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SIL (Safety Integrity Level) – Safety integrity level. The SIL technical standards were first established by the International Electrotechnical Commission (IEC), with IEC/TC65 being responsible for their implementation. The standardization technical committee responsible for SIL technology is the \"National Standardization Technical Committee for Process Industry Measurement, Control, and Automation\" (SAC/TC124), with the Secretariat located at the Comprehensive Technical and Economic Research Institute for Instruments and Meters in the machinery industry. SIL certification is divided into 4 levels in total: SIL1, SIL2, SIL3, and SIL4, covering both the product and system levels. Among them, the requirements for SIL4 are the highest. IEC61511, the functional safety requirement for safety instrumented systems, is a standard specifically designed for the functional safety of such systems in the process industry. It is a sector-specific standard issued by the International Electrotechnical Commission following the basic functional safety standard IEC61508. The equivalent standard for IEC61511 in China is GB/T 21109. In the process industry, instrument safety systems are used to carry out instrument safety functions, and the IEC61511 standard addresses the issue of what levels of safety integrity and performance instruments should achieve. For verifying the safety functions of safety-related devices, the SIL level is a safety integrity definition method that is widely recognized globally. For the process control industry, the main relevant international standards are IEC 61508 (the standard that serves as the basis for designing and operating safety instrumented systems). IEC 61511 focuses on systems used in process control applications; device designers follow IEC 61511 while also adhering to IEC 61508 when carrying out their designs.