Definition: Process variable

Process variables represent process data in the visualisation (values that are provided by the PLC as memory cells). The most important information contained in the process variable definition is the ItemID and the data type of the addressed PLC memory area.

In addition to the pure transfer of process data, a process variable definition supports the following special functions, among others:

Specification of limit values (maximum/minimum value) that can influence the variable quality
Specification of a substitute value
Access to data fields
Access to structures
Language/variable value-dependent conversion of process variable values(unit classes)

Parameter name	Description of the
Address/ItemID	Identifier of the process variables from the communication component.
Alias	Identifier of the object
Data type	Determines the structure and length of the process variable value.
Definition active	Determines whether the object definition is valid.
Unit class (display)	Reference to a language or variable-dependent conversion.
Unit class (process)	Reference to a variable-dependent conversion.
Individually writable	Determines whether the elements of a process variable of a complex data type can be written individually to the communication component.
Replacement value	Value that is passed on instead of the true process value
Substitute value mode	Determines when the replacement value is passed on.
Field size	Number of process variables for block-based access.
Comment	Optional commentary on the object.
Maximum value settings	Optional: Upper limit value (constant or variable) that the process variable may assume for a user input.
Minimum value settings	Optional: Lower limit value (constant or variable) that the process variable may assume for a user input.
OPC UA access rights	Defines whether and how the OPC UA client can access the variables via the OPC UA server.
Text	Localisable text for the object.
Variable options	Bit-coded settings for the process variable
Access type	Read/write authorisation for the process variable
Access path	OPC: Optional hardware-specific data path description for the PLC OPC UA: The namespace of the variables in the OPC UA server