Geokon 6350, Installation Manual, Page: 15 / 26

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2.4 Fluid Damping
The vibrating wire tilt sensor acts as a self-damping system when used in vibration free
environments. When external ground or structural vibrations exceed a certain threshold, the
pendulous mass will continue to “swing” and stable readings may not be possible. In such cases,
additional damping can be achieved by adding a viscous damping fluid to a small reservoir
contained in the sensor. A thin, wide “paddle” is connected to the mass and when the fluid is
added the pendulum is damped by the action of the paddle in the damping fluid (see Figure 2).
Damping fluid kits are available from Geokon (part number 6350-4).
Most in-place tiltmeter installations will not require this fluid. However, if the instrument gives
unstable outputs, or it is known that the structure is constantly vibrating, the fluid can be added.
The fluid is a very high viscosity silicone oil which must be injected into the sensor with a
syringe.
The sensor must be held upright during the injection of the fluid and at all times following the
injection. This makes it necessary to perform this operation in the field. The following applies
for a typical in-place installation.
1) Remove the clamp screw on the bottom side of the sensor (see Figure 2).
2) Using the syringe applied, first pull the piston from the syringe and squeeze the silicone from
the tube into the syringe. Replace the piston and start the fluid out of the “needle” end.
3) Inject 2.00 cc of the damping fluid into the hole in the sensor. Immediately following this
operation, the seal screw should be replaced in the sensor.
4) The sensor may now be attached to the mounting bracket.
2.5 Splicing and Junction Boxes
Terminal boxes with sealed cable entries are available from Geokon for all types of applications.
These allow many gages to be terminated at one location with complete protection of the lead
wires. The interior panel of the terminal box can have built-in jacks or a single connection with a
rotary position selector switch. Contact Geokon for specific application information.
Because the vibrating wire output signal is a frequency rather than a current or voltage,
variations in cable resistance have little effect on gage readings; therefore, splicing of cables has
no ill effects, and in some cases may in fact be beneficial. The cable used for making splices
should be a high quality twisted pair type, with 100% shielding and an integral shield drain wire.
When splicing, it is very important that the shield drain wires be spliced together. Always
maintain polarity by connecting color to color.