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PC-based continuous recording field seismograph

BERNARD PRICE INSTITUTE OF GEOPHYSICAL RESEARCH UNIVERSITY OF THE WITWATERSRAND, PRIVATE BAG 3, WITS 2050 South Africa

Abstract

Observations of teleseismic events at remote sites necessitated the development of a portable digital recorder that is capable of continuously recording the output of a three-component set of long-period transducers. A PC is used as a file management facility, operating in an intermittant or "sleeper mode." Each of the three components are digitized and stored in separate, intelligent A to D cards. When 28 K samples have been generated, a trigger is initiated, and on the transition of the next real time second the real time is latched and power is applied to the PC. The sample count between the trigger and the latched acknowledgment of the trigger provides an absolute time correlation. After the PC has powered up, the data are down-loaded from the three acquisition cards to a PC hard disk and the latched real time forms the header label of the data file. Power is then removed from the PC. Sampling at about 15 samples per second, the PC is switched on every 33, 45 minutes. Boot-up and data down-loading uses approximately 5 watts average power. The associated long-period transducers (Guralp CMG3) consume about 3 watts and the remaining electronics 2 watts. All the electronics are housed in a steel cabinet, and the system uses four solar panels charging two 105AH batteries. Data transfer to an internal 60 MByte tape streamer necessitates a visit to the station every 24 days.