What is Functional Block Diagram (FBD)?

The primary concept behind an FBD is data flow. A Functional block diagram describes a function between input and output through a functional block.

A FBD program is built using function blocks connected together to define the data exchange. The connecting lines will have a compatible information type at both ends.

• FBDs use data flows through feature blocks from left to right.
• Inputs and outputs can be inverted
• Function blocks can have variable argument list sizes
• When arguments are left off default values are used

A FBD contains..:

• All major components
• Interface to the outside world
• Interface between subsystems
• Identify power, data and structural interface
• Should answer how the statement of mission is fulfilled

Basic Functional Blocks:

Example for FBD program:

PLC Learning series: