What O means on a P&ID.
Some operating companies park oxygen analyzers under O when they've already burned A on something else and G on gas detection. Other specs leave it unassigned outright. The legend on the drawing set is the only source of truth. Guessing produces wrong tags on the I/O list.
Also stands for.
- No standard assignment
Common second letters.
| Tag | Meaning |
|---|---|
| OT | Transmitter, per the project legend |
Example tags.
| Tag | Meaning |
|---|---|
| OT-405 | Oxygen analyzer transmitter where the project has assigned O to oxygen service, per the project legend |
Typical placement.
Wherever the project legend allows.
Common questions
What does the ISA 5.1 first letter O stand for?
In ISA 5.1, the first letter O stands for User's choice. It can also stand for No standard assignment.
How is letter O typically used on a P&ID?
Wherever the project legend allows.
What second letters commonly follow O in ISA 5.1 tags?
Common combinations include OT (Transmitter, per the project legend).
What are example ISA 5.1 tags starting with O?
OT-405 (Oxygen analyzer transmitter where the project has assigned O to oxygen service, per the project legend).
Run it on your drawings.
Upload a P&ID set and see every tag read in the convention the drawing already uses.