Chapter 2. Introduction

The CMG-3ESPCD is a full-featured three-axis digital seismometer consisting of three sensors in a lightweight case, which can measure the North/South, East/West and vertical components of ground motion simultaneously, a built-in CMG-CD24 digitizer and a built-in CMG-EAM embedded acquisition module.

Each sensor is sensitive to ground vibrations in the frequency range 120 seconds to 50 Hz, a broadband frequency response made possible by advanced force-balance feedback electronics. Because of this wide response range, the 3ESPCD can replace many of the instruments conventionally used in a seismic observatory; it also produces true pulse-shape records suitable for modern earthquake mechanism analysis. Its small size and low weight make it an ideal choice for rapid deployment of low-noise installations.

The seismometer unit is self-contained apart from its 12 V DC power supply. Once levelled and centred, it will begin operating automatically. Its output is digitized within the sensor by the internal CD24 digitizer, which provides data streams to the embedded acquisition module. The instrument can be connected to a PC over a serial port or Ethernet network. The text- or web-based configuration interface provides complete control over the storage and transmission of data, as well as the instrument's centring and mass locking processes. Data stored in the internal memory can be written to an external USB drive at the touch of a button.

Each seismometer is delivered with a detailed calibration sheet showing its serial number, measured frequency response in both the long period and the short period sections of the seismic spectrum, sensor DC calibration levels, and the transfer function in poles/zeros notation.