| Hydrostatic leveling system (HLS) follows the principle that the liquid (deionized water or purified water) in it is always looking for equipotential surface, which uses connected reservoirs of water to determine the relative elevation difference of the monitoring points. It’s widely used in engineering survey because of its high accuracy, especially in precision engineering survey such as particle accelerators alignment. Deformation in the vertical direction of the particle accelerator is the main affecting factor in the operation of an accelerator, so it is always necessary to use HLS to monitor the deformation of key component parts in a particle accelerator.Firstly, considering the current development tendency of particle accelerator alignment, application of HLS used in particle accelerators home and abroad is introduced systematically and the relative issues and challenges are described. With the development of the new theory and technology of alignment used in large particle accelerator, an increasing number of new generation light sources were built successively, and the requirements of the alignment accuracy have become increasingly harsh, even micron-level precision is required in the large scale measurement. Therefore, increasing the HLS accuracy unilaterally cannot meet the demand in the alignment work in the future.This paper on the one hand mainly discusses the factors affecting the measurement accuracy of HLS through theoretical analysis and case studies. On the other hand, the theoretical study is verified by building multiple sets of HLS experimental verification system. And then the corresponding method and theory to eliminate the influencing factors are proposed. The main research contents and achievements are as follows:1. Studies on effects of uneven temperature change on HLS system are finished. Working medium of HLS system is liquid, so uneven temperature changes inevitably lead to changes of the density of the liquid, and then lead to the changes of the liquid volume, which will inevitably affect the measurement accuracy of HLS. Thus a set of reliable temperature compensation method is obtained through theoretical and experimental verification.2. Describing effect of different pressures on the surface of the fluid on the HLS readings, and the measure to eliminating the effect is proposed for reducing the source of errors. Firstly, using rubber ring to seal the sensor pot, and then, using isobaric connecting air pipe to connect sensors together to ensure the pressures on the surface of the fluid in different sensors pot are equivalent. Meanwhile, the effects of ground vibration and gravity anomaly on HLS readings are introduced briefly in this paper.3. In-depth studies on tidal effects (earth tide and oceanic load tide) on HLS readings are expounded in this paper. The earth is a complicated exercise body deformed under the action of various forces; any point on earth is affected by the gravitation of the sun and the moon besides the gravity and the rotational centrifugal force of the earth. Solid earth deforms periodically under the action of tidal force, and the tidal effects on the readings of HLS are non-ignorable, especially in the alignment of particle accelerator. Therefore, temperature compensation and pre-processing to the raw data is fatal with using software Tsoft. After finishing the harmonic analysis to the data with using Eterna, local tide model is calculated. In other words, the tidal effects on HLS readings are obtained. Finally, the local ground deformations are got by deleting the tidal effects.4. About20meters HLS testing platform have been built in Hefei light source. This platform is mainly used for verifying the accuracy of HLS is enough to distinguish the earth tide signal and the HLS reading changes was mainly due to the earth tide.5. A set of HLS was installed in Jingxian seismicstation for studies on tidal correction of observations from HLS, and further validating its reliability.6. Studies on tidal correction of the data based on HLS used at CERN and Spring-8is completed for studying the tidal correction model more widely. Studies on accuracy theory and validation of HLS system used in particle accelerators were first introduced in this paper. Studying relative affecting factors mentioned above by using multidisciplinary knowledge and experimental verification, more reliable and scientific evaluation criterion of HLS measuring accuracy can be provided for relative alignment work. The current research establishes a foundation for getting higher precision of measurement data for HLS used in new generation particle accelerator have been built and will be built in the future. |
