Guralp Systems CMG-3TB - Manual (Page 40)

CMG-3TB
11.Hang the strain relief unit and instrument(s) from the loop at
the other end of the cable. You are now ready to lower the
assembly into the borehole as described above.
3.4 Earthing a borehole sensor
To achieve the best performance from any borehole instrument, you
must make sure that the sensor electronics, its casing and the power
supply share a common, local ground, and that all power and data
lines are adequately protected against lightning and other transients.
This section describes techniques for grounding sensor equipment
which have proved effective in many installations. However, local
conditions are always paramount, and you should design your
installation with these in mind. Any regulations in force at your
chosen location must also be followed.
Installations with AC power supplies
If you are using mains (outlet) power, or some other AC power
distribution system, we recommend installing a fully isolating
transformer between it and the power supply for the instrument. This
will allow full control of the local grround.
A spark-gap surge protector should also be installed on the mains side
of the transformer, so that transient overvoltages are not transmitted
across it. Suitable protectors are available off the shelf from several
suppliers. On the sensor side, surge protection is installed as standard
within all new Güralp borehole sensors and control equipment. If your
surface installation includes third party electronics, digitizers, etc., you
may need to install additional protection where power and data lines
enter the surface enclosure. Contact Güralp Systems if you are unsure.
Within the installation, a single ground point should be established,
40 Issue C