MANUAL – REFLEX EZ-TRAC™ | 19
If you have been using a rather long survey interval, it may be worth
while rerunning the survey over the affected section of hole, using a
shorter interval. You then use the merge facility to join the
recalculated section into the original survey.
5.4 Survey station depth
The exact depth of a survey station is not critical, but the more
precisely the instrument is positioned at the survey station the more
accurate the survey.
If a hole deviates considerably, station accuracy may become more
important.
Drill rods generally have the same known length. This makes it easy,
simply by counting rods, to put the instrument where you want it in the
hole.
Coiled running systems, such as wire, pipe or rod, should be fully
calibrated or have a linear counter. However, it is possible, by
measuring out a given length on the ground or up the rig mast, to
mark equal intervals on the running system and count these as they
are wound into or out of the hole.
5.5 Centralization
Centralization, or the likelihood of the instrument lying parallel to the
hole, is also important for the survey accuracy.
If centralization – that is, hole inner diameter minus tool outer
diameter – is within a few millimetres, the possibility of misalignment
of the instrument is small. The accuracy of the survey will be
unaffected.
If however you run the instrument in a hole with much larger
diameter, the potential error could approach several degrees. If that is
repeated throughout the hole then, for every 100 metres, the error will
increase.
Generally, the problem is minimised on surveys taken while pulling
out of downward inclined holes. This advantage is not available in
upward holes.
In a horizontal or shallow inclined hole, gravity will try to pull the
instrument parallel to the axis of the hole. In steeper holes this may
not be valid.
5.6 Temperature
The temperature impacts the accuracy of the instrument. For full
survey accuracy of all parameters, the ambient temperature must be
within 0 ºC to +60 ºC.
5.7 Comparisons and Averaging
By performing a multi shot survey in both directions, repeatability
comparisons and averaging of results are possible. By averaging the
survey data, a more accurate result will be obtained.
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