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ISA Instrumentation Codes used in Process Control Systems

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 VariableSymbolType of InstrumentSymbol
Analyses A Alarm A
Burner B Users Choice B
Combustion B Controller C
Users Choice C Control valve CV
Users Choice D Trap CV
Voltage V Sensor (primary element) E
Flow Rate F Rupture disc E
Users Choice G Sight or gage glass G
Current (electric) I Monitor G
Power J Indicator I
Time K Control Station K
Level L Light (pilot/operation) L
Users Choice M Users Choice N
Users Choice

N

Flow Resistance Orifice O
Users Choice O Test point (sample point) P
Pressure / Vacuum P Recorder R
Radiation R Switch S
Speed (or Frequency) S Transmitter T
Temperature T Multifunction U
Multivariable U Valve/Damper V
Vibration V Well W
Weight (force) W Unclassified X
Unclassified X Relay Y
Event Y Driver Z
Position, dimension Z Actuator Z

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:

LI

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:

LI 08

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