ISA 5.1 letter codes.

Name: ISA 5.1 instrument identification letter codes
Creator: Tagsight
License: https://tagsight.io/terms
Keywords: ISA 5.1, instrument tags, measured variable, function codes, P&ID symbols

The first letter, second letter, and modifier letters of ISA 5.1 instrument identification. Each letter page lists the measured variable, the function letters that combine with it, and example tag patterns Tagsight extracts.

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All letters.

AAnalysisAlso: Composition, pH, Conductivity, sometimes BBurner, CombustionAlso: User's choice, some specifications CUser's choice, commonly ConductivityAlso: Concentration, Capacity DUser's choice, commonly DensityAlso: Differential, when prefixing another letter, e.g. DPT for differential pressure EVoltageAlso: Electrical, any electrical measurement FFlowAlso: Flow rate, Flow ratio, when prefixed FF GUser's choice, commonly Gauging or GasAlso: Position, dimension on some specs, rare HHandAlso: Manual operator action ICurrent, electricalAlso: Modifier. Indicator, when used as a second letter, e.g. FI, PI JPowerAlso: Scan, rare specifications KTime, time scheduleAlso: Time-rate of change LLevelAlso: Liquid level, Interface level, when service is two-phase MUser's choice, commonly MoistureAlso: Mass, rare NUser's choiceAlso: No standard assignment OUser's choiceAlso: No standard assignment PPressureAlso: Pressure differential, PDT, Vacuum, when service is sub-atmospheric QQuantityAlso: Totalized flow, Integrated quantity RRadiationAlso: Resistance, rare SSpeed, frequencyAlso: Modifier. Switch, when used as a second letter TTemperatureAlso: Temperature differential, when prefixed TD UMultivariableAlso: Calculated or composite measurement VVibration, mechanical analysisAlso: Modifier. Valve, when used as a second letter, e.g. FV, PV WWeight, forceAlso: Modifier. Well, TW. Thermowell XUnclassifiedAlso: Custom, one-off measurements not covered by other letters YEvent, state, presenceAlso: Modifier. Computing relay, when used as a second letter, e.g. FY, PY ZPosition, dimensionAlso: Open, closed status

ISA 5.1 letter codes at a glance.

The first letter names the measured variable; the succeeding letters name the function. One row per first letter, with the function letters it commonly combines with and an example tag.

Letter	Measured variable	Common function letters	Example tag
A	Analysis	T, I, IC, E, AH, SH	AT-205
B	Burner, Combustion	T, S, Y	BS-101
C	User's choice, commonly Conductivity	T, I, E	CT-201
D	User's choice, commonly Density	T, I, E	DT-401
E	Voltage	T, I, AH	ET-501
F	Flow	T, I, IC, Y, E, AL, AH, SH	FT-101
G	User's choice, commonly Gauging or Gas	T, AH, SH	GT-301
H	Hand	S, V, IC	HS-101
I	Current, electrical	T, I, E, Y	IT-505
J	Power	T, I	JT-605
K	Time, time schedule	Y, I	KY-301
L	Level	T, I, IC, G, SH, ALL, C	LT-301
M	User's choice, commonly Moisture	T, I	MT-401
N	User's choice	T	NT-105
O	User's choice	T	OT-405
P	Pressure	T, DT, I, IC, SV, RV, SHH, ALL	PT-501
Q	Quantity	I, Y, T, R	QI-205
R	Radiation	T, E, AH, SH	RT-901
S	Speed, frequency	T, I, AH, SH	ST-205
T	Temperature	T, I, IC, E, W, Y, SH, AHH	TT-201
U	Multivariable	T, I	UT-301
V	Vibration, mechanical analysis	T, E, AH, SHH	VT-101
W	Weight, force	T, I	WT-501
X	Unclassified	T, Y	XY-901
Y	Event, state, presence	S, AH	YS-201
Z	Position, dimension	T, I, S, SC, SO	ZSC-101

First letter by succeeding letter.

Read across the row: the first letter is what the tag measures, the column is the succeeding letter for what the instrument does, and the cell is the resulting ISA 5.1 tag. FT is a flow transmitter, LC is a level controller, PI is a pressure indicator. Add a middle function letter for a compound device: FIC is a flow indicating controller, PSH is a pressure switch, high.

Measured variable	I · Indicate	T · Transmit	C · Control	R · Record	S · Switch	V · Valve	E · Element	A · Alarm
A · Analysis	AI	AT	AC	AR	AS	AV	AE	AA
B · Burner, Combustion	BI	BT	BC	BR	BS	BV	BE	BA
C · User's choice, commonly Conductivity	CI	CT	CC	CR	CS	CV	CE	CA
D · User's choice, commonly Density	DI	DT	DC	DR	DS	DV	DE	DA
E · Voltage	EI	ET	EC	ER	ES	EV	EE	EA
F · Flow	FI	FT	FC	FR	FS	FV	FE	FA
G · User's choice, commonly Gauging or Gas	GI	GT	GC	GR	GS	GV	GE	GA
H · Hand	HI	HT	HC	HR	HS	HV	HE	HA
I · Current, electrical	II	IT	IC	IR	IS	IV	IE	IA
J · Power	JI	JT	JC	JR	JS	JV	JE	JA
K · Time, time schedule	KI	KT	KC	KR	KS	KV	KE	KA
L · Level	LI	LT	LC	LR	LS	LV	LE	LA
M · User's choice, commonly Moisture	MI	MT	MC	MR	MS	MV	ME	MA
N · User's choice	NI	NT	NC	NR	NS	NV	NE	NA
O · User's choice	OI	OT	OC	OR	OS	OV	OE	OA
P · Pressure	PI	PT	PC	PR	PS	PV	PE	PA
Q · Quantity	QI	QT	QC	QR	QS	QV	QE	QA
R · Radiation	RI	RT	RC	RR	RS	RV	RE	RA
S · Speed, frequency	SI	ST	SC	SR	SS	SV	SE	SA
T · Temperature	TI	TT	TC	TR	TS	TV	TE	TA
U · Multivariable	UI	UT	UC	UR	US	UV	UE	UA
V · Vibration, mechanical analysis	VI	VT	VC	VR	VS	VV	VE	VA
W · Weight, force	WI	WT	WC	WR	WS	WV	WE	WA
X · Unclassified	XI	XT	XC	XR	XS	XV	XE	XA
Y · Event, state, presence	YI	YT	YC	YR	YS	YV	YE	YA
Z · Position, dimension	ZI	ZT	ZC	ZR	ZS	ZV	ZE	ZA

Using a non-ISA standard.

Tagsight also reads KKS, IEC 81346, DIN 19227, NORSOK, JIS B 0125, and in-house operator conventions. Tags extract as drawn, no forced normalization to ISA 5.1.

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