Guralp Systems CMG-3T - Manual (Page 40)

CMG-3T
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 the entire process of unlocking and centring:
1 – 5. The unlocking process as described above.
6. The BUSY LED pulses to indicate that it is centring the Z
component. The mass position output does not change for a
while, as it is beyond the range of the output. However, after a
few pulses, the position of the Z component comes within range
and is centred. The pulses become more brief as this goes on,
until a pulse is missed (signifying that no corrective impulse is
needed.)
7. The N/S and E/W components follow in the same way, until all
three masses are centred and the process completes. 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
40 Issue N