An adaptive capacitive liquid level sensor

Abstract

The application discloses a self-adaptive capacitive liquid level sensor, which comprises a metal cylinder, a PCB circuit board, a reference electrode and a measuring electrode which are arranged on the PCB circuit board and are insulated from each other, the reference electrode is arranged at the bottom end of the PCB circuit board and is used for forming a reference capacitor with the metal cylinder, the measuring electrode is arranged above the reference electrode and is used for forming a measuring capacitor with the metal cylinder, and a controller is arranged for calculating the liquid level height after compensating the measuring capacitor by the reference capacitor. The capacitive liquid level sensor is provided with the reference electrode and the corresponding algorithm steps, so that the calculation of the liquid level height is irrelevant to the dielectric constant of the medium, thereby avoiding the detection error caused by the change of the dielectric constant, and the sensor can be applicable to the liquid level detection of different oil products in different environments.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of liquid level sensor, in particular to a self-adaptive capacitive liquid level sensor. BACKGROUND

[0002] Capacitive liquid level sensing technology has been adopted very early, and there are many liquid level meter products based on this principle. The sensors of this type generally adopt the principle of coaxial capacitor, the center probe and the peripheral cylinder form a measuring chamber, when the chamber is empty, the dielectric constant of air determines the size of the capacitance, after being filled with the measured liquid, the dielectric constant of the measured liquid determines the size of the capacitance, and the degree of filling the liquid is different, the size of the capacitance is also different, thus realizing liquid level detection.

[0003] Capacitive liquid level sensor can only accurately measure the liquid level when the dielectric constant of the measured liquid is very stable, however, in actual situation, it is impossible to ensure that the dielectric constant of the measured liquid is constant, for example, for different grades of fuel, even for the same grade of fuel mixed with impurities, at different temperatures, the dielectric constant is different, therefore, this brings a large error to the actual measurement, which is also the biggest disadvantage of capacitive liquid level sensor.

[0004] In addition, the existing capacitive liquid level sensor mostly adopts the measuring chamber structure composed of stainless steel cylinder and center copper rod, which has high material cost and is not conducive to adding other structures, so it is not conducive to adding other functions, such as temperature detection. SUMMARY

[0005] The present application aims to provide a self-adaptive capacitive liquid level sensor, which solves the disadvantages of the existing capacitive liquid level sensor, such as the error caused by the influence of the dielectric constant of the measured liquid, and the high production cost and the disadvantage of not being conducive to adding other functional structures.

[0006] The present application realizes the above-mentioned purpose through the following technical solutions:

[0007] A self-adaptive capacitive liquid level sensor, comprising:

[0008] a metal cylinder,

[0009] a PCB circuit board, the PCB circuit board is in a strip shape and is installed inside the metal cylinder, the PCB circuit board is provided with a reference electrode and a measurement electrode which are insulated from each other along the length direction, wherein the reference electrode is located at the bottom end position of the PCB circuit board and is used to form a reference capacitor with the metal cylinder, and the measurement electrode is located above the reference electrode and is used to form a measurement capacitor with the metal cylinder;

[0010] A controller configured to calculate the liquid level height by compensating the measurement capacitance with the reference capacitance, and the specific steps are as follows:

[0011] Step one, according to the capacitance measurement model of the reference electrode and the measurement electrode in the air, the following can be obtained:

[0012]

[0013]

[0014] Step two, according to the capacitance measurement model of the reference electrode and the measurement electrode after the reference electrode is submerged in the non-conductive liquid, the following can be obtained:

[0015]

[0016]

[0017] Step three, by compensating the measurement capacitance with the reference capacitance, the relationship between the liquid level height and the dielectric constant of the liquid is removed, and the specific steps are as follows:

[0018]

[0019]

[0020] Dividing formula 5 by formula 6 can obtain:

[0021]

[0022] Conversion can obtain:

[0023]

[0024] Step four, according to formula 8 to calculate the liquid level height H y ;

[0025] In the formula: ε A is the dielectric constant of air, ε O is the dielectric constant of the liquid, h R is the height of the reference electrode, d is the distance between the reference electrode and the measurement electrode and the metal cylinder, L is the width of the reference electrode and the measurement electrode, M is a constant, and Where k is the electrostatic force constant, H is the total height of the measurement electrode, H x is the height of the measurement electrode in the air, C RA is the reference capacitance in the air, C MA is the measurement capacitance in the air, C RO is the reference capacitance in the liquid, C M is the measurement capacitance in the partial liquid, and Δ is the corresponding parasitic capacitance, H yTo measure the height of the electrode in the liquid, that is, the liquid level.

[0026] The beneficial effect of the present invention is that the capacitive liquid level sensor, by setting a reference electrode and performing corresponding algorithm steps, makes the calculated liquid level height independent of the dielectric constant of the medium, thereby avoiding the detection error caused by the change of the dielectric constant. In this way, the sensor can be applied to liquid level detection of different oil products in different environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of the present invention;

[0028] In the figure: 1. Metal cylinder; 2. PCB circuit board; 3. Reference electrode; 4. Measuring electrode. DETAILED DESCRIPTION

[0029] The present application is described in further detail below in conjunction with the accompanying drawings. It is necessary to point out that the following specific implementation methods are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Technicians in this field can make some non-essential improvements and adjustments to the present application based on the above application content.

[0030] like Figure 1 As shown, an adaptive capacitive liquid level sensor includes:

[0031] Metal cylinder 1,

[0032] PCB circuit board 2, the PCB circuit board 2 is in the shape of an elongated strip and is installed inside the metal cylinder 1. The PCB circuit board 2 is provided with a reference electrode 3 and a measuring electrode 4 made of copper foil (or other conductive metal materials) and insulated from each other along the length direction. The reference electrode 3 is located at the bottom end of the PCB circuit board 2 and is relatively small in height, and is used to form a reference capacitor with the metal cylinder 1. The measuring electrode 4 is located above the reference electrode 3 and is substantially the entire length of the PCB circuit board 2, and is used to form a measuring capacitor with the metal cylinder 1. During installation, the sensor is installed upright in a liquid container (such as a car fuel tank), so that the metal cylinder 1 and the PCB circuit board 2 extend into the liquid, and the reference electrode 3 is immersed at the bottom. The liquid will flow into the metal cylinder 1 and contact the reference electrode 3 and the measuring electrode 4;

[0033] A controller (not shown in the figure) is configured to calculate the liquid level after compensating the measured capacitance with a reference capacitance.

[0034] The specific steps are:

[0035] Step 1: Based on the capacitance measurement model of the reference electrode and the measuring electrode in air, we can obtain:

[0036]

[0037]

[0038] Step two, according to the reference electrode and the measuring electrode in the non-conductive liquid submerged reference electrode after the capacitance measurement model can be obtained:

[0039]

[0040]

[0041] Step three, by the reference capacitance to the measuring capacitance compensation, remove the liquid level height and the relationship between the liquid dielectric constant, specifically:

[0042]

[0043]

[0044] Formula 5 divided by formula 6 can be obtained:

[0045]

[0046] Conversion:

[0047]

[0048] Step four, according to formula 8 to calculate the liquid level height H y ;

[0049] In the formula: ε A is the dielectric constant of air, ε O is the dielectric constant of liquid, h R is the height of the reference electrode, d is the distance between the reference electrode and the measuring electrode and the metal cylinder, L is the width of the reference electrode and the measuring electrode, M is a constant, and Where k is the electrostatic force constant, H is the total height of the measuring electrode, H x is the height of the measuring electrode in the air, C RA is the reference capacitance in the air, C MA is the measuring capacitance in the air, C RO is the reference capacitance in the liquid, C M is the measuring capacitance in the liquid, Δ is the corresponding parasitic capacitance (i.e. error), H y is the height of the measuring electrode in the liquid, i.e. the liquid level height.

[0050] It can be seen that through a specific algorithm steps, the final calculation formula 8 does not have dielectric constant, i.e. the liquid level height is independent of the dielectric constant of the medium, and C RA and C MAis the factory test calibration, which is a constant, C RO and C M The actual detected capacitance value result, h R is also a constant, i.e. only by reference to the capacitance and the measured capacitance, so as to avoid the detection error caused by the change of the dielectric constant, so that the sensor can be applied to different environments, different oil level detection.

[0051] The above-described embodiments only express several embodiments of the present application, which are described in detail and specifically, but cannot be understood as a limitation on the scope of the patent of the present application. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of protection of the present application.

Claims

1. An adaptive capacitive liquid level sensor, characterized in that: include: Metal cylinder, A PCB circuit board, the PCB circuit board being in the shape of an elongated strip and mounted inside the metal cylinder. The PCB circuit board is provided with a mutually insulated reference electrode and measuring electrode along its length. The reference electrode is located at the bottom end of the PCB circuit board and is used to form a reference capacitor with the metal cylinder. The measuring electrode is located above the reference electrode and is used to form a measuring capacitor with the metal cylinder. The controller is configured to calculate the liquid level height after compensating the measured capacitance by the reference capacitance, and the specific steps are as follows: Step 1: Based on the capacitance measurement model of the reference electrode and the measuring electrode in air, we can obtain: ； Step 2: Based on the capacitance measurement model of the reference electrode and the measuring electrode after the reference electrode is submerged in a non-conductive liquid, we can obtain: ； Step 3: Compensate the measurement capacitance with the reference capacitance to eliminate the relationship between the liquid level and the liquid dielectric constant. Specifically: ； Dividing Equation 5 by Equation 6 yields: ； Converted to: ; Step 4: Calculate the liquid level according to formula 8 ; Where: is the dielectric constant of air, is the dielectric constant of the liquid, is the height of the reference electrode, d is the distance between the reference electrode and the measuring electrode and the metal cylinder, L is the width of the reference electrode and the measuring electrode, M is a constant, and , where k is the electrostatic force constant, H is the total height of the measuring electrodes, To measure the height of the electrode in the air, is the reference capacitance in air, is the measured capacitance in air, is the reference capacitance in liquid immersion, is the measured capacitance in partial liquid submersion, To measure the height of the electrode in the liquid, that is, the liquid level.

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