Wide-range high-precision capacitance acquisition circuit and control method

Abstract

The invention provides a wide-range high-precision capacitance acquisition circuit and a control method, and relates to the technical field of airborne analog quantity acquisition, the circuit comprises a to-be-measured capacitor Cx, a first alternating current proportional amplification circuit and a second alternating current proportional amplification circuit, the to-be-measured capacitor Cx is connected with the first alternating current proportional amplification circuit through a switch S1, and the to-be-measured capacitor Cx is connected with the second alternating current proportional amplification circuit through a switch S2; the capacitor Cx to be tested is connected with the second alternating-current proportional amplification circuit through the switch S2; the first alternating-current proportional amplification circuit and the second alternating-current proportional amplification circuit respectively comprise a feedback resistor, a feedback capacitor and an operational amplifier which are connected in parallel; the switch S1 and the switch S2 are mutually exclusive, and the capacitance value of a feedback capacitor of the second alternating-current proportional amplifying circuit is at least five times of the capacitance value of the feedback capacitor of the first alternating-current proportional amplifying circuit. The requirement for expanding the range of the to-be-measured capacitor is met while the capacitance acquisition precision is guaranteed, the capacitance acquisition range is expanded, the generalization level is improved, and the method is particularly suitable for the field of airborne fuel oil liquid level measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of airborne analog quantity acquisition, and in particular to a wide-range high-precision capacitance acquisition circuit and a control method. Background Art

[0002] Fuel level measurement is a basic function of the aircraft fuel system, and its accuracy directly affects the flight plan and flight safety of the aircraft. At present, the dominant fuel level measurement technology is still the digital capacitive level sensor, and the commonly used measurement method is the AC proportional method, that is, the measured capacitance is measured by the proportional relationship between the excitation voltage, feedback voltage, measured capacitance and reference capacitance. However, when the feedback capacitance is determined, the range of the measured capacitance is limited by the excitation voltage and feedback voltage. For example, when the feedback capacitance is 100pF, considering the signal-to-noise ratio and the voltage range of the analog device, the range of the measured capacitance is only [20pF 500pF]. Therefore, in the face of the actual engineering needs of expanding the capacity of aircraft fuel tanks and expanding the range of measured capacitance, how to achieve cross-aircraft platform reuse of capacitance acquisition circuits while ensuring acquisition accuracy is an urgent problem to be solved. Summary of the invention

[0003] In view of this, the embodiments of the present application provide a wide-range, high-precision capacitance acquisition circuit and control method, which meet the demand for expanding the range of capacitance to be measured while ensuring the accuracy of capacitance acquisition, expand the range of capacitance acquisition, and improve the level of universality, which is particularly suitable for the field of airborne fuel level measurement.

[0004] The embodiment of the present application provides the following technical solution: a wide range high-precision capacitance acquisition circuit, the circuit comprising: a capacitance C to be measured x , a first AC proportional amplifier circuit and a second AC proportional amplifier circuit, the capacitor to be measured C x The capacitor C to be measured is connected to the first AC proportional amplifier circuit through the switch S1. x connected to the second AC proportional amplifier circuit via a switch S2, wherein the first AC proportional amplifier circuit and the second AC proportional amplifier circuit both include a feedback resistor, a feedback capacitor and an operational amplifier connected in parallel with each other;

[0005] The switch S1 and the switch S2 are mutually exclusive, and the capacitance of the feedback capacitor of the second AC proportional amplifier circuit is at least 5 times the capacitance of the feedback capacitor of the first AC proportional amplifier circuit.

[0006] According to an embodiment of the present application, the capacitor C to be measured x The capacitance range is 20pF-1500pF.

[0007] According to an embodiment of the present application, the feedback capacitance of the second AC proportional amplifier circuit is 500 pF, and the feedback capacitance of the first AC proportional amplifier circuit is 100 pF.

[0008] According to an embodiment of the present application, the feedback resistance value of the first AC proportional amplifier circuit and the feedback resistance value of the second AC proportional amplifier circuit are both 10 MΩ.

[0009] According to an embodiment of the present application, the switch S1 and the switch S2 are both single-pole single-throw switches.

[0010] According to an embodiment of the present application, the capacitor C to be measured x The capacitance value is calculated by the following formula:

[0011]

[0012] Wherein, V0 is the output voltage of the first AC proportional amplifier circuit or the second AC proportional amplifier circuit, C x is the capacitance to be measured, C f is the feedback capacitor, V i The capacitance C to be measured x The excitation voltage on .

[0013] According to an embodiment of the present application, the tolerance of the feedback capacitor is ±0.5 pF, and the capacitance of the feedback capacitor is based on the capacitance to be measured C x The capacitance range can be adjusted.

[0014] The present application also provides a control method for the wide range and high precision capacitance acquisition circuit as described above, comprising the following steps:

[0015] Step 1: Control switch S1 to turn off, switch S2 to turn on, and adjust the excitation voltage V i , so that the feedback voltage V0 of the second AC proportional amplifier circuit 2 Equal to 7Vrms, calculate the capacitance C to be measured x The initial value of

[0016] Step 2: According to the capacitor C to be tested x The initial value of the control switch S1 and switch S2 is turned on and off, and the excitation voltage V is collected. i , the feedback voltage V0 of the first AC proportional amplifier circuit 1 And the feedback voltage V0 of the second AC proportional amplifier circuit 2 ;in:

[0017] When the measured capacitance C x When the initial value is less than 100pF, the control switch S1 is turned on and the switch S2 is turned off, and the excitation voltage V is adjusted. iEqual to 7Vrms, collecting feedback voltage V0 1 ;

[0018] When the measured capacitance C x When the initial value is greater than 100pF and less than 224pF, the control switch S1 is turned on and the switch S2 is turned off, and the excitation voltage V is adjusted. i , so that the feedback voltage V0 1 Equal to 7Vrms, collect the excitation voltage V i ;

[0019] When the measured capacitance C x When the initial value is greater than 224pF and less than 500pF, the control switch S1 is turned off and the switch S2 is turned on to adjust the excitation voltage V i Equal to 7Vrms, collecting feedback voltage V0 2 ;

[0020] When the measured capacitance C x When the initial value is greater than 500pF, the control switch S1 is turned off, the switch S2 is turned on, and the excitation voltage V is adjusted. i , so that the feedback voltage V0 2 Equal to 7Vrms, collect the excitation voltage V i ;

[0021] Step 3: Based on the excitation voltage V i , feedback voltage V0 1 and feedback voltage V0 2 , calculate the capacitance C to be measured x The fine value of .

[0022] Compared with the prior art, at least one of the above-mentioned technical solutions adopted in the embodiments of this specification can achieve at least the following beneficial effects: In response to the engineering needs of expanding the capacity of aircraft fuel tanks and expanding the range of capacitance to be measured, the embodiments of the present invention design a wide-range, high-precision capacitance acquisition circuit and a working method. By configuring two AC proportional amplifier circuits with different feedback capacitances, the AC proportional amplifier circuit adapted to the feedback capacitance is selected according to the rough acquisition result of the capacitance to be measured. While ensuring the capacitance acquisition accuracy, the demand for expanding the range of capacitance to be measured is met, covering the capacitance acquisition range of 20pF-1500pF, expanding the use scenarios of the capacitance acquisition circuit, realizing the reuse of the capacitance acquisition circuit across aircraft platforms, and improving the level of generalization. It can be widely used in the field of industrial liquid level measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 It is a schematic diagram of a wide range and high precision capacitance acquisition circuit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0026] The following describes the implementation methods of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present application.

[0027] First, as Figure 1 As shown, the embodiment of the present invention provides a wide range high precision capacitance acquisition circuit, the circuit comprising: a capacitance C to be measured x , a first AC proportional amplifier circuit and a second AC proportional amplifier circuit, the capacitor to be measured C x The capacitor C to be measured is connected to the first AC proportional amplifier circuit through the switch S1. x The first AC proportional amplifier circuit is connected to the second AC proportional amplifier circuit through the switch S2, and the first AC proportional amplifier circuit and the second AC proportional amplifier circuit both include a feedback resistor, a feedback capacitor and an operational amplifier connected in parallel with each other; wherein the switch S1 and the switch S2 are mutually exclusive, and the feedback capacitor capacitance of the second AC proportional amplifier circuit is at least 5 times the feedback capacitor capacitance of the first AC proportional amplifier circuit.

[0028] In the embodiment of the present invention, the switch S1 and the switch S2 are both single-pole single-throw switches; the switch S1 and the switch S2 are mutually exclusive, that is, when the switch S1 is turned on, the switch S2 is turned off, and when the switch S1 is turned off, the switch S2 is turned on. xThe capacitance range is 20pF-1500pF. The capacitance of the feedback capacitor of the second AC proportional amplifier circuit is 500pF, and the capacitance of the feedback capacitor of the first AC proportional amplifier circuit is 100pF. The feedback capacitor is a specially selected high-precision capacitor with a tolerance of ±0.5pF. The capacitance of the feedback capacitor can be determined according to the capacitance to be measured C x The capacitance range can be adjusted.

[0029] In the embodiment of the present invention, the feedback resistor value of the first AC proportional amplifier circuit and the feedback resistor value of the second AC proportional amplifier circuit are both 10 MΩ, which are used for the DC path.

[0030] In the embodiment of the present invention, the capacitor C to be measured x The capacitance value is calculated by the following formula (1):

[0031]

[0032] Wherein, V0 is the output voltage of the first AC proportional amplifier circuit or the second AC proportional amplifier circuit, C x is the capacitance to be measured, C f is the feedback capacitor, V i The capacitance C to be measured x The excitation voltage on .

[0033] In a second aspect, an embodiment of the present invention provides a control method for a wide range and high precision capacitance acquisition circuit as described above, comprising the following steps:

[0034] Step 1: Control switch S1 to turn off, switch S2 to turn on, and adjust the excitation voltage V i , so that the feedback voltage V0 of the second AC proportional amplifier circuit 2 Equal to 7Vrms, calculate the capacitance C to be measured x The initial value of

[0035] Step 2: According to the capacitor C to be tested x The initial value of the control switch S1 and switch S2 is turned on and off, and the excitation voltage V is collected. i , the feedback voltage V0 of the first AC proportional amplifier circuit 1 And the feedback voltage V0 of the second AC proportional amplifier circuit 2 ;in:

[0036] When the measured capacitance C x When the initial value is less than 100pF, the control switch S1 is turned on and the switch S2 is turned off, and the excitation voltage V is adjusted. i Equal to 7Vrms, collecting feedback voltage V0 1 ;

[0037] When the measured capacitance Cx When the initial value is greater than 100pF and less than 224pF, the control switch S1 is turned on and the switch S2 is turned off, and the excitation voltage V is adjusted. i , so that the feedback voltage V0 1 Equal to 7Vrms, collect the excitation voltage V i ;

[0038] When the measured capacitance C x When the initial value is greater than 224pF and less than 500pF, the control switch S1 is turned off and the switch S2 is turned on to adjust the excitation voltage V i Equal to 7Vrms, collecting feedback voltage V0 2 ;

[0039] When the measured capacitance C x When the initial value is greater than 500pF, the control switch S1 is turned off, the switch S2 is turned on, and the excitation voltage V is adjusted. i , so that the feedback voltage V0 2 Equal to 7Vrms, the sampling excitation voltage V i ;

[0040] Step 3: Based on the excitation voltage V i , feedback voltage V0 1 and feedback voltage V0 2 , calculate the capacitance C to be measured x The fine value of .

[0041] When calculating specifically, Figure 1 As shown, according to the relationship between the input and output of the reverse proportional amplifier circuit, the AC excitation voltage V i , the proportional amplifier circuit output voltage V0 (including V0 1 and V0 2 ), the capacitor to be measured C x And the feedback capacitor C f The relationship shown in formula (2) is satisfied.

[0042]

[0043] In formula (2), the feedback capacitor C f It is known that the capacitor collection circuit collects the excitation voltage V i And the proportional amplifier circuit output voltage V0 calculates the capacitance C to be measured x Considering the accuracy limit of the analog-to-digital converter and the linear range of the analog circuit, the excitation voltage V i The closer the output voltage V0 of the proportional amplifier circuit is to the maximum value of the linear range of the analog-to-digital converter, the smaller its linear error is, the higher the voltage acquisition accuracy is, and the higher the accuracy of the calculated capacitance to be measured is.

[0044] Example 1

[0045] When using an AC proportional amplifier circuit for capacitance acquisition, when the reference capacitor C f Equal to 100pF, the capacitance to be measured C x Equal to 1500pF, AC excitation voltage V i And the feedback voltage V0 satisfies the relationship shown in formula (3):

[0046] V o =-15×V i (3)

[0047] Considering the voltage acquisition range of the analog-to-digital converter and the linear amplification region of the operational amplifier, when the feedback voltage V0 in formula (3) is set to a maximum of 7.00 Vrms, the excitation voltage V i It is only 0.47Vrms, the signal amplitude is too small, the signal-to-noise ratio is low, and the anti-interference ability is poor. Therefore, it is not feasible to change the measurement range from 20-5000pF to 20-1500pF without changing any hardware circuits.

[0048] In order to ensure the acquisition accuracy and expand the capacitance acquisition range, two different feedback capacitors are set, with capacitance values ​​of 100pF and 500pF respectively. Figure 1 As shown, the range of the capacitance interface is extended by using segmented acquisition, as follows:

[0049] Case 1: When the capacitor C to be tested x When it is less than 100pF, the control switch S1 is turned on and the switch S2 is turned off, and the excitation voltage V is adjusted. i Equal to 7Vrms, collecting feedback voltage V0 1 , when the capacitor C x When it is equal to 20pF, the feedback voltage V0 1 Minimum, 1.4Vrms;

[0050] Case 2: When the capacitor C to be tested x When the voltage is greater than 100pF and less than 224pF, the control switch S1 is turned on and the switch S2 is turned off, and the excitation voltage V is adjusted. i , so that the feedback voltage V0 1 Equal to 7Vrms, collect the excitation voltage V i , when the capacitor C x When it is equal to 224pF, the excitation voltage V i Minimum, 3.125Vrms;

[0051] Case 3: When the capacitor C x When the voltage is greater than 224pF and less than 500pF, the control switch S1 is turned off and the switch S2 is turned on to adjust the excitation voltage V iEqual to 7Vrms, collecting feedback voltage V0 2 , when the capacitance to be measured is equal to 224pF, the feedback voltage V0 2 Minimum, 3.125Vrms;

[0052] Case 4: When the capacitor C x When it is greater than 500pF, the control switch S1 is turned off, the switch S2 is turned on, and the excitation voltage V is adjusted. i , so that the feedback voltage V0 2 =7Vrms. When the capacitance Cx to be measured is equal to 1500pF, the excitation voltage V i Minimum, equal to 2.333Vrms.

[0053] In the above four cases, the minimum value of the excitation voltage and feedback voltage is 1.4Vrms, which is equal to the 20-500 acquisition range, and the signal-to-noise ratio meets the accuracy requirements.

[0054] It can be seen from the above contents of the embodiment of the present invention that the excitation voltage V i The closer it is to the output voltage V0 of the proportional amplifier circuit, the closer the amplification factor of the AC proportional amplifier circuit is to -1. x The range is 20pF-1500pF. When the feedback capacitance is 100pF, the amplification factor of the AC proportional amplifier circuit is -0.2 to -15. When the amplification factor of the proportional amplifier circuit is -15, when the output voltage V0 of the proportional amplifier circuit is 7Vrms, the excitation voltage V i is 0.467Vrms, the signal amplitude is too small, the signal-to-noise ratio is low, and the anti-interference ability is poor; when the feedback capacitance is 500pF, the amplification factor of the AC proportional amplifier circuit is -0.04 to -3, and the amplification factor of the proportional amplifier circuit is -0.04. When the excitation voltage V i When it is 7Vrms, the output voltage V0 of the AC proportional amplifier circuit is 0.28Vrms, the signal amplitude is too small, the signal-to-noise ratio is low, and the anti-interference ability is poor.

[0055] The wide range and high precision capacitance acquisition circuit proposed in the embodiment of the present invention is adopted, by setting two reference capacitors C f The AC proportional amplifier circuit channels are 100pF and 500pF respectively, for different ranges of the measured capacitance C x , select different AC ratio amplification circuit channels, and then expand the capacitor C to be tested. x While limiting the acquisition range, the amplification factor of the AC proportional amplifier circuit is limited to a reasonable range, thereby ensuring the accuracy of capacitance acquisition.

[0056] When the reference capacitor C fWhen the capacitance is 100pF and 500pF respectively, select the capacitance threshold C of the measured capacitance of different AC proportional amplifier circuits. thr It can be calculated by formula (4).

[0057]

[0058] When the capacitor C x When the reference capacitor C is between 20pF and 224pF, f For an AC proportional amplifier circuit channel of 100pF, the gain of the AC proportional amplifier circuit is -0.2 to -2.24, which is closer to -1 than -0.2 to -15.

[0059] When the capacitor C x When the reference capacitor C is between 224pF and 1500pF, f For an AC proportional amplifier circuit channel of 500pF, the gain of the AC proportional amplifier circuit is -0.448 to 3, which is closer to -1 than -0.04 to -3.

[0060] A wide range, high-precision capacitance acquisition circuit and control method according to the embodiment of the present invention realizes the reuse of capacitance acquisition circuits across aircraft platforms and has important application value. The embodiment of the present invention configures two AC proportional amplifier circuit channels with different feedback capacitances, selects the AC proportional amplifier circuit channel adapted to the feedback capacitance according to the initial acquisition result of the capacitance to be measured, and meets the demand for expanding the capacitance range to be measured while ensuring the capacitance acquisition accuracy, covering the capacitance acquisition range of 20pF-1500pF, and can be widely used in the field of industrial liquid level measurement.

[0061] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A wide range and high precision capacitance acquisition circuit, characterized in that: The circuit comprises: a capacitor C to be measured x , a first AC proportional amplifier circuit and a second AC proportional amplifier circuit, the capacitor C to be measured x The capacitor C to be measured is connected to the first AC proportional amplifier circuit through the switch S1. x connected to the second AC proportional amplifier circuit via a switch S2, wherein the first AC proportional amplifier circuit and the second AC proportional amplifier circuit both include a feedback resistor, a feedback capacitor and an operational amplifier connected in parallel with each other; The switch S1 and the switch S2 are mutually exclusive, and the capacitance of the feedback capacitor of the second AC proportional amplifier circuit is at least 5 times the capacitance of the feedback capacitor of the first AC proportional amplifier circuit.

2. The wide range and high precision capacitance acquisition circuit according to claim 1, characterized in that: The capacitance to be measured C x The capacitance range is 20pF-1500pF.

3. The wide range and high precision capacitance acquisition circuit according to claim 2, characterized in that: The feedback capacitance of the second AC proportional amplifier circuit is 500 pF, and the feedback capacitance of the first AC proportional amplifier circuit is 100 pF.

4. The wide range and high precision capacitance acquisition circuit according to claim 1, characterized in that: The feedback resistor value of the first AC proportional amplifier circuit and the feedback resistor value of the second AC proportional amplifier circuit are both 10 MΩ.

5. The wide range and high precision capacitance acquisition circuit according to claim 1, characterized in that: The switch S1 and the switch S2 are both single-pole single-throw switches.

6. The wide range and high precision capacitance acquisition circuit according to claim 1, characterized in that: The capacitance to be measured C x The capacitance value is calculated by the following formula: Wherein, V0 is the output voltage of the first AC proportional amplifier circuit or the second AC proportional amplifier circuit, C x is the capacitance to be measured, C f is the feedback capacitor, V i The capacitance C to be measured x The excitation voltage on .

7. The wide range and high precision capacitance acquisition circuit according to claim 1, characterized in that: The tolerance of the feedback capacitor is ±0.5pF, and the capacitance of the feedback capacitor is based on the capacitance to be measured C x The capacitance range can be adjusted.

8. A control method for a wide range high precision capacitance acquisition circuit as claimed in any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1: Control switch S1 to turn off, switch S2 to turn on, and adjust the excitation voltage V i , so that the feedback voltage V0 of the second AC proportional amplifier circuit 2 Equal to 7Vrms, calculate the capacitance C to be measured x The initial value of Step 2: According to the capacitor C to be tested x The initial value of the control switch S1 and switch S2 is turned on and off, and the excitation voltage V is collected. i , the feedback voltage V0 of the first AC proportional amplifier circuit 1 And the feedback voltage V0 of the second AC proportional amplifier circuit 2 ;in: When the measured capacitance C x When the initial value is less than 100pF, the control switch S1 is turned on and the switch S2 is turned off, and the excitation voltage V is adjusted. i Equal to 7Vrms, collecting feedback voltage V0 1 ; When the measured capacitance C x When the initial value is greater than 100pF and less than 224pF, the control switch S1 is turned on and the switch S2 is turned off, and the excitation voltage V is adjusted. i , so that the feedback voltage V0 1 Equal to 7Vrms, the sampling excitation voltage V i ; When the measured capacitance C x When the initial value is greater than 224pF and less than 500pF, the control switch S1 is turned off and the switch S2 is turned on to adjust the excitation voltage V i Equal to 7Vrms, collecting feedback voltage V0 2 ; When the measured capacitance C x When the initial value is greater than 500pF, the control switch S1 is turned off, the switch S2 is turned on, and the excitation voltage V is adjusted. i , so that the feedback voltage V0 2 Equal to 7Vrms, the sampling excitation voltage V i ; Step 3: Based on the excitation voltage V i , feedback voltage V0 1 and feedback voltage V0 2 , calculate the capacitance C to be measured x The fine value of .

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