Opinion: Technologies Must Coexist for PLC Multiplexing
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Check out the PLC4TRUCKS recently discovered that the first-silicon Intellon P-485 test devices could not communicate with each other when Air-Weigh multiplexing PLC products were operating on the vehicle. The consortium suggested that Air-Weigh drop its existing technology in favor of the yet unproven P-485 chip. We have very respectfully objected and declined.
Our customer base is expanding quite rapidly with the aftermarket adoption of on-board scale technology and OEM adoption of suspension monitoring and control. We will not abandon our proven PLC technology, which is commercially available and very inexpensive.
Currently, PLC users coexist with each other on the vehicle. Air-Weigh’s PLC communication technology is based on commercially available and proven modem components from SGS Thompson and others. The chip itself is available from several sources for less than $5 each. These components utilize robust and well-understood frequency modulation that has been used globally for over 75 years, both on wires and through the air, in everything from early transistor radios to modern computer modems.
The industry should understand that there will not be a singular tractor-trailer PLC communication technology that meets the needs of the current and future industry tractor-trailer systems — several multiplexed data buses coexist today, such as J1587 and J1939. Perhaps two or three PLC standards will emerge over the next five to 10 years. This is why Air-Weigh believes the Society of Automotive Engineers and The Maintenance Council must put coexistence standards in place now, with the same rigorousness of current electronics compliance standards.
Vehicle wiring harness bandwidth is limited, and Air-Weigh is but one of several users of this limited resource. Clearly, bandwidth utilization will have the most significant impact on the future of next-generation PLC technology.
Early in the century, the Federal Communications Commission recognized that the broadcast bandwidth was limited, so standards were created that provided for a variety of emerging technologies and programming options. We encourage the SAE and TMC to set similar standards before any single such technology consumes the majority of the wiring harness bandwidth. Limiting future technologies in order to simply “light the ABS lamp” doesn’t make good sense.
Air-Weigh assesses the usable vehicle wiring bandwidth to be about 400 KHz wide (from 100 KHz to about 500 KHz). Our PLC technology uses 10 KHz centered down near the low end of spectrum at 130 KHz. Qualcomm’s TrailerTRACS also uses about 10 KHz up near the high end of spectrum at around 450 KHz.
Obviously, there is room for a plurality of such systems, each with up to 9600 baud or higher data communication capability. And as differing system integration needs arise over the coming years, newer, faster, and cheaper PLC techniques likely will evolve, which the industry will want to accommodate.
The J1587 status and diagnostic network on the tractor is already nearing capacity, and there are an equally significant number of safety and productivity devices coming to the trailer. Nearly all of these devices will require status and control communication between tractor and trailer. This creates additional concerns surrounding tractor-trailer gateway traffic and tractor network capacity.
Air-Weigh endorses the PLC4TRUCKS effort to propose standards to transmit trailer ABS status and other J1708/J1587-type status and diagnostic information. We are counting on the consortium to be successful in this effort.
But we also recognize that the current P-485 device under development is not coexistent and, once completed, will still not meet the needs for vehicle control functions. It is apparent that with future changes to size and weight regulations, driver-controlled functions will become increasingly important to all fleets.
This issue of wiring harness bandwidth and coexistence needs continuing discussion to avoid costly corrective redevelopment and regulations in the future.
Air-Weigh, Eugene, Ore., is a manufacturer and distributor of on-vehicle weight scales and multiplexing junction boxes, which use PLC technology to communicate. Before Ambros joined Air-Weigh, he was Rockwell Highway Transport Technical Director on the Automated Fuel Tax and J.B. Hunt RoadRider development programs.
