Chapter 1. 1 Introduction

The CMG-40V-1 and CMG-40H-1 sensors are ultra-lightweight one-second response uniaxial seismometers with low noise and wide dynamic range. The transfer function of a CMG-40V/H-1 is identical to that of a conventional velocity output seismometer.

The 40V/H-1 has a rugged, waterproof stainless steel design for ease of installation. The lightweight sensor element is designed so that no mechanical clamping is required. Because of this, the 40V/H-1 is ready to record ground movements as soon as you provide it with 10-36 VDC power through its integrated cable. See Appendix A Connector pin-outs on page 31 for details.

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. The horizontal CMG-40H instrument includes a bubble-level for more accurate levelling.

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 40V/H-1 can be supplied with a response which is flat to velocity from 1 Hz to any of 50 Hz (0.02 s), 80 Hz (0.0125 s) or 100 Hz (0.001 s).

If you do not require high-frequency data, a low-pass filter may be installed at a frequency (below 50 Hz) that you specify.

Standard 40V/H-1 instruments output a signal representing ground velocity on a pair of balanced differential lines. An option is available which provides a second, parallel output at higher gain. The high-gain output has a sensitivity nominally 10 times higher than the standard (low-gain) output.