What A means on a P&ID.
Walk an analyzer building and you'll find a half-dozen AT-tagged transmitters next to as many AE probes, and the only way to know which one measures pH versus ClO2 versus dissolved oxygen is the service description on the I/O list. The tag itself tells you nothing useful. Sample conditioning lines, calibration solutions, and analyzer-specific quirks live in the datasheet. Bring it to the field walk or you're guessing.
Also stands for.
- Composition
- pH
- Conductivity, sometimes
- Concentration
Common second letters.
| Tag | Meaning |
|---|---|
| AT | Transmitter, AT. Analyzer transmitter |
| AI | Indicator, AI. Analyzer indicator |
| AIC | Indicating controller, AIC |
| AE | Sensor, primary element, AE. Analyzer probe |
| AAH | Alarm high, AAH |
| ASH | Switch high, ASH |
Example tags.
| Tag | Meaning |
|---|---|
| AT-205 | Analyzer transmitter on loop 205, could be pH, conductivity, ORP, gas chromatograph |
| AE-307 | Analyzer probe, the wetted sensor on loop 307 |
| AIC-410 | Analyzer indicating controller, e.g. PH control on a wastewater stream |
Typical placement.
On stream sample lines, fast loops near the equipment they measure. Analyzers often have a separate sample conditioning system drawn alongside. The AE, probe is in the process, the AT, transmitter or analyzer cabinet may be in a shelter 10-20 metres away.
Common questions
What does the ISA 5.1 first letter A stand for?
How is letter A typically used on a P&ID?
What second letters commonly follow A in ISA 5.1 tags?
What are example ISA 5.1 tags starting with A?
Run it on your drawings.
Upload a P&ID set and see every tag read in the convention the drawing already uses.