Nanometrics Trillium Compact, Руководство пользователя

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6. Lower the seismometer into the hole to the targeted depth ensuring that cable tie
wraps are tied around both the seismometer cable and the wire rope approximately
every 5 meters to keep them together and ensure that the load is placed on the load-
bearing wire rope and not on the seismometer cable.
7. Return to "Installing a Trillium Compact Posthole in a Cased Hole" on page 24 to
complete the installation.
2.8 Aligning a Trillium Compact Posthole to North
There are two typical methods for aligning a Trillium Compact Posthole to north. The method
used is usually determined by the depth of the hole where the unit is installed.
For shallow holes,
l
Align the north-south guide on the top of the pressure vessel to a surface line. See
"Aligning the Trillium Compact Posthole using a Surface Line" below for details.
For deeper holes,
l
Correlate the output of the seismometer with that of a temporarily installed
surface-based seismometer that is aligned to true north to calculate their relative
orientation. See "Aligning the Trillium Compact Posthole using a Surface seismometer"
on the next page .
2.8.1 Aligning the Trillium Compact Posthole using a Surface Line
If you are installing the Trillium Compact Posthole in a shallow hole (usually 2 m or less) where
the top of the seismometer pressure vessel is visible and the unit can be turned by hand after
being lowered into the hole, you can use the surface line method to align the instrument.
To align a Trillium Compact Posthole to north with a surface line:
1. Place a ruler, or stake a line, aligned to true north across the hole.
If you are using a magnetic compass, account for the local magnetic declination when
making the line across the hole.
Chapter 2 - Installing a Trillium Compact Posthole Seismometer
16889R10 • 2020-11-12 Page 27