ISA-TR5.1.01/ISA-TR77.40.01:2012(R2016)

ISA-TR5.1.01/ISA-TR77.40.01-2012 (R2016), Functional Diagram Usage, provides detailed guidance on the usage of functional diagrams for documenting application software in process control systems. It extends ANSI/ISA-5.1-2024 by offering practical examples and expanded symbol sets to represent both traditional and advanced control algorithms, including multivariable and adaptive controllers. This report covers definitions, symbol standards, diagram preparation methods, layout conventions and use-case examples such as single loops, two-element loops, cascade loops, motor-operated valve logic and motor breaker logic. It emphasizes clarity in representing control strategies independent of hardware specifics, supporting communication among engineers throughout system design and lifecycle stages. Annexes provide historical context, references and comprehensive symbol tables correlating ISA and ISO standards. The document aims to standardize and improve the understanding and documentation of control system functions using functional diagrams.