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

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ISA codes for Process Instrumentation

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