How to Program PLC Using Function Block Diagrams | OpenPLC

Summary

In this tutorial, the speaker demonstrates how to use Open PLC Editor to create Function Block Diagrams (FBDs) for PLC programming. Starting with creating a new project and defining Boolean variables, the video guides users through drawing an AND operation diagram and testing it with simulation. It then explains how to implement a latching function using OR and AND gates. The video emphasizes debugging and testing the logic, ensuring learners can create and troubleshoot FBDs efficiently in Open PLC Editor. This hands-on guide is perfect for beginners looking to understand PLC programming basics.

Takeaways

• 😀 Create a new project in Open PLC Editor by selecting an empty folder and naming it (e.g., 'test_fpd').
• 😀 Select 'Function Block Diagram' (FBD) as the language for your PLC project.
• 😀 Define your variables before starting the diagram: create 'input_a', 'input_b', and 'output' as Boolean types.
• 😀 Use the 'Create a New Block' option to draw your first function block (AND operation).
• 😀 Familiarize yourself with the built-in function blocks, such as the counter, timer, and logical blocks (AND, OR).
• 😀 For logical operations, drag and connect function blocks (e.g., AND block) and link them to the variables.
• 😀 After connecting the blocks, run the PLC simulation to check if the diagram behaves as expected.
• 😀 Use the Debug Instance to monitor the real-time values of variables during simulation.
• 😀 Toggle the input values (e.g., set 'input_a' to true and see how the output reacts based on the AND operation).
• 😀 Implement latching by combining an OR block and an AND block, ensuring that the output remains true when input_a is low.
• 😀 After testing, turn off 'input_b' to make the output false again, demonstrating how the latching mechanism holds the state.

Q & A

What is the purpose of this tutorial?

The purpose of the tutorial is to teach learners how to use Open PLC Editor to create and simulate function block diagrams (FBDs) for PLC programming, specifically focusing on an AND operation and a latching function.

What is the first step in setting up a new project in Open PLC Editor?

The first step is to create a new project by clicking the 'New Project' option, selecting an empty folder, and naming it (e.g., 'Test FPD'). This folder is then set as the default folder for the project.

Why is selecting the appropriate programming language important when creating a new project?

Selecting the appropriate programming language is crucial because it determines the type of function block diagrams you can create. In this tutorial, the Function Block Diagram (FBD) language is selected to work with logical functions and gates.

What are the three variables used in the example project?

The three variables used are Input A, Input B, and Output, all of which are of the Boolean data type.

Why are variable addresses not necessary for this example project?

In this example, variable addresses are not needed because the tutorial focuses on the logic of the function block diagram itself, rather than interacting with physical PLC hardware.

What does the AND function block do in the diagram?

The AND function block performs a logical AND operation between two inputs (Input A and Input B), and stores the result in the Output variable. The output becomes true only when both inputs are true.

How can the values of variables be monitored during the PLC simulation?

During the PLC simulation, the values of variables can be monitored by opening the debug instance and checking the values of Input A, Input B, and Output in the right-side panel.

What happens when Input A is set to false while Input B is true in the AND operation?

When Input A is set to false while Input B is true, the Output becomes false, since the AND operation requires both inputs to be true for the output to be true.

What is the latching function in the context of PLC programming?

The latching function in PLC programming ensures that once the output is set to true, it remains true even if one of the inputs (in this case, Input A) goes low. The output only resets when both inputs are false.

How is the latching function implemented using FBDs in this tutorial?

The latching function is implemented by using an OR gate and an AND gate. The OR gate latches the output based on Input A, and the AND gate ensures the output remains true until Input B is also turned off.