Engineering units and unit conversion

Engineering unit

Engineering units (Units of measurement) are standards for measurement of physical quantities that need clear definitions to be useful. Apis Click&Trace has a rich set of default engineering units that covers most purposes.

Quantity

In Apis Click&Trace the term quantity is used on physical properties that can be expressed by a set of equivalent engineering units. Examples of quantities are physical properties such as mass, volume, speed etc.

Quantity category

Quantity categories are varieties of quantities. They may be looked upon as sub-quantities of a category. The purpose of quantity categories is to provide alternative engineering units to a quantity in some cases. As an example, the quantity “mass” with quantity engineering unit g, may have a quantity category called “large scale mass” with engineering unit kg

Unit conversion

The purpose of the unit conversion system is to enable conversion between engineering units that belong to the same quantity. The conversion from a value given in QEU (Quantity Engineering Unit) to Engineering Unit 1 is described by the equation:

      xi=aixq+bi

where

      xi    - Value given in engineering unit 1

        ai   - Conversion factor of engineering unit 1

        xq   - Value given in quantity engineering unit

      bi     - Conversion offset of engineering unit 1

The conversion of a value given in engineering unit 1 (EU1) to engineering unit 2 (EU2) is logically performed in 2 steps:

  1. Convert from EU1 to QEU (Quantity Engineering Unit)
  2. Convert from QEU to EU2

The 2 steps can be combined by the following equation:

x2=(a2  / a1) x1 + (b2 - a2b1/a1)