Instrumentation · Free Excel and PDF
ISA Instrument Letter Codes Table (ISA 5.1)
Instrument letter codes table for reading and writing P&ID tag numbers, with the meaning of each letter in first and succeeding positions.
Excel (.xlsx)Print ready PDF46 rowsFree, no sign up
Download
- 46 rows of reference data
- Print ready A4 PDF
- How to Use sheet with steps
- Basis and standard stated
- Excel, Google Sheets and LibreOffice
- Free, no sign up, no macros
ISA 5.1 identification letters
| Letter | First letter (measured variable) | Succeeding letter (function) | Modifier |
|---|---|---|---|
| A | Analysis | Alarm | |
| B | Burner, combustion | User's choice | User's choice |
| C | User's choice | Control | Close |
| D | User's choice | Differential (modifier) | |
| E | Voltage | Sensor, primary element | |
| F | Flow | Ratio (modifier) | |
| G | User's choice | Glass, gauge, viewing device | |
| H | Hand | High | |
| I | Current | Indicate | |
| J | Power | Scan (modifier) | |
| K | Time, schedule | Control station | Time rate of change (modifier) |
| L | Level | Light | Low |
| M | User's choice | Middle, intermediate | |
| N | User's choice | User's choice | User's choice |
| O | User's choice | Orifice, restriction | Open |
| P | Pressure | Point (test connection) | |
| Q | Quantity | Integrate, totalise | Integrate (modifier) |
| R | Radiation | Record | Run |
| S | Speed, frequency | Switch | Safety (modifier), stop |
| T | Temperature | Transmit | |
| U | Multivariable | Multifunction | |
| V | Vibration, machine analysis | Valve, damper, louver | |
| W | Weight, force | Well, probe | |
| X | Unclassified | Unclassified | Unclassified |
| Y | Event, state, presence | Relay, compute, convert | |
| Z | Position, dimension | Driver, actuator |
Advertisement
Common tag examples
| Tag | Meaning |
|---|---|
| PT | Pressure transmitter |
| FT | Flow transmitter |
| LT | Level transmitter |
| TT | Temperature transmitter |
| PDT | Differential pressure transmitter |
| FE | Flow element (orifice, meter body) |
| TE | Temperature element (RTD, thermocouple) |
| PI | Pressure indicator (gauge) |
| LG | Level gauge (sight glass) |
| FIC | Flow indicating controller |
| LIC | Level indicating controller |
| FCV | Flow control valve |
| PSV | Pressure safety valve |
| XV | On off valve |
| LSHH | Level switch high high |
| PAL | Pressure alarm low |
| TW | Thermowell |
| FQI | Flow totaliser indicator |
| ZSO | Position switch open |
| SDV | Shutdown valve (common practice) |
About this Table
Instrument letter codes table for reading and writing P&ID tag numbers, with the meaning of each letter in first and succeeding positions.
Basis: ANSI/ISA 5.1 Instrumentation Symbols and Identification. 'User's choice' letters must be defined in the project legend.
How to use
- The first letter is the measured or initiating variable.
- Following letters are readout or output functions.
- Modifiers (D, F, H, L, S) refine the letter before them.
Notes
- SDV, ESDV and similar tags are common practice rather than strict ISA 5.1.
- Check the project P&ID legend for user's choice letters.
Related tools
Advertisement
Frequently Asked Questions
What does PT mean on a P&ID?
Pressure transmitter.
What is the difference between PI and PIC?
PI is a pressure indicator; PIC is a pressure indicating controller.
What does LSHH mean?
Level switch high high, usually a trip.
You May Also Like
Learn more on the blog
Instrument loop diagram to ISA 5.4
A practical guide on instrumentationblog.in that explains the engineering behind this table.
Read Full ArticleMore Engineering Reference Tables
Type K Thermocouple Table (mV vs °C)Temperature · Excel and PDFType J Thermocouple Table (mV vs °C)Temperature · Excel and PDFType T Thermocouple Table (mV vs °C)Temperature · Excel and PDFType E Thermocouple Table (mV vs °C)Temperature · Excel and PDFType N Thermocouple Table (mV vs °C)Temperature · Excel and PDFType R Thermocouple Table (mV vs °C)Temperature · Excel and PDFType S Thermocouple Table (mV vs °C)Temperature · Excel and PDFType B Thermocouple Table (mV vs °C)Temperature · Excel and PDFPt100 RTD Table (Ω vs °C)Temperature · Excel and PDFPt1000 RTD Table (Ω vs °C)Temperature · Excel and PDFThermocouple Tolerance Class Table (IEC 60584)Temperature · Excel and PDFRTD Tolerance Class Table (IEC 60751)Temperature · Excel and PDFCarbon Steel Pipe Schedule Chart (ASME B36.10M)Piping · Excel and PDFStainless Steel Pipe Schedule Chart (ASME B36.19M)Piping · Excel and PDFSteel Pipe Weight Chart (kg per metre)Piping · Excel and PDFPipe Inside Diameter and Flow Area ChartPiping · Excel and PDFNPS to DN Pipe Size ChartPiping · Excel and PDFFlange Pressure Temperature Rating Table (ASME B16.5)Piping · Excel and PDFSaturated Steam Table by TemperatureSteam and Water · Excel and PDFSaturated Steam Table by PressureSteam and Water · Excel and PDFSuperheated Steam TableSteam and Water · Excel and PDFWater Density and Viscosity TableSteam and Water · Excel and PDFWater Boiling Point vs Altitude TableSteam and Water · Excel and PDFAWG Wire Size Chart (AWG to mm²)Electrical · Excel and PDFMetric Cable Size and Resistance Table (IEC 60228)Electrical · Excel and PDFIP Rating Chart (IEC 60529)Electrical · Excel and PDFNEMA Enclosure Types Chart (NEMA 250)Electrical · Excel and PDFNEMA to IP Conversion ChartElectrical · Excel and PDFMotor Full Load Current Table (3 Phase)Electrical · Excel and PDFElectrical Wire Colour Code ChartElectrical · Excel and PDF4 to 20 mA Conversion TableInstrumentation · Excel and PDFSquare Root Flow and DP TableInstrumentation · Excel and PDFHazardous Area Zone and Gas Group TableInstrumentation · Excel and PDFHazardous Area Temperature Class Table (T1 to T6)Instrumentation · Excel and PDFSIL Level PFD and RRF Table (IEC 61508)Instrumentation · Excel and PDFCv to Kv Conversion TableInstrumentation · Excel and PDFNPT Thread Size Chart (ASME B1.20.1)Threads · Excel and PDFBSP Thread Size Chart (ISO 228 and ISO 7)Threads · Excel and PDFMetric Thread Pitch Chart (ISO 261)Threads · Excel and PDF