Guralp Systems CMG-40T - Manual (Page 17)

Operator's guide
the pier, so that nearby vibrations are not transmitted to the sensor.
A high-quality seismic vault can be incorporated into the construction plans of a
new building at relatively low cost. However, if you are not in a position to
build a dedicated vault, you can still reduce noise to a satisfactory level by
• installing below ground, in the basement or sub-basement of an existing
building;
• placing the sensor directly on a cement floor to improve contact; and
• locating the sensor in a quiet corner away from people and machinery
(e.g. air conditioning and heating systems, elevators, etc.)
Installation on higher floors is not recommended, especially for horizontal
sensors, since any “give” in the floor near the sensor will cause it to tilt slightly
and register a signal.
Temperature stability
The 40T can operate over a wide temperature range (–10 °C to +75 °C).
However, the sensor mass is sensitive to fluctuations in local temperature. This
affects the response of the instrument at long periods. Sunlight and other bright
lights can also cause small mechanical stresses that will be detected by the
sensor. You can minimise these effects by
• installing in a basement, where the temperature is normally more stable
than above ground;
• locating the sensor in a dark, protected corner, and
• enclosing it in an insulated box (expanded polystyrene works very well).
This also helps protect the sensor from air currents.
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