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The ISA standards and symbols are important for the P&IDs and documents describing the process control system.
ISA Instrumentation Codes used in Process Control Systems
Process Variable Symbol Type of Instrument Symbol
Sensor (primary element)
Sight or gage glass
Flow Resistance Orifice
Test point (sample point)
Pressure / Vacuum
Speed (or Frequency)
Example - ISA symbols for a Level Indicator
A level indicator will receive the symbol "L" for the process variable "Level", and "I" for the "Indicator" type of instrument. Both combines to:
For unique identification within a system it is common to add a number to the ISA code, by example the code for level indicator no. eight may be:
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ISA Instrumentation Codes used in Process Control Systems. [online] Available at: https://www.engineeringtoolbox.com/isa-iso-instrumentation-codes-d_37.html [Accessed Day Month Year].
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