P&ID Identification and Reference Designation


Letter Column 1 (Measured value) Column 2(Modifier) Column 3 (Readout/passive function) Column 4 (Output/active function) Column 5 (Function modifier)
A Analysis Alarm
B Burner, combustion User choice User choice User choice
C User’s choice (usually conductivity) Control Close
D User’s choice (usually density) Difference Deviation
E Voltage Sensor
F Flow rate Ratio
G User’s choice (usually gaging/gauging) Gas Glass/gauge/viewing
H Hand High
I Current Indicate
J Power Scan
K Time, time schedule Time rate of change Control station
L Level Light Low
M User’s choice Middle / intermediate
N User’s choice (usually torque) User choice User choice User choice
O User’s choice Orifice Open
P Pressure Point/test connection
Q Quantity Totalize/integrate Totalize/integrate
R Radiation Record Run
S Speed, frequency Switch Stop
T Temperature Transmit
U Multivariable Multifunction Multifunction
V Vibration, mechanical analysis Valve or damper
W Weight, force Well or probe
X User’s choice (usually on-off valve as XV) X-axis Accessory devices, unclassified Unclassified Unclassified
Y Event, state, presence Y-axis Auxiliary devices
Z Position, dimension Z-axis or Safety Actuator, driver or unclassified final control element