Inside the 3ESP
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:
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.
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.
The E/W component follows in the same way. All three masses are now centred and
the process completes.
After the sensor unlocks the masses, the first round of centring has to move the N/S
and E/W components all the way from their end stops, whilst the
Z
component is
often closer to the proper position. Because of this, the first Z centring operation
takes much less time than the others, and you may not notice it.
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, you should
start another centring cycle by activating the
CENTRE
command again. You will
probably need to initiate the centring process several times before the masses are
adequately centred.
34
Issue G - February 2016
