AiVibeFunction Block Diagram (FBD)
Function block diagram is a graphical IEC 61131-3 language in which a program is built by wiring together blocks, such as logic gates, timers, PID controllers and user-defined function blocks, so that signals flow from inputs to outputs.
In FBD, each block has typed inputs and outputs, and connections carry Boolean, numeric or structured values between them. Standard libraries provide logic, comparison, arithmetic, selection, timer and counter blocks. Function blocks keep internal state between executions, unlike functions, and engineers can encapsulate their own logic as reusable function blocks with defined interfaces. The network is executed in a defined order each time the containing program runs.
FBD is common in process control and DCS engineering, where control strategies are naturally expressed as signal flows: a transmitter value feeds a scaling block, which feeds a PID block driving a valve output. It is also widely used in safety PLC programming, where certified function blocks for emergency stop, guard monitoring and two-hand control are wired together.
FBD gives a clear picture of data flow and is easy to review, but large diagrams can sprawl, and feedback paths need care to keep execution order explicit. Complex algorithms are often written in structured text and wrapped as function blocks for use in FBD. The IEC 61499 standard builds on the same block concept with event-driven execution for distributed systems.
Key points
- Graphical IEC 61131-3 language based on interconnected blocks
- Function blocks retain internal state between calls; functions do not
- Natural fit for continuous process control and signal flows
- Widely used with certified blocks in safety PLC programming
- Complex algorithms are often written in ST and wrapped as blocks
Where AiVibe comes in
AiVibe designs and manufactures the AiAmbA AI Factory, whose edge devices and AI agents let people talk to PLC, CNC and robot controllers in plain language. Agents only propose changes, a trained operator confirms each one, and the AI Factory never replaces a machine's control or safety systems.