Geokon GK-604D, User Manual

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5) Make sure that the GK-604D IRA is set to Data Set 1.Take the first reading, pull
up on the cable until the next cable marker sits in the cable hold and, after a
short pause, take another reading.
6) Continue in this way until the top marker is reached, remove the cable hold,
pull the inclinometer out of the hole.
7) Twist the probe through 180 degrees then lower it to the bottom of the hole.
Tap the “Dataset 1” button to select data set 2.
8) Repeat steps 3 to 6.
9) Press the “ok” to save the data.
A.3 Checksums and “Face Errors” on Inclinometer Probes
Many users have expressed concern about checksums or “face errors” on
inclinometer probes. They are concerned with the affect of the “face error” on the
accuracy of the readings. The purpose of this section is to show that under normal
circumstances the affect of the “face error” or checksum is negligible even with
checksums as large as 2000. The only time a problem would arise is if the face
error or checksum was to change between the two halves of a survey. This
is why it is extremely important to not bang the probe on the bottom of the
borehole between survey halves, and to not handle the probe roughly while
out of the hole.
The term “face error” comes from surveying terminology. It is normal for all
theodolites to have a “face error” which is caused by imperfections of alignment of
the collimation axis and other misalignments. These “face errors” are removed
routinely by taking two readings of the theodolite: one angle is measured with the
face of the vertical scale on the left of the theodolite and another with the face of
the vertical scale on the right of the theodolite. The average of the two readings
“face right” and “face left” gives the true angle since the “face error” cancels
out.
Similarly with the inclinometer probe: the “face error” arises from the fact that the
axis of the inclinometer probe is not parallel with the electrical axis of the internal,
force-balance, servo- accelerometer transducer. Once again the “face error” is
eliminated by taking two surveys of inclinometer readings one with the wheels of
the inclinometer probe pointing in one direction and another with the wheels of the
probe at 180
°
to the first direction. If the first set of readings are all too large by the
amount of the “face error” then the second set of readings will be too small by the
amount of the “face error” and the average or sum of the two readings will be a
measure of the true inclination since the affect of the face error will be totally
eliminated.