Emerson Rosemount 3308A, Reference Manual

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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.
2.4.3 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
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%
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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 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).
Related information
Interface measurements
Transmitter overview Reference Manual
February 2020 00809-0100-4308
16 Rosemount 3308 Series