LTI TruPulse 360R User’s Manual Page 29
Copyright (c) [2017] Laser Technology, Inc. All Rights Reserved. Unauthorized duplication, in whole or in part, is strictly prohibited.
Local Magnetic Attractions
Local magnetic attractions are caused by objects of iron, steel, cobalt, nickel, and other
ferro-magnetic materials. Electric utility lines may also affect compass readings. Direct current
power utility lines will cause a fixed offset, and alternating currents will cause an unstable
compass reading. The effect that local attraction has on the compass depends upon the proximity
of the material to the compass and on the mass and strength of the local attraction. Small metallic
objects carried on or by the operator may affect the compass reading by as much as several
degrees. In some work situations, the strength of the interference could prevent the compass from
providing a useful azimuth. Usually the potential for local attraction can be determined by
visually inspecting the site or from local knowledge of any buried utilities.
The following objects may potentially affect the TruPulse 360R’s performance
and should be avoided:
Batteries Nails
Data collectors or computers Pin flags
Hatchets Portable radios
Homemade yokes Steel-rimmed eyeglasses
Magnetic antenna mounts or spring hinge
Metal watch bands Tripod tribrachs
Tripods
It is recommended that the data collector be located a minimum of 18 inches (46 centimeters)
away from the TruPulse 360R.
Field Tests for Local Magnetic Conditions
The following simple tests can be used in the field to test for local magnetic interference.
If you are working on a street, and you know its orientation relative to true North, aim
down the street and take a measurement. Nearly 80% of the streets in the US are
oriented in a north-south or east-west direction.
o The azimuth from the compass should match the known direction of the
street.
Choose a target at least 100 meters away (e.g., a pole) and shoot to it. Note the
azimuth. Then step backwards or forwards 1 meter (or 1 yard) along the sight line to
the target and shoot again.
o The second azimuth should be within 1/10th to 5/10ths of a degree of the
first azimuth. If it is, you are very likely within an anomaly-free area.
o For increased confidence, repeat the test to a target at 90 degrees to the
azimuth of the first target.
This third test can be performed if you are in a questionable area. Aim and measure to
your prospective next target and note the azimuth. Move to the next station and aim
and measure back to the original station.
o The azimuths should be 180 degrees different, plus or minus a few tenths
of a degree.
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