I. Standards Framework
What to look for in the standards framework.
Based on functional safety standard practices, the framework can be viewed through these six aspects: Foundation—IEC 61508 (Functional safety of electrical/electronic/programmable electronic safety-related systems; the foundational standard for the entire functional safety standard family); SIL—Safety Integrity Level (a discrete level—one of four possible levels—used to specify safety integrity requirements for safety functions assigned to electrical/electronic/programmable electronic safety-related systems; SIL 4 is the highest, SIL 1 the lowest); Probability—Safety integrity is the probability that a safety-related system will successfully perform the required safety function under specified conditions and within a specified time (IEC 61508 defines the SIL concept to quantify safety integrity); Attribute—SIL is an attribute of a safety function; Machinery—IEC 62061 (Functional safety of safety-related electrical, electronic, and programmable electronic control systems for machinery; directly adopts IEC 61508 principles—though some terminology differs to suit the machinery safety sector, it employs the same safety lifecycle principles and risk-based approach); Relationship—PL (Performance Level) for EN/ISO 13849-1 and SIL (Safety Integrity Level) for EN/IEC 62061 (mapping: a = no correspondence, b = SIL 1, c = SIL 1, d = SIL 2, e = SIL 3); Alignment—IEC 62061:2021 specifies requirements and recommendations for the design, integration, and validation of safety-related control systems (SCS) (applicable to control systems used—individually or in combination—to perform machine safety functions). This six-point framework provides a clear overview: IEC 61508 foundation, four SIL levels, probability of success, SIL as an attribute, IEC 62061 for machinery, and the correspondence between PL and SIL.
II.
Certification Levels
What to look for regarding certification levels.
Regarding safety PLC certification levels, the classification is understood as follows: PL (Performance Level)—represents a quantitative indicator of safety system reliability (levels a through e, with PLa being the lowest and PLe the highest; corresponding to hazard severity: minor risk PLa/PLb, moderate risk PLc, high risk PLd, extremely high risk PLe); Mandatory—EU spot checks currently mandate a minimum of PLd for high-risk equipment such as industrial automation systems, stamping presses, cutting machines, and robotic arms (higher risk necessitates higher architectural and PL levels); Common—Common safety PLC certification levels include SIL 3 (per IEC 61508), SIL 3 (per IEC 62061), and PL e (per ISO 13849-1; e.g., ABB AC500-S certified by TÜV SÜD Rail GmbH); Machinery—Rockwell ControlLogix CIP Safety I/O meets relevant standards (Cat. 4/PL e per EN ISO 13849-1; SIL 3 per IEC 61508; suitable for safety-related applications up to Cat. 4/PL e; Rockwell certificate 968/FSP 1806.02/24); Combination—GuardLogix 5570 controllers used with safety partners comply with SIL 3/SC 3 (per EN 61508) and PL e/Cat. 4 (per EN ISO 13849-1) (also refer to EN IEC requirements, EN 61131-2:2007 clauses 6.1–6.3 and 8, IEC 61131-2:2017, and Rockwell EC Type-Examination Certificate); Dual Standard—Fail-safe S7-1200 controllers can be used for safety tasks meeting SIL 3 (IEC 61508) and PL e (ISO 13849-1) (safety-related programs created in TIA Portal, STEP 7).
Safety configuration tools utilize LAD and FBD languages; regarding relays—the 3SK2 safety relay is designed to enable applications compliant with IEC 62061 (SIL 3) and ISO 13849-1 (PL e/Cat. 4) standards (Siemens equipment manual). The “Six Aspects of Safety Levels” cover: PL a–e ratings, the EU’s mandatory PL d requirement, SIL 3 combined with PL e, Cat. 4/PL e, dual-standard certification, and safety relay classification—providing clear definitions of these safety levels.
III.
Certification Details
What to look for regarding certification details.
Regarding the practical aspects of SIL certification, the key points are as follows: **Levels**—SIL certification comprises four levels, SIL1 through SIL4 (covering both product and system levels, with SIL4 having the most stringent requirements); **Content**—Functional safety certification primarily involves FSM (Functional Safety Management) assessment regarding documentation for safety equipment development processes, hardware reliability calculation and assessment, software assessment, environmental testing, and EMC (Electromagnetic Compatibility) testing; **Jurisdiction**—The national technical committee responsible for SIL technology standardization is SAC/TC124 (National Technical Committee on Industrial Process Measurement and Control and Automation; the secretariat is hosted by the Institute of Instrumentation Technology & Economy of Machinery Industry); **Process**—The certification process involves a manufacturer seeking compliance with IEC 61508, an independent entity (CB) reviewing the manufacturer’s efforts, and an accreditation body (AB) verifying the CB’s review practices (the process begins with the manufacturer establishing a business case for producing items capable of achieving a specific SIL—usually SIL2 or SIL3—followed by planning and development in accordance with IEC 61508 requirements); **Basis**—SIL certification is based on the IEC 61508 standard (adopted as GB/T in China); **Verification**—A higher Safety Integrity Level implies a higher probability that the required safety function will be successfully executed (depending on the mode of use of the safety-related system); **Certificates**—Certification is issued by third-party bodies (e.g., TÜV SÜD Rail GmbH, Rockwell certificates, EC Type-Examination Certificates). In summary, there are six key aspects: product and system levels, FSM documentation assessment, SAC/TC124 jurisdiction, CB review and AB verification, adherence to IEC 61508, and third-party certification.
IV.
Architectural Requirements
What to look for regarding architectural requirements.
Based on safety PLC architecture practices, the architecture is evaluated across six aspects: Independence—logic controllers are set up independently (SIL1 Safety Instrumented Functions [SIF] may share hardware with the Basic Process Control System [BPCS], whereas logic controllers for SIL2 and SIL3 SIFs must be separated from the BPCS; per Yunnan Provincial Department of Emergency Management guidelines); Redundancy—logic controllers are configured with redundancy (logic controllers for SIFs must be redundant; the level of redundancy must satisfy Safety Integrity Level [SIL] verification and calculation requirements; per Yunnan Provincial Department of Emergency Management); Compliance—logic controllers must meet SIL requirements (they must independently execute SIFs; per Yunnan Provincial Department of Emergency Management); Safety Functions—Mitsubishi QS safety PLCs comply with international safety standards (EN954-1 Category 4, ISO13849-1 PLe, IEC61508/JIS C 0508 SIL 3; capable of connecting to devices like emergency stop switches and light curtains to cut off power to hazard sources; per Mitsubishi Electric); STO—STO electronically cuts off the energy supply driving the servo motor (Mitsubishi safety function); SS1—SS1 controls motor deceleration to a stop, followed by STO (Mitsubishi); SS2—SS2 controls motor deceleration to a stop, followed by SOS (SOS monitors the stopped state without cutting off motor drive energy; SLS monitors robotic arm components to ensure speeds do not exceed limits; SLP monitors positions to ensure limits are not exceeded; per Mitsubishi)—The six architectural aspects—SIL2/3 independence, redundant controllers, compliance with SIL requirements for independent execution, hazard source cutoff, STO/SS1/SS2, and SLS/SOS/SLP—ensure architectural reliability.
V.
Model Selection and Implementation
What to consider for model selection and implementation.
Regarding the practical implementation of safety PLC selection, the approach involves six key aspects: **Selection**—Choosing Siemens SIMATIC S7-1500F/S7-1200F models based on safety standards (IEC 61508 SIL concepts, IEC 62061 machinery safety standards, Siemens Download Center); **Interfaces**—Connecting safety PLCs to devices like emergency stop switches and light curtains (cutting off hazard sources such as robot power, safety output OFF, Mitsubishi QS); **Combinations**—Using MSR100 series safety relays that comply with relevant standards (Cat. 4/PL e per EN ISO 13849-1; up to SIL 3 per EN IEC 62061/EN 61508; suitable for PL e and SIL 3 applications; Rockwell certification); **Training**—Functional safety engineer training (ISO 13849 safety-related parts of control systems; IEC 62061 functional safety of safety-related electrical/electronic/programmable electronic control systems; hazard identification and risk assessment per ISO 12100; UL Solutions); **Verification**—Conducting SIL verification for a Safety Instrumented Function (SIF) when its SIL rating is 1 or higher (requirements include meeting architectural constraints, calculating the average probability of failure on demand [PFDavg] to meet SIL report criteria, ensuring system capability meets SIL requirements, and addressing key factors influencing verification); and **Regulations**—Adhering to guidelines for Safety Instrumented Systems in the chemical industry (e.g., independent and redundant logic controller setups; Yunnan Provincial Department of Emergency Management). These six aspects ensure a feasible implementation strategy.
Conclusion
What are the safety PLC certification requirements for non-standard assembly lines?
The conclusion is that they are defined across five dimensions: framework, rating level, content, architecture, and practical implementation standards.
Framework—The IEC 61508 basic standard defines Safety Integrity Levels (SIL 1–4); IEC 62061 covers machinery safety (SIL) alongside ISO 13849-1 (PL a–e), with corresponding levels (PL d maps to SIL 2, PL e to SIL 3). Ratings—Common safety PLC certifications include SIL 3 (per IEC 61508/IEC 62061) and PL e (per ISO 13849-1, Cat. 4/PL e); EU spot checks mandate a minimum of PL d for high-risk equipment (e.g., stamping and cutting robotic arms). Scope—SIL certification covers two levels (product and system) and includes FSM assessment (development process and documentation management), hardware reliability calculations, software assessment, environmental testing, and EMC testing; it is administered by SAC/TC124 and involves third-party CB certification (e.g., TÜV). Architecture—SIL 2 and SIL 3 safety logic controllers are separated from Basic Process Control Systems (BPCS); features include redundant logic controllers, independent execution of Safety Instrumented Functions (SIF), safety functions (STO, SS1, SS2, SLS, SOS, SLP), and integration with E-stops and light curtains to cut power to hazard sources. Implementation—Component selection follows IEC 61508, IEC 62061, and ISO 13849-1 (e.g., S7-1500F/S7-1200F, GuardLogix, AC500-S, QS) with matching safety relays; SIL verification addresses architectural constraints, PFDavg calculations, and system capability;
functional safety training incorporates ISO 12100 risk assessment.
Industry Summary—Safety PLC certification in a nutshell: the “trio” of standards (IEC 61508, IEC 62061, ISO 13849-1), SIL 3 and PL e ratings, five key areas for CB certification, and redundant, independent power cutoff—master these four checkpoints, and certification is assured.
