Calibration method of HLS's sensor used in SSRF

The site of Shanghai Synchrotron Radiation Facility (SSRF) is of complicated geological conditions, and a system to monitor the uneven subsidence of foundation and key parts (different kinds of magnets) of the accelerators is a necessity. Considering actual conditions of the accelerator structure and the assembling place, a new type of sensor of hydrostatic levelling system (HLS) has been designed. In order to obtain the required measurement accuracy, every HLS's sensor was strictly calibrated. In this paper, we introduce the special calibration method to establish the HLS. The method has been used in the calibration for vessel sensor for SSRF.