ISA 5.1 letter codes.
The first letter, second letter, and modifier letters of ISA 5.1 instrument identification. Each letter page lists the measured variable, the function letters that combine with it, and example tag patterns Tagsight extracts.
ISA 5.1ISA 5.1
LetterMeasuresTag
PPressurePT-101
FFlowFT-205
TTemperatureTT-118
LLevelLT-330
AAnalysisAT-540
First + function letters·.xlsx .csv
Read one of your own drawings.
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All letters.
- AAnalysisAlso: Composition, pH, Conductivity, sometimes
- BBurner, CombustionAlso: User's choice, some specifications
- CUser's choice, commonly ConductivityAlso: Concentration, Capacity
- DUser's choice, commonly DensityAlso: Differential, when prefixing another letter, e.g. DPT for differential pressure
- EVoltageAlso: Electrical, any electrical measurement
- FFlowAlso: Flow rate, Flow ratio, when prefixed FF
- GUser's choice, commonly Gauging or GasAlso: Position, dimension on some specs, rare
- HHandAlso: Manual operator action
- ICurrent, electricalAlso: Modifier. Indicator, when used as a second letter, e.g. FI, PI
- JPowerAlso: Scan, rare specifications
- KTime, time scheduleAlso: Time-rate of change
- LLevelAlso: Liquid level, Interface level, when service is two-phase
- MUser's choice, commonly MoistureAlso: Mass, rare
- NUser's choiceAlso: No standard assignment
- OUser's choiceAlso: No standard assignment
- PPressureAlso: Pressure differential, PDT, Vacuum, when service is sub-atmospheric
- QQuantityAlso: Totalized flow, Integrated quantity
- RRadiationAlso: Resistance, rare
- SSpeed, frequencyAlso: Modifier. Switch, when used as a second letter
- TTemperatureAlso: Temperature differential, when prefixed TD
- UMultivariableAlso: Calculated or composite measurement
- VVibration, mechanical analysisAlso: Modifier. Valve, when used as a second letter, e.g. FV, PV
- WWeight, forceAlso: Modifier. Well, TW. Thermowell
- XUnclassifiedAlso: Custom, one-off measurements not covered by other letters
- YEvent, state, presenceAlso: Modifier. Computing relay, when used as a second letter, e.g. FY, PY
- ZPosition, dimensionAlso: Open, closed status
Using a non-ISA standard.
Tagsight also reads KKS, IEC 81346, DIN 19227, NORSOK, JIS B 0125, and in-house operator conventions. Tags extract as drawn, no forced normalization to ISA 5.1.