Guralp Systems CD1.1 - Manual (Page 75)

Operator's Guide
Channel: M8 Vertical 1.19µV/count
M9 North/South 1.20µV/count
MA East/West 1.19µV/count
CAL SIGNAL MONITOR
X2 / C2 3.216µV/count
The important details here are:
•
the sensitivities for the three “seismic” channels Z2, N2
and E2, which should be around 3.2µV/count;
•
the sensitivity for the “calibration”/auxiliary channel X2,
which should be around 3.2µV/count;
•
the calibrations for the mux (mass position) channels at
4sps, which should be around 300µV/count.
The “seismic” and “calibration” labels are only labels; it is
possible to digitise any analog signal on any channel (although
note the X channel is temporarily replaced by a calibration
signal when a calibration is initiated).
In the default configuration the mux channels of the DM24mk3
are artificially reduced to 16-bit resolution for compatibility with
the DM24mk2. This is the default setting, and leads to a
sensitivity of around 300µV/count. If the sample rate of the
mux channels is changed then the output is 24 bit and the
sensitivity becomes around 1.2µV/count.
12.1 Seismic sensors (velocity)
For velocity sensors, such as the CMG-3T, CMG-40T and CMG-
6T, the sensor's calibration value will be given as a value in
V/m/s (Vm
-1 s). Since Güralp sensors and digitisers are
differential, the calibration sheet will list the value as, for
example, 2×9778. The doubled value (in this case 19556)
should be used.
Example of a 3V (CMG-3 sensor, vertical component only) cal
sheet, relevant excerpts only:
WORKS ORDER: 12345 DATE: 01–Jan–1970
SERIAL NUMBER: V3XXX TESTED BY: A. N. Other
Velocity Output Mass Position Feedback Coil
June 2010 75