Function Block Diagram Programming in WindLDR

Quick Answer

WindLDR supports Function Block Diagram (FBD) as one of three IEC 61131-3 programming languages. FBD uses graphical blocks with wired inputs and outputs, making it intuitive for analog signal processing, PID control, and continuous process logic.

What Is FBD in WindLDR?

Function Block Diagram represents logic as interconnected graphical blocks. Each block performs a function (AND, OR, timer, counter, PID, math) and passes its output to downstream blocks via wires. FBD is preferred for applications involving analog signal chains and process control loops.

Mixing Languages

WindLDR allows different program blocks to use different languages. You can write discrete I/O control in ladder and analog processing in FBD within the same project. This flexibility lets you choose the best language for each part of the application.

Built-in Function Blocks

• Logic blocks — AND, OR, NOT, XOR, SR flip-flop
• Timer blocks — TON, TOF (equivalent to TMR, TMROF in ladder)
• Counter blocks — CTU, CTD, CTUD
• Math blocks — ADD, SUB, MUL, DIV, ABS, SQRT
• PID block — Full PID controller with auto-tune (see PID configuration guide)
• Comparison blocks — EQ, NE, GT, LT, GE, LE

Wiring Blocks

Drag blocks onto the FBD canvas, create input references (from tags or registers), wire block outputs to the next block's inputs, and connect final outputs to output references (registers or physical outputs). Execution order follows the wiring connections.

Example: Analog Signal Processing

An analog input scaling chain: Raw AI register → Scale block (0-4000 to 0-100 PSI) → Limit block (clamp 0-100) → Output to R register for display and alarm comparison.