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18
Basic Calibration Procedure (Continued)
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, to recalculate the constant and hence the number of
crank turns.
If there is a significant difference between the figure used for calculations in this manual, 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 also be
adjusted on the hectaremeter.
1 To recalculate the constant due to altered conditions or specific requirements use the formulae
detailed in Table 4 or 5 (Page 17).
2 To obtain the rolling circumference of the tyre:
Half 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 5 revolutions until the mark on
the tyre is again at 90
0
to the ground.
Measure the distance along the ground
and divide by 5 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 9). The disc calculator consists of
3 scales. An outer white scale (1) for all seed rates
above 30 kg/ha and an inner scale (2) for all seed rates
below 30 kg/ha. On the middle coloured scale (3) are all the gearbox
setting numbers to a maximum value of 100.
Fig 9
Setting Example (Desired Seed Rate 125kg/ha)
1 From the calibration procedure at a gearbox lever setting of “70”, a seed rate of 175 kg/ha
is obtained.
2 Turn the inner disc until the measured seed rate of 175kg/ha (A) is in line with the related
actual gearbox setting of “70”(B) (Fig 9).
3 Read off from the disc rule the necessary gearbox setting for the required seed rate of
125kg/ha (C). In this example the correct setting is “50” (D) (Fig 9).
4 To be on the safe side the new gearbox setting can be checked by another calibration test.