Emerson Process Management rosemount 3300 series Qwhuidfh, Probe is fully immersed in the liquid

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00809-0100-4811, Rev AA October 2002

Rosemount 3300 Series

,QWHUIDFH	Model 3302 is the ideal choice for measuring the interface of oil and water or
	other liquids with significant dielectric differences. It is also possible to
	measure interface with the Model 3301 in bridle/tank applications when the
	probe is fully immersed in the liquid.
Figure 2-6. Fully immersed
probe

BRIDLE_INTERFACE

Rigid twin lead, flexible twin lead and coaxial probes can be used to measure interfaces. However, the coaxial probe is the preferred choice. 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.

If interface is to be measured, the following criteria have to be fulfilled:

•The dielectric constant of the upper product must be known. The Radar Configuration Tools software has a built-in dielectric constant calculator to assist user´s in determining the dielectric constant of the upper product (see “Dielectrics” on page 4-21).

•The dielectric constant of the upper product must have lower dielectric constant than the lower product in order to have a distinct reflection.

•The difference between the dielectric constants for the two products must be larger than 10.

•Maximum dielectric constant for the upper product is 10 for the coaxial probe and 5 for twin lead probes.

•The upper product thickness must be larger than 8 inch (0.2 m) for the flexible twin lead probe and 4 inch (0.1 m) for the rigid twin lead and coaxial probes in order to distinguish the echoes of the two liquids.

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), and the maximum measuring range is only limited by the length of the coaxial and rigid twin lead probes.

For the flexible twin lead probe, the reduction of maximum measuring range (65 ft/20 m), can be gained from Figure 2-7 on page 2-10..

However characteristics varies widely between different applications. For other product combinations, consult factory.

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