M - User's choice, commonly Moisture.
Reference for the ISA 5.1 first letter M.
What M means on a P&ID.
Moisture is the working assignment for M on most plants. Dewpoint downstream of TEG units, water content in gas processing, chip moisture in pulp mills, raw mill moisture in cement. The tag itself doesn't tell you which one. The service description column does. Calibration intervals vary wildly between dewpoint sensors and bulk moisture analyzers, so don't assume one calibration plan covers your whole M scope.
Also stands for.
- Mass, rare
Common second letters.
| Tag | Meaning |
|---|---|
| MT | Transmitter, MT. Moisture transmitter |
| MI | Indicator, MI |
Example tags.
| Tag | Meaning |
|---|---|
| MT-401 | Moisture transmitter, common on natural gas dewpoint and dryer outlet streams |
Typical placement.
On gas-treatment streams, TEG dehydration, molecular sieve dryers and on solid-handling streams, cement raw mill, pulp mill chip moisture.
Common questions
What does the ISA 5.1 first letter M stand for?
In ISA 5.1, the first letter M stands for User's choice, commonly Moisture. It can also stand for Mass, rare.
How is letter M typically used on a P&ID?
On gas-treatment streams, TEG dehydration, molecular sieve dryers and on solid-handling streams, cement raw mill, pulp mill chip moisture.
What second letters commonly follow M in ISA 5.1 tags?
Common combinations include MT (Transmitter, MT. Moisture transmitter), MI (Indicator, MI).
What are example ISA 5.1 tags starting with M?
MT-401 (Moisture transmitter, common on natural gas dewpoint and dryer outlet streams).
Run it on your drawings.
Upload a P&ID set and see every tag read in the convention the drawing already uses.