Tractors can ‘Plough On’ ahead thanks to Contrinex’s Inductive sensors

Modern tractors are complex, very flexible and capable machines which are constantly being developed over the century since they replaced the traction engine. Contrinex’s rugged inductive sensors, available from PLUS Automation, are utilised by a family of tractors that offer their drivers the choice between all-wheel steering for example on difficult terrain and two-wheel steering for on-road use when moving between fields or hauling loads for example.

When two-wheel steering is selected, the front wheels are used for steering and the rear axle is locked in the straight-ahead position. To ensure the precise alignment of the rear axle and the tractor’s steering geometry, Contrinex’s inductive sensors are trusted to detect the straight-ahead position accurately and reliably. The sensor was selected because of its robustness and long sensing distance which remove the possibility of the sensor being accidentally damaged.


A family of exceptionally versatile multi-purpose tractors provide four-wheel drive and the choice to switch between front and all-wheel steering. This added complexity needs to be absolutely reliable, on all types of terrain and in all weather conditions, because it is not uncommon for tractors to work many long days, perhaps for 18 hours or more over consecutive days at busy times like at harvest.

All-wheel steering is advantageous on extreme terrain or where increased manoeuvrability is required, for example, loading and unloading in a congested farmyard or barns. However, the default two-wheel steering configuration using the front wheels is best suited for faster driving for example for hauling on the road, where the rear axle is locked in the straight-ahead position to prevent misalignment of the rear wheels.

A rugged, reliable and accurate sensor system is required to detect the straight-ahead position of the rear axle before it is locked. The sensor must withstand significant mechanical shock and vibration and also be impervious to water ingress. Additionally, it should accommodate the extremes of temperature experienced during all-year-round operation.


Despite the application being a demanding one, inductive sensors from the Contrinex ‘Basic’ range, the 600 Series are rugged, reliable and able to accommodate the required extremes of temperature.

An M8-sized sensor, in a V2A/AISI 303 stainless-steel body with vacuum-encapsulated electronics, is well suited to this cost-sensitive but mechanically demanding environment, and it is rated for operation at temperatures between -25oC and 70oC.

The sensor is mounted immediately below one end of the rack and detects the position of a narrow flange attached to each end of the vehicle’s hydraulic power-steering rack. A sensing distance of 2mm eliminates any possibility of accidental collision with the flange the flange as it passes over the sensing face.

The sensor selected has a PNP output with an integral M8 connector and is connected to the vehicle’s central controller via a flexible PVC-sheathed cable. Adding the sensor requires minimal modification to the vehicle’s control systems, and maintenance is simple and speedy.

The sensor detects the straight-ahead position of the vehicle’s rear axle repeatably and accurately, ensuring the correct, reliable engagement of two-wheel steering. Contrinex inductive sensors provide the customer with a cost-effective fit-and-forget solution to a challenging problem.

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