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CMG-DCM
alter the settings on the digitizer to reflect your choices; this done, you should
see the message New configuration successfully saved to
attached instrument.
If the DCM is connected to a PC running Güralp Systems' Scream! software,
you can also configure the digitizers from within Scream!. See the User Guide
for your digitizer model for more details.
General digitizer settings
Baud rate : The speed at which the digitizer will communicate with the DCM,
in bytes per second. This must match the baud rate the DCM is using for the
serial port linked to this digitizer. The DCM's baud rates can be altered on the
various Serial port configuration pages: see Section 4.3, “Serial port
configuration”.
You should ensure that the baud rate is high enough to allow all the data to be
transmitted at the rates you have chosen. As an example, for three streams
transmitting at 100 Hz, a rate of 9600 baud is usually sufficient. Modern
modems can normally operate at rates up to 57600 baud (~56 kbits/s), although
the telephone or transmission lines may not support such a high rate. The same
is true of radio telemetry links.
System ID and serial number : Together, these two fields uniquely identify data
originating from a particular instrument. Every data or status block sent by the
digitizer will contain them as the first two 32-bit fields in the header, each
encoded as a sequence of 6 base-36 numbers representing alphanumeric
characters. On delivery of the digitizer from the factory, the system ID is set to
the Güralp Systems works number, and the serial number is unique for that
digitizer (unless shared with an attached seismometer). You may reset these
values to any combination of up to 6 letters and numbers. For example, you may
wish to set the system ID to a more easily-recognised value, such as an
abbreviation of your institution's name.
Sensor type : If the sensor attached to the digitizer is a Güralp velocity sensor,
useful seismometer functions (such as sensor locking, centering, and
calibration) may be controlled through the digitizer and DCM. In order to be
able to do this, and to know which functions to make available, the digitizer
must be set up with the correct sensor type: one of CMG-40T, CMG-3ESP, or
CMG-3T. The sensor's type will be printed on its casing. If you have taken
delivery of a DCM already bonded to a sensor and digitizer, this field will have
been set for you at the factory, and should not be altered.
Timing source : The digitizer needs to be able to time-stamp accurately all data
that passes through it. It can set its clock either by receiving time signals from
the GPS satellite network using an attached Garmin GPS unit, or by taking time
information from a central site via the DCM (stream sync mode). In stream
sync mode, the digitizer expects to receive GCF packets from the central timing
68 Issue A