Duncan Enviro 740 - Calibration Constants and Seed Rate Calculator; Recalculating Calibration Constant; Using the Seed Rate Calculator Disc

20
fig 20
Recalculating the Constant
It is especially important in arable situations to
check the rolling circumference of the tyre when
in the cultivated area to be sown, and if necessary,
recalculate the constant and hence the number of crank
turns.
If there is a significant difference at that time from the figure
used for calculations in this manual (Fig 20), the constant
should be recalculated and hence the crank turns for those
particular conditions.
Note - If a significant difference is found in the rolling
circumference the H1 setting should be adjusted on the
hectaremeter. Refer P 24.
1 To recalculate the constant due to altered conditions or
specific requirements use the formulae in Fig 20.
2
To obtain the rolling circumference of the tyre 1/2 fill the
seed/fertiliser boxes or simulate
this loading.
Mark the tyre of the drill at 90
0
to the
ground and the point of contact with
a mark on the ground. Move the drill
forward 3 revolutions until the mark
on the tyre is again at 90
0
to the
ground. Measure the distance along
the ground and divide by 3 to give
the rolling circumference of the tyre.
Use of Seed Rate
Calculator
Determining the gear box
scale setting using the
calculator.
Usually the first calibration test yields
a different seed rate. However with
the value determined from the first
test it is possible to determine the
correct gearbox setting with the aid
of the enclosed disc calculator, Fig
21. The disc calculator consists of
3 scales. An outer white scale (Fig
High Speed
=
1.667
Constant
Rolling Circumference
of Tyre
Low Speed
=
1.038
Constant
Rolling Circumference
of Tyre
Rolling Circumference
used for calibration was... 3.76metres
(10 ply tyre)
Setting Example (Desired seed Rate 125kg/ha)
1 From the calibration procedure (described on P 17-19) at a gearbox lever
setting of “70” a seed rate of 175 kg/ha was obtained.
2 Turn the inner disc until the measured seed rate of 175kg/ha (Fig 21/A) is in
line with the related actual gearbox setting of “70”.(Fig 21/B)
3 Read off from the disc rule the necessary gearbox setting for the required
seed rate of 125kg/ha (Fig 21/C) In this example the correct setting is “50”
(Fig 21/D)
4 To be on the safe side the new gearbox setting can be checked by another
calibration test.
!