What is Control Reliability?

Q. What is Control Reliability from ANSI B11.26 and how do I compare it to ISO 13849-1 Performance Levels and Categories or IEC 62061 Safety Integrity Levels?


Control reliability is an important concept used in ANSI B11.26. It describes the control system’s ability to remain in a safe state in the event of a component failure. Safety related parts of control systems must conform but it can be confusing to understand how to achieve it and how performance levels and categories are related.


Control Reliability is defined in B11.26:2018 as:


“The capability of the machine control system, the engineering controls – devices, other control components and related interfacing to achieve a safe state in the event of a failure within their safety-related functions.”


In effect it says that the safety related parts of the control system must always fail to safe, ensuring that a single failure in any part will not result in an unsafe situation. However, in order to get wider understanding of what this means, it is important for anyone applying B11.26 to look for the informative note in clause 5.4.3. This gives a more quantitative way to define if a system meets control reliability by using the Category or Performance Level:


“While the requirements of control reliability are not directly comparable to the requirements of ISO 13849-1, for the purposes of this standard, complying with Category 3 or 4 and/or Performance Level d or e, at a minimum, will satisfy the requirements of control reliability.”



All Fortress product ranges therefore meet the requirements of control reliability with independent certification from TUV across all the ranges. Fortress’ mGard is the only range of mechanical interlocks independently certified to PLe applications. Get in contact with your local Fortress representative to find out more.


If you want to learn more about this or any other concepts in ANSI B11 standards, check out our Licensed Machinery Safety Specialist course specific to US standards on machinery safety.



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