Guralp Systems CMG-DCM build <10,000 - Manual (Page 109)

Acquisition Modules and Platinum Firmware Digitiser Configuration
STA/LTA triggers: Activate when the ratio of the short-term average to the
long-term average (of the input signal) exceeds a configured value.
Trigger input: The drop-down menu allows the selection of the input signal
to be used for these calculations, along with one of three filter settings. The
available filters have lower corner frequencies based on fixed fractions of the
sample frequency: specifically, 5%, 15% and 25% of the sample rate. The
upper corner is 0.9 times the Nyquist frequency (45% of the sample rate).
For example, if a tap configured for 25 samples per second, the three filters
offered will have pass-bands of:
• 1.25 Hz to 11.25 Hz (5% of 25 Hz is 1.25 Hz and, as the Nyquist
frequency for 25 samples per second is 12.5 Hz, 0.9 × 12.5 = 11.25);
• 2.5 Hz to 11.25 Hz (15% to 45% of the sample rate); and
• 6.125 Hz to 11.25 Hz (25% to 45% of the sample rate).
Note that the filtering specified here is applied to the specified tap output
before being used for trigger input but does not affect the tap output if it is
also used to generate continuous streams.
MAN-EAM-0003 109 Issue E - February 2014