E10160-200722
FOP
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1
PRODUCT
The FOP Fiber optic piezometer is a stable, robust pressure transducer, designed to allow
remote measurements of piezometric level and pore pressure over long periods of time. It
can be installed in boreholes (model
FOP, FOP-microPZ, FOP-PZ
), driven into soft ground
(model
FOP-P
), laid in trenches prior to fill replacement, or buried in concrete (models
FOP
and
FOP-F
). It can also be threaded to hydraulic or pneumatic lines (model
FOP-C
).
Each gauge is delivered with a calibration data sheet, which includes a gauge factor and/or
calibration factors and a temperature correction factor except for the FOP-microPZ and
FOP-PZ. These factors are determined through factory calibration.
Complete data logging systems are available, please consult Roctest website for details.
1.1 GAUGE CONSTRUCTION of FOP
The design of the pressure sensor is based on a non-contact measurement of the
deflection of a stainless steel diaphragm, as opposed to the more conventional measuring
of the diaphragm’s deformation. When the gauge is under pressure, there is a variation of
the Fabry-Perot cavity length made by the inner surfaces of the stainless steel diaphragm
on one side and the tip of an optical fiber on the other side as illustrated in Figure 1. The
geometry and material of the transducer are selected in order to obtain a linear relationship
between the deflection of the diaphragm and the applied pressure.
Figure 1: FOP Pressure Transducer
Figure 1: Schematic view of a FOP sensor
The mechanical robustness of the sensor is assured by the all welded stainless steel
construction, with no epoxy, sealing rubber, or other sort of polymeric materials.
The pressure transducer comes in three different types: gauge, absolute or differential
type. In the case of gauge type, the transducer comes with a vented cable, which keeps
the cavity at ambient atmospheric pressure. In the case of absolute transducer, the cavity
length is sealed under vacuum. Finally in the case of differential sensor, the cavity is to an
arbitrary pressure and comes with a vent connection. The pressure value displayed by the
P
Diaphragm
Fabry-Perot
cavity
length
Optical fiber
Filter
Stainless steel
diaphragm
Fiber-optic cable
Stainless steel housing
Feed-through
Connector