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How to consider the safety problem

In the design of security PLC, want to consider to many factors, the need for special design of a lot of. For example: a secure PLC emphasizes more on internal diagnosis, combination of hardware and software, can make the equipment testing its working state at any time of discomfort; a secure PLC with software, to use a series of special technology, can ensure the reliability of the software; a secure PLC with redundant function, even a partial failure, also to maintain the system operation; a secure PLC also has a security mechanism applied, not allowed through digital communication interface to read and write data inside.
Electronic circuit analysis software of special diagnosis, careful, plus all possible failure testing integrity of the design, to ensure the safety of PLC has the ability to measure the internal element potential risk more than 99% of the failure. A failure mode, effects and diagnostic analysis (FMEDA) method has been guiding design, this method will point out how each element is caused by system failure, and tell you how the system should detect the failure. TUV engineer will personally perform failure test, think of it as a part of their certification process.
The safety of PLC and conventional PLC in different lies in: PLC security needs to be safe third party certification of professional bodies, meet the demanding of the safety and reliability of the international standard. We must thoroughly using a systems approach, to design and to test the safety of PLC. Germany's TUV experts and American FM experts will verify and validate the security provided to PLC design and testing process, the independent third party.
The strict international standards of software used in safety PLC. These standards require special technology, avoid complexity. Further analysis and testing, and carefully check the operating system task interaction. This test consists of interactive operation in real time, such as multi task (when used) and interrupt. Also the need for a specific diagnosis, called "program flow control" and "data validation". Program flow check can ensure the basic functions can be executed in the proper order, the key data confirm that all data redundancy is stored in a memory, and the validity of this test before use. In the software development process, a secure PLC need additional software testing technology. In order to verify data integrity checks, must execute a series of "software fault injection testing, also is the human" the program vandalism, response to check whether PLC is running in safe mode is expected. Design and test software with detailed documentation, such third party inspectors will be able to understand the working principle of PLC, and the majority of software development without the use of the standard operating procedures, which also happens to explain why many garbage software will appear so many bugs cannot be found.

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