Guralp Systems Limited
MAN-ESP-0001 - 3ESP - Operator's Manual


1. Preliminary Notes 2. Introduction 3. Installing the 3ESP 4. Calibrating the 3ESP 5. Accessories 6. Inside the 3ESP 7. Appendices

Section Index: 2.1. Options

Chapter 2. Introduction

The CMG-3ESP is a three-axis seismometer consisting of three sensors in a sealed 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 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.


The 3ESP is designed for mounting 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.

Once levelled and centred, the 3ESP 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 hand-held control unit is supplied which can monitor the instrument's output.

The seismometer unit is self-contained apart from its 12 V power supply. Centring can be carried out by sending control signals to the instrument, either through the hand-held 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.

2.1 Options

2.1.1 Form factors

The CMG-3ESP can be supplied in several forms, besides its standard configuration:

Any of these can be supplied with integral digitizers and data modules, allowing the 3ESP to form a complete, integrated seismic installation.

2.1.2 Output types

The standard 3ESP has a single 26-pin mil-spec waterproof connector for signals, control and power.


A supplied breakout box connects to the sensor allowing separate connection to a power supply, recording system and hand-held control unit.

As an option the 3ESP can be supplied with other output connector types, e.g. standard 26-pin D sockets, to your own pin-out specification.

2.1.3 Sensor response

The 3ESP 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 6.1, page 30, 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.


1. Preliminary Notes 2. Introduction 3. Installing the 3ESP 4. Calibrating the 3ESP 5. Accessories 6. Inside the 3ESP 7. Appendices