Element Description

The prototype element with a concealed whip antenna.
For a short period of time, the prototype was operated with a concealed whip antenna. These proved to be problematical and they were later replaced.

Each element includes:

• A self contained solar-charged power supply
• A GPS time-keeping system
• A digital radio modem and associated antenna
• A 24-bit digital data acquisition system
• A low noise seismometer preamp
• A high gain vertical seismometer

The two 40-watt solar panels provide power to charge internal lead-acid batteries. At Lajitas, the panels produce sufficient power to run all the equipment within an hour of sun rise. Within a short time later, there is sufficient excess power to charge the batteries. Field tests (done inadvertently when a cable was disconnected), have demonstrated that the batteries supply enough power to run the system continuously for a week without any solar power and can recover within a full day of sunshine.

Batteries that supply power to the system during night hours.
Two deep cycle 6 volt golf cart batteries supply power to the electronics at each site. The initial installation used two golf cart batteries giving a capacity in excess of 1200 watt-hours. During later maintance, these were replaced with a more easily obtained single high capacity automotive battery.

A close-up of the GPS clock.
The clock is about 8 inches in diameter.

Mounted above the antenna is a GPS receiver that provides precise world time and location. Location is appended to state-of-health information unambiguously identifying each data stream (this has proved particularly useful when coordination between the field activities and data recording is difficult). Tests of the system indicate that the sample synchronization and timing accuracy of the system is better than two microseconds from world time. Thus samples from two different elements are always within 4 microseconds of each other.

The rest of the electronics at the site is within the borehole where it is protected from daily temperature extremes and is isolated from corrosive gases that may escape from the batteries. The box itself is well vented.