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Polarity Conventions
Unlike previous generations of Kinemetrics force balance accelerometers,
the EpiSensor uses a right-handed X Y, Z coordinate system with a positive
output for acceleration along each axis.
The EpiSensor will normally be aligned with X (channel 1) to the east, Y
(channel 2) to the north and Z (channel 3) upward. The signal has the same
polarity as the ground acceleration in the sensor coordinate system.
Positive polarity is the international standard in weak motion seismology.
With Kinemetrics' decision to adopt a positive polarity with the EpiSensor
FBA, it is now the standard in strong motion seismology as well.
Previous Kinemetrics FBA designs used an alternate coordinate system
(L, V, T) and produced a negative output for positive acceleration along
each axis. With modern feedback sensors, this historical convention dating
from the days of passive seismic sensors is losing acceptance. Today's user
requires an accelerometer that produces useful data without regard to the
internal workings of the sensor. The extended bandwidth, flat frequency
response and polarity of the EpiSensor meet these demands.
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