Safety Instrumented System
A Safety Instrumented System is an independent system of sensors, logic, and final elements designed to move a process to a safe state when defined conditions occur.
What this term means in maintenance
A Safety Instrumented System is an independent system of sensors, logic, and final elements designed to move a process to a safe state when defined conditions occur.
Main elements
An SIS normally includes:
- Sensors
- Logic solver
- Final elements
- Power and communication
- Diagnostic functions
Practical example
High reactor pressure is detected, the safety logic processes the signal, and emergency valves move the process to a safe state.
Maintenance requirements
Maintenance may include calibration, proof testing, bypass control, diagnostics, final-element testing, and documentation.
Independence
The SIS should retain suitable independence from normal process control according to the design.
Common mistake
Testing only the input sensor without confirming logic and final-element operation may not prove the complete safety function.
How this term differs
Safety Instrumented System is the overall sensor-logic-final-element system used to move a process to a safe state. It is related to Safety Integrity Level, Emergency Shutdown System, and Interlock, but these terms describe different records, measures, roles, strategies, or decisions and should not be used interchangeably.
Related concepts
Related maintenance terms
Keep exploring connected CMMS, reliability, and maintenance planning terms.
Safety Integrity Level
Safety Integrity Level is a defined level of risk reduction assigned to a safety instrumented function.
Proof Test
A proof test is a planned test used to reveal hidden dangerous failures and confirm that a protective or safety function can perform as required.
Emergency Shutdown System
An Emergency Shutdown System automatically or manually moves equipment or a process toward a safe state during a defined hazardous condition.
Glossary FAQs
- What does SIS stand for?
SIS stands for Safety Instrumented System.
- What are the main SIS elements?
Sensors, logic solver, and final elements.
- How is SIS maintained?
Through calibration, proof testing, diagnostics, bypass control, final-element testing, and records.