D - User's choice, commonly Density.
Reference for the ISA 5.1 first letter D.
What D means on a P&ID.
Density measurement is the dominant first-letter use. Coriolis meters often surface density as a secondary variable that gets its own D-prefix tag for trending. Be careful not to confuse D as a first letter with D as a modifier. PDT, differential pressure and TDT, differential temperature put the D in the second slot, where it means differential rather than density.
Also stands for.
- Differential, when prefixing another letter, e.g. DPT for differential pressure
Common second letters.
| Tag | Meaning |
|---|---|
| DT | Transmitter, DT. Density transmitter |
| DI | Indicator, DI |
| DE | Sensor, DE |
Example tags.
| Tag | Meaning |
|---|---|
| DT-401 | Density transmitter on loop 401, often Coriolis or radiometric |
| DI-415 | Density indicator |
Typical placement.
On streams where density is a process variable. Oil, water separators, slurry streams in mining, polymer reactor outlets, cryogenic services in LNG.
Common questions
What does the ISA 5.1 first letter D stand for?
In ISA 5.1, the first letter D stands for User's choice, commonly Density. It can also stand for Differential, when prefixing another letter, e.g. DPT for differential pressure.
How is letter D typically used on a P&ID?
On streams where density is a process variable. Oil, water separators, slurry streams in mining, polymer reactor outlets, cryogenic services in LNG.
What second letters commonly follow D in ISA 5.1 tags?
Common combinations include DT (Transmitter, DT. Density transmitter), DI (Indicator, DI), DE (Sensor, DE).
What are example ISA 5.1 tags starting with D?
DT-401 (Density transmitter on loop 401, often Coriolis or radiometric); DI-415 (Density indicator).
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