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 function (SIF)
One defined protective action with a target safety integrity.
A safety instrumented function (SIF) is a specific protective action — for example, high pressure causes a valve to close — with defined sensors, logic solver, final elements, response time, proof-test strategy, and required SIL.
See also: Safety instrumented system (SIS) · SIL · IEC 61511
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.