Guralp Systems CMG-CD24 - Manual (Page 32)

CMG-CD24
STA and LTA periods, together with the Ratio, without restarting the
digitiser (see section 3.2 on page 37.)
Since it is not generally advisable to trigger from broadband data, the
digitiser provides a set of standard bandpass filters to apply to the data
streams before they are tested for the trigger condition. This filtering
serves to maximise sensitivity within the frequency band of interest,
and filter out noise outside this band. You can select which bandpass
filter to use from the Bandpass filter drop-down menu. The corner
frequencies of the pass band of the filter are determined by the Nyquist
frequency, which depends on the sample 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.
The possible filter configurations are shown in the following table:
Rate (samples/s)
Bandwidth 1
(Hz)
Bandwidth 2
(Hz)
Bandwidth 5
(Hz)
1000 50 – 450 100 – 450 250 – 450
500 25 – 225 50 – 225 125 – 225
400 20 – 180 40 – 180 100 – 180
250 12.5-112.5 25-112.5 62.5-112.5
200 10-90 20-90 50-90
100 5-45 10-45 25-45
50 2.5-22.5 5-22.5 12.5-22.5
40 2-18 4-18 10-18
25 1.25-11.25 2.5-11.25 6.25-11.25
20 1-9- 2-9 5-9
10 0.5-4.5 1-4.5 2.5-4.5
8 0.4-3.6 0.8-3.6 2-3.6
5 0.25-2.25 0.5-2.25 1.25-2.25
4 0.2-1.8 0.4-1.8 1-1.8
2 0.1-0.9 0.2-0.9 0.5-0.9
1 0.05-0.45 0.1-0.45 0.25-0.45
As can be seen, the filter you choose defines the set of permissible
sample rates.
32 Issue C