First encounters
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.
3.3.1.3 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 Volts. 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.
3.3.2 The hand-held 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.
14
Issue G - November 2019
