C - User's choice, commonly Conductivity.
Reference for the ISA 5.1 first letter C.
What C means on a P&ID.
C is technically a user's-choice letter, but in practice everyone uses it for conductivity, especially on water-treatment streams and boiler feedwater. A few specs reserve it for concentration with the units pinned in the service description. Either way, read the drawing legend before assuming. The cost of guessing wrong is a misclassified loop in the I/O list.
Also stands for.
- Concentration
- Capacity
Common second letters.
| Tag | Meaning |
|---|---|
| CT | Transmitter, CT. Typically conductivity transmitter |
| CI | Indicator, CI |
| CE | Probe, CE. Conductivity cell |
Example tags.
| Tag | Meaning |
|---|---|
| CT-201 | Conductivity transmitter on loop 201 |
| CE-201 | Conductivity cell on the same loop |
Typical placement.
On water-treatment streams, boiler feedwater, demin water, condensate lines. Conductivity is the dominant use of the C prefix in process industries.
Common questions
What does the ISA 5.1 first letter C stand for?
In ISA 5.1, the first letter C stands for User's choice, commonly Conductivity. It can also stand for Concentration, Capacity.
How is letter C typically used on a P&ID?
On water-treatment streams, boiler feedwater, demin water, condensate lines. Conductivity is the dominant use of the C prefix in process industries.
What second letters commonly follow C in ISA 5.1 tags?
Common combinations include CT (Transmitter, CT. Typically conductivity transmitter), CI (Indicator, CI), CE (Probe, CE. Conductivity cell).
What are example ISA 5.1 tags starting with C?
CT-201 (Conductivity transmitter on loop 201); CE-201 (Conductivity cell on the same loop).
Run it on your drawings.
Upload a P&ID set and see every tag read in the convention the drawing already uses.