Guralp Systems CMG-DM24 - Manual (Page 30)

Operator’s Guide DM-24 Digitiser
Issue G January 2003 28
SENSOR CALIBRATION
The digitiser can generate either sinewave or step signals to calibrate the attached
seismometer.
Sinewave frequency can be from 10 Hz to 0.1 Hz (0.1 to 10 second period) and can be
applied to a particular component (via the built-in relay).
The step (squarewave) calibration is specified in minutes between changes in state.
The component to be calibrated is specified by Z, N/S, E/W and the frequency or period
by Hz or Seconds respectively. Note that only integers can be specified for
frequency/period, so to generate a 0.5 Hz signal use ‘2 Seconds’ or for a 0.25 second
period use ‘4 Hz’ .e.g. N/S 4 Hz SineWave will generate this signal in the
calibration coil of the north/south component.
The calibration signal will be automatically disconnected after the specified time. This
avoids the system being inadvertently left in the calibration mode. If the signal is
required for longer this can be specified, e.g. ‘5 Minutes’ will set the timer so that the
calibration is disconnected after 5 minutes - this timer is then reset to its default value of
2 minutes.
NOTE: Sinewave calibration signal starts and stops on the zero crossing.
Step calibration is specified by the Squarewave button, which generates a positive step
on the start of the next minute (of the internal clock) and a negative step the specified
number of minutes later (default 2 minutes). This calibration is also disconnected after
the same (specified) number of minutes after the negative edge.