Guralp Systems CMG-3T - Manual (Page 44)

CMG-3T
The hybrid feedback circuit contains a single capacitor in parallel with
a resistor, resulting in a single dominant pole. Below this frequency,
which can be varied from the standard 30 seconds, the response of the
seismometer is flat to ground acceleration. Above it, the response is
flat to velocity. Hybrid-feedback systems provide a stable response,
particularly for portable systems, with a high saturation level at high
frequencies and a high dynamic range at long periods.
An active low-pass filter provides a high-frequency cut-off point at a
frequency you specify. Without the filter, the velocity response is flat
up to 100 Hz. Outside the feedback loop there is an active high-pass
filter with a corner frequency of 0.01 Hz (100 s) or 0.005 Hz (200 s),
which serves to remove any DC offsets.
Conventional-response feedback
44 Issue N