RST Instruments VW2100, Инструкция по эксплуатации, Страница: 5 / 34

VW2100 Vibrating Wire Piezometer
Instruction Manual
ELM0005P RST Instruments Ltd. Page 5
1 I
NTRODUCTION
The RST Vibrating Wire Piezometer is a stable, robust pressure transducer designed
to allow very accurate remote measurements of piezometric levels and borehole
pressures over extended periods of time and through all conditions. The vibrating
wire pressure transducer output is a frequency signal which is unaffected by line
impedance and/or contact resistance of the conductor. This allows for the accurate
transmission of the frequency signal over very long distances. These types of
vibrating wire sensors can be installed in boreholes or driven into soft ground.
A standard integral thermistor is included within each transducer, which measures
the temperature of the transducer and its surroundings. This temperature information
is used to provide temperature correction to the output pressure readings. A gauge
calibration factor and temperature correction factor are supplied with each
manufactured gauge based on the factory calibrations which are carried out for each
sensor, immediately following manufacture.
A portable vibrating wire readout unit, such as the RST VW2106 Readout Unit, is
used to display the frequency of the vibrating wire which is proportional to the
pressure being applied to the vibrating wire transducer diaphragm. Additionally, the
VW2106 readout unit will display the transducer temperature directly in degrees
Celsius.
Complete data logging systems are available from RST to provide automated data
collection from vibrating wire transducers. Consult RST for more information, if
required.
F
IGURE
1-1 V
IBRATING
W
IRE
P
IEZOMETER
(0.7 MP
A
)
The RST VW piezometer is a Vibrating Wire diaphragm pressure sensor. Pressure
applied to the transducer diaphragm will cause a change in the Vibrating Wire
tension, resulting in a change to the resonant frequency, which is directly
proportional to the pressure change.
The Vibrating Wire sensors are made of two small diameter cylindrical parts joined
by a length of steel tubing. The diaphragm is welded to the front cylinder. A high
strength steel wire (the Vibrating Wire) is clamped to the center of the diaphragm,
then is run through the first cylinder, and then clamped to the base of the second
cylinder which is the end block. The Vibrating Wire is clamped to the diaphragm and
end block by low temperature hydraulic swaging which virtually welds the parts
together without affecting the elastic properties of the wire. All parts of the sensor,
other than the actual Vibrating Wire are machined from a high-grade stainless steel,
selected for its low yield and high corrosion resistance.