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Reference Manual

00809-0100-4811, Rev DA

Section 2: Transmitter Overview

January 2015

Transmitter Overview

 Surface foam and particles in the tank atmosphere are also circumstances that might

affect measuring performance.

 Coating/contamination can reduce the measuring range.

 Disturbing EMC environment in tank.

2.4.6 Interface

Rosemount 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 a Rosemount

3301 in applications where the probe is fully immersed in the liquid.

Figure 2-3. Interface Measurement with a Rosemount 3302 and a Rosemount 3301 (Fully

Immersed Probe)

Coaxial, Rigid Twin, Flexible Twin and Rigid Single lead probes can be used for measuring

interfaces. The coaxial probe is the preferred choice for clean liquids and when the bridle is not

fully immersed. In applications with a fully immersed probe, the twin lead probes are

recommended for nozzle installations, and the rigid single lead probe is best for bridle

mounting.

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 RCT software has a

built-in dielectric constant calculator to assist users in determining the dielectric

constant of the upper product (see “Dielectrics” on page 83).

 The dielectric constant of the upper product must have a 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.

 The 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 in. (0.2 m) for the flexible twin lead

probe, and 4 in. (0.1 m) for the rigid twin lead and coaxial probes in order to distinguish

the echoes of the two liquids.

Level

3302 3301

Interface Level

Level = Interface Level

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