BPM chamber displacement monitor in Hefei light source

The beam horizontal orbit at Hefei light source(HLS) was drifting all along while the storage ring was operating due to the drift of BPM chamber mainly caused by the thermal effect of synchrotron light. To monitor the BPM chamber motion for all BPMs, a BPM chamber motion measurement system is built in real-time to correct the reading of BPMs. The raster gauges are used to measure the displacement, and the displacement data are transmitted by RS485 serial network to an industrial personal computer which processes the data and sends them to HLS control system. The design of BPM chamber motion measurement system is described and the measurement results are given.