Guralp Systems CMG-3T - Manual (Page 11)

Operator's guide
Temporary installations can be protected against spurious vibrations
by
•
selecting a suitable site,
•
placing the instrument in a protective enclosure (an open-sided
box of 5 cm expanded polystyrene slabs, placed over the
instrument and taped down to exclude draughts, makes an
excellent thermal shield),
•
standing the sensor on bedrock where possible, or at least deep
in well-compacted subsoil;
•
clearing the floor of the hole of all loose material; and
•
using as little extra mass as possible in preparing the chamber.
After installation, the instrument case and mounting surface will
slowly return to the local temperature and settle in their positions.
This will take around four hours from the time installation is
completed. If you require long-period recording, you should re-zero
the instrument after this time.
2.3 Installing in vaults
You can install a 3T in an existing seismic vault with the following
procedure:
1. Unpack the sensors from their container, saving the shipping
boxes for later transportation.
2. Prepare the mounting surface, which should be smooth and free
of cracks. Remove any loose particles or dust, and any pieces of
loose surfacing. This ensures good contact between the
instrument's feet and the surface.
3. If it is not already present, inscribe an accurate North-South line
on the mounting surface.
4. Place the sensor over the scribed line, so that the brass and steel
pointers are aligned with the marked directions, with the brass
pointer facing North. This can be done by rotating the base of
the sensor whilst observing it from above. The brass pointer can
be found next to one of the feet.
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