ISA codes for Process Instrumentation

It is common to make letter combinations in PI&D diagrams according ANSI/ISA S5.1-1984 (R 1992) “Instrumentation symbols and identification”standard. In addition to the letter combination it is common with a succeeding number as a unique identification of the actual instrument. The numbering practice varies – some use a sequential number, others use a number related to the process line number or similar.

The below tutorial guides us about instrument tagplate assignment as per ISA standard

First Letter

First letter indicates a measured or initiating variable, or a modifier, such as Current (I), Speed (S) or Flow (F).

Measured or Initiating Variable

A – Analysis

B – Burner, combustion

C – User’s choice

D – User’s choice

E – Voltage

F – Flow rate

G- User’s choice

H – Hand

I – Current (electrical)

J – Power

K – Time, time schedule

L – Level

M- User’s choice

N- User’s choice

O- User’s choice

P – Pressure, vacuum

Q – Quantity

R – Radiation

S – Speed, frequency

T – Temperature

U – Multivariable

V – Vibration, mechanical analyses

W – Weight, force

X – Unclassified

Y – Event, state or presence

Z – Position, dimension


D – Differential

F – Ration (fraction)

J – Scan

K – Time rate of change

M – Momentary

Q – Integrate, totalizer

S – Safety

X – X-axis

Y – Y-axis

Z – Z-axis

Second or Succeeding Letters

Second or succeeding letters indicates a readout or passive function, output function or a modifier function.

Readout or Passive Function

A – Alarm

B – User’s choice

E – Sensor (primary element)

G- Glass, viewing device

I – Indication

L – Light

N- User’s choice

O- Orifice, restriction

P – Point (test connection)

R – Record

U – Multifunction

W – Well

X – Unclassified

Output Function

B – User’s choice

C – Control

K – Control Station

N- User’s choice

S – Switch

T – Transmit

U – Multifunction

V – Valve, damper, louver

X – Unclassified

Y – Relay, compute, convert

Z – Driver, actuator

Modifier Function

B – User’s choice

H – High

L – Low

M – Middle, intermediate

N- User’s choice

U – Multifunction

X – Unclassified

Examples – P&ID codes

1.Flowmeter – Indicating

FI 001

2.Temperature – Transmitter

TT 001

3.Control Valve

FV 001

4.Position Switch – High Level

ZSH 001

Also Read: List of Instrumentation Standards

Don't Miss Our Updates
Be the first to get exclusive content straight to your email.
We promise not to spam you. You can unsubscribe at any time.
Invalid email address

1 thought on “ISA codes for Process Instrumentation”

Leave a Comment