ISO/TR 8545:1984

Technical drawings — Installations — Graphical symbols for automatic control

The majority of symbols are shown in conjunction with their corresponding functional connection lines. The size of the symbols shall be related to the scale of the drawing. If a more detailed representation is required, symbols can be combined with designations indicated on the drawing or in a separate schedule. For representation on flow sheets for more advanced process systems, ISO 3511/1 is recommended.