Guralp Systems Scream - Manual (Page 86)

Scream! 4.5
3. Open the Configuration set-up window for the digitiser, and tick
Enable External Trigger Input to make it listen for triggers
coming from the digital instrument, and record data from
attached analogue instruments when it receives one (depending
on its Output control configuration).
4. UPLOAD the new configuration to the digitiser,
If a digitiser has both Enable External Trigger Output and Enable
External Trigger Input selected, it will record data when it receives an
external trigger as if it had triggered itself, but it will not send that
trigger on to other digitisers. It will only send a trigger message if its
own triggering criteria are satisfied.
For full details on external triggering, see the manual for your digitiser
or the technical notes available on the Güralp Systems website.
7.3.4 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
detriggers.
The two boxes at bottom right of the Triggering pane allow the user to
set the pre-trigger and post-trigger periods, in seconds. These values
determine the minimum length of time during which data will be
saved before the trigger condition occurs, and after it has lapsed.
Regardless of the intervals chosen, the data in the triggered streams
will begin on an integer second.
7.4 Mux Channels
Güralp digitisers provide a range of slow-rate auxiliary channels for
reporting the system's state of health and other diagnostic information,
known as multiplexed (“Mux”) channels. The number of Mux
channels depends on the model and configuration of your digitiser.
Generally, three channels are used to report the sensor mass position.
In addition to these, depending on the digitiser options selected, up to
twelve Mux channels may be configured for the user's own purposes.
Some digitisers have a separate AUXILIARY port which can be used to
input signals which are digitised to these channels.
86 Issue K