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Transmitter Overview
August 2017
2.3.2
In-tank obstructions
The Rosemount 3308 Series Transmitter is relatively insensitive to objects in the tank since the radar
signal is transmitted along a probe.
Avoid physical contact between probes and agitators as well as applications with strong fluid movement
unless the probe is anchored. If the probe can move within 1 ft. (30 cm) away from any object, such as an
agitator, during operation then probe tie-down is recommended.
In order to stabilize the probe for side forces, you have the option to either hang a weight at the probe
end (flexible probes only) or fix/guide the probe to the tank bottom.
2.3.3
Interface level measurement
Rosemount 3308 Series Transmitter is well suited for measuring the interface of oil and water, or other
liquids with significant dielectric differences.
Figure 2-6. Interface Level Measurement
A. Product Level
B.
Interface Level
All probes can be used for measuring interfaces. Single probes are the preferred choice in almost all
applications but depending on the application and installation geometries a coaxial probe or a flexible
twin probe may be a better fit.
For measuring the interface level, the transmitter uses the residual wave of the first reflection. Part of the
wave, which was not reflected at the upper product surface, continues until it is reflected at the lower
product surface. The speed of this wave depends fully on the dielectric constant of the upper product.
The maximum allowable upper product thickness/measuring range is primarily determined by the
dielectric constants of the two liquids. Target applications include interfaces between oil/oil-like and
water/water-like liquids. For such applications the upper product dielectric constant is low (<3) and the
lower product dielectric constant is high (>20). Refer to
further interface application guidelines.
Emulsion layers
Sometimes there is an emulsion layer (mix of the products) between the two products which, depending
on its characteristics, will affect interface measurements. Please consult factory for guidelines on how to
handle emulsion layers.
8
PRELIMINARY
B
A
B
Reference Manual
00809-0100-4308, Rev CA
"Interface measurements" on page 119
for
Transmitter Overview
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