The technical report, ISA-TR5.1.01-ISA-TR77.40.01-2012, Functional Diagram Usage, expands upon and illustrates usage of function block symbols and functions, and prepares examples in development of complex function block symbols and functions.


The purpose of this technical report is to provide advice and guidance in documenting application software through functional diagrams.

A Word from the Chairman

This report is an extension of ANSI/ISA-5.1-2009, Instrumentation Symbols and Identification. The intent of this report is to provide further information and practical examples on the usage of Functional Diagrams for documenting application software. In addition, the intent of this report is to illustrate the similarities and differences between ISA and ISO symbols and functional diagrams. It is hoped that this report will be a handy reference to design engineers who are directly involved in the generation or review of function diagrams.

Functional diagrams were first employed when discrete and electric analog control systems were designed. Professional societies such as Scientific Apparatus Makers Association (SAMA), ISA, and ISO provided guidelines as to industry usage of functional diagrams. The popular but older standards: PMC 22.1-1981, Functional Diagramming of Instrument and Control Systems; ISA 5.2-1976, Binary Logic Diagram for Process Operation; and ISO 3511, Graphical Symbols for Diagrams are available for industry use. The work within this technical report maintains historical practices while expanding on new algorithms and practices.

For more information, please contact the subcommittee chairman Dan Lee, or Eliana Brazda, ISA Standards Administrator, via or phone (919) 990-9228.