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August, 1999
PRECISION AGRICULTURE RESEARCH
A joint project between the University of Nebraska andSuccessful Farming magazine was presented at the recent Agricultural Engineeringmeeting. For each of the tests in the case studies, the weight measured by theyield monitor was compared to a weigh wagon after each combine pass.
In the case study, two farmers on level slope, high yieldingcorn, were asked to operate their combines under-capacity (20-30% reduction inspeed), over-capacity (20-30% increase in speed) and at their typical speed.
Farmer A had a Case-IH 2366 with an 8-row head and an AFSyield monitor. It was calibrated at the beginning of the season using 22% cornrun at four flow rates (½, ¾, full and 1-ccapacity); additional loads were added to the calibration as the seasonprogressed (lower moisture contents). Under-capacity was 3.0 mph; full-capacity4 to 4-1/2 mph; over-capacity 5 to 5-1/2 mph.
Farmer A had no significant differences between the weighwagon and yield monitor at normal capacity; significant differences were foundat both the under- and over-capacity runs. Although Farmer A followed therecommended method of calibrating at varying capacities, these errors exceed theadvertised claims and additional review appears to be merited.
Farmer B had a John Deere 9500 series with a 6-row head andan Ag Leader 3000 yield monitor. It was calibrated using several loads of 17%moisture corn. Under-capacity was 2-1/2 mph; full-capacity 3-1/2 mph;over-capacity 4-1/2 mph.
Farmer B consistently overestimated the weights compared to the weigh wagon.The error decreased as the operating speed increased, reflecting the calibrationhaving been done at higher combine capacities. Since the header was oversizedfor the combine capacity, the combine could not be overloaded. The observederrors indicated that the monitor was not adequately calibrated for the fullrange of combine operations. The errors exceeded the advertised claims andadditional review appears to be merited.
In the third case study, Farmer C had a John Deere 9500series with a 6-row head and an Ag Leader 2000 yield monitor. It was calibratedat the beginning of the season at 6-speeds (1-1/2 to 4 mph). The combine was runover a 5-10% slope at 4 mph downhill, and 2 to 4 mph uphill (a total of 5passes).
Conclusions
Calibration at various grain flow rates are important for accurate measurement; observed errors exceeded 10% when compared to weigh wagon results.
Slope effects need additional review to determine if more accurate area measurement is required; a 6% difference was measured between up and down slope travel.
For best accuracy, a constant flow rate of grain moving through the combine is more important than a constant combine speed.
Roger Brook
Paper copy of the paper is available on request to:brook@msue.msu.edu pleaseinclude your US Postal address.
