What Q means on a P&ID.
Custody-transfer metering and batch operations are the two places Q earns its keep. Totalized mass or volume matters as much as the rate, sometimes more. The FT is the rate. The QI is the total. Modern PLCs integrate in code, so the Q tag often appears on the HMI without a corresponding hardware device in the field. Bid-time count it as one of the trickier rows because it's not a wired channel.
Also stands for.
- Totalized flow
- Integrated quantity
Common second letters.
| Tag | Meaning |
|---|---|
| QI | Indicator, QI. Quantity indicator, often a totalizer |
| QY | Computing element, QY. Integrator |
| QT | Transmitter, QT. Quantity, totalizer transmitter |
| QR | Recorder, QR. Quantity recorder, the running total logged over time |
Example tags.
| Tag | Meaning |
|---|---|
| QI-205 | Totalized flow indicator on loop 205 |
| QT-205 | Quantity transmitter sending the running total to the control system |
| QR-310 | Quantity recorder logging totalized volume on a custody-transfer meter |
Typical placement.
On custody-transfer metering stations and batch-totalization points. Quantity is almost always derived from a flow measurement, FT by an integrator, QY, so Q-prefix tags coexist with F-prefix tags on the same loop.
Common questions
What does the ISA 5.1 first letter Q stand for?
In ISA 5.1, the first letter Q stands for Quantity. It can also stand for Totalized flow, Integrated quantity.
How is letter Q typically used on a P&ID?
On custody-transfer metering stations and batch-totalization points. Quantity is almost always derived from a flow measurement, FT by an integrator, QY, so Q-prefix tags coexist with F-prefix tags on the same loop.
What second letters commonly follow Q in ISA 5.1 tags?
Common combinations include QI (Indicator, QI. Quantity indicator, often a totalizer), QY (Computing element, QY. Integrator), QT (Transmitter, QT. Quantity, totalizer transmitter), QR (Recorder, QR. Quantity recorder, the running total logged over time).
What are example ISA 5.1 tags starting with Q?
QI-205 (Totalized flow indicator on loop 205); QT-205 (Quantity transmitter sending the running total to the control system); QR-310 (Quantity recorder logging totalized volume on a custody-transfer meter).
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