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4220 Flow Meter
Section 4 Submerged Probe Installation
4-2
The probe has several ports through which liquid enters the body
to contact the pressure transducer. The only way for the probe to
malfunction is for all the ports to be completely blocked. Most
substances likely to cover the probe are somewhat porous, which
still allows the hydrostatic pressure of the flow stream over the
probe to reach the transducer.
4.1.1 Functionality Under
Solids
Consequently, the probe will normally continue to function even
when covered with several inches of silt or sand. Note however,
that porous solids, such as wood chips or other organic material
that may swell considerably when soaked in water, can interfere
with the correct operation of the pressure transducer. In extreme
cases, swelling material can put enough pressure on the dia-
phragm of the pressure transducer to deform it. This will ruin
the submerged probe by introducing a permanent offset to the
pressure transducer.
Note
Always install the probe where it will be under water, even if
only an inch or so. The probe cannot measure levels that fall
below its location in the stream.
4.1.2 Minimum Reliable
Detection Level
It is important to note that there is a practical minimum water
level below which the submerged probe cannot reliably measure
level. This minimum level is approximately equal to the height of
the probe body, 0.1 ft. (1.3 in. or 0.030 m).
Liquid levels lower than this will be below the levels used to cali-
brate the sensor. The submerged probe level sensor will continue
to measure levels less than 0.1 ft.; however, the accuracy of the
measurement in this range is not guaranteed. Consequently, you
should always use the submerged probe with caution in very low
flow situations.
4.2 Submerged Probe
Nose Sections
Teledyne Isco provides three nose sections, each designed for spe-
cific flow stream conditions.
A complete list of nose sections and their part numbers can be
found in Appendix B.
Standard Nose Section – The standard nose section works in
any flow stream and will be installed on your probe unless oth-
erwise specified in your order. It is particularly well suited for
flow streams with high velocities because its shape overcomes
hydraulic problems that develop in these flow streams. At veloc-
ities exceeding 5 feet per second (1.5 meters per second),
localized low-pressure areas form near the submerged probe,
which can result in erroneous level readings. The length of the
nose section (3.87 inches or 9.84 cm) minimizes low-pressure
areas by allowing the flow stream to stabilize before it reaches
the probe’s entrance ports.
Standard Nose
Section