Installing the 3TB in a borehole
4 Installing the 3TB in a borehole
Before installing any instrument in a borehole, you should prepare the installation
site.
•
Clean the area around the borehole head, so there is clear access all around it.
•
Keep the borehole capped at all times except when inserting or removing the
instrument, so that debris and tools do not accidentally fall in.
•
Lay out the cables beside the borehole, or set up a cable drum nearby, so that
they do not become tangled.
•
Ensure the tripod is tall enough to hang the entire installation (sensor and
strain relief unit or digitizer) from it, with the sensor off the ground.
•
Use a winch with a depth gauge if possible, or measure out the cable
beforehand.
Most installations are equipped with a strain-relief unit, which consists of a metal
arm that swings out from the load-bearing cable to wedge against the side of the
borehole. This removes any strain in the load-bearing cable and prevents vibrations
from the surface from being transmitted to the instrument.
Note:
In installations with a down-hole digitizer, the strain-relief
arm is fitted to the base of the digitizer sonde; the phrase “strain
relief unit” in the following instructions should be taken to refer to
the digitizer's strain relief arm.
Note:
In installations with a surface digitiser, the strain-relief arm is
built into the surge suppression sonde; the phrase “strain relief unit”
in the following instructions should be taken to refer to the surge
suppressor's strain relief arm.
4.1 Installing a sensor with hole lock unit
1. If your system has a separate surge-suppressor sonde, connect the captive
cable from the surge-suppressor to the connector on top of the sensor and
connect the signal cable to the top of the sensor. Otherwise, connect the
signal cable directly to the connector on top of the sensor. Ensure that the
“O”-rings inside the housing are clean and well greased. If necessary, apply a
coat of extra silicon grease to the 'O'-rings – Dow Corning Molykote 111 is
suitable. Tighten the knurled connector nut to its end stop. It may be
necessary to wiggle the connector several times during tightening in order to
ensure that the connector is screwed fully home.
21
Issue G - November 2019
