Guralp Systems CMG-DCM build <10,000 - Manual (Page 121)

Acquisition Modules and Platinum Firmware Digitiser Synchronisation
time-stamp log-file entries - it does make direct synchronisation to GPS the
least accurate of the three options available.
We recommend the following synchronisation strategy:
• If GPS is available, synchronise the digitiser(s) directly to GPS and
synchronise the acquisition module to the RTSTATUS packets from the
digitiser.
• If GPS is not available but an internet connection can be used,
synchronise the acquisition module to internet NTP and enable the
NMEA output, to which the digitiser can then be synchronised.
• If neither GPS nor internet NTP are available, contact technical support
for advice.
9.2 RTSTATUS packets
Where a CMG-EAM or CMG-DCM is used with an external GPS-synchronised
GSL digitiser, the digitiser can emit special synchronisation packets called
RTSTATUS packets. These are transmitted along the same link as the data
packets. Platinum units can use these as a time source for NTP: see section
7.4 on page 84 for more details.
Note: RTSTATUS packets are available with MkIII DM24 units.
Earlier units, such as MkIIs, are not capable of generating these
packets. With MkIIs, however, the system clock can be set from
GCF status block timestamps by enabling this feature on the expert
settings of the appropriate serial port GCF input page.
Note: RTSTATUS packets are available with CD24 units running
firmware revision 279 and above.
MAN-EAM-0003 121 Issue E - February 2014