14 November 1997

Spreader rate by weight

FOR years most spreaders have relied on a volumetric metering system (a variable sized aperture) to control the amount of fertiliser released from a hopper on to the spinners, yet fertiliser applications are assessed in weight.

The solution to this historic problem – which takes little if any account of changes in fertiliser density or conditions – is, of course, to employ a metering system activated by weight.

And that is what Greenland claims to have done with its new Rotaflow RS-XL EDW spreader. Four load cells monitor and compare the weight of fertiliser in the hopper with the forward speed of the tractor, constantly calibrating the spreader.

But life is not that simple. When a spreader works on slopes, the load cells, which only measure vertical forces, do not record weight accurately.

To overcome this hitch, the Greenland spreader is equipped with a fifth load cell attached to a weighted pendulum. By always staying in the vertical the degree of slope is recorded enabling the computer to compensate for any perceived weight loss on the other four load cells.

In use, the operator makes an initial calibration which, says Greenland, does not have to be particularly accurate – the spreader assesses the rate it should be spreading at.

Variations in forward speed, fertiliser density or climatic conditions are automatically compensated, so the required application rate is maintained.

Using load cells beneath the hopper enables Greenlands Rotaflo RS-XLfertiliser spreader to constantly maintain application rate.