Q - Quantity
Reference for the ISA 5.1 first letter Q. 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.
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.
- Totalized flow
- Integrated quantity
Common second letters.
Indicator, QI. Quantity indicator, often a totalizer
Computing element, QY. Integrator
Transmitter, QT. Quantity, totalizer transmitter
Recorder, QR. Quantity recorder, the running total logged over time
Example tags.
Totalized flow indicator on loop 205
Quantity transmitter sending the running total to the control system
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.