CN102589644A - Capacitance type liquid level sensor - Google Patents

Capacitance type liquid level sensor Download PDF

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Publication number
CN102589644A
CN102589644A CN2011100071357A CN201110007135A CN102589644A CN 102589644 A CN102589644 A CN 102589644A CN 2011100071357 A CN2011100071357 A CN 2011100071357A CN 201110007135 A CN201110007135 A CN 201110007135A CN 102589644 A CN102589644 A CN 102589644A
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liquid level
capacitance
microprocessor
inductive switch
induction electrode
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CN102589644B (en
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周荣
谌清平
吴金炳
惠滨华
肖强
丁央舟
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Suzhou Luzhiyao Technology Co Ltd
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Suzhou Luzhiyao Technology Co Ltd
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Abstract

The invention relates to a capacitance type liquid level sensor, which comprises a liquid level sensing switch (20) and a microprocessor (21). The liquid level sensing switch (20) is provided with a sensing electrode (201), and the sensing electrode (201) is connected with the microprocessor (21). The capacitance type liquid level sensor is provided with the sensing electrode, is placed on the surface of a closed container or a pipeline or a utensil, and carries out liquid level detection by the aid of a capacitance type touch sensing principle. Compared with a traditional 'liquid level sensor', the capacitance type liquid level sensor only has one sensing electrode, is small in volume and high in accuracy and interference resistance, a circuit structure is simple, reliability of a product is improved, the service life of the product is prolonged, and the cost of the product is lowered. In addition, the capacitance type liquid level sensor is contactless, and is simple and convenient in installation, utilization and maintenance.

Description

A kind of capacitance level transducer
Technical field
The present invention relates to liquid level control field, more specifically, relate to a kind of capacitance level transducer.
Background technology
There is a kind of capacitance type sensor in traditional liquid level control field, and its principle is following, can know from physics, and when ignoring the edge effect of two parallel metal sheets, two capacitors that parallel metal sheet constitutes, show that like Fig. 1 its electric capacity C is:
C=ε oε rS/D (1)
ε o: permittivity of vacuum, ε o=8.85*10 -12(F/m);
ε r: the relative dielectric constant of medium between pole plate, vacuum medium, ε r=1;
Area (the m that the S=pole plate hides each other 2);
D=polar plate spacing (m);
Existing capacitance type sensor is exactly according to three parameters (S, D, ε in the formula (1) r) in any amount change, cause that electric capacity C changes.That is to say, if the variation of parameter to be detected (like displacement, pressure, liquid level etc.) causes S, D, ε rChange one of in three parameters, realize parameter measurement with regard to the change of corresponding electric capacity capable of using.Therefore, capacitance type sensor commonly used can be divided into three major types usually: pole span change type capacitive transducer (changing D), area change type capacitive transducer (changing S) and media variations type capacitive transducer (change ε r).This sensor has individual common characteristic, and needing two induction electrodes, the capacitance of surveying is electric capacitys between two induction electrodes all.In some airtight volume, pipeline or vessel, installation another one induction electrode very difficulty perhaps is placed on induction electrode in the solution for a long time, and situation such as corrosion can take place induction electrode.
Summary of the invention
Above-mentioned defective to existing liquid level sensor the invention provides a kind of improved capacitance level transducer, is single induction electrode of the working method of a kind of employing " capacitance charge transfer ", and volume is little simultaneously, the capacitance level transducer that cost is low.
A kind of capacitance level transducer of the present invention comprises liquid level inductive switch (20) and microprocessor (21); Wherein said liquid level inductive switch (20) has induction electrode (201); Induction electrode (201) connects said microprocessor (21); Microprocessor (21) connects liquid level inductive switch (20) through input/output end port (210), to said liquid level inductive switch (20) repeated charge and the inductance capacitance (Cf) that detects said induction electrode (201) generate the liquid level detection signal (AD0, ADf).
Preferably, said microprocessor (21) further comprises: capacitance charge carry circuit (211), to stray capacitance (Ch) repeated charge and the electric charge transfer of said liquid level inductive switch (20) and microprocessor (21); Analog to digital converter (212), and the input signal values of liquid level inductive switch (20) after sampling acquisition electric charge shifts repeatedly (AD1, ADh); Digital signal processing module (213), to sampling sampling repeatedly keep the said input signal values that analog to digital converter (212) conversion back obtained (AD1, ADh) deposit, difference comparison operation and digital filtering processing obtain the Level Detection signal (AD0, ADf).
Preferably, said charge transfer circuit (211) comprises that first discharges and recharges terminal (RA0), first CS (K1), and second discharges and recharges terminal (RA1), second CS (K2) and charge transfer switch (K0); Wherein first discharge and recharge terminal (RA0) through said first CS (K1) connection said liquid level inductive switch (20); Second discharges and recharges terminal (RA1) connects microprocessor through second CS (K2) stray capacitance (Ch); Charge transfer switch (K0) connects said liquid level inductive switch (20) and said stray capacitance (Ch) and controls the electric charge transfer of the two.
Preferably, said digital signal processing module (213) comprises register (2131), deposit the said input signal values that keeps being obtained after analog to digital converter (212) conversion through sampling repeatedly (AD1, ADh); Differential ratio is than computing module (2132), and keep back obtained some of analog to digital converter (212) conversion (AD1 ADh) carries out the difference comparison operation and obtains several differential signals (ADn) to said input signal values to sampling repeatedly; Digital filtering processing module (2133), to said several differential signals (ADn) carry out digital filtering handle to obtain said Level Detection signal (AD0, ADf).
Preferably, said induction electrode (201) is a sheet metal.
Preferably, said induction electrode (201) is provided with the very thin insulation crust of sealing.
Capacitance level transducer of the present invention has adopted the principle of work of " capacitance charge transfer "; When the liquid in the container surpasses or is lower than said induction electrode; The capacitance that the microprocessor input/output end port is connected changes, thereby detects the variation of internal tank liquid level accurately, and capacitance level transducer of the present invention adopts an induction electrode; Be placed on the surface of airtight volume, pipeline or vessel, utilize the capacitance touch principle of induction to carry out Level Detection.Compare with traditional " liquid level sensor ", have only an induction electrode, volume is very little, and accuracy is high; Circuit structure is simple, and antijamming capability is strong, has increased reliability of products and life-span; Reduced cost of products, and be contactless, installed, use, keeped in repair all simple and convenient.
Description of drawings
Fig. 1 is the structural representation of capacitor
Fig. 2 is the structural representation of the capacitance level transducer of the embodiment of the invention;
Fig. 3 is the structural representation of digital signal processing module;
Fig. 4 is a synoptic diagram of using the liquid level intelligent controller of above-mentioned capacitance level transducer.
Embodiment
By specifying technology contents of the present invention, structural attitude, realized purpose and effect, give explanation below in conjunction with embodiment and conjunction with figs. are detailed.
Embodiment 1,
Fig. 2, Fig. 3 and Fig. 4 are the structural representations of the capacitance level transducer of the embodiment of the invention.A kind of capacitance level transducer comprises liquid level inductive switch (20) and microprocessor (21); Wherein said liquid level inductive switch (20) has induction electrode (201); Induction electrode (201) is a sheet metal, and it is provided with the very thin insulation crust of sealing 202.Said sheet metal and insulation crust 202 all are placed on the surface of volume, pipeline or the vessel of carrying liquid.
Induction electrode (201) connects said microprocessor (21); Microprocessor (21) connects liquid level inductive switch (20) through input/output end port (210); Exist fixing outside to disperse stray capacitance (Co) in its connection line; Concordant with liquid level inductive switch (20) or when surpassing, the shell of spacer insulator layer (202) and vessel between induction electrode (201) and the liquid 31 forms inductance capacitance (Cf) between induction electrode (201) and the liquid 31 when the liquid level of the liquid in the container 32 31; When liquid 31 liquid levels were lower than inductive switch (20), inductance capacitance Cf value was zero.
Said microprocessor (21) further comprises: the stray capacitance (Ch) of capacitance charge carry circuit (211), microprocessor (21), analog to digital converter (212) and digital signal processing module (213).Said charge transfer circuit (211) comprises that first discharges and recharges terminal (RA0), first CS (K1), and second discharges and recharges terminal (RA1), second CS (K2) and charge transfer switch (K0); Wherein first discharge and recharge terminal (RA0) through said first CS (K1) connection said liquid level inductive switch (20); Second discharges and recharges terminal (RA1) connects microprocessor through second CS (K2) stray capacitance (Ch); Charge transfer switch (K0) connects said liquid level inductive switch (20) and said stray capacitance (Ch) and controls the electric charge transfer of the two.
Capacitance charge carry circuit (211) is to stray capacitance (Ch) repeated charge and the electric charge transfer of said liquid level inductive switch (20) and microprocessor (21); Analog to digital converter (212), and the input signal values of liquid level inductive switch (20) after sampling acquisition electric charge shifts repeatedly (AD1, ADh); Digital signal processing module (213), to sampling repeatedly keep the said input signal values that analog to digital converter (212) conversion back obtained (AD1, ADh) deposit, difference comparison operation and digital filtering processing obtain the Level Detection signal (AD0, ADf).
Said digital signal processing module (213) comprises register (2131), deposit the said input signal values that keeps being obtained after analog to digital converter (212) conversion through sampling repeatedly (AD1, ADh); Differential ratio is than computing module (2132), and keep back obtained some of analog to digital converter (212) conversion (AD1 ADh) carries out the difference comparison operation and obtains several differential signals (ADn) to said input signal values to sampling repeatedly; Digital filtering processing module (2133), to said several differential signals (ADn) carry out digital filtering handle to obtain said Level Detection signal (AD0, ADf).
Capacitance level transducer of the present invention adopts " capacitance charge transfer " working method; Directly linked to each other with induction electrode in the liquid level inductive switch by microprocessor (CPU), said microprocessor has I/O (I/O) port of analog to digital converter 212 (A/D) translation function.(as: water, formic acid, methyl alcohol, ethanol, acetone, liquid ammonia, n-hexyl alcohol, glycerine, ore or latex etc. are in container, pipeline or vessel the time when the higher conductor of specific inductive capacity; The higher conductor of specific inductive capacity is coupled between insulator (insulation crust 202 and vessel shell) and induction electrode 201 and produces inductance capacitance Cf; The capacitance of input/output end port 210 connections of microprocessor 21 is changed; The inductance capacitance Cf that is produced between liquid that the liquid level change that detects microprocessor 21 causes and the induction electrode 201, thus the detection signal of representing fluid level condition generated.Owing to have outside distribution stray capacitance Co at liquid level inductive switch 20; And microprocessor chip inside has stray capacitance Ch; The inductance capacitance Cf that is produced between liquid 31 and the induction electrode 201 and outside distribution stray capacitance Co and stray capacitance Ch differ little; In order to eliminate Ch and the Co influence to Level Detection, microprocessor 21 adopts difference A/D comparison operation method to detect inductance capacitance Cf, thereby reaches the purpose of detecting liquid level.
As shown in Figure 2, capacitance level transducer of the present invention comprises liquid level inductive switch 20 and microprocessor 21; Wherein said liquid level inductive switch 20 has induction electrode 201; Induction electrode 201 connects said microprocessor 21.When liquid level in the container 32 rises to concordant below induction electrode or surpass induction electrode 201; The inductance capacitance Cf that is produced between liquid 31 and the induction electrode 201 can be from certain value that is raised to above freezing; When liquid level in the container 32 is reduced to induction electrode when below, then inductance capacitance Cf=0.Liquid level inductive switch 20 also has outside distribution stray capacitance Co.Like Fig. 2, microprocessor 21 connects liquid level inductive switch 20 through its input/output end port 210.Microprocessor 21 carries out repeated charge through 210 pairs of said liquid level inductive switches 20 of its input/output end port, and detects the inductance capacitance Cf of said induction electrode 201 repeatedly, according to variation generation liquid level detection signal AD0 or the Adf of inductance capacitance Cf.
Wherein, the structure of said microprocessor 21 further comprises: capacitance charge carry circuit 211, and analog to digital converter 212 and digital signal processing module 213, and the chip internal of microprocessor 21 also has stray capacitance Ch.
Capacitance charge carry circuit 211 is connected to outside said liquid level inductive switch 20 through input/output end port 210, and control discharges and recharges repeatedly with electric charge the stray capacitance Ch of said liquid level inductive switch 20 and microprocessor 21 and shifts.Particularly, said charge transfer circuit 211 comprises that first discharges and recharges terminal RA0, the first CS K1, and second discharges and recharges terminal RA1, the second CS K2 and charge transfer switch K0; Wherein first discharge and recharge terminal RA0 and connect said liquid level inductive switch 20 through the said first CS K1; Second discharges and recharges terminal RA1 connects microprocessor through the second CS K2 stray capacitance Ch; Charge transfer switch K0 connects inductance capacitance Cf and the outside distribution stray capacitance Co and the said stray capacitance Ch of said liquid level inductive switch 20; And the electric charge of controlling the two shifts, thereby makes inductance capacitance Cf and outside distribution stray capacitance Co and said stray capacitance Ch reach charge balance.
Analog to digital converter 212 is sampled repeatedly, maintenance, analog to digital conversion (A/D conversion); Obtaining the transfer of process electric charge reaches after the charge balance; Liquid level inductive switch 20 some to input signal values AD1 and ADh also are the input signal values on inductance capacitance Cf and the outside distribution stray capacitance Co.
Digital signal processing module 213, to sampling repeatedly keep that analog to digital converter (212) conversion back obtained said some to input signal values deposit, difference comparison operation and digital filtering handle, and obtains Level Detection signal AD0 or ADf.
When operate as normal, the charge transfer switch K0 in the charge transfer circuit 211 breaks off, and the first CS K1 and the second CS K2 are closed; First discharge and recharge terminal RA0 level be changed to " 0 ", make inductance capacitance Cf and outside distribution stray capacitance Co the discharge; Second discharge and recharge terminal RA1 level be changed to " 1 ", make stray capacitance Ch charging.Then; The first CS K1 and the second CS K2 break off; Charge transfer switch K is closed, stray capacitance Ch is charged, behind three's charge balance to inductance capacitance Cf and outside distribution stray capacitance Co; Analog to digital converter 212 is sampled, maintenance, A/D conversion, obtains the first input signal values ADh on inductance capacitance Cf and the outside distribution stray capacitance Co.
Afterwards, the charge transfer switch K0 in the charge transfer circuit 211 breaks off, and the first CS K1 and the second CS K2 are closed; First discharge and recharge terminal RA0 level be changed to " 1 ", make inductance capacitance Cf and outside distribution stray capacitance Co the charging; Second discharge and recharge terminal RA1 level be changed to " 0 ", make stray capacitance Ch discharge.Then; The first CS K1 and the second CS K2 break off; Charge transfer switch K0 is closed, inductance capacitance Cf and outside distribution stray capacitance Co is charged, behind three's charge balance to stray capacitance Ch; Analog to digital converter 212 is sampled once more, maintenance, A/D conversion, obtains the second input signal values AD1 on inductance capacitance Cf and the outside distribution stray capacitance Co.、
The structure of digital signal processing module 213 is as shown in Figure 3, comprises register 2131, and differential ratio is than computing module 2132 and digital filtering processing module 2133.Register 2131 deposit through sample repeatedly, maintenance, A/D conversion, the said input signal values ADh and the AD1 that are obtained; Differential ratio is somely carried out the difference comparison operation to the first and second input signal values ADh and AD1 than what computing module obtained more than 2132 pairs after over-sampling keeps analog to digital converter (212) conversion, obtain several differential signals ADn.Digital filtering processing module 2133; Again to through sample repeatedly, maintenance, A/D conversion; Several differential signals ADn that is obtained carries out dynamic tracking and digital filtering is handled; Filtering common mode, DM EMI, and obtain final Level Detection signal AD0 or ADf, this Level Detection signal AD0 or ADf have reflected the electric capacity of liquid level inductive switch 20.Wherein, if the liquid in containers height below induction electrode 201, promptly Cf is 0, Co remains unchanged, the Level Detection signal AD0 that obtain this moment also is constant; If the liquid in containers level perhaps surpasses induction electrode 201; Then generate inductance capacitance Cf between liquid and the induction electrode 201; Will change the electric capacity of liquid level inductive switch 20; Be that capacitance value is (Cf+Co), the Level Detection signal ADf that generate this moment also can with AD0 have bigger different, thereby can reach the purpose of contactless detecting liquid in containers liquid level.
As shown in Figure 4, the present invention also provides a kind of liquid level intelligent controller of using above-mentioned capacitance level transducer, comprising: liquid level inductive switch 20, microprocessor 21, light-emitting diode display 22 and Drive and Control Circuit 23; Wherein: said liquid level inductive switch 20 has induction electrode 201; Induction electrode 201 connects said microprocessor 21; Microprocessor 21 connects liquid level inductive switch 20 through input/output end port 210, and said liquid level inductive switch 20 is discharged and recharged and detect the inductance capacitance Cf of said induction electrode 201, thereby generates liquid level detection signal AD0 or ADf; Light-emitting diode display 22 dynamically shows under the control of microprocessor 21; Drive and Control Circuit 23 is carried out the drive controlling that liquid 31 pumps into or pumps under the control of microprocessor 21.Wherein, the inner structure of microprocessor 21 is identical with Fig. 3 related content with Fig. 2 with working method, repeats no more at this.
Embodiment 2,
All the other are identical with embodiment 1, and difference is that said induction electrode 201 is rectangular sheet; Its outer insulation course 202 that covers; Said insulation course 202 is processed for insulating material such as PET, PC, PE or PS, can adopt hot pressing to be adhesive on the induction electrode 201, and its thickness generally is no more than 0.2mm.Induction electrode 201 is insulated layer 202 parcel covering fully; Place it in vessel surface; Its length direction is vertical with surface level; When the higher conductor of specific inductive capacity (as: water, formic acid, methyl alcohol, ethanol, acetone, liquid ammonia, n-hexyl alcohol, glycerine, ore or latex etc.) is in container, pipeline or vessel; The higher conductor of specific inductive capacity is coupled between insulator (insulation course 202 and vessel shell) and induction electrode 201 and produces inductance capacitance Cf, and the capacitance of input/output end port 210 connections of microprocessor 21 is changed, and this capacitance changes with the coupling area between liquid 31 and the induction electrode 201; The inductance capacitance Cf that is produced between liquid 31 that the liquid level change that detects microprocessor 21 causes and the induction electrode 201, thus the detection signal of representing fluid level condition generated.Owing to have outside distribution stray capacitance Co at liquid level inductive switch 20; And microprocessor chip inside has stray capacitance Ch; The inductance capacitance Cf that is produced between liquid 31 and the induction electrode 201 and outside distribution stray capacitance Co and stray capacitance Ch differ little; In order to eliminate Ch and the Co influence to Level Detection, microprocessor 21 adopts difference A/D comparison operation method to detect inductance capacitance Cf, thereby reaches the purpose of detecting liquid level.Present embodiment can show the numerical value of liquid level in real time, rather than just monitors some liquid level point.
Capacitance level transducer of the present invention has adopted the principle of work of " capacitance charge transfer "; When the liquid level in the container surpasses or is lower than said induction electrode; The capacitance that the microprocessor input/output end port is connected changes, thereby detects the variation of internal tank liquid level accurately.Capacitance level transducer of the present invention adopts an induction electrode, is placed on the surface of airtight volume, pipeline or vessel, utilizes the capacitance touch principle of induction to carry out Level Detection.Compare with traditional " liquid level sensor ", have only an induction electrode, volume is very little, and accuracy is high; Circuit structure is simple, and antijamming capability is strong, has increased reliability of products and life-span; Reduced cost of products, and be contactless, installed, use, keeped in repair all simple and convenient.
The above is merely embodiments of the invention; Be not so limit claim of the present invention; Every equivalent structure or equivalent flow process conversion that utilizes instructions of the present invention and accompanying drawing content to be done; Or directly or indirectly be used in other relevant technical fields, all in like manner be included in the scope of patent protection of the present invention.

Claims (6)

1. a capacitance level transducer is characterized in that, comprises liquid level inductive switch (20) and microprocessor (21); Wherein said liquid level inductive switch (20) has induction electrode (201); Induction electrode (201) connects said microprocessor (21); Microprocessor (21) connects liquid level inductive switch (20) through input/output end port (210); To induction electrode (201) repeated charge of said liquid level inductive switch (20) and the inductance capacitance (Cf) that detects said induction electrode (201) generate the liquid level detection signal (AD0, ADf).
2. capacitance level transducer according to claim 1; It is characterized in that; Said microprocessor (21) further comprises: capacitance charge carry circuit (211), to stray capacitance (Ch) repeated charge and the electric charge transfer of said liquid level inductive switch (20) and microprocessor (21); Analog to digital converter (212), and the input signal values of liquid level inductive switch (20) after sampling acquisition electric charge shifts repeatedly (AD1, ADh); Digital signal processing module (213), to sampling repeatedly keep the said input signal values that analog to digital converter (212) conversion back obtained (AD1, ADh) deposit, difference comparison operation and digital filtering processing obtain the Level Detection signal (AD0, ADf).
3. capacitance level transducer according to claim 2; It is characterized in that said charge transfer circuit (211) comprises that first discharges and recharges terminal (RA0), first CS (K1); Second discharges and recharges terminal (RA1), second CS (K2) and charge transfer switch (K0); Wherein first discharge and recharge terminal (RA0) through said first CS (K1) connection said liquid level inductive switch (20); Second discharges and recharges terminal (RA1) connects microprocessor through second CS (K2) stray capacitance (Ch); Charge transfer switch (K0) connects said liquid level inductive switch (20) and said stray capacitance (Ch) and controls the electric charge transfer of the two.
4. capacitance level transducer according to claim 2 is characterized in that, said digital signal processing module (213) comprises register (2131), deposit the said input signal values that keeps being obtained after analog to digital converter (212) conversion through sampling repeatedly (AD1, ADh); Differential ratio is than computing module (2132), and keep back obtained some of analog to digital converter (212) conversion (AD1 ADh) carries out the difference comparison operation and obtains several differential signals (ADn) to said input signal values to sampling repeatedly; Digital filtering processing module (2133), to said several differential signals (ADn) carry out digital filtering handle to obtain said Level Detection signal (AD0, ADf).
5. according to the arbitrary described capacitance level transducer of claim 1 to 4, it is characterized in that said induction electrode (201) is a sheet metal.
6. capacitance level transducer according to claim 5 is characterized in that, said induction electrode (201) is provided with the very thin insulation crust of sealing (202).
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CN105074395A (en) * 2013-06-19 2015-11-18 住友理工株式会社 Capacitance-type liquid level detection device
CN105074395B (en) * 2013-06-19 2018-04-03 住友理工株式会社 Capacitance type liquid level detection device
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CN109238401A (en) * 2018-09-14 2019-01-18 杭州热博科技有限公司 Liquid level detection device and method
WO2021042230A1 (en) * 2019-09-02 2021-03-11 Texas Instruments Incorporated Container disturbance filtering for capacitive liquid level sensing
US11287301B2 (en) 2019-09-02 2022-03-29 Texas Instruments Incorporated Container disturbance filtering for capacitive liquid level sensing
CN112161673A (en) * 2020-09-15 2021-01-01 厦门晶尊微电子科技有限公司 Accurate capacitive liquid level detection circuit and adjustment mode
CN112161673B (en) * 2020-09-15 2022-06-17 厦门晶尊微电子科技有限公司 Accurate capacitive liquid level detection circuit and adjustment mode

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