Document Projects Consistently with the Updated ISA5.1 Standard

In project documents used to specify, purchase, track, install and maintain instrumentation and control system components, consistency is important. The International Society of Automation (ISA) has long known that and supported such consistency through its standards. Seventy-five years after it was first introduced, ISA has published an update of its most widely used and internationally recognized standard: ANSI/ISA-5.1: Instrumentation and Control -Symbols and Identification.

This standard provides symbols, both basic and non-basic, for binary operating functions. It is intended to symbolize the binary operating functions of a system in a manner that can be applied to any class of hardware, whether it be electronic, electrical, fluidic, pneumatic, hydraulic, mechanical, manual, optical or other. It provides a method of logic diagramming of binary interlock and sequencing systems for the startup, operation, alarm and shutdown of equipment and processes.

The symbols and identification methods outlined in the standard are intended as conceptualizing aids, design tools and teaching devices. They are concise and function as a specific means of communication for all types and kinds of technical, engineering, procurement, construction and maintenance documents. This includes identification schemes and graphic symbols for drawings and documentation systems used in the construction and maintenance of industrial plants, including instrumentation and control diagrams, loop diagrams, electrical schematics and functional and binary logic diagrams.

A common misconception is that this standard is a piping and instrument diagram (P&ID) standard. Although it does cover the instrumentation and control portion of P&IDs and process flow diagrams (PFDs), it does not cover the piping, mechanical and other aspects of these drawings.
 

A long and proud history

The symbols and identification systems described in this standard accommodate advances in technology and reflect the collective industrial experience gained since the original 1949 ISA recommended practice, RP-5.1, was revised, affirmed and subsequently published as ANSI/ISA5.1-1984. The 1949 recommended practice and the 1984 standard were published as nonmandatory rather than as mandatory consensus documents.

The 1992 revision was published with mandatory and nonmandatory requirements. It incorporated key elements of ISA5.3-1983: “Graphic Symbols for Distributed Control/Shared Display Instrumentation, Logic and Computer Systems.”

The 2009 revision was published with significant changes as technological advances resulted in the evolution from a hardware (instruments)-centric standard to a hardware/software (automation)-centric standard. Key elements of ISA5.2-1976: “Binary Logic Diagrams for Process Operations” were incorporated. Binary logic symbols of Scientific Apparatus Makers Association (SAMA) PMC 22.1-1981: “Functional Diagramming of Instrument and Control Systems” were also incorporated. Graphic symbol dimension tables were incorporated to establish minimum mandatory dimensions for the symbols.

Nonmandatory examples were moved to a new Annex B: “Graphic symbol guidelines” (Informative) to provide some limited assistance in the application or were removed for inclusion into future technical reports to provide special practices and requirements of particular interest groups and/or specific industries.