ISA codes for Process Instrumentation

ISA instrumentation codes and combinations

It is common to make letter combinations in PI&D diagrams according ANSI/ISA S5.1-1984 (R 1992) "Instrumentation symbols and identification" standard.

In addition to the letter combination it is common with a succeeding number as a unique identification of the actual instrument. 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

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