Guralp Systems CMG-DM24 - Manual (Page 49)

Operator’s Guide DM-24 Digitiser
Issue G January 2003 47
5. DIGITISER DATA ACQUISITION & TELEMETRY
Guralp Systems provides complete broadband seismological data acquisition solutions.
All of the equipment is modular in connectivity. The equipment comprises of
broadband sensors with a choice of digitisers, SAM units for data Storage and
Acquisition and the CRM for data Combining and Repeating.
Due to the modular nature of the equipment and the power offered to the user from
Guralp Systems’ SCREAM! Software, complete system set-ups are highly flexible,
allowing rapid deployment of equipment tailored to the customers requirements.
Over the page is a diagram of some of the combinations possible of data acquisition,
transmission over a desired medium and collection for subsequent analysis. Shown
below are two examples of typical arrangements.
Example 1:
Two 3 channel analogue sensors could be connected to a CMG-DM24, then via a
direct cable link to an acquisition computer. This could then retransmit via
telephone modems or the internet.
Example 2:
Up-to seven sensor arrays could be connected to a Guralp SAM (Storage and
Acquisition Module) or CRM(Combiner/Repeater Module) unit. These units can
combine several serial input channels into one serial stream for transmission via a
radio modem, cable or, using a serial server, directly over the internet. A GPS can
be used on the CRM or SAM, instead of each digitiser, to synchronise and time
stamp all the data streams.
The CRM is designed specifically as a telemetry repeater station. Incoming RS232 data
streams from Guralp digitisers will be at 9600, 19200 or 38400 baud depending upon
sample rates, number of channels and compression factor.
The CRM combines the asynchronous incoming data streams and outputs at an
appropriate baud rate (up to 115200 baud output). For example four incoming streams
at 9600 baud will be output at 38400 (assuming the transmission medium can sustain
this baud rate; ie some radio modems may have lower baud capacity).
The SAM unit functions in a similar manner to the CRM, except it has a SCSI hard
drive to store data. If, for instance, the transmission link is less than 100% effective or
in danger of being disrupted, the SAM continuously records all the data in a ring buffer.
Should the transmission link then be lost, this ensures no data is also lost.
The main design purpose of the SAM though, is where there is no means of transmitting
data from a remote or difficult site, where it can store data over long periods, depending
upon the quantity of data and disc size (9 Gb standard, other options are available).