Guralp Systems CMG-DCM - Manual (Page 106)

CMG-DCM Data Communications Module
7.1 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 6.2, page 82.
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.
On delivery of the digitizer from the factory, the System ID is set to the
Güralp Systems works order number, and the Serial number is set to
the serial number for that digitizer.
You can set the System ID to any combination of up to 5 letters (A – Z)
and numbers. The Serial number can be up to 4 characters long, also
using letters and numbers only. 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, mass control functions (such as sensor locking, unlocking and
centering) may be performed through the digitizer and DCM.
Different types of sensor have different functions available. This field
allows you to change the type announced by the digitizer.
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 source (which may have
its own GPS unit, or take signals from one of the radio time standards).
The DCM can recognise GCF timing packets and will pass them on to
all connected digitizers.
106 Issue F