CN117451136A - Liquid helium level sensor preparation method, liquid helium level sensor and detection method - Google Patents
Liquid helium level sensor preparation method, liquid helium level sensor and detection method Download PDFInfo
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- 239000007788 liquid Substances 0.000 title claims abstract description 249
- 239000001307 helium Substances 0.000 title claims abstract description 156
- 229910052734 helium Inorganic materials 0.000 title claims abstract description 156
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 title claims abstract description 156
- 238000002360 preparation method Methods 0.000 title claims abstract description 13
- 238000001514 detection method Methods 0.000 title abstract description 13
- 229910001220 stainless steel Inorganic materials 0.000 claims abstract description 58
- 239000010935 stainless steel Substances 0.000 claims abstract description 58
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 claims abstract description 30
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims abstract description 29
- 239000000395 magnesium oxide Substances 0.000 claims abstract description 27
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 claims abstract description 24
- 238000004519 manufacturing process Methods 0.000 claims abstract description 5
- 238000010438 heat treatment Methods 0.000 claims description 59
- 238000003466 welding Methods 0.000 claims description 22
- 238000000034 method Methods 0.000 claims description 20
- 238000005303 weighing Methods 0.000 claims description 8
- 238000005520 cutting process Methods 0.000 claims description 3
- 238000001035 drying Methods 0.000 claims description 3
- 230000000149 penetrating effect Effects 0.000 claims description 3
- 239000000843 powder Substances 0.000 claims description 3
- 238000005096 rolling process Methods 0.000 claims description 3
- 238000007789 sealing Methods 0.000 claims description 3
- 230000004044 response Effects 0.000 abstract description 7
- 230000008859 change Effects 0.000 description 11
- 238000002474 experimental method Methods 0.000 description 9
- 238000005259 measurement Methods 0.000 description 9
- 238000012360 testing method Methods 0.000 description 8
- 230000008569 process Effects 0.000 description 7
- 239000007789 gas Substances 0.000 description 4
- 239000012071 phase Substances 0.000 description 4
- 238000012546 transfer Methods 0.000 description 4
- 238000004458 analytical method Methods 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 3
- 238000009835 boiling Methods 0.000 description 3
- 238000007405 data analysis Methods 0.000 description 3
- 239000012808 vapor phase Substances 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000001704 evaporation Methods 0.000 description 2
- 230000008020 evaporation Effects 0.000 description 2
- 239000007791 liquid phase Substances 0.000 description 2
- 238000010791 quenching Methods 0.000 description 2
- 230000000630 rising effect Effects 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 230000000087 stabilizing effect Effects 0.000 description 2
- 238000004804 winding Methods 0.000 description 2
- 230000001174 ascending effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000010408 film Substances 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 125000004435 hydrogen atom Chemical class [H]* 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 239000002887 superconductor Substances 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 238000009785 tube rolling Methods 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
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F25/00—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume
- G01F25/20—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume of apparatus for measuring liquid level
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/60—Superconducting electric elements or equipment; Power systems integrating superconducting elements or equipment
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Abstract
The invention discloses a liquid helium level sensor preparation method, a liquid helium level sensor and a detection method, wherein the preparation method comprises the following steps: manufacturing a liquid helium liquid level sensor entity, and calibrating the manufactured liquid helium liquid level sensor to obtain a standard working curve of the liquid helium liquid level sensor; the liquid helium level sensor comprises an NbTi superconducting wire, an enamelled copper wire, a current input wire, a positive electrode voltage measuring wire, a current output wire, a negative electrode voltage measuring wire, magnesium oxide, an inner stainless steel tube and an outer stainless steel tube, wherein the current input wire and the positive electrode voltage measuring wire are connected with the rear end of the NbTi superconducting wire, the current output wire and the negative electrode voltage measuring wire are connected with the rear end of the enamelled copper wire, the magnesium oxide is wrapped outside the NbTi superconducting wire and the enamelled copper wire, and the inner stainless steel tube is armored outside the magnesium oxide, the outer stainless steel tube is armored outside the inner stainless steel tube and provided with a micro flow channel. The liquid helium level sensor has the advantages of small working input power, high working response speed, small detection error, high detection precision and the like.
Description
Technical Field
The invention relates to the technical field of low-temperature liquid level detection, in particular to a liquid helium level detection device and method.
Background
Liquid helium, liquid hydrogen, liquid nitrogen and other low-temperature liquids play an important role in the fields of aerospace, medical technology and the like. Among them, liquid helium has a boiling point of 4.2K (at-268.95 ℃ C.) and is a low-temperature source with the lowest boiling point. In order to ensure the safety, economy and environmental protection of the low-temperature liquid in the transportation, storage and use processes, the accurate, quick and stable measurement of the liquid level is significant.
The current low-temperature liquid level measurement devices comprise a capacitive liquid level meter, an ultrasonic liquid level meter, a static pressure liquid level meter, a superconducting liquid level meter, a transmission line type liquid level meter and a float type liquid level meter. Although these methods are the main methods of low-temperature liquid level measurement at present, the measurement is still susceptible to the property change, signal interference and the like of the low-temperature liquid, so that the measurement accuracy is reduced.
The superconducting liquid level measuring technology is to correlate liquid level with total pressure drop on the superconducting line of the sensor to measure liquid level, and when the superconducting liquid level sensor is immersed in liquid helium, the superconducting line inside the superconducting liquid level sensor is simultaneously in helium working medium environments of gas phase and liquid phase. The critical temperature of the superconducting wire is slightly higher than the temperature of liquid helium, so that the entire sensor is in a superconducting state without external heating. In order to establish a correspondence between the output voltage of the superconducting sensor and the liquid level, it is necessary to heat the superconducting wire. By heating, the superconducting wire loses superconductivity in the gas phase portion, while the liquid phase portion remains in a superconducting state. Therefore, by measuring the output voltage change of the superconducting wire, the level of the liquid helium can be judged.
The superconductive liquid level sensor is divided into three types of superconductive wire self-heating, resistance heating and heating wire heating according to the heating mode. Heating by a heating wire: the mode of winding the heating wire on the top of the superconducting wire has low response speed, and the problems of large error, large medium evaporation and the like exist in the structure of winding the heating wire on the whole superconducting wire and connecting the heating wire beside the superconducting wire in parallel. Superconducting wire self-heating: doping modification is needed to be carried out on the material so as to reduce the critical temperature Tc of the superconducting wire, which is difficult to realize for NbTi superconducting wires; while heating requires a large current drive, also introducing a large amount of heat and poor accuracy. Resistance heating: the mode of connecting a plurality of resistors in series can generate great errors, and simultaneously, larger heat is introduced; when a single resistor is connected in series, the precision is required to be improved.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a liquid helium liquid level sensor preparation method, a liquid helium liquid level sensor and a detection method, so as to solve the technical problem of accurately detecting the liquid helium liquid level and solve the defects of the existing superconducting liquid level sensor in the aspects of response time, heating power, detection accuracy and the like.
The preparation method of the liquid helium level sensor comprises the following steps:
i) Manufacturing a liquid helium level sensor, comprising:
a) Preparing an NbTi superconducting wire and an enamelled copper wire, respectively penetrating the NbTi superconducting wire and the enamelled copper wire into two mutually parallel axial straight holes on a magnesium oxide cylinder, then filling the magnesium oxide cylinder into a first stainless steel tube, and then rolling the first stainless steel tube to ensure that the diameter of the first stainless steel tube is reduced and the length of the first stainless steel tube is increased, so that the magnesium oxide cylinder is tightly filled in the first stainless steel tube;
b) Cutting off the front part and the rear part of the first stainless steel tube to obtain an effective sensing section containing NbTi superconducting wires inside;
removing part of magnesium oxide in the front end of the effective sensing section to lead out the front end part of the NbTi superconducting wire and the front end part of the enamelled copper wire, and then welding the front end part of the NbTi superconducting wire and the front end part of the enamelled copper wire;
removing part of magnesium oxide in the rear end of the effective sensing section to lead out the rear end part of the NbTi superconducting wire and the rear end part of the enamelled copper wire, welding a heating resistor at the rear end of the NbTi superconducting wire, welding a current input wire at the rear end of the heating resistor, and welding a positive voltage measuring wire at the welding part of the NbTi superconducting wire and the heating resistor; welding a current output wire at the rear end of the enamelled copper wire, and welding a negative voltage measuring wire at the rear end of the enamelled copper wire;
c) Welding a second stainless steel tube with the effective sensing section of the first stainless steel tube in the step b), leading out a current input lead, a positive electrode voltage measuring line and a negative electrode voltage measuring line from the second stainless steel tube, filling magnesia powder into the second stainless steel tube, and sleeving a third stainless steel tube with a micro-channel outside the first stainless steel tube and the second stainless steel tube to obtain a sensor primary product;
d) Placing the sensor primary product into an oven for drying, and then sealing pipe orifices at two ends of the sensor primary product to obtain a liquid helium level sensor finished product;
II) calibrating a finished product of the liquid helium level sensor, comprising:
1) Weighing the total weight m of the liquid helium level sensor and the empty dewar by an electronic scale 1 ；
2) Adding liquid helium into a Dewar flask, vertically inserting a liquid helium level sensor into the Dewar flask and ensuring that the lowest end of the liquid helium level sensor is inserted into the bottom of a liner of the Dewar flask; then the total weight m of the liquid helium level sensor and the dewar tank filled with liquid helium is obtained by weighing by an electronic scale 2 According to m 1 And m 2 Obtaining the weight delta m=m of liquid helium in the dewar tank 2 -m 1 The method comprises the steps of carrying out a first treatment on the surface of the According to the relationship among the density, the mass and the volume of the liquid helium, the volume of the liquid helium is obtained:
according to the relation between the cavity volume and the cavity height of the Dewar, the volume is V Liquid and its preparation method The liquid level height H corresponding to the liquid helium;
3) The positive electrode and the negative electrode of the programmable direct current power supply are respectively connected with a current input wire and a current input wire of the liquid helium level sensor, and the positive electrode and the negative electrode of the data acquisition instrument are respectively connected with a positive electrode voltage measuring wire and a negative electrode voltage measuring wire;
4) Current scanning: the programmable power supply outputs stepped incremental current to the liquid helium liquid level sensor, the data acquisition instrument acquires output voltages corresponding to different-size current, and the minimum current for enabling the liquid helium liquid level sensor to work stably is found according to the relation between the input current and the output voltage;
5) And introducing a minimum working current into the liquid helium liquid level sensor in a constant current mode, recording output voltage corresponding to the initial liquid level height H, then lifting the sensor at each time by using the fixed adjustment height H to simulate liquid level drop, recording the output voltage corresponding to each liquid level, and fitting a standard working curve describing the relationship between the liquid level height and the output voltage according to recorded data.
A liquid helium level sensor manufactured by the liquid helium level sensor manufacturing method.
Further, the diameter of the NbTi superconducting wire is 45 μm.
Further, the micro-channels on the third stainless steel tube are round holes or strip-shaped holes which are uniformly distributed.
Further, the standard operating curve of the liquid helium level sensor with a heating resistance of 1Ω is:
y＝-0.0087x+4.42017
the standard operating curve of the liquid helium level sensor with a heating resistance of 5.1 Ω is:
y＝-0.00829x+4.09796
the standard operating curve of the liquid helium level sensor with a heating resistance of 10Ω is:
y＝-0.00692x+3.54234
in the standard working curve, x is the liquid helium level, and y is the output voltage of the liquid helium level sensor.
The method for detecting the liquid helium level by using the liquid helium level sensor comprises the following steps:
1) Vertically inserting a liquid helium level sensor into a container filled with liquid helium, so that the end part of the liquid helium level sensor is in contact with the bottom of the container;
2) Introducing a minimum working current into the liquid helium level sensor, and collecting the output voltage of the liquid helium level sensor;
3) Substituting the output voltage obtained in the step 2) into the standard working curve of the liquid helium level sensor to obtain the liquid level height of the liquid helium in the container.
The invention has the beneficial effects that:
1. according to the liquid helium liquid level sensor, the superconducting wire is heated by connecting the heating resistor at the end part of the NbTi superconducting wire, and the superconducting wire resistor in liquid helium is 0, and the resistor of the enamelled copper wire is very small and can be ignored, so that the heating of the superconducting wire in liquid helium and the enamelled copper wire can be ignored, and the liquid helium liquid level sensor adopts the minimum working current, so that the heating input power is small, the evaporation of liquid helium can be further reduced when the liquid level is detected, and the detection precision can be further improved.
2. According to the invention, the magnesium oxide column is tightly filled in the stainless steel tube after being broken by adopting a tube rolling mode, so that the rapid heat transfer speed between the NbTi superconducting wire and the magnesium oxide can be improved, the heat emitted by the heating resistor can be more rapidly transferred downwards through the magnesium oxide, the heating speed of the NbTi superconducting wire above the liquid level can be improved, and the response speed of the sensor can be improved. And because the stainless steel pipe with the micro-flow channel is sheathed outside the sensor, the stainless steel pipe with the micro-flow channel can further improve the heat transfer speed between the liquid helium and the sensor, so that the heat downwards transferred by the magnesium oxide can be quickly diffused into the liquid helium through the stainless steel pipe with the micro-flow channel, the influence of the heat on the superconducting performance caused by the temperature rise of the NbTi superconducting wire below the liquid level can be avoided, and experiments prove that the micro-flow channel with the strip-shaped groove can accelerate the stability of the output voltage of the sensor, thereby being beneficial to improving the detection efficiency and the corresponding speed.
3. Experiments prove that the response time of the liquid helium level sensor is less than 1s, and the response speed is high.
4. Experiments prove that the liquid helium level sensor has high detection precision and small error.
Drawings
FIG. 1 is a schematic diagram of a liquid helium level sensor.
Fig. 2 is a diagram of the shape of the inner cavity of the dewar for calibration experiments.
FIG. 3 is a graph of voltage output for three liquid helium level sensors.
FIG. 4 shows the variation of the sensor output voltage at different regions of the current sweep.
Fig. 5 is a graph of voltage output of sensors with different heating resistances at constant current output.
FIG. 6 shows voltage output values for different liquid level heights during the liquid level elevation process. (a) r=1Ω, i=50ma; (b) r=5.1Ω, i=46 mA; (c) r=10Ω, i=40ma.
FIG. 7 shows the results of the liquid level resolution test for three sensors.
Fig. 8 is a graph showing voltage output curves before and after the micro flow channel is added.
Detailed Description
The invention is further described below with reference to the drawings and examples.
Embodiment one: the preparation method of the liquid helium level sensor comprises the following steps:
i) Manufacturing a liquid helium level sensor, comprising:
a) Preparing an NbTi superconducting wire 1 and an enamelled copper wire 2, respectively penetrating the NbTi superconducting wire and the enamelled copper wire into two mutually parallel axial straight holes on a magnesium oxide cylinder 3, then filling the magnesium oxide cylinder into a first stainless steel tube 4, and then rolling the first stainless steel tube to reduce the diameter and increase the length of the first stainless steel tube, so that the magnesium oxide cylinder is tightly filled in the first stainless steel tube.
b) And cutting off the front part and the rear part of the first stainless steel tube to obtain an effective sensing section containing NbTi superconducting wires.
And removing part of magnesium oxide in the front end of the effective sensing section to lead out the front end part of the NbTi superconducting wire and the front end part of the enamelled copper wire, and welding the front end part of the NbTi superconducting wire and the front end part of the enamelled copper wire.
Removing part of magnesium oxide in the rear end of the effective sensing section to lead out the rear end part of the NbTi superconducting wire and the rear end part of the enamelled copper wire, welding a heating resistor 5 at the rear end of the NbTi superconducting wire, welding a current input wire 6 at the rear end of the heating resistor, and welding a positive electrode voltage measuring wire 7 at the welding part of the NbTi superconducting wire and the heating resistor; and a current output wire 8 is welded at the rear end of the enamelled copper wire, and a negative voltage measuring wire 9 is welded at the rear end of the enamelled copper wire.
c) And b) welding a second stainless steel pipe 10 with the effective sensing section of the first stainless steel pipe in the step b), leading out a current input wire, a positive electrode voltage measuring wire and a negative electrode voltage measuring wire from the second stainless steel pipe, filling magnesia powder 11 into the second stainless steel pipe, and sleeving a third stainless steel pipe 13 with a micro-channel 12 outside the first stainless steel pipe and the second stainless steel pipe to obtain a sensor primary product.
d) And (3) putting the sensor primary product into an oven for drying, and then sealing the pipe orifices at the two ends of the sensor primary product to obtain a liquid helium level sensor finished product.
II) calibrating a finished product of the liquid helium level sensor, comprising:
1) Weighing the total weight m of the liquid helium level sensor and the empty dewar by an electronic scale 1 。
2) Adding liquid helium into a Dewar flask, vertically inserting a liquid helium level sensor into the Dewar flask and ensuring that the lowest end of the liquid helium level sensor is inserted into the bottom of a liner of the Dewar flask; then the total weight m of the liquid helium level sensor and the dewar tank filled with liquid helium is obtained by weighing by an electronic scale 2 According to m 1 And m 2 Obtaining the weight delta m=m of liquid helium in the dewar tank 2 -m 1 The method comprises the steps of carrying out a first treatment on the surface of the According to the relationship among the density, the mass and the volume of the liquid helium, the volume of the liquid helium is obtained:
the density ρ of the liquid helium at a temperature of 4.2K was 125.41kg/m 3 . According to the relation between the cavity volume and the cavity height of the Dewar, the volume is V Liquid and its preparation method Liquid level H corresponding to liquid helium.
3) The positive electrode and the negative electrode of the programmable direct current power supply are respectively connected with a current input wire and a current input wire of the liquid helium level sensor, and the positive electrode and the negative electrode of the data acquisition instrument are respectively connected with a positive electrode voltage measuring wire and a negative electrode voltage measuring wire.
4) Current scanning: the programmable power supply outputs stepped incremental current to the liquid helium liquid level sensor, the data acquisition instrument acquires output voltages corresponding to different-size current, and the minimum current for enabling the liquid helium liquid level sensor to work stably is found according to the relation between the input current and the output voltage.
5) And introducing a minimum working current into the liquid helium liquid level sensor in a constant current mode, recording output voltage corresponding to the initial liquid level height H, then lifting the sensor at each time by using the fixed adjustment height H to simulate liquid level drop, recording the output voltage corresponding to each liquid level, and fitting a standard working curve describing the relationship between the liquid level height and the output voltage according to recorded data.
The three liquid helium level sensors prepared by the liquid helium level sensor preparation method in the above embodiment obviously comprise an NbTi superconducting wire and an enamelled copper wire with the front ends mutually connected, a current input wire and a positive voltage measurement wire which are connected with the rear ends of the NbTi superconducting wire, a current output wire and a negative voltage measurement wire which are connected with the rear ends of the enamelled copper wire, magnesium oxide tightly wrapped outside the NbTi superconducting wire and the enamelled copper wire, and an inner stainless steel tube (the inner stainless steel tube consists of the first stainless steel tube and the second stainless steel tube) sheathed outside the magnesium oxide and an outer stainless steel tube (namely the third stainless steel tube) sheathed outside the inner stainless steel tube and provided with micro channels. The diameter of the NbTi superconducting wire of the first liquid helium level sensor is 45 mu m, and the resistance value of the heating resistor is 1 omega; the diameter of the NbTi superconducting wire of the second liquid helium level sensor is 45 mu m, and the resistance value of the heating resistor is 5.1 omega; the diameter of the NbTi superconducting wire of the second liquid helium level sensor is 45 mu m, and the resistance value of the heating resistor is 10Ω; the micro-channels on the third stainless steel tube of the three liquid helium level sensors are uniformly distributed strip-shaped holes.
The calibration test for the three liquid helium level sensors is specifically as follows:
according to the preparation method of the liquid helium liquid level sensor, the electronic weighing process adopted for calibrating the three prepared liquid helium liquid level sensors is 150kg, the actual precision is 5g, the liquid level height error corresponding to the 5g precision is 0.2033mm, the conversion precision is about 0.0407%, and the calibration experiment requirement is met. The dimensions of the inner cavity of the dewar used in the calibration test are shown in fig. 2, and the relationship between the inner cavity volume v and the liquid level x is as follows:
when x is less than or equal to 1.25dm,maximum valueCapacity 16.35L;
when 1.25dm < x <3.05dm, "=16, 35+6.25pi (-1.25), maximum capacity 51.675L;
when 3.05dm is less than or equal to x,maximum capacity 68.025L;
the liquid helium mass in the Dewar is obtained through weighing, the liquid helium volume is calculated, and then the liquid level height H of the liquid helium in the Dewar is calculated according to the formula.
The three liquid helium level sensors are subjected to current scanning, and as the critical current density of the superconducting wire is unknown, larger current cannot be directly introduced, so that the superconducting wire is prevented from being quenched directly due to the fact that the current is too large. Therefore, the experiment adopts stepwise increasing current to scan, observes the voltage change at two ends of the superconducting wire, and determines the minimum working current capable of maintaining the normal working of the superconducting wire under the liquid level height. The experiment adopts a programmable power supply as a current source, wherein a step-type incremental current scanning function is preset, the scanning time is set to be 50s, the current scanning range is 0-100 mA, the change rate is 2mA/s, and three sensors adopt current scanning results as shown in 3. As can be seen from the figure, the three sensors can detect voltage changes in less than 1s, i.e. the response times are less than 1s. The rate of voltage change depends on the resistor heating power and its thermal coupling efficiency with the NbTi wire. From the data analysis, the quench times and minimum operating currents for the three sensors are shown in table 1.
TABLE 1 analysis of different heating resistance current scan results
The voltage change will mainly go through four phases when the sensor current is stepped up from 0 to 100 mA. As shown in fig. 4, the current scanning result of the liquid helium level sensor with the resistance value of the heating resistor of 5.1 Ω is shown. From the initial data analysis, the output voltage will remain briefly zero for less than 0.1 seconds starting from an initial current of 0mA up to the first breakdown zone (Z1), mainly because the portion of the sensor exposed to the vapor phase is still in the superconducting phase. In the first zone (Z1), the voltage across the sensor suddenly changes and part of the NbTi superconducting wire near the resistor becomes normal due to thermal quenching of the top heating resistor. In this region, heat transfer from the wire to the surrounding cold helium gas is by gas convection.
In zone 2 (Z2), the voltage increases monotonically with current, the superconducting line in the region, which is mainly the vapor phase, gradually becomes normal, and the voltage increases linearly with the current. Until zone 3 (Z3) voltage increases abruptly, the superconductor portion immersed in liquid helium becomes normal and surrounded by a thin film of helium, the heat transfer in this zone being primarily by a film boiling mechanism. In zone 4 (Z4), the voltage on the superconducting wire increases monotonically, representing a simple resistance, mainly due to the continuous increase in current and the gradual heating of a small portion of the superconducting wire below the liquid surface to the normal state.
And according to the current scanning result, the minimum working current of the sensor under different heating resistances can be obtained. The sensor works under the minimum working current, so that the heat input to the system can be effectively reduced, and the measuring precision of the sensor is improved. Therefore, in the subsequent experiments, the power supply is used as a constant current source and works under the minimum working current, and different liquid levels are simulated by controlling the sensing positions.
The level drop is simulated by controlling the sensor rise. In the experimental process, on the basis of the liquid level height H, the sensor is lifted three times by the adjustment height h=20mm, and four different liquid level heights in the liquid level descending process are simulated. The calibration test also starts at the highest position of the sensor, lowers the sensor at the same intervals, simulates the stability and repeatability of the sensor during the liquid level rising process, and finally returns to the initial liquid level height H. The minimum operating current test results are shown in fig. 5:
as can be seen from fig. 5, when the output is at a constant minimum operating current, the output voltage of the sensor increases sharply from 0, and the output voltage of the sensor can be stabilized over several seconds. At this time, the superconducting wire of the vapor phase part is changed from the superconducting state to the normal state, the superconducting wire of the smaller section below the liquid level is heated to the normal state, and after the sensor is stabilized, the part below the liquid level is almost unchanged or the variation is very small, so that the sensor has good stability.
Meanwhile, as can be seen from fig. 5, when the heating resistors of three different resistance values are operated with the minimum operation current, the time for the sensor to reach stability decreases as the resistance value increases. From the concrete numerical analysis, the time for the 1 Ω heating resistor to stabilize at 50mA current was about 5s, the time for the 5.1 Ω heating resistor to stabilize at 46mA current was about 3s, and the time for the 10 Ω heating resistor to stabilize at 40mA current was about 2s. It can be seen that, within a certain range, the time for the sensor to reach stability decreases as the resistance of the heating resistor increases.
As shown in fig. 6, when the three sensors are supplied with a constant current of the minimum working current, the voltage output curves in the process of simulating the rise and fall of the liquid level have good linear relationship, namely, the liquid level height and the output voltage of the sensors have higher linear relationship.
Through a calibration test, the standard working curves of the three liquid helium level sensors are obtained as follows:
the liquid helium level sensor with the heating resistance of 1 omega has the standard working curve as follows:
y＝-0.0087x+4.42017,R 2 ＝0.99979
the liquid helium level sensor with the heating resistance of 5.1 omega has the standard working curve as follows: :
y＝-0.00829x+4.09796,R 2 ＝0.99995
the liquid helium level sensor with the heating resistance of 10 omega has the standard working curve as follows:
y＝-0.00692x+3.54234,R 2 ＝0.99999
from the standard working curve, the linear correlation between the liquid level and the output voltage is higher, R 2 Are all greater than 0.999. The output voltage is reduced along with the increase of the liquid level height, and the output voltage is transmitted to the sensorThe analysis of the change curve of the output voltage along with the liquid level height can obtain that the sensitivity of voltage output can be 8.707mV/mm, 8.011mV/mm and 6.966mV/mm respectively by calibrating the three sensors of 1 omega, 5.1 omega and 10 omega in the liquid level range of 60-130 mm.
The sensor is used for simulating the liquid level rising, and the relationship between the liquid level height and the output voltage of the sensor is obtained as follows:
the liquid helium level sensor with the heating resistance of 1 omega has the standard working curve as follows:
y＝-0.0087x+4.42567,R 2 ＝0.99951
the liquid helium level sensor with the heating resistance of 5.1 omega has the standard working curve as follows: :
y＝-0.0078x+4.06893,R 2 ＝0.99964
the liquid helium level sensor with the heating resistance of 10 omega has the standard working curve as follows:
y＝-0.00699x+3.54946,R 2 ＝0.99988
from the standard operation curves obtained from the above-described ascending and descending sensors, the sensor repetition error is small.
The minimum resolution of the sensor is detected through experiments, the method is that under a certain liquid level height, a voltage output curve under the liquid level height is measured firstly, then the sensor is controlled to ascend and descend slowly, and the minimum scale which can cause output voltage change and can be stable is observed, namely the liquid level sensitivity. After the sensor output voltage signal stabilizes, at 30s, the sensor is controlled to move the sensor slowly up and down, respectively, until the liquid level output voltage is observed to change and stabilize. As shown in fig. 7, in combination with the test data analysis, the minimum level change amount capable of causing the voltage change and stable was about 1mm, i.e., the minimum resolution of the three sensors was 1mm.
The beneficial effects of the micro-channel structure of the sensor are verified:
the micro-channel is a strip-shaped groove with the width of 1mm, the liquid helium liquid level sensor with the heating resistance of 1 omega is compared with the voltage output curve of the stainless steel tube with the micro-channel before and after being additionally provided with the micro-channel under the same current driving, the result is shown in the figure, and as can be seen from the figure, under the same condition, after the sensor is additionally provided with the long-groove micro-channel, the output voltage increasing rate is increased, the time for stabilizing the sensor is reduced by about 0.5s compared with the time for stabilizing the sensor without the micro-channel, and the stability of the output voltage of the sensor can be accelerated by the micro-channel with the strip-shaped groove, so that the detection efficiency is improved.
The method for detecting the liquid helium level by using the liquid helium level sensor in the embodiment comprises the following steps:
1) Vertically inserting a liquid helium level sensor into a container filled with liquid helium, so that the end part of the liquid helium level sensor is in contact with the bottom of the container;
2) Introducing a minimum working current into the liquid helium level sensor, and collecting the output voltage of the liquid helium level sensor;
3) Substituting the output voltage obtained in the step 2) into the standard working curve of the liquid helium level sensor to obtain the liquid level height of the liquid helium in the container.
The experimental test results are shown in the following table:
table 2 sensor forward travel measurement data
Table 3 sensor back-travel measurement data
Claims (7)
1. The preparation method of the liquid helium level sensor is characterized by comprising the following steps of: the method comprises the following steps:
i) Manufacturing a liquid helium level sensor, comprising:
a) Preparing an NbTi superconducting wire and an enamelled copper wire, respectively penetrating the NbTi superconducting wire and the enamelled copper wire into two mutually parallel axial straight holes on a magnesium oxide cylinder, then filling the magnesium oxide cylinder into a first stainless steel tube, and then rolling the first stainless steel tube to ensure that the diameter of the first stainless steel tube is reduced and the length of the first stainless steel tube is increased, so that the magnesium oxide cylinder is tightly filled in the first stainless steel tube;
b) Cutting off the front part and the rear part of the first stainless steel tube to obtain an effective sensing section containing NbTi superconducting wires inside;
removing part of magnesium oxide in the front end of the effective sensing section to lead out the front end part of the NbTi superconducting wire and the front end part of the enamelled copper wire, and then welding the front end part of the NbTi superconducting wire and the front end part of the enamelled copper wire;
removing part of magnesium oxide in the rear end of the effective sensing section to lead out the rear end part of the NbTi superconducting wire and the rear end part of the enamelled copper wire, welding a heating resistor at the rear end of the NbTi superconducting wire, welding a current input wire at the rear end of the heating resistor, and welding a positive voltage measuring wire at the welding part of the NbTi superconducting wire and the heating resistor; welding a current output wire at the rear end of the enamelled copper wire, and welding a negative voltage measuring wire at the rear end of the enamelled copper wire;
c) Welding a second stainless steel tube with the effective sensing section of the first stainless steel tube in the step b), leading out a current input lead, a positive electrode voltage measuring line and a negative electrode voltage measuring line from the second stainless steel tube, filling magnesia powder into the second stainless steel tube, and sleeving a third stainless steel tube with a micro-channel outside the first stainless steel tube and the second stainless steel tube to obtain a sensor primary product;
d) Placing the sensor primary product into an oven for drying, and then sealing pipe orifices at two ends of the sensor primary product to obtain a liquid helium level sensor finished product;
II) calibrating a finished product of the liquid helium level sensor, comprising:
1) Weighing the total weight m of the liquid helium level sensor and the empty dewar by an electronic scale 1 ；
2) Adding liquid helium into a Dewar flask, vertically inserting a liquid helium level sensor into the Dewar flask and ensuring that the lowest end of the liquid helium level sensor is inserted into the bottom of a liner of the Dewar flask; weighing by electronic scale to obtain total weight of liquid helium level sensor and dewar tank filled with liquid heliumQuantity m 2 According to m 1 And m 2 Obtaining the weight delta m=m of liquid helium in the dewar tank 2 -m 1 The method comprises the steps of carrying out a first treatment on the surface of the According to the relationship among the density, the mass and the volume of the liquid helium, the volume of the liquid helium is obtained:
according to the relation between the cavity volume and the cavity height of the Dewar, the volume is V Liquid and its preparation method The liquid level height H corresponding to the liquid helium;
3) The positive electrode and the negative electrode of the programmable direct current power supply are respectively connected with a current input wire and a current input wire of the liquid helium level sensor, and the positive electrode and the negative electrode of the data acquisition instrument are respectively connected with a positive electrode voltage measuring wire and a negative electrode voltage measuring wire;
4) Current scanning: the programmable power supply outputs stepped incremental current to the liquid helium liquid level sensor, the data acquisition instrument acquires output voltages corresponding to different-size current, and the minimum current for enabling the liquid helium liquid level sensor to work stably is found according to the relation between the input current and the output voltage;
5) And introducing a minimum working current into the liquid helium liquid level sensor in a constant current mode, recording output voltage corresponding to the initial liquid level height H, then lifting the sensor at each time by using the fixed adjustment height H to simulate liquid level drop, recording the output voltage corresponding to each liquid level, and fitting a standard working curve describing the relationship between the liquid level height and the output voltage according to recorded data.
2. A liquid helium level sensor produced by the method of producing a liquid helium level sensor of claim 1.
3. A liquid helium level sensor according to claim 2, wherein: the method is characterized in that: the diameter of the NbTi superconducting wire is 45 mu m.
4. A liquid helium level sensor according to claim 3, wherein: the micro-channels on the third stainless steel tube are round holes or strip-shaped holes which are uniformly distributed.
5. A liquid helium level sensor according to claim 4, wherein: the resistance value of the heating resistor is 1 omega-10Ω.
6. A liquid helium level sensor according to claim 2, wherein:
the standard operating curve of the liquid helium level sensor with a heating resistance of 1 Ω is:
y＝-0.0087x+4.42017
the standard operating curve of the liquid helium level sensor with a heating resistance of 5.1 Ω is:
y＝-0.00829x+4.09796
the standard operating curve of the liquid helium level sensor with a heating resistance of 10Ω is:
y＝-0.00692x+3.54234
in the standard working curve, x is the liquid helium level, and y is the output voltage of the liquid helium level sensor.
7. A method of detecting liquid helium level using the liquid helium level sensor of claims 2-6, wherein: comprising the following steps:
1) Vertically inserting a liquid helium level sensor into a container filled with liquid helium, so that the end part of the liquid helium level sensor is in contact with the bottom of the container;
2) Introducing a minimum working current into the liquid helium level sensor, and collecting the output voltage of the liquid helium level sensor;
3) Substituting the output voltage obtained in the step 2) into the standard working curve of the liquid helium level sensor to obtain the liquid level height of the liquid helium in the container.
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