A method to establish height datum online based on absolute hydrostatic leveling system

The fourth generation light source HEPS under construction in China demands higher alignment accuracy. However, it is difficult to improve height accuracy based on the overlap method of geometric and tracker leveling. Based on the study of hydrostatic leveling systems for ground settlement monitoring, this paper proposes a new method, Absolute Hydrostatic Leveling System (AHLS), for establishing height datum. The principle of establishing height datum for AHLS is described in detail, and it is emphasized that absolute calibration of the level is crucial for implementing this plan. A set of absolute calibration methods for non-contact absolute hydrostatic level is proposed, including measuring key dimensions of the level and precise measurement of liquid depth. The absolute calibration accuracy reaches 0.031 mm. The height accuracy of validating an AHLS between two points within 10 m using a laser tracker is more than 0.05 mm. The results demonstrate the feasibility of using AHLS to establish absolute height datum with high precision. With this method, the absolute height of each point can be obtained independently without any accumulated errors, allowing the establishment of height datum with high precision on a large scale. This approach can be used in the next generation of accelerator devices and also represents a novel method for achieving high-precision vertical monitoring.