Lightweight aviation fuel measurement circuit and method

Abstract

The lightweight aviation oil measuring circuit and method of the present application, the circuit comprises: a control circuit, a follow-up circuit, a hysteresis comparison circuit, a reverse circuit, a current limiting resistor, a measured oil sensor Cx and a voltage conversion circuit. The measuring method is: setting the high voltage threshold and the low voltage threshold of the charge and discharge of the measured oil sensor Cx; collecting the square wave signal output by the circuit; measuring and calculating the positive pulse width, the negative pulse width and the period, and filtering the signals; and using formula calculation method or table lookup method to obtain the capacitance value of the measured oil sensor capacitor Cx. The circuit structure and calculation method of the present application are simple, and the problems of complex traditional acquisition circuit, large printed board area and many system resources are solved.

Description

Technical Field

[0001] This invention belongs to the technical field of airborne electronic equipment, and particularly relates to a lightweight aviation fuel quantity measurement circuit and measurement method. Background Technology

[0002] Accurate measurement of aviation fuel levels can reduce the amount of spare fuel carried on an aircraft, thereby improving flight economy to some extent. Currently, various aircraft models use capacitive fuel level sensors, which are characterized by a tiny capacitance signal at the pF level. Therefore, the aircraft's fuel level is obtained through dedicated measurement circuitry for acquisition, compensation, and calculation.

[0003] Traditional oil level sensor detection circuits have many measurement steps, are complex in structure and use, and occupy a large amount of printed circuit board area and system resources.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a lightweight aviation fuel quantity measurement circuit and method, solving the problems of traditional measurement methods involving multiple measurement steps, large circuit area, and high system resource consumption. The technical solution of this invention has many beneficial effects, as described below:

[0006] A lightweight fuel level detection circuit is provided, comprising a control circuit, a follower circuit, a hysteresis comparison circuit, an inverting circuit, a current-limiting resistor, a fuel level sensor Cx, and a voltage conversion circuit, wherein:

[0007] The control circuit is used to control the operating state of the circuit;

[0008] The follower circuit is used to acquire the voltage of the measured oil quantity sensor Cx and transmit it to the hysteresis comparison circuit.

[0009] The hysteresis comparator circuit is used to form the high and low voltage thresholds for charging and discharging the fuel level sensor Cx, and the output of the comparator circuit is input to the inverting circuit.

[0010] The inverting circuit is used to invert the output of the hysteresis comparator circuit and input it to the current limiting resistor.

[0011] The current-limiting resistor is connected to the output terminal of the reverse circuit and the measured fuel level sensor Cx, and is used to limit the charging and discharging current of the fuel level sensor in order to provide energy safety protection for the fuel level sensor.

[0012] The measured fuel quantity sensor Cx measures the amount of aviation fuel, which is represented by a small capacitance signal.

[0013] The voltage conversion circuit is used to convert the ±15V square wave voltage of the operational amplifier into a sampling voltage of 5V or 3.3V acceptable to the controller, which is acquired by an external acquisition device.

[0014] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0015] By using an operational amplifier hysteresis circuit, the automatic charging and discharging of the fuel level sensor capacitor is achieved without the need for other control signals. The capacitance value of the fuel level sensor is calculated by collecting the charging and discharging time. Only one control signal and one data acquisition interface are required, resulting in a simple structure and calculation process with minimal system resource consumption. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the lightweight aviation fuel measurement circuit proposed in this invention.

[0018] Figure 2 This is a schematic diagram showing the relationship between the change in capacitance value of the measured oil level sensor and the waveform acquired by the measurement circuit.

[0019] Figure 3 This is a schematic diagram of the oil quantity measurement method based on the circuit described in this invention. Detailed Implementation

[0020] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this invention, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0022] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0023] Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that aspects can be practiced without these specific details. To enable those skilled in the art to better understand the invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined as "first" and "second" may explicitly or implicitly include one or more of that feature. In the description of the invention, unless otherwise stated, "a plurality of" means two or more.

[0024] See Figure 1 The lightweight fuel level detection circuit shown includes a control circuit, a follower circuit, a hysteresis comparator circuit, an inverting circuit, a current-limiting resistor, a fuel level sensor Cx, and a voltage conversion circuit, wherein:

[0025] The control circuit is used to control the operating state of the circuit;

[0026] The follower circuit is used to acquire the voltage of the measured oil quantity sensor Cx and transmit it to the hysteresis comparator circuit;

[0027] The hysteresis comparator circuit is used to form the high and low voltage thresholds for charging and discharging the fuel level sensor Cx. The output of the comparator circuit is input to the inverting circuit.

[0028] The inverting circuit is used to reverse the output of the hysteresis comparator circuit and input it to the current-limiting resistor;

[0029] A current-limiting resistor is connected to the output of the reverse circuit and the fuel level sensor Cx under test. It is used to limit the charging and discharging current of the fuel level sensor in order to provide energy safety protection for the fuel level sensor.

[0030] The fuel quantity sensor Cx measures the amount of aviation fuel, which is represented by a small capacitance signal.

[0031] The voltage conversion circuit converts the ±15V square wave voltage from the operational amplifier into a 5V or 3.3V acquisition voltage acceptable to the controller. This acquisition voltage is then acquired by an external data acquisition unit. Specifically:

[0032] Follower circuit includes,

[0033] The output of the fuel level sensor Cx is connected to the positive input of the integrated operational amplifier U1, and the inverting input of the integrated operational amplifier U1 is connected to the output of U1.

[0034] The hysteresis comparator circuit includes an integrated operational amplifier U2, resistors R1 and R2. The output of operational amplifier U1 is connected to the input of resistor R1, and the output of resistor R1 is connected to the non-inverting input of operational amplifier U2. The inverting input of operational amplifier U2 receives the externally input hysteresis circuit voltage comparison value V. cmp The input terminals of resistor R2 are connected to both the control circuit and the positive input terminal of integrated operational amplifier U2. The hysteresis comparator circuit is used for:

[0035] When the voltage of sensor Cx reaches the high voltage threshold, the output voltage of the hysteresis comparator circuit will be reversed from low to high, and the state of sensor Cx will change from charging to discharging.

[0036] When the voltage of sensor Cx discharges to the low voltage threshold, the output voltage of the hysteresis comparator circuit is also triggered to reverse from high to low, and the state of sensor Cx changes from discharging to charging.

[0037] The high threshold voltage of a hysteresis circuit is calculated by the following formula:

[0038]

[0039] In the formula, V H This is the high threshold voltage value of the hysteresis circuit. When the input voltage is greater than or equal to this voltage, the circuit output level is reversed; V cmp The voltage comparison value for the hysteresis circuit; R1 and R2 are the resistance values; V oL This is the voltage when the hysteresis circuit outputs a low level.

[0040] The low threshold voltage of a hysteresis circuit is calculated by the following formula:

[0041]

[0042] In the formula, V L V is the low threshold voltage value of the hysteresis circuit. oH This is the voltage when the hysteresis circuit outputs a high level.

[0043] The inverting circuit includes:

[0044] The integrated operational amplifier U3, current-limiting resistor Ro, resistor R3, and resistor R4 are connected. The input terminal of resistor R3 is connected to the output terminal of integrated operational amplifier U2, and the output terminal of resistor R3 is connected to the inverting input terminal of integrated operational amplifier U3. The non-inverting terminal of integrated operational amplifier U3 is grounded. The output terminal of resistor R3 is connected to the input terminal of resistor R4, and the output terminal of resistor R4 is connected to the output terminal of integrated operational amplifier U3. The output of integrated operational amplifier U3 forms a voltage that is reversed by the voltage of integrated operational amplifier U2.

[0045] The current-limiting resistor Ro is connected to the output terminal of the reverse circuit and the measured fuel level sensor Cx. It is used to limit the charging and discharging current of the fuel level sensor and realize energy safety protection for the fuel level sensor.

[0046] Voltage conversion circuit, including N-type MOSFET and resistor R S The gate of the MOSFET is connected to the output terminal of the integrated operational amplifier U2, the source is grounded, and the drain is connected to the resistor R. S An external data acquisition unit collects the drain voltage of the MOSFET.

[0047] Secondly, a measurement method for a lightweight fuel level detection circuit is provided, suitable for measuring aviation fuel level. The method is characterized by using the aforementioned lightweight fuel level detection circuit, setting high and low voltage thresholds for the charging and discharging of the fuel level sensor Cx; acquiring the square wave signal output by the acquisition circuit; measuring and calculating the positive pulse width, negative pulse width, and period of the signal, and filtering it; and obtaining the capacitance value of the fuel level sensor Cx using a formula calculation method or a table lookup method. This method is simple and solves the problems of complex traditional acquisition circuits, which occupy a large printed circuit board area and require significant system resources. The measurement method includes:

[0048] S1. When the enable circuit control switch input is low, the optocoupler is turned off, and the sensor Cx enters the cyclic charging and discharging state, waiting for the lightweight oil quantity detection circuit to collect the square wave signal. When the frequency of the square wave signal is relatively stable, it enters the acquisition state.

[0049] S2. Acquire the output square wave signal, measure and calculate the positive pulse width, negative pulse width and period of the signal;

[0050] Acquire the square wave signal output by the lightweight oil level detection circuit, and calculate the positive pulse width, negative pulse width, and period of the signal, for example, through the frequency acquisition circuit.

[0051] S3. Perform digital filtering on the calculated positive pulse width, negative pulse width and period of the signal. Digital filtering methods include sliding window averaging, IIR, FIR, or median filtering.

[0052] S4. Based on the positive pulse width, negative pulse width, and period information of the square wave signal obtained in S3, the positive pulse width corresponds to the capacitor discharge time, i.e., t. H→L The negative pulse width corresponds to the capacitor charging time, i.e., t. L→H ,in:

[0053] The capacitance C of the measured oil level sensor Cx is calculated by the charging time. x The expression is:

[0054]

[0055] In the formula, t L→H This represents the charging time for the capacitor voltage to rise from a low threshold to a high threshold, or...

[0056] The capacitance value of the measured oil quantity sensor Cx is calculated by the discharge time:

[0057]

[0058] In the formula, t H→L This indicates the discharge time for the capacitor voltage to drop from a high threshold to a low threshold.

[0059] S5. When the control circuit switch is disabled, the circuit stops operating.

[0060] For example, this lightweight aviation fuel measurement circuit includes: a control circuit, a follower circuit, a hysteresis comparator circuit, a reverse circuit, a current-limiting resistor, a fuel level sensor Cx, and a voltage conversion circuit. The control circuit is used to control whether the circuit enters the operating state. In this embodiment, as... Figure 1 As shown, the control circuit consists of an optocoupler, which isolates the control voltage from the circuit's operating voltage. The control logic level is inverted; that is, when the control terminal is disabled, the control output level is high (1), the optocoupler conducts, and the voltage between resistors R1 and R2 is pulled to a constant -15V. Furthermore, the voltage at the negative input of operational amplifier U3 is negative, therefore U3 outputs a constant high level, and the circuit does not operate. When the control terminal is enabled (0), the optocoupler does not conduct, and the circuit operates normally.

[0061] The follower circuit, implemented by U1, is used to acquire the voltage of the measured oil quantity sensor Cx and transmit it to the hysteresis comparator circuit.

[0062] The hysteresis comparator circuit, implemented by U1, R1, and R2, is used to establish the high and low voltage thresholds for charging and discharging the fuel level sensor Cx. When the sensor Cx voltage reaches the high voltage threshold, the output voltage of the hysteresis comparator circuit is triggered to reverse from low to high, and the Cx state changes from charging to discharging. Similarly, when the Cx voltage discharges to the low voltage threshold, the output voltage of the hysteresis comparator circuit is triggered to reverse from high to low, and the Cx state changes from discharging to charging.

[0063] The high threshold voltage of a hysteresis circuit is calculated by the following formula:

[0064]

[0065] In the formula, V H This is the high threshold voltage value of the hysteresis circuit. When the input voltage is greater than or equal to this voltage, the circuit output level is reversed; V cmp The voltage comparison value for the hysteresis circuit; R1 and R2 are the resistance values; V oL This is the voltage when the hysteresis circuit outputs a low level.

[0066] The low threshold voltage of a hysteresis circuit is calculated by the following formula:

[0067]

[0068] In the formula, V L V is the low threshold voltage value of the hysteresis circuit. oH This is the voltage when the hysteresis circuit outputs a high level.

[0069] In this embodiment, R1 and R2 are respectively set to 1K and 9K, V cmp Take it as 0V, the V output of the operational amplifier oH +13V, V oL Given a voltage of -13V, the high and low thresholds can be calculated to be +1.44V and -1.44V, respectively.

[0070] The inverting circuit, consisting of U3, R3, and R4, is used to invert the output of the hysteresis comparator circuit.

[0071] The current-limiting resistor, Ro, is connected to the output of the reverse circuit and the fuel level sensor Cx under test. It is used to limit the charging and discharging current of the fuel level sensor and realize energy safety protection for the fuel level sensor.

[0072] The fuel quantity sensor Cx measures the amount of aviation fuel, which is characterized as a small capacitance signal at the pF level.

[0073] Relationship between capacitor voltage and charge / discharge time:

[0074]

[0075] In the formula, t is the charging and discharging time; V Ct V is the capacitor voltage at time t; C0 V is the initial voltage value of the capacitor; R is the resistance value of the current-limiting resistor in the RC circuit; i This is the input voltage value for the RC circuit.

[0076] The charging time for the measured capacitor voltage to rise from a low threshold to a high threshold:

[0077]

[0078] In the formula, t L→H This indicates the charging time for the capacitor voltage to increase from a low threshold to a high threshold.

[0079] Accordingly, the measured capacitance is calculated using the charging time:

[0080]

[0081] The discharge time of the measured capacitor voltage from the high threshold to the low threshold:

[0082]

[0083] In the formula, t H→L This indicates the discharge time for the capacitor voltage to drop from the high threshold to the low threshold.

[0084] Accordingly, the capacitance under test is calculated using the discharge time:

[0085]

[0086] When the capacitor charges and the voltage reaches the high-level threshold of the hysteresis circuit, it triggers a level reversal in the hysteresis circuit, further causing the capacitor to enter a discharging state. Similarly, when the capacitor discharges and the voltage reaches the low-level threshold of the hysteresis circuit, it triggers a level reversal in the hysteresis circuit, causing the capacitor to recharge. When the capacitance value of the measured fuel level sensor changes, the charging and discharging rate of the circuit will change accordingly. Furthermore, the frequency of the square wave output by the hysteresis circuit will also change, such as... Figure 2 As shown.

[0087] The voltage conversion circuit consists of a MOSFET and a resistor R. S This component is used to convert the ±15V square wave voltage of the operational amplifier into a 5V or 3.3V voltage acceptable to the controller. In this embodiment, it is converted to 3.3V so that the controller can acquire circuit measurement signals.

[0088] The aviation fuel quantity measurement method based on the above circuit is as follows: Figure 3 As shown, it includes the following steps:

[0089] S1. Enable the circuit control switch and wait for the circuit to stabilize;

[0090] S2. Acquire the output square wave signal, measure and calculate the positive pulse width, negative pulse width and period of the signal;

[0091] S3. Filter the calculated positive pulse width, negative pulse width, and period of the signal;

[0092] S4. Based on the positive pulse width, negative pulse width, and period information of the square wave signal obtained in S3, the positive pulse width corresponds to the capacitor discharge time, i.e., t. H→L The negative pulse width corresponds to the capacitor charging time, i.e., t. L→H The capacitance value of the measured oil quantity sensor Cx is obtained by using the formula calculation method (Equations 6 and 8) / table lookup method;

[0093] S5. When the control circuit switch is disabled, the circuit stops operating.

[0094] The product provided by this invention has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are merely for the purpose of helping to understand the core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to the invention without departing from the principles of the invention, and these improvements and modifications also fall within the protection scope of the invention claims.

Claims

1. A lightweight oil level detection circuit, characterized in that, Includes control circuit, follower circuit, hysteresis comparator circuit, inverting circuit, current limiting resistor, and oil quantity sensor. Cx And voltage conversion circuit, wherein: The control circuit is used to control the operating state of the circuit; The follower circuit is used to acquire the measured oil quantity sensor. Cx The voltage is transmitted to the hysteresis comparator circuit. The hysteresis comparator circuit is used to form an oil quantity sensor. Cx The high and low voltage thresholds for charging and discharging are compared, and the output of the comparison circuit is input to the inverting circuit. The inverting circuit is used to invert the output of the hysteresis comparator circuit and input it to the current limiting resistor; The current-limiting resistor is connected to the output terminal of the reverse circuit and the measured fuel quantity sensor. Cx It is used to limit the charging and discharging current of the fuel level sensor in order to provide energy safety protection for the fuel level sensor; The measured oil quantity sensor Cx, Used for measuring aviation fuel quantity, characterized as a small capacitance signal; The voltage conversion circuit is used to convert the ±15V square wave voltage of the operational amplifier into a sampling voltage of 5V or 3.3V acceptable to the controller, which is sampled by an external acquisition device. The follower circuit includes an integrated operational amplifier U1, and the fuel level sensor Cx The output of is connected to the positive input terminal of the integrated operational amplifier U1, and the inverting input terminal of the integrated operational amplifier U1 is connected to the output terminal of U1; The hysteresis comparator circuit includes an integrated operational amplifier U2, resistors R1 and R2. The output terminal of the integrated operational amplifier U1 is connected to the input terminal of resistor R1, and the output terminal of resistor R1 is connected to the non-inverting input terminal of the integrated operational amplifier U2. The inverting input terminal of the integrated operational amplifier U2 receives the externally input hysteresis circuit voltage comparison value. The input terminal of resistor R2 is connected to both the control circuit and the positive input terminal of integrated operational amplifier U2. When sensor Cx When the voltage charging reaches the high voltage threshold, it will trigger the hysteresis comparator circuit to reverse the output voltage from low to high, and the sensor... Cx The state changes from charging to discharging; When sensor Cx When the voltage discharges to the low voltage threshold, the hysteresis comparator circuit is also triggered to reverse its output voltage from high to low, and the sensor... Cx The state changes from discharging to charging; The high threshold voltage of the hysteresis circuit is calculated by the following formula: （1） In the formula, This is the high threshold voltage value of the hysteresis circuit. When the input voltage is greater than or equal to this voltage, the circuit output level is reversed. This is the voltage comparison value for the hysteresis circuit; and These are the values ​​of the resistance; This is the voltage when the hysteresis circuit outputs a low level. The low threshold voltage of the hysteresis circuit is calculated by the following formula: （2） In the formula, This is the low threshold voltage value for the hysteresis circuit. This is the voltage when the hysteresis circuit outputs a high level.

2. The lightweight oil level detection circuit according to claim 1, characterized in that, The inverting circuit includes: an integrated operational amplifier U3, a current-limiting resistor Ro, a resistor R3, and a resistor R4. The input terminal of resistor R3 is connected to the output terminal of integrated operational amplifier U2, and the output terminal of resistor R3 is connected to the inverting input terminal of integrated operational amplifier U3. The non-inverting terminal of integrated operational amplifier U3 is grounded. The output terminal of resistor R3 is connected to the input terminal of resistor R4, and the output terminal of resistor R4 is connected to the output terminal of integrated operational amplifier U3. The output of integrated operational amplifier U3 forms a voltage that is the reverse of the voltage of integrated operational amplifier U2. The current-limiting resistor Ro is connected to the output of the reverse circuit and the oil quantity sensor being measured. Cx It is used to limit the charging and discharging current of the fuel level sensor, thereby achieving energy safety protection for the fuel level sensor; The voltage conversion circuit includes an N-type MOSFET and a resistor R. S The gate of the MOSFET is connected to the output terminal of the integrated operational amplifier U2, the source is grounded, and the drain is connected to the resistor R. S An external data acquisition unit collects the drain voltage of the MOSFET.

3. A method for measuring fuel level using a lightweight fuel level detection circuit, applicable to the measurement of aviation fuel level, characterized in that, Using the lightweight oil level detection circuit as described in any one of claims 1 to 2, the measurement method includes: S1: Enable circuit control switch input is low; when the optocoupler is off, the sensor... Cx Enter the cyclic charging and discharging state, wait for the lightweight oil quantity detection circuit to collect the square wave signal, and wait for the square wave signal frequency to stabilize before entering the acquisition state; S2: Acquire the output square wave signal, measure and calculate the positive pulse width, negative pulse width and period of the signal; Acquire the square wave signal output from the lightweight fuel level detection circuit, and calculate the positive pulse width, negative pulse width, and period of the signal; S3: Perform digital filtering on the calculated positive pulse width, negative pulse width, and period of the signal; S4: Based on the positive pulse width, negative pulse width, and period information of the square wave signal obtained in S3, the positive pulse width corresponds to the capacitor discharge time, i.e. Negative pulse width corresponds to capacitor charging time, i.e. ,in: The sensor calculates the measured oil quantity based on the charging time. Cx capacitance value C x The expression is: （3） In the formula, This represents the charging time for the capacitor voltage to rise from a low threshold to a high threshold, or... The sensor calculates the measured oil quantity based on the discharge time. Cx Capacitance value: （4） In the formula, This indicates the discharge time for the capacitor voltage to drop from a high threshold to a low threshold. S5: The control circuit switch is disabled, and the circuit stops operating.

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