Guralp Systems CMG-DM24 - Manual (Page 47)

Operator's guide
Each channel Z, N/S and E/W can be calibrated separately. For most
triaxial digital instruments, each channel calibrates the corresponding
axis of the instrument; simply select one of the Z, N/S and E/W check
boxes to calibrate that axis. Some instruments use only one calibration
loop, which is reproduced for all three components: if you have one of
these instruments, you should select Z to calibrate the sensor.
The calibration signal is digitized at the same rate as the highest-rate
data stream you have selected for either continuous or triggered
output. It is returned on a channel ending Cn (n = 0 – 7). The auxiliary
analogue channel is interrupted whilst calibration is active.
The Duration box tells the digitizer how long to provide the
calibration signal before disconnecting. This avoids the system being
inadvertently left in calibration mode. The default is 2 minutes.
All Güralp digitizers can produce either sine-wave or square-wave
(step) calibration signals; newer models can also carry out broadband
noise calibration. The Sine wave calibration signal always starts and
stops on the zero crossing. The frequency or period is given by the
boxes at the top, right-hand side of the dialogue. Only integers
between 1 and 10 may be specified for either frequency or period, so to
generate a 0.5 Hz signal you should select Period and set the time to 2
(seconds). Likewise, if you require a 0.25 second period you should
select Frequency and set the rate to 4 (Hz). In this manner, you can
select frequencies ranging from 0.1 to 10 Hz (10 to 0.1 s periods).
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