Using the DM24
SLOW
is the size, in hours, for lower sample rates <
SPS
STATUS
is the size, in hours, for status stream files.
The default settings are:
1 40 4 12 HOURFILES
With these settings, the system will start a new file every hour for streams with a
sample rate
≥
40 samples per second.
Lower sample rate streams will have files which last 4 hours – so the file names will
have the sequence “
YYMMDD00
,
YYMMDD04
,
YYMMDD08
” etc.
Status files will have 12 hour granularity
i.e.
“
YYMMDD00
and
YYMMDD12
”.
Note that status streams are recorded as plain text files with the extension '
.txt
'.
All other streams are recorded with the extension '
.gcf
' which is the same format
used by 'Scream!' (
i.e.
a series of 1-kilobyte GCF data blocks), consequently the files
can be viewed and processed by Scream!, simply by “drag and dropping” or right-
clicking to select the option.
Due to bandwidth and processing limitations, it may not always be possible to record
continuous streams with particularly high sample rates. Note that when triggers are
in use, the sample rates of streams transmitted over the serial port will typically
increase considerably. If your application involves sample rates higher than 250
samples per second, you should verify to your own satisfaction correct operation
(under triggered conditions, if necessary) with your own USB devices before
permanent installation.
4.6.4 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 sample-per-second 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.
33
Issue U - December, 2021
