CMG-3TB
8. Fix the signal cable to the main lifting cable about 1 m above the
strain relief mechanism using a metal clamp (a nylon cable tie
may be sufficient for shallow installations.) Leave a little slack
in the signal cable between the clamp and the strain relief
mechanism.
9. Position the assembly over the top of the borehole. Do not allow
it to drag across the ground.
10.Lower the sensor so that its base is level with the borehole
mouth. Set the depth gauge on the winch to zero.
11.Calculate how much lifting cable must be lowered into the
borehole, taking into account the length of the sensor and the
strain relief assembly or digitizer.
If you are installing a 3TB in a deep borehole, the weight of the
sensor will stretch the load bearing cable slightly. Remember to
allow for this when raising or lowering the sensor in the
following steps, since allowing the instrument to strike the
bottom of the borehole will damage it.
12.Begin lowering the sensor down the borehole, keeping track of
the depth reached.
13.At approximately 20 m intervals, fix the signal cable to the load
bearing cable using metal clamps (nylon cable ties every 5 m
may be sufficient for shallow installations). This will ensure
that the signal cable does not become kinked or trapped within
the borehole. Leave a little slack on the signal cable each time,
so that it does not bear any weight. Too much slack, however,
will cause the cable to scrape against the borehole casing.
34
Issue C
