Instrument Abbreviations used in P&ID Diagrams

• Generally, the P&ID abbreviations are composed of two or three letters followed by numbers.
• The process variable such as Flow, Level, Pressure, and Temperature to be controlled is indicated by the first letter in P&ID abbreviation as F, L, P, and T.
• The controlling function of the instrument such as Indication, Recording, Transmitter and controlling is indicated by the second letter in P&ID abbreviation as I, R, T, and C.For example, an instrument abbreviation “LT” indicates a “Level Transmitter”.
• The third letter when included in the instrument abbreviation of P&ID indicates the special function to describe a dual function such as recording and controlling, or indicating and controlling. For example, instrument abbreviations like
  1. FIC indicates a Flow Indicator and Controller. 
  2. TRC indicates Temperature Recorder and Controller.
  3. PAL indicates a Pressure Alarm Low. This PAL describes the alarm function in case of lower pressure conditions.

• The combination of alphabets from A to Z represents the specific functions and identification of instruments in the Piping and Instrumentation Diagram.
• The concept of P&ID is versatile and it is known as the heart and key of industrial processes.
• Representation of instrument abbreviations used in P&IDs with the standard set of symbols defined by ISA 5.1.

The below table consists of some possible combinations of instrument abbreviations for various process variables.

1.The first column denotes various process variables.

2.The second column denotes the measured variable or indicating variable.

3.The third column denotes the controller function of various process variables such as Recording and Indicating.

4.The fourth column denotes device readout they may be either Recording or Indicating.

Some instrument abbreviations along with their functions used with P&ID symbols to represent Piping and Instrument diagram are shown in Table 1.

Some possible combinations for various instruments used for measuring variables are represented by the first letter shown in below Table 2.

The main objective of making some possible combinations of these process instruments is to understand the purpose for what they are being used in an instrumentation diagram or process flow diagram.

Below Table 3 shows some instrument abbreviations for devices like switches, alarms, transmitters, solenoids, relays, primary elements, test points, probe, view glass, as well as final elements.

What do Tag Numbers on P&ID Diagrams represent?

• The tag numbers on the Piping and instrumentation diagrams representthe identification of the instrument used for the particular control system in a process station.
• These tag numbers are associated with a process variable followed by its function performed such as indicating and controlling process control loops such as Flow, Level, Pressure, and Temperature.

What are Switches & Alarm Devices?

1. Switching Device (S):

• This is known as a selector switch.
• This enables the mode selection from manual mode (M) to auto mode (A in case of DCS), or local (L) to remote (R) by simply rotating.
• It is a device used for switching on or switching off equipment such as motors, pumps, valves, and so on.
• These are used for alarm activation to alert human operators to take special action or for initiating process and safety interlocks used to trip the system.

2. Alarm device (A):

• It is an annunciator device to alert an operator. This may be a sound or lighting device.
• This alarm is triggered by a current signal of 4 20 mA coming from a transmitter.

3. High and Low Alarms:

• The letters H and L indicate the level of High or Low. But during some undefined conditions, these may be omitted.
• In the case of the level transmitter, this signal can be used in the soft program to assign alarms for low and high i.e. LAL & LAH.

The P&ID diagrams of some instruments shown below are grouped by separate tables

Comprehensive P&ID Abbreviations (A–Z)

This below table covers 50+ key abbreviations across Flow, Level, Pressure, Temperature, Safety, Valves, and Miscellaneous categories.

Abbreviation	Meaning	Function/Description
A	Alarm	Indicates abnormal condition (high, low, etc.)
AE	Analyzer Element	Primary sensing device for analyzers
AI	Analyzer Indicator	Displays analyzer reading
AL	Alarm Low	Alarm condition at low limit
AH	Alarm High	Alarm condition at high limit
AR	Alarm Recorder	Records alarm events
AS	Alarm Switch	Activates alarm circuit
C	Control	General control function
CV	Control Valve	Final element to regulate flow, pressure, etc.
D	Differential	Indicates differential measurement (e.g., DP)
DP	Differential Pressure	Measurement of pressure difference
E	Element	Primary sensing element
FE	Flow Element	Device to measure flow (e.g., orifice, venturi)
FI	Flow Indicator	Local or remote display of flow
FIC	Flow Indicator Controller	Controls and indicates flow
FT	Flow Transmitter	Transmits flow signal (4-20 mA)
FY	Flow Relay	Secondary instrument for flow loop
FCV	Flow Control Valve	Controls flow in the process
G	Glass / Gauge	Visual inspection device (e.g., LG, PG, TG)
H	Hand / High	Manual operation or high-level condition
HS	Hand Switch	Manual control switch
I	Indicator	Displays variable in the field or control room
LIC	Level Indicator Controller	Controls and indicates level
LG	Level Gauge	Sight glass for liquid level
LSH	Level Switch High	Activates at high-level setpoint
LSL	Level Switch Low	Activates at low-level setpoint
LT	Level Transmitter	Measures and transmits liquid level
LCV	Level Control Valve	Regulates level in vessels/tanks
M	Motor	Used in MOVs (Motor Operated Valves)
MOV	Motor Operated Valve	Remote operated on/off valve
P	Pressure	Process variable for pressure
PG	Pressure Gauge	Local indication of pressure
PI	Pressure Indicator	Indicates pressure value
PIC	Pressure Indicator Controller	Controls and indicates pressure
PSH	Pressure Switch High	Activates alarm/trip on high pressure
PSL	Pressure Switch Low	Activates alarm/trip on low pressure
PSV	Pressure Safety Valve	Safety relief device for pressure
PT	Pressure Transmitter	Measures and transmits pressure
PRV	Pressure Relief Valve	Protects system from overpressure
PY	Pressure/Position Relay	Used for valve positioners
R	Recorder	Records process variable trend
T	Temperature	Process variable for temperature
TG	Temperature Gauge	Local temperature indication
TI	Temperature Indicator	Displays temperature value
TIC	Temperature Indicator Controller	Controls and indicates temperature
TRC	Temperature Recorder Controller	Records and controls temperature
TT	Temperature Transmitter	Measures and transmits temperature
TY	Temperature Relay	Relay device in temp loop
V	Valve	General valve (manual or control)
VG	View Glass	Inspection glass in process line
X	Solenoid/On-Off	Device for binary (open/close) control
XV	On/Off Valve (Solenoid Operated)	Isolates or diverts flow
Y	Relay / Computing Function	Secondary device (e.g., FY, TY, PY)
Z	Position	Position measurement (e.g., valve position)
SDV	Shutdown Valve	Isolates system in emergency
ESD	Emergency Shutdown	Part of safety system (SIS loop)
SIS	Safety Instrumented System	Instrumented protection system

Instrument Function / Process Variable Table

Purpose: Helps readers quickly understand what each instrument does relative to process variables.

Process Variable	Instrument Function	Typical Abbreviations	Example
Flow	Measure / Control	FI, FT, FIC, FCV	FIC-101: Flow Indicator Controller
Level	Measure / Control	LT, LIC, LCV, LG	LIC-102: Level Indicator Controller
Pressure	Measure / Control	PI, PT, PIC, PSV, PRV	PIC-103: Pressure Indicator Controller
Temperature	Measure / Control	TI, TT, TIC, TRC	TIC-104: Temperature Indicator Controller

Switches and Alarm Devices Table

Purpose: Clarifies the alarm and switch types with their P&ID abbreviations – currently described in text, can be tabular for SEO readability.

Device Type	Abbreviation	Function	Example
Switching Device	S	Selector switch for manual/auto or local/remote	S-101
Alarm Device	A	Alerts operator via sound/light	AH-102 (High Alarm)
Low Alarm	LAL	Triggered at low process variable	LAL-103
High Alarm	LAH	Triggered at high process variable	LAH-104

Control Function Combinations Table

Purpose: Shows how first, second, and third letters combine for specific functions (highlighting FIC, TIC, TRC, etc.)

First Letter	Second Letter	Third Letter	Meaning
F	I	C	Flow Indicator & Controller
T	R	C	Temperature Recorder & Controller
P	A	L	Pressure Alarm Low
L	I	C	Level Indicator & Controller

Tag Numbering Example Table

Purpose: Explains how loop numbers and tags are assigned in a P&ID.

Tag	Meaning	Loop Number / Location
LT-101	Level Transmitter	Loop 101, Tank T-101
FIC-102	Flow Indicator Controller	Loop 102, Pump P-102
TIC-103	Temperature Indicator Controller	Loop 103, Heat Exchanger E-103

Device Category / Color Coding Table

Purpose: assigns colors to device type for easier field use.

Device Category	Example Abbreviations	Recommended Color
Measuring / Transmitting	FI, FT, TI, TT, LT	Blue
Controlling / Final Element	FIC, TIC, LCV, FCV	Green
Alarm / Safety	AH, LAL, LAH, PSV, ESD	Red
Switch / Relay	S, PY, FY, TY	Yellow
Visual / Manual	LG, VG, PG, TG	Grey