ANSI/ISA-S5.1-1984 Instrumentation Symbols and Identification

LETTER	FIRST LETTER	SECOND LETTER
A	Analysis	Alarm
B	Burner, Combustion	User's Choice
C	User's Choice	Control
D	User's Choice
E	Voltage	Sensor (Primary Element)
F	Flow Rate
G	User's Choice	Glass (Sight Tube)
H	Hand (Manually Initiated)
I	Current (Electric)	Indicate
J	Power
K	Time or Time Schedule	Control Station
L	Level	Light (pilot)
M	User's Choice
N	User's Choice	User's Choice
O	User's Choice	Orifice, Restriction
P	Pressure, Vacuum	Point (Test Connection)
Q	Quantity
R	Radiation	Record or Print
S	Speed or Frequency	Switch
T	Temperature	Transmit
U	Multivariable	Multifunction
V	Vibration, Mechanical Analysis	Valve, Damper, Louver
W	Weight, Force	Well
X	Unclassified	Unclassified
Y	Event, State or Presence	Relay, Compute
Z	Position, Dimension	Driver, Actuator, Unclassified