BARTINGTON INSTRUMENTS
Page 26 of 61 OM1800/26
easily identified features in the landscape on the north/south and east/west directions from
the magnetically clean area selected above.
Note:
Be sure to remove the compass from the area afterwards or it will interfere with the
setup procedure.
2. Operate the instrument in Scan Mode (see
Scan Mode (Grid Mode)
) in the 100nT range, in the
direction of the arrow marked on the connector junction block of each Grad-01-1000L sensor
(see
Figure 6
). Keeping the sensors over the magnetically clean reference point, measure the
errors as follows:
Error
Cause
Maximum value
North/South
Misalignment of the sensors in the
direction of the heading direction
arrow.
When the arrow points north/
south.
East/West
Misalignment of the sensors at
right angles to the direction of the
arrow.
When the arrow points east/west.
Vertical
Imbalance between the top
(reference) sensor and the lower
(measuring) sensor.
When the gradiometer is inverted.
Offset
A fixed zero offset error
regardless of the orientation of the
gradiometer.
n/a
Note:
For optimum results, the difference in the gradiometer readings should vary by no
more than about
±
0.2nT for any of the above tests, and the offset error should also be less
than 0.2nT. If any error exceeds this value, adjust the gradiometer to reduce the variation
as indicated below.
15.4. Adjustment
Note:
The following is written assuming a dual sensor gradiometer system is used.
The procedure is the same for a single system, but read ‘sensor’ and ‘arrow’ instead of
‘sensors’ and ‘arrows’.
Note:
This procedure must be carried out with the gradiometer over the low gradient site
selected earlier. The operator must rotate the complete gradiometer assembly to align the
sensors as required by the program, but must keep the assembly static, and the sensor
tubes as vertical as possible, while the instrument carries out the necessary adjustments.
Note:
If only one sensor is used, keep the sensor over the same point while the assembly
is rotated. If two sensors are used, the routine sets both sensors at the same time, and
