Tag naming conventions

Why it matters

The same pump appears in the P&ID, the I/O list, the PLC program, HMI tags, SCADA, alarm texts, the historian and maintenance systems. If each uses a different name, every integration step needs a translation table — and errors creep in.

Instrument letter codes (ISA-5.1 style)

The first letter is the measured variable, the following letters the function; a loop number follows: PT-101, TIC-205. Many plants use KKS or another plant-specific scheme instead — follow the plant standard.

A practical structure

<area>_<equipment>_<signal>
U20_P101_Run        (command)
U20_P101_RunFb      (feedback)
U20_PT101_PV        (process value)
U20_PT101_AlmHH     (alarm)

Rules

• Same base name everywhere; only suffixes differ by signal.
• Fixed suffix vocabulary: Cmd, Fb, PV, SP, Out, AlmH, AlmHH, Flt, Mode.
• Allowed characters: letters, digits, _ — tools and protocols treat others differently (OPC UA strings, SQL, CSV).
• Do not encode PLC addresses in names; addresses change.
• Keep the tag list as a single source of truth and generate PLC/HMI/SCADA tags from it where possible.