CN105352565B - Differential capacitance level sensor - Google Patents
Differential capacitance level sensor Download PDFInfo
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- CN105352565B CN105352565B CN201510729454.7A CN201510729454A CN105352565B CN 105352565 B CN105352565 B CN 105352565B CN 201510729454 A CN201510729454 A CN 201510729454A CN 105352565 B CN105352565 B CN 105352565B
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- 239000000463 material Substances 0.000 claims abstract description 28
- 238000012545 processing Methods 0.000 claims abstract description 15
- 239000003990 capacitor Substances 0.000 claims description 56
- 230000035945 sensitivity Effects 0.000 claims description 16
- 238000006243 chemical reaction Methods 0.000 claims description 7
- 238000012937 correction Methods 0.000 claims description 6
- 238000001914 filtration Methods 0.000 claims description 2
- 238000000034 method Methods 0.000 claims description 2
- 230000008569 process Effects 0.000 claims description 2
- 238000005259 measurement Methods 0.000 abstract description 10
- 230000008878 coupling Effects 0.000 abstract description 4
- 238000010168 coupling process Methods 0.000 abstract description 4
- 238000005859 coupling reaction Methods 0.000 abstract description 4
- 230000007774 longterm Effects 0.000 abstract description 4
- 230000007547 defect Effects 0.000 abstract description 3
- 239000011344 liquid material Substances 0.000 abstract description 2
- 239000011343 solid material Substances 0.000 abstract description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 4
- 230000008859 change Effects 0.000 description 4
- 238000004891 communication Methods 0.000 description 4
- 229910052802 copper Inorganic materials 0.000 description 4
- 239000010949 copper Substances 0.000 description 4
- 238000010586 diagram Methods 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 238000000691 measurement method Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 1
- 230000006870 function Effects 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 230000001960 triggered effect Effects 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
- G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
- G01F23/26—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields
- G01F23/263—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields by measuring variations in capacitance of capacitors
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Electromagnetism (AREA)
- Thermal Sciences (AREA)
- Fluid Mechanics (AREA)
- General Physics & Mathematics (AREA)
- Electronic Switches (AREA)
- Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
Abstract
The invention discloses a sensor (material level sensor) for realizing material position measurement by utilizing a differential capacitance measurement principle, which comprises a plane electrode forming a differential capacitance, a differential capacitance sensor special circuit for converting differential capacitance signals into electric signals and performing signal processing, and a microprocessor for arranging the differential capacitance sensor special circuit and the signal processing. The invention overcomes the defect that the existing single-capacitance material level sensor is easily influenced by external factors such as temperature, humidity, adjacent object coupling capacitance, electromagnetic interference and the like, has stronger anti-interference capability and better long-term stability, and can be widely used for measuring the material level of liquid and solid materials.
Description
Technical Field
The invention relates to a capacitance sensor for measuring a material position, in particular to a sensor (material level sensor) for measuring the material position based on a differential capacitance measurement principle.
Background
In industrial automation and other fields, there is a need to detect the position of liquid or solid materials in a container. A capacitive material position sensor (level sensor) based on the principle of capacitance measurement is one of the sensors widely used for level measurement.
The existing capacitance level sensor generally causes a single capacitance change measurement method based on a material position, but the sensor based on a single capacitance measurement principle is easily influenced by various external factors, such as temperature and humidity of a measurement environment and coupling capacitance of adjacent objects, so that the capacitance value of the single capacitance sensor can be changed. Particularly, in an industrial production environment, the single-capacitance sensor is easily interfered and is triggered by mistake due to serious electromagnetic interference. Therefore, the existing capacitive level sensor has the defects of relatively poor anti-interference capability and long-term stability, and the wide application of the capacitive level sensor in various fields is prevented.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, it is an object of the present invention to provide a capacitive material position sensor (level sensor) that overcomes the above-mentioned drawbacks.
The invention realizes the measurement of the material position in the container by utilizing the differential capacitance measurement principle. The differential capacitance level sensor thus constituted has an output proportional to the difference of 2 capacitances (C1-C2) instead of the value of the individual capacitance C1 or C2. Because external factors such as temperature, humidity and coupling capacitance of adjacent objects and the influence of electromagnetic interference on 2 adjacent capacitances are the same, the influence of the external factors on the output of the differential capacitance level sensor based on the differential capacitance measurement principle is far smaller than the influence of the same factors on the level sensor based on the single capacitance, the differential capacitance level sensor has stronger anti-interference capability and better long-term stability, and the defect that the existing single capacitance level sensor is easily influenced by the external factors is overcome.
The technical scheme of the invention is that the sensor consists of a differential capacitor (C1-C2) consisting of a capacitor C1 and a capacitor C2, a differential capacitor sensor special circuit and a microprocessor. As a preferred scheme of the invention, the capacitors C1 and C2 are formed by planar electrode plate capacitors, 2 electrodes forming the capacitor C1 are positioned on the front surface of the circuit board, and the corresponding area of the back surface of the circuit board where the capacitor C1 is positioned is covered by the grounded circuit board copper coating. The 2 electrodes forming the capacitor C2 are positioned on the back surface of the circuit board, and the corresponding area of the front surface of the circuit board where the capacitor C2 is positioned is covered by the grounded copper clad circuit board.
As a further technical scheme of the invention, the differential capacitors C1-C2 formed by the planar electrode plates are converted into electric signals through a differential capacitance sensor special circuit (ASIC) and can be selectively input into a microprocessor for further processing.
As a further technical scheme of the invention, the differential capacitance sensor special circuit (ASIC) in the sensor is composed of a programmable differential capacitance-voltage conversion circuit, a programmable zero point correction circuit, a programmable amplifying circuit, a programmable band-pass filter circuit, a temperature compensation circuit, an analog output buffer module, a programmable comparator circuit, a digital processing circuit, a digital output driving module, a one-time programmable OTP or multiple-time programmable EEPROM memory and an I/O communication interface module. The programmable parameters of the dedicated circuit can be set by the interface communication module.
As a further technical scheme of the invention, the zero point and the sensitivity of the sensor can be adjusted by a programmable zero point correction circuit and a programmable amplifying circuit.
As another preferable scheme of the invention, the zero point and the sensitivity of the sensor can be adjusted through an external adjustable resistor.
As another preferable scheme of the invention, the digital processing circuit of the special circuit has the functions of programmable power-on delay, short-circuit protection, programmable digital filtering, pulse width programmable Pulse (Pulse) output circuit and the like.
As another preferred embodiment of the present invention, the programmable comparator circuit has programmable upper and lower limits and programmable return difference.
As another preferred scheme of the invention, the analog and digital outputs of the special circuit of the differential capacitive sensor can be connected to a microprocessor for further digital signal processing, and the I/O port of the microprocessor is connected with the I/O port of the special circuit of the differential capacitive sensor to set the parameters inside the special circuit of the differential capacitive sensor.
Drawings
FIG. 1 is a differential capacitive level sensor of the present invention.
FIG. 2 is a block diagram of a differential capacitive level sensor specific circuit of the present invention.
FIG. 3 is a block diagram of a differential capacitive level sensor system of the present invention.
Detailed Description
Please refer to the accompanying drawings. It should be noted that the illustrations provided in the present embodiment merely illustrate the basic concept of the present invention by way of illustration, and only the components related to the present invention are shown in the drawings and are not drawn according to the number, shape and size of the components in actual implementation, and the form, number and proportion of the components in actual implementation may be arbitrarily changed, and the layout of the components may be more complicated.
The invention is realized by the following modes for carrying out the invention in further detail with reference to the accompanying drawings, wherein: as shown in fig. 1, the capacitors C1 and C2 are formed by flat electrodes on a double-layer circuit board.
The capacitor C1 is positioned on the front surface of the double-layer circuit board and consists of 2 plane electrode plates, a polar plate 1 and a polar plate 2, and the capacitor is used for sensing the position of materials in the container. The back surface, namely the corresponding position of the back surface of the circuit board, is coated with copper by the grounded circuit board to serve as a shielding layer of the capacitor C1.
The capacitor C2 is positioned on the back surface of the double-layer circuit board and consists of 2 planar electrode plates, a polar plate 3 and a polar plate 4, the capacitor is used as a reference capacitor, and the back surface, namely the front surface of the circuit board is correspondingly provided with a shielding layer of the capacitor C2 by copper coating of the circuit board which is grounded.
If a multilayer circuit board, such as a 4-layer circuit board, is used, the first layer of the circuit serves as 2 plates, plate 1 and plate 2 of the capacitor C1, the second layer of the circuit board is Grounded (GND) as a shielding layer of the capacitor C1, the third layer of the circuit board is Grounded (GND) as a shielding layer of the capacitor C2, and the 4 th layer of the circuit board serves as 2 plates, plate 3 and plate 4 of the capacitor C2.
The shape of the capacitor plate of the present invention is not limited to the shape shown in fig. 1, and various planar capacitors formed by other electrode shapes, such as a rectangular planar capacitor, a comb-shaped planar capacitor, and other planar capacitors can be used as the capacitors forming the differential capacitance level sensor of the present invention.
As shown in fig. 1, the plate 1 of C1 is connected to the positive (+) input terminal of the differential capacitance sensor dedicated circuit, the plate 3 of the capacitor C2 is connected to the negative (-) input terminal of the differential capacitance sensor dedicated circuit, the plate 2 of the capacitor C1 is connected to the plate 4 of the capacitor C2, as the common plate of the differential capacitance (C1-C2) composed of C1, C2, connected to the common terminal (COMM) of the differential capacitance sensor dedicated circuit.
Fig. 2 is a block diagram of a differential capacitive sensor application specific circuit (ASIC) for use with the present invention. The differential capacitance sensor special circuit (ASIC) is composed of a programmable differential capacitance-voltage conversion circuit, a programmable zero correction circuit, a programmable amplifying circuit, a programmable band-pass filter circuit, a temperature compensation circuit, an analog output buffer module, a programmable comparator circuit, a digital processing circuit, a digital output driving module, a one-time programmable OTP or multiple-time programmable EEPROM memory and an I/O communication interface module. The programmable parameters of the dedicated circuit can be set by the interface communication module. As shown in fig. 2, the zero point, sensitivity, and comparator threshold of the dedicated circuit can be set by an external adjustable resistor.
The differential capacitors (C1-C2) are converted into electrical signals by a differential capacitance sensor dedicated circuit, and signal processing is performed by the circuit to output an analog quantity signal Sout and a switching quantity signal Dout and a Pulse output signal Pulse. As shown in fig. 3, the outputs Sout, dout, pulse of the dedicated circuits may also be optionally input to the microprocessor for further processing.
When the material position is measured, the front surface of the circuit board where the C1 is positioned is attached to a container filled with the material. When the position of the material in the container changes, the capacitor C1 changes along with the change of the position of the material, and the capacitor C2 is insensitive to the change of the position of the material because the grounded circuit board copper-clad between the capacitor C2 and the material is used as a shielding layer, so that the differential capacitor (C1-C2) and the position of the material form a certain corresponding relation. If the sensor is interfered by other external factors, such as electromagnetic interference and humidity change, the influence of the external factors on the capacitance is the same because the distances of C1 and C2 are very close, so that the differential capacitance (C1-C2) is not influenced by the other external factors.
The differential capacitor (C1-C2) is converted into an electric signal by a programmable differential capacitor-voltage conversion circuit in the differential capacitor sensor special circuit, and then enters a zero point adjusting module of the special circuit, when the materials in the container are empty, the zero point adjusting module in the ASIC circuit is adjusted through an external adjustable resistor or set through a microprocessor, so that the Sout of the sensor is the preset zero point of the sensor. When the material gradually rises and reaches a preset position, the sensor sensitivity module in the ASIC circuit is adjusted through an external adjustable resistor or set through a microprocessor, so that the output Sout of the sensor reaches the preset sensitivity. Since adjusting the sensitivity of the sensor may have an effect on the zero point of the sensor, the above zero point, sensitivity setting process may be repeated as necessary until the zero point, sensitivity, has reached a predetermined value.
If the working temperature range of the sensor is wider, the zero point and the sensitivity of the sensor can be compensated by using a temperature compensation module of the zero point and the sensitivity in a special circuit so as to improve the working of the sensor at different temperatures.
If the output of the switching value is needed, after the Sout is set, the threshold value of the programmable comparator of the special circuit can be set through an external adjustable resistor or through a microprocessor, so that the output of the comparator is overturned, the noise is filtered through a digital processing module in the special circuit, and the output of the digital output module Dout is overturned under the condition that the output of the comparator meets a certain pulse width. If the Pulse output is required, a Pulse with a certain width can be selectively output at the Pulse port.
Because external factors such as temperature, humidity and electromagnetic interference and the influence of the coupling capacitance of external objects on 2 adjacent equivalent capacitances are the same, and because the output of the sensor is related to the difference value of the capacitances and C1-C2 instead of the absolute value of the capacitance, the differential capacitance material sensor greatly reduces the influence of the external factors on the sensor.
In summary, the invention utilizes the measurement method of the differential capacitance, and reduces the influence of the external factors on the sensor according to the principle that the differential capacitance formed by 2 adjacent capacitors is zero after subtracting the capacitance changes caused by the changes of the external temperature, the humidity, the electromagnetic interference and other external factors, thereby improving the anti-interference capability and the long-term stability of the sensor.
The above embodiments are merely illustrative of the principles of the present invention and its effectiveness, and are not intended to limit the invention. Modifications and variations may be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is intended that all equivalent modifications and variations of the invention be covered by the claims, which are within the ordinary skill of the art, be within the spirit and scope of the present disclosure.
Claims (8)
1. The sensor is characterized by comprising a differential capacitor, a differential capacitor sensor special circuit (ASIC) and a microprocessor, wherein the differential capacitor is connected to the differential capacitor input end of the differential capacitor sensor special circuit, the output of the differential capacitor sensor special circuit can be connected to the microprocessor for further digital signal processing, and an I/O port of the microprocessor is connected with an I/O port of the differential capacitor sensor special circuit to set parameters inside the differential capacitor sensor special circuit;
the differential capacitor is formed on the double-layer circuit board and comprises a first capacitor and a second capacitor;
The two electrodes forming the first capacitor are positioned on the front surface of the double-layer circuit board, and the corresponding area of the back surface of the double-layer circuit board where the first capacitor is positioned is covered by the grounded circuit board copper-clad;
The two electrodes forming the second capacitor are positioned on the back surface of the double-layer circuit board, and the corresponding area of the front surface of the double-layer circuit board where the second capacitor is positioned is covered by the grounded circuit board copper-clad;
When the material position is measured, the front surface of the double-layer circuit board where the first capacitor is positioned is stuck to a container filled with the material;
the sensor is arranged on the outer wall of the container, and when the materials in the container are empty by utilizing the microprocessor or the adjustable resistor, the output zero point of the sensor is set;
when the materials are gradually raised and reach a preset position, the sensitivity of the sensor is adjusted through a microprocessor or an adjustable resistor, so that the sensitivity of the sensor meets the requirement;
The setting process is repeated until both the output zero point and the sensitivity of the sensor reach predetermined values.
2. The sensor according to claim 1, wherein the differential capacitance sensor dedicated circuit is composed of a programmable differential capacitance-voltage conversion circuit (C-V conversion circuit), a programmable zero point correction circuit, a programmable amplifying circuit, a programmable filter circuit, a temperature compensation circuit, a programmable comparator circuit, a digital processing circuit, an output buffer circuit, etc., the differential capacitance of the material position in the sensing container is connected to the differential capacitance-voltage conversion circuit, and after being converted into an electrical signal by the differential capacitance-voltage conversion circuit, the electrical signal sequentially passes through the programmable zero point correction circuit, the programmable amplifying circuit, the programmable filter circuit, the temperature compensation circuit, the programmable comparator circuit, the digital processing circuit finally enters the microprocessor for processing.
3. The sensor of claim 1, wherein the zero point and the sensitivity of the sensor can be adjusted by a programmable zero point correction circuit and a programmable amplifying circuit in a dedicated circuit, and the temperature coefficient of the zero point and the sensitivity can be compensated by a temperature compensation module of the dedicated circuit.
4. The sensor of claim 1, wherein the zero point and sensitivity of the sensor are also adjustable by an external adjustable resistor.
5. The sensor of claim 1, wherein the frequency response of the sensor is adjustable by a programmable bandpass filter.
6. The sensor of claim 1, wherein the digital processing circuit has a programmable power-on delay, a short-circuit protection function, a programmable digital filtering function, and an output programmable pulse function.
7. The sensor of claim 1, wherein the programmable comparator circuit has programmable upper and lower limits and programmable return difference.
8. The sensor of claim 1, wherein when the material reaches a predetermined position, a threshold of the sensor is set by a microprocessor or an externally connected adjustable resistor, a return difference is generated, and a pulse width is output, so that the output of the sensor meets a predetermined requirement.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201510729454.7A CN105352565B (en) | 2015-11-02 | 2015-11-02 | Differential capacitance level sensor |
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| Application Number | Priority Date | Filing Date | Title |
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| CN201510729454.7A CN105352565B (en) | 2015-11-02 | 2015-11-02 | Differential capacitance level sensor |
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| CN105352565A CN105352565A (en) | 2016-02-24 |
| CN105352565B true CN105352565B (en) | 2024-05-07 |
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Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105920703B (en) * | 2016-05-19 | 2022-06-03 | 中国人民解放军总医院 | Infusion flow monitor |
| WO2018035321A1 (en) * | 2016-08-17 | 2018-02-22 | Ksr Ip Holdings Llc. | Capacitive fluid level sensor for rapid response |
| CN107870020B (en) * | 2017-12-26 | 2019-12-17 | 太原理工大学 | Three coaxial cable capacitance type water level measuring device |
| CN108692791A (en) * | 2018-03-30 | 2018-10-23 | 厦门乐人电子有限公司 | Liquid level detection device and liquid container |
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| US3950653A (en) * | 1975-01-24 | 1976-04-13 | Agridustrial Electronics, Inc. | Instrument for sensing level of granular materials |
| JPH05281254A (en) * | 1992-03-31 | 1993-10-29 | Fujikura Ltd | Semiconductor acceleration sensor |
| CN2345965Y (en) * | 1998-09-11 | 1999-10-27 | 奚立仁 | Capacitive level meter |
| CN101087135A (en) * | 2006-06-08 | 2007-12-12 | 孙滕谌 | Plane capacitance sensor and method for detecting environmental change of motorcar glass |
| WO2008062146A1 (en) * | 2006-11-23 | 2008-05-29 | Sagentia Limited | Position sensor |
| TW201114179A (en) * | 2009-10-08 | 2011-04-16 | Sitronix Technology Corp | Capacitance sensing circuit with anti-electromagnetic interference function |
| CN201876293U (en) * | 2010-05-21 | 2011-06-22 | 董福贵 | Capacitance induction type material level detector |
| EP2348293A1 (en) * | 2009-12-01 | 2011-07-27 | Hirschmann Automotive GmbH | Method for capacitive measurement of fluid level and concentration of fluids |
| CN104748812A (en) * | 2015-03-28 | 2015-07-01 | 智恒（厦门）微电子有限公司 | Differential-capacitor type small article counting sensor |
| CN204575095U (en) * | 2015-05-11 | 2015-08-19 | 天津吉诺科技有限公司 | A kind of capacitive transducer with shield assembly |
-
2015
- 2015-11-02 CN CN201510729454.7A patent/CN105352565B/en active Active
Patent Citations (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3950653A (en) * | 1975-01-24 | 1976-04-13 | Agridustrial Electronics, Inc. | Instrument for sensing level of granular materials |
| JPH05281254A (en) * | 1992-03-31 | 1993-10-29 | Fujikura Ltd | Semiconductor acceleration sensor |
| CN2345965Y (en) * | 1998-09-11 | 1999-10-27 | 奚立仁 | Capacitive level meter |
| CN101087135A (en) * | 2006-06-08 | 2007-12-12 | 孙滕谌 | Plane capacitance sensor and method for detecting environmental change of motorcar glass |
| WO2008062146A1 (en) * | 2006-11-23 | 2008-05-29 | Sagentia Limited | Position sensor |
| TW201114179A (en) * | 2009-10-08 | 2011-04-16 | Sitronix Technology Corp | Capacitance sensing circuit with anti-electromagnetic interference function |
| EP2348293A1 (en) * | 2009-12-01 | 2011-07-27 | Hirschmann Automotive GmbH | Method for capacitive measurement of fluid level and concentration of fluids |
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| CN204575095U (en) * | 2015-05-11 | 2015-08-19 | 天津吉诺科技有限公司 | A kind of capacitive transducer with shield assembly |
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