Guralp Systems CMG-3T - Manual (Page 37)

Operator's guide
adjustment motors. It responds to commands sent on three input lines
by grounding for 0.2 – 7 seconds.
The signals you can send 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
clamped.)
While a command is taking place, if you are using a Hand-held Control
Unit, its 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 routine operation,
the lines are controlled from the breakout box, Hand-held Control Unit
or digitizer. If you send control signals to the 3T manually, you must
ensure that the lines are pulled high after sending the signal, or the
equipment may be damaged. A “biased-OFF” type switch can be used
for this purpose.
LOCK
This command locks the masses 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).
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