Process Instrumentation - ISA Codes
It is common to make letter combinations in PI&D diagrams according ANSI/ISA S5.1-1984 (R 1992) "Instrumentation symbols and identification".
In addition to the letter combination a succeeding number as a unique identification of the actual instrument is commonly used. The numbering practice varies - some use a sequential number, others use a number related to the process line number or similar.
First Letter
First letter indicates a measured or initiating variable, or a modifier, such as Current (I), Speed (S) or Flow (F).
Measured or Initiating Variable
- A - Analysis
- B - Burner, combustion
- C - User's choice
- D - User's choice
- E - Voltage
- F - Flow rate
- G- User's choice
- H - Hand
- I - Current (electrical)
- J - Power
- K - Time, time schedule
- L - Level
- M- User's choice
- N- User's choice
- O- User's choice
- P - Pressure, vacuum
- Q - Quantity
- R - Radiation
- S - Speed, frequency
- T - Temperature
- U - Multivariable
- V - Vibration, mechanical analyses
- W - Weight, force
- X - Unclassified
- Y - Event, state or presence
- Z - Position, dimension
Modifier
- D - Differential
- F - Ration (fraction)
- J - Scan
- K - Time rate of change
- M - Momentary
- Q - Integrate, totalizer
- S - Safety
- X - X-axis
- Y - Y-axis
- Z - Z-axis
Second or Succeeding Letters
Second or succeeding letters indicates a readout or passive function, output function or a modifier function.
Readout or Passive Function
- A - Alarm
- B - User's choice
- E - Sensor (primary element)
- G- Glass, viewing device
- I - Indication
- L - Light
- N- User's choice
- O- Orifice, restriction
- P - Point (test connection)
- R - Record
- U - Multifunction
- W - Well
- X - Unclassified
Output Function
- B - User's choice
- C - Control
- K - Control Station
- N- User's choice
- S - Switch
- T - Transmit
- U - Multifunction
- V - Valve, damper, louver
- X - Unclassified
- Y - Relay, compute, convert
- Z - Driver, actuator
Modifier Function
- B - User's choice
- H - High
- L - Low
- M - Middle, intermediate
- N- User's choice
- U - Multifunction
- X - Unclassified
Examples - P&ID codes
Flowmeter - Indicating
- FI 001
Temperature - Transmitter
- TT 001
Control Valve
- FV 001
Position Switch - High Level
- ZSH 001
Related Topics
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• Process Control Systems
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• Process Control Systems Documentation
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• Temperature Measurements
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