A PLC data type (UDT) is a complex, user-defined data type that is used for the declaration of a tag. It represents a data structure made up of several components of different data types. The components can also be derived from another PLC data type, from an ARRAY or directly using the STRUCT keyword as a structure. The nesting depth is hereby limited to 8 levels.
You can change a PLC data type (UDT) centrally and use it repeatedly in the program code. All locations of use are updated automatically.
Advantages of the PLC data types:
Simple data exchange via block interfaces among several blocks
Group data according to the process control
Transferring a parameter as a data unit
Using a PLC data type
You can declare PLC data types as a type when creating data blocks. Based on this type, you can create a number of data blocks, all of which have the same data structure. These data blocks can be adapted by entering different actual values for the corresponding task.
For instance, create a PLC data type for a recipe for blending paints. You can then assign this data type to several data blocks, each of which contains different quantity information.
The following figure shows this application:
