Influence of the guide rail irregularity on low-frequency test results of seismometers on shake table
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摘要:
对振动台在大行程移动过程中导轨不平顺引起的倾斜效应进行了理论分析，选择0.1 Hz及以下频点开展振动台导轨不平顺引起的台面倾斜对测试结果影响的定量化分析。结果表明，振动台面在移动过程中的不确定倾斜对地震计水平分量灵敏度的影响大于对垂直分量灵敏度的影响。采用高精度水平仪获取水平振动台在不同行程下的运动轨迹起伏变化，并基于倾斜效应的影响机制，用Labview语言实现补偿系统，在地震计的振动测试中对测试结果进行动态补偿。测试结果表明，经过动态补偿，导轨不平顺不再对灵敏度校准结果存在明显制约，可大幅提高地震计的低频测试精度。
Abstract:This paper theoretically analyzed the influence of the guide rail irregularity on calibration of very-broadband seismometers under long stroke motions on shake table, and then quantitatively analyzed the oblique effect on calibration of seismometers on shake table due to the guide rail irregularity at 0.1 Hz and lower frequencies. The results indicate that oblique effect has a larger impact on sensitivity of the horizontal component than that of the vertical component. Higher-precision level meter was used to get the motion trace of the horizontal shake table under long stroke. Based on the influence mechanism of the guide rail irregularity and the data obtained from the level meter, a dynamic compensation system was designed with the software language of Labview. Test results suggest that the calibration accuracy is significantly improved at lower frequencies. Therefore, the dynamic compensating method is effective for very-broadband seismometer testing on shake table.
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Keywords:
- shake table /
- guide rail irregularity /
- long stroke /
- dynamic compensation
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图 1 导轨不平顺情况下地震计受到的重力加速度作用
g为重力加速度，ag为重力加速度在地震计灵敏轴方向产生的分量，x为振动台的位移，A为振动台位移的最大幅值，θ为俯仰角
Figure 1. Gravity acceleration on the seismometer resulted by guide rail irregularity
g is the acceleration of gravity，ag is the acceleration on sensitivity axis of the seismometer due to gravity，x is displacement of the shake table，A is maximum displacement of the shake table，θ is the pitch angle
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图 2 振动频率为0.1 Hz时不同行程下地震计CMG-3T输出速度失真度和台面加速度失真度的变化
Figure 2. Output velocity distortions of seismometer CMG-3T and shake table acceleration distortion at different positions at 0.1 Hz
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图 3 振动频率为 0.01 Hz时不同行程下地震计CMG-3T输出速度失真度和台面加速度失真度变化
Figure 3. Velocity distortions of seismometer CMG-3T and shake table acceleration distortion at different positions at 0.01 Hz
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图 5 导轨补偿前后的地震计CMG-3ESPC灵敏度变化
Figure 5. Sensitivity of seismometer CMG-3ESPC before and after compensation for guide rail
表 1 振动台校准结果
Table 1 Calibration results of shake tables
设备名称 加速度校准结果不确定度 频带
/Hz溯源方式 16 Hz 0.1—100 Hz 0.01—0.1 Hz 低频振动标准装置（水平/垂直） 0.8% 1.5% 3% 0.008 33—160 校准 *委托中国计量科学研究院校准。 
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表 2 0.1和0.01 Hz时地震计CMG-3T在垂直振动台不同行程时的灵敏度
Table 2 Sensitivities of seismometer CMG-3T on vertical shake table at different positions at 0.1 and 0.01 Hz
f /Hz 行程/mm 灵敏度/（V·s·m−1） 0.1 2.00 987.96 4.05 987.97 5.99 988.04 7.99 988.08 11.99 988.75 0.01 14.49 837.24 19.35 837.27 25.92 837.60 35.39 837.96 44.45 838.13 57.86 837.17
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表 3 0.01 Hz时地震计CMG-3T在水平振动台测试时灵敏度随行程的变化
Table 3 Sensitivities of seismometer CMG-3T on horizontal shake table at different positions at 0.01 Hz
行程/mm 灵敏度/（V·s·m−1） 行程/mm 灵敏度/（V·s·m−1） 10.04 964.17 44.81 1129 20.01 1074 58.47 1093 27.48 1113 73.04 1072
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表 4 水平振动台测试时地震计CMG-3T补偿前后的灵敏度
Table 4 Sensitivities of seismometer CMG-3T before and after compensation at different frequencies on horizontal shake table
f /Hz 地震计输出
电压值/V补偿前灵敏度
/（V·s·m−1）补偿后灵敏度
/（V·s·m−1）f /Hz 地震计输出
电压值/V补偿前灵敏度
/（V·s·m−1）补偿后灵敏度
/（V·s·m−1）0.10 8.19 994.87 994.85 0.04 5.24 997.54 994.21 0.08 8.59 995.31 994.51 0.03 3.94 999.73 993.79 0.07 7.52 994.04 993.00 0.02 3.91 992.31 969.63 0.06 7.84 996.36 994.88 0.015 2.87 971.45 932.55 0.05 6.54 996.61 994.47 0.01 1.71 866.41 791.47
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