24-bit Digital OBS
Seismic Recorder
Model DAS-6502






The DAS-6502 is a rugged, ultra low power, high-performance, versatile 24-bit resolution OBS seismic recorder. It is designed for the most demanding requirements in high performance marine seismic research.

This state-of-the art seismic recorder features 4 to 8 channels with high resolution ADC's on each channel that ensures no channel to channel skew, and a very low-power, high-performance DSP that controls the data acquisition, real-time digitization and filtration.

The system can be installed in existing Benthos or titanium sphere installations, or ordered in a ready to deploy Benthos system. For those installations that have a continuous communication link, the 6503 sensor digitizer is a perfect solution.

The 6502 OBS Recorder is configured on the surface using a PC. Timing is preset in advance using the system GPS. Accurate calibration of the crystal oscillator requires running the system for about two days, preferably at the anticipated ocean bottom installation temperature. The True Real Time™ system corrects the oscillator frequency to within 0.016 ppm. Once below the surface, the extremely stable, very low power, temperature controlled crystal oscillator maintains accurate timing for the duration of the experiment.

The large SRAM buffer reduces the duty cycle for the PC and disks, whose operation may generate unwanted noise. A typical duty cycle would run the PC and disks for approximately 2 minutes every 5-8 hours for 3 channels @ 100sps with a 16 MB RAM buffer. The data stored on the large capacity disk is easily removable upon retrieval.


FEATURES
  • 24-bit high resolution

  • 132B dynamic range

  • Operates in both trigger and continuous mode

  • Multiple trigger passband pre-filters

  • High accuracy GPS timing

  • Large capacity PC compatible removable hard disk

  • 4 to 8 channels

  • Analog and digital alias filtering
SPECIFICATIONS
INPUT CHANNELS
Type: Differential or Single-Ended
Data Channels: 3+1 ; opt. up to 8; Specify Differential or Single-Ended
State-of-Health 4th Channel: Standard: 24-bit resolution, optional external connector
Gain: 1,2,4,8,16,32,64 progammable
Differential Input Signal Range: Programmable: 2.5, 20 V
Dynamic Range: >132 dB @ 100 sps (rms to FS)
Analog Anti-Aliasing Filter: >100 dB @ primary sampling rate
Input Impedance 2.5V - 1Mohm;
20 V - 26kohm
Overvoltage Protection 40 V
DIGITIZER
Type: 24-bit delta-sigma converter in each channel (320 kHz)
Sampling Rates: 0.1, 1, 10, 20, 40, 80, 100, 200, 500, 1000, 2000, 4000 sps
Digital Filter >130 dB @ 200 sps (FIR)
CMR @ 50, 60 Hz 120dB
Phase Linear within the passband
TIMING SYSTEM
Type: True Real Time PLL controlled, GPS-referenced
Maximum Accuracy : <1 microsec (Software Selectable)
HOW TO ORDER Crystal Oscillator Standard: 25ppm; Optional TCXO 1 ppm/year
Basic DAS-
6502OBS Configuration
The standard configuration includes 4 channels , 10Gb hard drive, single ended sensor input, and GPS antenna/receiver.
Channel Configuration

option -8CH,

Differential Sensor Input Configuration option -DI
Microsoft Windows O/S option -MSW
Removable 12Gb, 20Gb, or 30Gb Drives option -xxGb (specify capacity, must turn power off to remove)
Internal Modem option -56IM
LAN option option -LAN
Sensor Options EP-300 Broadband,
EP-105 Broadband,
SP-400 Medium Period Seismometer,
R-1 Rotational Seismometer
Supplies and Accessories External Battery pack w/ charger (specify voltage)
PC removable disk frame
Hard Disk (specify capacity)
General Spares GPS antenna/receiver
Keypad
Set of spare boards
Charger
Battery (specify capacity)
   





S Printer Friendly Format For Specifications

Crystal Frequency Correction Resolution 0.016 ppm
EVENT DETECTORS
Type: STA/LTA, up to 6 independent detec-tors in frequency domain
Trigger Pre-filter Up to 6 trigger passbands
Pre-event data buffer Up to 90 seconds (@100 sps)
Post-event buffer User configured - no limitations
Trigger channels May be controlled by one, several or all 6 detectors associated with any physical or virtual acquisition channel
Calibration 5V square wave (others optional)
Calibration Duration User selectable
POWER
Voltage: 6 - 16 Vdc
Overvoltage protection: 60 V
Power consumption ~0.60W (4 channels, 100 sps, cycled)
USER INTERFACE
Remote PC: RS232 com2 port
MASS STORAGE
Hard Disk 10Gb standard, optional to 32Gb
Disk/File Compatibility: Any PC
Temperature Range: -10 to +50C (built-in automatic heater for optional hard disk)
Data Formats: Mini-SEED w/Steim-2 compression up to x6 CSS 3.0: long integer; separate data description in ASCII
COMMUNICATION
Standard Retreival Removable EIDE disk cartridge
Ethernet Optional LAN card
ENVIRONMENTAL PARAMETERS
Housing Aluminum
Operating Temperature 0 to +50C
Humidity 100% RH
Size L10 x W 9 x D7"
(265x127x76mm)
Weight ~2.2 kg
CONNECTORS: REAR PANEL, WATERPROOF
Power Miniature PICO Series Lumber Connector
Data Channels (4) and sensor power Subminiature DB15
Serial port Subminiature DB9
GPS Subminiature DB9
 

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