Anaheim, CA —Concerned over a lack of openness, engineers and sensor manufacturers are pushing for standards that would simplify networking of industrial sensors. Speaking at the recent Sensors Expo here, both groups said that new standards need to be adopted as a means of dealing with the proliferation of network buses now available in the industrial marketplace. By some counts, there are now more than 60 proprietary network buses, many of which are incompatible with the sensors and controllers offered by competing companies.
The new standards—IEEE P1451.3 and P1451.4—call for an open method for tying sensors to network buses. "This would be a big step forward for the transducer makers," says Lee Eccles, senior principal engineer for flight test at Boeing Commercial Airplane Group (Seattle, WA). "Few of them have the wherewithal to go out and support tens of different buses. This lets them concentrate on their area of expertise, rather than on the entire industrial market."
Under IEEE P1451.3 and .4, makers of transducers and other sensors wouldn't need to design their products for compatibility with all industrial buses. Instead, IEEE calls for sensors to connect to a standard "transducer bus," which would interface with the proprietary buses—such as Profibus, DeviceNet, or SDS—through an interface known as an NCAP (Network Capable Application Processor). The new standards would complement two existing standards—IEEE 1451.1 and .2.
Under IEEE's proposed 1451.3 guideline, transducers would connect to a standard bus, which would interface with proprietary buses through a network translator, known as NCAP.
These two newest edicts call for implementation of the transducer bus, along with greater bandwidth and versatility in networked systems. Buses specified under P1451.3 would operate at 50 MHz, compared to 1 MHz under earlier specifications. Advances in P1451.4 would accommodate analog transducers.
For OEM engineers, the proposed standards could help eliminate the wiring problems caused by discrete, point-to-point wiring of sensors. Boeing, for example, plans to use IEEE 1451-based systems for flight test applications on its 777 aircraft. By connecting pressure transducers to a bus, instead of using discrete wiring, Boeing engineers say they can dramatically reduce the thickness of wiring bundles. In past programs, such as the Boeing 747, each sensor was separately wired to a multiplexer in the aircraft's fuselage. Doing it that way, the wiring bundles in the aircraft's wings were often a foot thick. In contrast, Boeing engineers say that networking could reduce the bundle to about a half-inch thick in the 777.
Engineers can, of course, network their sensors today without an open standard. But networking today requires dependence on suppliers who often market closed systems. "We're all looking for plug-and-play," notes Dan Jones, president of IncreMotion Associates (Thousand Oaks, CA), an industrial consulting firm. "But too often today we get plug-and-pray."
If network standards can be adopted, industrial consultants say that OEM design engineers would be the biggest beneficiaries. "Everyone agrees that open controls are the wave of the future," says Tom Bullock, president of Industrial Controls Consulting (Fond du Lac, WI). "With open controls, you could buy products from five different vendors, hook them together and have them work. But we need a single standard that everyone can adhere to."