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Personnel Protection System (PPS) at SLAC is a global safety system responsible for protecting personnel from radiation hazards. The system’s functional design shares similar concepts with machinery safeguarding, though the complexity of PPS is much higher due to its wide geographic distribution, large numbers of devices, and multiple sources of hazards. In this paper, we will first introduce the multilayer distributed control system architecture of SLAC’s PPS, which serves three beam programs, e.g., LCLS, LCLS-II and FACET-II, that exist in the same 4km linear accelerator infrastructure. Composed of 50+ sets of redundant safety PLCs and 20+ access control PLCs, SLAC’s PPS has five layers: beam program, beam switching and permit, zone access control, zone safety control and sensor/shutoff subsystems. With this architecture, safety functions often involve multiple controllers across several layers, make it a challenge on system analysis, design, and testing. Therefore, in this paper, we will also discuss SIL verification, and PPS’s functional safety related issues for this type of complex systems.
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