Glossary · Distributed automation and IEC 61499
Distributed function block
Also known as: Distributed FB
German: Verteilter Funktionsbaustein
In distributed automation, a distributed function block is a function block whose functionality is realized by parts executing on several devices, which cooperate over communication connections; in IEC 61499, this is achieved by distributing a subapplication or the blocks of an application across resources.
- IEC 61499
In one sentence
A distributed function block's functionality is spread over several devices that cooperate through communication connections.
Example
A coordination function for two robots is split so that one part runs on each robot controller and both parts exchange events over the network.
How it applies
- Engineering: Functions that involve several machine units are often best implemented close to each unit. The function is designed as one logical unit and then split across devices. In IEC 61499, a composite function block always runs within one resource, so distributable structures are built as subapplications.
- Communication: The parts communicate through communication service interface function blocks, such as publish/subscribe or client/server blocks. The design must define what happens when messages are delayed or lost.
- Testing: Test the distributed function as a whole on the target network, not only its parts.
- Documentation: Document the logical function and its distribution: which part runs where, which messages connect them and which failure behavior applies. Keep the term's meaning explicit in project documents, because IEC 61499 itself does not define a function block type with this name.
Distributed function block vs. composite function block
A Composite function block groups blocks within one resource. A distributed function spans several resources or devices.