Guralp Systems CMG-3ESPCD User Manual
Page 50
CMG-3ESPCD Digital Broadband Seismometer
Using Scream!
5.1.3.2 Level
Using the Level triggering method, a trigger is generated whenever one of the
selected components reaches a certain level above the baseline. You can
select which tap is monitored from the Data source drop-down menu, and the
channel(s) to be considered from the Channel column of the table. The values
in the Level column are the number of counts above the baseline that channel
must reach before a trigger is generated.
As with the STA/LTA method, the values of the Level will often be the same
for all selected channels. 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 Level triggering method on a particular channel,
you can use the Control window to change the level at which the system
triggers without restarting the digitiser (see section 5.2 on page 53).
5.1.3.3 External triggering
When a digitiser or digital sensor triggers, it sends the trigger itself to
connected devices, as well as any extra data that it has been configured to
record. You can configure other digitisers to respond to this signal by
triggering in turn. This is an option which you can specify at the time of
manufacture. For further details, please contact [email protected].
5.1.3.4 Pre-trigger and post-trigger recording
In order to capture all of a seismic event, it is often useful to be able to record
data immediately preceding the trigger. Güralp digitisers have an internal
buffer of some seconds which allows this data to be added to the triggered
stream. Pre-trigger data are particularly useful for emergent-type signals,
where the system does not trigger until one phase after the first arrival. In
addition, to ensure that the coda of each event is included, some seconds of
data are recorded after the system de-triggers.
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Issue B - November 2013