CN102589644B - Capacitance type liquid level sensor - Google Patents
Capacitance type liquid level sensor Download PDFInfo
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- CN102589644B CN102589644B CN201110007135.7A CN201110007135A CN102589644B CN 102589644 B CN102589644 B CN 102589644B CN 201110007135 A CN201110007135 A CN 201110007135A CN 102589644 B CN102589644 B CN 102589644B
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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
Technical field
The present invention relates to liquid level control field, more specifically, relate to a kind of capacitance level transducer.
Background technology
Traditional liquid level control field, has a kind of capacitance type sensor, and its principle is as follows, from physics, and in the time ignoring the edge effect of two parallel metal sheets, two capacitors that parallel metal sheet forms, as Fig. 1 shows, 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 S=pole plate hides mutually
2);
D=polar plate spacing (m);
Existing capacitance type sensor is exactly according to three parameters (S, D, ε in formula (1)
r) in any one amount change, cause that electric capacity C changes.That is to say, if the variation of detected parameter (as displacement, pressure, liquid level etc.) causes S, D, ε
rchange one of in three parameters, just can utilize the change of corresponding electric capacity to realize parameter measurement.Therefore, conventional capacitance type sensor can be divided into three major types conventionally: pole span change type capacitive transducer (changing D), area change type capacitive transducer (changing S) and Measuring Apparatus of Medium Changing Type sensor (change ε
r).This sensor has a common feature, needs two induction electrodes, and the capacitance of surveying is electric capacity between two induction electrodes all.In some airtight volume, pipeline or vessel, another one induction electrode is installed very difficult or for a long time induction electrode is placed in solution, can there is the situations such as corrosion in induction electrode.
Summary of the invention
For the above-mentioned defect of existing liquid level sensor, the invention provides a kind of improved capacitance level transducer, be a kind of single induction electrode of the working method that adopts " capacitance charge transfer ", 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 described microprocessor (21); Microprocessor (21) connects liquid level inductive switch (20) by input/output end port (210), to described liquid level inductive switch (20) repeated charge and detect described induction electrode (201) inductance capacitance (Cf) generate liquid level detection signal (AD0, ADf).
Preferably, described microprocessor (21) further comprises: capacitance charge carry circuit (211), and stray capacitance (Ch) repeated charge to described liquid level inductive switch (20) and microprocessor (21) and electric charge shift; Analog to digital converter (212), sampling obtains the input signal values (AD1, ADh) of the rear liquid level inductive switch (20) of electric charge transfer repeatedly; Digital signal processing module (213), to the described input signal values (AD1 that sampling obtains after keeping analog to digital converter (212) to change repeatedly, ADh) deposit, differential comparison computing and digital filtering processing obtain liquid level detection signal (AD0, ADf).
Preferably, described charge transfer circuit (211) comprises that first discharges and recharges terminal (RA0), the first gauge tap (K1), second discharges and recharges terminal (RA1), the second gauge tap (K2) and charge transfer switch (K0); Wherein first discharge and recharge terminal (RA0) and connect described liquid level inductive switch (20) by described the first gauge tap (K1); Second discharges and recharges terminal (RA1) connects microprocessor stray capacitance (Ch) by the second gauge tap (K2); Charge transfer switch (K0) connects described liquid level inductive switch (20) and described stray capacitance (Ch) and controls the electric charge transfer of the two.
Preferably, described digital signal processing module (213) comprises register (2131), deposits the described input signal values (AD1, ADh) obtaining after keeping analog to digital converter (212) to change through repeatedly sampling; Differential comparison computing module (2132), what keep repeatedly sampling obtaining after analog to digital converter (212) conversion somely carries out differential comparison computing to described input signal values (AD1, ADh) and obtains several differential signals (ADn); Digital filtering processing module (2133), carries out digital filtering to described several differential signals (ADn) and processes the described liquid level detection signal of acquisition (AD0, ADf).
Preferably, described induction electrode (201) is a sheet metal.
Preferably, described 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 container exceedes or during lower than described induction electrode, the capacitance that can make microprocessor input/output end port connect changes, thereby detect accurately the variation of internal tank liquid level, capacitance level transducer of the present invention adopts an induction electrode, be placed on the surface of airtight volume, pipeline or vessel, utilize capacitance touch principle of induction to carry out liquid level detection.Compared with traditional " liquid level sensor ", only have an induction electrode, volume is very little, and accuracy is high, circuit structure is simple, and antijamming capability is strong, has increased reliability and the life-span of product, reduce cost of products, and be contactless, installed, use, keeped in repair all simple and convenient.
Brief description of the 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 present invention;
Fig. 3 is the structural representation of digital signal processing module;
Fig. 4 is the schematic diagram of the liquid level intelligent controller of the above-mentioned capacitance level transducer of application.
Embodiment
By describing technology contents of the present invention, structural attitude in detail, being realized object and effect, below in conjunction with embodiment and coordinate accompanying drawing to be explained in detail.
Embodiment 1,
Fig. 2, Fig. 3 and Fig. 4 are the structural representations of the capacitance level transducer of the embodiment of the present 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.Described sheet metal and insulation crust 202 are all placed on the surface of volume, pipeline or the vessel of carrying liquid.
Induction electrode (201) connects described microprocessor (21); Microprocessor (21) connects liquid level inductive switch (20) by input/output end port (210), in its connection line, there is fixing outer scattered stray capacitance (Co), in the time that the liquid level of the liquid 31 in container 32 is concordant with liquid level inductive switch (20) or exceed, the shell of spacer insulator layer (202) and vessel between induction electrode (201) and liquid 31, between induction electrode (201) and liquid 31, form inductance capacitance (Cf), when liquid 31 liquid levels are during lower than inductive switch (20), inductance capacitance Cf value is zero.
Described microprocessor (21) further comprises: stray capacitance (Ch), analog to digital converter (212) and the digital signal processing module (213) of capacitance charge carry circuit (211), microprocessor (21).Described charge transfer circuit (211) comprises that first discharges and recharges terminal (RA0), the first gauge tap (K1), second discharges and recharges terminal (RA1), the second gauge tap (K2) and charge transfer switch (K0); Wherein first discharge and recharge terminal (RA0) and connect described liquid level inductive switch (20) by described the first gauge tap (K1); Second discharges and recharges terminal (RA1) connects microprocessor stray capacitance (Ch) by the second gauge tap (K2); Charge transfer switch (K0) connects described liquid level inductive switch (20) and described stray capacitance (Ch) and controls the electric charge transfer of the two.
Capacitance charge carry circuit (211), stray capacitance (Ch) repeated charge to described liquid level inductive switch (20) and microprocessor (21) and electric charge shift; Analog to digital converter (212), sampling obtains the input signal values (AD1, ADh) of the rear liquid level inductive switch (20) of electric charge transfer repeatedly; Digital signal processing module (213), keep the described input signal values (AD1 obtaining after analog to digital converter (212) conversion to repeatedly sampling, ADh) deposit, differential comparison computing and digital filtering processing obtain liquid level detection signal (AD0, ADf).
Described digital signal processing module (213) comprises register (2131), deposits the described input signal values (AD1, ADh) obtaining after keeping analog to digital converter (212) to change through repeatedly sampling; Differential comparison computing module (2132), what keep repeatedly sampling obtaining after analog to digital converter (212) conversion somely carries out differential comparison computing to described input signal values (AD1, ADh) and obtains several differential signals (ADn); Digital filtering processing module (2133), carries out digital filtering to described several differential signals (ADn) and processes the described liquid level detection signal of acquisition (AD0, ADf).
Capacitance level transducer of the present invention adopts " capacitance charge transfer " working method, directly be connected with the induction electrode in liquid level inductive switch by microprocessor (CPU), described microprocessor is with I/O (I/O) port of analog to digital converter 212 (A/D) translation function.When the higher conductor (as: water of specific inductive capacity, formic acid, methyl alcohol, ethanol, acetone, liquid ammonia, n-hexyl alcohol, glycerine, ore, or latex etc. is at container, in pipeline or vessel time, the conductor that specific inductive capacity is higher is coupled and produces inductance capacitance Cf between insulator (insulation crust 202 and vessel shell) and induction electrode 201, the capacitance that can make the input/output end port 210 of microprocessor 21 connect changes, microprocessor 21 detects liquid level and changes the inductance capacitance Cf producing between the liquid that causes and induction electrode 201, thereby generate the detection signal that represents fluid level condition.Owing to thering is outside distribution stray capacitance Co at liquid level inductive switch 20, and microprocessor chip inside has stray capacitance Ch, the inductance capacitance Cf producing between liquid 31 and induction electrode 201 and outside distribution stray capacitance Co and stray capacitance Ch differ little, impact liquid level being detected in order to eliminate Ch and Co, microprocessor 21 adopts difference A/D comparison operation method to detect inductance capacitance Cf, thereby reaches the object 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 described microprocessor 21.When liquid level in container 32 rises to concordant or while exceeding induction electrode 201 from induction electrode below, the inductance capacitance Cf producing between liquid 31 and induction electrode 201 can be from certain value that is raised to above freezing, in the time that liquid level in container 32 is reduced to induction electrode below, inductance capacitance Cf=0.Liquid level inductive switch 20 also has outside distribution stray capacitance Co.As Fig. 2, microprocessor 21 connects liquid level inductive switch 20 by its input/output end port 210.Microprocessor 21 carries out repeated charge by its input/output end port 210 to described liquid level inductive switch 20, and repeatedly detects the inductance capacitance Cf of described induction electrode 201, generates liquid level detection signal AD0 or Adf according to the variation of inductance capacitance Cf.
Wherein, the structure of described 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 described liquid level inductive switch 20 by input/output end port 210, and control repeatedly discharges and recharges with electric charge and shifts the stray capacitance Ch of described liquid level inductive switch 20 and microprocessor 21.Particularly, described charge transfer circuit 211 comprises that first discharges and recharges terminal RA0, the first gauge tap K1, and second discharges and recharges terminal RA1, the second gauge tap K2 and charge transfer switch K0; Wherein first discharge and recharge terminal RA0 and connect described liquid level inductive switch 20 by described the first gauge tap K1; Second discharges and recharges terminal RA1 connects microprocessor stray capacitance Ch by the second gauge tap K2; Charge transfer switch K0 connects inductance capacitance Cf and outside distribution stray capacitance Co and the described stray capacitance Ch of described liquid level inductive switch 20, and control the two electric charge shift, thereby make inductance capacitance Cf and outside distribution stray capacitance Co and described stray capacitance Ch reach charge balance.
Analog to digital converter 212 is sampled repeatedly, maintenance, analog to digital conversion (A/D conversion), after acquisition process electric charge shifts and reaches charge balance, liquid level inductive switch 20 some to input signal values AD1 and ADh are also the input signal values on inductance capacitance Cf and outside distribution stray capacitance Co.
Digital signal processing module 213, keep repeatedly sampling obtaining after analog to digital converter (212) conversion described some to input signal values deposit, differential comparison computing and digital filtering processing, obtain liquid level detection signal AD0 or ADf.
In the time of normal work, the charge transfer switch K0 in charge transfer circuit 211 disconnects, the first gauge tap K1 and the second gauge tap K2 closure; The first level that discharges and recharges terminal RA0 is set to " 0 ", makes inductance capacitance Cf and outside distribution stray capacitance Co electric discharge; The second level that discharges and recharges terminal RA1 is set to " 1 ", makes stray capacitance Ch charging.Then, the first gauge tap K1 and the second gauge tap K2 disconnect, charge transfer switch K closure, stray capacitance Ch is charged to inductance capacitance Cf and outside distribution stray capacitance Co, when after three's charge balance, analog to digital converter 212 is sampled, maintenance, A/D conversion, obtains the first input signal values ADh on inductance capacitance Cf and outside distribution stray capacitance Co.
Afterwards, the charge transfer switch K0 in charge transfer circuit 211 disconnects, the first gauge tap K1 and the second gauge tap K2 closure; The first level that discharges and recharges terminal RA0 is set to " 1 ", makes inductance capacitance Cf and outside distribution stray capacitance Co charging; The second level that discharges and recharges terminal RA1 is set to " 0 ", makes stray capacitance Ch electric discharge.Then, the first gauge tap K1 and the second gauge tap K2 disconnect, charge transfer switch K0 closure, inductance capacitance Cf and outside distribution stray capacitance Co are charged to stray capacitance Ch, when after three's charge balance, analog to digital converter 212 is sampled again, maintenance, A/D conversion, obtains the second input signal values AD1 on inductance capacitance Cf and outside distribution stray capacitance Co.、
The structure of digital signal processing module 213 as shown in Figure 3, comprises register 2131, differential comparison computing module 2132 and digital filtering processing module 2133.Register 2131 is deposited through repeatedly sampling, maintenance, A/D conversion, the described input signal values ADh and the AD1 that obtain; Differential comparison computing module 2132 somely carries out differential comparison computing to the first and second input signal values ADh and AD1 to what obtain after over-sampling keeps analog to digital converter (212) conversion above, obtains several differential signals ADn.Digital filtering processing module 2133, again to through repeatedly sampling, maintenance, A/D conversion, several differential signals ADn obtaining carries out dynamically following the tracks of and digital filtering processing, filtering common mode, differential mode interference, and obtaining final liquid level detection signal AD0 or ADf, this liquid level detection signal AD0 or ADf have reflected the electric capacity of liquid level inductive switch 20.Wherein, if liquid in containers height below induction electrode 201, Cf is that 0, Co remains unchanged, now obtain liquid level detection signal AD0 be also constant; If liquid in containers height flushes or exceedes induction electrode 201, between liquid and induction electrode 201, generate inductance capacitance Cf, will change the electric capacity of liquid level inductive switch 20, be that capacitance value is (Cf+Co), the liquid level detection signal ADf now generating also can from AD0 have larger different, thereby can reach the object 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 applying 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: described liquid level inductive switch 20 has induction electrode 201; Induction electrode 201 connects described microprocessor 21; Microprocessor 21 connects liquid level inductive switch 20 by input/output end port 210, described liquid level inductive switch 20 is discharged and recharged and detected the inductance capacitance Cf of described 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 driving control 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, does not repeat them here.
Embodiment 2,
All the other are identical with embodiment 1, and difference is, described induction electrode 201 is rectangular sheet, its outer insulation course 202 that covers, the insulating material such as described insulation course 202 is PET, PC, PE or PS are made, and can adopt hot pressing to be adhesive on induction electrode 201, and its thickness is generally no more than 0.2mm.Induction electrode 201 is insulated layer 202 parcel covering completely, place it in vessel surface, its length direction is vertical with surface level, when the higher conductor (as: water of specific inductive capacity, formic acid, methyl alcohol, ethanol, acetone, liquid ammonia, n-hexyl alcohol, glycerine, ore, or latex etc.) at container, in pipeline or vessel time, the conductor that specific inductive capacity is higher is coupled and produces inductance capacitance Cf between insulator (insulation course 202 and vessel shell) and induction electrode 201, the capacitance that can make the input/output end port 210 of microprocessor 21 connect changes, this capacitance changes with the coupling area between liquid 31 and induction electrode 201, microprocessor 21 detects liquid level and changes the inductance capacitance Cf producing between the liquid 31 that causes and induction electrode 201, thereby generate the detection signal that represents fluid level condition.Owing to thering is outside distribution stray capacitance Co at liquid level inductive switch 20, and microprocessor chip inside has stray capacitance Ch, the inductance capacitance Cf producing between liquid 31 and induction electrode 201 and outside distribution stray capacitance Co and stray capacitance Ch differ little, impact liquid level being detected in order to eliminate Ch and Co, microprocessor 21 adopts difference A/D comparison operation method to detect inductance capacitance Cf, thereby reaches the object of detecting liquid level.The present embodiment can show the numerical value of liquid level in real time, instead of 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 container exceedes or during lower than described induction electrode, the capacitance that can make microprocessor input/output end port connect changes, thereby detects accurately the variation of internal tank liquid level.Capacitance level transducer of the present invention adopts an induction electrode, is placed on the surface of airtight volume, pipeline or vessel, utilizes capacitance touch principle of induction to carry out liquid level detection.Compared with traditional " liquid level sensor ", only have an induction electrode, volume is very little, and accuracy is high, circuit structure is simple, and antijamming capability is strong, has increased reliability and the life-span of product, reduce cost of products, and be contactless, installed, use, keeped in repair all simple and convenient.
The foregoing is only embodiments of the invention; not thereby limit the scope of the claims of the present invention; every equivalent structure or conversion of equivalent flow process that utilizes instructions of the present invention and accompanying drawing content to do; or be directly or indirectly used in other relevant technical fields, be all in like manner included in scope of patent protection of the present invention.
Claims (3)
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), and described induction electrode (201) is a sheet metal; Induction electrode (201) connects described microprocessor (21); Microprocessor (21) connects liquid level inductive switch (20) by input/output end port (210), induction electrode (201) repeated charge to described liquid level inductive switch (20) and detect described induction electrode (201) inductance capacitance (Cf) generate liquid level detection signal (AD0, ADf); Described microprocessor (21) further comprises: capacitance charge carry circuit (211), and stray capacitance (Ch) repeated charge to described liquid level inductive switch (20) and microprocessor (21) and electric charge shift; Analog to digital converter (212), sampling obtains the input signal values (AD1, ADh) of the rear liquid level inductive switch (20) of electric charge transfer repeatedly; Digital signal processing module (213), keep the described input signal values (AD1 obtaining after analog to digital converter (212) conversion to repeatedly sampling, ADh) deposit, differential comparison computing and digital filtering processing obtain liquid level detection signal (AD0, ADf); Described charge transfer circuit (211) comprises that first discharges and recharges terminal (RA0), the first gauge tap (K1), second discharges and recharges terminal (RA1), the second gauge tap (K2) and charge transfer switch (K0); Wherein first discharge and recharge terminal (RA0) and connect described liquid level inductive switch (20) by described the first gauge tap (K1); Second discharges and recharges terminal (RA1) connects microprocessor stray capacitance (Ch) by the second gauge tap (K2); Charge transfer switch (K0) connects described liquid level inductive switch (20) and described stray capacitance (Ch) and controls the electric charge transfer of the two.
2. capacitance level transducer according to claim 1, it is characterized in that, described digital signal processing module (213) comprises register (2131), deposit the described input signal values (AD1, ADh) obtaining after keeping analog to digital converter (212) to change through repeatedly sampling; Differential comparison computing module (2132), what keep repeatedly sampling obtaining after analog to digital converter (212) conversion somely carries out differential comparison computing to described input signal values (AD1, ADh) and obtains several differential signals (ADn); Digital filtering processing module (2133), carries out digital filtering to described several differential signals (ADn) and processes the described liquid level detection signal of acquisition (AD0, ADf).
3. capacitance level transducer according to claim 1, is characterized in that, described induction electrode (201) is provided with the very thin insulation crust of sealing (202).
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| JP6022413B2 (en) * | 2013-06-19 | 2016-11-09 | 住友理工株式会社 | Capacitive liquid level detector |
| CN104535135B (en) * | 2015-01-22 | 2018-11-09 | 上海飞科电器股份有限公司 | Non-contact type liquid level detecting device and method |
| CN106289444A (en) * | 2015-06-02 | 2017-01-04 | 大日科技股份有限公司 | Material detection device |
| WO2017189009A1 (en) * | 2016-04-29 | 2017-11-02 | Hewlett-Packard Development Company, L.P. | Printing apparatus and methods for detecting fluid levels |
| WO2017195001A1 (en) * | 2016-05-13 | 2017-11-16 | Arcelormittal | Method for obtaining a height of a material stacked in a coke oven |
| CN107782408B (en) * | 2016-08-29 | 2023-12-19 | 佛山市顺德区美的电热电器制造有限公司 | Liquid level detection circuit, liquid level detection method and wall breaking machine |
| PL237479B1 (en) * | 2017-10-10 | 2021-04-19 | Strozynski Bartlomiej Firma Bolecki | Detector for contactless measurement of the liquid presence and quantity and method of the measurement |
| CN109238401B (en) * | 2018-09-14 | 2021-05-07 | 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 |
| CN110836711A (en) * | 2019-11-08 | 2020-02-25 | 厦门英杰华机电科技有限公司 | Liquid level detection device for ink-jet printer and detection method thereof |
| 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 |
| CN115578963A (en) * | 2022-10-27 | 2023-01-06 | 苏州路之遥科技股份有限公司 | Method for driving LCD by using common IO |
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