Device networking 101: your first installation


Somewhere in the world each day, an engineer decides to use a device level network instead of point-to-point wiring. A survey taken at a DeviceNet workshop in Chicago showed the #1 reason for investigating networks was: 'They're sexy.' True, we all like to blaze new trails, but in the pragmatic world of manufacturing, there must be a sound justification.

Q Why are you doing this?

  • Modularity-aids disassembly and re-assembly of the system; and allows easy replacement of failed components;

  • Wiring simplification-reduces system assembly time and mistakes;

  • Open architecture-maximizes choices and keeps prices competitive;

  • Preventative maintenance-so devices can warn users before something goes wrong;

  • Configurability-allows parameters to be set 'on the fly,' which adds functionality and saves time;

  • More information-networked device may provide additional process data, which may also be important for sending data to the enterprise; and finally

  • Cost savings-on huge installations, you will save money. However, most benefits are realized over time, not with the first installation. Subsequent advantages will prove much more valuable than shaving pennies up front.

Q Topology requirements?

A The dimensions and physical layout of your system make a big difference in which network you choose. Primary topologies include:

  • Trunk with drops-DeviceNet, AS-i, CANopen, ControlNet, Interbus, FOUNDATION Fieldbus H1;

  • Linear 'daisy chain'-Profibus; and

  • Star-Ethernet 10Base-T, 100Base-T

Is your system a long conveyor, a compact machine, or does it cover an entire shop floor? Physically draw out your system and see how nodes will be clustered together.

Q Speed, data requirements?

A Does your I/O need to be scanned every 2 msec? Or is 500 msec okay? Do your devices send a few bits of data, or hundreds of bytes? Are you mixing simple and complex devices on the same network? To answer these questions, determine the 'hard limits' and worst-case requirements of your design.

Which networks are available on specific devices you've chosen? This issue may force your hand, or at least limit your choices, if you are required to use a specific brand of PLC or other component.

Q How will you distribute power?

A Some networks deliver 24 V or loop current to devices, while others do not. This can be a convenience and/or a complication that you should consider.

Q Which network to use?

A After you've answered all of the previous questions, you're ready to choose a network. Secure some reference information. A useful Fieldbus Comparison Chart and white paper, '8 Fieldbuses & Industrial Ethernet,' are available by sending an e-mail to

Q Using multiple networks?

A Some OEMs must ship machines with any one of two to four different networks, especially if they have international customers. Careful planning can make this much easier. Some more questions to answer include:

  • Can you find devices that use the same mounting holes across multiple networks?

  • Can you use the same programs and software, instead of rewriting it each time you switch networks?

  • Can you use common configuration tools?

  • Can you use the same or similar connectors and wiring trays?

Q What about connectors?

A Most networks support a variety of connector schemes, from terminal blocks to waterproof connectors. Sometimes the expense of connectors is offset by convenience and reduced wiring problems.

Starting small

If this is your first network-based system, start with a small project and grow from there. If it's a large system, engage a systems integrator who has done this before.

Perry Sink, training director, Synergetic Micro Systems (Downers Grove, Ill.), produces diagnostic tools, PC and embedded interfaces for industrial networks, and is located at .

No comments
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by...
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
Choosing controllers: PLCs, PACs, IPCs, DCS? What's best for your application?; Wireless trends; Design, integration; Manufacturing Day; Product Exclusive
Variable speed drives: Smooth, efficient, electrically quite motion control; Process control upgrades; Mobile intelligence; Product finalists: Vote now; Product Exclusives
Machine design tips: Pneumatic or electric; Software upgrades; Ethernet advantages; Additive manufacturing; Engineering Leaders; Product exclusives: PLC, HMI, IO
This article collection contains the 5 most referenced articles on improving the use of PID.
Learn how Industry 4.0 adds supply chain efficiency, optimizes pricing, improves quality, and more.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Cyber security cost-efficient for industrial control systems; Extracting full value from operational data; Managing cyber security risks
Drilling for Big Data: Managing the flow of information; Big data drilldown series: Challenge and opportunity; OT to IT: Creating a circle of improvement; Industry loses best workers, again
Pipeline vulnerabilities? Securing hydrocarbon transit; Predictive analytics hit the mainstream; Dirty pipelines decrease flow, production—pig your line; Ensuring pipeline physical and cyber security