  The beam position monitor (BPM) system is of most importance in a light
source. The capability of the BPM depends on the resolution of the system. The
traditional standard deviation on the raw data method merely gives the upper
limit of the resolution. Principal component analysis (PCA) had been introduced
in the accelerator physics and it could be used to get rid of the actual
signals. Beam related informations were extracted before the evaluation of the
BPM performance. A series of studies had been made in Shanghai Synchrotron
Radiation Facility (SSRF) and PCA was proved as an effective and robust method
in the performance evaluations of our BPM system.
