Influence of the Great Earthquake in Japan on my country's Precision Measuring Instruments

by:Gewinn     2022-05-11
On March 11, a strong earthquake of magnitude 9.0 occurred in the Tohoku region of Japan. Cai Chenguang, an associate researcher at the Vibration and Shock Laboratory of the Institute of Mechanics and Acoustics of the Chinese Academy of Metrology, said in an interview with reporters that such a large earthquake will have some impact on my country's precise measurement and measurement. The Vibration and Shock Laboratory where Cai Chenguang works is a laboratory specializing in the measurement of vibration, shock and rotational speed. Vibration and shock speed measurement is a multi-disciplinary dynamic measurement technology. It is widely used in many scientific research and engineering fields such as machinery manufacturing, vehicles and ships, aerospace geophysics, geological and geophysical exploration, and plays a very important role in the construction of the national economy. Cai Chenguang said that the impact of the earthquake in Japan on precise measurement and measurement can be divided into two stages in terms of time: the first stage is when the earthquake and aftershocks continue to occur; the second stage is the post-earthquake geological stability period. The magnitude of the earthquake in Japan reached 9.0. The released energy was relatively large, and its low-frequency vibration components were transmitted farther, which had a significant impact on my country's high-precision measuring instruments. It is understood that high-precision measurement and measurement instruments have extremely high requirements for environmental vibration. The American Institute of Environmental Science and Technology recommends after a large number of theoretical and experimental studies that the measurement at the micron level requires that the environmental vibration in the 1-100 Hz frequency band be controlled below 12.5 μm/s (VC-C level), otherwise the precision measurement cannot be guaranteed. measurement accuracy. For example, in order to ensure the measurement accuracy of a 1000 times precision microscope, the environmental vibration must be strictly controlled, otherwise there will be the problem of losing pixels, or even losing the whole frame image; for scanning electron microscopes and transmission microscopes with higher measurement accuracy For electron microscopes, the environmental vibration is required to be controlled at the VC-D level (that is, the environmental vibration in the 1-100 Hz frequency band is controlled below 6 μm/s); for nano-scale precision measurements, such as semiconductor linewidth, adenosine triphosphate and DNA measurement, The requirements for environmental vibration are higher. The National Institute of Standards and Technology (NIST) has also conducted extensive research on nanometer-scale metrology, establishing environmental vibration standards that nanometer metrology needs to meet. According to Cai Chenguang, due to the impact of the earthquake in Japan, the environmental vibration of the China Institute of Metrology is far beyond the level of control required for precision measurement. 'Although some precision laboratories in the Changping base of the Metrology Institute are located 14 meters underground, which can isolate part of the seismic waves propagating on the surface, they cannot effectively attenuate the low-frequency seismic waves propagating in depth, which makes the high-precision measuring instruments unable to work normally.' He gave an example. It is said that due to the influence of the earthquake, the precision mass comparator will not be stable for a long time, so that the high-precision mass value cannot be transmitted and traced; the nano-scale precision measuring instrument will also be affected and cannot work normally. Cai Chenguang said that at present, the Changping Base of the China Institute of Metrology has not established a real-time monitoring system for environmental vibration, and it is still impossible to evaluate the specific impact of incidents such as the Great Japan Earthquake on the high-precision metrology traceability system in real time, effectively and accurately. 'Our country now urgently needs to establish a real-time monitoring system for environmental vibration.' In addition to the direct impact of seismic waves on precision measurement, precision measurement and measurement will also be affected during the post-earthquake geological stability period. According to Cai Chenguang, the earthquake will cause a certain degree of geological movement, which requires a long period of stability after the earthquake. For example, the liquefaction of the ground will cause the ground to tilt, and the tilt angle of the ground will continue to drift and change during the stable geological conditions. The ground tilt angle is a key parameter in the precision navigation system and needs to be accurately measured. According to reports, in the stable state of geological conditions, the cumulative change of the ground inclination angle is small, which will not cause too much initial error to the precision navigation system. When an earthquake occurs, the inclination angle shift caused by geological movement and geological liquefaction will greatly change the local inclination angle, thus bringing about a large initial error. Therefore, it is necessary to monitor the tilt angle for a long period of time after the earthquake, so as to ensure the accuracy of the navigation measurement. 'There are many precision vibration isolation platforms in the Changping Base of Metrology Institute, and many measurement systems on these platforms are sensitive to tilt angles. For example, in length measurement, the laser platform and the measured platform may be on two adjacent platforms of two meters. If the inclination angle of the ground changes by 0.001 degrees, there will be a displacement change of 35 microns in the vertical direction, and such a large displacement change cannot even be measured at the micron level, let alone nanometer measurement.” Cai Chenguang said that my country It is urgent to establish an inclination angle measurement system and a monitoring system to ensure the accuracy and reliability of the recurrence of measurement values u200bu200bin my country.
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