Guralp Systems CMG-3ESPCD User Manual
Page 78
CMG-3ESPCD Digital Broadband Seismometer
Inside the 3ESPCD
motors. It responds to commands sent on three input lines by grounding for
0.2 – 7 seconds. The signals sent to the microprocessor are termed LOCK,
UNLOCK, and CENTRE. Each command acts on the vertical, N/S and E/W
masses in turn. The microprocessor prevents the system from attempting
incompatible actions (e.g. centring when the masses are locked).
While a command is taking place, the BUSY LED will flash; you can use this
for diagnostic purposes. See the description of each command for full details.
When no command is active, i.e. all three lines are high, the control
microprocessor goes into a power-saving mode. In integrated instruments,
such as the 3ESPCD, the lines are controlled by the digitiser.
7.1.2.1 LOCK
This command locks the vertical mass and clamps the horizontal sensors by
tilting them up to their end stops. If LOCK is activated when the masses are
already locked, the processor will unlock them and attempt to lock again.
This is useful if you suspect that the locking procedure has failed.
In detail, the process acts as shown in the following graph. The top three
streams are the mass position outputs of each component (Z, N/S and E/W,
respectively), whilst the bottom one represents the state of the BUSY LED (up
= on).
In the three-stage process, the vertical mass is locked with a motorised
micrometer, and the N/S and E/W sensor bases are tilted to their end stops. At
some point during each tilting stage, the position of the relevant mass will flip
78
Issue B - November 2013