QUESTION:

I need to find a control network with sufficient vendor and industry support—a control network for which I can find multiple sources of controllers, motors, drives, sensors, power controllers, HMIs, pneumatic components, and hydraulic components. What’s my best option?

– From January 2007 Control Design

Ethernet Is the Answer
We use Ethernet as a machine interconnect network almost exclusively. Ethernet is the most popular PC network, and PCs are becoming more common as industrial control elements and platforms for developing operator interfaces.

There are some specialty applications—multiaxis synchronized motion systems or systems polling a lot of data—that require time-critical data gathering at 20 msec or faster scan rates. In these applications, Ethernet’s lack of determinism can be an issue, but bandwidth advances being made will continue to erase these constraints.

We often configure operator interfaces using Visual Basic (VB), and it’s easy to interact with an Ethernet network using VB software. Other HMI packages for the PC also support Ethernet, so designers’ choices aren’t constrained. We’ve worked with various remote I/O, different drives, and many PLCs. The majority of new devices support Ethernet connectivity.

For example, we recently finished developing an inkjet marking system for a machine that boxes apples. We used VB to develop the operator interface and Ethernet to connect to the inkjet print head. In the old days, proprietary hardware and software would have been used, but the open system approach using Ethernet made the system much easier to design and maintain.

Another benefit of Ethernet is that it allows users to combine standard off-the-shelf components for network hardware, providing a choice of manufacturer and vendor and, ultimately, the best price.

A side note: Ethernet media is standardized, but different manufacturers will support different Ethernet protocols. Users need to be aware of this as they define how hardware is integrated.

Although we think an Ethernet network gives many benefits to control system designers, we’re not advocating plopping a control system onto an existing Ethernet business network. Control networks need to be exclusively for control.

Clay Horste, Engineer, Concept Systems

We Like Modbus
In our experience as an industrial communications software developer and supplier, Modbus and Modbus/TCP are the most prevalent by far at the controller/instrumentation level. Since our inception in 1994, Modbus has been the leader due to the many devices and software that implement the protocol. This  broad support is due to several reasons:

• Open, standards-based protocol
• Easy to deploy, scalable, and small footprint
• Media independent
• Available conformance testing

Modbus/TCP has become the No. 1 protocol for industrial Ethernet. We believe this is a result of more devices becoming Ethernet-enabled combined with a very small learning curve when moving from Modbus to Modbus/TCP.

Many devices that implement proprietary protocols also implement Modbus and/or Modbus/TCP, providing compatibility with a huge number of Modbus-enabled software packages, SCADA systems, and devices.

We see growing demand for EtherNet/IP, though not at the rate of Modbus/TCP. While EtherNet/IP comes with a wealth of pre-defined object specifications that handle a broad range of device types and includes mechanisms for bridging and routing, we believe the slower rate of adoption is partly due to the complexity of the multi-layered protocol.

Mark Markarian, Vice President of Engineering, Automated Solutions

Network Must Support Your Machine
The convergence of motion control and I/O networks has become an increasingly important evolutionary step in machine control because the market sees device networks incorporating motion control capabilities and motion control networks incorporating I/O capabilities.

In tandem, the latest generation of technologies and standards has further expanded the network capabilities with:

• Multi-master capabilities that reduce network traffic and improve event handling 
• IEEE 1588 standard for time-based synchronization 
• Self-healing networking technology for high-availability systems
• Ethernet-compliant networks that use existing, unmodified Ethernet, and reduce the number of specialized networks
• Ethernet-based networks that make modifications to Ethernet standards, and provide some level of compatibility for linking with standard Ethernet-compliant networks.

The challenge for end users and machine builders is to choose the networking technology that provides device interoperability during the lifecycle of the system. The requirements for networking technology should consider the designers’ efforts to incorporate alternative devices in both the motion control subsystem and in ancillary equipment.