Function Block Diagrams | PLC Programming

Summary

In this video, the concept of Function Block Diagrams (FBD) for PLC programming is introduced, focusing on how this programming language can simplify tasks for engineers. The script explains the structure and purpose of FBDs, their key components, and how they can represent logical operations like AND, OR, and NOT gates, as well as more complex tasks like timers and counters. Comparisons with ladder diagrams are made to show the ease and flexibility of FBDs. The video concludes with a preview of upcoming content on implementing FBDs in OpenPLC software, highlighting its versatility for PLC programming.

Takeaways

• 😀 Function Block Diagrams (FBD) are a standard programming language for PLCs, offering a simpler approach for engineers compared to ladder diagrams.
• 😀 A function block is a unit of the program that performs a specific task, using inputs to generate outputs through a set of instructions.
• 😀 In function block diagrams, inputs are placed on the left side and outputs on the right side, with the logic in between performing the task.
• 😀 Function blocks can represent standard logical operations like AND, OR, NOT, or even custom user-defined functions like averaging inputs.
• 😀 IEC symbols are used to create function block diagrams, with horizontal and vertical lines to connect blocks, and connectors for distant points.
• 😀 Function block diagrams can simplify logical functions compared to ladder diagrams, making them a suitable alternative in PLC programming.
• 😀 Function blocks can represent logical gates like AND, OR, and NOT, as well as more complex functions like timers, counters, and latching operations.
• 😀 Function blocks allow for straightforward implementation of ladder logic operations, such as OR and AND operations, with clear visual mapping.
• 😀 In function block diagrams, even more complex operations like Exclusive OR (XOR) can be implemented by combining logical operations such as inversion and AND/OR gates.
• 😀 The upcoming video will cover the use of Open PLC software, a free tool that supports multiple PLC programming languages, including function block diagrams.

Q & A

What is a Function Block Diagram (FBD) used for in PLC programming?

A Function Block Diagram (FBD) is a graphical programming language used to design control logic for PLCs. It represents a set of instructions that perform specific tasks, where inputs are processed to generate outputs.

How does a function block diagram differ from ladder diagrams in PLC programming?

While ladder diagrams are based on electrical relay logic and are widely used in industrial settings, function block diagrams are simpler and more direct for engineers. They provide a more intuitive approach to representing complex tasks and functions.

What are the main elements that make up a function block diagram?

The main elements of a function block diagram are function blocks (which contain instructions to generate outputs), connectors (horizontal and vertical lines that link blocks), and input/output terminals (inputs on the left and outputs on the right).

What are the standard IEC symbols used in function block diagrams?

The standard IEC symbols used in function block diagrams include function blocks themselves, connectors to link them, and lines to show connections. Horizontal and vertical lines are commonly used for connecting function blocks and distant points.

Can a user define custom function blocks in a function block diagram?

Yes, users can define custom function blocks to perform specific tasks that are not covered by standard blocks. For example, a user can create blocks for averaging inputs or other specialized operations.

How are inputs and outputs represented in a function block diagram?

In a function block diagram, inputs are always placed on the left side of the block, while outputs are placed on the right side. The function block itself processes these inputs and generates the corresponding outputs.

What does a function block diagram for an OR operation look like?

In a function block diagram for an OR operation, the two inputs are assigned to the input terminals of an OR block, and the result of the OR operation is placed at the output terminal. It’s a direct and simple representation.

How can a ladder diagram be implemented in a function block diagram?

A ladder diagram can be translated into a function block diagram by identifying the logical operations being performed (e.g., AND, OR) and using the corresponding function blocks. For example, an AND operation in a ladder diagram can be represented by connecting inputs to an AND function block.

What is the function block diagram equivalent of a latching operation?

In a function block diagram, a latching operation can be implemented by OR-ing input A with output Q and then AND-ing the result with input B. This logic ensures that the output remains on even if input A goes low.

What is the next step in learning after understanding function block diagrams in this course?

The next step is to learn how to implement and simulate function block diagrams in PLC programming software. In the following video, a new software, Open PLC, will be introduced for programming PLCs using function block diagrams and ladder diagrams.