Calibration circuit of digital capacitance oil quantity sensor

Abstract

The utility model discloses a calibration circuit of a digital capacitance oil quantity sensor, which comprises an adjustable capacitor and a sampling channel switching circuit, the input end of the sampling channel switching circuit is respectively connected with the adjustable capacitor and an oil level height induction capacitor of the sensor, and the output end of the sampling channel switching circuit is connected with a capacitance conversion circuit. The sampling channel switching circuit comprises an analog switch A1, an analog switch A2, a switch S1 and a switch S2, two ends of an oil level height sensing capacitor of the sensor are respectively connected with the analog switch A1 and a pin S1 of the analog switch, and the analog switch A1 is in short circuit with a control end C1 of the pin S1 of the analog switch and is connected with the switch S1; the two ends of the adjustable capacitor are connected with the analog switch A1 and the S2 pin of the analog switch respectively, and the control end C2 of the analog switch A1 and the control end C2 of the S2 pin of the analog switch are in short circuit and connected with the switch S2. According to the utility model, the digital capacitance oil quantity sensor can complete calibration work without oil adding and discharging tests, and has good practicability.

Description

Technical Field

[0001] The utility model belongs to the technical field of fuel measurement equipment, and in particular relates to a calibration circuit of a digital capacitance fuel quantity sensor. Background Art

[0002] At present, digital capacitive fuel level sensors have been widely used on aircraft. They are usually composed of a fuel level sensing capacitor located in the fuel tank and a capacitive signal processing circuit located outside the fuel tank. Compared with traditional non-digital capacitive fuel level sensors, they can meet the aircraft fuel measurement needs without the need for a matching fuel computer and a dedicated measurement cable. They can directly convert the capacitance value output by the fuel level sensing capacitor located in the fuel tank into a digital value related to the fuel level, and transmit the aircraft fuel level information to the aircraft avionics system. Digital capacitive fuel level sensors are mostly used in helicopters and aircraft or drones with a small number of fuel tanks. However, the above-mentioned digital capacitive fuel level sensors currently have the following disadvantages:

[0003] ① The calibration test process is complicated. After the sensor is assembled, it is necessary to conduct an oil filling and draining test on the sensor through an oil filling and draining test bench to simulate the capacitance value of the sensor when it is installed on the aircraft fuel tank when it is empty and full of oil, so as to complete the sensor calibration work, which makes the production efficiency of the digital capacitive oil level sensor low.

[0004] ② It is necessary to design a special oil filling and draining test bench. Since the digital capacitive oil level sensor is designed to adapt to the aircraft installation structure and has different forms of mounting flanges, it is necessary to design different oil filling and draining test benches for different types of sensors, which makes the production cost of the digital capacitive oil level sensor relatively high.

[0005] ③ There are safety hazards in the calibration process. During the refueling and defueling test, the test personnel need to be exposed to the volatile environment of aviation fuel, which has high requirements for safety management and great safety hazards. Utility Model Content

[0006] The utility model aims to provide a calibration circuit for a digital capacitance oil level sensor, aiming to solve the above-mentioned problem.

[0007] The utility model is mainly realized through the following technical solutions:

[0008] A calibration circuit for a digital capacitive oil quantity sensor comprises an adjustable capacitor and a sampling channel switching circuit, wherein the input end of the sampling channel switching circuit is respectively connected to the adjustable capacitor and the oil level sensing capacitor of the sensor, and the output end is connected to the capacitance conversion circuit; the sampling channel switching circuit is used to connect the adjustable capacitor to the capacitance conversion circuit so that the digital capacitive oil quantity sensor completes the calibration work; the sampling channel switching circuit is used to connect the oil level sensing capacitor of the sensor to the capacitance conversion circuit so that the digital capacitive oil quantity sensor completes the fuel measurement work;

[0009] The sampling channel switching circuit includes an analog switch A1, an analog switch A2, and switches S1 and S2. The two ends of the oil level sensing capacitor of the sensor are respectively connected to the analog switch A1 and the S1 pin of the analog switch. The control end C1 of the analog switch A1 and the S1 pin of the analog switch is short-circuited and connected to the switch S1. The two ends of the adjustable capacitor are respectively connected to the analog switch A1 and the S2 pin of the analog switch. The control end C2 of the analog switch A1 and the S2 pin of the analog switch is short-circuited and connected to the switch S2.

[0010] In order to better implement the utility model, further, the sampling channel switching circuit also includes a resistor R1 and a resistor R2. The resistor R1 and the resistor R2 are respectively arranged in parallel between the control terminal C1 and the switch S1 and between the control terminal C2 and the switch S2, and the other ends of the resistor R1 and the resistor R2 are grounded.

[0011] In order to better implement the present invention, further, the sampling channel switching circuit also includes a resistor R3 and a resistor R4, the switch S1 and the switch S2 are connected to the power supply through the resistor R3 and the resistor R4 respectively, and the resistor R3 and the resistor R4 are used for current limiting.

[0012] In order to better realize the utility model, further, the adjustable capacitor includes a plurality of adjustable capacitors arranged in parallel, and the adjustable capacitor is used to simulate the capacitance value of the oil level height sensing capacitor of the sensor when the oil is empty and full.

[0013] In order to better implement the utility model, further, the adjustable capacitor is composed of adjustable capacitors C1 and C2 arranged in parallel.

[0014] In order to better implement the present invention, further, the range of the adjustable capacitor C1 is greater than the range of the adjustable capacitor C2, and the accuracy of the adjustable capacitor C2 is greater than the accuracy of the adjustable capacitor C1.

[0015] The beneficial effects of the utility model are as follows:

[0016] The utility model can make the digital capacitance oil level sensor complete the calibration work without the need to perform the oil filling and draining calibration test, and it is also unnecessary to design a special oil filling and draining test bench for it, thereby improving the production efficiency and saving the production cost. In addition, since the entire calibration process does not need to be completed in an environment with fuel, the calibration work of the digital capacitance oil level sensor is also safer and has better practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a principle block diagram of the calibration circuit of the digital capacitive oil level sensor in Example 1;

[0018] Figure 2 is a circuit schematic diagram of a calibration circuit for a digital capacitive oil level sensor in Example 1;

[0019] Figure 3 This is a calibration flow chart of the calibration circuit of the digital capacitive oil level sensor in Example 1. DETAILED DESCRIPTION

[0020] Embodiment 1:

[0021] A calibration circuit for a digital capacitive oil level sensor, such as Figure 1 As shown, a calibration circuit and a capacitance conversion circuit (capacitance signal processing circuit) are installed on the sensor circuit board, and the calibration circuit includes an adjustable capacitor and a sampling channel switching circuit. The input end of the sampling channel switching circuit is respectively connected to the adjustable capacitor and the oil level sensing capacitor of the sensor, and the output end is connected to the capacitance conversion circuit. The sampling channel switching circuit is used to connect the adjustable capacitor or the oil level sensing capacitor of the sensor to the capacitance conversion circuit.

[0022] When the adjustable capacitor is connected to the capacitance signal processing circuit, the digital capacitance oil level sensor can complete the calibration work; when the oil level height sensing capacitor of the sensor is connected to the capacitance signal processing circuit, the digital capacitance oil level sensor can complete the fuel measurement work. Specifically, the adjustable capacitor is composed of adjustable capacitors, and capacitors with different adjustable ranges and different precisions can be selected according to the required calibration accuracy requirements to simulate the capacitance value of the oil level height sensing capacitor of the sensor when the oil is empty and full of oil through series, parallel, etc.

[0023] Preferably, if Figure 2 As shown, the specific circuit structure of the utility model is as follows:

[0024] The adjustable capacitor is composed of a large-range adjustable capacitor C1 and a high-precision adjustable capacitor C2, and the large-range adjustable capacitor C1 and the high-precision adjustable capacitor C2 are arranged in parallel. Among them, the sampling channel switching circuit is composed of an analog switch A1, an analog switch A2, a resistor R1, a resistor R2, a resistor R3, a resistor R4, and switches S1 and S2.

[0025] The large-range adjustable capacitor C1 and the high-precision adjustable capacitor C2 are connected in parallel with one end to the S2 pin of the analog switch A1, and the other end to the S2 pin of the analog switch A2. The control end C2 of the S2 pins of the analog switch A1 and the analog switch A2 is short-circuited and connected to the switch S2. One end of the oil level sensing capacitor is connected to the S1 pin of the analog switch A1, and the other end is connected to the S1 pin of the analog switch A2. The control end C1 of the S1 pins of the analog switch A1 and the analog switch A2 is short-circuited and connected to the switch S1. One end of the resistor R1 and the resistor R2 are connected to the power supply ground, and the other end is connected to the switch S1 and the switch S2 respectively. The resistor R3 and the resistor R4 are respectively connected between the switch S1 and the power supply and between the switch S2 and the power supply for current limiting.

[0026] like Figure 3 As shown, the specific calibration steps of the utility model are as follows:

[0027] Step 1: Before assembling the oil level sensing capacitor and the sensor circuit board, use a capacitance tester to test the dry capacitance value C of the oil level sensing capacitor of the sensor when it is empty of oil. 0 ;

[0028] Step 2: Use formula C f =ε r ×C 0 Calculate the capacitance value C when the sensor is full of oil f , where ε r is the relative dielectric constant of fuel;

[0029] Step 3, the switch S2 is opened and the switch S1 is closed, so that the adjustable capacitors C1 and C2 are not connected to the capacitance conversion circuit, so as to facilitate the adjustment of the capacitance value of the adjustable capacitor;

[0030] Step 4: Adjust the adjustable capacitors C1 and C2 so that the parallel capacitance of C1 and C2 is equal to C 0 ;

[0031] Step 5: Close the switch S2 and open the switch S1, so that the adjustable capacitors C1 and C2 are connected to the capacitor conversion circuit and the air-oil calibration is completed;

[0032] Step 6: Open the switch S2 and close the switch S1, so that the adjustable capacitors C1 and C2 are not connected to the capacitance conversion circuit, so as to facilitate the adjustment of the capacitance of the adjustable capacitor;

[0033] Step 7: Adjust the adjustable capacitors C1 and C2 so that the parallel capacitance of C1 and C2 is equal to C f ;

[0034] Step 8: Close the switch S2 and open the switch S1, so that the adjustable capacitors C1 and C2 are connected to the capacitor conversion circuit and the full oil calibration is completed;

[0035] Step 9: After the full fuel calibration is completed, switch S2 is opened and switch S1 is closed, so that the oil level sensing capacitor of the sensor is connected to the capacitor conversion circuit to measure the fuel level.

[0036] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A calibration circuit for a digital capacitive oil level sensor, characterized in that: It includes an adjustable capacitor and a sampling channel switching circuit, wherein the input end of the sampling channel switching circuit is respectively connected to the adjustable capacitor and the oil level sensing capacitor of the sensor, and the output end is connected to the capacitance conversion circuit; the sampling channel switching circuit is used to connect the adjustable capacitor to the capacitance conversion circuit so that the digital capacitance oil quantity sensor completes the calibration work; the sampling channel switching circuit is used to connect the oil level sensing capacitor of the sensor to the capacitance conversion circuit so that the digital capacitance oil quantity sensor completes the fuel measurement work; The sampling channel switching circuit includes an analog switch A1, an analog switch A2, and switches S1 and S2. The two ends of the oil level sensing capacitor of the sensor are respectively connected to the analog switch A1 and the S1 pin of the analog switch. The control end C1 of the analog switch A1 and the S1 pin of the analog switch is short-circuited and connected to the switch S1. The two ends of the adjustable capacitor are respectively connected to the analog switch A1 and the S2 pin of the analog switch. The control end C2 of the analog switch A1 and the S2 pin of the analog switch is short-circuited and connected to the switch S2.

2. A calibration circuit for a digital capacitive oil level sensor according to claim 1, characterized in that: The sampling channel switching circuit further includes a resistor R1 and a resistor R2. The resistor R1 and the resistor R2 are respectively connected in parallel between the control terminal C1 and the switch S1 and between the control terminal C2 and the switch S2. The other ends of the resistor R1 and the resistor R2 are grounded.

3. A calibration circuit for a digital capacitive oil level sensor according to claim 2, characterized in that: The sampling channel switching circuit further includes a resistor R3 and a resistor R4. The switch S1 and the switch S2 are connected to the power supply through the resistor R3 and the resistor R4 respectively. The resistor R3 and the resistor R4 are used for current limiting.

4. A calibration circuit for a digital capacitive oil level sensor according to any one of claims 1 to 3, characterized in that: The adjustable capacitor includes a plurality of adjustable capacitors connected in parallel, and the adjustable capacitor is used to simulate the capacitance value of the oil level sensing capacitor of the sensor when the oil level is empty and when the oil level is full.

5. A calibration circuit for a digital capacitive oil level sensor according to claim 4, characterized in that: The adjustable capacitor is composed of adjustable capacitors C1 and C2 which are arranged in parallel.

6. A calibration circuit for a digital capacitive oil level sensor according to claim 5, characterized in that: The measuring range of the adjustable capacitor C1 is greater than the measuring range of the adjustable capacitor C2, and the precision of the adjustable capacitor C2 is greater than the precision of the adjustable capacitor C1.

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