Sedona XPRESSion Evaluator Reference Guide

Define Unit VI

Establishes a user-defined physical unit for use in other unit definitions as well as in user-defined variables.

The XPRESSion Evaluator comes with an extensive library of physical units predefined for use in expressions. These built-in unit definitions may be viewed by running the Expr Eval Config Utility VI and selecting the Units tab.

error in (no error) describes any error conditions prior to this VIs execution.
initialize (F) specifies whether or not to initialize the internal database of user-defined units. If TRUE, then all unit definitions currently in memory will be deleted. If FALSE, then unit name described by unit abbreviation and base units is appended to the internal database of user-defined physical units.
unit name is the full name of the physical units being defined.
unit abbreviation is the common abbreviation of the physical unit to be defined.
unit definition is a string expression that allows the user to enter a custom unit definition in terms of existing units. The required format for the custom unit definition is:

<conv factor> <unit string expression>

where <conv factor> is the number required to scale the units in <unit string expression> to the appropriate base units used by the XPRESSion Evaluator. <conv factor> will often be used to describe units outside the MKS standard. For example, the unit "inches" cannot be expressed exactly in powers of the MKS base units, so a conversion factor is required. Some simple unit definition strings are:

0.0254 m

N m

kg J in

Note that newtons (N) and joules (J) can themselves be decomposed into fundamental units, but the XPRESSion Evaluator will take care of that for you, so that you needn’t bother describing compound units it terms of the fundamental units only. Note also that the unit abbreviation must be used and not the full unit name.
quantity is the physical quantity associated with unit name. For example, joules have a physical quantity of energy, while meter describes length, and kilogram denotes mass.
error out contains error information. If the error in cluster indicated an error, the error out cluster contains the same information. Otherwise, error out describes this VIs error status.
index out
unit specifier