Process Characteristics; Dielectric Constant; Foam And Turbulence; Condensation - Emerson Rosemount 5408 Reference Manual

Transmitter Overview
November 2016
2.2

Process characteristics

2.2.1

Dielectric constant

A key parameter for measurement performance is reflectivity. A high dielectric constant of
the media provides better reflection and enables a longer measuring range.
In addition to the dielectric constant, the measuring range depends on the microwave
frequency, antenna size, and the process conditions (see
2.2.2

Foam and turbulence

Foaming liquids or turbulence may cause weak and varying surface echo amplitudes. The
effects of turbulence are usually minor, but in the most challenging conditions, the
transmitter may be mounted in a still pipe. In addition, measurement performance can be
optimized by enabling the appropriate process conditions parameters, see
conditions" on page
Measurement in foamy applications depends largely on the foam properties. When the
foam is light and airy, the actual product level is measured. For heavy and dense foam, the
transmitter may measure the level of the foam's upper surface. The Double Surface
Handling function allows the user to select if the foam layer or product surface should be
used as output.
2.2.3

Condensation

Generally, the radar signal is unaffected by condensation and low pressure steam. However,
heavy condensation can effect the measurement. In such applications, air purging may be
required to prevent clogging of the antenna.
In high temperature applications, it is recommended to insulate the tank nozzle. Insulation
prevents the nozzle from becoming a cold spot, and thus reduces the amount of water build
up and condensation on the antenna.
If the temperature in the tank is much higher than the ambient temperature (i.e. tank is
heated and located in a cold area), it might be necessary to heat trace the nozzle in addition
to the insulation.
2.3

Vessel characteristics

2.3.1

In-tank obstructions

The transmitter should be mounted so that objects such as heating coils, ladders, agitators
and so on are not in the radar signal path. These objects may cause false echoes resulting in
reduced measurement performance. However, the transmitter has built-in functions
designed to reduce the influence from disturbing objects where such objects cannot be
totally avoided.
Vertical and inclined structures cause minimal effect since the radar signal is scattered
rather than directed back to the antenna.
4
PRELIMINARY
171.
Reference Manual
00809-0100-4408, Rev AA
"Measuring range" on page
"Process
Transmitter Overview
121).