How to Choose the Best Safety PLC for Your Industry


Implementing safety instrumented systems (SIS) in compliance with IEC 61511 necessitates careful planning, particularly when choosing a safety programmable logic controller (PLC).

How to Choose the Best Safety PLC for Your Industry

This comprehensive manual will delve into critical concerns and queries to ensure your safety PLC’s optimal performance and reliability. We will look at the differences between safety PLCs and standard PLCs, as well as the selection criteria and the latest advancements in safety PLC technology.

How do you compare Safety PLC and Standard PLC?

Safety PLC vs. Regular PLC: Understanding the Difference

Performance vs. Safety Integrity Level (SIL)

  • Standard PLCs are primarily intended for use in routine control applications. They are categorized depending on parameters such as program capacity, I/O handling, communication speed, and overall processing speed.
  • On the other hand, safety PLCs prioritize Safety Integrity Level (SIL) capabilities, dependability, and fault tolerance over performance criteria. Choosing the needed SIL level (SIL 1, SIL 2, or SIL 3) is an important first step in selecting a safety PLC for a new SIS or an extensive upgrade project.

What’s right for you? PLC or Safety PLC?

Complex Functions and Communication

  • Safety PLCs excel at controlling a wide range of Safety Instrumented Functions (SIF). They efficiently handle complex logic, sequences, and time delays, making them useful for applications where relays or hard-wired logic would be too complex. 
  • Furthermore, safety PLCs can use serial communication lines to provide data and warnings to control systems and operator workstations. This feature ensures that the safety system can deliver beneficial diagnostics to the control layer while maintaining its integrity.

How to choose a Safety PLC?

  • To decide if a safety PLC or a conventional PLC is best for your project, evaluate the trade-offs between safety, complexity, and expense. There is no one-size-fits-all answer; the optimum alternative is determined by your unique circumstances and preferences. 
  • Generally speaking, a safety PLC is the way to go if your project has high safety needs or dangers and you are willing to spend more for a trustworthy system. 
  • A normal PLC, on the other hand, is the preferable choice if your project has minimal or moderate risk requirements or hazards and you need a functional system. If your project requires a mix of safety and complexity, you may need to use both types of PLCs to optimize performance and cost.

Programmable Logic Solver Systems and Software Suppliers: Navigating the Options

Diverse Options

  • Various suppliers offer SIL-capable safety PLC logic solvers on the market. These range from single-channel to triplicated configurations designed for excellent availability and safety. 
  • When evaluating possibilities, it is critical to thoroughly evaluate application needs and select a supplier who not only meets technical specifications but also provides extensive assistance.

Key Questions for Suppliers

When assessing potential suppliers, consider asking the following questions:

  • What is the system’s claimed SIL capabilities (e.g., SIL 1, SIL 2, or SIL 3)?
  • Who accomplished this system’s SIL capability certification (exida,  TÜV Rheinland, etc.)?
  • What level of Hardware Fault Tolerance (HFT) is required to meet the claimed SIL capability?
  • How are cybersecurity requirements assured with the safety PLC?
  • Can the supplier provide a functional safety manual conforming to IEC 61508-2 edition 2 Annex D?
  • Is there a sister control system (BPCS) with authorized communications links for the SIS logic solver?
  • Are there any hardware or software application program limitations that must be implemented in order to achieve the stated SIL?
  • What utility software is needed to configure and/or compile the application program?
  • What is the SIS logic solver’s programming language (e.g., Function Block Diagram / Ladder / Other)?
  • What are the system’s ongoing proof test requirements?

Support and General Questions for Suppliers: Ensuring Long-Term Success

Ensuring Ongoing Support

The long-term success of a safety PLC system relies on adequate support. Consider the following questions when assessing support:

  • How is the system & software supported in your region?
  • What kind of specialized training is required to program the system?
  • What kind of specialized training is required to maintain the system hardware?
  • Do you have any recommendations for third-party integrators who can configure the system?
  • Do you provide direct configuration / programming support for the system?
  • How long do you plan to support this system?
  • Do you have a functional safety management system (FSMS) for SIS project implementation?

User Reviews and Testimonials

  • While technical specifications are important, user experiences can provide useful information. 
  • Seek user evaluations or testimonials from businesses that have successfully implemented the safety PLC of choice. 
  • Case studies from the real world can demonstrate practical applications and outcomes.

Safety PLC/Logic Solver Suppliers List (2023): Exploring Reputable Options

Explore offerings from reputable suppliers such as ABB, Emerson, GE, Hima, Honeywell, Pilz (machinery safety), Rockwell, RTP, Schneider, Siemens and Yokogawa.  Each supplier brings unique strengths and a global presence to the market. 

Industry-Specific Considerations: Tailoring Solutions to Your Needs

  • Consider the unique needs of different industries (e.g., manufacturing, oil and gas, chemical) when choosing a safety PLC. 
  • Emphasize industry-specific requirements to ensure the selected system aligns with the demands of your sector.

Emerging Technologies: Staying Ahead of the Curve

Regulatory Compliance: Meeting Standards beyond IEC 61511

  • Emphasize the significance of selecting a safety PLC that not only complies with IEC 61511 but also with industry-specific standards and regulations. Regulatory compliance is critical for both legal and operational reasons.
  • These PLCs meet the required safety standards, achieving up to PL(performance levels ) “e” according to ISO 13849-1:2023 or SIL 3 according to IEC 61508.

Scalability: Adapting to Future Needs

Address the scalability of the safety PLC system. Consider how well the system can accommodate future expansion and adapt to evolving safety needs within your organization. A scalable solution ensures long-term viability and flexibility.

Cost Considerations: Balancing Performance and Budget

Discuss the cost factors associated with safety PLCs. While performance and reliability are paramount, it’s essential to balance these factors with budget constraints. Understanding the total cost of ownership is crucial for making informed decisions.

User-Friendly Interface: Streamlining Operation and Maintenance

  • Highlight the importance of a user-friendly interface in the selection process. An intuitive interface contributes to ease of programming and system configuration, streamlining operation and maintenance processes.
  • Safety-functionality modifications can be simply implemented through programming rather than device replacement and associated rewiring. 

Training and Education: Maximizing System Potential

Discuss the availability of training programs and educational resources offered by the supplier. Adequate training ensures that users can maximize the potential of their safety PLC investment, reducing the risk of operational issues.


  • In conclusion, choosing a safety PLC involves a multifaceted approach, considering technical specifications, user experiences, industry-specific needs, and future trends. 
  • The safety PLC is a pivotal component in ensuring the safety and reliability of your systems, but success also depends on factors such as supplier support, regulatory compliance, and scalability. 
  • By carefully navigating these considerations, decision-makers can select a SIL-capable safety PLC that not only meets current requirements but also adapts to the dynamic landscape of industrial safety.

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Sundareswaran Iyalunaidu

With over 24 years of dedicated experience, I am a seasoned professional specializing in the commissioning, maintenance, and installation of Electrical, Instrumentation and Control systems. My expertise extends across a spectrum of industries, including Power stations, Oil and Gas, Aluminium, Utilities, Steel and Continuous process industries. Tweet me @sundareshinfohe

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