CMG-3V
Instead, you should either move the instrument to a narrower
section of the borehole and try again, or contact Güralp Systems
to ft a longer hole lock, quoting accurate measurements of your
borehole.
12.Power up the instrument from a suitable power supply.
13.Level and centre the sensor (see
Section 3.5, “Levelling and
centring”
) so that it can be tested.
14.Check that the sensor is functioning correctly by connecting a
meter or monitoring device to the sensor outputs. If the sensor
fails to register ground movements, contact Güralp Systems.
15.Lock the sensor masses once more, tension the load bearing cable
and retract the hole lock arm.
16.Gently lower the sensor to the required depth. At approximately
20 m intervals, fx the signal cable to the load bearing cable using
metal clamps (nylon cable ties every 5 m may be sufcient for
shallow installations). This will ensure that the signal cable does
not become kinked or trapped within the borehole. Leave a liile
slack on the signal cable each time, so that it does not bear any
weight. Too much slack, however, will cause the cable to scrape
against the borehole casing.
17.Fix the sensor system into the borehole using the hole lock arm
(see
Section 2.5, “Operating the hole lock”
).
If you are installing a 3V in a deep borehole, the weight of the
sensor will stretch the load bearing cable slightly. Remember to
allow for this when raising or lowering the cable in the following
steps.
18.Use the winch to drag the assembly up within the borehole for a
distance of 15 – 30 cm. This will ensure that the hole lock arm and
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