Function Block Diagrams (FBD)

Short definition

Function Block Diagrams (FBD) is a graphical programming language for PLC systems in accordance with IEC 61131-3. It visualizes control logic as a network of function blocks that are connected by signal flow lines. FBD is similar to electronic circuit diagrams and signal flow diagrams from the Control engineering. In membrane filtration systems, FBD is preferably used for complex control tasks, mathematical calculations and the integration of prefabricated function blocks, as it enables structured, modular programming.

Programming concept

FBD programs consist of graphical blocks that represent functions (AND, OR, timer) or complex function blocks (PID controller, analog processing). Inputs are located on the left, outputs on the right of the block. Signal processing takes place from left to right along the connecting lines. Complex algorithms are encapsulated in reusable function blocks. Standard functions in accordance with IEC 61131-3 ensure manufacturer independence. Modern development environments offer extensive libraries for control, motion control and communication. The graphical representation makes it easier to understand data flows and dependencies.

Areas of application

Function Block Diagrams are particularly suitable for control engineering and mathematical tasks in membrane filtration systems. They enable intuitive representation of PID control loops, signal processing and calculations. FBD is often used in combination with Ladder Logic used: Binary logic in Ladder, continuous control in FBD. The modularity facilitates maintenance and reuse of proven algorithms.

Typical areas of application:

PID control of pressure, flow rate and temperature
Mathematical calculations for material balances and KPIs
Analog value processing and scaling
Cascade controls and feedforward structures
Integration of manufacturer-specific technology modules

Summary

Function Block Diagrams enable structured, modular programming of complex control and calculation tasks with a high degree of clarity. They are ideal for control-oriented engineers and promote reusability through libraries. For plant engineers, they mean efficient engineering, improved maintainability and standardized implementation of sophisticated control algorithms in membrane filtration plants.