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Simple function block diagram

The Function Block Diagram (FBD) is a graphical language for programmable logic controller design,[1] that can describe the function between input variables and output variables. A function is described as a set of elementary blocks. Input and output variables are connected to blocks by connection lines.

Inputs and outputs of the blocks are wired together with connection lines, or links. Single lines may be used to connect two logical points of the diagram:

  • An input variable and an input of a block
  • An output of a block and an input of another block
  • An output of a block and an output variable

The connection is oriented, meaning that the line carries associated data from the left end to the right end. The left and right ends of the connection line must be of the same type.

Multiple right connection, also called divergence can be used to broadcast information from its left end to each of its right ends. All ends of the connection must be of the same type.

Function Block Diagram is one of five languages for logic or control configuration[2] supported by standard IEC 61131-3 for a control system such as a Programmable Logic Controller (PLC) or a Distributed Control System (DCS). The other supported languages are ladder logic, sequential function chart, structured text, and instruction list.

See also[edit]


  1. ^ R. W Lewis (2001) Modelling Distributed Control Systems Using IEC 61499. p. 9
  2. ^ W. Bolton (2011) Programmable Logic Controllers. p. 14

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Function_block_diagram — Please support Wikipedia.
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82 news items


Fri, 01 Apr 2016 04:48:45 -0700

“The ability to use different programming languages, whether Function Block Diagram, Continuous Flow Chart, Structured Text, Sequential Flow Chart or others, represents a powerful advantage over other software options,” Descôteaux says.
Control Design
Wed, 10 Feb 2016 09:50:36 -0800

Ladder diagram is all that is needed for typical machine control applications. Do yourself a favor and use it. By Dave Perkon, technical editor. Feb 10, 2016. Print Email. inShare. - A A A A +. 1 of 2 < 1 | 2 > View on one page. About the author. Dave ...

Machine Design

Machine Design
Mon, 01 Jun 2015 12:57:23 -0700

are switches while ( ) is the action command. Another programming language is function block diagram (FBD). It describes functions between input and output variables. The function, represented by blocks, connects input and output variables. FBD is ...
Automation World
Mon, 23 Nov 2015 09:48:45 -0800

Some of these attributes include a function block diagram with live data and error indication, multi-language support, a dashboard view, multi-language support, a configurable interface and integrated video tutorials. Additional features that ...
ManufacturingTomorrow (press release)
Thu, 24 Mar 2016 05:00:00 -0700

The bundle provides SoftPLC functions with support for IEC-61131-3 standard programming languages including Ladder Diagram (LD), Instruction List (IL), Function Block Diagram (FBD), among others. Engineers can easily devise and maintain motion ...

Assembly Magazine

Assembly Magazine
Thu, 04 Jun 2015 11:15:55 -0700

The system configuration tool uses a function block diagram format that consists of pre-engineered and pretested safety function blocks, as well as a set of Boolean functions. As the function block configuration is created, a corresponding logic ladder ...

Assembly Magazine

Assembly Magazine
Wed, 01 May 2013 11:44:29 -0700

It includes the textual programming languages structured text and instruction list; the graphical programming languages ladder diagram and function block diagram; and the structuring tool sequential function chart. The goal of PLCopen is to enable ...

Wordsun (press release)

Wordsun (press release)
Wed, 16 Sep 2015 03:41:15 -0700

The AC500-S safety CPU is programmed using standard editors such as Structured Text (ST), Ladder (LD) or Function Block Diagram (FBD), making it easy for users to migrate control architectures to a new levels of safety. This facilitates a quick ...

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