New trends and old friends in network choices

"ABB’s wireless technology WISA (Wireless Interface to Sensors and Actuators) is designed specifically for on-line sensor/actuator communication in factory automation control applications," adds Jeffrey. “This means hundreds of nodes have to communicate in the 10 msec range. This requires a previously unheard-of level of timing and high reliability, especially in the presence of a wide variety of industrial disturbances.”

Jeffrey says work is ongoing to add position encoders, other machine sensors and field I/O devices to the product list. He also says it may be possible in the near future to power actuators and even motors via the electromagnetic field. The implications of this technology are interesting, if not staggering. Jeffrey is talking about the possibility of a completely wireless machine; that is, no power wires, no I/O wiring, and no hardwired machine network. The only contact the machine would have to the outside world would be from its base station and PLC.

Extend the concept to hazardous areas, unit process controllers, skid-mounted systems, distillation columns, machine tools, and anything else that can be enclosed in an electromagnetic field, and it could spell the end to all the standard fieldbuses, device buses and I/O networks. This is definitely a development to watch.

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Publish-Subscribe in Real Time

ANOTHER POTENTIAL network trend involves the newest real-time networking system for the WinTel platform: the OMG Data-Distribution Service (DDS). This is a publish-subscribe scheme that works with Windows operating systems. It hasn’t exactly caught fire, but it shows promise in its ability to make WinTel systems more suitable for networking in an industrial environment.

“Many real-time applications must model some of their communication patterns as a pure data-centric exchange where applications publish, supply or stream data, which is then available to any interested application,” explains Gerardo Pardo-Castellote, Ph.D., chairman of the DDS Standards Committee and chief technology officer of Real-Time Innovations. These applications include industrial automation and distributed control. The lack of standards in this area forced application developers to use proprietary solutions or develop the infrastructure themselves. With the recent introduction of the OMG Data-Distribution Service for Real Time Systems, there are now COTS products that provide this infrastructure.”

In a nutshell, this means the classic way of accessing data remotely in a standard WinTel system, using simple read and write instructions, doesn’t work well in real time. An instantaneous response can’t be guaranteed in an Ethernet LAN or WAN where computers enter and leave, and links have sporadic faults. The data-centric scheme in DDS, however, provides the performance, predictability and resource control required by embedded and real-time systems.

Kuka Controls recently announced the successful integration of RTI’s version of DDS (NDDS) into its VxWin operating system. The combination allows Wind River VxWorks and Windows XP Embedded to run on the same host processor and share data with a publish-subscribe scheme. Operations are unaffected by Windows “events,” ensuring failsafe real-time operations.

RTI intends to market its DDS product into the industrial space. “We will combine our NDDS with new tools for distributed system visualization, analysis and real-time debugging,” says Stan Schneider, CEO of RTI. “This platform will simplify design, ease development, and improve the quality and performance of real-time embedded systems in industrial automation applications.”