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6. Geotechnical Instruments Installation and Operation Tips
1. Handling caution
Engineering measuring instrument is precisely
manufactured and sensitive. Don't drop it and don't allow it
to be exposed to external shocks. In particular, the VW
measuring instrument is likely to see its zero point changed
due to shocks.
2. Caution for storing calibration report
Calibration report is provided with each sensor.
Information at the moment of calibration includes
barometric pressure, calibration temperature, and
temperature sensor in use, calibration data, conversion
ratio and classification of signal cable by color. Therefore,
you should be careful with storing the information until all
work is done. In case the report is lost, tracking data and
product might be impossible.
3. Operation by an engineer
All the process should be operated by a skilled engineer to
prevent inappropriate choices such as errors of instrument
choice, installation and operation which make impossible
near-permanent calculation.
4. The need for shielding
It is common that sensor sends a weak electronic signal.
And sensor is under the influence of electromagnetic
induction, electrostatic induction static electricity
electrification generated when other control machine is on.
In particular, given that environmental condition of
engineering work involving welding, generator, motor,
antenna, and watery surface is poor, shielding and ground
wire should be connected in the case of output device
connection.
5. Caution for signal cable extension
There would be no problem that VW sensor outputting
frequency signal is connected for extension .in the case
that a sensor generating Voltage is connected for
extension, electronic sensors are vulnerable to changes in
resistance value. Therefore, the length of the cable plays
a big influence. So, you should adjust resistance change
value with adjustment value toward a sectional length of
signal cable by manufacturers. Also, extension seam part
should be finished up with Splice Kit (Epoxy).
6. The use of protection tube for signal cable
In the case of laying under the ground, dams, vulnerable
foundation, concrete structures can have a big
displacement, a source of signal cable disconnection. In
the case of ground construction, given the construction
condition, heavy equipment operation and frequent moving
construction can be a source of disconnection or sensor
damage. Therefore, caution should be taken for the
protection of sensors and signal cables. And minimize the
dangerous factors by using new construction pipe for
drainage system.
7. Installation of Amplifier with sensors generating mV
Engineering measuring machine generating electronic
signal has a 200-300 m transmission distance. In the case
Junction Box and Terminal Box have a long distance from
the measuring machine, an amplifier should be installed in
proportion of measurement distance to prevent drop of
voltage for sensor transmission.
5
8. Atmospheric pressure adjustment
When manometer is chosen as sensor, it is very sensitive
to change in atmospheric pressure. Therefore, for precise
measurement, places such as dams, valleys, the sea and
reclaimed lands with high fluctuation of atmospheric
pressure should adjust head height according to the
difference of the pressure by using mercury barometer.
9. Lighting rod construction
In the case of large engineering work near water such as
dams, lakes, the sea and large fields, valleys, lighting rods
connecting each sensor individually should be constructed
to protect sensors. Within the influence of over voltage,
sensors are likely to function poorly.
10. Caution for filter use in pressure sensors
Pressure sensors such as negative pore water pressure
have attached filters. Upon installation, make sure to let air
out of the inside of the filter. Given that densities of air
contraction and water are different, remained air might
cause an error to measured value. Also, at places where
unsaturated soil or negative pore water pressure are
expected, it is recommended to use 1μm high-density
ceramic filter.
11. Caution for bearing plate in use for load cell
For maintaining consistent measured value and high
precision, the use of bearing plate is important, during
installation of hard cell on Earth Anchor, heat processed
steel materials should be manufactured with the enough
thickness to endure unloading load and with the density of
within 0.5 degree in top-down parallel lines. High quality
products should be used for cone for spilt, cone-plate and
mutual taper processed density.
12. Sensor temperature adjustment
An element of VW sensors uses wire rod (used for piano
string) so that coefficient of linear expansion metallic
materials hold can cause errors of margin and sensors of
electricity and electron hold an adjustment factor. For
precise measurement, adjust the difference of temperature
with a mercury thermometer.
13. Auto Data Acquisition System requires UPS
In South Korea, relatively temporary blackout (0.5
seconds) is frequent. So overloading owing to simultaneous
uses of equipment and accumulated power cables on sites
are likely to cause ordinary and temporary blackouts,
leading to computer Down and errors of built-in software.
Therefore, When Auto Data Acquisition System is operated;
UPS(Uninterruptable Power Supply) must be used to
minimize dangerous factors.
14. Caution for the choice of VW output unit
Manufactures of VW sensors and output units usually cover
600~3,200Hz (360~10,240 10
possible measurement range. And they design sensors
taking into consideration the purpose of sensors, durability,
and precision. Therefore, when Mode for unit choice of
output unit within this range is changed, you must select
sophisticated output unit-making measurement possible
or 1666∼312 μsec) for
3
2
Hz
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