Guralp Systems CMG-DM24S12AMS - Manual (Page 22)

CMG-DM24S12AMS Operator's guide
The STA and LTA columns allow you to set the intervals over which the
two averages are calculated, in seconds. Typically, the time interval for
the short term average should be about as long as the signals you want
to trigger on, while the long term average should be taken over a much
longer interval. Both the STA and LTA values are recalculated
continually, even during a trigger.
The Ratio column determines by what factor the STA and LTA must
differ for the trigger to be passed. Finding the ratio most suited to your
needs is best done by experiment. Too high a value will result in events
being missed, while too low a value will result in spurious non-seismic
noise triggering the system. Like the averages, their ratio is continuously
recalculated for all components. Note that none of the boxes are allowed
to be empty, and so you will need to enter the new value before
removing the old one. Alternatively, you can use the up and down
cursor keys to change the values.
For example, setting the STA to 1 second, the LTA to 10 seconds and the
Ratio to 4 would give rise to the following trigger behaviour:
22 Issue B