The CMG-3ESP Compact is a full-featured three-axis seismometer consisting of three sensors in an ultra-lightweight case, which can measure the north/south, east/west and vertical components of ground motion simultaneously.
Each sensor is sensitive to ground vibrations in the frequency range 0.003 – 50 Hz, a broadband frequency response made possible by advanced force-balance feedback electronics. Because of this wide response range, the 3ESP Compact 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 3ESP Compact will produce the best results if it is mounted on a hard, near-horizontal surface well coupled to the bedrock. After levelling and orienting the case, you can perform accurate adjustments internally by sending the instrument control signals. These electronics allow it to compensate for a tilt of up to 3 ° from horizontal.
The seismometer unit is self-contained apart from its 12 V power supply. Once levelled and centred, it will begin operating automatically. It outputs analogue voltages representing ground velocity on balanced differential lines. These voltages can be recorded using a separate logging device or digitizer. For testing and installation purposes, a handheld control unit is supplied which can monitor the instrument's output. Centring and mass locking can be carried out by sending control signals to the instrument, either through the handheld control unit or through an attached Güralp digitizer.
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.
The 3ESP Compact can be supplied with an integral digitizer, which is mounted on top of the mechanics to form a complete, lightweight digital seismometer suitable for autonomous installations.
The standard 3ESP Compact has a single 26-pin mil-spec waterproof connector for signals, control and power.
As an option, the 3ESP Compact can be supplied with other output connector types, e.g. standard 26-pin D sockets, to your own pinout specification.
The 3ESP Compact can be supplied with a response which is flat to velocity from 100 Hz to any of 0.1 Hz (10 s), 0.033 Hz (30 s), 0.016 Hz (60 s), 0.01 Hz (100 s) or 0.0083 Hz (120 s). Alternatively, a hybrid response function may be provided. See Section 5.1, page 38, for more details.
If you do not require high-frequency data, a low-pass filter may be installed at a frequency (below 100 Hz) that you specify.