Guralp Systems CMG-3TB - Manual (Page 9)

Operator's guide
Studs have the advantage of being smaller than skids, but the contact
points are very close to each other. You should evaluate the various
locking methods available to see which works best in your borehole.
The spring inside the lock provides around 60 kg of force at its locking
position. A DC actuator retracts the arm into the body of the lock so
that the sensor mechanism can be installed and removed. The actuator
consists of a 14 W DC motor with a planetary reduction gearhead,
which drives the nut of a ball lead screw through the helical drive
gears. The thread of the lead screw is prevented from turning, and so
moves linearly when the nut turns.
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 three-jaw hole lock
A three-jaw hole lock is available which gives better grip on the
borehole casing, but is bulkier and heavier than the single-arm lock.
This is the standard option for uniaxial instruments; it can be installed
in boreholes between 3.5” / 89 mm and 7” / 178 mm in diameter.
The three-jaw hole lock consists of a set of three active clamp arms
attached to a compression spring, which forces them to swing out from
the sonde and wedge themselves against the borehole wall. Serrated
steel jaws at the end of each arm provides maximum grip against the
borehole casing. This configuration ensures that the sonde body is
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