PLC Function Blog Diagram (FBD)

Function Blog Diagram, whose short name is FBD, is not a highly preferred type of PLC programming language, but it allows us to do even the longest operations in a short way in most places and is easy to interpret.

Although Function Block Diagram type is not one of the most commonly used PLC programming languages, it allows us to do even the longest operations in a short way in most places and is easy to interpret.

It is generally used where there is a continuous circulation/loop or to interpret many inputs at the same time.
One of the places I especially use is alarm function blogs and I prefer it especially for scale commands.

In order to create the FDB routine, we right-click on MainTask, click to create a new routine,

and after entering the name of the routine from the opened tab,

we select its type Function Block Diagram. Thus, our routine is created.

Before the logic within this routine may execute, we do need to add a JSR Instruction within the “Main Routine” of this task. This is done exactly the same way as we’ve done it for ladder logic based routines.

It is the same as the working logic in the ladder. When we drag input from the Instruction section in the function blocks and drop it into your workspace, we need to click on it and assign a tag.

Function Block Input

If you right-click the workspace and click the add element button, the window with the whole instruction will pop up and you can find the instruction you want by searching for it yourself.

For example, when we select SCL for the scale command and say add, the command comes up, but you cannot see many features of the command in the block, so we need to enter the block properties and select which properties we will use.

Input reference instructions for input values ​​We use output reference instructions for output.