Safety instrumented systems: the boundary between control and protection
Basic SIS and SIF concepts, independence, SIL targets, proof testing, bypasses, and the questions to answer before connecting safety to a control system.
Safety instrumented system (SIS)
Independent protective system that detects hazards and trips safely.
A safety instrumented system (SIS) uses sensors, a safety logic solver, and final elements to detect hazardous conditions and drive the process to a safe state. One SIS can implement multiple independent safety instrumented functions.
See also: Safety instrumented function (SIF) · IEC 61511 · SIL
Use the concept: 4–20 mA loop scaling · Compressed air leak cost calculator · Engineering unit converter
In depth
Hazardous area classification, explained
Zones, divisions, gas groups and temperature classes decide which equipment may sit in a classified area. IP and NEMA ratings answer a different question.
PLC analog input scaling: raw counts, 4–20 mA and diagnostics
Map raw counts into engineering units, check the configured channel range, and keep signal-quality diagnostics separate from the displayed value.