Guralp Systems CMG-CD24 - Manual (Page 34)

CMG-CD24
3. The values in the Level column are the number of counts above
the baseline that channel must reach before a trigger is generated.
The values are determined from the Details window for the
channel under consideration. Note that the offset must be set to
zero in order to determine the real baseline value.
The Level values will be the same for each channel unless the
“Common values” check-box is deselected.
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.
3.1.3.3 External triggering
When a digitiser or digital sensor triggers, it can send a notification
signal to connected devices. 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 ordering.
As an example, to instruct a stand-alone digitiser with digital trigger
inputs to respond to trigger notifications generated by an attached
digital sensor:
1. Open the Configuration setup window for the digital sensor, and
check Enable External Trigger Output to make it send trigger
notifications to connected devices.
2. UPLOAD the new configuration to the digital sensor.
3. Open the Configuration setup window for the digitiser, and
check Enable External Trigger Input to make it listen for
notifications coming from the digital instrument and record data
from its 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 notification as if it had triggered itself, but it will not
send that trigger notification on to other digitisers. It will only send a
trigger notification if its own triggering criteria are satisfied.
3.1.3.4 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
34 Issue C