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.
Process Variable | Symbol | Type of Instrument | Symbol |
---|---|---|---|
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 |