Fuel oil density sensor and fuel oil density measuring method

Abstract

The invention discloses a fuel oil density sensor and a fuel oil density measuring method. The fuel oil density sensor comprises a density measuring circuit and a density assembly, according to the resonance period T and the fixed density coefficients K0 and K2 of the fuel oil, the real-time fuel oil density rho is obtained through calculation; the processing unit is used for sequentially screening the obtained square wave signals of the resonant frequency to obtain frequency signals of which the resonant period is between preset values, calculating to obtain a first frequency average value after obtaining n times of frequency signals, and obtaining n-1 times of frequency signals again to obtain a second frequency average value; calculating the obtained (n-1) times of frequency signals and the first frequency average value to obtain a second frequency average value, sequentially circulating, calculating the frequency average value of the (n-1) times of frequency signals obtained again and the frequency average value obtained by the previous calculation within the preset output time, and outputting the frequency average value obtained after the preset output time, and a resonance period T is obtained according to the output frequency average value. According to the invention, the problem of low measurement precision of the aircraft fuel oil density is solved, and the measurement precision of the fuel oil density is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of fuel density measurement of aerospace aircraft, and in particular relates to a fuel density sensor and a fuel density measurement method. Background Art

[0002] The fuel density sensor is an important component in the aerospace aircraft system and is mainly responsible for measuring the fuel density.

[0003] Traditional fuel density sensors use resistor plates to configure density coefficients, which results in density coefficient acquisition errors and occasional failures in density component excitation feedback caused by long cables on board, thus affecting the measurement accuracy of fuel density. With the annual improvement of aerospace aircraft performance, the requirements for fuel density measurement accuracy are constantly increasing, and traditional density sensors are gradually unable to meet the needs of fuel density measurement. Summary of the invention

[0004] The object of the present invention is to provide a fuel density sensor and a fuel density measurement method to solve the problem of low accuracy in measuring aircraft fuel density.

[0005] The present invention is achieved through the following technical solutions:

[0006] A fuel density sensor, comprising: a density measurement circuit and a density component, wherein the density measurement circuit comprises a sine wave excitation circuit, a signal acquisition and processing circuit and a processing unit connected in sequence;

[0007] The sine wave excitation circuit is used to generate a sine wave with a fixed frequency as an excitation signal for the density component;

[0008] The signal acquisition and processing circuit is used to obtain and process the sinusoidal fuel frequency carrier signal fed back by the density component, and output a resonant frequency square wave signal;

[0009] The processing unit is used to obtain the resonance period T according to the acquired resonance frequency square wave signal, and calculate the fuel density ρ according to the resonance period T and the fixed density coefficients K0 and K2 of the fuel;

[0010] The processing unit sequentially screens the acquired resonant frequency square wave signals to obtain frequency signals with a resonant period between preset values, obtains the frequency signals n times and calculates the first frequency average value, obtains the frequency signals n-1 times again and calculates the second frequency average value by adding the acquired n-1 frequency signals and the first frequency average value, and repeats the process in sequence. Within a preset output time, the frequency average value of the frequency signals n-1 times acquired again and the frequency average value calculated last time is calculated, the frequency average value obtained after the preset output time has passed is output, and the resonant period T is obtained based on the output frequency average value.

[0011] In some embodiments, the fuel density ρ is calculated based on the resonance period T and the fixed density coefficients K0 and K2 of the fuel. The calculation formula of the fuel density ρ is:

[0012] ρ=K0+K2T 2 (1).

[0013] In some embodiments, the signal acquisition and processing circuit includes a resonant circuit and a vibration pickup amplifier circuit connected in sequence, the resonant circuit is used to denoise the sinusoidal fuel frequency carrier signal fed back by the density component, and the vibration pickup amplifier circuit is used to amplify and shape the resonant frequency sinusoidal wave signal output by the resonant circuit.

[0014] In some embodiments, the resonant circuit includes a pickup coil and a resonant capacitor connected in parallel, and the capacitance value of the resonant capacitor is determined according to the pickup coil and the resonant cylinder in the density assembly, and the capacitance value of the resonant capacitor is:

[0015]

[0016] Among them, C is the capacitance of the resonant capacitor, L is the inductance of the pickup coil, and f is the resonant frequency of the resonant cylinder.

[0017] In some embodiments, the density measurement circuit further includes a D / A conversion circuit, the input end of which is connected to the output end of the processing unit, for converting the fuel density into a corresponding DC voltage signal as an output signal.

[0018] In some embodiments, the density measurement circuit also includes a V / I conversion circuit, the input end of the V / I conversion circuit is connected to the output end of the D / A conversion circuit, and is used to convert the DC voltage signal corresponding to the fuel density into a DC current signal as an output signal.

[0019] In some embodiments, an upper shell is further included, the density measurement circuit is integrated and installed in the upper shell, the density component is installed in the oil tank, and the upper shell is installed on the oil tank.

[0020] In some embodiments, the upper shell and the oil tank are detachably connected.

[0021] The present invention also relates to a fuel density measurement method of the above-mentioned fuel density sensor, comprising:

[0022] A fixed frequency sine wave is input to the density component to excite the density component to vibrate;

[0023] Collect and process the sinusoidal fuel frequency carrier signal fed back by the density component, and output a resonant frequency square wave signal;

[0024] The obtained resonant frequency square wave signal is screened to obtain a frequency signal with a frequency between preset values, and after obtaining the frequency signal n times, the first frequency average value is calculated, and after obtaining the frequency signal n-1 times again, the obtained n-1 frequency signal and the first frequency average value are calculated to obtain the second frequency average value, and the cycle is repeated successively. Within the preset output time, the frequency average value of the frequency signal obtained n-1 times again and the frequency average value obtained by the previous calculation is calculated, and the frequency average value obtained after the preset output time has passed is output, and the resonance period T is obtained according to the output frequency average value;

[0025] The fuel density ρ is calculated based on the resonance period T and the fixed density coefficients K0 and K2 of the fuel.

[0026] In some embodiments, it also includes:

[0027] The step of converting the fuel density into a corresponding DC voltage signal;

[0028] The step of converting the DC voltage signal corresponding to the fuel density into a DC current signal as an output signal.

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

[0030] 1. The present invention adopts a fixed frequency sine wave generated by a density measurement circuit as an excitation signal of a density component, thereby avoiding occasional failure of excitation feedback of a density component caused by a long cable; and reads a fixed density coefficient stored in a memory of the density measurement circuit to replace the traditional method of transmitting the density coefficient by collecting voltage of a resistor plate, thereby avoiding an error in collecting the density coefficient; and then uses a processing unit in the density measurement circuit to sequentially screen the acquired resonant frequency square wave signal to obtain a frequency signal with a resonant period between preset values, and after obtaining n frequency signals, calculates the first frequency average value, and after obtaining n-1 frequency signals again, calculates the acquired n-1 frequency signals and the first frequency average value to obtain the second frequency average value, and repeats the cycle in sequence. Within a preset output time, the frequency average value of the n-1 frequency signals acquired again and the frequency average value calculated last time is calculated, and the frequency average value obtained after the preset output time has passed is output, and the resonant period T is obtained according to the output frequency average value. The resonant period T obtained by this method has high accuracy, and the processing unit calculates the fuel density ρ according to the resonant period T and the fixed density coefficients K0 and K2 of the fuel, thereby improving the measurement accuracy of the fuel density.

[0031] 2. The capacitance value of the resonant capacitor is determined according to the vibration pickup coil and the resonant tube in the density component to suppress frequency noise and improve the measurement accuracy of fuel density.

[0032] 3. The density measurement circuit is integrated and installed in the upper shell, realizing the miniaturization and high integration of the fuel density sensor.

[0033] 4. The density measurement circuit is integrated and installed in the upper shell, and the density component is installed in the fuel tank. The upper shell and the fuel tank are detachably connected, which solves the problem that the traditional built-in fuel density sensor cannot be disassembled after being installed in the fuel tank. When the density measurement circuit fails, the density measurement circuit in the upper shell can be quickly disassembled for easy repair. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 1 is a block diagram of the working principle of the fuel density sensor in an embodiment of the present invention.

[0036] Figure 2 4 is a flowchart of a processing unit in an embodiment of the present invention.

[0037] Figure 3 FIG. 1 is a circuit diagram a of the FPGA in an embodiment of the present invention.

[0038] Figure 4 FIG. 2 is a circuit diagram b of the FPGA in an embodiment of the present invention.

[0039] Figure 5 4 is a circuit diagram of a crystal oscillator in an embodiment of the present invention.

[0040] Figure 6 FIG. 4 is a circuit diagram of a memory in an embodiment of the present invention.

[0041] Figure 7 4 is a circuit diagram of an asynchronous serial port transceiver in an embodiment of the present invention.

[0042] Figure 8 4 is a circuit diagram of a vibration pickup amplifier circuit in an embodiment of the present invention.

[0043] Fig. 9 4 is a circuit diagram of a D / A conversion circuit in an embodiment of the present invention.

[0044] Fig.10 4 is a circuit diagram of a V / I conversion circuit in an embodiment of the present invention.

[0045] Fig.11 Schematic diagram of the structure of the fuel density sensor in an embodiment of the present invention.

[0046] Wherein: 1-upper shell, 2-lower shell, 3-density measurement circuit, 4-density component. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0048] Example 1

[0049] A fuel density sensor, referring to Figure 1 and Figure 2 , including: a density measurement circuit 3 and a density component 4, the density measurement circuit 3 includes a sine wave excitation circuit, a signal acquisition and processing circuit and a processing unit connected in sequence;

[0050] The sine wave excitation circuit is used to generate a fixed frequency sine wave as an excitation signal for the density component; the fixed frequency sine wave generated by the density measurement circuit 3 is used as the excitation signal for the density component, thereby avoiding occasional failure of the excitation feedback of the density component 4 caused by the long cable.

[0051] The signal acquisition and processing circuit is used to obtain and process the sinusoidal fuel frequency carrier signal fed back by the density component 4, and output a resonant frequency square wave signal;

[0052] The processing unit is used to obtain the resonance period T according to the acquired resonance frequency square wave signal, and calculate the real-time fuel density ρ according to the resonance period T and the fixed density coefficients K0 and K2 of the fuel;

[0053] The processing unit sequentially screens the acquired resonant frequency square wave signals to obtain frequency signals with a resonant period between preset values, obtains the frequency signals n times and calculates the first frequency average value, obtains the frequency signals n-1 times again and calculates the second frequency average value by adding the first frequency average value, and repeats the process in sequence. Within a preset output time, the frequency average value of the frequency signals n-1 times acquired again and the frequency average value calculated last time is calculated, and the frequency average value obtained after the preset output time is output, and the resonant period T is obtained based on the output frequency average value.

[0054] The processing unit is used to screen the obtained resonant frequency square wave signal in sequence to obtain a frequency signal with a resonant period between 60us-65us, and the first frequency average value is calculated after obtaining 16 frequency signals, and the second frequency average value is obtained by calculating the 15 obtained frequency signals and the first frequency average value after obtaining 15 frequency signals again, and the frequency average value of the 15 obtained frequency signals and the frequency average value calculated last time is cycled in sequence. Within the preset output time, the frequency average value of the 15 obtained frequency signals again and the frequency average value calculated last time is calculated, and the frequency average value obtained after 2s is output, and the resonant period T is obtained according to the output frequency average value. The resonant period T obtained by this method has high accuracy, and the processing unit calculates the fuel density ρ according to the resonant period T and the fixed density coefficients K0 and K2 of the fuel, thereby improving the measurement accuracy of the fuel density.

[0055] The sine wave excitation circuit includes an operational amplifier D1016 and an operational amplifier D1017 which are connected in sequence.

[0056] Reference Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 and Figure 7 The processing unit includes FPGA D1031, crystal oscillator D1033, memory D1038, and asynchronous serial port transceiver D1035. The input end of the FPGA is connected to the output end of the signal acquisition and processing circuit. The FPGA is connected to the SPI interface of the crystal oscillator and the memory respectively through the transceiver interface of the asynchronous serial port transceiver; the crystal oscillator outputs a 50M clock base frequency for timing.

[0057] Reference Figure 2 , the algorithm IP core of the FPGA in the processing unit obtains the resonance period T according to the acquired resonance frequency square wave signal, and at the same time, the algorithm IP core of the FPGA reads the fixed density coefficients K0 and K2 of the fuel stored in the memory through the asynchronous serial port transceiver. The algorithm IP core of the FPGA is used to read the fixed density coefficient stored in the memory of the density measurement circuit 3 to replace the traditional method of transmitting the density coefficient using the resistor plate voltage acquisition method, thereby avoiding the density coefficient acquisition error.

[0058] In some embodiments, the fuel density ρ is calculated based on the resonance period T and the fixed density coefficients K0 and K2 of the fuel. The calculation formula of the fuel density ρ is:

[0059] ρ=K0+K2T 2 (1).

[0060] In some embodiments, the signal acquisition and processing circuit includes a resonant circuit and a vibration pickup amplifier circuit connected in sequence, the resonant circuit is used to denoise the sinusoidal fuel frequency carrier signal fed back by the density component 4, and the vibration pickup amplifier circuit is used to amplify and shape the resonant frequency sinusoidal wave signal output by the resonant circuit.

[0061] Among them, refer to Figure 8 The vibration pickup amplifier circuit includes an operational amplifier D1016, an operational amplifier D1017 and an operational amplifier D1021 which are connected in sequence.

[0062] The signal-to-noise ratio of the sinusoidal fuel frequency carrier signal processed by the resonant circuit is improved, meeting the circuit requirements, but the signal strength of the sinusoidal fuel frequency carrier signal is still weak and the amplitude is uncertain, so the sinusoidal fuel frequency carrier signal processed by the resonant circuit is amplified and shaped by the signal of the vibration pickup amplifier circuit; the vibration pickup amplifier circuit adopts a two-stage fixed gain amplifier circuit for amplification, the operational amplifier D1016 is the first stage amplifier circuit, the first stage amplifier circuit amplifies the sinusoidal fuel frequency carrier signal by 4.3 times, the operational amplifier D1017 is the second stage amplifier circuit, the second stage amplifier circuit amplifies the sinusoidal fuel frequency carrier signal by another 5.7 times, and the total amplification multiple of the sinusoidal fuel frequency carrier signal by the two-stage amplifier circuit is 4.3 times × 5.7 times = 24.51 times; the two-stage amplifier circuits are both same-end amplification, which increases the input resistance of the amplifier circuit and reduces the influence on the previous stage amplifier circuit.

[0063] The amplitude of the amplified sinusoidal fuel frequency carrier signal exceeds the bias voltage of the follower of operational amplifier D1021. Operational amplifier D1021 shapes the amplified sinusoidal fuel frequency carrier signal into a square wave signal, outputs a resonant frequency square wave signal of 3.3V, and clamps the amplitude of the resonant frequency square wave signal to 3.3V for collection by the processing unit.

[0064] In some embodiments, the resonant circuit includes a pickup coil and a resonant capacitor connected in parallel. The capacitance value of the resonant capacitor is determined according to the pickup coil and the resonant cylinder in the density component 4. The capacitance value of the resonant capacitor is:

[0065]

[0066] Among them, C is the capacitance of the resonant capacitor, L is the inductance of the pickup coil, and f is the resonant frequency of the resonant cylinder.

[0067] The input end of the resonant circuit is used to obtain the sinusoidal fuel frequency carrier signal fed back by the density component 4, and the output end of the resonant circuit is connected to the input end of the operational amplifier D1016; the resonant capacitor is capacitor C1041.

[0068] The vibration period of aviation fuel RP3 varies with the temperature of the resonance cylinder. However, according to the type of fuel and resonance cylinder, it can be determined that the vibration period range is generally between 60us-65us, and the corresponding frequency range is 15.4kHz-16.7kHz. If the midpoint resonance frequency of 16kHz is selected, then:

[0069]

[0070] The inductance L of the vibration pickup coil is about 0.1H, so the capacitance of capacitor C1041 can be calculated to be 1000pF. By selecting a capacitor that matches the fuel and the resonance cylinder, the vibration information picked up can be completely saved and pulled down, frequency noise can be suppressed, and the fuel density measurement accuracy can be improved.

[0071] In some embodiments, the density measurement circuit 3 further includes a D / A conversion circuit, the input end of which is connected to the output end of the processing unit, for converting the fuel density into a corresponding DC voltage signal as an output signal.

[0072] Among them, refer to Fig. 9 The D / A conversion circuit includes a D / A converter D1039. The fuel density is converted into a DC voltage proportional to the fuel density value by the D / A converter D1039. The DC voltage corresponding to the fuel density is output using a 1V-5V standard sensor output voltage interface. The D / A converter periodically outputs a DC voltage corresponding to the fuel density after every 1s.

[0073] In some embodiments, the density measurement circuit 3 also includes a V / I conversion circuit, the input end of the V / I conversion circuit is connected to the output end of the D / A conversion circuit, and is used to convert the DC voltage signal corresponding to the fuel density into a DC current signal as an output signal.

[0074] Among them, refer to Fig.10 The V / I conversion circuit adopts a practical improved version of the Howland current source circuit. Compared with the Howland current source circuit, the output current direction in the circuit principle is the same as the input voltage direction, which is the same as the actual circuit situation and is convenient to use. The V / I conversion circuit includes a conversion resistor R1078 and an operational amplifier D1037; the conversion resistor is used to control the V / I conversion coefficient, and the operational amplifier D1037 constitutes a common-phase summation circuit and a voltage follower to ensure a stable output of 4mA-20mA DC current. The host computer uses a 4mA-20mA standard sensor current interface to collect the DC current corresponding to the fuel density output by the V / I conversion circuit.

[0075] During long-distance transmission, the 4mA-20mA current signal is more stable than the 1V-5V voltage signal and is not easily affected by cable resistance and attenuated. Therefore, using a DC current signal instead of a DC voltage signal to transmit fuel density can reduce signal attenuation during long-distance transmission, ensure the accuracy of the signal transmitted to the host computer, and improve the measurement accuracy of fuel density.

[0076] In some embodiments, reference Fig.11 The fuel density sensor also includes an upper shell 1 and a lower shell 2. A density measurement circuit 3 is integrated in the upper shell, and a density component 4 is arranged in the lower shell.

[0077] Among them, the components in the density measurement circuit are all packaged in the smallest military standard, and are integrated and installed in the upper shell with the highest integration, realizing the miniaturization and high integration of the fuel density sensor. While the density measurement circuit 3 is integrated and installed in the upper shell, it is ensured that the installation method and installation size of the sensor of the present application remain unchanged with the original density sensor, and the structure and size in the fuel tank remain unchanged, without affecting the installation of other products in the fuel tank, and only the length of the upper shell 1 outside the fuel tank is increased, without affecting the installation of cables and pipelines outside the fuel tank.

[0078] In some embodiments, the upper shell 1 and the lower shell 2 are detachably connected.

[0079] A detachable split structure is adopted between the upper shell 1 and the lower shell 2, which solves the problem that the traditional built-in fuel density sensor cannot be disassembled after being installed in the fuel tank. When the density measurement circuit 3 fails, the density measurement circuit 3 in the upper shell can be quickly disassembled for easy repair.

[0080] The present invention also relates to a fuel density measurement method of the above-mentioned fuel density sensor, comprising:

[0081] Input a fixed frequency sine wave to the density component 4 to excite the density component 4 to vibrate;

[0082] Collect and process the sinusoidal fuel frequency carrier signal fed back by the density component 4, and output a resonant frequency square wave signal;

[0083] The obtained resonant frequency square wave signal is screened to obtain a frequency signal with a frequency between preset values, and after obtaining the frequency signal n times, the first frequency average value is calculated, and after obtaining the frequency signal n-1 times again, the obtained n-1 frequency signal and the first frequency average value are calculated to obtain the second frequency average value, and the cycle is repeated successively. Within the preset output time, the frequency average value of the frequency signal obtained n-1 times again and the frequency average value obtained by the previous calculation is calculated, and the frequency average value obtained after the preset output time has passed is output, and the resonance period T is obtained according to the output frequency average value;

[0084] The fuel density ρ is calculated based on the resonance period T and the fixed density coefficients K0 and K2 of the fuel.

[0085] In some embodiments, the fuel density measurement method further includes:

[0086] The step of converting the fuel density into a corresponding DC voltage signal;

[0087] The step of converting the DC voltage signal corresponding to the fuel density into a DC current signal as an output signal.

[0088] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A fuel density sensor, characterized in that: include: A density measurement circuit and a density component, wherein the density measurement circuit comprises a sine wave excitation circuit, a signal acquisition and processing circuit, and a processing unit connected in sequence; The sine wave excitation circuit is used to generate a sine wave with a fixed frequency as an excitation signal for the density component; The signal acquisition and processing circuit is used to obtain and process the sinusoidal fuel frequency carrier signal fed back by the density component, and output a resonant frequency square wave signal; The processing unit is used to obtain the resonance period T according to the acquired resonance frequency square wave signal, and calculate the fuel density ρ according to the resonance period T and the fixed density coefficients K0 and K2 of the fuel; The processing unit sequentially screens the acquired resonant frequency square wave signals to obtain frequency signals with a resonant period between preset values, obtains the frequency signals n times and calculates the first frequency average value, obtains the frequency signals n-1 times again and calculates the second frequency average value by adding the acquired n-1 frequency signals and the first frequency average value, and repeats the process in sequence. Within a preset output time, the frequency average value of the frequency signals n-1 times acquired again and the frequency average value calculated last time is calculated, the frequency average value obtained after the preset output time has passed is output, and the resonant period T is obtained based on the output frequency average value.

2. A fuel density sensor according to claim 1, characterized in that: The fuel density ρ is calculated based on the resonance period T and the fixed density coefficients K0 and K2 of the fuel. The calculation formula of the fuel density ρ is: p=K0+K2T 2 (1)。 3. A fuel density sensor according to claim 1, characterized in that: The signal acquisition and processing circuit includes a resonant circuit and a vibration pickup amplifier circuit connected in sequence. The resonant circuit is used to perform noise removal on the sinusoidal fuel frequency carrier signal fed back by the density component, and the vibration pickup amplifier circuit is used to perform signal amplification and shaping on the resonant frequency sinusoidal wave signal output by the resonant circuit.

4. A fuel density sensor according to claim 3, characterized in that: The resonant circuit includes a pickup coil and a resonant capacitor connected in parallel. The capacitance value of the resonant capacitor is determined according to the pickup coil and the resonant cylinder in the density component. The capacitance value of the resonant capacitor is: Among them, C is the capacitance of the resonant capacitor, L is the inductance of the pickup coil, and f is the resonant frequency of the resonant cylinder.

5. A fuel density sensor according to claim 1, characterized in that: The density measurement circuit also includes a D / A conversion circuit, the input end of which is connected to the output end of the processing unit and is used to convert the fuel density into a corresponding DC voltage signal as an output signal.

6. The density measurement circuit according to claim 5 is characterized in that: The density measurement circuit also includes a V / I conversion circuit, the input end of which is connected to the output end of the D / A conversion circuit, and is used to convert a DC voltage signal corresponding to the fuel density into a DC current signal as an output signal.

7. A fuel density sensor according to claim 1, characterized in that: It also includes an upper shell, the density measurement circuit is integrated and installed in the upper shell, the density component is installed in the oil tank, and the upper shell is installed on the oil tank.

8. A fuel density sensor according to claim 7, characterized in that: The upper shell and the oil tank are detachably connected.

9. A method for measuring fuel density based on the fuel density sensor according to any one of claims 1 to 8, characterized in that: include: A fixed frequency sine wave is input to the density component to excite the density component to vibrate; Collect and process the sinusoidal fuel frequency carrier signal fed back by the density component, and output a resonant frequency square wave signal; The obtained resonant frequency square wave signal is screened to obtain a frequency signal with a frequency between preset values, and after obtaining the frequency signal n times, the first frequency average value is calculated, and after obtaining the frequency signal n-1 times again, the obtained n-1 frequency signal and the first frequency average value are calculated to obtain the second frequency average value, and the cycle is repeated successively. Within the preset output time, the frequency average value of the frequency signal obtained n-1 times again and the frequency average value obtained by the previous calculation is calculated, and the frequency average value obtained after the preset output time has passed is output, and the resonance period T is obtained according to the output frequency average value; The fuel density ρ is calculated based on the resonance period T and the fixed density coefficients K0 and K2 of the fuel.

10. A fuel density measurement method according to claim 9, characterized in that: Also includes: The step of converting the fuel density into a corresponding DC voltage signal; The step of converting the DC voltage signal corresponding to the fuel density into a DC current signal as an output signal.

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