First encounters
6. Return the instrument to broadband mode by selecting
BB VEL
from the
Velocity Select
switch.
3.4.3
Zeroing a 40TD digital instrument
The offset potentiometers in a 40TD are in the same place as on the 40T. To access
them, you will need to remove the digitiser module, which lies on top of the sensor
itself. You can monitor the mass position outputs of the sensor using a Hand-held
Control Unit and an adapter cable, available from Güralp Systems.
To change the offsets of a 40TD without digital centring:
1. Check the bubble level on the lid of the instrument, to ensure it is not tilted. If
necessary, re-level the instrument by adjusting its feet. Take care not to
disturb the instrument during the subsequent operations.
2. Unscrew the vent cap on the lid to allow the air pressure to equalise.
13
Issue F - June 2019
