Agriculture Reference
In-Depth Information
Table 12.1
Errors of yield sensing systems for combine harvesters in practical use with fi eld
experiments
Period of
study, total
area, number of
grain tank loads
Combine
harvester
models,
grain spec.
Relative
calibrat.
error
in
% (av.)
Sensing system (in bold),
Meter (in italics),
Manuf.
(in brackets)
Stand.
dev. of rel.
error
in %
Light-barrier, system 2,
CERES 2,
(RDS)
3 years, 140 ha,
179 tank
loads
3 models,
4 grain
species
−0.14
3.43
Radiation, system 3,
FLOWCONTROL,
(MASSEY FERG.)
2 years, 140 ha,
132 tank
loads
2 models,
2 grain
species
−1.01
4.07
Force, system 5,
YM 2000,
(AGLEADER) or
LH565
(LH AGRO)
3 years, 130 ha,
182 tank
loads
3 models,
4 grain
species
−1.83
4.06
For system numbers see Fig.
12.2
(Demmel
2001
)
window. The material velocity, which was obtained from the elevator speed, was
used to calculate mass fl ow. Similar systems are used in food processing.
A number of
yield measurement systems
developed in the USA use the force/
impact measurement and is likewise fi tted into the elevator head in the discharge
path of the corn. The sensor consists either of a baffl e plate that is fi tted to a force-
measuring cell (AgLeader, Case) or of a curved plate fi tted to a spring element
measuring the displacement way (John Deere) or of a curved plate mounted in
patented geometry to a force measurement cell to compensate varying friction force
(Strubbe et al.
1996
; Strubbe
1997
). Corn hitting the baffl e plate or the curved
plate causes a force effect to the bending bar, the spring element or the load cell,
which is electrically sensed with strain gauges or the displacement sensor (Fig.
12.2
,
systems 4-6). Since this impact is the product of mass and velocity, it is possible
to calculate the mass fl ow. The material velocity is obtained, in turn, from the
elevator velocity.
All systems consist of the sensor element, processing, monitoring and data
storage units in the cab and have the possibility to integrate information from a
moisture sensor. Today most of the systems are factory installed accessories; some
products can be retrofi tted to some combines (Demmel
2001
).
Some authors report the evaluation of a single yield sensor under specifi c situations
in the fi eld (
e.g.
Perez-Munoz and Colvin
1994
, Senaei and Yule
1996
).
Extensive studies on the
measuring accuracy
of several sensing systems were
carried out in the years 1991-1995 (Demmel
2001
). The fi eld experiments
(Table
12.1
) were supplemented by joint test bench trials in 2000 and 2001 (Kormann
et al.
1998
; Demmel
2001
).
The level of accuracy in the fi eld experiments was determined by counter weighing
the grain tank loads on calibrated and certifi ed platform scales. The measuring
systems were examined, in part, on different combine harvester models with
different grain types in lightly to medium rolling fi elds (Table
12.1
).
The mean relative error represents a measure of the calibration quality. It should
be zero ideally, or at least close to zero. This requirement was successfully achieved
