CMG-3V
borehole casing. This confguration ensures that the sonde body is held
parallel to the axis of the borehole and prevented from twisting or
slipping under the infuence of ground vibrations.
The motor has a power system separate from that of the sensor, and can
be controlled from the surface using a hole lock control unit. Once the
sonde is installed, the hole lock control unit may be removed. Without
power, the hole lock will not be able to retract, and the sensor will be
secured.
The single-jaw hole lock
A single-jaw hole lock is available which is smaller and lighter than the
three-jaw lock, but does not grip the borehole casing with as much force.
The single jaw hole lock is the standard option for triaxial borehole
instruments. It consists of an active clamp arm and a number of skids or
studs on the sonde body. The arm is aiached to a compression spring,
which forces it to swing out from the sonde and wedge the body against
the borehole wall. A serrated steel jaw at the end of the arm provides
maximum grip against the borehole casing. The skids or studs and the
locking arm together form a multi-point clamp, which aligns the sonde
body parallel to the axis of the borehole and holds it frmly in place so
that it cannot twist or slip under the infuence of ground vibrations.
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