Guralp Systems CMG-DM24 - Manual (Page 40)

Operator’s Guide DM-24 Digitiser
Issue G January 2003 38
SENSOR CALIBRATION
Command
Syntax Comments
SENSOR-TYPE n SENSOR TYPE Where ‘n’ is the number 1
to 4
1. CMG-40T no mass lock
or centring
2. CMG-3ESP manual
lock, remote centring
3. CMG-3T upgraded
analogue instrument
4. CMG-3TD digital
borehole instrument
SINEWAVE SINEWAVE See text below
SQUAREWAVE SQUAREWAVE See text below
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, orE/W and the frequency or
period by HZ or SECOND respectively. Note that only integers can be specified for
frequency/period, so to generate a 0.5 Hz signal use ‘2 SECOND’ 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 by using the MINUTE command,
e.g. ‘5 MINUTE’ 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 start and stops on the zero crossing.
Step calibration is specified by the command SQUAREWAVE , 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.
e.g. E/W 10 MINUTE SQUAREWAVE would be used to generate a long period step
function suitable for calibrating a 360 second response instrument.