Guralp Systems Scream - Manual (Page 92)

Scream! 4.5
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 two minutes. The Period and Frequency are ignored.
The Broadband Noise calibration signal consists of a constant stream
of white noise, which lasts for the specified number of minutes. The
Period and Frequency are ignored.
8.4 Mass Control
Many Güralp instruments respond to control signals to centre, unlock,
and lock the sensor masses. These signals are generated by the
digitiser. You can tell the digitiser to send a signal using the Centre
Now, Lock Now and UnLock Now buttons on the Mass Control tab.
If you tick the Monitor progress check-box, the window will remain
open during the process, and the mass positions will be displayed in
the Vertical, N/South and E/West boxes. If you leave Monitor progress
clear, the window will close while the operation takes place. You can
still monitor the mass positions by selecting the appropriate streams
and opening a WaveView window for them.
Depending on which Sensor Type you have chosen in the System tab
(see above), not all the control signals will be available. For example,
CMG-3ESP sensors can be centred from Scream!, but must be locked
92 Issue K