Guralp Systems CMG-DM24 - Manual (Page 41)

Operator's guide
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 checked channels. If you want to use different values for
some channels, you should un-check the Common values 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 digitizer.
External triggering
When a digitizer or digital sensor triggers, it signals the fact to
connected devices, as well as sending any extra data that it has been
configured to transmit. You can configure other digitizers to respond
to this signal by triggering in turn. This is an option which you can
specify at the time of manufacture. See Section 6.3, page 97, for details
of how to set up an installation for external triggering.
As an example, to instruct a stand-alone digitizer with digital inputs to
respond to triggers generated by an attached digital sensor:
1. Open the Configuration setup window for the digital sensor, and
check Enable External Trigger Output - this causes it to send
triggers to connected devices;
2. UPLOAD the new configuration to the digital sensor;
3. Open the Configuration setup window for the digitizer, and
check Enable External Trigger Input - this causes it to listen for
triggers coming from the digital instrument, and to record data
from any attached analogue instruments when it receives one
(depending on its Output control configuration); then
4. UPLOAD the new configuration to the digitizer.
If a digitizer 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 relay the
trigger on to other digitizers. It will only send a trigger message if its
own triggering criteria are satisfied. This prevents triggering loops.
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