Guralp Systems Limited
Section Index: 3.1 Installing in vaults 3.2 Setting up

Chapter 3. Installing the CMG-EDU

3.1 Installing in vaults

The CMG-EDU is a sensitive instrument designed to measure extremely small movements of the ground. These movements are the sum of all the vibrations arriving at the instrument: as well as distant earthquakes and nearby tremors, the ground responds to surf on nearby beaches, quarry blasts, heavy machinery, traffic, and even people moving around the building. Temperature changes and air currents in the same room as the sensor can also affect its output.

3.1.1  Choosing a location

When studying natural earth movements, any other effects introduce unwanted noise into the system. It is therefore important to choose an appropriate site for the instrument, ideally in an underground vault with the sensor installed on a concrete pier that is in direct contact with the bedrock.


This setup has a number of advantages:

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

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.

3.1.2  Temperature stability

The CMG-EDU 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


3.1.3  Other considerations

3.2 Setting up

Once you have chosen suitable locations for the sensor, digitizer and GPS, you need only connect the various components and supply them with power. The digitizer and sensor will begin working immediately.