The effect of transmission code and safety code on SIL in Safety-Critical System

This paper discusses the message model arming at safety-related communication (SRC) in railway safety-critical system (SCS), and analyzes the effect of transmission code and safety code on safety integrity level (SIL) of railway SCS & communication failures. It is found that system safety could not always be improved when transmission code is lengthened out. So the paper gives a new concept that is called safety effective length of transmission code (SELTC), provides its mathematical definition and calculation formula, points out its two important properties, and proves its rationality. The new concept is very helpful to analyze and design the SRC.