Guralp Systems CMG-5T - Manual (Page 12)

CMG-5T
3 Calibration
The 5T is supplied with a comprehensive calibration document, and it
should not normally be necessary to calibrate it yourself. However,
you may need to check that the response and output signal levels of
the sensor are consistent with the values given in the calibration
document.
3.1 Absolute calibration
The sensor's response (in V/ms -2 ) is measured at the production stage
by tilting the sensor through 90 ° and measuring the acceleration due
to gravity. Local g at the Güralp Systems production facility is known
to an accuracy of 5 digits. In addition, sensors are subjected to the
“wagon wheel” test, where they are slowly rotated about a vertical
axis.
The response of the sensor traces out a sinusoid over time, which is
calibrated at the factory to range smoothly from 1g to –1g without
clipping.
3.2 Relative calibration
The response of the sensor, together with several other variables, is
measured at the factory. The values obtained are documented on the
sensor's calibration sheet. Using these, you can convert directly from
voltage (or counts as measured in Scream!) to acceleration values and
back. You can check any of these values by performing calibration
experiments.
Güralp sensors and digitizers are calibrated as described below.
12 Issue E