Definition: Unit class

Unit classes enable the variable-value or language-dependent conversion of process variables by the variable server. The reference of a process variable to a unit class is established by the parameters unit class (process)/(display). The conversion can take place at two points in time.

When exchanging data between the communication component and variable server using a variable-dependent unit class: The converted value is distributed throughout the system as a process variable value. Archiving, for example, would only save the converted value.
When exchanging data between the variable server and visualisation using a language-dependent or variable-dependent unit class: Only the visualisation receives the converted value. This is useful, for example, for language-dependent unit switching (metres/inch), particularly in a client-server system with several clients of different languages.

Switching depending on the current language setting of a client.
Switching depending on a process variable.

A language-dependent unit class cannot be used in the unit class (process) parameter of a process variable.
If a variable-dependent unit class is specified in the Unit class (display) parameter of a process variable, it almost always makes sense in a client-server system to mark the switching variable of the unit class as "client-internal" (see Variable options parameter).

Unit class (variable-dependent)

Name	Description of the
Comment	Optional commentary on the object.
Name	Name of the object.
Switchover variable (unit class)	Variable for switching between the unit objects

Unit class (language-dependent)

Name	Description of the
Comment	Optional commentary on the object.
Name	Name of the object.
Standard language	Defines the unit to be used if no unit object has been defined for the current language.