CMG-3V
15.When you have reached the boiom, use the winch to lif the
package slightly, taking the slack of the cable. This ensures that
the sensor is hanging vertically within the borehole, and is no
longer in contact with the sand bed.
At this point, you may wish to use an inclinometer monitor unit
to check that the instrument is sufciently close to vertical to be
properly centred. See
“The inclinometer monitor unit” in Section
2.4
for details.
16.Calculate the volume of dry sand required to fll the gap between
the sensor and the borehole liner to the level of the top of the
sensor (
v = πr
2
h
using the internal radius of the borehole, less the
volume of the instrument determined in step 1.)
17.Pour this sand into the borehole. If you can, check how much of
the sensor is covered with sand. Do not overfll the hole.
18.Carefully slacken the load bearing cable. This will engage the
locking arm of the strain relief mechanism and secure the
installation within the borehole.
19.Without pulling or lifing the sensor, lightly shake the cables to
remove any sand that may have fallen onto them or onto the
strain relief mechanism.
20.Clamp the load bearing cable to the top of the borehole, and
remove the winch.
21.The sensor can now be centred and unlocked (see
Section 3.5,
“Levelling and centring”
) ready for use.
3.3 Assembling the winch
If required, Güralp Systems can provide a winch suitable for installing a
borehole sensor. The winch and tripod are supplied as a set of parts
which you can assemble on site:
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