CN107121708B - Absolute gravity measurement system and measurement method - Google Patents
Absolute gravity measurement system and measurement method Download PDFInfo
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- CN107121708B CN107121708B CN201710388867.2A CN201710388867A CN107121708B CN 107121708 B CN107121708 B CN 107121708B CN 201710388867 A CN201710388867 A CN 201710388867A CN 107121708 B CN107121708 B CN 107121708B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V7/00—Measuring gravitational fields or waves; Gravimetric prospecting or detecting
- G01V7/14—Measuring gravitational fields or waves; Gravimetric prospecting or detecting using free-fall time
Abstract
The invention provides an absolute gravity measurement system and a measurement method, wherein the absolute gravity measurement comprises the following steps: free falling device, laser interferometry device and vibration isolation platform. The free falling device comprises a shell, a vacuum bin arranged in the shell and a power device in transmission connection with the vacuum bin. The power device is used for controlling the vacuum bin to move in the vertical direction. The falling body is arranged in the vacuum bin. The bottom of the vacuum bin is provided with a vacuum bin observation window for observing the free falling body movement of the falling body. The absolute gravity measurement system further includes a vacuum bin displacement measurement device disposed within the housing. The vacuum bin displacement measuring device comprises a grating ruler arranged in the shell and a reading head fixedly arranged on the vacuum bin shell. The absolute gravity measurement system further comprises an air refractive index measurement device for measuring the air refractive index inside the housing.
Description
Technical Field
The invention relates to the technical field of precise instruments, in particular to an absolute gravity measurement system and a measurement method.
Background
The absolute gravimeter is an instrument for calculating the absolute value of gravitational acceleration by measuring the response of a sensitive element to a gravitational field, and plays an important role in measuring, mapping, earthquake, geophysical, resource exploration, auxiliary navigation and other fields. Absolute gravimeters can be divided into two categories depending on the linearity of the sensing element: the classical free falling absolute gravimeter uses laser wavelength as length measurement reference standard, atomic clock frequency as time measurement reference standard, angle reflecting prism as sensitive element, mach-Zehnder laser interferometer to measure free falling motion displacement of angle reflecting prism in vacuum. Every time the falling prism moves by a distance of one half of the laser wavelength, the light intensity detected by the photodetector changes by one whole period. The photoelectric detector converts the optical signal into an electric signal with the mean value of zero, the falling body movement track can be reversely deduced by measuring the zero crossing time of the electric signal, and the gravity acceleration value is obtained by fitting. The other is atomic interferometry absolute gravimeter, which uses atomic energy fraction probability response to gravitational fields to measure gravitational acceleration values.
Because of the late maturation and high complexity of atomic interferometry, absolute gravimeters in wide use today are still classical free-fall absolute gravimeters. Micro-g LaCoste developed FG-5 type absolute gravimeter based on the early JILA type absolute gravimeter. The gravity meter adopts a drag-free falling cavity technology, so that the influence of residual air is effectively reduced, and a reference prism in the laser interferometer is placed in a Super Spring to form a vibration isolation system, so that the influence of ground micro-vibration on a measurement result is reduced. In addition, the vibration isolation system of the gravity meter is arranged in line with the vacuum falling cavity, so that Abbe's principle is met, and measurement accuracy and reliability can be improved. The FG-5X absolute gravimeter developed on the basis is provided with a compensation mass block, so that the influence of ground bounce effect on a measurement result can be reduced. The uncertainty of these two instruments can be up to 2 muGal. In addition, IMGC-02 type absolute gravimeter developed by Italian national institute of metering (INRIM) adopts a drop-on-drop movement mode, and the uncertainty can reach 9 MuGal. NIM series absolute gravimeter was developed by the national institute of metrology, which was involved in international absolute gravimeter comparison many times, with uncertainty better than 10 μgal. The subject group independently develops a T-1 type high-precision absolute gravimeter in 2011. The gravity meter also adopts a classical free falling body structure, realizes falling body release by using an elastic pull-down mode, and collects output signals of the miniaturized laser interferometer by using a high-speed signal acquisition system, wherein the uncertainty can reach the mu Gal level. In order to improve the maneuverability of the instrument, micro-g corporation also developed an A-10 portable absolute gravimeter. The gravity meter simplifies the whole structure of the system by reducing the vacuum cavity and vibration isolation system, simplifying the laser interferometer, selecting a small ion pump to replace the original ion pump, and the like, and can be quickly disassembled and assembled, thereby being convenient for moving between measuring sites. The accuracy of the A-10 type portable absolute gravimeter can reach 10 MuGal.
In all absolute gravimeters described above, the falling process of the falling body takes place entirely in a vacuum chamber of relatively large volume, and generally with an ion pump to maintain the vacuum in the chamber, to reduce disturbances to the falling body movement, such as air damping, air buoyancy, etc. The absolute gravimeters can realize high-precision measurement in laboratory environments, but the absolute gravimeters are complex and heavy in system and are not suitable for field measurement in severe environments.
For this reason, it is necessary to design an absolute gravimeter that is lighter, simpler, more flexible and more reliable. Although the above-mentioned a-10 type portable absolute gravimeter is smaller than other gravimeters, the conventional structure is still used, the volume reduction is limited, and an ion pump is still needed to maintain vacuum during transportation, and if an emergency such as system outage is encountered, there is a risk of vacuum leakage.
Disclosure of Invention
Based on the above, it is necessary to provide an absolute gravity measurement system and a measurement method which are light, simple, have higher mobility and reliability, and are suitable for field measurement under severe environments.
An absolute gravity measurement system, comprising:
the free falling body device is used for realizing free falling body movement of falling bodies;
the laser interferometry device is used for tracking the falling body to perform free falling body movement so as to acquire a laser interference fringe signal;
the vibration isolation platform is arranged between the free falling body device and the laser interferometry device and is used for isolating the influence of ground vibration on measurement, wherein:
the free falling body device comprises a shell, a vacuum bin arranged in the shell and a power device in transmission connection with the vacuum bin, wherein the power device is used for controlling the motion of the vacuum bin in the vertical direction, the falling body is arranged in the vacuum bin, and a vacuum bin observation window is arranged at the bottom of the vacuum bin and used for observing the free falling body motion of the falling body;
the absolute gravity measurement system further comprises a vacuum bin displacement measurement device arranged in the shell, wherein the vacuum bin displacement measurement device comprises a grating ruler arranged in the shell and a reading head fixedly arranged in the shell of the vacuum bin;
the absolute gravity measurement system further comprises an air refractive index measurement device for measuring the air refractive index inside the housing.
In one embodiment, the free-falling body device comprises a support frame arranged inside the shell, wherein the support frame comprises a straight guide rail arranged vertically;
the vacuum bin is slidably arranged on the linear guide rail and driven by the power device to move along the linear guide rail;
the grating ruler is arranged on the supporting frame and is arranged in parallel with the linear guide rail at intervals, so that the grating ruler and the reading head are arranged oppositely.
In one embodiment, a supporting structure is fixedly arranged on the inner wall of the vacuum bin and used for supporting the falling body.
In one embodiment, the vacuum chamber is a welding seal, and the vacuum degree in the vacuum chamber is 10 -6 Pa to 10 -4 Pa。
In one embodiment, an air absorbent is disposed within the vacuum chamber.
In one embodiment, a first reflecting prism is arranged in the falling body and is used for reflecting the measuring laser emitted by the laser interferometry device;
the second reflecting prism is arranged in the vibration isolation platform and used for reflecting the measuring laser reflected by the first reflecting prism.
In one embodiment, the laser interferometry device comprises:
the first light splitting element is used for splitting the collimated laser into the test laser and the reference laser which are perpendicular to each other, and the test laser is transmitted to the first reflecting prism and is reflected to the second reflecting prism through the first reflecting prism;
a second beam splitter for combining the reference laser light passing through the second beam splitter and the test laser light reflected to the second beam splitter via the second reflecting prism;
a photodetector for converting interference fringes formed by the measurement laser light and the reference laser light synthesized via the second spectroscope into an analog signal.
In one embodiment, the air refractive index measuring device includes a sensor disposed inside the housing for sensing temperature, air pressure and humidity inside the housing.
In one embodiment, the absolute gravity measurement system further comprises:
the digital signal processor is electrically connected with the power device and the sensor and is used for controlling the power device and collecting the temperature, the air pressure and the humidity inside the shell through the sensor;
the computer is connected with the digital signal processor and is used for sending an instruction to the power device through the digital signal processor so as to control the power device, and calculating the refractive index of air in the shell according to the temperature, the air pressure and the humidity in the shell, which are transmitted back by the digital signal processor;
the computer acquires laser interference fringe signals sent by the laser interference device and vacuum bin displacement signals sent by the vacuum bin displacement measuring device through the data acquisition card; and
and the atomic clock is connected with the data acquisition card and provides a standard clock reference signal for the data acquisition card.
An absolute gravity measurement method employing the absolute gravity measurement system of any of the embodiments above, comprising:
the vacuum bin is controlled by the power device to vertically move downwards from the top of the shell, so that the falling body can freely fall;
tracking the falling body through the laser interferometry device to perform free falling movement so as to acquire a laser interference fringe signal;
measuring a vacuum bin displacement signal when the vacuum bin falls through the vacuum bin displacement measuring device;
measuring the air refractive index inside the shell by the air refractive index measuring device; and
and calculating absolute gravity acceleration according to the laser interference fringe signal, the vacuum bin displacement signal and the air refractive index.
The absolute gravity measurement system can be separated from the operation of the ion pump, so that the absolute gravity measurement system is simplified, and the convenience and reliability of the field operation of the absolute gravity measurement are improved. In addition, the technical scheme of the application also comprises a vacuum bin displacement measuring device and an air refractive index measuring device, so that the absolute gravity measuring method can be corrected by measuring vacuum bin displacement information by the vacuum bin displacement measuring device and measuring the air refractive index inside the shell by the air refractive index measuring device, and a more accurate measuring result can be obtained. Therefore, the absolute gravity measurement system has the advantages of portability, simplicity, higher maneuverability and reliability and suitability for field measurement in severe environments.
Drawings
FIG. 1 is a schematic diagram of an absolute gravity measurement system according to one embodiment of the present invention;
FIG. 2 is a front view of the internal structure of a free fall device of an absolute gravimetric measurement system in one embodiment of the invention;
FIG. 3 is a side view of the internal structure of the free-fall device of FIG. 2;
FIG. 4 is a schematic diagram of the internal structure of a vacuum chamber of an absolute gravimetric measurement system in one embodiment of the invention;
FIG. 5 is a schematic view of the optical path structure of a laser interferometry device of an absolute gravity measurement system according to an embodiment of the present invention;
FIG. 6 is a block diagram of an absolute gravity measurement system in one embodiment of the invention;
FIG. 7 is a schematic diagram of the free fall motion profile measurement of an absolute gravimetric measurement system in one embodiment of the invention.
Description of the main reference signs
Absolute gravity measurement system 100
Free-fall device 10
Top flange 11
Housing 12
Main cavity 13
Bottom viewing window 14
Bottom flange 15
Vibration isolation platform 20
Laser interferometry device 30
Collimation laser 31
Reflective element 32
First spectroscopic element 33
Second spectroscopic element 34
Lens 35
Photodetector 36
Digital signal processor 40
Computer 50
Data acquisition card 60
Atomic clock 70
Vacuum chamber 110
Copper pipe 111
Drop body 112
Vacuum chamber top plate 113
First reflecting prism 114
Vacuum slave bin floor 115
Support structure 116
Vacuum chamber observation window 117
Vacuum chamber side wall 119
Vacuum chamber displacement measuring device 120
Grating ruler 122
Reading head 124
Mounting base 126
Air refractive index measuring device 130
Power plant 140
Control motor 142
Flexible coupling 143
Synchronous belt 144
Travel switch 145
First synchronous pulley 146
Second synchronous pulley 148
Support frame 150
Frame top plate 151
Guide rail bracket 152
Linear guide 154
Slider 155
Vacuum cartridge connector 156
Frame base 157
Second reflecting prism 214
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Referring to fig. 1, an embodiment of the present invention provides an absolute gravity measurement system 100 for measuring absolute gravity values at different locations of the earth. The absolute gravity measurement system 100 includes a free fall device 10, a vibration isolation platform 20, a laser interferometry device 30, a vacuum bin displacement measurement device 120, and an air refractive index measurement device 130.
The free-falling device 10 is disposed on the vibration isolation platform 20, and is used for realizing free-falling motion of the falling body 112. The free-falling body device 10 comprises a shell 12, a vacuum bin 110 arranged in the shell 12, and a power device 140 in transmission connection with the vacuum bin 110. The drop body 112 is disposed within the vacuum chamber 110. The power device 140 may control the vacuum chamber 110 to move in the direction of gravity, thereby allowing the falling body 112 to perform free-falling movement. The interior of the housing 12 is at atmospheric pressure. It will be appreciated that the bottom of the housing 12 also has a bottom viewing window 14 that allows laser light to enter to detect the drop 112.
The vibration isolation platform 20 is disposed between the free falling device 10 and the laser interferometry device 30, and is used for isolating the influence of bottom vibration on measurement. The laser interferometry device 30 may emit a measurement laser and track the drop 112 with the measurement laser to obtain a laser interference fringe signal of the drop 112 as it moves in free-falling. The vacuum bin displacement measuring device 120 is used for measuring a vacuum bin displacement signal when the vacuum bin 110 falls. The vacuum chamber displacement measuring device 120 includes a grating scale 122 disposed inside the housing 12, and a reading head 124 fixedly mounted to the outer shell of the vacuum chamber 110. The air refractive index measuring device 130 is disposed inside the housing 12, and is used for measuring the air refractive index inside the housing 12.
Referring to fig. 2-3, the housing 12 may be comprised of a top flange 11, a main cavity 13, a bottom flange 15, and a bottom viewing window 14. Wherein the top flange 11, the main cavity 13 and the bottom flange 15 may be made of an aluminum alloy material for reducing the weight of the free-falling device 10. It will be appreciated that the materials of the top flange 11, the main cavity 13 and the bottom flange 15 are not limited to aluminum alloys, but may be made of other metallic materials. It is to be understood that the structural shape of the housing 12 is not limited as long as a receiving space can be formed.
In one embodiment, a support frame 150 may be provided inside the freefall apparatus 10 for mounting the vacuum cartridge 110. The support frame 150 includes a frame top plate 151, a rail bracket 152, and a frame bottom plate 157. The rail bracket 152 is fixed between the frame top plate 151 and the frame bottom plate 157. The guide rail bracket 152 is provided with a linear guide rail 154. The vacuum chamber 110 is slidably disposed on the linear guide 154 so as to be slidable along the linear guide 154. It will be appreciated that the linear guide 154 may be provided with a slider 155. The slider 155 is linearly movable along the linear guide 154. The vacuum chamber 110 may be secured to the slider 155 by a vacuum chamber connection 156. Thus, the vacuum chamber 110 can move linearly along the linear guide rail 154 under the control of the power unit 140 to realize free falling motion of the falling body 112.
The grating scale 122 may be fixedly mounted to the support frame 150. Specifically, both ends of the grating scale 122 may be fixed to the frame top plate 151 and the frame bottom plate 157, respectively. The grating scale 122 is disposed parallel to and spaced apart from the linear guide 154. The read head 124 is disposed on the vacuum cartridge 110. Specifically, the read head 124 may be secured to the vacuum cartridge 110 by a connector 126. Thus, the movement of the readhead 124 relative to the grating scale 122 is the movement of the vacuum cartridge 110 relative to the support frame 150. So that the displacement of the reading head 124 is equivalent to the displacement of the vacuum cartridge 110. Thus, the vacuum bin displacement measuring device 120 may measure displacement information of the vacuum bin 110, that is, vacuum bin displacement information, through the grating scale 122 and the reading head 124. It will be appreciated that the measuring range of the grating ruler 122 should be greater than the maximum speed of the vacuum chamber 110. The instantaneous acceleration of the vacuum chamber 110 may be greater than the gravitational acceleration. In one embodiment, the grating scale 122 can continuously output 0V square wave or 5V square wave with a measuring resolution of 2×10 -6 m。
The power unit 140 may be any power unit capable of providing power as long as it can control the vertical movement of the vacuum chamber 110 in the gravity direction. The power unit 140 is operative to provide power to control the movement of the vacuum cartridge 110 along the linear track 154. In one embodiment, the power plant 140 includes a control motor 142, a flexible coupling 143, a timing belt 144, a travel switch 145, a first timing pulley 146, and a second timing pulley 148. The control motor 142 may be mounted to the support frame 150 through the housing 12. The rotating shaft of the control motor 142 is connected with the flexible coupling 143. The flexible coupling 143 is connected to the first timing pulley 146. The first synchronization pulley 146 is mounted to the frame top plate 151. The second timing pulley 148 is mounted to the frame base 147. The timing belt 12 is wound around the first timing pulley 146 and the second timing pulley 148 and is fixedly connected to the vacuum chamber connection 156. The control motor 142 may drive the vacuum chamber connecting member 156 to move through the first timing pulley 146 and the timing belt 144, thereby achieving the ascent and descent of the vacuum chamber 110 and the free fall of the falling body 112. The travel switch 145 is fixedly mounted on the rail bracket 152. After the vacuum cartridge connection 156 contacts the travel switch 145, the control motor 142 stops rotating.
Referring to fig. 4, in one embodiment, the vacuum chamber 110 includes copper tubing 111, a vacuum chamber top plate 113, a vacuum chamber side wall 119, a vacuum chamber bottom plate 115, and a vacuum chamber viewing window 117. The vacuum chamber side wall 119 is disposed between the vacuum chamber top plate 113 and the vacuum chamber bottom plate 115, and together form a closed vacuum chamber. The drop body 112 is placed within the vacuum chamber. The copper pipe 11 is used for vacuumizing the vacuum cavity. The vacuum chamber top plate 113, the vacuum chamber side wall 119, and the vacuum chamber bottom plate 115 may be sealingly connected together by welding. The vacuum chamber viewing window 117 is disposed in the vacuum chamber bottom plate 115. Laser light may enter the interior of the vacuum chamber 110 through the vacuum chamber viewing window 117. It will be appreciated that the vacuum chamber viewing window 117 and the vacuum chamber bottom plate 115 may also be sealingly connected by welding. It will be appreciated that the vacuum chamber 110 material should have a certain strength and be suitable for use as a vacuum chamber, which may be, but is not limited to, metal. In one embodiment, the vacuum cartridge 110 is made of an aluminum alloy material. A support structure 116 may also be disposed on the inner wall of the vacuum chamber 110, for supporting the drop body 112. It will be appreciated that grooves may also be provided on the support structure 11 to cooperate with the raised structures provided on the drop body 112 to provide for stable placement of the drop body 112 on the support structure 116. In one embodiment, the support structure 116 is a support ring. The drop body 112 rests on the support ring. The drop body 112 is also provided with a first reflecting prism 114 inside. The first reflecting prism 114 may reflect the laser light incident from the vacuum chamber observation window 117 for measurement. It will be appreciated that the configuration of the first reflecting prism 114 is not limited and may be selected as desired.
The vibration isolation platform 20 can be composed of a mechanical spring and a precise control system so as to realize an intrinsic oscillation period exceeding 20 seconds and have a good effect of isolating ground vibration. The vibration isolation platform 20 may be suspended with a second reflecting prism 214, which is used to cooperate with the laser interferometry device 30 to form an optical path, and to transmit the laser reflected by the first reflecting prism 114 of the falling body 112 to the laser interferometry device 30. It will be appreciated that the configuration of the second reflecting prism 214 is not limited and may be selected as desired.
The laser interferometry device 30 is used to measure laser fringe signals of the free-falling motion of the falling body 112. The laser interference fringe signal is used to calculate the absolute gravitational acceleration of the drop 112. It will be appreciated that the configuration of the laser interferometry device 30 is not limited as long as the above-described functionality is achieved. Referring also to fig. 5, in one embodiment, the laser interferometry device 30 may include a collimated laser 31, a reflecting element 32, a first beam splitting element 33, a second beam splitting element 34, a lens 35, and a photodetector 36. The collimated laser 31 is used to emit collimated laser light, which may be composed of one laser and a collimator. The reflecting element 32 is configured to reflect the collimated laser light emitted by the collimated laser 31 into the first spectroscopic element 33. It will be appreciated that the reflective element 32 is an optional element when the collimated laser light directly enters the first beam splitting element 33. The first spectroscopic element 33 may separate the collimated laser light into a test laser light and a reference laser light. The test laser and the test laser are perpendicular to each other. The test laser light is input to the first reflecting prism 114 and is reflected to the second light splitting element 34 via the first reflecting prism 114. The reference laser light is input to the second light splitting element 34 and combined with the test laser light before entering the photodetector 36. The reference laser light and the test laser light passing through the second spectroscopic element 34 may pass through the lens 35 and enter the photodetector 36. The photodetector 36 may convert interference fringes formed by the measurement laser light and the reference laser light, which are photosynthetic via the second spectroscopic element 34, into an analog signal. It will be appreciated that the lens 35 may also be an optional element. The first beam splitter element 33 and the second beam splitter element 34 may be beam splitters.
Referring to fig. 6, the absolute gravity measurement system 100 may further include a digital signal processor 40, a computer 50 connected to the digital signal processor 40, a data acquisition card 60, and an atomic clock 70. The digital signal processor 40 is electrically connected to the power unit 140 and the air refractive index measuring unit 130. The digital signal processor 40 is used for controlling the power device 140 and collecting the temperature, air pressure and humidity inside the housing 12 through the air refractive index measuring device 130. The computer 50 is configured to send instructions to the power unit 140 via the digital signal processor 40 to control the power unit 140, and calculate the refractive index of air inside the housing 12 according to the temperature, air pressure and humidity inside the housing 12 returned by the digital signal processor 40. The data acquisition card 60 is electrically connected with the vacuum bin displacement measuring device 120, the laser interference device 130 and the computer 50. The computer 50 acquires the laser interference fringe signal sent by the laser interference device 30 and the vacuum bin displacement signal sent by the vacuum bin displacement measuring device 120 through the data acquisition card 60. The atomic clock 70 is connected to the data acquisition card 60, and the atomic clock 70 provides a standard clock reference signal for the data acquisition card 60. The atomic clock 70 may be any reference clock, such as a rubidium atomic clock. The digital signal processor 40 may use any form of embedded processor.
How the free-falling body device 10 achieves free-falling body movement of the falling body 112 is described in detail below.
(1) Rotation of the control motor 142 causes the vacuum cartridge connector 156 to move upwardly and to drive the vacuum cartridge 110 upwardly, thereby transporting the vacuum cartridge 110 and the drop body 112 disposed therein to a top position of the housing 12.
(2) After the vacuum cartridge connection 156 contacts the travel switch 145, the control motor 142 stops rotating.
(3) The vacuum cartridge connector 156 is moved downward by the reverse rotation of the control motor 142. The vacuum cartridge 110 accelerates downward movement with the vacuum cartridge connector 156. The acceleration of motion of the vacuum chamber 110 is greater than the acceleration of gravity. The drop body 112 is separated from the support structure 116, and the drop body 112 is only subjected to gravity and begins to move downward as a free-falling body.
(4) The control motor 10 is decelerated as the vacuum chamber 110 moves downward to the bottom position of the housing 12. The support structure 116 comes again into contact with the falling body 112 in free-falling motion and moves together in a decelerating motion until it is stationary.
(5) Repeating the steps (1) - (4) above, the free-falling motion of the falling body 112 may be repeatedly achieved.
Compared with the prior art, the technical scheme of the application adopts a high vacuum maintenance technology, and maintains the vacuum degree in the miniaturized vacuum bin through a welding sealing technology, so that the falling body free falling body movement is skillfully realized. The adoption of the miniaturized vacuum bin enables the gravity meter to be separated from the ion pump, simplifies an absolute gravity measurement system, and improves the convenience and reliability of the absolute gravity measurement field operation. In addition, the technical scheme of the application also comprises a vacuum bin displacement measuring device and an air refractive index measuring device, so that the absolute gravity measuring method can be corrected by measuring vacuum bin displacement information by the vacuum bin displacement measuring device and measuring the air refractive index inside the shell by the air refractive index measuring device, and a more accurate measuring result can be obtained. Therefore, the absolute gravity measurement system has the advantages of portability, simplicity, higher maneuverability and reliability and suitability for field measurement in severe environments.
The embodiment of the application also provides an absolute gravity measurement method adopting the absolute gravity measurement system 100, which comprises the following steps:
controlling the vacuum chamber 110 to vertically move downwards from the top of the shell 12 through the power device 140, so that the falling body 112 does free falling body movement;
tracking the falling body 112 through the laser interferometry device 30 for free falling movement to acquire laser interference fringe signals;
measuring a vacuum bin displacement signal when the vacuum bin 110 falls by the vacuum bin displacement measuring device 120;
measuring the refractive index of air inside the housing 12 by the air refractive index measuring device 130; and
and calculating absolute gravity acceleration according to the laser interference fringe signal, the vacuum bin displacement signal and the air refractive index.
The following describes how absolute gravitational acceleration is calculated from the laser interference fringe signal, the vacuum bin displacement signal, and the air refractive index. During a drop period, the vacuum chamber 110 drops along with the drop body 112. The displacement of the drop body 112 relative to the vacuum chamber 110 and the displacement of the vacuum chamber 110 relative to the laser interferometry device 30 are changed during the drop. The above-mentioned change will result in a change in the optical path length of the measuring arm, at which point the laser interference fringe signal cannot characterize the absolute value of the displacement of the drop body 112, but the trajectory of the drop body 112 should be reconstructed by analyzing the change in the optical path length of the measuring arm, as follows.
Referring to fig. 7, the positional relationship between the vacuum chamber 110 and the falling body 112 is shown at the time i (solid line) and the time i+1 (broken line) in the falling process. A rectangle represents the vacuum chamber 110 and a right triangle represents the first corner reflecting prism 114 within the drop body 112. The arrows represent the measuring arm beams at times i (solid line) and i+1 (dashed line). x is the displacement of the falling body 112, y is the vacuum chamber displacement of the vacuum chamber 110, both take vertical downward positive directions, and subscript i indicates their respective values at time i. Let the measurement arm optical path be z, then the change from time i to time i+1, z, is:
z i+1 -z i ＝2(y i+1 -y i )(n TPf -n vac )+2(x i+1 -x i )n vac (1)
in n TPf Indicating the refractive index of air near the measuring arm of the laser interferometer, n vac Is the refractive index of the residual gas in the vacuum bin. From equation (1), it can be seen that by measuring the vacuum chamber displacement y and the air refractive index n TPf With the laser interference fringe signal z, the free-falling trajectory x in vacuum can be reconstructed. These three physical quantities are obtained by the laser interferometry device 30, the vacuum bin displacement measurement device 120, and the air refractive index measurement device 130 of the absolute gravimetric measurement system 100, respectively. Therefore, the accurate free fall trajectory of the falling body 112 can be calculated from the three physical quantities, thereby calculating the absolute gravitational acceleration.
Since the vacuum chamber 110 described in this application falls with the falling body 112, the laser path change measured by the laser interferometry device 35 is no longer equivalent to the free falling body motion displacement of the falling body according to equation (1). The vacuum bin displacement measuring device 120 and the air refractive index measuring device 130 are installed in the free falling body device 10 to cooperate with the laser interferometry device 30, so that the accuracy of the measurement result can be ensured.
In the several embodiments provided in the present invention, it should be understood that the disclosed related apparatus and method may be implemented in other manners. For example, the apparatus embodiments described above are merely illustrative, e.g., the division of the modules or units is merely a logical functional division, and there may be additional divisions when actually implemented, e.g., multiple units or components may be combined or integrated into another system, or some features may be omitted, or not performed. Alternatively, the coupling or direct coupling or communication connection shown or discussed with each other may be an indirect coupling or communication connection via some interfaces, devices or units, which may be in electrical, mechanical or other form.
The units described as separate units may or may not be physically separate, and units shown as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.
In addition, each functional unit in the embodiments of the present invention may be integrated in one processing unit, or each unit may exist alone physically, or two or more units may be integrated in one unit. The integrated units may be implemented in hardware or in software functional units.
Those skilled in the art will appreciate that implementing all or part of the processes of the methods of the embodiments described above may be accomplished by computer programs stored on a computer readable storage medium, such as a computer system, and executed by at least one processor in the computer system to implement processes including embodiments of the methods described above. The storage medium may be a magnetic disk, an optical disk, a Read-Only Memory (ROM), a random-access Memory (Random Access Memory, RAM), or the like.
The above examples merely represent a few embodiments of the present invention, which are described in more detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.
Claims (10)
1. An absolute gravity measurement system, comprising:
the free falling body device is used for realizing free falling body movement of falling bodies;
the laser interferometry device is used for tracking the falling body to perform free falling body movement so as to acquire a laser interference fringe signal;
the vibration isolation platform is arranged between the free falling body device and the laser interferometry device and is used for isolating the influence of ground vibration on measurement, and is characterized in that:
the free falling body device comprises a shell, a vacuum bin arranged in the shell and a power device in transmission connection with the vacuum bin, wherein the power device is used for controlling the motion of the vacuum bin in the vertical direction, the falling body is arranged in the vacuum bin, and a vacuum bin observation window is arranged at the bottom of the vacuum bin and used for observing the free falling body motion of the falling body;
the absolute gravity measurement system further comprises a vacuum bin displacement measurement device arranged in the shell, wherein the vacuum bin displacement measurement device comprises a grating ruler arranged in the shell and a reading head fixedly arranged in the shell of the vacuum bin;
the absolute gravity measurement system further comprises an air refractive index measurement device for measuring the air refractive index inside the housing.
2. The absolute gravimetric measurement system of claim 1, wherein the free-fall device comprises a support frame disposed within the housing, the support frame comprising a vertically disposed linear rail;
the vacuum bin is slidably arranged on the linear guide rail and driven by the power device to move along the linear guide rail;
the grating ruler is arranged on the supporting frame and is arranged in parallel with the linear guide rail at intervals, so that the grating ruler and the reading head are arranged oppositely.
3. The absolute gravimetric measurement system of claim 1, wherein said vacuum chamber inner wall is fixedly provided with a support structure for supporting said drop body.
4. The absolute gravimetric measurement system of claim 1, wherein said vacuum chamber is a welded seal, and wherein the vacuum in said vacuum chamber is 10 degrees vacuum -6 Pa to 10 -4 Pa。
5. The absolute gravimetric measurement system of claim 4, wherein an air absorbent is disposed within said vacuum chamber.
6. The absolute gravity measurement system of claim 1, wherein a first reflecting prism is disposed in the drop body for reflecting the measurement laser light emitted from the laser interferometry device;
and a second reflecting prism is arranged in the vibration isolation platform and is used for reflecting the measuring laser reflected by the first reflecting prism.
7. The absolute gravimetric measurement system of claim 6, wherein said laser interferometry device comprises:
the first light splitting element is used for splitting the collimated laser into test laser and reference laser which are perpendicular to each other, and the test laser is transmitted to the first reflecting prism and is reflected to the second reflecting prism through the first reflecting prism;
a second beam splitter for combining the reference laser light passing through the second beam splitter and the test laser light reflected to the second beam splitter via the second reflecting prism;
a photodetector for converting interference fringes formed by the measurement laser light and the reference laser light synthesized via the second spectroscope into an analog signal.
8. The absolute gravimetric measurement system of claim 1, wherein said air refractive index measurement device comprises a sensor disposed within said housing for sensing temperature, air pressure and humidity within said housing.
9. The absolute gravity measurement system of claim 8, further comprising:
the digital signal processor is electrically connected with the power device and the sensor and is used for controlling the power device and collecting the temperature, the air pressure and the humidity inside the shell through the sensor;
the computer is connected with the digital signal processor and is used for sending an instruction to the power device through the digital signal processor so as to control the power device, and calculating the refractive index of air in the shell according to the temperature, the air pressure and the humidity in the shell, which are transmitted back by the digital signal processor;
the computer acquires laser interference fringe signals sent by the laser interferometry device and vacuum bin displacement signals sent by the vacuum bin displacement measurement device through the data acquisition card; and
and the atomic clock is connected with the data acquisition card and provides a standard clock reference signal for the data acquisition card.
10. An absolute gravity measurement method employing the absolute gravity measurement system of any of claims 1-9, comprising:
the vacuum bin is controlled by the power device to vertically move downwards from the top of the shell, so that the falling body can freely fall;
tracking the falling body through the laser interferometry device to perform free falling movement so as to acquire a laser interference fringe signal;
measuring a vacuum bin displacement signal when the vacuum bin falls through the vacuum bin displacement measuring device;
measuring the air refractive index inside the shell by the air refractive index measuring device; and
and calculating absolute gravity acceleration according to the laser interference fringe signal, the vacuum bin displacement signal and the air refractive index.
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| CN109061758B (en) * | 2018-07-31 | 2023-08-18 | 湖北省地震局 | Steel belt offset falling body center driving mechanism for absolute gravimeter |
| CN109471191B (en) * | 2018-11-13 | 2021-07-06 | 中国地震局地震研究所 | Aviation gravity measurement method and equipment |
| CN112014895B (en) * | 2020-08-05 | 2021-07-16 | 中国地震局地球物理研究所 | Method and equipment for measuring absolute gravity under dynamic environment |
| CN112698415B (en) * | 2020-12-02 | 2023-04-07 | 杭州微伽量子科技有限公司 | Movable gravity measurement laboratory |
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