Signal conditioning is provided by the Data Acquisition System (DAS). The DAS consists of preamplifiers, Analog-to-Digital (A/D) converters, time signal receiver, on-site data storage, telemetry interface, and provides state-of-health information to both local and remote users.
Preamplifiers are necessary to condition and adjust the analog output of the sensor so as to match impedance and gain levels on the input to the A/D converter.
The Delta-Sigma A/D converters have become widely accepted by data acquisition designers because of their high performance. Delta-Sigma modulation utilizes oversampling and digital filtering to achieve high performance A/D conversion and filtering at low cost. They are used in all modern seismic recorders and acquisition systems. It is important to note that the effective resolution of a Delta-Sigma A/D converter is dependent on the sampling rate.
Quanterra Q330 and Baler
- 3 and 6 channels
- Dynamic range >130 dB RMS
- Self-noise less than 1 count RMS
- 1W power consumption
- Internal memory 8 Mb, 20 Gb on local disk
- Weight 8 lbs
- Cost (including on-site data storage and telemetry interface) $10,000
Reftek 130-01
- 3 channels
- Dynamic range >130 dB RMS
- Self-noise less than 1 count RMS
- 1W power consumption
- Internal memory 2 Gb
- Weight 4.5 lbs
- Cost (including on-site data storage and telemetry interface) $9,000
Miniature Seismic Recorder DAS
Reftek "Texan"
- 1-3 channels
- Dynamic range 120 dB RMS
- Self-noise several counts RMS
- D-cell battery power
- Weight 2.5 lbs
- Cost (includes flash memory, no telemetry) $3,200
A/D Converter Characteristics
Sampling Rate: The sampling rate determines the limit of the frequencies that can be reproduced digitally. A/D converters must use anti-aliasing filters to remove all signals above the Nyquist frequency.
Resolution: The smallest analog increment corresponding to 1 LSB (Least Significant Bit). For converters, resolution is normally expressed in bits, where the numbers of analog levels is equal to 2**n bits.
Dynamic Range: The ratio between the largest and smallest amplitude which can be converted by the A/D converter and is commonly expressed in Decibel (dB).
EarthScope is a partnership extending throughout the Earth science community, including more than 100 universities, the National Science Foundation, US Geological Survey, National Aeronautics and Space Administration, Department of Energy, regional seismic networks and state geological surveys.
