Guralp Systems CMG-CD24 - Manual (Page 39)

Operator's Guide
Each channel calibrates the corresponding component of the
instrument. Select one or all components for calibration.
On three-channel digitisers, the calibration signal is digitised at a
slower rate and returned as a Mux channel (see above) ending MB. On
eight-channel models, it is returned as a full speed channel ending Xn,
where n is an integer specifying the tap (as for the normal outputs).
The Duration box tells the digitiser how long to provide the calibration
signal before disconnecting. This avoids the system being
inadvertently left in calibration mode. The default is 2 minutes. If
you change this setting, it will revert to the default value after one
calibration stage.
All Güralp digitisers 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 specified in the
boxes at bottom left. 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).
You can specify step calibration by selecting the Square wave button.
The square wave consists of a positive step at the start of the next
minute of the digitiser’s internal clock, followed by a negative step
after a specified number of minutes. After a further delay of the same
number of minutes, the calibration signal is disconnected. The default
is 2 minutes. The Period and Frequency are ignored.
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