1756-RM001B-EN-P, Using ControlLogix in SIL2 ... - Tuv-fs.com

8-2 General Requirements for Application SoftwareSIL2 ProgrammingSafety Concept of the ControlLogix systemThe safety concept of SIL2 assumes, that:• the programming system (PS) hardware and firmware workscorrectly (that is, programming system errors can be detected).• the user applies the logic correctly, that is, user programmingerrors can be detected.For the initial start-up of a safety-related ControlLogix system, theentire system must be checked by a complete functional test. After amodification of the application program, the modified program orlogic must be checked.For more information on how users should handle changes to theirapplication program, see the Changing Your Application Programsection on page 9-6.General Guidelines forApplication SoftwareDevelopmentThe application software for the intended SIL2 systems is intended tobe developed by the system integrator and/or user. The developermust follow good design practices including the use of:• Functional specifications• Flow charts• Timing diagrams• Sequence charts• Program review• Program validationAll logic should be reviewed and tested. To facilitate reviews andreduce unintended responses, developers should limit the set ofinstructions to basic Boolean/ladder logic (such as examine On/Off,Timers, Counters, etc.) whenever possible. This set should includeinstructions that can be used to accommodate analog variables, suchas:• Limit tests• Comparisons• Math instructionsSee Appendix B, System Self-Testing andUser-Programmed Responses, for details.Publication 1756-RM001B-EN-P - October 2003