Glossary · Distributed automation and IEC 61499
Composite function block
Also known as: Composite FB, CFB
German: Zusammengesetzter Funktionsbaustein
In IEC 61499, a composite function block is a function block type whose behavior is defined by an internal network of function block instances, connected to its own event and data interface.
- IEC 61499
- Standards
In one sentence
An IEC 61499 composite function block contains a network of function blocks behind its own event and data interface.
Example
A composite function block Conveyor encapsulates blocks for the motor, two sensors and a jam detection, so that the application uses one conveyor block per section.
How it applies
- Engineering: Composite function blocks create hierarchy and reuse. They hide internal details behind a clean interface, similar to a Subsystem in systems engineering. A composite block has no ECC of its own; events at its interface are passed to the internal blocks.
- Distribution: A composite function block is mapped as a unit to one resource. To distribute parts of a structure across devices, IEC 61499 uses subapplications instead.
- Testing: Test the composite block as a unit after its internal blocks have been tested individually.
- Documentation: Document the external interface and the purpose; include the internal network diagram for maintainers. Users of the block need the interface, not every internal detail.
Composite function block vs. subapplication
Both contain networks of function blocks. A composite function block is always executed within one resource. A subapplication can be split across several resources and devices during mapping.