ISO 3511-2:1984

ISO 3511-2:1984 - Overview

ISO 3511-2:1984, "Process measurement control functions and instrumentation - Symbolic representation - Part 2: Extension of basic requirements", extends the basic instrument-symbol set established in Part 1. It provides standardized graphical and letter-code conventions to communicate measurement and control functions on technical drawings (P&ID, schematic and process flow diagrams). The part is aimed at instrument specialists, process and piping engineers, layout designers and operators who need unambiguous, cross-disciplinary symbol conventions.

Key topics and technical requirements

• Extension of Part 1: Adds supplementary symbols and expands the letter-code vocabulary used to identify instrument functions and modifiers. Definitions from ISO 3511-1 apply.
• Letter code system: Standardized first-letter (measured/initiating variable) and succeeding-letter (display/output) codes; conventions for modifiers and user-assigned letters (user’s choice, X for unclassified).
• Instrument signal lines: Standard line designations for electrical (E), pneumatic (A), hydraulic (L), capillary, and conducted radiation signals.
• Primary and sensing elements: Symbols for flow primary elements (orifice plate, venturi, nozzle, turbine, variable-area and other meters) and the concept of tagging sensing elements separately (examples: PT for pressure transmitter, PE for external pressure cell).
• Level and pressure connections: Standard symbols for tank gauges, float types, integrally mounted instruments, and differential/pressure regulator taps.
• Actuating elements: Graphical symbols for diaphragm, piston, rotary motor, solenoid actuators (including manual and remote reset), and solenoid/volume boosters.
• Signal modifiers and functions: Analog functions such as addition, square-root extraction, selectors (high/low), limiting, reversing, gain/attenuation, bias and characterizing relays, and digital/analog conversion.
• Binary logic and control: Basic binary logic elements (AND, OR, NOT, time lag) harmonized with IEC Publication 117-15 and representation of the action of binary signals on analogue signals.
• Local control panels: Convention to indicate instruments on local control panels (horizontal line across the symbol) and panel identification practice.

Practical applications and users

ISO 3511-2 is used to produce clear, standardized:

• Piping and instrumentation diagrams (P&IDs)
• Schematic and process flow diagrams
• Instrumentation schedules and loop diagrams

Primary users:

• Instrumentation and control engineers
• Process, mechanical and piping designers
• Control system integrators and panel designers
• Plant operations, maintenance and safety engineers

Benefits include improved interdisciplinary communication, reduced drawing ambiguity, and consistent documentation for installation, testing and operation.

Related standards

• ISO 3511-1: Basic requirements (definitions & fundamental letter codes)
• ISO 3511-3: Detailed symbols for instrument interconnection
• ISO 3511-4: Symbols for process computer/interface/display
• IEC 117-15: Graphical symbols - binary logic elements (coordination with IEC)