Measurement Principle - Emerson Rosemount 5408 Reference Manual

Reference Manual
00809-0100-4408, Rev BA
Section 2
Measurement principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 3
Process characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 4
Vessel characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 6
Application examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 6
Components of the transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 9
System integration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 10
2.1

Measurement principle

The Rosemount
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
Figure
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
Figure 2-2
Figure 2-1. FMCW-method
Frequency (GHz)
f
max
f
in
f
f
out
f
min
Transmitter Overview
Transmitter Overview
™
5408 and 5408:SIS are two-wire transmitters for continuous level measurements over
2-1).
for a schematic overview of the signal processing.
t f d=Distance
Transmitted signal
Reflected signal
Time (s)
Transmitter Overview
November 2017
f f
out in
d
3