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 |
