Chapter 1. 1 Introduction

The CMG-40T-1 is an ultra-lightweight seismometer consisting of three sensors in a sealed case, which can measure the north/south, east/west and vertical components of ground motion simultaneously. The transfer function of the CMG-40T-1 is identical to that of a conventional velocity-output seismometer.

The 40T-1 has a rugged, waterproof stainless steel design for ease of installation. The lightweight sensor elements are designed so that no mechanical clamping is required. Because of this, the 40T-1 is ready to record ground movements as soon as you provide it with power. In addition, the sensor does not have to be levelled or centred as long as the base is within 3 ° of horizontal. For the best results, however, you should install where possible on a hard, near-horizontal surface well coupled to the bedrock.

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.

1.1 1.1 Response options

The 40T-1 can be supplied with a response which is flat to velocity from 100 Hz or 50 Hz to any of 1 s, 2 s (0.5 Hz) or 10 s (0.1 Hz).

Standard 40T-1 instruments output signals representing ground velocity on three pairs of balanced differential lines. An option is available which provides a second, parallel set of outputs at higher gain. The high-gain outputs have a sensitivity nominally 10 times higher than the standard (low-gain) outputs.