Piping and instrumentation designations 

Letter

Category

Processing function

A

Analysis

Alarm, message

B

Optical measurement (e.g. flame monitoring)

Limitation

C

Control

D

Density

Differential

E

Electrical voltage

– (must not be used)

F

Flow rate

Ratio

G

Distance, length, position

– (must not be used)

H

aManual entry, manual intervention

Upper limit, on, open

I

Current

Analogue display

J

Electrical output

– (must not be used)

K

Time-based function

Temporal rate of change, e.g. for acceleration or calculation of a deduction

L

Filling level

Lower limit, off, closed

M

Moisture

– (must not be used)

N

Electrical actuation (all electronic consumers, e.g. motor, heating)

– (must not be used)

O

Local or PCS status display of binary signals

P

Pressure

Point (test) connection

Q

Quantity or number, material characteristics*, quality factors*, analysis* (apart from D, M, V)

Integral, quantity or sum

R

Radiation variables

Value recorded

S

Speed or frequency (including acceleration)

Binary control function or switching function (not safety relevant)

T

Temperature

– (must not be used)

U

– (must not be used)

V

Vibration, mechanical analysis, torque

– (must not be used)

W

Weight, mass, force

– (must not be used)

X

– (for meanings not listed)

– (for meanings not listed)

Y

Hydraulic or pneumatic actuation (switching, change, restriction by servovalve for example)

Computing function

Z

Binary control function or switching function (safety relevant)

 

The code letters for EMC technology according to EN 62424:2014-05 are used.
* the meaning for Q is taken from the predecessor DIN 19227-1 1993-10.

Example of application of nomenclature to steam boiler equipment: 

Equipment of a steam boilerEquipment of a steam boiler
 

Example 1:

Example 2: