Chapter 10. Digitiser specifications
Seismic channels | Number | 4 – 8 |
Format | 32 bit | |
Inputs | Differential with transient protection; ±10 V input range | |
Input impedance | 1 MΩ, 10 nF | |
Common mode rejection ratio | 110 dB at 10 Hz | |
Mux channels | Number and Format | Eight 24-bit channels |
Inputs | Single ended; ±10 V input range | |
GPS | Unit | External GPS (CMGGPS2) |
Power | supplied through GPS connector | |
Time format | NMEA | |
Max. cable length | 50 m | |
Sensor control | Functions available | Lock, unlock and centre sensor (active low CMOS); enable calibration |
Sensor calibration | Types | Sine and square wave; adjustable amplitude and frequency |
Digital signal processing | Type | Texas TMS320CV33 |
Hardware sampling rate | 2 KHz | |
Sample output rates | 6 cascaded rates, each 2, 4, or 5 times lower than the previous rate | |
Anti-aliasing filters | 2 pole | |
Low-pass filters | FIR | |
Out-of-band rejection | 140 dB | |
In-band ripple | –140 dB | |
Trigger modes | STA/LTA, threshold, external trigger | |
Digitiser performance | Output format | 32 bit |
Noise-free resolution (NPR) | 22.5 bits at 20 samples/s; 21.5 bits at 100 samples/s | |
Absolute accuracy | 0.5% standard (0.1% optional) | |
Type | 5th-order, single-bit, low‑pass noise shaper | |
Clock | Oscillator | 8 × 10–7 standard (5 × 10–8 oven-controlled optional) |
External receiver interface | GPS or GLONASS: RS232 and PPS | |
External receiver synchronisation | <50 µs | |
Internal thermometer | Accuracy | ±0.33 °C (30 °C) |
Linearity | ±0.5 °C | |
Resolution | 0.0625 °C | |
Power | Supply | +10 to +24 V DC |
Current at 12 V DC | ~0.12 A |