Guralp Systems CMG-3T - Manual (Page 39)

Operator's guide
Again, you can use the BUSY LED to monitor the progress of
unlocking.
1. The instrument checks to see whether the Z, N/S and E/W
masses are locked.
2. The instrument checks the N/S and E/W sensor bases.
3. The Z component is unlocked.
4. The N/S and E/W components are unlocked. These are quicker
than the Z component.
5. (see graph below) The N/S sensor base is unlocked, followed by
the E/W base. These processes take longer still.
•
After unlocking, the instrument automatically performs a round
of centring (see below).
CENTRE
This command re-centres the masses. If the masses are clamped, or if
the sensor mass positions do not exceed ± 1.2 V, the CENTRE
command does nothing. Otherwise, it attempts to zero the output of
the vertical, N/S and E/W sensors in sequence by exerting small extra
forces on the boom. For the vertical sensor, a motor-driven adjuster
presses a small spring lever against the boom until the mass position
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