A passive clutter suppression circuit for an aviation rotation speed signal and a design method thereof

Abstract

The application belongs to the technical field of clutter suppression, and provides a passive clutter suppression circuit for an aviation rotating speed signal and a design method thereof. The principle of the rotating speed signal of the airplane is analyzed, appropriate capacitors are selected, and the clutter in the rotating speed signal is filtered to the maximum extent without affecting the transmission of the airplane signal itself. The shortcomings of using shielding lines to filter only spatial electromagnetic clutter are overcome. Not only the clutter generated by the space coupling of the magnetic motor, the generator and the communication navigation device of the airplane itself can be filtered, but also the clutter generated by the power grid fluctuation can be filtered, so that the normal display of the rotating speed is realized. According to the specific rotating speed signal parameters of different airplanes, the passive clutter suppression circuit can be designed by the design method provided by the application, so that the airplane rotating speed signal is more pure, the rotating speed jump caused by the rotating speed clutter is reduced, and the safety of the navigation airplane during flight is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of clutter suppression, and particularly relates to a passive clutter suppression circuit for an aviation rotating speed signal and a design method thereof, which can be applied to the aviation aircraft maintenance industry. BACKGROUND

[0002] In the field of aviation aircraft maintenance, the purity of the aircraft rotating speed signal directly affects the accuracy of the flight instrument data and the flight safety. The traditional clutter suppression technology mainly reduces the clutter interference generated by the spatial electromagnetic field coupling through the way of adding a shielding layer outside the signal line. However, such a passive shielding scheme has significant limitations: firstly, it can only weaken the electromagnetic clutter (such as the spatial coupling interference generated by the magneto, generator, communication navigation equipment, etc.) that invades through the spatial radiation approach, but cannot suppress the power grid fluctuation clutter that is transmitted through the power network; secondly, the shielding layer may introduce signal attenuation or impedance mismatch problems, affecting the transmission quality of the original rotating speed signal. In addition, due to the compact equipment layout and complex electromagnetic environment of the aviation aircraft, the rotating speed sensor signal of the aircraft is easily subjected to the double interference of the spatial coupling clutter and the power grid transmission clutter, resulting in phenomena such as rotating speed jump and data distortion in the instrument display. The existing technology lacks a coordinated suppression scheme for the two types of clutter, and it is difficult to meet the needs of the aviation aircraft for high precision and high reliability of the rotating speed signal, which has become a key technical bottleneck restricting flight safety. SUMMARY

[0003] The purpose of the application is to overcome the existing defects, provide a passive clutter suppression circuit for an aviation rotating speed signal and a design method thereof. Through the design method of the clutter suppression circuit, a passive clutter suppression circuit can be designed according to the specific engine rotating speed signal parameters of the aircraft, which can suppress the clutter generated by the complex electromagnetic environment of the aviation aircraft, so as to make the rotating speed signal more pure, reduce the rotating speed jump caused by the rotating speed clutter, and improve the safety of the aviation aircraft during flight.

[0004] In order to solve the above technical problems, the application provides the following technical scheme:

[0005] A design method of a passive clutter suppression circuit for an aviation rotating speed signal includes the following steps:

[0006] (1) Analyze the sensor principle of the target aircraft model, obtain the principle of the internal rotating speed signal formation of the sensor, the equivalent amplifier model and the equivalent resistance value;

[0007] (2) Determine the relationship between the engine rotating speed and the signal frequency, verify the mechanism of the engine parameter collector triggered by the rising edge / falling edge of the square wave, and determine that the duty cycle change does not affect the counting of the engine parameter collector;

[0008] (3) Measure the voltage recognition range of the engine parameter collector to the speed signal, and determine the threshold voltage of the engine parameter collector;

[0009] (4) Analyze the characteristics of the clutter signal, and identify that the clutter is a high-frequency sharp pulse and only affects the signal in the high-level stage;

[0010] (5) Based on the high-frequency characteristics of the clutter signal, a passive clutter suppression circuit composed of a capacitor is designed, which is connected in series between the signal line and the ground line between the speed sensor and the engine parameter collector;

[0011] (6) Determine the capacitor value range through the charging time constant formula, and the constraint condition is that the selected capacitor value should be charged to the voltage value that the engine parameter collector can recognize within the allowed shortest charging time;

[0012] (7) Test the filtering effect of the minimum unit capacitor in parallel by using the cumulative progressive method to determine the optimal capacitor value;

[0013] (8) Select two safety capacitors in series to improve the voltage resistance and safety, and form the final clutter suppression circuit.

[0014] Further, in step (2), the relationship between the engine speed and the acquisition signal frequency is:

[0015] RPM=40*f

[0016] Where RPM is the engine speed and f is the acquisition signal frequency.

[0017] Further, in step (6), the capacitor value range is calculated by the following formula:

[0018] , and t≥1 / (V*2)

[0019] Where t is the half cycle time corresponding to the maximum speed, R is the internal pull-up resistor value of the engine parameter collector, is the minimum voltage that the engine parameter collector can recognize, and V is the maximum recognition frequency of the target model.

[0020] Further, in step (7), the cumulative progressive method is used to test the filtering effect of the minimum unit capacitor in parallel to determine the optimal capacitor value, including:

[0021] Using the cumulative progressive method, a capacitor of 0.01uf is used as the smallest cumulative unit, and the capacitor is connected in parallel between the speed sensor signal line and the ground line of the aircraft through the breadboard and test line, then the aircraft is tested, and whether the interference still exists is observed. If the interference still exists, another 0.01uf capacitor is connected in parallel, and so on, until the capacitor value range is reached.

[0022] Another purpose of the present application is to provide a passive spurious wave suppression circuit for an aviation rotating speed signal, comprising two safety capacitors connected in series, a female plug connected to the two safety capacitors, and a test interface connected in parallel between the two safety capacitors.

[0023] Further, the safety capacitor has a capacitance of 0.22uf.

[0024] In combination with the above technical solution, the present application has the following beneficial effects compared with the prior art:

[0025] The design method of the present application can make the designed passive spurious wave suppression circuit have equal filtering effect on space coupling spurious waves and physical coupling spurious waves (i.e. physical coupling of spurious waves through the power grid, internal of GEA, or lead wire); the spurious wave suppression effect is good, does not affect the GEA rotating speed indication, and has a wide frequency range of resistance to spurious wave signals; after failure of the device (e.g. breakdown by power surge, or other factors), the original rotating speed display of the aircraft is not affected, i.e. the rotating speed display of the aircraft will return to the state without the spurious wave suppression device.

[0026] The present application analyzes the principle of the aircraft rotating speed signal, filters the spurious waves in the rotating speed signal to the maximum extent through ingenious capacitor combination, without affecting the transmission of the aircraft signal itself, overcomes the shortcomings of using shielding wires to filter only space electromagnetic spurious waves, and can not only filter the spurious waves generated by the space coupling of the aircraft itself magneto, generator, and communication navigation device, but also filter the spurious waves generated by power grid fluctuations, thereby realizing normal display of the rotating speed. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, illustrate the present application together with the embodiments thereof, and explain the present application, but do not constitute a limitation of the present application. In the drawings:

[0028] Figure 1 is a flowchart of the design method provided by the embodiment of the present application;

[0029] Figure 2 is a rotating speed sensor principle diagram of the SR20G3 aircraft provided by the embodiment of the present application;

[0030] Figure 3 is a spurious wave characteristic diagram provided by the embodiment of the present application;

[0031] Figure 4 is a GEA signal superposition simulation diagram affected by spurious waves provided by the embodiment of the present application, wherein (a) is a high-frequency triangular wave, (b) is a square wave, and (c) is a superimposed signal received by the GEA;

[0032] Figure 5 is a waveform diagram after using capacitor rectification provided by the embodiment of the present application;

[0033] Figure 6 is an equivalent circuit diagram for suppressing spurious waves using a capacitor provided by an embodiment of the present application;

[0034] Figure 7 is a schematic diagram of a passive spurious wave suppression circuit for an aviation rotation speed signal provided by an embodiment of the present application. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present application are described below in conjunction with the accompanying drawings, in which it is understood that the preferred embodiments described below merely for the purpose of illustrating and explaining the present application, and are not intended to limit the present application.

[0036] Embodiment 1: as shown in the figure, it is an embodiment of a design method of a passive spurious wave suppression circuit for an aviation rotation speed signal provided by the present application, comprising the following steps: Figure 1

[0037] S1: analyzing the principle of the sensor of the target model, obtaining the principle of the internal rotation speed signal formation of the sensor, the equivalent amplifier model and the equivalent resistance value;

[0038] S2: determining the relationship between the engine rotation speed and the signal frequency, verifying the mechanism of the engine parameter collector triggered by the rising edge / falling edge of the square wave, and determining that the duty cycle change does not affect the counting of the engine parameter collector;

[0039] S3: measuring the voltage recognition range of the engine parameter collector to the rotation speed signal, and determining the threshold voltage of the engine parameter collector;

[0040] S4: analyzing the characteristics of the spurious wave signal, identifying that the spurious wave is a high-frequency sharp pulse and only affects the signal in the high-level stage;

[0041] S5: based on the high-frequency characteristics of the spurious wave signal, designing a passive spurious wave suppression circuit composed of a capacitor, which is connected in series between the signal line and the ground line between the rotation speed sensor and the engine parameter collector;

[0042] S6: determining the capacitance value range by the charging time constant formula, and the constraint condition is that the selected capacitance value should be charged to the voltage value recognizable by the engine parameter collector within the allowed shortest charging time;

[0043] S7: using the cumulative progressive method to test the filtering effect of the minimum unit capacitor in parallel, and determining the optimal capacitance value;

[0044] S8: selecting two safety capacitors in series to improve the voltage resistance and safety, and forming the final spurious wave suppression circuit.

[0045] ​It should be noted that the sensor principle of the target model is analyzed, and the purpose is to determine the connection mode and the value range of the capacitance in the later circuit design. The threshold value of the engine parameter collector in different aircrafts may be different due to the circuit design, which needs to be determined according to the level signal accepted by the collector.

[0046] As preferred, in step S2 of the embodiment of the application, the relationship between the engine speed and the acquisition signal frequency is:

[0047] RPM=40*f

[0048] Wherein, RPM is the engine speed, and f is the acquisition signal frequency.

[0049] Further, in step S6, the capacitance value range is calculated by the following formula:

[0050] , and t≥1 / (V*2)

[0051] Wherein, t is the half cycle time corresponding to the maximum speed, R is the resistance value of the internal pull-up resistor of the engine parameter collector, is the minimum voltage that can be recognized by the engine parameter collector, and V is the maximum recognition frequency of the target model. The value of V is related to the maximum speed that can be recognized by the model, that is, the sensor signal output frequency under the maximum speed, which needs to be measured by an oscilloscope.

[0052] As preferred, in step S7 of the embodiment of the application, the cumulative progressive method is used to test the filtering effect of the minimum unit capacitance to determine the optimal capacitance value, including:

[0053] Using the cumulative progressive method, taking 0.01uf capacitance as the minimum cumulative unit, connecting the capacitance through the breadboard and test line in parallel between the speed sensor signal line and ground line of the aircraft, then the aircraft is tested, and whether the speed signal still exists interference is observed, if the interference still exists, another 0.01uf capacitance is connected in parallel, and so on, until the value range of the capacitance is reached.

[0054] Next, taking SR20G3 aircraft as an example, the specific scheme of the passive clutter suppression circuit for the aviation speed signal is further described.

[0055] (1) The sensor principle of the specific model is analyzed, and the principle of the internal speed signal formation of the sensor, the equivalent amplifier model and the equivalent resistance value (R) need to be analyzed and measured.

[0056] For example, Figure 2As shown, the left frame is the internal principle diagram of SR20G3 aircraft sensor, the probe part is a Hall element, which is used to sense the magnetic field change of rotating parts, thereby generating a small voltage change, which is sent to the trigger circuit and amplifier circuit in the back end, and finally the signal is sent to the amplifier triode, through the internal pull-up resistor of GEA (engine parameter collector), and finally a square wave signal with a duty cycle of 50% is formed, that is, PWM wave.

[0057] (2) The collection and analysis of the speed signal of a specific aircraft model requires analyzing the mathematical relationship between the aircraft speed and the signal frequency, and analyzing the triggering mechanism of the internal counter of the aircraft signal collector.

[0058] When the speed increases, the frequency of the signal increases, but the duty cycle of the signal remains unchanged. The internal GEA calculates the aircraft engine speed by sensing the frequency of the signal. The relationship between the engine speed RPM and the signal frequency f is:

[0059] RPM=40*f

[0060] Therefore, through analysis, it can be determined that the internal engine speed indication principle of GEA is: the frequency counter is triggered by the rising or falling edge. The duty cycle of PWM does not affect the GEA counting within the range of (0%, 100%).

[0061] (3) Measurement of the voltage recognition range of the speed signal of a specific aircraft model.

[0062] Through experiments, it is found that when the high-level voltage of the PWM wave is greater than 3.5V, it can be correctly recognized by GEA, that is, the threshold voltage of GEA counting is 3.5V.

[0063] The characteristics of the noise are measured by experimental method. The noise signal will produce a downward spike on the high level of the PWM wave. Through the above analysis, it can be known that when the downward spike amplitude is lower than about 3.5V, it will be counted by the internal counter of GEA, thereby changing the frequency of the PWM wave, resulting in distortion of the aircraft engine speed.

[0064] (4) Analysis and identification of the characteristics of the noise signal.

[0065] The characteristics of the speed noise signal are that when the triode inside the speed sensor (see Figure 2 ) is turned off, the signal line is in a suspended state, which is more susceptible to electromagnetic noise signals. Electromagnetic signals or electromagnetic pulses are coupled to the signal line to form noise signals. The overall performance of the noise signal is that in the high level stage of the speed signal square wave, a high-frequency upward or downward spike pulse appears. As Figure 3 shown.

[0066] When the three-level tube is turned on, the signal line is grounded, and at this time, even if there are spurious signals, the spurious signals will be grounded and will not enter the GEA. High-level downward spike pulse, when falling to the low-level highest identification voltage of GEA, GEA considers that an identification pulse is identified, which will make the speed indication instantaneously large, and if multiple downward spike pulses are encountered in a short time, the GEA may measure a frequency greater than 3500 RPM corresponding to the speed of the speedometer. The above analysis also explains why the SR20G3 speed signal has been large for many years and will not be small when it is affected by spurious signals.

[0067] (5) Based on the mathematical analysis of the spurious signal, the capacitance value range of the passive spurious signal suppression device is designed, which requires a pre-capacitor to be inserted into the signal line and the bottom line between the sensor and the aircraft GEA as a pre-passive spurious signal suppression circuit. The capacitance value range is obtained as follows:

[0068] The most suitable capacitance value is selected through theoretical analysis and calculation to form a spurious signal suppression device to filter spurious signals, and the analysis process is as follows:

[0069] Mathematical characteristics of spurious signals:

[0070] The signal frequency is high, several orders of magnitude higher than the speed signal frequency.

[0071] Let the frequency of a certain spurious signal be f 杂波 ,

[0072] f 杂波 = K * f 方波

[0073] The amplitude of the spurious signal can be assumed to be A;

[0074] According to Fourier transform, any signal can be decomposed into a combination of infinite sinusoidal signals, i.e. the superposition of infinite sinusoidal signals with fundamental frequency f and harmonic frequency n*f, n∈[1,∞).

[0075] According to the characteristics of the spurious signal, the spurious signal is simplified as a high-frequency triangular wave, and the signal emitted by the sensor itself is a square wave signal, so the signal finally accepted by GEA is the superposition of high-frequency triangular wave and square wave signal. The simulation of spurious signals is shown. Figure 4

[0076] The mathematical expression of the spurious signal is:

[0077]

[0078] wherein​ ;

[0079] The expression of the square wave signal is (the square wave signal is a determined maximum amplitude of 5V, and all are positive values):

[0080] Wherein ;

[0081] Therefore, the superimposed signal waveform function after the clutter is:

[0082] (6) Obtain the capacitance value range of the passive clutter suppression device under the condition of multiple restrictions:

[0083] The focus of the application is how to design the passive clutter suppression device, which requires to reduce the amplitude of the to the maximum extent, and does not affect the input of the original rotation speed signal. If the passive clutter suppression device is designed, only passive electronic components such as capacitors, inductors and resistors can be used to design the clutter suppression device. After repeated tests and demonstrations, it is found that only capacitive components can be used to design the clutter suppression device, and the introduction of inductors or resistors in the circuit will make the signal shape change too much, and the input distortion occurs. The following is the demonstration process of the selection of the capacitance value of the clutter suppression device of the application:

[0084] As shown in Figure 5 , it is the waveform diagram after using capacitor rectification, wherein is the highest capacitor voltage that can be reached in each charging period, T 充电 = 1 / 2 * T 方波 That is, when the transistor inside the rotation speed sensor is turned off, the 5V voltage source inside the GEA charges the capacitor through R. When the transistor is turned on, the capacitor discharges through the transistor. Due to the existence of 5V power supply and resistor R, when the capacitor discharging is terminated, the voltage across the capacitor is equal to the saturation voltage drop of the transistor, which is 0.14V according to the rotation speed sensor chip manual. It drops to about 0 at the moment after the vertex, because the potential at point A of the capacitor is pulled down to 0.14V by the transistor when the transistor is turned on, but the voltage across the capacitor does not change at this moment. As shown in Figure 6 , it is the equivalent circuit diagram for using capacitors to suppress clutter in the embodiment of the application.

[0085] Since GEA can only recognize the signal when ≥ 3.5V, the selected capacitance value should be charged to at least 3.5V (3.5V has a recognition margin) within the allowed minimum charging time [3500 RPM, 87.5 Hz].

[0086] If the 0.14V reserved voltage at the beginning of the capacitor charging is ignored, the calculation condition for the capacitor will be more severe and conservative if it starts from 0V, because it is more difficult for the capacitor to charge to 3.5V within the specified time if it starts from 0V than from 0.14V.

[0087] According to the principle of circuit analysis, we know that:

[0088] Then:

[0089] Because: ≥ 3.5V

[0090] Therefore: ≤ 1-3.5 / 5 = 0.3

[0091] Therefore ≤ 0.3, according to the definition of exponential function Always greater than 0, so take the logarithm of both sides, the direction of inequality does not change, then:

[0092] -t / RC ≤ ln(0.3) = -1.2040

[0093] Multiply both sides by -1, the direction of inequality changes, then:

[0094] t / RC ≥ 1.2040

[0095] C ≤ t / (R*1.2040), and t ≥ 1 / (87.5*2) (corresponding to half the period at the maximum recognition speed of 3500rpm)

[0096] So When t = 1 / (87.5*2), it can be guaranteed that the capacitor will be within the range of 3500RPM, Always greater than 3.5V, ensuring that GEA can indicate normally.

[0097] (7) Based on the design and demonstration of the safety of the passive clutter suppression device for the aircraft speed signal, the clutter suppression device is connected between the speed sensor and the GEA, which will not cause damage to other equipment, and the heat energy released by the capacitor can be ignored.

[0098] Through analysis, it is determined that the addition of the capacitor type clutter suppression device will not cause damage to existing equipment, and the clutter suppression device will not affect the normal display of the speed:

[0099] Assuming that the maximum limit of the capacitor value is 0.157uF, according to the definition of power:

[0100]

[0101] Since a capacitor completes one charge-discharge cycle, according to the formula for capacitor charging energy, the energy stored in a single charge is:

[0102]

[0103] The power of the energy released by the capacitor is:

[0104]

[0105] And because of frequency Therefore, the following formula can be transformed into:

[0106] MATLAB calculations show that when hour, .

[0107] The energy released by the capacitor will be absorbed by other electronic components and eventually dissipated as heat. As can be seen from the above deduction, the energy released by the capacitor is very small and its impact on other aircraft equipment is almost negligible.

[0108] (8) Design of passive clutter suppression circuit based on constraints. Through the design methods in steps (1) to (7), the constraints of the passive clutter suppression circuit have been determined. The schematic diagram of the passive clutter suppression circuit is designed based on these constraints, as shown below. Figure 7 As shown.

[0109] (9) Obtaining the final capacitance value under experimental conditions. The initial design method only determined the range of capacitance values, but it is necessary to determine the capacitance value with the best clutter suppression effect through experiments. Although theoretically, the larger the capacitance value, i.e., the closer it is to 0.157uF, the more obvious the filtering effect of the capacitor on clutter, another factor needs to be considered, i.e., the larger the capacitance value, the more obvious the filtering effect of the capacitor on clutter. According to the formula...

[0110] but The smaller, the more likely it is to cause The capacitor is closer to the trigger voltage of the GEA's internal counter. At this point, even a small disturbance will cause the GEA's internal counter to trigger more easily, which will reduce the filtering effect on noise. Therefore, the specific capacitor size to choose needs to be tested experimentally on the aircraft. The specific method is as follows:

[0111] An incremental accumulation method was adopted, using a 0.01uf capacitor as the smallest accumulation unit. A faulty aircraft with clutter interference was selected, and the capacitor was connected in parallel between the aircraft speed sensor signal line and ground via a breadboard and test leads. The aircraft was then test-run to observe whether the interference still existed. If the interference still existed, another 0.01uf capacitor was connected in parallel, and so on, until the capacitance value was reached.

[0112] (10) Select the safety capacitor, PCB circuit production, electronic components welding, to suppress the shell and interface design, complete the invention.

[0113] Examples:

[0114] Through the design method of step (1) ~ step (8), the capacitance value of SR20G3 aircraft signal clutter suppression device is determined:

[0115] After measurement, it is known that the SR20G3 aircraft GEA internal pull-up resistor R=30.1KΩ. Therefore:

[0116]

[0117] That is, the capacitance C ≤0.157uF, that is, the GEA can be guaranteed to indicate normally in the range of 0~3500RPM speed.

[0118] Through the experimental method of step (9), it is determined that when the capacitance value is 0.1uF, the clutter suppression effect is best, so this example is composed of two series 0.22uF (equivalent 0.11uF) capacitors to form a passive clutter signal suppression circuit.

[0119] The capacitor used in this example is selected as a safety capacitor. Because the safety capacitor is open circuit when it fails, if the capacitor is punctured, it will not cause the sensor signal line and ground short circuit, thereby affecting the speed display. By adopting two capacitors in series, the withstand voltage value is twice that of a single capacitor, which can improve the safety margin.

[0120] This example has calculated C ≤0.157uF, but to use a capacitor with how much capacitance will make the filtering effect best and not affect the speed itself, a large number of experiments and a large amount of cost need to be carried out on the real aircraft. The following will introduce the process of obtaining the capacitance value:

[0121] First, select a fault aircraft that can produce stable clutter. By consulting the fault data of a unit managed aircraft, a fault aircraft is finally selected for capacitance acquisition experiment.

[0122] First, make a test line, which can be connected in parallel to the signal line and ground line of the sensor, and a breadboard is connected at the end of the test line.

[0123] Through calculation, the 0.001 uf level capacitor has limited filtering effect, therefore, when determining the capacitor value, the cumulative method is adopted, that is, a 0.01 uf capacitor is inserted into the breadboard, and then the airplane is ground tested for 1 hour, firstly, whether the capacitor can effectively filter the noise is observed, and secondly, whether the capacitor has influence on other signals of the airplane is observed. If the filtering effect is not good, a 0.01 uf capacitor is connected in parallel on the breadboard, and the total capacitor value becomes 0.02 uf, and then the ground test is performed for 1 hour. In this way, the test is performed for 15 times, and the capacitor value is gradually accumulated to 0.15 uf. Finally, it is obtained through experiment that when the capacitor value is about 0.1 uf, the filtering effect is the best.

[0124] Due to the specification limitation of the market safety capacitor, two 0.22 uf safety capacitors are selected to be connected in series, and the scheme of equivalent 0.11 uf capacitor can achieve good filtering effect.

[0125] The embodiment of the present application provides a passive noise suppression circuit for an aviation rotating speed signal, which comprises two safety capacitors connected in series, a female plug connected to the two safety capacitors, and a test interface connected in parallel between the two safety capacitors.

[0126] In use, the passive noise suppression circuit can be integrated on a PCB circuit board, and packaged by a shell, and the female plug is extended on the side of the shell, so that a passive noise suppression device is obtained. In use, a male plug of DB9 needs to be introduced between the signal line and the ground line of the target airplane rotating speed sensor, the male plug is inserted into the female plug, and the screws at both ends of the plug are locked, so that the device can suppress the noise of the airplane rotating speed signal through the noise suppression circuit, and the normal display of the airplane rotating speed is not affected.

[0127] It should be understood that, although each step in the flowchart of each embodiment of the present application is displayed in sequence according to the arrow, these steps are not necessarily executed in sequence according to the arrow. Unless otherwise specified in the present application, the execution of these steps has no strict sequence limitation, and these steps can be executed in other sequences. Moreover, at least part of the steps in each embodiment can include multiple sub-steps or multiple stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution sequence of these sub-steps or stages is not necessarily sequential, but can be executed in rotation or alternation with at least part of other steps or sub-steps or stages of other steps.

[0128] Finally, it should be noted that the above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art will appreciate that the technical solutions described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalent ones. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A design method of a passive spur rejection circuit for an aeronautical rotation speed signal, characterized in that, The design method comprises the following steps: (1) analyzing the principle of the sensor of the target model, obtaining the principle of the internal rotation speed signal of the sensor, an equivalent amplifier model and an equivalent resistance value; (2) determining the relationship between the engine rotation speed and the signal frequency, verifying the mechanism of the engine parameter collector triggered by the rising edge / falling edge of the square wave, and determining that the duty cycle change does not affect the counting of the engine parameter collector; (3) measuring the voltage recognition range of the engine parameter collector to the rotation speed signal, and determining the threshold voltage of the engine parameter collector; (4) analyzing the characteristics of the clutter signal, identifying the clutter as a high-frequency sharp pulse and only affecting the signal in the high-level stage; (5) based on the high-frequency characteristics of the clutter signal, designing a passive clutter suppression circuit composed of a capacitor, which is connected in series between the signal line and the ground line between the rotation speed sensor and the engine parameter collector; (6) determining the capacitor value range through the charging time constant formula, and the constraint condition is that the selected capacitor value should be charged to the voltage value recognizable by the engine parameter collector within the shortest charging time allowed by the rotation speed signal; The capacitor value range is calculated by the following formula: and t > 1 / (V*2) Wherein, t is the half cycle time corresponding to the maximum speed, R is the internal pull-up resistor value of the engine parameter collector, The minimum voltage that can be identified by the engine parameter collector, V is the maximum identification frequency of the target model; (7) using the cumulative progressive method to test the filtering effect of the minimum unit capacitor in parallel to determine the optimal capacitor value; (8) selecting two safety capacitors in series to improve the voltage resistance and safety, forming the final clutter suppression circuit.

2. The method of designing an aircraft-oriented passive spurious signal rejection circuit for a speed signal according to claim 1, characterized in that In step (2), the relationship between the engine rotation speed and the signal frequency is: RPM=40*f Wherein, RPM is the engine rotation speed, and f is the signal frequency.

3. The method of designing an aircraft-oriented passive spurious signal rejection circuit for a speed signal as recited in claim 1, wherein In step (7), the cumulative progressive method is used to test the filtering effect of the minimum unit capacitor in parallel to determine the optimal capacitor value, which comprises: Using the cumulative progressive method, taking 0.01uf capacitor as the minimum cumulative unit, connecting the capacitor in parallel between the rotation speed sensor signal line and the ground line of the aircraft through the breadboard and test line, then the aircraft is tested, and whether the rotation speed signal still exists interference is observed, if the interference still exists, another 0.01uf capacitor is connected in parallel, and so on, until the optimal capacitor value is reached.

4. A passive spurious signal rejection circuit for an aircraft rotation speed signal designed by the design method according to any one of claims 1 to 3, characterized in that, The passive clutter suppression circuit for the aviation rotation speed signal comprises two safety capacitors connected in series, and the two safety capacitors are connected with a female plug, and a test interface is connected in parallel between the two safety capacitors.

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