Larson Davis System 824, Technical Reference Manual

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12-20 824 Reference Manual 9/29/09
R =.05087g / 1216186
R = 4.182748 x 10^-8
now use this R as the reference to get the readings in linear
units from dB like this:
L = R * 10^(D/20)
L = 4.182748g x 10^-8 * 10^(121.7dB/20)
L = 4.182748g x 10^-8 * 10^(6.085)
L = 4.182748g x 10^-8 * 1216186
L = 0.05087g
Another example, this time down 20 dB:
L = 4.182748g x 10^-8 * 10^(101.7dB/20) = 5.087 x 10^-3 =
.005087g
How can I manually enter a calibration offset so that the decibel levels (dB) from the
FFT option of the 824 are relative to 1 micro-meter per second squared?
The calibration offset is calculated with this formula (±5%
accurate):
LCAL = 20 log(4.467 nanovolts / Vref)
Where LCAL is the calibration offset being calculated, Vref
is the desired reference voltage (the voltage that would read
0 dB) and 4.467 nanovolts is a constant set by the 824's
electronic design (4.467x10-9).
Example: It is desirous to display 140dB for 1 g due to the
relationship that 1 g is 10 meters per second squared (m/s2)
and 1 micrometer per second squared (mm/s2) is a common
reference level. Given that an accelerometer with a
sensitivity of 0.1V/g has a sensitivity of 0.01 volts per meter
per second squared (10 mV/m/s2). The voltage at 1 mm/s2
would be 0.01 microvolt (calculated ratio-metrically since