Determination and correction of the errors of a PDS coordinate system

The PDS microdensitormeter has a high positional repeatability but low coordinate systematic accuracy because of the errors of the PDS mechanism. To improve the PDS coordinate system, a method to determine and correct the errors of PDS coordinate system with a glass grid is developed and applied to the PDS of Purple Mountain Observatory (PMO). With the method, the coordinate systematic errors of the PDS at PMO are reduced from ± 5 microns to ± 1 micron. The results of an astrometric application confirmed the effect of the method.