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ISA Instrument Letter Codes Cheat Sheet

The complete ISA 5.1 identification letter table on one printable page, with the most common instrument tag combinations explained.

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A one page A4 sheet to print, pin up in the workshop or keep on your phone. Everything on it is also shown below.

Letter	First letter: variable	Modifier	Readout / passive	Output	Modifier
A	Analysis		Alarm
B	Burner, combustion		User’s choice	User’s choice	User’s choice
C	User’s choice (often conductivity)			Control
D	User’s choice (often density)	Differential
E	Voltage		Sensor, primary element
F	Flow, flow rate	Ratio
G	User’s choice		Glass, gauge, viewing device
H	Hand				High
I	Current (electrical)		Indicate
J	Power	Scan
K	Time, schedule	Time rate of change		Control station
L	Level		Light		Low
M	User’s choice (often moisture)				Middle, intermediate
N	User’s choice		User’s choice	User’s choice	User’s choice
O	User’s choice		Orifice, restriction
P	Pressure		Point (test) connection
Q	Quantity	Integrate, totalize
R	Radiation		Record
S	Speed, frequency	Safety		Switch
T	Temperature			Transmit
U	Multivariable		Multifunction	Multifunction
V	Vibration, mechanical analysis			Valve, damper, louver
W	Weight, force		Well
X	Unclassified	X axis	Unclassified	Unclassified	Unclassified
Y	Event, state, presence	Y axis		Relay, compute, convert
Z	Position, dimension	Z axis		Driver, actuator, final element

Tag	Meaning
PT	Pressure transmitter
PDT	Pressure differential transmitter
FIC	Flow indicating controller
TE / TT	Temperature element / transmitter
LSHH	Level switch high high
FCV / FV	Flow control valve
XV	On/off (shutdown) valve
PSV	Pressure safety valve
ZSO / ZSC	Position switch open / closed
HS	Hand switch

What does FIC stand for?

Flow indicating controller: F is flow, I indicate, C control.

What is the difference between PT and PI?

PT is a pressure transmitter (sends a signal); PI is a pressure indicator such as a gauge.

What does the letter Z mean?

Position or dimension as the first letter, for example ZSO is a position switch open.

Instrument index: 10 essential columns

A practical guide on instrumentationblog.in that explains the theory behind this cheat sheet.