Guralp Systems CD1.1 - Manual (Page 76)

CD1.1 Tools for Platinum
V/m/s
(Differential) Output
(Acceleration
output) V/m/s² Constant
Amp/m/s²
VERTICAL 2×9778 1559 0.02
The important fields are the velocity output, used in this
section, and the mass position output, used in section 12.2 .
The CD1.1 calibration value for seismic sensors should be in
units of nm/count, which is the displacement response. To
convert from a velocity gain to a displacement gain, it is
necessary to divide the velocity gain by 2πf. Taking into
account conversion from µV to V and from m to nm, we
introduce a scale factor of 1000, leading to:
C=1000
S
G
⋅ 2πf — CD1.1 calibration value for seismic sensor
with velocity response, where C is the calibration value in
nm/count, S is the digitiser sensitivity in µV/count, G is the gain
of the instrument in V/m/s, and f is the frequency of the
calibration point in Hz.
12.2 Seismic sensors (acceleration)
For sensors such as the CMG-5T with an acceleration response,
or for mass position channels (which are also measuring an
acceleration), the following method should be used to compute
the CD1.1 calibration value.
As Güralp sensors and digitisers are differential, the instrument
gain value (in V/m/s² or Vm
-1 s 2 ) on the calibration sheet is
written as e.g. 2×0.512. Use the doubled value (in this case
1.024). This does not apply to mass positions/mux channels,
which are single-ended.
Example of a 5T cal sheet, relevant excerts only:
WORKS ORDER: 12345 DATE: 01–Jan–1970
SERIAL NUMBER: T5XXX TESTED BY: A. N. Other
OUTPUT at 1g 5 volts
Acceleration
Response V/m/s²
VERTICAL 2×0.510
NORTH/SOUTH 2×0.510
EAST/WEST 2×0.511
76 Issue C