Industrial Engineer · phase 3 of 16 · noun
Function Block Diagram (FBD)
IEC 61131-3 graphical language that connects functions and function blocks with signal lines.
The Explain card
- Plain English
- FBD draws logic as boxes wired together with signal lines. Each box is a function or a function block, and the lines carry values from one output to the next input.
- Example
- A temperature input feeds a scaling block, which feeds a PID block, which feeds an analog output block. You read the loop left to right like a flow chart.
- Why it matters
- Continuous signal processing that is a mess of parallel rungs in ladder is one clean diagram in FBD. It is the natural home for loops, math and drive control, and it shows data flow rather than sequence.
- Hook
- Ladder shows what switches, FBD shows what flows.
Word knowledge
How the word is built, where it came from, and what it sits beside in memory.
In a sentence
During commissioning, the engineer used a Function Block Diagram to trace the pressure signal from the analog input module to the PID block.
Why these words
- function Latin functio, performance or execution specifies an operation performed within the control logic
- block Middle English blok, from Old French bloc presents an operation or reusable unit as a bounded element
- diagram Greek diagramma, figure marked out identifies the phrase as the name of a technical drawing
Where it came from
- Origin
- English compound using function from Latin functio, block from a Germanic source through Old French, and diagram from Greek diagramma
- Entered the language
- 20th century
- What changed
- Function moved from performance or execution to a specified operation, block gained the sense of a distinct technical unit, and diagram retained its sense of a drawn representation.
How it is spelled
- Pattern
- function keeps the Latin-derived ending -tion
- Pattern
- block uses ck after a short vowel
- Pattern
- diagram keeps the Greek-derived element -gram
- Breaks the pattern
- diagram doubles its final m in diagrammed and diagramming
- Breaks the pattern
- the abbreviation FBD uses uppercase initials without periods
Spelled like
- operation
- construction
- clock
- stock
- telegram
- program
Broken into chunks
-
function
- functional
- functionality
-
block
- blocking
- blockage
-
gram
- telegram
- program
What it sits beside
Same subject
- Ladder Diagram
- Structured Text
- Sequential Function Chart
- PID function block
- analog input module
Same shape
- block diagram
- logic diagram
- wiring diagram
IEC 61131-3 graphical language names
engineering diagram names
- block diagram
- wiring diagram
- network diagram
Where it sits in the deck
Phase 3: PLC Program Organization and Execution
How the logic is arranged and how the scan actually runs it, which is the difference between code that works and code that works every time.
