Guralp Systems CMG-3ESPCD User Manual
Page 42
CMG-3ESPCD Digital Broadband Seismometer
Using Scream!
Güralp digitisers initially sample incoming data at a high rate (e.g. 512,000 Hz
for the DM24), which is then filtered and reduced to a lower rate (decimated)
using an on-board digital signal processing unit, or DSP. The DSP has several
filtering-decimation stages, which run one after the other. Stages which can
produce output are called taps. The Güralp DM24 can output 4 taps
simultaneously. The input to the tap chain is fixed at 2,000 samples per
second.
Each configurable tap can be set to a different decimation factor by choosing
values from the drop-down menus on the left. Decimation factors of 2, 4, 5, 8,
and 10 are available. The numbers visible in the drop-down menu of each tap
are the data rates that each of the possible decimation factors will provide,
given the settings of the taps above it. Only integer (Hz) data rates are
allowed: thus, for example, if one tap emits data at 25 Hz, the only possible
further decimation factor is 5.
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 (20Hz).
Note: 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. A, B, C;
2, 3, 4; 9, A, B), unless you type Z in which case they will revert to
Z, N, and E.
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Issue B - November 2013