PLC learning series 7: Functional Block Diagram program, symbols

What is Functional Block Diagram (FBD)?

The primary concept behind an FBD is data flow. A Functional block diagram describes a function between input and output through a functional block.

A FBD program is built using function blocks connected together to define the data exchange. The connecting lines will have a compatible information type at both ends.

  • FBDs use data flows through feature blocks from left to right.
  • Inputs and outputs can be inverted
  • Function blocks can have variable argument list sizes
  • When arguments are left off default values are used

A FBD contains..:

  • All major components
  • Interface to the outside world
  • Interface between subsystems
  • Identify power, data and structural interface
  • Should answer how the statement of mission is fulfilled

Basic Functional Blocks:

Example for FBD program:

PLC Learning series:

PLC learning Series I: What is PLC? Functions of PLC
PLC learning series 2: PLC programming languages
PLC learning series 3: PLC Architecture and wiring of PLC
PLC learning series 5: 8 Rules for ladder diagram programming
PLC learning series 6: PLC process Scan basics
PLC learning series 8: Instruction List programming
PLC learning series 9: PLC selection criteria.
PLC learning Series 10: PLC timers
PLC learning series 11 : How to interface PLC with SCADA?
PLC learning series 12: Troubleshooting PLC
PLC learning Series 13: Counters in PLC


Instrumentation Engineer

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