Units of Measure

AVEVA Unified Engineering uses dimensional analysis of base dimensions to automatically calculate units of measure (UoM) conversions for compound units.

Attributes of physical quantities

Real attributes, such as stored, derived, and user defined, can be assigned a physical dimension. Assigning a physical dimension to a real attribute determines the type of data stored in these attributes wherever and whenever they occur in the database. The most common dimensions of attributes are of length (internally set to either DIST or BORE). There are other physical dimensions you can assign to a real attribute, such as density, mass, and pressure.

The following physical dimensions are available in the AVEVA.Core.Database interface.

The dimension of an attribute is held in the database in its ambiguously named UNIT field. There are a set of standard specific units that the system will understand. Ideally, the unit qualifier should be appended to the value (for example, 6.5in.), but it can often be recognized if separated from its value. For each unit, there is an abbreviated form, a long form, and a full form (which are often identical).

Values of physical quantities

A value of a real physical quantity has a numerical value (the number) and defines units of measure, which are the units in which the quantity is measured. For example, a distance can be 25.4mm or 1in. Regardless of the number, the distance is the same because there is a known conversion factor between millimetres and inches.

You can enter the value into the system with a unit qualifier that determines the dimension of the physical quantity and sets its value in those units. The system automatically converts from the input unit to the database unit, and from database unit to a presentation unit (for example, the current unit) by using internally defined conversion factors. For compound units (for example, from pound per square inch to pascal), the conversion factors of the component units are combined.

The internal conversion units used are sourced as accurately as possible. Some conversions are arithmetically exact. For example, inches:mm and SI conversions as listed by Bureau International des Poids et Mesures.

Units of Measure table