Chapter 1. Introduction
The DM16-R8 is a 16 bit, 8 input-channel digitizer, configured in a standard 1U 19inch rack unit. The primary purpose of the instrument is for use in a seismic data collection station with multiple telemetric input channels.
The eight individual differential input channels are accessed via isolated BNC plugs on the front panel, labelled from A to H. Alternatively, all eight inputs are provided at the rear of the 19inch unit via a single 25pin ‘D’ plug (see pin-outs in appendices).
Other features include
A built-in Digital Signal Processor (Motorola 56002), providing simultaneous multiple sample rate data streams at user selectable rates. Up to 3 streams of data for each component are available at sample rates from 200 samples/second down to 2 sps.
Accurate time synchronisation to external GPS or serial time code.
A single GPS can be cascaded down multiple DM16 digitizers.
Precision microprocessor controlled time-base synchronises Analogue to Digital Converters and DSP, and time-stamps data blocks.
Control microprocessor (Hitachi H8) formats and buffers data in on-board 512k RAM ring buffer.
Compressed data format (Güralp Compressed Format) for efficient storage and transmission.
Serial data output RS232 or RS422 at user selectable baud-rates.
Low system power consumption, typically 210-220mA.
Differential high input impedance pre-amplifiers of 1MΩ
Common mode rejection ratio exceeding 90dB
The input stages of all the differential amplifiers are protected against excessive input voltages and limited to ±10V.. Each input is furnished with an inductor and capacitor network to filter out the high frequency signals and enable a minimum of 100dB of common mode rejection.
To minimise ground loops the differential power supply is isolated. Two sets of dedicated dc-dc converters ensure low noise dc supply voltages to the input stages and the digitizer electronics.
1.1 Options
Güralp Systems also manufacture a 16-channel DM16 unit, the DM16R16. This is a 2U rack-mount module containing two 8-channel digitizers with cascaded output. A single GPS unit can synchronize both digitizers to the same time base.
The DM16R16 can optionally be supplied with an internal CMG-DCM data communications module. The DCM is a low-power network device running a full Linux operating system, providing a cost-effective way to connect multiple analogue data sources to a modern TCP/IP network. The DM16R16DCM also fits within a 2U rack space.