Geokon 6300, Инструкция по эксплуатации

Страница: 13 / 24

7
2.3 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 "dither" 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.
Most in-place 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 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)
After connecting the sensor to the gauge tubing already in the casing, and after removal of
the clamping screw, use 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 silicone
oil out of the "needle" end.
2) Now, inject 2.00 cc into the hole in the sensor. Immediately following this operation, the seal
screw should be replaced in the sensor.
3) The sensor may now be lowered into the casing.
2.4 Splicing and Junction Boxes
Because the vibrating wire output signal is a frequency rather than current or voltage, variations
in cable resistance have little effect on gauge readings and, therefore, splicing of cables has little
effect and, in some case, may be beneficial. For example, if multiple sensors are installed in a
borehole, and the distance from the borehole to the terminal box or datalogger is great, a splice
could be made to connect the individual cables to a single multi-conductor cable. This
multiconductor cable would then be run to the readout station. For such installations it is
recommended that the transducer be supplied with enough cable to reach the top of the casing
plus enough extra to make splicing possible.
The cable used for making splices should be a high-quality twisted pair type with 100%
shielding (with integral shield drain wire). When splicing, it is very important that the shield
drain wires be spliced together! Splice kits recommended by Geokon incorporate casts placed
around the splice then filled with epoxy to waterproof the connections. When properly made, this
type of splice is equal or superior to the cable itself in strength and electrical properties. Contact
Geokon for splicing materials and additional cable splicing instructions.
Junction boxes and terminal boxes are available from Geokon for all types of applications. In
addition, portable readout equipment and datalogging hardware are available. Contact Geokon
for specific application information.