Function symbols and their uses:


Shape like circles, squares, diamonds, hexagons, and lines used to represent the hardware and software instruments and functions as follows:


  • Discrete Devices and Functions, represents discrete hardware instruments and functions that are implemented in non-microprocessor-based systems similar to single-case transmitters, controllers, indicators etc.
  • Shared Devices and Functions, represents shared and distributed software analog instruments and functions that are implemented in microprocessor-based systems similar to distributed control or programmable logic control systems.


  • Shared On–Off Devices and Functions, represents shared and distributed on–off software instruments and functions that are implemented in microprocessor-based control systems similar or equal to a distributed control or programmable logic control systems.



  • Computer Devices and Functions, represents shared and distributed on–off software instruments and functions that are implemented in a computer-based control system


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