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IEC TS 62720:2017 โ Identification of Units of Measurement for Computer-Based Processing
💡 Key Insight: In an era of automated manufacturing, digital twins, and cross-border data exchange, ambiguity in units of measurement can cause catastrophic errors. IEC TS 62720 provides a standardized identification system that enables computers to unambiguously interpret any unit of measurement used in product data, engineering specifications, and scientific documentation.
1. Scope and Purpose
IEC TS 62720 specifies identifiers for units of measurement to support computer-based processing of product data. It provides a comprehensive survey of quantities with associated collections of internationally standardized as well as non-standardized units used in business and science. The standard covers any standard or non-standard units of measure currently in use across two or more distinct ethno-linguistic groups or nations, at least in one domain of industry, for which an explicit method of conversion to a known standard unit is well documented.
The need for this standard arises from the growing complexity of digital data exchange in engineering, manufacturing, and scientific domains. When product data sheets, technical catalogues, or engineering specifications are exchanged between organizations, countries, or software systems, the units of measurement accompanying quantitative data must be unambiguously interpretable by computer systems. Without standardized identifiers, a value like “100” could represent 100 mm, 100 inches, or 100 arbitrary units — a potentially dangerous ambiguity in safety-critical applications. IEC TS 62720 assigns unique machine-readable identifiers to each unit, enabling automated validation, conversion, and processing of quantitative product data.
✅ Why This Matters: The 1999 Mars Climate Orbiter was lost due to a unit mismatch between metric and imperial systems. IEC TS 62720 was designed to prevent exactly this type of costly error in automated data exchange between engineering systems and across international supply chains.
2. The International System of Quantities and Units
2.1 Relationship Between Quantities and Units
IEC TS 62720 is built upon the foundation of the International System of Quantities (ISQ) and the International System of Units (SI). The ISQ defines the base quantities from which all other quantities are derived through dimensional analysis, while the SI provides the corresponding base and derived units. The standard recognizes seven base quantities — length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity — with their corresponding SI base units (metre, kilogram, second, ampere, kelvin, mole, and candela).
2.2 SI Prefix System
A critical component of IEC TS 62720 is the systematic treatment of SI prefixes, which enable the expression of very large or very small quantities using the same base unit. The standard specifies both the decimal-based prefixes (from yocto, 10-24, to yotta, 1024) and the binary-based prefixes (kibi, mebi, gibi, tebi, pebi, exbi) used in information technology. The rules for combining prefixes with unit names and symbols are precisely defined to prevent common errors.
| Prefix | Symbol | Factor (Base 10) | Typical Application |
|---|---|---|---|
| yocto | y | 10-24 | Particle physics masses |
| nano | n | 10-9 | Nanotechnology, semiconductor fabrication |
| milli | m | 10-3 | Pharmaceutical dosing, precision measurement |
| kilo | k | 103 | Electrical power, voltage levels |
| mega | M | 106 | Power generation, telecommunications |
| giga | G | 109 | Frequency bands, data storage |
| tera | T | 1012 | High-power laser systems |
| yotta | Y | 1024 | Cosmological calculations |
⚠️ Common Pitfall: A frequent source of errors in data processing is the confusion between SI decimal prefixes (kilo = 1000) and IEC binary prefixes (kibi = 1024). IEC TS 62720 explicitly addresses this distinction, requiring that binary prefixes be used only for quantities based on powers of 2, such as digital storage and memory addressing.
3. Unit Identification for Computer Processing
3.1 The IEC Common Data Dictionary (CDD)
The second edition of IEC TS 62720 introduced a significant architectural change: the detailed unit definitions are maintained in the IEC Common Data Dictionary (CDD) at cdd.iec.ch, rather than being embedded in the document itself. This approach enables rapid maintenance and update of unit identifiers without requiring a full revision cycle of the technical specification. The CDD assigns an International Registration Data Identifier (IRDI) to each unit, providing a globally unique, machine-readable reference that can be used in any data exchange format.
3.2 Identifier Structure
Each unit identifier in IEC TS 62720 follows a structured format that encodes the quantity type, unit name, and conversion factor. The identifier system is designed to be compatible with ISO/IEC 11179 (Metadata Registries) and can be integrated into product data exchange formats such as STEP (ISO 10303), XML schemas, and JSON-LD contexts. The identifiers support hierarchical relationships between quantities (e.g., length is a base quantity; area and volume are derived quantities) and between units (e.g., metre is the SI base unit; kilometre and millimetre are prefixed variants).
| Quantity | Unit Name | Unit Symbol | Code Example |
|---|---|---|---|
| Length | metre | m | IEC62720-01-001 |
| Mass | kilogram | kg | IEC62720-01-002 |
| Time | second | s | IEC62720-01-003 |
| Electric current | ampere | A | IEC62720-01-004 |
| Temperature | kelvin | K | IEC62720-01-005 |
| Voltage | volt | V | IEC62720-02-001 |
| Power | watt | W | IEC62720-02-002 |
| Frequency | hertz | Hz | IEC62720-02-003 |
💡 Practical Note: The CDD contains over 500 registered unit identifiers covering quantities used across all IEC technical domains — from electrical engineering and electromagnetic compatibility to nuclear instrumentation and fibre optics. Engineers can query the CDD online to find the correct identifier for any unit used in their product documentation.
4. Engineering Design Insights
💡 Practical Takeaways for Engineers:
- Data exchange compliance: When designing product data exchange systems (e.g., for supply chain integration or digital catalogue publishing), always reference IEC TS 62720 identifiers rather than relying on free-text unit descriptions. This prevents parsing errors and ensures interoperability with other systems that implement the same standard.
- Non-SI units: The standard does not prohibit non-SI units (e.g., inch, pound, degree Fahrenheit) but assigns them standardized identifiers with explicit conversion factors. This pragmatic approach acknowledges that many industries continue to use traditional units while enabling unambiguous computer processing.
- Binary vs. decimal prefixes: In data processing and telecommunications contexts, always use IEC binary prefixes (KiB, MiB, GiB) for quantities based on powers of 2, and SI decimal prefixes (kB, MB, GB) for quantities based on powers of 10. The standard provides clear guidance on when each prefix system is appropriate.
- Integration with metadata systems: IEC TS 62720 identifiers are designed to integrate seamlessly with ISO/IEC 11179 metadata registries, enabling organizations to build comprehensive, standards-compliant product data dictionaries that support automated unit validation and conversion.
5. Frequently Asked Questions
Q1: Is IEC TS 62720 a mandatory standard or a guideline?
IEC TS 62720 is a Technical Specification (TS), not a full International Standard (IS). A TS is published when the subject is still under technical development or when full consensus for an IS cannot yet be achieved. It is voluntary unless referenced by a contract or regulation. However, its identifiers are widely adopted in IEC CDD and increasingly used in product data exchange frameworks across multiple industries.
Q2: How does IEC TS 62720 relate to UN/CEFACT and other trade data standards?
IEC TS 62720 is complementary to trade data standards such as UN/CEFACT (United Nations Centre for Trade Facilitation and Electronic Business). While UN/CEFACT focuses on commercial and logistics data, IEC TS 62720 provides the technical unit identifiers needed for engineering and scientific product data. Organizations implementing both standards can achieve end-to-end digital integration from engineering specification through procurement and logistics.
Q3: Can IEC TS 62720 handle compound units like “kWh” or “m/s”?
Yes, the standard addresses compound and derived units through the dimensional analysis framework inherited from the ISQ. Each derived unit has a defined relationship to the base units, and the CDD includes identifiers for commonly used compound units. For complex or domain-specific compound units not yet registered, the identifier structure allows extension while maintaining compatibility with the base system.
Q4: What was the major change from Edition 1.0 (2013) to Edition 2.0 (2017)?
The most significant change was moving the detailed unit definitions from the document body into the IEC Common Data Dictionary (CDD). This decoupled the maintenance of unit identifiers from the document revision cycle, enabling faster updates and additions. Edition 2.0 also added Annex B (referencing the CDD) and Annex C (providing an abridged listing of quantities and units with their codes), while removing the previous Annexes D and E.
