AiVibeSafety Instrumented System (SIS)
A safety instrumented system is an independent automation system of sensors, logic solvers and final elements that takes a process to a safe state when predefined conditions are violated, implementing one or more safety instrumented functions.
Each safety instrumented function (SIF) consists of sensors, such as pressure or level transmitters, a logic solver, typically a safety PLC certified for the application, and final elements such as shutdown valves or motor contactors. When a measurement crosses a trip point, the SIF acts, for example by closing a feed valve on high pressure. Voting arrangements such as one-out-of-two or two-out-of-three balance protection against dangerous failures with avoidance of spurious trips.
SIS are used in oil and gas, refining, chemicals, pharmaceuticals and power generation as one of several layers of protection, alongside the basic process control system, alarms with operator response, relief devices and physical containment. Emergency shutdown, burner management and high-integrity pressure protection systems are common examples.
IEC 61511 governs the SIS life cycle in the process industry, from hazard and risk assessment and SIL determination through design, installation, validation, operation, proof testing and modification; ANSI/ISA-61511 is its adoption in the United States. The SIS should be sufficiently independent of the basic process control system that a control system failure does not compromise the safety function. Bypasses, overrides and changes require formal management, and work on an SIS must be carried out by competent personnel under site procedures.
Key points
- Sensors, logic solver and final elements form each safety instrumented function
- Takes the process to a safe state when trip conditions are met
- One of several independent layers of protection
- IEC 61511 governs the SIS life cycle in the process industry
- Bypasses and modifications require formal management of change
Where AiVibe comes in
AiVibe designs and manufactures the AiAmbA AI Factory, whose edge devices and AI agents let people talk to PLC, CNC and robot controllers in plain language. Agents only propose changes, a trained operator confirms each one, and the AI Factory never replaces a machine's control or safety systems.
Related terms
- Safety Integrity Level (SIL)PLC & Industrial Control
- IEC 61508PLC & Industrial Control
- Functional SafetyPLC & Industrial Control
- Distributed Control System (DCS)PLC & Industrial Control
- Safety PLCPLC & Industrial Control
- Alarm Management (ISA-18.2)PLC & Industrial Control