Guralp Systems CMG-6TD - Manual (Page 52)

CMG-6TD Configuration with Scream!
To the right of each decimation factor menu is a grid of check-boxes. These
boxes mark which streams of data to generate at each sample rate. The
screen-shot above shows a possible configuration for a triaxial instrument.
Every channel of the digitiser may be output at any tap; currently, all three
axes are being output at Tap 2 (20 Hertz).
If you want to change the names used for the channels, click in the white box
containing a Z in the above picture, and type a letter or number. It will name
the channels with a sequence of letters or numbers beginning with the one
you choose (e.g. A­B­C, 2­3­4, 9­A­B), unless you type Z in which case they
will revert to Z, N, and E.
Each combination of channel and tap has two check-boxes. The upper
check-box of each pair activates continuous output, whilst the lower activates
triggered output. In the example above, the digitiser will output data
continuously for all three channels at Tap 2, but never for any other taps. If
you do not need all the streams to output at all rates, you should leave boxes
clear to save communications capacity. You cannot select both continuous
and triggered output for the same channel and tap.
When you enable a triggered stream, the digitiser will output data in that
stream only when a particular set of trigger criteria are met. This is shown
diagrammatically as data passing through a switch. In the example above, we
might want the high-rate data from Tap 0 to be generated only when an event
registers at some other tap. To do this, tick one or more of the lower set of
check-boxes for Tap 0.
With this configuration uploaded, Tap 2 will continue to produce output at all
times, but Tap 0 will also emit data whenever the trigger criteria are met. The
Triggering button is now shown in red to remind you that the trigger is active.
Every ticked check-box in this window will give rise to a data stream coming
from the digitiser, which will be displayed in Scream!'s main window when
Scream! first receives some data from it. Every stream is identified by a
six-character code, where the first four characters identify the digitiser, and
the last two characters identify the individual stream. The first four
characters are set by default to the serial number of the digitiser; you can
change this on the System ID pane (see section 5.1.1 on page 50) or from the
digitiser's console.
5.1.3 Triggering
In its standard configuration, the 6TD outputs continuous data at a sample
rate you specify. In addition to this, Güralp digitisers can run a triggering
algorithm on the data they acquire. This allows you to record data
continuously at a relatively low sample rate, but record at a much higher
sample rate during short periods when the trigger is active. The parameters
controlling the triggering algorithm, and controlling the data output once the
MAN-T60-0002 52 Issue F - February 2014