampling circuit composed of OA, resistors R8 and R13 for I / V conversion, converting the current value into a voltage value with a corresponding amplification factor. This voltage value is then differentially amplified by OA, with the amplification factor determined by the gain switching circuit composed of chip U6 under the control of the MCU processor's built-in software. The MCU processor's built-in software uses the voltage value acquired through the second ADC port to determine if the gain ratio is appropriate. If the gain ratio is unsuitable, it can switch the addresses of different analog switches on chip U6 to select different gain resistors until a suitable gain level is found. The final current-to-sampled voltage is output to PA1 of the MCU processor, i.e., the second ADC port, after passing through resistor R12, for ADC acquisition.

[0061] When the MCU processor acquires the voltage-to-current conversion voltages input to ports PA1 and PA2, it should adhere to the principle of the highest possible sampling rate. This is to minimize the peak acquisition error caused by the inability to acquire the two signals synchronously, as well as the error in the subsequent calculation results. Under this principle, the first and second voltage data should be acquired independently in a time-division manner. While maintaining the highest possible sampling rate achievable by the ADC, the sine wave periods of the first and second voltage data should be completely acquired separately using a timer in conjunction with the ADC's continuous conversion function.

[0062] The MCU processor performs peak lookup on the complete sine waves of the first and second voltage data collected. It finds the first and second maximum voltages. The second maximum voltage is then divided by the gain of the two-stage amplification of op-amp U4 and op-amp U5, and then divided by the sampling resistance value of resistor R8 to obtain the second current.

[0063] Depend on The capacitance value of the capacitor under test can be calculated, where C represents the capacitance value of the capacitor under test; I represents the second current; V represents the first maximum voltage; and f represents the operating frequency of the capacitor under test.

[0064] By comparing the capacitance value of the capacitor to be tested with the oil level correspondence table, the oil level can be determined.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. An oil level detection system based on the software amplitude identification principle, comprising an MCU processor, characterized in that, The MCU processor includes a first ADC port, a second ADC port, and a DAC port capable of outputting a sinusoidal voltage. The DAC port is connected to the capacitor under test (UUT) via a smoothing and shaping circuit. A voltage sampling circuit is provided between the UUT and the first ADC port, and a current sampling circuit is provided between the UUT and the second ADC port. The voltage sampling circuit is used to acquire the sinusoidal voltage across the UUT, and the current sampling circuit is used to acquire the current flowing through the UUT and convert the current signal into a voltage signal. The MCU processor has a built-in detection unit, which includes a time-division multiplexing acquisition module and a filtering and calculation module. The time-division multiplexing acquisition module is used to independently acquire signals from the first ADC port or the second ADC port in a time-division multiplexing manner. The filtering and calculation module is used to filter out the maximum value in the signal, calculate the capacitance value of the UUT based on the filtered maximum value, and calculate the output oil level based on the capacitance value of the UUT. A current amplification circuit and a gain switching circuit are connected sequentially between the current sampling circuit and the second ADC port. The current amplification circuit is used to amplify the signal from the current sampling circuit by a factor, and the gain switching circuit is used to connect the current amplification circuit with different gain resistors to obtain different gain factors.

2. The oil level detection system based on the software amplitude discrimination principle according to claim 1, characterized in that, The smoothing and shaping circuit includes a resistor R1 and a capacitor C2 connected in series between the DAC port and the capacitor under test. A resistor R4 is connected in parallel on one side of the resistor R1, and a resistor R5 is connected in parallel on one side of the capacitor C2.

3. The oil level detection system based on the software amplitude discrimination principle according to claim 2, characterized in that, An overcurrent protection circuit is connected between the smoothing and shaping circuit and the capacitor under test. The overcurrent protection circuit includes an operational amplifier U2 and a resistor R2. The input terminal of the operational amplifier U2 is connected to the output terminal of the smoothing and shaping circuit, and the output terminal of the operational amplifier U2 is connected to the resistor R2 to form a voltage follower circuit.

4. The oil level detection system based on the software amplitude discrimination principle according to claim 3, characterized in that, The voltage sampling circuit includes an operational amplifier U3, a resistor R3, and a resistor R7. The inverting input terminal of the operational amplifier U3 is connected to the capacitor under test through the resistor R3, the non-inverting input terminal of the operational amplifier U3 is connected to the capacitor under test through the resistor R7, and the output terminal of the operational amplifier U3 is connected to the first ADC port.

5. The oil level detection system based on the software amplitude discrimination principle according to claim 4, characterized in that, The current sampling circuit includes an operational amplifier U4, resistors R8 and R9, and a capacitor C7. The inverting input of the operational amplifier U4 is connected to the capacitor under test through resistor R8, and the non-inverting input of the operational amplifier U4 is connected to resistor R9. A capacitor C7 is connected in parallel between resistor R9 and the negative power supply terminal of the operational amplifier U4. The output of the operational amplifier U4 is connected to the second ADC port through a current amplification circuit and a gain switching circuit.

6. The oil level detection system based on the software amplitude discrimination principle according to claim 5, characterized in that, The current amplification circuit includes an operational amplifier U5, resistors R10, R12, and R14. The inverting input of the operational amplifier U5 is connected to the capacitor under test through resistor R10, the non-inverting input of the operational amplifier U5 is connected to the output of the operational amplifier U4 through resistor R14, and the output of the operational amplifier U5 is connected to the MCU processor through resistor R12.

7. The oil level detection system based on the software amplitude discrimination principle according to claim 6, characterized in that, The gain switching circuit includes a chip U6 and a gain resistor. The chip U6 includes several parallel switching adjustment branches, all of which are connected to the RG1 port of the operational amplifier U5. The chip U6 also includes several analog switches, which are connected to the RG2 port of the operational amplifier U5 through the gain resistor. The input port of the chip U6 is connected to the MCU processor.

8. A method for oil level detection based on the software amplitude discrimination principle, implemented based on the oil level detection system according to any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Enable the DAC control module in the MCU processor and set a timing of 1μs to drive the N sinusoidal signal data generated before the DMA shift in the MCU processor to be output through the DAC port; Step 2: Smooth and shape the signal output from the DAC port using a smoothing and shaping circuit, and increase the bias voltage of the sine wave signal; Step 3: The MCU processor independently starts the voltage acquisition single channel and continuously acquires K sets of first voltage data from the voltage sampling circuit under the drive of the built-in timer of the MCU processor; Step 4: The MCU processor independently starts the single channel of current acquisition and continuously acquires K sets of second voltage data from the current sampling circuit under the drive of the built-in timer of the MCU processor; Step 5: The MCU processor extracts the first maximum voltage from the K sets of first voltage data, the MCU processor extracts the second maximum voltage from the K sets of second voltage data, calculates the second current using the second maximum voltage, and calculates the capacitance value of the capacitor under test using the first maximum voltage and the second current. Step 6: Calculate the oil level based on the capacitance value of the capacitor under test.

9. The oil level detection method based on software amplitude discrimination principle according to claim 8, characterized in that, In step 5, the formula for calculating the capacitance value of the capacitor to be tested is as follows: ； Where: C represents the capacitance value of the capacitor under test; I represents the second current; V represents the first maximum voltage; and f represents the operating frequency of the capacitor under test.

Images