Guralp Systems CMG-DM24 User Manual

Page 27

Operator’s Guide DM-24 Digitiser

Issue G January 2003

PROGRAMMING TRIGGER PARAMETERS

In general, it is not advisable to trigger from broadband data. The button near
the bottom of the Configuration Setup window therefore allows the user to
select from a set of standard bandpass filters from a pull-down menu ( a full list
of options is given later in the STA/LTA chapter). The chosen filter will be
applied to the streams from the triggering components before they are tested
for the trigger condition. The corner frequencies of the pass band of the filter
are determined by the Nyquist frequency, which is given by the sampling rate
of the triggering data. The three filter options have pass bands between 10 %
and 90 %, between 20 % and 90 % and between 50% and 90% of the data’s
Nyquist frequency, respectively.

Trigger criteria: Trigger criteria for the simple short term average/long term average

(STA/LTA) trigger function may be set in the Trigger Setup window,
accessed by clicking on the Trigger button near the bottom of the Output
Control window.

Ratio of
STA/LTA needed
to declare a
trigger

LTA

STA