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Dynamic Weighing for Accurate Fertilizer Application

2016-05-11 16:29   Article Source:Source Journal of Agricultural   View Times:
The mass flow of fertilizer spreaders must be calibrated for different types of fertilizer. To obtain an accurate fertilizer application a manual calibration procedure has to be repeated frequently.

An automatic calibration is possible when actual fertilizer mass flow is known. One method to determine mass flow is to monitor the weight decrease of the spreader during fertilizer application. When spreader weight differs significantly from the applied amount of fertilizer according to the current calibration, the dose controller calibration is adjusted.

In this research a dynamic weighing system for automatic flow controller calibration is presented (figure 1). Monitoring of spreader weight also offers the opportunity to log spreader performance, which is important for on farm evaluation of crop yield to the applied fertilizer strategy.

figure 1

Materials and Method

Two strain gauge load cells are mounted on a frame between tractor hitch and spreader as sketched in the figure below. The entire spreader rests vertically on load cell A, suspended by a reversed parallellogram. Load cell B measures a known load which gives information on vertical acceleration and on inclination of the spreader. figure 2


The dynamic weighing filter algorithm consists of a low pass filter for the load cell signals and a proportional correction from load cell B on load cell A. Figure 3 shows the results of filtering and correction of a dynamic signal acquired at 2 m/s driving velocity on rough surface.

figure 3

The filter and correction procedure delay is 1 second and the standard deviation of the determined mass is 1.8 kg for this experiment.

The algorithm to adjust the calibration of the flow controller is based on a linear regression between predicted weight decrease at current calibration and weight decrease measured by dynamic weighing.

A calibration adjustment is permitted when the level of the 99% confidence interval of this linear regression coefficient is equal to or below the accuracy of the current calibration.

figure 4

With an initial calibration accuracy preset at 10%, a simulation shows how the algorithm starts to adjust calibration after a mass decrease of 35 kg. A calibration accuracy of 1% is reached after spreading approximately 150 kg. of fertilizer. 

Respective topics: Dynamic Weighing  
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