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.

The 2024 revision

The 2024 revision of this standard changed the title from “Instrumentation Symbols and Identification” to “Instrumentation and Control Symbols and Identification” to emphasize that symbols for control are also included. This revision was published with significant changes to improve the readability of the document by organizing notes with corresponding tables; simplifying table numbering; providing definition consistency and clarification; eliminating redundant text; by adding new symbols, recognizing alternate symbols, notation and identification for new automation technology; adding new sections for normative reference, abbreviation and bibliography; and adding the loop instrument diagrams symbol table. The changes made in the 2024 revision are listed in Annex A of that document.

This revision moved nonmandatory Annex A and Annex B from the 2022 revision into separate technical reports for easier maintenance and to reduce the size of the standard. The new technical reports are ISATR5.1.02, “Instrumentation and Control Identification System Guidelines,” and ISA-TR5.1.03, “Instrumentation and Control Graphic Symbols Guidelines.” These TRs provide examples and information on the application of requirements in the standard. Examples in these TRs were updated with additions, revisions and deletions. The changes made in these TRs are listed in Annex A of the respective document. Users are encouraged to read and use these TRs together with the standard.
 

Looking ahead

The plan for the ISA5.1 Working Group of the ISA5 committee is to now develop a technical report on instrumentation and control content of PFDs and P&IDs. While ISA5.1 deals with instrumentation and control content on various engineering drawings—including PFDs and P&IDs—this new TR will provide guidance and examples specific to PFDs and P&IDs. This will include guidance to help users decide on the level of detail of instrumentation and control they want to show on their PFDs and P&IDs and what information should be provided at a minimum.

The updated ISA5.1 standard and its accompanying ISA technical reports are available for purchase online. Anyone interested in participating in the ISA5.1 Working Group is asked to contact ISA Standards (standards@isa.org). For information on obtaining any of ISA standards documents and reports, visit www.isa.org/findstandards.

This feature originally appeared in the October 2024 issue of InTech digital magazine.