Guralp Systems CMG-SAM - Manual (Page 7)

Operator’s Guide CMG SAM & CMG CRM
1. INTRODUCTION
The Güralp Systems Storage and Acquisition Modules (SAM’s) and Combiner-
Repeater Modules (CRMs) are designed to provide the optimum solution for high
performance Seismic Data Acquisition Systems, from a single autonomous sensor, to a
multi-channel, multi-sensor seismic array.
The SAMs and CRMs are available with 2, 4 or 6 input ports, which can each accept
digital inputs from 3-component broadband instruments or digital telemetry links.
The CRM combines data from an array of instruments and outputs it as a single stream
for further transmission. For example, a standard CRM with 2 ports will combine two
3-component sensors plus state of health data sources into one (higher rate) output
stream. The single combined output can then be sent via radio, telephone or digital
telemetry.
The SAM can function in a similar manner as the CRM but includes the ability to store
the combined data on a removable hard disc. The SAM can therefore be used where a
telemetry link is unreliable or impractical. The stored data can be retrieved on, say, a
monthly basis (depending upon the amount of data and disc size). The SAM’s output
port could be used to check an array of remote instruments whilst on site changing SCSI
discs.
As part of the continuing development of all our products, the latest SAM has enhanced
features, a Combine Repeater and Storage Module with dual functionality. This can be
obtained either with or without a backup disc. The new SAM is flash programmable
and can perform a stream synchronisation function, ie. where the SAM is collecting data
from an array of instruments, the timing function for the whole array can be performed
by the SAM unit with a GPS, rather than each individual instrument operating timing
functions independently. Because of this enhancement, the front panel has a different
layout and connector pinouts should be checked in the back of this manual.
The CMG-SAM module writes continuous data to a solid state Silicon File Data Buffer,
and archives data from the silicon file to an internal hard disk. Data is stored on disk in
Güralp Compressed Format (GCF). GCF uses a difference algorithm to express all data
as 32, 16 or 8-bit differences, depending on the dynamic range required for the data
block. GCF reduces baud rates and storage capacities compared to non-compressed
data formats. The basic SAM system includes the Hitachi H8 16 Mhz microprocessor,
2 UARTs, 4 Mb silicon file data buffer and hard disk data storage (9 Gb SCSI as
standard, with optional larger sizes or 2½ inch disc drives).
The output or Aux port means the SAM can download to, and is fully configurable
through a PC serial port. Depending upon the users telemetry link and using Guralps
SCREAM software, the SAM becomes transparent and the user can configure any of the
attached instruments remotely.
To obtain the highest available resolution and noise performance from the digitisers
particular attention has been paid to the design of power supply and isolation of
analogue and digital circuitry (all serial i/o ports are optically isolated).
Issue D March 2001 5