installation under these conditions is unavoidable. The instrument shield wire should
be well grounded, but isolated from sources of external electrical interference.
In situations where vibrating wire piezometers and packers are used at the same
time in standpipes or wells, special care must be taken to avoid damaging or cutting
the cable jacket with the packer equipment or tools. Any cuts in the cable jacket will
allow water entry, which can potentially result in damage or failure of the vibrating
wire sensor.
5.1 FILTER SATURATION
High air entry ceramic or low air entry sintered stainless steel filters are available.
The filters are intended to protect the delicate diaphragm area of the vibrating wire
piezometer while allowing the transmission of external pressures. The filters and
bottom cavity of the piezometer body must be saturated to allow the accurate
transmission of hydraulic pressures to the vibrating wire diaphragm. Filter saturation
provides the following reading advantages:
• There is no fluid movement in a saturated environment - only pressure
transmission. This reduces the possibility of the filter becoming clogged with
debris due to oscillating water movement;
• Decreased response times due to pressure changes, which means increased
sensor sensitivity;
• Ensure hydraulic continuity between the pore water and the piezometer
diaphragm in unsaturated soils, which will provide the highest accuracy of
pressure measurement.
5.2 LOW AIR ENTRY SINTERED STAINLESS-STEEL FILTERS
Total saturation of the filter is necessary for accurate reading results. For the
standard filter supplied, the low air entry filter, saturation will start to occur as the
piezometer is lowered into the water. Water will be forced into the filter, compressing
the air in the space between the filter stone and the pressure sensitive diaphragm.
Given enough time, this air will dissolve into the water until the space below the
diaphragm and within the filter is entirely saturated. This could take multiple days,
which could mean slightly inaccurate reading results the first few days.
The following procedure will speed up the filter saturation process and allow accurate
readings to be taken immediately:
• Turn the vibrating wire piezometer upside down. Remove the end filter assembly,
which is held in place with an internal O-ring.
• Submerge the inverted piezometer in a bucket of flat water (water which has
been sitting for 24 hours). This will fill the space above the piezometer diaphragm
with water.
• While keeping the piezometer submerged, slowly replace the filter housing onto
the inverted piezometer end, allowing the water to be forced out through the filter
sinter.
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