BARTINGTON INSTRUMENTS
Page 25 of 61 OM1800/26
automatically applies corrections, must be carried out in a previously selected low magnetic
gradient area.
Note:
The setting-up procedure takes only a few minutes. It should be carried out after the
instrument has been assembled and left switched on for about 15 minutes. The rotational
errors should be checked occasionally, at the original set-up position, and the setting up
procedure repeated as necessary.
Note:
Setting up a single sensor unit is carried out with the operator holding the unit in the
normal way. Setting up a dual sensor unit may be carried out with or without the harness.
15.2. Selecting a Site for Error Measurement and Adjustment
Note:
Before attempting to set up the instrument or make any measurements, ensure the
operator is completely free of magnetic materials: see
Operator Magnetic Hygiene
.
To check the sensor errors and apply corrections, the sensor must be positioned in a low
magnetic gradient environment.
1. Select a site away from roads, drains and any possible magnetic objects. The instrument set-
up will only be as good as the area used for the set-up, so select the area with care.
2. Switch on the power using the
ON/OFF
switch, select the appropriate settings from the
Set
parameters
menu, and then leave the sensor to warm up for a few minutes.
3. Select
Start scan
and scan the operating area whilst holding the instrument vertically straight
and keeping the sensors pointing in a constant direction. Search for an area where the
reading on the display does not vary by more than about 0.5nT when moving about 1m in
any direction. The two sensors may not have the same value before completing the set-up
process so it is important to concentrate only on the variations at this stage.
4. When a convenient spot has been found, ensure that the reading from either sensor does not
change by more than about 2nT when raising the sensors vertically from about 30 to 60cm
above the surface.
5. Mark this reference area for future use.
Note:
When operating with two or more gradiometers, both units can be checked
independently over the same reference point as necessary.
15.3. Error Measurement
1. To measure and correct the errors in the sensors, it is necessary to know the directions of
magnetic north/south and east/west with reasonable accuracy. Use a compass to determine
