8 offset adjustment – Guralp Systems CMG-5TD User Manual
Page 15
Operation
5.8
Offset adjustment
When the instrument is installed in it’s final position and correctly aligned,
the approximate level should be checked using the bubble level on the top of
the casing. The bubble should lie completely within the scribed ring. To
check the DC offsets, read the RIC value for each acceleration stream in the
SCREAM window. No adjustment is necessary if these values are less than or
equal to ±5000 counts.
To adjust the DC offsets, remove the screwed cover protecting the adjustment
screws, as shown in the diagram below.
Warning: GSL instruments are assembled at near to sea level. When
using the instrument at altitude, there may be a considerable
pressure differential between the air inside the casing and the
external atmosphere. This could cause the sealed cap to fly off with
considerable force when initially released. Take care that this does
not cause injury.
Selecting the channels in turn, adjust the level screws to reduce the RIC
values to less than ±5000 counts, repeating until consistent results are
obtained on all three channels. When offset adjustment is complete, replace
the protective cover firmly.
It is likely that, after the cover is installed, the accelerometer outputs will drift
until the system establishes temperature equilibrium with it’s environment
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Issue D - April 2013