Guralp Systems CMG-DM24 - Manual (Page 27)

Operator's guide
System operation
USB memory sticks and disk drives normally have an LED indicating
activity. This will flash as each block is written, so a few flashes every
10 seconds would be expected from a DM24 producing 100 sps data.
Since data blocks are recorded to their corresponding files in real time,
only the current/latest block can be lost when a USB stick is detached;
all other stream files will have been closed/saved.
When a USB stick is plugged in, the system interrogates it to
determine the free space. This operation can take a minute or more
depending on the capacity of the USB device. When the operation has
been completed, the system reports the available space using the LCD
and, also, in the status stream, as in the example below:
2008 10 3 13:18:49 USB Flash stick Recording started NO NAME
D:/>
USB File granularity :
For sample rates >= 40 sps : 1 hour files otherwise 4 hour files
except status ; 12 hour files
2008 10 3 13:19:52 USB Stick space remaining 3.9GB
The system will regularly (after each 5MB of data storage – typically an
hour or 2 of running) report the space available in GB/MB and as a
predicted duration in days/hours (based on the utilization rate for the
previous 5MB).
Recording to a USB device stops automatically when there is less than
100k free space. To record more data, the device must be replaced with
a freshly formatted one.
USB devices can be removed/replaced at any time, but the system does
not additionally buffer the data so a small amount will be lost during
the changeover. In DUPLICATE mode all data would also still be in the
internal flash.
An example of a status display is shown below. This is taken from the
status stream (*00) of a DM24 fitted with a USB host controller after
several minutes of operation.
October 2009 27