Japan Earthquake Influences China's Precision Measuring Instruments

On March 11, a magnitude 9.0 earthquake struck northeastern Japan. Cai Chenguang, an associate researcher at the Institute of Mechanics and Acoustics at the Institute of Mechanics and Acoustics of the Chinese Academy of Sciences, said in an interview with this reporter that such a strong earthquake will have some impact on China's precision measurement and measurement.

Cai Chenguang's Vibration and Shock Research Lab is a laboratories specialized in vibration, shock, and speed measurement. Vibration shock speed measurement is a multidisciplinary dynamic measurement technology. It is widely used in many scientific research and engineering fields such as machinery manufacturing, vehicle and ship, aerospace geophysics, and geophysical exploration. It plays a very important role in the national economic construction. Cai Chenguang said that the impact of Japan’s earthquake on precision measurement and measurement can be divided into two phases in terms of time: the first phase is when earthquakes and aftershocks continue to occur; the second phase is the post-earthquake geological stability cycle.

The magnitude of the earthquake in Japan reached 9.0, releasing a large amount of energy and transmitting low-frequency vibration components far, which has a significant impact on China's high-precision measuring instruments.

It is understood that high-precision measurement and measurement instruments have extremely high requirements for environmental vibration. The U.S. Institute of Environmental Science and Technology has recommended extensive theoretical and experimental research. Micron-scale measurements require ambient vibration in the 1 to 100 Hz band to be controlled below 12.5 μm/sec (VC-C class), otherwise precision measurements cannot be guaranteed. measurement accuracy. For example, for a precision microscope of 1000 times, in order to ensure its measurement accuracy, it is necessary to strictly control the environmental vibration, otherwise there will be problems of missing pixels or even losing the entire frame of the image; and for scanning electron microscopes and transmissions with higher measurement accuracy Electron microscopy requires ambient vibration control in the VC-D class (ie, ambient vibration in the 1 to 100 Hz band is controlled below 6 μm/sec); for nano-scale precision measurements such as semiconductor linewidth, adenosine triphosphate, and DNA measurements, The requirements for environmental vibration are higher. The National Institute of Standards and Technology (NIST) has also conducted a large number of researches on the measurement of nanometer scales and established the environmental vibration standards that nanometric metrology needs to meet.

According to Cai Chenguang, due to the influence of the earthquake in Japan, the environmental vibration of the China Institute of Metrology far exceeds the amount of precision that precision measurement requires. “Although some precision laboratories of the Changping Base of the Metrology Institute are located 14 meters underground and can segregate some of the surface-borne seismic waves, they cannot effectively attenuate deep-spread low-frequency seismic waves, making high-precision measuring instruments unable to work properly.” It is said that due to the influence of earthquakes, precision mass comparators will not be stable for a long time, resulting in high-quality mass values ​​that cannot be transmitted and traced; nano-scale precision measuring instruments will also be affected and will not work properly.

Cai Chenguang said that at present, the Chinese Academy of Metrology Sciences Changping Base has not yet established a real-time monitoring system for environmental vibration, and it is still unable to evaluate in real time, effectively and accurately the specific impact of such incidents in Japan on high-precision measurement traceability systems. "China now urgently needs to establish a real-time monitoring system for environmental vibration."

In addition to the direct effects of seismic waves on precision measurements, the post-earthquake stability cycle, precision measurements, and metering are also affected. According to Cai Chenguang, the earthquake will cause a certain degree of geological movement, requiring a long period of stabilization after the earthquake. For example, due to the liquefaction of the ground, the tilt of the ground will cause a continuous drift in the stability of the geological conditions. The ground tilt angle is a key parameter in a precision navigation system and requires accurate measurement.

According to reports, under the stable geological conditions, the cumulative change in the ground tilt angle is small and will not cause too much initial error in the precision navigation system. When the earthquake occurs, the tilt angle shift caused by geological movement and geology liquefaction will greatly change the local tilt angle, leading to a larger initial error. Therefore, the inclination angle needs to be monitored for a long time after the earthquake to ensure the accuracy of navigation measurement.

“There are many precision vibration isolation platforms at the Changping Base of the Metrology Institute. Many measurement systems on these platforms are sensitive to the tilt angle. For example, in length measurement, the laser platform and the platform under test may be on two adjacent platforms of two meters. If the inclination of the ground surface changes by 0.001 degrees, a 35-micron displacement will occur in the vertical direction. Such a large displacement change cannot be tolerated even if it is measured in micrometers, not to mention the nanometer measurement. Cai Chenguang said, China It is urgent to establish a tilt angle measurement system and monitoring system to ensure the accuracy and reliability of the recurrence of measurement values ​​in China.