Guralp Systems CMG-DM16R8, Руководство по эксплуатации

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CMG-DM16
Triggering of all three components from vertical channel 100Hz
tap, filter from 5 to 45 Hz
Sta = 1, Lta = 50, Sta/Lta = 10, pre-trigger = 40, post-
trigger = 70
This section describes the triggering algorithm and gives
several examples of typical system configurations that may be
used. It is intended to be read along with the digitizer
Configuration Section of the Operator’s Guide.
4.1 Using the triggering system
The digitizer Configuration Section of the Operator’s Guide
describes in detail how to configure the system to output
continuously at up to 3 different sample rates, selectable within
certain constraints by the user. Typically, you may only wish to
record one sample rate as continuous data, but it may be
useful to record selected time periods at a higher sample rate
The triggering algorithm used is a standard STA/LTA ratio test
on a bandpass filtered signal. An individual channel,
corresponding to an individual seismometer component can be
defined as the trigger channel, or triggers can be permitted on
any channel. Details of the various parameters related to the
triggering process are given in the following sections.
Pre-trigger bandpass filtering
As the digitizer is normally used with a Güralp Systems Limited
broadband seismometer the raw data is very broadband. To
enhance the performance of the triggering algorithm, the raw
input data is bandpass filtered prior to running it through the
triggering system. This filtering serves to maximise sensitivity
within a specific frequency band of interest, and to reject noise
outside this band, for example from oceanic microseisms. The
system is provided with a choice of 3 inbuilt generic bandpass
filters (wide, medium and narrow) which are slaved to the
defined tap output sample rates defined using the samples/sec
command. The filters all have a low pass corner at 90% of the
Nyquist frequency of the selected tap, and the wide, medium
and narrow filters have high pass corner frequencies at 10%,
20% and 50% of the Nyquist frequency respectively. For
example, if we consider the 100 samples/sec tap defined above
(Tap#1) the low pass corner for each filter will be at 45Hz, and
the high pass corners will be at 5Hz, 10Hz and 25Hz.
18 Issue C