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ANUAL
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OCUMENT
305801,
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EVISION
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Figure 5: Details of leveling feet.
Operational Details
Choice of Digitizer
The instantaneous dynamic range of the sensor is greater than that of any modern seismic digitizer,
particularly when operating on the 4g and 2g ranges. 26-bit digitizers (such as the Q330HR) are
preferred for utilizing the greatest part of this range. More conventional 24-bit digitizers also work well,
however, the self-noise of a properly installed sensor is well below that of the input noise of the
digitizer. Some digitizers provide integrated preamplifiers. While these are useful for investigation of the
exact levels of sensor self-noise, their use will greatly reduce the full-scale range of the sensor. This
effectively defeats the purpose of a “strong motion accelerometer”!
Typically, the best system
performance will be achieved by use of a Q330HR (26-bit) digitizer, with its preamplifiers OFF.
Full-Scale Range Selection
Sensor dynamic range is typically highest on the highest full-scale range settings (+/-4g and +/-2g),
where the 1 Hz dynamic range is in excess of 160 dB. However, sensor self-noise typically drops with
range setting (although noise on 0.5g and 0.25g ranges are practically identical).
The choice of (peak)
full-scale range should ensure that there is near-zero chance of clipping due to maximum local
accelerations. Users should select ranges above the maximum expected signal.
AUTOZERO Mode
The AUTOZERO system records and corrects the sensor offsets
in situ
. This correction cancels fixed
mechanical offsets in the sensor element, as well as tilt-related offsets due to sensor mounting. It injects
a separate feedback current that is automatically generated to cancel the observed offset. AUTOZERO is
either OFF (standard mode), or ON. Any time that the sensor is RESET, or it experiences a Power-ON-
RESET, or the AUTOZERO is explicitly set via the various control interfaces, the sensor re-calculates and
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August 2015