Agriculture Reference
In-Depth Information
Fig. 12.2
Grain output and grain fl ow measurement systems for combine harvesters
mass fl ow by accounting for the grain density (hl-weight) that was determined with
a measuring cylinder and a spring scale.
Two systems on the market (Claas Quantimeter and RDS Ceres) operate with a
light barrier in the upper part of the feed-fl ow side of the clean grain elevator
(Fig.
12.2
, system 2). The grain piles on the elevator paddles interrupt the light
beam. From the length of the dark phase and from calibration functions, the height
and hence the volume of the grain load on the paddles is calculated. The zero tare
value is obtained from the darkening rate when the elevator is running empty. A tilt
sensor is used to compensate for the infl uence of non-uniform loading of the elevator
paddles on a side slope. The hl-weight for transforming into
mass-fl ow
is determined
with a beam-balance. In all recording systems, this is converted into the area yield
by referencing to the harvested area, which is calculated from the cutting width
and the harvesting speed (wheel sensor). Finally, with all combine yield sensing
systems, the grain fl ow and the yield can be adjusted to standard moisture by using
a continuously operating moisture sensor in the clean grain elevator.
For directly
determining the mass
of the grain fl ow, either a force/impact
measurement principle or on the absorption of gamma rays by mass in a radiometric
measuring system is used.
One early measurement system, which was taken from the market a few years
ago, operated according to the radiometric principle (Massey Ferguson Flowcontrol).
The grain discharged from the elevator paddles passed through a region between a
weakly radioactive source (Americium 241, activity 35 MBq) and a radiation sensor.
As it did so, radiation was absorbed (Fig.
12.2
, system 3). The degree of absorption
corresponded to the mass per unit area of the grain in the region of the measuring
