Guralp Systems CMG-3ESPCD - Manual (Page 33)

CMG-3ESPCD Digital Broadband Seismometer Calibrating the 3ESPCD
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Injecting a sinusoidal current of known amplitude and frequency
allows the system response to be determined at a spot frequency.
However, before the calibration measurement can be made the system
must be allowed to reach a steady state; for low frequencies, this will
take a long time. In addition, several measurements must be made to
determine the response over the full frequency spectrum.
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Injecting broadband noise into the calibration coil gives the response of
the whole system, which can be measured using a spectrum analyser.
Calibration is performed using the built-in DM24 digitiser, which can
generate step and sinusoidal calibration signals as well as broadband noise,
and integrated scripts within Güralp Systems' Scream! software.
Initiating a calibration closes a relay which normally isolates the feedback
electronics from the calibration signal generator and causes signals of the
specified nature to be generated and routed through the feedback system. You
can then measure the signal's equivalent velocity using Scream!
4.3 Calibration with Scream!
Sine-wave, step and broadband noise calibrations are available. In this
section, broadband noise calibration will be used to determine the complete
sensor response in one action.
1. In Scream!'s main window, right-click on the digitiser's icon and select
Control.... Open the Calibration pane.
2. Select the calibration channel corresponding to the instrument, and
choose Broadband Noise. Select the component you wish to calibrate,
MAN-C3E-0002 33 Issue B - November 2013