Guralp Systems CD1.1 - Manual (Page 74)

CD1.1 Tools for Platinum
12 Calibration Values
In the channel subframe description field, the calibration of the
sensor and digitiser can be given. Current Güralp hardware is
not capable of automatically filling out these fields, so they
must be entered manually. If left empty, default values of 1.0
will be used for both the calibration gain and period.
In order to fill out the calibration value, a period within the pass
band of the sensor must be chosen. 1s is often a good choice
and simplifies the calculations. In any case, the period T is
computed from the frequency at which the gain is considered,
which will be referred to as f in the calculations below.
T =
1
f
— relationship between period T (seconds) and
frequency f (Hz).
It is the value T which goes into the calibration period or calper
field of the gdi2cd11 configuration and is stored in the channel
subframe description.
The digitiser sensitivity of the corresponding channel must also
be known. This is given in units of µV/count, and is nominally
3.2µV/count for a CMG-DM24mk3 seismic channel (Z, N, E or X)
or (again nominally) 300µV/count for a mux position channel
(M8, M9, MA, MB, MC, MD, ME, MF).
Example of DM24 cal sheet (relevaant excerpt only):
VELOCITY CHANNELS
Channel: Z2 Vertical 3.196µV/count
N2 Noth/South 3.207µV/count
E2 East/West 3.189µV/count
MASS POSITION CHANNELS
Sample rate: 4 samples/sec (Default)
Channel: M8 Vertical 305.912µV/count
M9 North/South 307.497µV/count
MA East/West 305.506µV/count
Sample rate: 1 samples/sec
74 Issue C