Guralp Systems CMG-5T - Manual (Page 7)

Operator's Guide
If the performance so far has been as expected, the instrument may be
assumed to be in working order and you may proceed to install the
unit for trial recording tests. Most likely, however, you will need to
adjust the mass deflection offset (see Section 2.4, page 8.)
2.3 Installing the sensor
You will need a solid surface such as a concrete floor to install the 5T.
If you are in any doubt about how to install the sensor, you should
contact Güralp Systems.
1. Prepare the surface by scribing a N/S orientation line, and
installing a grouted-in fixing bolt around the middle of the line.
A 6 mm (0.25 in) threaded stud is suitable, or an expanding-nut
rock bolt or anchor terminating in a threaded stud. The bolt
should be about 120 mm (5 in) long.
2. Place the accelerometer over the stud, on the scribed base-line,
and rotate to bring the orientation line and studs accurately in
alignment with it. The accelerometer has no levelling feet, but
can use an internal simulated level adjustment to compensate as
long as it is fixed to a hard, clean surface within 1 ° of the
horizontal.
3. Fix the accelerometer in place using a fixing nut with spring
washer. Do not over-tighten.
4. If required, make a screening box for the sensor, to shield it
from draughts and sharp changes of temperature. A suitable box
can be constructed from expanded polystyrene slabs (e.g. 5 cm
building insulation slabs) with sealed joints between them and a
hole drilled for the connector. You can then use high-grade glass
fibre sealing tape to fix the leads in position and fasten the box
to the mounting surface. Commercial duct sealing tape is ideal.
5. Connect the sensor to your digitizing equipment or Control Unit
to start receiving signals.
Temporary installations
5T sensors are ideal for monitoring vibrations at field sites, owing to
their ruggedness, high sensitivity and ease of deployment. Temporary
installations will usually be in hand-dug pits or machine-augered
holes. Once a level base is made in the floor, the accelerometer can be
sited there and covered with a box or bucket. One way to produce a
level base is to use a hard-setting liquid:
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