Building block diagrams

Back to Basics: The term “block diagram” refers to a type of diagram used by engineers to visualize system interactions at a high level. Block-diagram visualization allows system engineers to separate needs analysis from system design, and start system-level design before finishing component-level designs.

03/01/2008


The term “block diagram” refers to a type of diagram used by engineers to visualize system interactions at a high level. Block-diagram visualization allows system engineers to separate needs analysis from system design, and start system-level design before finishing component-level designs.

 

Many authors have attempted to lay down formal rules for building block diagrams. In general, however, these rules tend to have limited applicability. As Captain Jack Sparrow’s crew likes to say: “We think of them more as guidelines than as actual rules.”

 

Some useful guidelines include:

 

  • Represent subsystems by rectangle shapes.

  • Interconnect blocks with unidirectional directed (arrow) lines.

  • Identify each block with a subsystem name.

  • Write transfer function formulas for each output into the each block.

  • Label all inputs and outputs with an appropriate variable designation (such as Vi for input voltage and Vo for output voltage).

Block diagrams styles are almost infinitely variable.

Valid block diagram styles vary enormously. Sometimes block diagrams in Control Engineering use two dimensional rectangular shapes, sometimes they use three dimensional boxes, and sometimes they use graphical representations. What is always important is that the visual representation portrays the important relationships in a concise and easily understandable way.

 

Function block programming

 

Because block diagrams are a visual language for describing actions in a complex system, it is possible to formalize them into a specialized programmable logic controller (PLC) programming language. Function block diagrams are one of five programming languages defined in part 3 of the IEC 61131 standard. Since this is a real, bona fide computer programming language, it is highly formalized with strict rules for how diagrams are to be built.

 

Directed lines are used to connect input variables to function inputs, function outputs to output variables, and function outputs to inputs of other functions.

 

It is important to keep in mind that these blocks portray mathematical or logical operations that occur in time sequence. They do not represent the physical entities, such as processors or relays, that perform those operations.

 

The rules require logical sequence to go from left to right and top to bottom. This rule expresses the fact that the function block diagram is a computer language depicting actions that happen in time sequence.

 

Software packages are available to make building specialized block diagrams for most engineering disciplines. Microsoft’s Visio Technical includes templates for general purpose, as well as special purpose, block diagrams. Of course, engineers have been scratching out block diagrams by hand on paper, chalkboard, and backs of envelopes for centuries, and this method is often the quickest and easiest way to organize your thoughts.

 

 

 

 

Author Information

C.G. Masi is a senior editor at Control Engineering. Contact him at charlie.masi@reedbusiness.com .

 



No comments
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by...
Each year, a panel of Control Engineering editors and industry expert judges select the System Integrator of the Year Award winners.
Control Engineering Leaders Under 40 identifies and gives recognition to young engineers who...
Learn more about methods used to ensure that the integration between the safety system and the process control...
Adding industrial toughness and reliability to Ethernet eGuide
Technological advances like multiple-in-multiple-out (MIMO) transmitting and receiving
Big plans for small nuclear reactors: Simpler, safer control designs; Smarter manufacturing; Industrial cloud; Mobile HMI; Controls convergence
Virtualization advice: 4 ways splitting servers can help manufacturing; Efficient motion controls; Fill the brain drain; Learn from the HART Plant of the Year
Two sides to process safety: Combining human and technical factors in your program; Preparing HMI graphics for migrations; Mechatronics and safety; Engineers' Choice Awards
The Ask Control Engineering blog covers all aspects of automation, including motors, drives, sensors, motion control, machine control, and embedded systems.
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
News and comments from Control Engineering process industries editor, Peter Welander.
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
This is a blog from the trenches – written by engineers who are implementing and upgrading control systems every day across every industry.
Anthony Baker is a fictitious aggregation of experts from Callisto Integration, providing manufacturing consulting and systems integration.
Integrator Guide

Integrator Guide

Search the online Automation Integrator Guide
 

Create New Listing

Visit the System Integrators page to view past winners of Control Engineering's System Integrator of the Year Award and learn how to enter the competition. You will also find more information on system integrators and Control System Integrators Association.

Case Study Database

Case Study Database

Get more exposure for your case study by uploading it to the Control Engineering case study database, where end-users can identify relevant solutions and explore what the experts are doing to effectively implement a variety of technology and productivity related projects.

These case studies provide examples of how knowledgeable solution providers have used technology, processes and people to create effective and successful implementations in real-world situations. Case studies can be completed by filling out a simple online form where you can outline the project title, abstract, and full story in 1500 words or less; upload photos, videos and a logo.

Click here to visit the Case Study Database and upload your case study.