Agricultural Machinery: Harvester and Seeder Hydraulic Cylinders

Displacement measurement on agricultural machinery is increasing with the spread of autonomous driving and precision farming. Typical measuring points include header height and reel position on a harvester, contour-following mechanisms and down-force adjustment on a seeder, boom lift and levelling, and tractor rear-hitch position. All of these mechanisms work in the field — mud, straw debris, dust, rain and washdown, severe jolting, and long seasonal storage. The first priority in selection is survivability and maintenance-free operation; accuracy comes second.

Functional role of displacement measuring points on agricultural machines

Header-height feedback is used for contour following: the header is held at a set height above the ground as the terrain undulates, reducing uneven stubble and soil-entry damage. Down-force and contour-stroke feedback on a seeder are used to keep sowing depth consistent, which directly affects emergence rate. Boom-lift and levelling feedback are used to maintain spray height, which affects droplet-deposition uniformity. The shared character of all three is that the control objective is “following”, not “precise positioning”, so a 20-100 μm resolution grade is sufficient; the emphasis should be on response and reliability.

Four constraints of the field environment

First, high-pressure washdown: after the working season the whole machine is washed with a high-pressure water jet. Ordinary-rated connectors take in water easily; IP69K is recommended at washdown locations (for measured differences between ratings see what IP65/67/68/69K really mean). Second, jolting and shock: field-surface excitation is strong; vibration and shock ratings should cover the actual duty (for example of the order of 25 g vibration / 100 g shock). Third, straw wrapping and debris: an exposed rod is easily scored by wrapping material; in-cylinder mounting is preferred. Fourth, wide temperature and long storage: winter storage temperatures are low; the distinction between operating temperature and storage temperature must be checked (see operating temperature vs. storage temperature).

Measuring-point schemes

Why in-cylinder is preferred

Agricultural cylinders are mostly medium- to low-pressure systems. In-cylinder mounting places the rod entirely inside a deep bore in the piston rod, avoiding the three risks of straw wrapping, mud envelopment and knocks, and adding no external installation space. The implementation prerequisite is that the piston rod can take a deep bore (minimum bore generally ≥12.7 mm) and meet the pressure rating (by series: Series 16/16R is 350 bar working / 530 bar peak, Series 17/17EX is 350/600 bar, Series 19 in-cylinder is 300/600 bar; agricultural machines are usually well below this). For in-cylinder products see Series 16 in-cylinder. The exposed electronics head relates to whole-machine mobile duty; see Series 13 mobile hydraulic. General points for a hydraulic closed loop are given in hydraulic cylinder position-control schemes; shared experience with construction machinery is in construction-machinery cylinder position schemes.

Whole-machine CAN network and operational data

Agricultural machines commonly use a CAN bus architecture. Specifying a CANopen (DSP406 profile) displacement sensor lets it hang directly on the vehicle network, reducing wiring and carrying diagnostic information. See Series 194 CANopen and the networking notes in the practical fieldbus guide. Once position data are aligned with worked area, speed and GNSS position, operational-quality reports such as sowing-depth distribution and header-height distribution can be generated — the foundation data of precision farming. Magnet selection and mounting details (remanence, temperature coefficient, anti-loosening) are given in selecting the permanent magnet (position magnet).