E10160-200722
FOP
Page 2
universal readout unit from Roctest is directly in engineering units either in imperial (psi)
or SI (bar) system.
Models FOP and FOP-C
The model FOP piezometer is designed to be embedded in earth fills and concrete, or
inserted into
boreholes and pipes as small as 19 mm (3/4”). One end is fitted with an insert
that holds a micrometric high air or low air entry filter. The opposite end contains the cable
entry, fitted with watertight feed-through connector. All parts are made of stainless steel.
The filter is set in the front end of the piezometer and sealed with an o-ring. With the filter in
place, the diaphragm is protected from solid particles, and senses only the fluid pressure to
be measured. The filter housing easily removable for calibration and saturation can also be
replaced with a female or male pipe thread adapter to use the gauge as a pressure
transducer (Model FOP-C).
Model FOP-P
The model FOP-P piezometer is designed to be driven into unconsolidated fine grain
materials such as sand, silt, or clay. The external housing is a thick walled cylinder fitted
with a pointed shoe at one end, and a male thread adapter at the cable entry, fitting "EW"
standard drill rods. Four port holes above the point hold micrometric filters. The cable passes
through the threaded end, and can be fed through push rods leading to the surface. The
cable entry is fitted with watertight feed-through connector. Both high and low air entry filters
are available.
Model FOP-F
The model FOP-F piezometer is a thick wall version of the FOP piezometer with an outside
diameter of 25.4mm.
Model FOP-MicroPZ and FOP-PZ
The model FOP-MicroPZ and FOP-PZ piezometers are based on non-contact deflection
measurement of a miniature MOMS (Micro Optical Mechanical System) pressure sensor
manufactured using photolithographic techniques. The pressure transducer has a flexible
diaphragm assembled on top of a sealed vacuumed cavity, and the pressure measurement is
based on Fabry-Perot white-light interferometry. Pressure creates a variation in the length of a
Fabry-Perot cavity consisting of the inner surface of the flexible diaphragm on one side and a
reference optical surface attached to the lead optical fiber on the other side.
The mechanical robustness for the FOP-microPZ is assured by the stainless protection sleeve
and a porous stainless steel filter which protects the sensing element from solid particles,
allowing the piezometer to sense only the fluid pressure to be measured. The total diameter of
the sensor, including the housing, is only 4.8 mm and its total length is only 54 mm.
The MOMS pressure sensor is mass-produced in batches on glass and silicon wafers using
well established photolithographic technologies derived from the semiconductor industry.
The model FOP-PZ is composed of the same miniature MOMS pressure sensor but this one
is protected inside a PVC housing of 15.9mm of diameter. The fiber optic cable passed through
a plastic cable gland on one side and at the pressure entry there is a porex HDP filter. The