| Gravitational field is one of the Earth's basic fields which reflects the internal structure and change of the Earth. High precise absolute gravitate observation is the base to research the Earthquake Prediction, Solid Earth Sciences and Exploration. Although many countries have begun to design their own absolute gravitate gravimeter (AG), only the U.S.A has the breakthrough of key technologies of AG and formed their own products, for example the FG5, A10 and others, But these products are expensive and Export Control by the U.S.A, and also have a very long period to repair. Our country is one of countries who began to develop the absolute gravimeter at the first time. Last century, the NIM-?and NIM-?absolute, which were developed by the National Institute of Metrology P.R.China, have got the High-tech level in the International Comparison of Absolute Gravimeters. But because of the investment, technology of Machining and electronics and information technology, our country has not developed our brand of the absolute gravimeter. As the progress of the precision of Time Base, Length Base, high precise digitizer and Precision Control, broadband, high precise vibration monitoring technology, it is possible to solve the key technical difficulties and develop our own high precise AG.First of all, this paper comprehensive describes the developments of AG and then quantitative estimates the possible error sources. The whole research focus on these three kinds of key technologies: First, the study on the servo controlling of the free-fall body (FB). By using the digital control technology, we achieved the requirements of precise and stability in controlling the FB. By designing of the Coaxial Gear System and the theory motion curve, the motion of the servo motor was identified. By the calculation of the mechanism of FB servo controlling, the motor power was identified. So, on the condition of minimizing the system vibration, we successfully solve technology in the FB Servo Tracking.Second, the study on the algorithm of rebuilding the trace of FB and the technology of the disturbance inhibition. The digital interference signal, which used to get the Time and distance coordinates of the FB's trace by using the digital signal processing, can be got from the high speed digitizer. And the time base of the digitizer is provided by the Rubidium Atomic Clock. The error simulation confirmed the truth that the mean error of this algorithm is 0.0005?Gal. And then, we got the vibration signal of the reference prism which was synchronously collected of the digitizer to develop a new algorithm to inhibit the disturbance which can introduce the error in the measurement result of AG.Third, the study on the compensating the error of interferometry. In this section, the influence of the mirrors to the light parallelism in the ideal plane, the study of the splitting ratio of the first side of the beam splitter, the theory of the adjustment of the light vertical were studied and the errors coming from these units have been confirmed. These studies also identified the design ideas in the interferometry system, and solved the high precise measurement of AG.Through the study of these three sections, we built the experimental prototype successfully. After the error experiments in the international absolute gravity reference point, in Beijing national geophysics observatory, the prototype's systematic bias is-55?Gal(no Error Correction), the precision is less than 10?Gal during the 2 hours measurements. And we also own the ability to design the even more precision AG. |
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