Glossary · Requirements and interfaces
Engineering unit
Also known as: unit of measure
In systems engineering, an engineering unit is the unit and scaling used to interpret a measured or commanded value. A raw number at an interface has no reliable meaning until its engineering unit is defined.
- Data and interfaces
- Systems engineering
In one sentence
The engineering unit defines unit and scaling of a value; a mismatch turns correct raw data into a wrong speed, pressure or position.
Example
A drive reports speed as a raw integer; the interface specification states that 1 count equals 0.1 mm/s, so the safety PLC and the HMI both scale it the same way.
How it applies
- Integrated systems: State unit, scaling factor, offset and range for every safety-relevant value in the interface specification. Raw counts, percentages and fixed-point values are the typical sources of error.
- Machine safety: A unit mismatch can make a limit ineffective, for example a speed limit configured in mm/s but evaluated in m/min. Plausibility checks can catch some, but not all, of these errors.
- Technical documentation: Use the same engineering units in parameter lists, HMI texts and manuals. Name the unit next to every limit value.
- Evidence: When the unit or scaling changes, treat it as a data model version change and re-verify the affected functions.