CN106768172A - Extremely low relative dielectric constant medium level gauging implementation method - Google Patents
Extremely low relative dielectric constant medium level gauging implementation method Download PDFInfo
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- CN106768172A CN106768172A CN201510810672.3A CN201510810672A CN106768172A CN 106768172 A CN106768172 A CN 106768172A CN 201510810672 A CN201510810672 A CN 201510810672A CN 106768172 A CN106768172 A CN 106768172A
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- electric capacity
- dielectric constant
- relative dielectric
- extremely low
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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
Abstract
Extremely low relative dielectric constant medium level gauging implementation method, belong to detection technique field, including radially coaxially assembling and constitute testing capacitance two pole plates inner and outer pipe electrode, connect the coaxial cable core wire of two electrodes respectively, and by driving source, transformer, compare the signal conversion unit that electric capacity and detector are constituted.Wherein, the screen layer of two coaxial cables is connected to the signal ground of signal conversion unit；The output of driving source is input into as primary winding；There are transformer two secondary windings to export and electric capacity one end and the interior electrode coaxial cable core wire other end are compared in connection respectively；External electrode coaxial cable core wire and the other two ends connecting detection device input for comparing electric capacity.The present invention eliminates influence of the interference capacitors to testing capacitance on two bars connecting lines, and realizes that differential fashion is measured with electric capacity is compared by secondary windings, improves detection sensitivity, strengthens antijamming capability.
Description
Technical field
The present invention relates to a kind of extremely low relative dielectric constant medium level gauging implementation method, belong to detection technique field.
Background technology
For fields such as petrochemical industry, food medicine, new energy applications, the application of cryogenic media is more and more extensive, to storage tank
The demand that interior medium surplus carries out accurate sensing also becomes more universal and urgent.Method based on dielectric constant Cleaning Principle is become
There is no-movable part, be unaffected by the magnetic field and attract attention.For such cryogenic media, relative dielectric constant is relatively low
It is its common feature, therefore its detection sensitivity is low, it is necessary to assure have and resist external interference factor capability of influence by force.By taking liquid helium as an example,
Relative dielectric constant variable quantity is even as low as 0.05, and sensitivity is only about the 0.06% of water.
In A of CN 102589648 " LNG liquid level gauges and level measuring method " etc. in the prior art, it is open describe by it is interior,
The coaxial capacitance liquid level sensor that outer tube is constituted, testing capacitance is formed using inner cylinder and outer tube structure, and inside and outside electrode is connected respectively
The heart yearn and screen layer of same coaxial cable.
Find that the sensor of the structure has major defect and is in use：It is larger and become by heart yearn and shielding interlayer numerical value
The line capacitance influence of change, causes sensitivity low, and stability is poor, and the certainty of measurement of real testing capacitance is not high.So, it is existing
Structure is smaller to change in dielectric constant for gas, liquid, i.e., the liquefied natural gas (about 1.62) of low relative dielectric constant, or even
For liquid nitrogen (about 1.43), liquid oxygen (about 1.48), it is difficult to meet certainty of measurement, in addition reliability service requirement.
In the U of CN 202362049 " liquefied gas pair coaxial capacitance sensors ", compared to the knot in the Y of CN 2700847
Structure, increased the outermost layer cylinder being conductively connected with inner cylinder.This mode increases testing capacitance by way of electric capacity parallel connection, improves
Signal to noise ratio, but the complexity of its structure improves, and bulk is increased, and performance improvement is still relatively limited, be can only be used to relative
Dielectric constant can not excessively low, length of cable is limited, required precision is general occasion.
In 201510801439.9 " the deep cooling medium liquid level determining approach in space propultion ", employ with, in,
The signal connecting line of outer conductor structure, the guarantee of its degree of precision depend on it is interior, in, the complete encirclement between outer conductor.
But lead to the home residing for detection circuit from the pole low temperature environment residing for sensor, and basin when normally running often in
Elevated pressures (more than 5MPa), the structure cannot ensure to seal reliably and with long-term, if the treatment such as separated switching, accuracy will be bright
It is aobvious to reduce.
Prior art can not very well solve problem above, normal especially for the extremely low relative dielectric with liquid helium, liquid hydrogen as representative
The level sensing of number medium.
The content of the invention
The present invention is in view of the shortcomings of the prior art, provide a kind of extremely low relative dielectric constant medium level gauging implementation method.
The present invention uses following technical scheme to achieve the above object：
Extremely low relative dielectric constant medium level gauging implementation method, it is characterised in that：Radially from inside to outside, interior pipe electrode 1,
Outer electrode tube 2 is coaxially assembled and keeps interval, and 1,2 constitute two pole plates of testing capacitance and sent into by driving through coaxial cable 3,4
Source, transformer, compare the signal conversion unit that electric capacity and detector constitute and processed；1 is connected with 3 heart yearn one end, and 2 and 4
Heart yearn one end connects, and 3,4 screen layer is connected to the signal ground of signal conversion unit；The output of driving source is used as at the beginning of transformer
Level winding input；There are transformer two secondary windings to export and electric capacity one end and the 3 heart yearn other ends are compared in connection respectively；4 heart yearns
It is input into the other two ends connecting detection device for comparing electric capacity.
The high frequency sinusoidal ac voltage signal that driving source as shown in claim 1 is fixed for amplitude.
Transformer as shown in claim 1 has with centre tapped two secondary windings, and centre cap connection signal conversion is single
The signal ground of unit, two secondary windings output voltages are equal in magnitude, in opposite direction.
Comparing electric capacity as shown in claim 1 is low-temperature coefficient electric capacity, plays offset sensor initial value, improves sensitivity
Effect.
Detector as shown in claim 1 is the anti-phase scaling circuit being made up of operational amplifier, and testing capacitance connection is anti-
Phase input, the size of detector output voltage is linear with testing capacitance.
The beneficial effects of the invention are as follows：The characteristic of very little is lost using Transformer Winding, obtains close to preferable alternating voltage
Signal source, in addition in anti-phase scaling circuit inverting input virtual earth state, eliminate two bars connecting lines on interference capacitors
Influence to testing capacitance, and realize that differential fashion is measured with electric capacity is compared by secondary windings, improve detection sensitivity, enhancing
Antijamming capability.
Brief description of the drawings
Fig. 1 is structural representation of the invention, including：Pipe electrode, 2 outer electrode tubes, 3 coaxial cables, 4 coaxial electricals in 1
Cable, driving source, transformer, compare electric capacity, detector.
Fig. 2 is that signal conversion unit constitutes example, wherein：Vs driving sources, T transformers, Cx testing capacitances, Cs compare
Electric capacity, R feedback resistances, GND signal grounds, A amplifiers.
Specific embodiment
The present invention is further described in detail below in conjunction with the accompanying drawings：
Sensor Cleaning Principle is briefly introduced first.Extremely low relative dielectric constant medium level sensing is based on dielectric constant variable type electricity
Hold Fundamentals of Sensors, i.e., according to top to be detected for the difference between gas phase media constant and liquid phase medium dielectric constant is detected.
Metal outer pipe internal diameter is made for b, metal inner pipe external diameter a, the relative dielectric constant of gaseous medium is k1, the phase of liquid medium
It is k2 to dielectric constant, permittivity of vacuum is k0, and metal inner and outer pipe effective length, i.e., maximum detection is highly H.Then when
When liquid level is h, theoretical according to dielectric constant variable type capacitance sensor, measuring sensor capacitance Cm can be calculated with following formula：
Permittivity of vacuum k0 is, it is known that sensor for designing, a, b, H determine；After testing medium determines, k1,
K2, etc. parameter also fix.Therefore, Cm is linear with the liquid level h of liquid medium.
Obviously,Initial fixed values when respective sensor liquid level is zero.When other parameters determine, measure sensitive
Degree and k2-k1It is directly proportional, that is, is proportional to gas phase, the difference of the relative dielectric constant of liquid phase.For liquid helium, gas, liquid pair
D-value of dielectric constant is only 0.05, is the 0.06% of pure water, the 8% of liquefied natural gas.
As shown in Figure 1, extremely low relative dielectric constant medium level gauging implementation method, including：Radially from inside to outside,
Interior pipe electrode 1, outer electrode tube 2 coaxially assembles and keep interval, 1,2 constitute testing capacitances two pole plates and through coaxial cable 3,
4 feedings by driving source, transformer, compare the signal conversion unit that electric capacity and detector constitute and processed；1 and 3 heart yearn one end connect
Connect, 2 are connected with 4 heart yearn one end, and 3,4 screen layer is connected to the signal ground of signal conversion unit；The output conduct of driving source
Primary winding is input into；Transformer has two secondary windings outputs and electric capacity one end is compared in connection and 3 heart yearns are another respectively
End；4 heart yearns and the other two ends connecting detection device input for comparing electric capacity.
Described driving source is the high frequency sinusoidal ac voltage signal that amplitude is fixed.In theory, the capacitive reactance of electric capacity and capacitance size
It is inversely proportional with the AC signal frequency by electric capacity.Larger capacitive reactance is more easily detected.For the medium of extremely low relative dielectric constant
Level gauging, sensor capacitance initial value and its change equal very little that actual design is obtained, generally in the scope of several pF to tens of pF
It is interior.Accordingly, it would be desirable to apply a-c cycle higher.But frequency is too high, the additional non-ideal factors such as loss are also brought along, increased
Detection difficulty.It is preferred that frequency is between 5kHz to 100KHz.
Described transformer has with centre tapped two secondary windings, and centre cap connects the signal ground of signal conversion unit,
Two secondary windings output voltages are equal in magnitude, in opposite direction.Preferably, primary, secondary are equipped with screen layer, reduce
Harmful parasitic parameter.
Described comparing electric capacity is low-temperature coefficient electric capacity, plays offset sensor initial value, improves sensitivity effect.It is preferred that
Ground, the sensor initial capacitance value compared when electric capacity is zero with liquid level is identical, by 1 fixed capacity and 1 fine-tuning small capacitances simultaneously
Joint group is closed to be realized.
Detector is the anti-phase scaling circuit being made up of operational amplifier, testing capacitance connection inverting input, detector
The size of output voltage is linear with testing capacitance.It is preferred that the open-loop gain of operational amplifier is more than 100dB, biasing
Voltage is less than 50 μ A.
The characteristic of very little is lost using Transformer Winding, obtains close to preferable ac voltage signal source, in addition anti-phase ratio
The virtual earth state of inverting input in computing circuit, eliminates influence of the interference capacitors to testing capacitance on two bars connecting lines, and
Realize that differential fashion is measured with electric capacity is compared by secondary windings, improve detection sensitivity, strengthen antijamming capability.
The composition example of signal conversion unit shown in accompanying drawing 2, its by ac-excited source Vs, transformer T, compare electric capacity Cs,
Feedback resistance R, signal ground GND, operational amplifier A composition.
The secondary windings connection driving source Vs of transformer T, secondary center tap termination signal ground GND, secondary windings is removed
The remaining end connection of the other end, secondary windings of the either end connection inner tube coaxial cable outside centre cap compares the one of electric capacity Cs
End；The other end of the other end and connection outer coaxial tube cable core that compare electric capacity Cs is commonly connected to operational amplifier A
Inverting input；Connect the screen layer other end of inner and outer pipe coaxial cable, amplifier A in-phase input end and signal ground
GND is connected；Feedback resistance two ends are respectively connecting to the inverting input and output end of amplifier A；The output end of amplifier A and letter
Voltage Vo between number ground is the signal for obtaining sensor capacitance to be measured conversion.
The number of turn is identical between transformer secondary output winding strap centre cap, and two groups of coils of secondary windings.Ac-excited source Vs is carried
Voltage supplied signal, and be connected with the armature winding of transformer.Then according to electromagnetic induction principle, secondary windings will obtain two relatively
Signal ground GND is equal in magnitude, and the ac voltage signal of opposite in phase, amplitude is related to driving voltage and turn ratio.
Due to the resistance very little of Transformer Winding coil, i.e., equivalent to ac voltage signal source internal resistance very little, close to ideal.
The heart yearn for connecting inner tube coaxial cable is in parallel with the signal source with the electric capacity that shielding interlayer is present, will not be to flowing through sensor electricity to be measured
The electric current for holding Cx produces influence.And from above-mentioned connected mode and operational amplifier principle, amplifier A is operated in negative-feedback shape
Under state, the voltage between the inverting input and signal ground GND of amplifier A is believed that zero substantially.Therefore, connection outer coaxial tube electricity
Although there is electric capacity with shielding interlayer in the heart yearn of cable, but due to equipotential, therefore in the absence of leakage current.Now, electricity to be measured is flowed through
The electric current of appearance is believed that all by feedback resistance R.
Therefore, if transformer just, secondary turn ratio be N: 1, transformer secondary output Same Name of Ends is taken from connection Cx one end, is not examining
When electric capacity Cs is compared in worry, the voltage Vo between the output end and signal ground of amplifier A is：
It can be seen that, when other conditions are constant, turn ratio N and increase feedback resistance R is reduced, output detection sensitivity can be improved.
But for the extremely low relative dielectric constant medium such as liquid helium, liquid level change causes the variable quantity of electric capacity smaller, i.e., Cs is in full dose in above formula
Variable quantity in journey is smaller, constrains final detection sensitivity, and is unfavorable for suppressing noise.
Therefore, above formula adds the reference capacitance Cs for balancing testing capacitance in an initial condition to improve measurement sensitivity.Due to
What secondary windings was obtained is that two relative signal ground GND are equal in magnitude, and the ac voltage signal of opposite in phase, Cs, Cx's is another
End comes together in the inverting input of operational amplifier A respectively, and the voltage that detection is obtained is changed into：
When under Cs and gas phase primary condition, that is, correspond to Cx when liquid level is 0 it is equal in magnitude when, inject the electric current of inverting input
Just cancel each other, flow through the electric current of feedback resistance R for 0, the voltage Vo between the output end and signal ground of amplifier A, that is, examine
It is 0 to survey output voltage.
When the liquid level between sensor plate gradually increases, the electric current for importing operational amplifier end of oppisite phase starts to become big, loses flat
Weighing apparatus is acted on, and the change according to Vo sizes is to be proportional to actual liquid level highly, you can complete level sensing.
By above-mentioned implementation, the influence of line capacitance and its change to measuring is eliminated, significantly improves detection sensitivity,
Antijamming capability is enhanced, it is ensured that certainty of measurement.
The present invention is able in liquid helium (gas, liquid is to D-value of dielectric constant only about 0.05) medium level gauging in superconduction scientific research
Checking, embodies high accuracy and stability.
The present invention is to provide a kind of medium level gauging implementation method for extremely low relative dielectric constant, its performance improvement
Realize that there is more universal applicability.For personnel in the art, under the premise without departing from the principles of the invention, can
To make some retouchings and improvement, protection scope of the present invention is also should be regarded as.
Claims (5)
1. extremely low relative dielectric constant medium level gauging implementation method, it is characterised in that：Radially from inside to outside, interior pipe electrode 1,
Outer electrode tube 2 is coaxially assembled and keeps interval, and 1,2 constitute two pole plates of testing capacitance and sent into by driving through coaxial cable 3,4
Source, transformer, compare the signal conversion unit that electric capacity and detector constitute and processed；1 is connected with 3 heart yearn one end, and 2 and 4
Heart yearn one end connects, and 3,4 screen layer is connected to the signal ground of signal conversion unit；The output of driving source is used as at the beginning of transformer
Level winding input；There are transformer two secondary windings to export and electric capacity one end and the 3 heart yearn other ends are compared in connection respectively；4 heart yearns
It is input into the other two ends connecting detection device for comparing electric capacity.
2. extremely low relative dielectric constant medium level gauging implementation method as claimed in claim 1, it is characterised in that：Described
Driving source is the high frequency sinusoidal ac voltage signal that amplitude is fixed.
3. extremely low relative dielectric constant medium level gauging implementation method as claimed in claim 1, it is characterised in that：Described
Transformer has with centre tapped two secondary windings, and centre cap connects the signal ground of signal conversion unit, two secondary around
Group output voltage is equal in magnitude, in opposite direction.
4. extremely low relative dielectric constant medium level gauging implementation method as claimed in claim 1, it is characterised in that：Described
Compare electric capacity for low-temperature coefficient electric capacity, play offset sensor initial value, improve sensitivity effect.
5. extremely low relative dielectric constant medium level gauging implementation method as claimed in claim 1, it is characterised in that：Described
Detector is the anti-phase scaling circuit being made up of operational amplifier, testing capacitance connection inverting input, detector output electricity
The size of pressure is linear with testing capacitance.
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| CN201510810672.3A CN106768172A (en) | 2015-11-23 | 2015-11-23 | Extremely low relative dielectric constant medium level gauging implementation method |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107870020A (en) * | 2017-12-26 | 2018-04-03 | 太原理工大学 | A kind of triaxial cable capacity water level measuring device |
| CN109387260A (en) * | 2017-08-14 | 2019-02-26 | 宝盟电气股份公司 | Sensor device for the liquid level of potential measurement in a reservoir |
| CN112729641A (en) * | 2020-12-01 | 2021-04-30 | 上海空间推进研究所 | System and method for measuring response time of cold air thruster based on variable dielectric capacitance bridge |
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| GB2043259B (en) * | 1978-11-24 | 1983-08-03 | Drexelbrook Controls | Level measurement system |
| CN1828315A (en) * | 2006-01-24 | 2006-09-06 | 东北大学 | High voltage alternate driver circuit for determining micro capacitance |
| CN203232327U (en) * | 2013-04-24 | 2013-10-09 | 济南大学 | Liquid level measurement control device |
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2015
- 2015-11-23 CN CN201510810672.3A patent/CN106768172A/en active Pending
Patent Citations (3)
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|---|---|---|---|---|
| GB2043259B (en) * | 1978-11-24 | 1983-08-03 | Drexelbrook Controls | Level measurement system |
| CN1828315A (en) * | 2006-01-24 | 2006-09-06 | 东北大学 | High voltage alternate driver circuit for determining micro capacitance |
| CN203232327U (en) * | 2013-04-24 | 2013-10-09 | 济南大学 | Liquid level measurement control device |
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| 吴建平: "《传感器原理及应用 第2版》", 31 March 2012, 北京：机械工业出版社 * |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109387260A (en) * | 2017-08-14 | 2019-02-26 | 宝盟电气股份公司 | Sensor device for the liquid level of potential measurement in a reservoir |
| CN107870020A (en) * | 2017-12-26 | 2018-04-03 | 太原理工大学 | A kind of triaxial cable capacity water level measuring device |
| CN107870020B (en) * | 2017-12-26 | 2019-12-17 | 太原理工大学 | Three coaxial cable capacitance type water level measuring device |
| CN112729641A (en) * | 2020-12-01 | 2021-04-30 | 上海空间推进研究所 | System and method for measuring response time of cold air thruster based on variable dielectric capacitance bridge |
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Application publication date: 20170531 |