CN103017864A - Tubular three-electrode capacitive liquid level detection sensor and detection method - Google Patents

Abstract

The invention discloses a tubular three-electrode capacitive liquid level detection sensor and a detection method, and belongs to the technical field of detection. A capacitive three-parameter detection method is adopted, and the liquid level detection is completed by integrating a combined capacitive sensor which consists of three pole plates. When a container is in a stationary state, three capacitive sensors can be used for respectively measuring the liquid level in the container, and the liquid level in the container can also be comprehensively evaluated by comparing the measuring valves of the three capacitive sensors, so the redundancy, reliability and robustness of the measuring information are improved. When the container is in a moving state, because the detection sensor is provided with a three-electrode structure, three measuring output capacitors provide the sufficient information redundancy, including inclining conditions of the container and the like, and the outputted capacitive valves of the three sensors can be integrated to evaluate the height of the liquid level in the container. The detection sensor and the detection method have the advantages that the structure is simple, the manufacture cost is low, the information redundancy is high, the reliability and the robustness are high, and the precision is high.

Description

A kind of tubular three electrode capacitance formula liquid level detecting sensor and detection methods

Technical field

The invention belongs to the detection technique field, relate to more precisely a kind of liquid level detecting sensor and method that adopts electric field technology, be used for the evaluation to dynamic container liquid level.

Background technology

At present, liquid level sensor is widely used in various fields, wherein most of liquid level detection all is the technology that forms towards constant vessel, and float level meter, ultrasonic level gage, fiber optic liquid height meter, differential pressure type level gauge, cylindrical two electrode capacitance formula liquid level gauges etc. are arranged in the implementation.

But a major defect of these methods is just can not accurately to detect when container is in dynamically among (time and when inclination and upright), needs extra detection and error compensation for container lean this moment.In addition, traditional liquid level detects and mostly adopts the measurements such as one-parameter such as single capacitor, and the information redundancy of measuring system is low, and its reliability and robustness are subject to certain restrictions.

Summary of the invention

For the deficiency of Technology of Level Detection of the prior art, the present invention proposes that a kind of measuring accuracy is high, reliability and robustness are good, can be applicable in the dynamic container container lean be disturbed self compensation liquid level detecting sensor and detection method.

Specifically, the present invention takes following technical scheme to realize: a kind of tubular three electrode capacitance formula liquid level detecting sensors, comprise the arc sheet shape electrode of three same sizes, columniform plastic tube, screen layer, screen layer is attached to plastic tube outer wall, three arc sheet shape electrode pastes are at plastic pipe inner wall, three arc sheet shape electrodes are equal along the interval of plastic pipe inner wall between any two, and the height of each arc sheet shape electrode is identical with the height of plastic tube, injects fluid to be measured in the plastic tube.

Further aspect of the present invention is: described three arc sheet shape electrodes are between any two along the 1 millimeter arc length that is spaced apart of plastic pipe inner wall.

The present invention also comprises a kind of method that adopts above-mentioned tubular three electrode capacitance formula liquid level detecting sensors to carry out the liquid level detection, the steps include: in plastic tube, to inject first fluid to be measured, then measure the value of three arc sheet shape electrodes electric capacity between any two, obtain again the liquid level of fluid to be measured according to formula (1):

L(C ₁,C ₂,C ₃)＝α ₀+α ₁C ₁+α ₂C ₂+α ₃C ₃ （1）

In the above-mentioned formula (1), L is the liquid level of fluid to be measured, C ₁, C ₂, C ₃Three arc sheet shape electrodes electric capacity between any two, α ₀, α ₁, α ₂, α ₃Be coefficient;

Wherein, α ₀, α ₁, α ₂, α ₃Can utilize various known liquid level L _k, (k=1,2 ..., m) and the corresponding capacitance C that measures _1k, C _2k, C _3k, (k=1,2 ..., m) adopt least square method to calculate, its process is as follows:

If L _kAnd L (C _1k, C _2k, C _3k) between variance be: (Δ _k) ²=[L _k-L (C _1k, C _2k, C _3k)] ², total total m liquid level test point, then its mean square deviation R is as described in the formula (2):

$R=\frac{1}{m}\underset{k=1}{\overset{m}{\mathrm{\Σ}}}{[L_k-L(C_{1k},C_{2k},C_{3k})]}^2$

$=\frac{1}{m}\underset{k=1}{\overset{m}{\mathrm{\Σ}}}{[L_k-({\mathrm{\α}}_0+{\mathrm{\α}}_1{C}_{1k}+{\mathrm{\α}}_2{C}_{2k}+{\mathrm{\α}}_3{C}_{3k})]}^2$

$=f({\mathrm{\α}}_0,{\mathrm{\α}}_1,{\mathrm{\α}}_2,{\mathrm{\α}}_3)---\left(2\right)$

Principle according to mean square deviation R minimum gets:

$\frac{\∂R}{\∂{\mathrm{\α}}_0}=0$ $\frac{\∂R}{\∂{\mathrm{\α}}_1}=0$ $\frac{\∂R}{\∂{\mathrm{\α}}_2}=0$ $\frac{\∂R}{\∂{\mathrm{\α}}_3}=0$

Again formula (2) is brought into top 4 equatioies respectively to α ₀, α ₁, α ₂, α ₃Ask the local derviation computing and put in order:

$\left\{\begin{array}{c}{\mathrm{\&alpha;}}_{0}m+{\mathrm{\&alpha;}}_1\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{1k}+{\mathrm{\&alpha;}}_2\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{2k}+{\mathrm{\&alpha;}}_3\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{3k}=\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{L}_k\\ {\mathrm{\&alpha;}}_0\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{1k}+{\mathrm{\&alpha;}}_1\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{1\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="121217190424.png,121217190429.png"\; state="\{\{state\}\}">k</figure-callout>}}^2+{\mathrm{\&alpha;}}_2\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{1k}{C}_{2k}+{\mathrm{\&alpha;}}_3\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{1k}{C}_{3k}=\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{1k}{L}_k\\ {\mathrm{\&alpha;}}_0\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{2k}+{\mathrm{\&alpha;}}_1\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{1k}{C}_{2k}+{\mathrm{\&alpha;}}_2\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{2\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="121217190424.png,121217190429.png"\; state="\{\{state\}\}">k</figure-callout>}}^2+{\mathrm{\&alpha;}}_3\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{2k}{C}_{3k}=\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{2k}{L}_k\\ {\mathrm{\&alpha;}}_0\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{3k}+{\mathrm{\&alpha;}}_1\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{1k}{C}_{3k}+{\mathrm{\&alpha;}}_2\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{2k}{C}_{3k}+{\mathrm{\&alpha;}}_3\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{3\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="121217190424.png,121217190429.png"\; state="\{\{state\}\}">k</figure-callout>}}^2=\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{3k}{L}_k\end{array}\right\}$

Separate at last this with α ₀, α ₁, α ₂, α ₃For 4 yuan of linear function groups of unknown number to obtain α ₀, α ₁, α ₂, α ₃Value.

Beneficial effect of the present invention is as follows: the present invention has electric capacity tri-consult volume detection mode, liquid level detects the combination capacitor formula sensor fusion that is comprised of tri-electrode and finishes, concrete fusion process can adopt the multivariate regression method, namely at first use liquid level judgement schematics of fitting of a polynomial, then try to achieve coefficient in the polynomial expression with the sensor output capacitance value experimental data base of known liquid level and least square method, adopt again at last this polynomial expression to estimate unknown liquid level information.When container remains static, but the equal liquid levels in the independent measurement container of 3 capacitive transducers also can compare their measured value and come liquid level in the comprehensive evaluation container, improved the metrical information redundancy, reliability and robustness; When container is kept in motion (time and when inclination and upright), because sensor has 3 electrode structures, its 3 measure output capacitances provides the enough information that comprises container lean situation etc. redundant, the output capacitance value that can merge 3 sensors is estimated the height of liquid level in the container, thereby reach the self-compensating effect of the interference that in the liquid level evaluation procedure container lean is brought, final measuring accuracy is improved.The present invention is simple in structure, low cost of manufacture, information redundancy are high, and reliability and robustness are good, and precision is high.

Description of drawings

Fig. 1 is plan structure schematic diagram of the present invention.

Fig. 2 side-looking structural representation of the present invention.

Among the above figure, 1 is the first electrode, and 2 is the second electrode, 3. is third electrode, and 4 is screen layer, and 5 is plastic tube, and 6 is fluid to be measured, C ₁Be the electric capacity between the first electrode 1 and the second electrode 2, C ₂Be the electric capacity between the second electrode 2 and the third electrode 3, C ₃Be the electric capacity between the first electrode 1 and the third electrode 3.

Embodiment

Below in conjunction with accompanying drawing, describe the present invention.

As shown in Figure 1, 2, tubular three electrode capacitance formula liquid level detecting sensors of the present invention comprise arc sheet shape electrode the first electrode 1, the second electrode 2, third electrode 3, columniform plastic tube 5, the screen layer 4 of three same sizes.Screen layer 4 close attachment are at plastic tube 5 outer walls.The first electrode 1, the second electrode 2, third electrode 3 closely are attached to plastic tube 5 inwalls, and the first electrode 1, the second electrode 2, third electrode 3 equate along the interval of plastic tube 5 inwalls between any two, formed in twos 3 capacitive transducers between electrode.The height of the first electrode 1, the second electrode 2, third electrode 3 is highly identical with plastic tube 5.Plastic tube 5 interior injection fluids to be measured 6.Wherein, the first electrode 1, the second electrode 2, third electrode 3 can specifically be made as 1 millimeter arc length along the interval of plastic tube 5 inwalls between any two.

The principle of tubular three electrode capacitance formula liquid level detecting sensors of the present invention is, when the space in the fluid to be measured 6 inflow plastic tubes 5, the change of the electrolyte specific inductive capacity between the capacitive transducer pole plate that forms in twos between the first electrode 1, the second electrode 2, the third electrode 3 has caused the variation of electric capacity between the two-plate, the liquid level existence function relation of the Changing Pattern of this electric capacity and fluid to be measured 6, thus can utilize this relation to detect the liquid level of fluid to be measured 6.Particularly, the relation between them can be come match with following polynomial expression.

L(C ₁,C ₂,C ₃)＝α ₀+α ₁C ₁+α ₂C ₂+α ₃C ₃

In the above-mentioned formula, L is the liquid level of fluid to be measured 6, C ₁, C ₂, C ₃Respectively the electric capacity between the first electrode 1 and the second electrode 2, the second electrode 2 and third electrode 3, the first electrode 1 and the third electrode 3, α ₀, α ₁, α ₂, α ₃Be coefficient.

And α ₀, α ₁, α ₂, α ₃Can utilize various known liquid level L _k(k=1,2 ..., m) and corresponding measured capacitance values C _1k, C _2k, C _3k, (k=1,2 ..., the experimental data base between m) adopts least square method to calculate, and detailed process is as follows:

If L _kAnd L (C _1k, C _2k, C _3k) between variance be: (Δ _k) ²=[L _k-L (C _1k, C _2k, C _3k)] ², always have m liquid level test point, then its mean square deviation R is:

$R=\frac{1}{m}\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{[L_k-L(C_{1k},C_{2k},C_{3k})]}^2$

$=\frac{1}{m}\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{[L_k-({\mathrm{\&alpha;}}_0+{\mathrm{\&alpha;}}_1{C}_{1k}+{\mathrm{\&alpha;}}_2{C}_{2k}+{\mathrm{\&alpha;}}_3{C}_{3k})]}^2$

$=f({\mathrm{\&alpha;}}_0,{\mathrm{\&alpha;}}_1,{\mathrm{\&alpha;}}_2,{\mathrm{\&alpha;}}_3)$

Principle according to mean square deviation R minimum gets:

$\frac{\&PartialD;R}{\&PartialD;{\mathrm{\&alpha;}}_0}=0$ $\frac{\&PartialD;R}{\&PartialD;{\mathrm{\&alpha;}}_1}=0$ $\frac{\&PartialD;R}{\&PartialD;{\mathrm{\&alpha;}}_2}=0$ $\frac{\&PartialD;R}{\&PartialD;{\mathrm{\&alpha;}}_3}=0$

The expression formula of mean square deviation R is brought into top 4 equatioies respectively to α ₀, α ₁, α ₂, α ₃Ask the local derviation computing and put in order:

$\left\{\begin{array}{c}{\mathrm{\&alpha;}}_{0}m+{\mathrm{\&alpha;}}_1\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{1k}+{\mathrm{\&alpha;}}_2\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{2k}+{\mathrm{\&alpha;}}_3\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{3k}=\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{L}_k\\ {\mathrm{\&alpha;}}_0\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{1k}+{\mathrm{\&alpha;}}_1\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{1\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="121217190424.png,121217190429.png"\; state="\{\{state\}\}">k</figure-callout>}}^2+{\mathrm{\&alpha;}}_2\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{1k}{C}_{2k}+{\mathrm{\&alpha;}}_3\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{1k}{C}_{3k}=\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{1k}{L}_k\\ {\mathrm{\&alpha;}}_0\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{2k}+{\mathrm{\&alpha;}}_1\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{1k}{C}_{2k}+{\mathrm{\&alpha;}}_2\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{2\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="121217190424.png,121217190429.png"\; state="\{\{state\}\}">k</figure-callout>}}^2+{\mathrm{\&alpha;}}_3\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{2k}{C}_{3k}=\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{2k}{L}_k\\ {\mathrm{\&alpha;}}_0\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{3k}+{\mathrm{\&alpha;}}_1\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{1k}{C}_{3k}+{\mathrm{\&alpha;}}_2\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{2k}{C}_{3k}+{\mathrm{\&alpha;}}_3\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{3\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="121217190424.png,121217190429.png"\; state="\{\{state\}\}">k</figure-callout>}}^2=\underset{k=1}{\overset{m}{\mathrm{\&Sigma;}}}{C}_{3k}{L}_k\end{array}\right\}$

Separate at last this with α ₀, α ₁, α ₂, α ₃For 4 yuan of linear function groups of unknown number get its calibration value.

Therefore, the method that the present invention adopts above-mentioned tubular three electrode capacitance formula liquid level detecting sensors to carry out the liquid level detection is, first at plastic tube 5 interior injection fluids to be measured 6, then measure the value of the electric capacity between the first electrode 1 and the second electrode 2, the second electrode 2 and third electrode 3, the first electrode 1 and the third electrode 3, obtain again the liquid level of fluid to be measured 6 according to the relational expression of described electric capacity and liquid level.

Although the present invention is with preferred embodiment openly as above, embodiment be not limit of the present invention.Without departing from the spirit and scope of the invention, any equivalence of doing changes or retouching, belongs to equally the present invention's protection domain.Therefore protection scope of the present invention should be take the application's the content that claim was defined as standard.

Claims (3)

1. one kind tubular three electrode capacitance formula liquid level detecting sensors, it is characterized in that: comprise the arc sheet shape electrode of three same sizes, columniform plastic tube, screen layer, screen layer is attached to plastic tube outer wall, three arc sheet shape electrode pastes are at plastic pipe inner wall, three arc sheet shape electrodes equate along the interval of plastic pipe inner wall between any two, the height of each arc sheet shape electrode is identical with the height of plastic tube, injects fluid to be measured in the plastic tube.

2. a kind of tubular three electrode capacitance formula liquid level detecting sensors according to claim 1 is characterized in that: described three arc sheet shape electrodes are between any two along the 1 millimeter arc length that is spaced apart of plastic pipe inner wall.

3. one kind is adopted the claims 1 or 2 described tubular three electrode capacitance formula liquid level detecting sensors to carry out the method that liquid level detects, it is characterized in that: in plastic tube, inject first fluid to be measured, then measure the value of three arc sheet shape electrodes electric capacity between any two, obtain again the liquid level of fluid to be measured according to formula (1):

（1）

In the above-mentioned formula (1), LThe liquid level of fluid to be measured, C ₁, C ₂, C ₃Three arc sheet shape electrodes electric capacity between any two,

Be coefficient;

Wherein,

Can utilize various known liquid levels L _k ,( k=1,2 ..., m) and the corresponding capacitance of measuring C _1k, C _2k, C _3k, ( k=1,2 ..., m) adopt least square method to calculate, its process is as follows:

If L _k With L( C _1k, C _2k, C _3k) between variance be: (Δ _k) ²=[ L _k- L( C _1k, C _2k, C _3k)] ², total total mIndividual liquid level test point, then its mean square deviation RAs described in formula (2):

（2）

According to mean square deviation RMinimum principle gets:

Again formula (2) is brought into top 4 equatioies right respectively

Ask the local derviation computing and put in order:

Separate at last this with

For 4 yuan of linear function groups of unknown number to obtain

Value.

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