Upgrade of the BPM system for the BEPC storage ring

The Beijing Electron Positron Collider (BEPC) is a machine with a designing energy up to 2.8 GeV. Thirty-two button-type beam position monitors (BPMs) are used for the position measurement of the colliding e ⁺e^- beams in the storage ring. In order to improve the measurement resolution and reduce the measurement time, the hardware and the software of the BPM system have been partially modified at last year and have been tested with beams. The BPM processing electronics and the measurement behavior can be fully controlled by a personal computer (PC) in the local control room. The measured beam position data are stored in the memory on another PC, which serves as a communication server. These data can be accessed by the main computer in the central control room through the network. The short-term reproducibility of the measurement is better than 10 microns. The measurement time for scanning all 32 BPMs is about 11 seconds. The reliability of the measurement is assured by the self-consistency check. The dynamic range of the system is over 81 dB and the minimum measurable beam intensity is less than 0.5 mA. This paper describes the hardware and the software of our upgraded BPM system. The performances of the BPM system are also given