CN2525487Y - Capacitance level meter - Google Patents

Abstract

A capacitance level meter is provided with two sensors. The output capacitances of the two sensors respectively are Cs1=B1 S1+A1 and Cs2= B2S2 + A2, wherein, S1 and S2 represent the areas of capacitance dipping the liquid, the equivalent capacitances A1 and A2 are fixed values, inductive reactances X11 and X12 are used to do resonance with the equivalent capacitances A1 and A2 to make the current flowing into the syntonic circuit be zero. Therefore, Cs1 and Cs2 are only relevant to B1 S1 and B2 S2. A meter capable of realizing the read-around ratio of voltage or current is used for comparing the output signals of the two sensors of B1 S1 and B2 S2. Therefore, the conclusions are reached that the measured valve is only relevant to the ratio of capacitance areas of the two sensors dipping in the liquid S1 and S2 and has nothing to do with other factors,. The measured value is not affected by the change in specific inductive capacity .

Description

A kind of capacitance liquid level meter

(1) technical field: the present invention relates to a kind of capacitance liquid level meter of measuring liquid measure, be used in particular for measuring the gasoline storage capacity in the vehicles petrol tank.

(2) background technology: the reading of capacitance liquid level meter often is subjected to the variable effect of dielectric Constant and produces error on the market.

(3) summary of the invention: it is irrelevant that the object of the invention provides a kind of capacitance liquid level meter reading and dielectric change in dielectric constant of making, only relevant with the area in electric capacity is immersed in liquid, accurately measures a kind of capacitance liquid level meter of storage liquid measure.

The present invention seeks to realize like this, this capacitance liquid level meter comprises sensor and Displaying Meter, and its principle of work is: two of sensor D are set, external alternate electrical signal, as survey conductive body, the capacitor plate of sensor will apply one deck insulating material, first sensor D ₁Capacitor C s ₁With second sensor D ₂Capacitor C s ₂Be immersed in the liquid as electrode, be immersed in the long-pending S that is respectively in liquid the inside ₁And S ₂When changing between the electrode of liquid level at capacitance type sensor of fluid to be measured, be equivalent to the variation of medium between pole plate, thereby cause the variation of electric capacity, the 120th page of record of " sensor practical application circuit design " first published that the Huang Xianwu that publishes according to publishing house of University of Electronic Science and Technology etc. writes: capacitance liquid level meter sensor output capacitance Cx=A+Bx, A, B are and the sensor construction size that the constant that measured medium is relevant, x are liquid level.Also can be scaled sensor output capacitance Cs=A+BS by this formula, S is immersed in the liquid area for capacitor C s, and A, B are and the capacitance structure size the relevant constant of measured medium.It is in parallel with equivalent capacity BS that the equivalent electrical circuit of capacitor C s can be equivalent capacity A, and equivalent capacity A is a definite value, capacitor C s and inductive reactance X _L(inductive reactance X in parallel _LWith equivalent capacity A resonance), form sensor D, because inductive reactance X _LWith the resonant circuit resistance infinity that equivalent capacity A forms, the electric current that external circuit flows into this resonant circuit is zero, and so, sensor D output capacitance Cs just becomes with equivalent capacity A irrelevant, and is only relevant with equivalent capacity BS.This point, also available mathematical formulae represent that sensor D output capacitance Cs=A+BS is as capacitor C s and inductive reactance X _LWhen in parallel, reactance is: $\frac{1}{\mathrm{j\ωCs}+\frac{1}{j{X}_K}}=\frac{1}{\mathrm{j\ω}(\mathrm{BS}+A)+\frac{1}{j{X}_L}}=\frac{1}{\mathrm{j\ωBS}+\mathrm{j\ωA}-\frac{j}{X_L}}$ As A and X _LResonance

The time, the reactance of sensor D equals So first sensor D ₁Output capacitance Cs ₁At this moment be B only ₁S ₁, second sensor D ₂Output capacitance Cs ₂At this moment be B only ₂S ₂Sensor output voltage or electric current respectively with B ₁S ₁, B ₂S ₂Proportional.With can realize voltage or current indication the time than the instrument measurement sensor, can realize the ratio of two sensor output voltages or electric current, equal two capacitor C s ₁, Cs ₂Be immersed in the area S in the liquid ₁And S ₂Ratio, so, just realized that the reading of capacitance liquid level meter is not influenced by dielectric change in dielectric constant, only be immersed in liquid in capacity area relevant.

Because the design of capacitance liquid level meter of the present invention, the output capacitance that makes sensor only be immersed in liquid in two capacity areas than relevant, irrelevant with other factors, so influenced by the medium change in dielectric constant and the shortcoming that produces error with regard to having overcome capacitance liquid level meter reading on the market, if it being used the vehicles such as automobile gets on, replace present automobile float-type sensor, can cancel mechanical transmission mechanism, overcome existing float-type sensor error and reach the 10-25% shortcoming.Improve measuring accuracy, volume simple in structure is little.

(4) description of drawings:

Fig. 1, sensor device synoptic diagram.(1) be container, (2) are split pin, Cs ₁, Cs ₂Be electric capacity, X _L1, X _L2Be inductive reactance, D ₁, D ₂Be sensor.

Fig. 2, sensor equivalent circuit diagram.A ₁, A ₂, B ₁S ₁, B ₂S ₂Be equivalent capacity, X _L1, X _L2Be inductive reactance. Frame of broken lines interior resonance circuit.

(5) embodiment: from Fig. 1, Fig. 2, this capacitance liquid level meter is provided with two sensors, capacitor C s ₁, Cs ₂The lower end is positioned at container (1) bottom, and it is fixing that the upper end is exported pin (2), capacitor C s ₁With inductive reactance X _L1(inductive reactance X in parallel _L1With equivalent capacity A ₁Resonance), form first sensor D ₁, capacitor C s ₂With inductive reactance X _L2(inductive reactance X in parallel _L2With equivalent capacity A ₂Resonance), form second sensor D ₂, capacitor C s ₁And Cs ₂As sensor D ₁, D ₂Electrode be immersed in the liquid, along with liquid measure changes, an electrode part has appearred in air, a part is immersed in the liquid, S ₁And S ₂Be respectively capacitor C s ₁And Cs ₂Be immersed in the area in the liquid, when changing between the electrode of liquid level at capacitance type sensor of fluid to be measured, be equivalent to the dielectric variation of interpolar, thereby cause electric capacitance change, first sensor D ₁Output capacitance Cs ₁=A ₁+ B ₁S ₁, second sensor D ₂Output capacitance Cs ₂=A ₂+ B ₂S ₂, A ₁, A ₂, B ₁, B ₂For with capacitor arrangement size, the relevant constant of measured medium, capacitor C s ₁Equivalent electrical circuit be equivalent capacity A ₁With equivalent capacity B ₁S ₁Parallel connection, capacitor C s ₂Equivalent electrical circuit be equivalent capacity A ₂With equivalent capacity B ₂S ₂Parallel connection, equivalent capacity A ₁, A ₂Be a definite value, at this moment inductive reactance X _L1, X _L2Respectively with electric capacity A ₁, A ₂Form resonant circuit, because resonant circuit resistance infinity, the electric current that external circuit flows into this resonant circuit is zero, so, and sensor D ₁, D ₂Shu Chu capacitor C s respectively ₁, Cs ₂Just become and equivalent capacity A ₁, A ₂Irrelevant, only and B ₁S ₁, B ₂S ₂Relevant, see Fig. 2.The voltage of two sensors output or electric current respectively with B ₁S ₁, B ₂S ₂Proportional.All can realize voltage or current indication than instrument measurement sensor with logolmeter, logarithmic amplifier, electromagnetic type petrol gauge etc., just can obtain $\frac{V_2}{V_1}=\frac{B_1{s}_1}{B_2{s}_2},\frac{I_1}{I_2}=\frac{B_1{s}_1}{B_2{s}_2}$

The ratio that has more than proved absolutely two sensor output voltages or electric current equals two capacitor C s ₁And Cs ₂Be immersed in the area S in the liquid ₁And S ₂Ratio, so, just realized that the reading of capacitance liquid level meter is not influenced by dielectric change in dielectric constant, only be immersed in liquid in capacity area relevant.

Claims (2)

1. One, a kind of sensor of capacitance liquid level meter comprises capacitor C s ₁, Cs ₂With inductive reactance X _L1, X _L2, it is characterized in that: capacitance liquid level meter is provided with two sensor D ₁, D ₂, capacitor C s ₁With inductive reactance X _L1Parallel connection, inductive reactance X _L1With equivalent capacity A ₁Resonance is formed a sensor D ₁, capacitor C s ₂With inductive reactance X _L2Parallel connection, inductive reactance X _L2With equivalent capacity A ₂Resonance is formed another sensor D ₂
2. Two, according to the sensor of the described capacitance liquid level meter of claim 1, it is characterized in that: inductive reactance X _LCan adopt inductance L.