Guralp Systems CMG-DM24S12AMS - Manual (Page 17)

CMG-DM24S12AMS Operator's guide
Güralp instruments output data sampled at 2000 Hz, which is then
filtered and reduced to a lower rate (decimated) using an on-board digital
signal processing unit, or DSP. The DSP has four filtering-decimation
stages, which run one after the other. The output of each stage is called a
tap. The first filter stage, tap 0, is pre-set to reduce the data by a factor of
10 to 200 samples/second.
Each of the three remaining taps may be configured for 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 record at each sample rate.
The screenshot above shows a possible configuration for a triaxial
instrument (similar to a CMG-5TD connected to one of the ports
DIGITAL A – F).
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.
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 unchecked to save communications capacity. You cannot
check both continuous and triggered output for the same channel and
tap.
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