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绝对重力仪在地球物理等领域有着广泛的应用, 其普遍采用激光干涉式或原子干涉式的测量原理. 现有的绝对重力仪主要利用垂直隔振系统来减小地面振动对参考镜的影响以提升仪器的测量精密度. 但在激光干涉式绝对重力仪中, 隔振系统对仪器自振效应等固定相位振动噪声的响应可能引入系统误差, 即影响测量准确度; 在原子干涉式绝对重力仪中也可能有尚未标定的振动来源通过隔振系统引入系统误差. 本文对现有绝对重力仪中使用的4种典型隔振系统进行理论分析及仿真建模, 以自振脉冲、地脉动和随机振动这3种典型信号为输入, 分析激光干涉式绝对重力仪中隔振系统内参考镜的真实振动及其对重力测值的影响, 并通过实验对比评估了其中两种系统在实际重力仪中的性能. 结果表明, 当仪器运行期间存在自振脉冲等固定相位振动噪声时, 隔振系统中参考镜振动引入的系统误差可能达到10 μGal (1 μGal = 1 × 10 –8m/s 2)及以上. 使用性能更好的隔振系统或在实际测量中对该系统误差进行修正, 有望进一步提高国产激光干涉式绝对重力仪的测量精度.Absolute gravimeter, an instrument which is applied to laser interferometry or atom interferometry for measuring the gravitational acceleration g(approximately 9.8 m/s 2), plays an important role in metrology, geophysics, geological exploration, etc. To achieve a high accuracy of several microGals (μGal, 1μGal = 1 × 10 –8m/s 2), a vertical vibration isolator is widely employed in the absolute gravimeter to protect the reference object (a retro-reflector or a mirror) from being disturbed by ground vibration noises. However, the reference object in vibration isolator may still move due to isolator’s response to the impulse caused by the self-vibration effect in laser-interferometry gravimeter, or the forced vibration of the ferromagnetic component in the isolator under the varying magnetic field of magneto-optical traps (MOTs) in atom-interferometry gravimeter. This vibration of the reference object has a fixed phase relative to the detection of the free-fall of a falling object or atoms, leading an additional systematic error to be introduced into measured gvalue. In this paper, the physical models of four typical vertical vibration isolators used in the current absolute gravimeters are introduced, i.e. a passive Minus K isolator, a passive Lacoste isolator, a one-stage active isolator, and a double-stage active isolator. The simulation models of these isolators are also created with specific resonance periods. Taking a laser-interferometry gravimeter for example, the responses of these isolators under impulse input are analyzed, proving that the real vibration of the reference object, namely the output of each isolator, has a fixed phase relative to the detection of the fringe signal, which indicates the trajectory of the free-falling object, hence resulting in an additional systematic error. To provide a detailed evaluation, firstly the vibration of the reference object under an impulse, a seismic noise, and a random noise, which represent typical ground vibrations, are obtained by running the simulation. Then the corresponding errors in the calculation of gvalue are presented. Besides, the experimental results of T-1 laser-interferometry gravimeter at a noisy site in Tsinghua University, with either a Minus K isolator or a Superspring isolator used, are compared with the simulated results. According to the above simulations and experiments, the systematic error introduced by the vibration of resonance object in a Minus K isolator or a one-stage active isolator under impulse can respectively exceed 600 μGal or 10 μGal, while the error with the object in a Lacoste isolator or a double-stage active isolator can be neglected. Therefore, it is better to use a double-stage active vibration isolator in absolute gravimeter to avoid this systematic error and achieve higher measurement accuracy. With more information about the forced vibration in the isolators under varying magnetic fields of MOT, the systematic error introduced by the vibration of reference object can also be specifically evaluated in the future.
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] -
测量参数 数值 振动信号 参数 数值 单次测量中采集的
下落物体运动时长/ms120 信号1: 自振效应导致的脉冲 速度/(mm·s–1) 0.1 采集电路触发时刻与下落物体释放瞬间的延时/ms 30 信号2: 第1种地脉动
(正弦信号)幅值/nm 5 单组测量包含的下落次数 100 信号2: 第1种地脉动
(正弦信号)频率/Hz 0.2 单组测量期间相邻两次测量的时间间隔/s 20 信号3: 第2种地脉动
(正弦信号)幅值/nm 2 相邻两组测量的时间间隔/h 1 信号3: 第2种地脉动
(正弦信号)频率/Hz 3 总测量组数 12 信号4: 代表随机振动的
高斯白噪声PSD
/(m2·Hz–1)2.5×10–17 
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隔振类型 输入信号 自振脉冲
(信号1)地脉动及随机振动
(信号2—4)综合振动
(信号1—4)无隔振 5.1 ± 15.1 21.0 ± 74.9 –121.8 ± 90.4 Minus K型
(被动式)655.8 ± 0.4 2.1 ± 2.0 658.5 ± 2.5 Lacoste型
(被动式)0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 一级主动式 –15.9 ± 0.0 –0.4 ± 0.2 –15.9 ± 0.2 二级主动式 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 下载:
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隔振类型 结果类型 实测结果
(综合信号)仿真结果
(综合信号)无隔振 –52.0 ± 110.0 –40.7 ± 123.3 Minus K型(被动式) 655.2 ± 77.8 656.5 ± 3.3 一级主动式 — –16.0 ± 0.3 Superspring型
二级主动式–6.7 ± 12.6 0.0 ± 0.0 下载:
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隔振类型 采样起点t1/ms 34 35 36 无隔振 –84.6 ± 314.7 215.6 ± 334.0 154.2 ± 294.5 Minus K型
(被动式)658.6 ± 8.1 660.8 ± 9.2 660.7 ± 7.7 一级主动式 –16.2 ± 0.7 –16.1 ± 0.8 –17.3 ± 0.7 二级主动式 0.0 ± 0.0 0.0 ± 0.0 0.1 ± 0.0 下载:
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隔振类型 下落间隔/s 30 20 10 7 3 无隔振 –168.0 ± 328.5 215.6 ± 334.0 176.7 ± 281.9 49.7 ± 322.1 –281.3 ± 295.2 Minus K型(被动式) 658.5 ± 9.4 667.5 ± 8.1 631.2 ± 9.2 937.9 ± 8.7 1037.1 ± 8.5 一级主动式 –16.3 ± 0.7 –15.4 ± 0.8 –15.7 ± 0.7 –16.5 ± 0.8 –16.8 ± 0.8 二级主动式 0.0 ± 0.0 0.0 ± 0.0 0.1 ± 0.0 0.1 ± 0.0 0.2 ± 0.0 下载:
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隔振类型 地脉动信号 19个正弦信号 2个正弦信号 无隔振 226.3 ± 297.3 215.6 ± 334.0 Minus K型(被动式) 662.4 ± 8.3 644.2 ± 7.8 一级主动式 –15.1 ± 0.8 –16.2 ± 0.7 二级主动式 0.1 ± 0.0 0.0 ± 0.0 下载:
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隔振类型 结果类型 仿真值
(真实振动信号)仿真值
(设计信号)实测值 无隔振 –264.5 ± 849.3 –513.9 ± 678.3 471.5 ± 676.6 Minus K型
(被动式)646.0 ± 16.5 629.1 ± 18.8 876.7 ± 615.6 一级主动式 –12.1 ± 2.5 –17.9 ± 1.5 — 二级主动式 1.8 ± 0.1 0.0 ± 0.0 –20.0 ± 62.6 下载:
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[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36]
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