Glossary · Distributed automation and IEC 61499
Function block instance
Also known as: FB instance, Instance
German: Funktionsbausteininstanz
In IEC 61499 and IEC 61131-3, a function block instance is a named, individual occurrence of a function block type with its own copy of the type's data, which is used in an application, network or program.
- IEC 61499
- Standards
In one sentence
A function block instance is a named occurrence of a function block type with its own data, used in a network or program.
Example
The type FB_Valve is instantiated as V101, V102 and V103; each instance stores its own position feedback and fault state.
How it applies
- Engineering: Types are designed once; instances are placed in networks and programs. In IEC 61499, instances are what gets mapped to resources and deployed to devices. Instance names often follow plant tag numbers, which links the software to the P&ID or electrical drawings.
- Parameterization: Instances can receive individual parameter values through data inputs or initial values while sharing the type's behavior.
- Change management: Updating a type changes all instances. Tools may allow instances to keep an older type version until they are updated deliberately.
- Documentation: Instance lists (instance name, type, location, parameters) connect software documentation with plant documentation. Keep them generated from the project where possible.
Function block instance vs. function block type
The Function block type defines interface and behavior. The instance is one concrete use of it with its own data. The same distinction exists between a class and an object in object-oriented programming.