Chapter 2 Transmitter Overview; Measurement Principle - Emerson Rosemount 5408 Reference Manual

2 Transmitter Overview
2.1

Measurement principle

The Rosemount
measurements over a broad range of liquids, slurries, and solids. The measurement
principle is fast-sweep Frequency Modulated Continuous Wave (FMCW).
The transmitter continuously emits signal sweeps with a constantly varying frequency
towards the product surface. Since the transmitter continuously changes the frequency of
the transmitted signal, there will be a difference in frequency between the transmitted and
the reflected signals (see
The frequency of the reflected signal is subtracted from the frequency of the signal
transmitted at that moment, resulting in a low frequency signal which is proportional to
the distance to the product surface. This signal is further processed to obtain fast, reliable,
and highly accurate level measurements. See
signal processing.
Figure 2-1:
Δf≈d=distance
A.
B.
C.
D.
Rosemount 5408 and 5408:SIS Level Transmitters
™
5408 and 5408:SIS are two-wire transmitters for continuous level
Figure
FMCW-method
Frequency (GHz)
Time (s)
Transmitted signal
Reflected signal
2-1).
Figure 2-2
Transmitter Overview
for a schematic overview of the
3