C - User's choice, commonly Conductivity
Reference for the ISA 5.1 first letter C. 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.
Read one of your own drawings.
Drop a P&ID, instrument index, or schedule. Tagsight reads it to the tag and opens a workspace you keep when you sign in.
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Also stands for.
- Concentration
- Capacity
Common second letters.
Transmitter, CT. Typically conductivity transmitter
Indicator, CI
Probe, CE. Conductivity cell
Example tags.
Conductivity transmitter on loop 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.