Guralp Systems CMG-5TD User Manual
Page 17
Operation
Parameters from most of the commands are stored to the battery-backed
CMOS and only take effect when the digitiser is rebooted. When you click the
“Download” button from the digitiser configuration interface, the parameters
you have chosen are transferred to the digitiser and it is automatically
rebooted. You will notice a data gap in the traces in the Waveview window
corresponding to the digitiser you have rebooted. This occurs because the
reboot automatically clears the data buffer and resets the output block
counter.
To access the digitiser configuration dialogue from Scream, double-click on
the digitiser's icon in the Available Streams window (NOT the Local or COM
port icons). Alternatively, you can right-click on the digitiser's icon and then
select “Configure” from the pop-up menu.
The following sections correspond to the different tabs available in the
configuration dialogue.
5.9.1 System ID
System Identifier and Serial Number: The digitiser type is identified by its
system identifier and serial number. These two parameters are stored as the
first two 32-bit fields in the header of each data and status block generated by
the digitiser, in order to indicate the block's origin. Each of these parameters
consists of 6 alphanumerics encoded as base 36 numbers. On delivery from
the factory, the system identifier and the serial number are, respectively, set to
the GSL works order number and the seismometer’s serial number. Either
parameter can be reset to any convenient combination of letters and numbers,
such as an abbreviation of your institution and the deployment site code.
Sensor Type: This field will be pre-programmed at the factory for the proper
sensor type (CMG-5T).
GPS Type: The digitiser can utilize time signals from different sources.
Options available are NMEA (Garmin or Trimble) GPS receivers or stream
synchronization. When using stream synchronization, time signals from a
GPS antenna are sent via telemetry from a central site to the digitiser. In order
to synchronize with the time standard in use, the correct option must be
selected.
5.9.2 Output control
Sampling rate: The output of the digitiser’s analogue-to-digital converters
(ADC) is sampled at 2 kHz. These data are filtered and reduced to lower rates
using a digital signal processor (DSP). The DSP has four cascaded
filter/decimation stages, each of which can be programmed for decimation
factors of ÷2, ÷4, ÷5, ÷8 or ÷10. The output of each stage is called a “tap”.
Each stage may be configured for a different decimation factor.
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Issue D - April 2013