Inside the 3TB
6.2.3 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 sensor 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.
This graph shows a typical centring process:
1. The
BUSY
LED pulses to indicate that it is centring the Z component. Each
pulse corresponds to a small force on the mass. The pulses become more
spaced out as this goes on, until a pulse is missed, signifying that no
corrective impulse is needed.
2. The N/S component follows in the same way. The mass position output does
not change for a while, as the true mass position is outside the range of the
output. In this case, the pulses cause the mass to overshoot the central
position, and a second group of pulses in the opposite direction is applied to
bring it into line.
64
Issue G - November 2019
