6 December 1996

Perfect network out of reach

Farm machinery and computer technology are here to stay –

Andrew Pearce boots up our Communications Special with a look at integrated control of tractor and implement systems

REMEMBER CANbus? Its a form of network, devised to let hoards of electronic messages pass between different parts of a machine (or between machines) without equivalent hoards of wires.

Just two cables is all it takes, with electronic "gatekeepers" allowing and ordering small packets of information onto the system, where they zing along to be picked up by any brain, sensor or actuator that needs them.

CANbus is only one of several sorts of network, all of which are based on a Bosch system developed in the late 1980s. Massey, New Holland and Fendt are already using variants to control tractor hitches and such. Electronic specialists like RDS and Dickey-John have their own networks up and running in precision farming control systems, passing data on (say) spot fertiliser rate between the tractor and spreader. All these systems – some CANbus-based, some not – work just fine. So are we set for that great day when any tractor talks to any implement and vice versa?

Not quite. At present the possibility is spluttering along like a banger with a soggy fuse. All the time any one makers network is talking among itself theres no problem, but finding a common language.

There are three possible standards, all perilously close but not quite close enough to work together. In the United States, the Society of American Engineers-recommended J1939 standard is already being implemented on heavy trucks. Although J1939 is a high-spec system capable of speedy and complex data swapping, so far its mainly been developed for communication within a machine rather than between machines. So its application to tractor/implement control is presently limited.

The next two possibles – DIN 9684 and ISO 11783 – were conceived around the same time and were intended to standardise control between machines. The Germans are solidly behind the DIN standard; its a simpler system than the one the Americans are using with different wires and connectors. In DIN 9684, emphasis falls more on the implement than the tractor.

On the face of it, the potentially international standard ISO 11783 ought to be the answer. Parallelling the USAs J1939 in data-handling ability, it puts the emphasis back on the tractor, but uses completely different wiring and connections to the previous two alternatives so cant swap data with either. But as ISO standards are only achieved by international agreement and this one has been bogged down by international wrangling, nothing concrete is likely for at least a couple of years.

Finding a common standard for data exchange on a tractor/implement network (red) is proving tricky. International wrangling has a lot to answer for.(Diagram courtesy of Silsoe Research Institute.)