How functional block diagram works in a PLC?

A graphical programming language which is a representation of function blocks and logic gates is known as functional block diagram.


When the PLC was created, logic gates and their use in integrated logic circuits were well understood. Using a specialized graphics painting application, connection lines are used to connect the various symbols in Function Block programming.

The machine language equivalent can be generated automatically based on a schematic like this one. The figure is an example of a typical Functional Block Diagram (FBD). Three key elements of a Functional Block Diagram.

  • Identification of the Input
  • Description of the logic that will take place in the Module,
  • Description of the Output

For there to be a high level of output at C, the input at A needs to be high while the input at B needs to be low. Only when both of the AND gate’s inputs are high or true, the output of the AND gate will be high or true. The flow of control may be followed quite easily using this graphical representation of the technique.

Placing blocks in the circuit

The FBD programming language requires that we arrange blocks in the form of a circuit diagram, connect the blocks using wires, and may or may not include descriptive labels and comments. There are three distinct sorts of blocks represented by icons located on the Tools.

Constants Basic Functions Special Functions On the icon for the Constants in [FBD], a row with eleven icons displays as follows:

The functions I, Input, Q, Output, and M, Memory location or flag, are the most often used. A row of eight icons appears when operating the Basic Functions icon in [FBD]:

The graphic above shows six of these without an arrow. The two arrow-shaped icons stand for edge triggering.

How ladder logic differs from function block diagram?

Ladder Logic should be read from left to right and top to bottom. Many lines of ladder logic can be essentially transformed into boxes using function block diagrams.

Advantages of Functional Block Diagram

More popularity is being seen for the usage of function blocks in programming programmable logic controllers (PLCs). The main advantages of employing function blocks diagram are:

  • Simplicity,
  • Less training requirement
  • Reusability.
  • Outstanding motion controls
  • Reading visual blocks is simpler
  • Merge codes to save time

Functional block diagrams (FBDs) are a graphical programming language used in programmable logic controllers (PLCs) to create complex logic functions. In FBD programming, a process is broken down into individual functions, each represented by a block.

Each block in an FBD represents a specific function or operation. These blocks are interconnected using lines that represent the flow of data and signals between the blocks. Blocks can be combined to create more complex functions, with inputs and outputs defined by the block’s configuration.

FBDs can be used to create complex logical operations that incorporate multiple inputs and outputs. For example, an FBD could be used to control a conveyor belt by incorporating input signals from sensors that detect the presence of products on the belt, and output signals that control the speed and direction of the belt motor.

FBD programming is typically done using specialized software tools, which allow the programmer to create and manipulate blocks, connect blocks using lines, and define the inputs and outputs for each block. Once the FBD is programmed, it is downloaded to the PLC and executed by the controller in real-time.

Overall, FBDs are a powerful programming language for creating complex logical functions in PLCs. They provide a graphical representation of the logic, making it easier for programmers to visualize and understand the operation of the system.

A functional block diagram (FBD) is a programming language used in programmable logic controllers (PLCs) to graphically represent the logic functions of a control system.

In FBD programming, the logic of the control system is represented by interconnected function blocks. These function blocks contain instructions that perform specific logic operations, such as AND, OR, NOT, and timers.

The inputs and outputs of the function blocks are connected by wires, which represent the flow of data between the blocks. The inputs and outputs can be physical signals from sensors and actuators, or they can be internal variables within the PLC program.

The FBD programming language allows the programmer to easily design and modify complex control systems by arranging and connecting these function blocks. It is a graphical and intuitive way to program a PLC, especially for engineers who are not experienced in traditional text-based programming languages.

Once the FBD program is designed and entered into the PLC, it can be executed in real-time to control the operation of a machine or process. The PLC will continuously monitor the inputs to the function blocks, execute the logic operations specified by the blocks, and update the outputs accordingly.