What W means on a P&ID.
Watch the slot. W in the first position is weight. W in the second position is well, as in TW, thermowell. The protective sheath that a TE inserts into. Two unrelated meanings, decided by position. Weigh feeders, load cells, and batch hoppers in cement, mining, and food processing all carry first-letter W tags where charge weight is the controlled variable rather than rate.
Also stands for.
- Modifier. Well, TW. Thermowell
Common second letters.
| Tag | Meaning |
|---|---|
| WT | Transmitter, WT. Weight transmitter, often a load cell |
| WI | Indicator, WI. Weigh scale display |
Example tags.
| Tag | Meaning |
|---|---|
| WT-501 | Weight transmitter on a hopper or vessel, often a load-cell signal |
| WI-501 | Weigh-scale indicator, panel display |
Typical placement.
On hoppers, bins, batch tanks, and weigh feeders. Solid-handling industries, cement, mining, food use W-prefix tags more than fluid-handling industries.
Common questions
What does the ISA 5.1 first letter W stand for?
In ISA 5.1, the first letter W stands for Weight, force. It can also stand for Modifier. Well, TW. Thermowell.
How is letter W typically used on a P&ID?
On hoppers, bins, batch tanks, and weigh feeders. Solid-handling industries, cement, mining, food use W-prefix tags more than fluid-handling industries.
What second letters commonly follow W in ISA 5.1 tags?
Common combinations include WT (Transmitter, WT. Weight transmitter, often a load cell), WI (Indicator, WI. Weigh scale display).
What are example ISA 5.1 tags starting with W?
WT-501 (Weight transmitter on a hopper or vessel, often a load-cell signal); WI-501 (Weigh-scale indicator, panel display).
Run it on your drawings.
Upload a P&ID set and see every tag read in the convention the drawing already uses.