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BARTINGTON INSTRUMENTS
Page 57 of 61 OM1800/26
For a single sensor gradiometer, the first mark should be at 1m from the end and subsequent
marks at 2m intervals. This corresponds to the arrangement in
Figure 12
. For a dual sensor
gradiometer, the first mark should be at 2m, and subsequent marks at intervals of 4m as in
Figure 13
. These are to be used at the edges of the Grid to show the traverse limits and align the
trapeze when the centres of the ends of the trapeze are placed on the marks on the start and
finish ropes.
A.7. Setting Out the Area
Before setting out the area, switch on the gradiometer to allow the maximum warm up time
before setting up the instrument.
Set out the site using standard survey techniques such as a total station at some national Grid
reference point. Establish the positions of the corners of the Grids and mark with the bamboo
canes. Select the first Grid to be surveyed and loop the edge lines over the canes at opposite
sides of the Grid to mark the start and finish of the traverses.
A.8. Setting up the Gradiometer
•
See also
Checking and Adjusting the Sensors
.
Note:
Ensure that the instrument has been switched on for at least 15 minutes prior to
setting up.
Note:
Before setting up, always check the operator for magnetic materials. Run the
instrument in Scan Mode fixed in one position and check that the readings do not change
when the operator moves close to the upper and lower sensors. (See also
Operator
Magnetic Hygiene
.)
Note:
As rotational and tilt errors are likely to be present prior to setting up, it is essential
to hold the sensor in one orientation whilst searching the ground for a low gradient area
over which to set up.
A.9. Logging Data
•
See also
Survey Operation (Grid Mode)
.
At the edge of the Grid where the survey will start, stretch the trapeze across the Grid with the
centre marks of the trapeze bars over the first marks of the ropes, as in
Figure 15
for a single
sensor gradiometer or
Figure 16
for a dual sensor unit.
The trapeze lines then mark the position of the first two traverses, 0.5 and 1.5m from one end of
the Grid. Remember that the first traverse will start in a clockwise direction. When using a single
sensor gradiometer, the operator will carry the sensor over the first traverse line and back along