Operator's guide
The
hybrid
feedback circuit contains a single capacitor in parallel with a
resistor, resulting in a single dominant pole at 0.033 Hz (30 s). Below this
frequency, the response of the seismometer is fat t o g round
acceleration; above it, the response is fat to velocity. (Other values for
the acceleration-velocity corner can be provided upon request.) 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 flter provides a high-frequency cutof point at a
frequency you specify. Without the flter, the velocity response is fat
up to 100 Hz. Outside the feedback loop there is an active high-pass
flter with a corner frequency of 0.01 Hz (100 s) or 0.005 Hz (200 s),
which serves to remove any DC ofsets.
December 2004
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