MANUAL – REFLEX EZ-TRAC™ | 14
5 About Survey Accuracy
This chapter describes the survey accuracy of REFLEX EZ-TRAC™ and
explains the sources of errors.
5.1 Introduction
REFLEX™
surveying instruments are designed to provide accurate
and reliable survey data.
The range and typical error of the parameters measured by
REFLEX EZ-TRAC™ are shown in the table below.
Figure 3 Range and typical error
Parameter Range Typical error
Azimuth 0º to 360º ± 0.35º
Dip ± 90º from horizontal ± 0.25º
Magnetic field strength 0 to 100,000 nT ± 50 nT
Magnetic dip ± 90º from horizontal ± 0.25º
Gravity tool face 0º to 360º ± 0.25º
Magnetic tool face 0º to 360º ± 0.35º
5.2 Magnetic interference
As for all magnetic instruments, any interference from man-made or
natural magnetism will disturb the magnetometers, which will result in
incorrect measurements.
Magnetic instruments try to measure their own heading relative to the
direction of the magnetic north. If that field direction is distorted by
e.g. a deposit of magnetite, the instrument will simply record a
deviation of the hole. You will not know whether that is a real
deviation or simply distortion of the magnetic vector.
Incorrect interpretation of azimuth data in mineral exploration may
result in heavy costs. These may range from trying to straighten an
apparently deviated hole to sinking shafts in the wrong position.
In construction projects, where anomalies are more often man-made,
the results may be equally serious. The most common are voids in
grout and freeze curtains, ground anchor interference and incorrect
geotechnical data.
5.2.1 Man-made interference from within the hole
It is vital that the instrument does not come closer than three meters
to rods, casing or other in-hole tools made from any form of ferrous,
magnetic metal.
All measurements must always be made in an open section of the
hole, unless it is lined with plastic or other non-ferrous casing or rod.
If ferrous metal rod or wire is used to run the instrument into the hole,
a minimum of three 1.5 meter long aluminium extension rods have to
be used.
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