Guralp Systems CMG-3TB - Manual (Page 19)

Operator's guide
need to move the instrument.
To unlock the instrument, hold down the ENABLE and UNLOCK
buttons (or the UNLOCK switch on a breakout box) for at least six
seconds. The sensor's microcontroller will free the vertical, N/S and
E/W sensor masses in turn and ready them for use. Once this is done,
the controller automatically starts a centring cycle. If you issue an
UNLOCK command when the masses are already free, the instrument
will attempt to lock the masses first, and then unlock them in
sequence as normal.
To lock the instrument, hold down the ENABLE and LOCK buttons (or
the LOCK switch) for at least six seconds. The sensor's microcontroller
will lock the vertical sensor mass, followed by the N/S and E/W sensor
masses in turn. After this, the controller locks the base of the
horizontal instrument, tilting it until it is held against its end stop. The
instrument is now protected against accelerations up to 10
g, and is
ready for transportation.
Centring
To centre the instrument, hold down ENABLE and CENTRE buttons
(or the CENTRE switch) for at least six seconds. If the masses are
locked, the microcontroller will do nothing. Otherwise, it attempts to
zero the output of the vertical, E/W, and N/S sensors in sequence by
exerting a small extra force on the boom. For the vertical sensor, a
motor-driven adjuster presses a small spring lever against the boom
until the mass position output indicates an offset close to zero. In the
case of the horizontal sensors, the sensor frame is tilted on its base
plate. Again, the controller monitors the mass position sensor and
stops the centring process once it reaches its lowest offset.
After successful centring, the mass position outputs should be in the
range 0.1 – 0.8 V. If the centring process leaves the mass position
outputs above ±1.1 V, start another centring cycle. You will probably
need to perform several rounds of centring before the masses are ready.
The handheld control unit
This portable control unit provides easy access to the seismometer's
control commands, as well as displaying the output velocity and mass
position (
i.e. acceleration) on an analogue meter.
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