CN114526863B - Ultralow temperature vacuum measurement calibration device and method based on GM refrigerator cooling - Google Patents
Ultralow temperature vacuum measurement calibration device and method based on GM refrigerator cooling Download PDFInfo
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- 238000005259 measurement Methods 0.000 title claims abstract description 48
- 238000001816 cooling Methods 0.000 title claims abstract description 19
- 238000000034 method Methods 0.000 title claims abstract description 12
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 7
- 229910052802 copper Inorganic materials 0.000 claims description 7
- 239000010949 copper Substances 0.000 claims description 7
- 238000005219 brazing Methods 0.000 claims description 6
- 238000012937 correction Methods 0.000 claims description 6
- 230000035945 sensitivity Effects 0.000 claims description 6
- 238000005086 pumping Methods 0.000 claims description 5
- 238000004364 calculation method Methods 0.000 claims description 3
- 238000010438 heat treatment Methods 0.000 claims description 3
- 229910001220 stainless steel Inorganic materials 0.000 claims description 3
- 239000010935 stainless steel Substances 0.000 claims description 3
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- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
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- 239000001307 helium Substances 0.000 description 2
- 229910052734 helium Inorganic materials 0.000 description 2
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 238000009413 insulation Methods 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 230000005855 radiation Effects 0.000 description 2
- 239000010409 thin film Substances 0.000 description 2
- 239000010963 304 stainless steel Substances 0.000 description 1
- 229910000589 SAE 304 stainless steel Inorganic materials 0.000 description 1
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- 230000007646 directional migration Effects 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 230000002706 hydrostatic effect Effects 0.000 description 1
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- 238000000691 measurement method Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L27/00—Testing or calibrating of apparatus for measuring fluid pressure
- G01L27/002—Calibrating, i.e. establishing true relation between transducer output value and value to be measured, zeroing, linearising or span error determination
- G01L27/005—Apparatus for calibrating pressure sensors
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Abstract
The invention discloses an ultralow temperature vacuum measurement calibration device and method based on GM refrigerator cooling, belonging to the technical field of measurement and calibration, wherein the device comprises a measuring end of a three-way connecting piece connected with a standard vacuum gauge, an air exhaust end connected with an air exhaust system, an air inlet end connected with an air supply system and connected with the upper part of a measuring pipe, the middle part of the measuring pipe is contacted with the upper part of a cold screen, and the lower part of the measuring pipe is welded with the upper part of a calibration chamber in the cold screen; the lower part of the cold shield is connected with a primary cold head of the GM refrigerator, the lower part of the calibration chamber is connected with a temperature control block, and the temperature control block is connected with a secondary cold head of the GM refrigerator; a connecting hole is reserved in the middle of the calibration chamber, a through hole is formed in the cold screen, one end of the pressure guide pipe is connected with the connecting hole, and the other end of the pressure guide pipe is connected with a calibrated vacuum gauge arranged outside the vacuum shell through the through hole. After the pressure guiding pipe is calibrated, the calibrated vacuum gauge and the pressure guiding pipe can be used for measuring the vacuum degree in a low-temperature (4K-300K) narrow environment.
Description
Technical Field
The invention relates to the technical field of measurement and calibration, in particular to an ultralow temperature vacuum measurement calibration device and method based on GM refrigerator cooling.
Background
In a low-temperature vacuum environment of 77K-4K, because the low-temperature vacuum is in a property and a state different from the normal temperature, and the isotropic neutral gas pressure intensity adopted at the normal temperature, the concept of the vacuum degree represented by the hydrostatic force, the low-temperature pressure intensity under the high vacuum loses the original physical significance to a certain degree. At normal temperature, theories such as Maxwell velocity distribution, cosine law, mean free path, gas heat conduction equation, gas migration equation and the like established on the basis of the concept of fluid mechanical pressure better accord with objective reality, and at low temperature, as the temperature moves to a cryogenic temperature region, heat transpiration and molecular precipitation effects are formed due to directional migration caused by local cryogenic in a vacuum container, so that the above principles, concepts and laws are deviated in different degrees. Therefore, the measurement at low temperature needs to be calibrated.
Since the surface of a material tends to release gas into a vacuum volume at a certain rate under vacuum, the conventional vacuum measurement method cannot measure the partial vacuum degree under vacuum, especially in a narrow space (such as a multilayer heat insulation or porous material), and the material has low conductance and large surface area, so that the vacuum degree inside the material tends to be much higher than that of a vacuum chamber. In order to measure the partial vacuum in the vacuum chamber, a pressure pipe with a sufficiently small inner diameter can be used, which leads from the part with the lower vacuum in the vacuum chamber to the vacuum-pipe measuring opening. After the inner diameter is reduced, the conductance of the pressure guiding pipe can be greatly reduced, and meanwhile, the air release of the wall surface can influence the measurement, so that a more rigorous requirement is provided for the measurement of the local vacuum degree.
In the related art, the invention patent application with publication number CN102944358A discloses a high and low temperature vacuum calibration device and method, which realizes 1 × 10 by arranging a vacuum gauge on a temperature control plate -4 ～1×10 5 The accurate calibration of different temperature points of the vacuum gauge in the temperature range of-140 ℃ to +100 ℃ in the Pa range. However, it cannot calibrate the situation that the pressure measuring point is in a low-temperature and narrow environment when the vacuum gauge is at normal temperature, and the measurement relation and system cannot meet the calibration of the temperature point lower than-140 ℃ (133K) because the vacuum measurement principle changes at low temperature.
Disclosure of Invention
The invention aims to realize accurate calibration of different temperature points within a temperature range of 4K-300K in a narrow environment.
The invention solves the technical problems through the following technical means:
in one aspect, the present invention provides an ultra-low temperature vacuum measurement calibration apparatus based on GM refrigerator cooling, the apparatus comprising: the device comprises a three-way connecting piece, a standard vacuum gauge, a calibrated vacuum gauge, a fine adjustment valve, a vacuum calibration chamber arranged in a vacuum shell, a temperature control block, a measuring pipe, a cold screen and a GM refrigerator;
the measuring end of the three-way connecting piece is connected with the standard vacuum gauge, the air exhaust end is connected with an air exhaust system through a valve, the air inlet end is connected with an air supply system through a fine adjustment valve and is connected with the upper part of the measuring pipe, the middle part of the measuring pipe is contacted with the upper part of the cold screen, and the lower part of the measuring pipe is welded with the upper part of the vacuum calibration chamber in the cold screen;
the lower part of the cold shield is connected with a primary cold head of the GM refrigerator, the lower part of the vacuum calibration chamber is connected with the temperature control block, and the temperature control block is connected with a secondary cold head of the GM refrigerator;
the vacuum calibration chamber is characterized in that a connecting hole is reserved in the middle of the vacuum calibration chamber, a through hole is formed in the cold shield, one end of the pressure leading pipe is connected with the connecting hole, and the other end of the pressure leading pipe is connected with the vacuum gauge to be calibrated, wherein the vacuum gauge to be calibrated is arranged outside the vacuum shell through the through hole.
In the invention, the vacuum gauge to be calibrated is arranged in a vacuum shell, namely, the vacuum gauge is in a normal temperature state, the pressure guide pipe is led out from the vacuum calibration chamber, penetrates through the cold screen and is connected with the vacuum gauge to be calibrated, the middle part of the measuring pipe is contacted with the upper part of the cold screen, the heat loss of a secondary cold head of the GM refrigerator can be reduced to the greatest extent, the GM refrigerator and a reasonable structural design are adopted, the temperature uniformity of the whole vacuum calibration chamber can be ensured to be maintained to be +/-0.5K while the vacuum calibration chamber is maintained at a lower temperature (4K), the vacuum gauge to be calibrated is in a normal temperature environment, the pressure guide pipe is connected with the vacuum calibration chamber, the measurement environment of a standard vacuum gauge is controlled and the measurement principle of the standard vacuum gauge is updated, and after the calibration of the pressure guide pipe is completed, the vacuum gauge to be calibrated and the pressure guide pipe can be used for measuring the vacuum degree in a low-temperature (4K-300K) narrow environment.
Further, the measuring pipe comprises an upper straight pipe, an upper corrugated pipe, a lower straight pipe and a lower corrugated pipe from top to bottom in sequence, the upper straight pipe is welded with a leading pipe on a flange I of the vacuum shell, the lower straight pipe is in contact with the upper portion of the cold shield, the lower corrugated pipe is welded with the upper portion of the vacuum calibration chamber, and the lower end of the lower corrugated pipe is in non-contact with the lower straight pipe.
Furthermore, the wall pipe thickness of the upper straight pipe and the lower straight pipe is 0.5mm, and the wave ratio of the upper corrugated pipe to the lower corrugated pipe is 1.6.
Furthermore, the vacuum shell adopts a sleeve type structure, the upper part of the vacuum shell is welded with a second flange, the second flange is connected with the first flange, the upper part and the middle part of the vacuum shell are detachably connected, and the middle part and the lower part of the vacuum shell are detachably connected.
Furthermore, the cold shield adopts a left-right two-half structure, and the periphery of the outer wall of the cold shield is provided with a connecting part;
the cold shield is prepared from T2-grade red copper.
Further, the vacuum calibration chamber comprises an upper half part and a lower half part, wherein a concave-convex groove for vacuum brazing is formed in the joint of the upper half part and the lower half part, and the upper half part and the lower half part are vacuum brazed to form a spherical hollow structure.
Furthermore, the pressure guiding pipe is a stainless steel pipe with an inner wall subjected to electropolishing treatment, and the air release rate of the inner wall of the pressure guiding pipe is less than 1/100 of the flow conductance of the pressure guiding pipe.
Further, the vacuum gauge to be calibrated is a thin film capacitance vacuum gauge.
Further, the one-level cold head of the GM refrigerator provides the cold energy of 70W @100K, and the two-level cold head provides the cold energy of 1.5W @ 4K.
Furthermore, the periphery of the cold shield and the periphery of the vacuum calibration chamber are both wrapped with vacuum multilayer heat-insulating materials, and the temperature control block is a red copper block wound with heating resistance wires.
In another aspect, the present invention provides a GM refrigerator cooling-based ultra-low temperature vacuum measurement calibration method for performing calibration using the GM refrigerator cooling-based ultra-low temperature vacuum measurement calibration apparatus as described above, the calibration method comprising:
opening the standard vacuum gauge and the measuring tube to stabilize the standard vacuum gauge;
starting the air extraction system, opening the valve, extracting air from the vacuum calibration chamber and the measuring tube to ensure that the vacuum degree displayed by the reading of the standard vacuum gauge is less than 1 multiplied by 10 -6 A limiting vacuum degree of Pa;
starting the GM refrigerator and the temperature control block to enable the temperature in the vacuum calibration chamber to reach the required calibration temperature and the temperature is balanced, opening the fine adjustment valve, and introducing the calibration gas in the gas supply system into the vacuum calibration chamber;
when the gas pressure in the vacuum calibration chamber reaches the balance and the reading of the calibration vacuum gauge reaches the required calibration pressure, the fine adjustment valve is closed, and the pressure reading p of the standard vacuum gauge is respectively recorded 1 And a pressure reading p of said calibrated gauge 2 ；
Calculating a standard pressure p of the vacuum calibration chamber t ：
Wherein,
as a temperature correction factor, T 0 Measuring the temperature, T, of the gauge tube for the vacuum in said standard vacuum gauge t Represents the lowest measured temperature of the calibration chamber,
for sensitivity correction factor under low temperature conditions, K i I =1,2, is the sensitivity of a certain gas.N, alpha are the sum of residual gas partial pressure ion flows with different coefficients, I e Is a stream of electrons;
according to the standard pressure p t And a pressure reading p of said calibrated gauge 2 And calculating a calibration factor c:
and measuring a plurality of vacuum degree values of each order of magnitude of vacuum degree, and taking an average value of calibration factors obtained by each measurement calculation as a final calibration factor to calibrate the pressure leading pipe.
The invention has the advantages that:
(1) The invention is characterized in that a calibrated vacuum gauge is arranged in a vacuum shell, namely, the calibrated vacuum gauge is in a normal temperature state, a pressure guide pipe is led out from a vacuum calibration chamber, the pressure guide pipe penetrates through a cold screen and is connected with the calibrated vacuum gauge, the middle part of a measuring pipe is contacted with the upper part of the cold screen, the heat loss of a secondary cold head of a GM refrigerator can be reduced to the maximum extent, the GM refrigerator and a reasonable structural design are adopted, the temperature uniformity of the whole vacuum calibration chamber can be kept within +/-0.5K while the vacuum calibration chamber is kept at a lower temperature (4K), the calibrated vacuum gauge is in a normal temperature environment, the pressure guide pipe is connected with the vacuum calibration chamber, and the calibrated vacuum gauge and the pressure guide pipe can be used for vacuum degree measurement in a low-temperature (4K-300K) narrow environment by controlling the measurement environment of a standard vacuum gauge and updating the measurement principle of the standard vacuum gauge after the calibration of the pressure guide pipe is completed.
(2) By arranging the measuring tube, an upper straight tube of the measuring tube is welded with a leading tube on a flange I of the vacuum shell, a lower straight tube is contacted with the upper part of the cold shield, and a lower corrugated tube is welded with the upper part of the vacuum calibration chamber, so that the temperatures of the lower straight tube and the cold shield can be almost equal, and the heat loss of a secondary cold head of the GM refrigerator is reduced to the maximum extent; meanwhile, the integral temperature of the lower straight pipe can be guaranteed to be larger than 100K, helium and hydrogen can not be condensed by a wall surface at low temperature, and the fact that the vacuum degree of a calibration chamber is measured by a standard vacuum gauge at low temperature can be further guaranteed.
(3) Because the refrigerating capacity of the GM refrigerator is limited, and the volume of the vacuum calibration chamber needs to be more than or equal to 20 times of the total volume of the measuring pipeline, the upper straight pipe of the measuring pipe is welded with the leading pipe on the flange I of the vacuum shell, the upper part of the vacuum shell is welded with the flange II, and the flange II is fixedly connected with the flange I.
(4) The cold screen adopts a structure of left and right halves, and the structure can still install the cold screen after the vacuum calibration chamber and the measuring tube inside the cold screen are installed.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
FIG. 1 is a block diagram of a GM refrigerator cooling based ultra-low temperature vacuum measurement calibration apparatus in a first embodiment of the present invention;
FIG. 2 is a cross-sectional view of a GM refrigerator cooled ultra-low temperature vacuum measurement calibration apparatus in a first embodiment of the present invention;
FIG. 3 is a structural view of a measurement pipe in a first embodiment of the invention;
FIG. 4 is a structural view of a vacuum housing in a first embodiment of the invention;
FIG. 5 is a cross-sectional view of a vacuum enclosure in a first embodiment of the invention;
FIG. 6 is a graph showing simulation results of the ultra-low temperature vacuum measurement calibration apparatus based on GM refrigerator cooling according to the present invention
FIG. 7 is a flow chart of a GM refrigerator cooling based ultra-low temperature vacuum measurement calibration method in a second embodiment of the present invention.
In the figure:
1-a three-way connection; 2-standard vacuum gauge; 3-a fine adjustment valve; 4-measuring tube; 5-a vacuum calibration chamber; 6-a pressure guiding pipe; 7-temperature control block; an 8-GM refrigerator; 9-cold shielding; 10-vacuum gauge calibrated; 11-a valve; 12-an air extraction system; 13-a vacuum housing;
41-straight pipe feeding; 42-upper bellows; 43-lower straight pipe; 44-lower bellows; 31-flange two; 32-flange one; 33-a first fixed part; 34-a second fixed part; 35-a third fixed part; 36-a fourth fixation section; 37-lead tube structure; 38-vacuum housing upper part; 39-vacuum housing middle; 40-vacuum housing lower part.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1 to 2, an embodiment of the present invention proposes an ultra-low temperature vacuum measurement calibration apparatus based on GM refrigerator cooling, the apparatus including: the device comprises a three-way connector 1, a standard vacuum gauge 2, a calibrated vacuum gauge 10, a micro-regulating valve 3, a vacuum calibration chamber 5 arranged in a vacuum shell 13, a temperature control block 7, a cold screen 9, a measuring pipe 4 and a GM refrigerator 8;
the measuring end of the three-way connecting piece 1 is connected with the standard vacuum gauge 2, the air exhaust end is connected with an air exhaust system 12 through a valve 11, the air inlet end is connected with an air supply system through a fine adjustment valve 3 and is connected with the upper part of the measuring pipe 4, the middle part of the measuring pipe 4 is contacted with the upper part of the cold screen 9, and the lower part of the measuring pipe is welded with the upper part of the vacuum calibration chamber 5 in the cold screen 9;
the lower part of the cold shield 9 is connected with a primary cold head of the GM refrigerator 8, the lower part of the vacuum calibration chamber 5 is connected with the temperature control block 7, and the temperature control block 7 is connected with a secondary cold head of the GM refrigerator 8;
a connecting hole is reserved in the middle of the vacuum calibration chamber 5, a through hole is formed in the cold screen 9, one end of the pressure guide pipe 6 is connected with the connecting hole, and the other end of the pressure guide pipe is connected with the vacuum gauge 10 to be calibrated, which is arranged outside the vacuum shell 13, through the through hole.
In this embodiment, survey the middle part of buret 4 and the upper portion contact of cold screen 9, but the calorific loss of 8 second grade coldheads of GM refrigerator of furthest reduction, through adopting GM refrigerator 8 and reasonable structural design, can be with vacuum calibration room 5 when keeping lower temperature (4K), guarantee that the holistic temperature uniformity of vacuum calibration room 5 maintains at 0.5K, and by school vaccum meter 10 be in normal atmospheric temperature environment, be connected with vacuum calibration room 5 through pressure tube 6, through the measuring environment of control standard vacuometer 2 and update its measurement principle, after pressure tube 6 calibrates the completion, by school vaccum meter 10 and pressure tube 6 can be used to the vacuum measurement under the low temperature (4K ~ 300K) narrow environment.
Further, the vacuum gauge to be calibrated is a thin film capacitance vacuum gauge.
The calibrated vacuum gauge is a vacuum gauge which can not be pumped, and the relationship between the measured value and the gas type is very small, so that the calibrated vacuum gauge can be regarded as an absolute vacuum gauge.
In one embodiment, as shown in fig. 3, the measuring tube 4 comprises, from top to bottom, an upper straight tube 41, an upper bellows 42, a lower straight tube 43, and a lower bellows 44, the upper straight tube 41 is welded to the flange one 32 of the vacuum housing 13, the middle of the lower straight tube 43 contacts the upper portion of the cold shield 9, the upper end of the lower bellows 44 is welded to the upper portion of the vacuum calibration chamber 5, and the lower end of the lower bellows 44 does not contact the lower straight tube 43.
In this embodiment, the middle of the lower straight tube 43 contacts the upper part of the cold shield 9, so that the temperature of the middle of the lower straight tube 43 is almost equal to that of the cold shield 9, the temperature of the lower straight tube 43 can be maintained near 110K, and the heat loss of the secondary cold head of the GM refrigerator 8 is reduced to the maximum extent; the integral temperature of the lower straight pipe 43 can be guaranteed to be larger than 100K, so that helium and hydrogen cannot be condensed on the wall surface of the measuring pipe 4 at low temperature, and the accuracy of the vacuum degree of the vacuum calibration chamber 5 measured by the standard vacuum gauge 2 at low temperature can be further guaranteed.
In an embodiment, the wall tube thickness of each of the upper straight tube 41 and the lower straight tube 43 is 0.5mm, and the wave ratio of the upper corrugated tube 42 to the lower corrugated tube 44 is 1.6, which can make the temperature of the middle part of the lower straight tube 43 close to that of the cold screen 9, thereby reducing the cold loss of the cold screen 9 to the maximum extent.
In this embodiment, the upper straight tube 41 and the lower straight tube 43 are thin-walled tubes, which can reduce heat conduction.
In one embodiment, as shown in fig. 4 to 5, the vacuum housing 13 is of a sleeve type structure, the upper portion of the vacuum housing 13 is welded to the second flange 31, the second flange 31 is connected to the first flange 32, the upper portion and the middle portion of the vacuum housing 13 are detachably connected, and the middle portion and the lower portion of the vacuum housing 13 are detachably connected.
The vacuum shell 13 is of a sleeve type structure and is divided into an upper part, a middle part and a lower part, the upper part 38 of the vacuum shell is welded with the second flange 31, the second flange 31 is connected with the first flange 32 through screws, the first flange 32 is welded with the measuring pipe 4 through a pipe guiding structure 37, the upper part 38 of the vacuum shell is convexly provided with a first fixing part 33, the middle part 39 of the vacuum shell is convexly provided with a second fixing part 34 and a third fixing part 35, the lower part 40 of the vacuum shell is convexly provided with a fourth fixing part 36, the upper part and the middle part are connected in a matched mode through the first fixing part 33 and the second fixing part 34, and the middle part and the lower part are connected in a matched mode through the third fixing part 35 and the fourth fixing part 36.
Specifically, the upper part and the middle part are connected through a caliper screw, the middle part and the lower part are connected through a screw, the middle part is disassembled from the screw and then can be placed to the bottom, and the internal structure of the vacuum shell 13 is conveniently disassembled.
It should be noted that, because the cooling capacity of the GM refrigerator 8 is limited, and the volume of the vacuum calibration chamber 5 needs to be greater than or equal to 20 times of the total volume of the measuring pipe 4, the upper straight pipe 41 of the measuring pipe 4 is welded to the lead pipe on the flange one 32 of the vacuum housing 13, the upper portion of the vacuum housing 13 is welded to the flange two 31, and the flange two 31 is fixedly connected to the flange one 32, if the measuring pipe 4 is placed at the flange at the bottom of the vacuum calibration chamber 5, the problems of large volume of the calibration chamber, insufficient cooling capacity of the refrigerator, and the like occur, and therefore, the vacuum housing is designed into a complete cylinder structure.
In one embodiment, the cold shield 9 is in a left-right two-half structure, and a connecting part is arranged around the outer wall of the cold shield 9;
the cold shield 9 is made of T2-grade red copper.
It should be noted that the connecting parts arranged around the cold shield 9 can be lugs for fastening bolts, the structure can ensure that the cold shield 9 can still be installed after the calibration chamber inside the cold shield 9 and the measuring tube 4 are installed, the fastening lugs can ensure that the gap between the two halves of the cold shield 9 is as small as possible, thereby reducing radiation heat leakage, and after the cold shield 9 is installed, the top of the cold shield 9 is contacted with the lower straight tube 43 of the measuring tube 4; the cold shield 9 has two functions, namely, the temperature of the lower straight pipe 43 can be maintained near 110K, the normal working temperature of the lower straight pipe is ensured, and the heat radiation protection is provided for the calibration chamber 5 arranged inside and the secondary cold head and the temperature control block 7 of the GM refrigerator 8, so that the heat leakage of internal components of the cold shield is greatly reduced.
In one embodiment, the vacuum calibration chamber 5 comprises an upper half and a lower half, wherein a concave-convex groove for vacuum brazing is arranged at the joint of the upper half and the lower half, the upper half and the lower half are in a spherical hollow structure through vacuum brazing, the spherical structure is an ideal structure of the vacuum calibration chamber, the calibration error of the structure is minimal, and in addition, in order to improve the smoothness of the inner wall of the calibration chamber 5, optimize the ultimate vacuum degree of the calibration chamber 5 and prevent the high-temperature oxidation of the copper calibration chamber, the connection of the upper half and the lower half is in a vacuum brazing mode.
In this embodiment, the concave-convex groove of looks adaptation is set up in the junction of the first half and the lower half of vacuum calibration room 5, can make things convenient for vacuum brazing, and first half is connected with surveying buret 4, and the lower half passes through bolted connection with temperature control block 7, and vacuum calibration room 5 middle part is provided with the connecting hole, supplies to draw pressure pipe 6 to draw the vacuum that awaits measuring from vacuum calibration room 5. After the pressure guiding pipe 6 is led out from the vacuum calibration chamber 5, the outer wall of the pressure guiding pipe contacts with a through hole formed in the cold screen 9, and the heat led in from the pressure guiding pipe 6 can be reduced.
In one embodiment, the pressure guiding tube 6 is a stainless steel tube with an electropolished inner wall, and the conductance of the pressure guiding tube 6 is at least 100 times the pumping speed of the gauge of the vacuum gauge 10.
In the embodiment, the pressure guiding pipe 6 is a 304 stainless steel pipe with the inner diameter of 3mm, the inner wall of the pressure guiding pipe is electropolished to reduce the air discharge rate, and the air discharge rate passes through the vacuum calibration chamber 5 and the cold screen 9 and is finally connected to the vacuum gauge 10 to be calibrated; and the conductance of the pressure guiding pipe 6 is required to be at least 100 times of the pumping speed of the gauge of the vacuum gauge 10 to avoid the influence of the pumping effect of the vacuum gauge on the measurement result.
In an embodiment, the one-stage cold head of the GM refrigerator 8 provides cold energy of 70w @100k, the two-stage cold head provides cold energy of 1.5w @4k, and this specification can ensure that the temperature difference between any point in the calibration chamber 5 is less than 1K.
In one embodiment, the periphery of the cold shield 9 and the periphery of the vacuum calibration chamber 5 are wrapped with vacuum multi-layer insulation to minimize the thermal load on the primary and secondary coldheads of the refrigeration system.
In one embodiment, the temperature control block 7 is a red copper block wrapped with a heating resistance wire.
In one embodiment, the valve 11 is an ultra-high vacuum all-metal flapper valve, and the trim valve 3 is an ultra-high vacuum all-metal trim valve 3, which can improve the ultimate vacuum of the calibration system.
In one embodiment, the standard vacuum gauge 2 is an ionization gauge having a large range.
The simulation result of the ultralow temperature vacuum measurement calibration device in the embodiment is shown in fig. 6, and it can be seen from the simulation diagram that the bottom temperature of the quasi chamber is 4.38K, and the top temperature is 4.60K, so that the requirement that the temperature uniformity is less than 1K is met; the temperature of a straight pipe below the measuring pipe is 103.51K, and the requirement that the temperature is more than 100K is met.
In addition, as shown in fig. 7, an embodiment of the present invention further provides a GM refrigerator cooling-based ultra-low temperature vacuum measurement calibration method for performing calibration using the GM refrigerator cooling-based ultra-low temperature vacuum measurement calibration apparatus according to the above embodiment, where the calibration method includes the following steps:
s10, opening the standard vacuum gauge and the measuring tube, and enabling the standard vacuum gauge to be stable for 24 hours;
s20, starting the air extraction system, opening the valve, and extracting air from the vacuum calibration chamber and the measuring tube so that the vacuum degree displayed by the reading of the standard vacuum gauge is less than 1 x 10 -6 A limiting vacuum degree of Pa;
s30, starting the GM refrigerator and the temperature control block to enable the temperature in the vacuum calibration chamber to reach the required calibration temperature and balance the temperature, opening the fine adjustment valve, and introducing the calibration gas in the gas supply system into the vacuum calibration chamber;
s40, when the gas pressure in the vacuum calibration chamber reaches balance and the reading of the calibration vacuum gauge reaches the required calibration pressure, closing the fine adjustment valve and respectively recording the pressure reading p of the standard vacuum gauge 1 And a pressure reading p of said calibrated gauge 2 ；
S50, calculating the standard pressure p of the vacuum calibration chamber t ：
Wherein,
as a temperature correction factor, T 0 The temperature of the vacuum measuring gauge pipe in the standard vacuum gauge is measured in K, the general value is 420K t Represents the lowest measured temperature of the calibration chamber, in K,
for sensitivity correction factors under low temperature conditions, K i For the sensitivity of a certain gas, i =1, 2.. N (when a certain degree of temperature is reached, condensation of a certain gas occurs, expressed as (K) on the denominator 1 K 2 …K n ) And (4) alpha is the sum of residual gas partial pressure ion flows with different coefficients (the variable coefficient partial pressure ion flows are subject to the superposition principle). Thus alpha, also called the mixed ion current of the residual gas, is measured directly by the ion current amplifier), I) e Is a stream of electrons;
according to the standard pressure p t And a pressure reading p of said calibrated gauge 2 And calculating a calibration factor c:
wherein c is dimensionless, p 2 Measured values for the vacuum gauge to be calibrated, in units: pa, the standard pressure is related to the temperature measurement range of the vacuum gauge to be calibrated, and the temperature range is 4K-300K;
and S60, taking a plurality of vacuum degree values for each order of magnitude of vacuum degree to measure, and taking an average value of calibration factors obtained by each measurement calculation as a final calibration factor to calibrate the pressure guiding pipe.
In this embodiment, by using the measurement device in the above embodiment, after the calibration of the pressure guiding tube is completed, the calibrated vacuum gauge and the pressure guiding tube can be used for vacuum measurement in a low-temperature (4K-300K) narrow environment by controlling the measurement environment of the standard vacuum gauge and updating the measurement principle thereof, and the calibration accuracy of the pressure guiding tube is ensured by obtaining an average value through multiple measurements.
In the description of the specification, reference to the description of "one embodiment," "some embodiments," "an example," "a specific example," or "some examples" or the like means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (9)
1. An ultra-low temperature vacuum measurement calibration apparatus based on GM refrigerator cooling, the apparatus comprising: the device comprises a three-way connecting piece, a standard vacuum gauge, a calibrated vacuum gauge, a fine adjustment valve, a vacuum calibration chamber arranged in a vacuum shell, a temperature control block, a measuring pipe, a cold screen, a GM refrigerator and a pressure guiding pipe;
the measuring end of the three-way connecting piece is connected with the standard vacuum gauge, the air exhaust end is connected with an air exhaust system through a valve, the air inlet end is connected with an air supply system through a fine adjustment valve and is connected with the upper part of the measuring pipe, the middle part of the measuring pipe is contacted with the upper part of the cold screen, and the lower part of the measuring pipe is welded with the upper part of the vacuum calibration chamber in the cold screen;
the lower part of the cold shield is connected with a primary cold head of the GM refrigerator, the lower part of the vacuum calibration chamber is connected with the temperature control block, and the temperature control block is connected with a secondary cold head of the GM refrigerator;
a connecting hole is reserved in the middle of the vacuum calibration chamber, a through hole is formed in the cold screen, one end of the pressure guide pipe is connected with the connecting hole, and the other end of the pressure guide pipe is connected with the vacuum gauge to be calibrated arranged outside the vacuum shell through the through hole;
the measuring pipe sequentially comprises an upper straight pipe, an upper corrugated pipe, a lower straight pipe and a lower corrugated pipe from top to bottom, the upper straight pipe is welded with a leading pipe on a flange I of the vacuum shell, the lower straight pipe is in contact with the upper portion of the cold shield, the lower corrugated pipe is welded with the upper portion of the vacuum calibration chamber, and the lower end of the lower corrugated pipe is in non-contact with the lower straight pipe.
2. The GM refrigerator cooled ultra-low temperature vacuum measurement calibration apparatus of claim 1, wherein the wall tube thickness of both the upper straight tube and the lower straight tube is 0.5mm, and the wave ratio of the upper bellows and the lower bellows is 1.6.
3. The ultra-low temperature vacuum measurement calibration apparatus based on cooling of GM refrigerator of claim 1, wherein the vacuum enclosure is of a telescopic structure, the upper part of the vacuum enclosure is welded to a second flange, the second flange is connected to the first flange, the upper part and the middle part of the vacuum enclosure are detachably connected, and the middle part and the lower part of the vacuum enclosure are detachably connected.
4. The ultra-low temperature vacuum measurement calibration device based on GM refrigerator cooling of claim 1, wherein the cold shield is in a structure of left and right halves, and the outer wall of the cold shield is arranged with a connection part around;
the cold shield is prepared from T2-grade red copper.
5. The GM refrigerator cooled ultra-low temperature vacuum gauge calibration apparatus of claim 1, wherein the vacuum calibration chamber comprises an upper half and a lower half, wherein a joint of the upper half and the lower half is provided with a relief groove for vacuum brazing, and the upper half and the lower half are vacuum brazed to form a spherical hollow structure.
6. The ultra-low temperature vacuum measurement calibration device based on GM refrigerator cooling of claim 1, wherein the pressure guiding tube is a stainless steel tube with an electropolished inner wall, and the inner wall of the pressure guiding tube has a outgassing rate less than 1/100 of its conductance.
7. A GM refrigerator cooled ultra-low temperature vacuum measurement calibration apparatus as claimed in any one of claims 1-6, where the GM refrigerator's primary cold head provides 70W @100K cold and secondary cold head provides 1.5W @4K cold.
8. The GM refrigerator cooled ultra-low temperature vacuum measurement calibration apparatus according to any one of claims 1-6, wherein the periphery of the cold shield and the periphery of the vacuum calibration chamber are both wrapped with vacuum multilayer insulation material, and the temperature control block is a red copper block wrapped with heating resistance wires.
9. A GM refrigerator cooled ultra-low temperature vacuum measurement calibration method for calibration using the GM refrigerator cooled ultra-low temperature vacuum measurement calibration apparatus of any one of claims 1-8, the calibration method comprising:
opening the standard vacuum gauge and the measuring tube to stabilize the standard vacuum gauge;
starting the air pumping system, opening the valve, and pumping the vacuum calibration chamber and the measuring tube so as to enable the vacuum degree displayed by the reading of the standard vacuum gauge to be less than 1 multiplied by 10 -6 A limiting vacuum degree of Pa;
starting the GM refrigerator and the temperature control block to enable the temperature in the vacuum calibration chamber to reach the required calibration temperature and the temperature to be balanced, opening the fine adjustment valve, and introducing the calibration gas in the gas supply system into the vacuum calibration chamber;
when the gas pressure in the vacuum calibration chamber reaches the balance and the reading of the standard vacuum gauge reaches the required calibration pressure, closing the fine adjustment valve and respectively recording the pressure reading p of the standard vacuum gauge 1 And a pressure reading p of said calibrated gauge 2 ；
Calculating a standard pressure p of the vacuum calibration chamber t ：
Wherein,
as a temperature correction factor, T 0 Measuring the temperature, T, of the gauge tube for the vacuum in said standard vacuum gauge t Represents the lowest measured temperature of the calibration chamber,
for sensitivity correction factor under low temperature conditions, K i I =1, 2.. For the sensitivity of a certain gas, n, α is the sum of partial pressure ion flows of the remaining gas with different coefficients, I e Is a stream of electrons;
according to said standard pressure p t And a pressure reading p of said calibrated gauge 2 And calculating a calibration factor c:
and measuring a plurality of vacuum degree values of each order of magnitude of vacuum degree, and taking an average value of calibration factors obtained by each measurement calculation as a final calibration factor to calibrate the pressure leading pipe.
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