ISO 3511-3:1984

Overview

ISO 3511-3:1984 - "Process measurement control functions and instrumentation - Symbolic representation - Part 3: Detailed symbols for instrument interconnection diagrams" defines a comprehensive set of detailed graphical symbols used to show external connections between equipment units in process measurement and control systems. Part 3 complements ISO 3511/1 and 3511/2 by detailing components on interconnection diagrams (single-line or multi-line) and is intended for design, installation and maintenance drawings in the process industries. The standard does not replace electrical symbols of IEC Publication 117 and refers users to IEC Publication 113 Part 5 for guidance on preparing interconnection diagrams and tables.

Key topics and technical requirements

• Scope and purpose: Symbols are for interconnection diagrams that communicate external connections between instruments, not internal circuitry.
• Symbol categories:
  • Non‑converting instruments: indicators, recorders, counters, selectors.
  • Converting instruments: transmitters, converters, controllers, amplifiers, signal memory and computing relays.
  • Detectors: flow, temperature, level, pressure devices (nozzles, wells, insertion pipes, thermocouples, floats, electrodes, sonic/radioactive/photoelectric detectors).
  • Correcting units and actuators: valves, diaphragm/piston/solenoid/rotary/spring/float actuators and accessories (limit switches, lock-up, fail‑safe indications).
• Representation rules:
  • Single-line or multi-line diagrams allowed; can be combined with or replaced by tables if clarity is preserved.
  • Terminals may be placed on any basic symbol; contact symbols should be shown open by default.
  • Specific symbol orientation rules (e.g., closed-loop controller apex angle = 90°; arrow orientation indicates output action and remains vertical when rotated).
• Definitions: clear terms such as point of measurement, instrument, panel-mounted vs locally-mounted instrument, correcting unit, actuating element, set value and interconnection diagram.

Applications and who uses it

ISO 3511-3 is practical for:

• Instrumentation and control engineers creating P&IDs and interconnection/wiring diagrams
• Process design and automation teams specifying field device connections
• Draftsmen and CAD specialists standardizing technical drawings
• Maintenance and operations personnel interpreting control system layouts
• Suppliers and contractors producing consistent documentation for installation and commissioning

Benefits include improved clarity, reduced misinterpretation, and consistent cross-discipline communication in process measurement and control documentation.

Related standards

• ISO 3511-1 (Basic requirements)
• ISO 3511-2 (Extension of requirements)
• ISO 3511-4 (Process computer/interface symbols)
• IEC Publication 117 (Recommended graphical symbols)
• IEC Publication 113 Part 5 (Preparation of interconnection diagrams and tables)

Keywords: ISO 3511-3, instrument interconnection diagrams, symbolic representation, process measurement, control instrumentation, P&ID symbols, detectors, actuators.