Tuesday, February 8, 2011

Functional Specification of SFC Implementation





Allen Bradley recommends that you develop a specification design for your programming application. The specification of design is a conceptual view of your application and is used to determine your SFC (Sequential Function Chart) and ladder logic requirements.

The design activity is begun with the functional specification and move on to the detail analysis. Based on the detail analysis, you can enter your programs and test them. When testing is complete, you are ready to implement the programs in your application.

This model also allows for interaction of the activities at the different levels. The detailed analysis can be used as the basis for developing your testing requirements and procedures. Because the functional specification is good thought out, it can be used as the program sign off document.

Not all machine processes can be controlled with an SFC implementation; the following description of the program development model is generalized to fit most processes. The SFC power is that it is a descriptive programming language that you can use to describe your process in terms of machine states and transition conditions. Because this description executes your control of process, your SFC provides the link between these two legs of the model development.

The specification of functional represents a very general view of your process or a description of operation. Identify the events and the overall order in which they have to occur. This specification of functional can be in any form: written statement, flowcharts, or rough draft SFC (Sequential Function Chart). Use the form that is most familiar to you. Allen Bradley recommends that you’re beginning diagrams and your finished program.

If you are using new platform or Secure PLC-5 processor, you also determine the number of Main Control Programs (MCPs) and the programming method for each during this phase. Use MCPs when you are describing your process in terms of function or in terms of geography. You can break down those functions into ladder programs, structure text, or sequential function charts (SFCs).



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