Guralp Systems CMG-3TB - Manual (Page 26)

CMG-3TB
3 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. In installations with a downhole
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.
3.1 Installing a sensor with hole lock unit
1. Connect the signal cable to the connector on top of the sensor.
Ensure that the “O”-rings inside the housing are clean, and
tighten the knurled connector nut to its end stop.
26 Issue C