A safety PLC differs from conventional PLCs in that it needs to be certified for safety by a third-party professional organization and meet stringent international standards for safety and reliability. There is a need for a thorough systematic approach to the planning and testing of safety PLCs. TUV*** in Germany and FM*** in United States provide independent third-party validation and validation of the planning and testing process for safety PLCs.
The safety programmable logic manipulator (PLC) is designed for special purpose machines and equipment for critical handling and safe applications. These manipulators are often part of the Safety Appearance System (SIS) and are used to detect potential risks in process industry environments. Once a risk is detected, the SIS program automatically switches the process to a safe posture. Speaking of which, the user may have a series of questions: How does a conventional PLC compare to a safety PLC after so many years of successful use? Why can't conventional PLCs be used in critical handling and safety applications?
A safety PLC is specially planned to accomplish two important objectives:
1. The system will not fail (redundant operation methods are selected), even if the failure of components is unavoidable;
2. The failure is within the guessable range, and once it fails, the system will enter a safe form.
There are many factors to take into account when planning a safety PLC, and a lot of special planning is required. For example, a safety PLC emphasizes internal diagnosis, combined with hardware and software, which can allow the equipment to detect the discomfort of its own operation status at any time; A safety PLC has software, which requires a series of special skills to ensure the reliability of the software; A safety PLC has a redundant function, even if a part of it fails, it can keep the system running; A safety PLC also has an additional security mechanism that does not allow the internal data to be read and written at will through the digital communication interface.
A safety PLC differs from conventional PLCs in that it needs to be certified for safety by a third-party professional organization and meet stringent international standards for safety and reliability. There is a need for a thorough systematic approach to the planning and testing of safety PLCs. TUV*** in Germany and FM*** in United States provide independent third-party validation and validation of the planning and testing process for safety PLCs.
Special electronic circuitry, detailed diagnostic software analysis, and integrity planning to test all possible failures ensure that the safety PLC has the ability to determine more than 99% of the potential risk failures of internal components. Planning is guided by a failure mode, effect, and diagnosis analysis (FMEDA) approach that indicates how each component caused the system failure and tells you how the system should detect the failure. TUV engineers perform failure testing as part of their certification process.
Stringent international standard software is used in safety PLCs. These standards require special skills and avoid complexity. Take a closer look at the mission interactions of the operating system with further analysis and quizzes. This type of test involves real-time interactions, such as multi-mission (when applied) and abort. A special type of diagnosis is also required, known as "program flow manipulation" and "data confirmation". Program flow viewing ensures that basic functions are performed in the correct order, data confirmation enables all critical data to be stored redundantly in memory, and validity tests are performed before use. In the software development process, a safety PLC requires additional software testing skills. In order to verify the integrity of the data, it is necessary to perform a series of "software failure injection" tests, i.e., deliberate damage to the program to see if the PLC's response is operating in the estimated safe way. Software planning and testing comes with specific documentation so that third-party viewers can understand how the PLC works, and most software developers don't use this standard operating process, which is why so many bugs of unwanted software go undetected
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