- A tag is an address, not a label: it must be unique, stable and parseable by a machine.
- Four ordered segments — area, unit, device, measurement — map cleanly onto the ISA-95 equipment hierarchy.
- Never encode units, ranges or vendor names in the tag; those belong in metadata.
Tag names outlive the SCADA system that created them. They survive migrations, get copied into reports, become MQTT topics and end up in analytics five years later. Treat the naming convention as an interface, and design it once.
The four segments
We use AREA_UNIT_DEVICE_MEASUREMENT. The first two segments follow the equipment hierarchy of ANSI/ISA-95, published internationally as IEC 62264-1: enterprise, site, area, work centre, work unit.[1] The device segment follows the loop/function identification conventions of ISA-5.1, so an instrument's letters mean the same thing on a P&ID and in the historian.[2] Where a client already runs a reference-designation system such as IEC 81346, we map onto theirs rather than imposing ours.[3]
| Context | Tag | Reads as |
|---|---|---|
| Tank farm | TF01_TK204_LT001_LEVEL | Tank farm 1, tank 204, level transmitter 001, level |
| Compressor station | CS02_C300_PT014_PRESS | Station 2, compressor 300, pressure transmitter 014, pressure |
| Solar plant | PV01_INV07_MTR001_ACTIVE_POWER | PV field 1, inverter 7, meter 001, active power |
| Genset | GEN01_ENG_RPM | Generator 1, engine, shaft speed |
Rules that stop tags rotting
- Use A–Z, 0–9 and underscore only. MQTT topic names are UTF-8 but the specification reserves +, # and / as wildcards and separators, so keep them out of segment content.[4]
- Pad numeric instances to a fixed width (TK004, not TK4) so lexical and numeric ordering agree.
- Keep the measurement segment from a controlled vocabulary — LEVEL, PRESS, TEMP, FLOW, ACTIVE_POWER, ENERGY, STATE.
- Give every tag a description, engineering unit and range in metadata, which is where OPC UA's information model expects them to live (IEC 62541).[5]
When a tag must change, publish both old and new for one full reporting period, mark the old one superseded with a reason, and retire it in the catalogue. Never delete history.
Naming review before commissioning
Common questions
What is a good SCADA tag naming convention?
Four ordered segments — AREA_UNIT_DEVICE_MEASUREMENT — where the first two follow the ISA-95 (IEC 62264-1) equipment hierarchy and the device segment follows ISA-5.1 loop identification, so a letter means the same thing on the P&ID and in the historian.
Should units or ranges go in the tag name?
No. A tag is an address, not a label. Units, ranges, vendor names and descriptions belong in metadata, where they can be corrected without breaking every trend, alarm and report that references the address.
How do SCADA tags map to MQTT topics?
The same ordered segments become topic levels, so a tag translates to a topic without a lookup table. That keeps subscriptions parseable by machine and keeps wildcards meaningful at the area and unit levels.
What if the client already has a naming standard?
We map onto theirs rather than imposing ours. Where a reference-designation system such as IEC 81346 is already in use, the existing designation stays authoritative and our structure is the mapping layer.
Sources for every claim above
Each footnote in the article links here. Standards are cited by designation so you can verify the current edition with the issuing body.
- [1]IEC 62264-1:2013 (ANSI/ISA-95.00.01) — Enterprise-control system integration — Part 1: Models and terminologyIEC / ISA · International Electrotechnical Commission · 2013View source
- [2]ANSI/ISA-5.1-2022 — Instrumentation Symbols and IdentificationISA · International Society of Automation · 2022View source
- [3]IEC 81346-1:2022 — Industrial systems, installations and equipment: Structuring principles and reference designationsIEC · International Electrotechnical Commission · 2022View source
- [4]MQTT Version 5.0 — OASIS Standard, §4.7 Topic Names and Topic FiltersOASIS · OASIS Open · 2019View source
- [5]IEC 62541 — OPC Unified Architecture (information model parts)IEC · International Electrotechnical Commission · 2020View source
- [6]Sparkplug Specification 3.0 — MQTT topic namespace and state management for IIoTEclipse Foundation / Eclipse Sparkplug Working Group · Eclipse Foundation · 2022View source
- [7]ISO 14224:2016 — Collection and exchange of reliability and maintenance data for equipmentISO · International Organization for Standardization · 2016View source