VW2100 Vibrating Wire Piezometer
RST Instruments Ltd.
Page 9
It is not recommended to install the piezometer if the calibration record sheet CF
value cannot be confirmed by the field calibration test. The instrument will need to be
inspected and undergo a full shop function test and re-calibrated before being
returned to service. Contact RST for further information.
If the diameter of the water filled borehole is too small, the volume of water that the
vibrating wire piezometer cable displaces, when raised or lowered into position,
could potentially raise, or lower the borehole water level. This effect may seriously
impact the accuracy of the above detailed Field Calibration Check. Note that this
potential effect will be further dependent on the available permeability of the borehole
to absorb small amounts of volume change.
To avoid this potential problem, it is recommended that the water filled borehole used
for Field Calibration Checks be large enough in diameter so that the potential error
caused by cable volume displacement will be insignificant in the calculation of the
pressure change. It is recommended to use a borehole diameter that is a minimum of
10 times greater than the wire diameter. A borehole with a moderate degree of
permeability would be preferred to a “tight” borehole.
4
R
EADING
P
ROCEDURES
4.1
VW
I
NSTRUMENT
R
EADINGS
It is strongly recommended that the instruction manual for the RST VW2106 Readout
Unit be read thoroughly before proceeding. Failure to become familiar with the
function and operation of the VW2106 Readout could potentially result in damage to
the VW2106 Readout unit and/or the vibrating wire sensors that are connected to it.
4.2
I
NITIAL
I
NSPECTION AND
C
HECK
R
EADINGS
A full inspection of all received vibrating wire instrumentation equipment is required
immediately upon receipt at site to ensure that the vibrating wire instruments have
not been damaged in any way during shipment and are fully functional/ready for use.
Test readings should be taken of each vibrating wire instrument and compared to the
vibrating wire instrument reading information provided on the Calibration Record
sheet. Any discrepancies should fully investigated and satisfactorily resolved before
the vibrating wire instrument is released for field installation and service.
The individual performing the inspection and initial test readings must be familiar with
the vibrating wire instrument operation and contents of this instruction manual.
4.3
I
NITIAL
R
EADINGS
Vibrating wire piezometers differ from other types of pressure sensors as the core of
the vibrating wire sensor is manufactured with an initial tension. The piezometers
have a positive B-Unit reading without any external pressure being applied. Vibrating
wire piezometers are acutely sensitive to pressure changes at zero point as there is
no zero-point hysteresis to overcome. The determination of vibrating wire instrument