E10160-200722
FOP
Page 4
CONSTRUCTION
Model:
FOP
FOP-P
FOP-C
FOP-F
Housing:
Miniature
Push-in
point with
EW thread
Threaded
(1/4-18NPT
female
standard)
Thick wall
Diaphragm Material:
17-4 PH Stainless steel
Outside diameter in mm:
19
33.4
19
25.4
Cable diameter:
3 or 7mm
Filter types
Two types of filters are available: high air entry ceramic or low air entry sintered stainless
steel filters.
The table below summarizes the main differences between the two filter models.
Stainless steel filter
low air pressure entry
pore diameter: ~50 µm
Ceramic filter
high air pressure entry
pore diameter: ~1 µm
Filter generally used.
Filter usually installed for use in
unsaturated fine grain material.
Does not allow suction measurements.
If water level drops below the
piezometer and that a suction builds up,
the filter can de-saturate. But as soon as
the water level comes up, it will re-
saturate easily.
Allow measuring suction to -100 kPa.
If negative pressure is more important,
the filter will de-saturate and readings will
become incorrect.
Air entry pressure: ~10 kPa
Air entry pressure: ~450 kPa
Small time lag.
More important time lag.
Easy to saturate and install.
Need to be saturated under vacuum.
Allows fine grain infiltration.
Helps prevent fine grain infiltration.