Guralp Systems CMG-6TD User Manual
Page 55
Configuration with Scream!
For example, setting the STA to 1 second, the LTA to 10 seconds and the Ratio
to 4 would give rise to the following trigger behaviour:
Usually, the values of the STA and LTA periods, and of the Ratio, will be the
same for all selected channels. For convenience, Scream! will automatically
fill in other values to match ones you enter. If you want to use different
values for some channels, you should clear the Common values check-box
before altering them.
Once you have enabled the STA/LTA triggering method on a particular
channel, you can use the Control window to change the values of the STA
and LTA periods, together with the Ratio, without restarting the digitiser (see
section 5.1 on page 49).
Since it is not generally advisable to trigger from broadband data, the digitiser
provides a set of standard bandpass filters to apply to the data streams before
they are tested for the trigger condition. This filtering serves to maximise
sensitivity within the frequency band of interest, and filter out noise outside
this band. You can select which bandpass filter to use from the Bandpass
filter drop-down menu. The corner frequencies of the pass band of the filter
are determined by the Nyquist frequency, which is half the sampling
frequency of the triggering data. The three filter options have pass bands
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Issue F - February 2014