Guralp Systems CMG-1T - Manual (Page 9)

Operator’s Guide CMG-1T Ocean Bottom
Seismometer
September, 1999, Issue C Section 1, Page 1
1. INTRODUCTION
The qualities of Güralp Systems Limited’s broadband sensors (Ref 1) clearly
opened up a new era in ocean bottom and ocean bottom borehole seismology.
A pilot experiment which deployed CMG-3 sensors (Refs 2 and 3) clearly
indicated some of the advantages that can be ascertained from broadband
sensors installed under water. The only disadvantage of CMG-3 as an ocean
bottom instrument is the sensor mass locking mechanism. While the CMG-3
locking mechanism is adequate for most , if not all, conventional installations,
due to increased reliability requirements, a new foolproof patented locking
mechanism has been designed. The CMG-1T sensor uses this unique mass
locking mechanism which virtually eliminates the possibility of sensor pivots or
springs being damaged.
The CMG-1T OBS seismometer consists of three solid body CMG-1
seismometer components. The three component sensors are organised to be
orthogonal to each other. The base plate of the sensors is fixed to the bottom
plate of the levelling dish as shown in the following diagram. The analogue
electronics for the sensors are stacked above the sensors. The OBS analogue
electronics are specially designed to have low power consumption, and the
quiescent current consumption of the sensor system is 26 mAmps from a 12
Volts supply.