Caracappa, A. Danneil, C. Della Penna, A.J. Fliller, R.P. Padrazo, D. Singh, O. JACoW Geneva, Switzerland 978-3-95450-177-9 10.18429/JACoW-IBIC2016-TUPG38 English 427-430 TUPG38 operation storage-ring PLC monitoring diagnostics Contribution to a conference proceedings 2017 2017-02 http://dx.doi.org/10.18429/JACoW-IBIC2016-TUPG38 http://jacow.org/ibic2016/papers/tupg38.pdf A requirement for top-off operations at the NSLS-II facility is at least 50mA stored ring current. The Stored Beam Current Monitor (SBCM) is part of the NSLS-II Personnel Protection System (PPS) that determines the storage ring current based on Pick-Up Electrode (PUE) readings. The SBCM selects the 500 MHz component of the PUE signal and downconverts it to about 2 MHz. The 2 MHz signal is rectified, averaged down to a bandwidth of 500 Hz, and compared to a threshold voltage equivalent to 55mA of stored beam. A redundant SBCM system was also constructed and these two systems must agree that the stored beam is above the threshold to enable top-off operations. The SBCM is also required to remain accurate over wide range of possible bunch patterns and bunch intensity distributions. Under normal conditions for top-off operations the SBCM measurement accuracy is about 1%. The SBCM was commissioned in 2015 as part of the Top-Off Safety System (TOSS) which is responsible for ensuring safe top-off operations at NSLS-II.