ISA 5.4 : 1991

1 Purpose
2 Scope
3 Applications
  3.1 Serve many purposes
  3.2 Design
  3.3 Construction
  3.4 Start-up
  3.5 Operation
  3.6 Maintenance
  3.7 Modification
4 Definitions
5 Content
6 Format
7 Symbols
  7.1 Instrument connection and action information
  7.2 General terminal of bulkhead symbol
  7.3 Instrument terminals or ports
  7.4 Instrument system energy supply
  7.5 Identification of instrument action
8 Examples

ISA-5.4-1991, Instrument Loop Diagrams, provides a framework for creating and using instrument loop diagrams in various industries such as chemical, petroleum and power generation. It emphasizes the importance of these diagrams for design, construction, operation, maintenance and modification of instrumentation systems. It outlines the minimum content requirements for loop diagrams, including the identification of components, interconnections, energy sources and process lines. ISA-5.4 also discusses optional information that can enhance the effectiveness of the diagrams. It aims to improve communication between technical and non-technical personnel and to encourage participation in the standards development process. Additionally, it acknowledges the need for consistency in format and symbols used in the diagrams, referencing ISA-5.1 for instrumentation symbols and identification.