VEGA VEGAPULS 41 4 … 20 mA; HART compact sensor - Manual (Page 5)

VEGAPULS 41 – 4 … 20 mA 5
26620-EN-041227
Reflected radar power dependent on the dielectric
constant of the measured product
2
0
0
10
25 %
40 %
5
10
5 %
20
30
40
50
%
4 6 8 12 14 16 18
20
ε
r
t t
Time transformation
VEGAPULS radar sensors can achieve this
through a special time transformation proce-
dure which spreads out the more than 3.6
million echo images per second into a quasi
slow-motion picture, then freezes and proc-
esses them.
Hence, it is possible for the radar sensors to
process the slow-motion pictures of the sen-
sor environment precisely and in detail in
cycles of 0.5 to 1 second without using time-
consuming frequency analysis (e.g. FMCW,
required by other radar techniques).
Virtually all products can be measured
Radar signals display physical properties
similar to those of visible light. According to
the quantum theory, they propagate through
empty space. Hence, they are not depend-
ent on a conductive medium (air), and they
spread out like light at the speed of light.
Radar signals react to two basic electrical
properties:
- the electrical conductivity of a substance
- the dielectric constant of a substance.
All products which are electrically conductive
reflect radar signals very well. Even slightly
conductive products provide a sufficiently
strong reflection for a reliable measurement.
All products with a dielectric constant
ε
r
of
more than 2.0 reflect radar pulses sufficiently
(note: air has a dielectric constant
ε
r
of 1).
Signal reflectivity grows stronger with in-
creasing conductivity or increasing dielectric
constant of the product. Hence, virtually all
products can be measured.
emission - reflection - reception
Meas.
distance
1 ns
278 ns
Pulse sequence
The radar pulses are emitted by the antenna
system as pulse packages with a pulse
duration of 1 ns and pulse intervals of
278 ns; this corresponds to a pulse package
frequency of 3.6 MHz. In the impulse inter-
vals, the antenna system operates as a re-
ceiver. Signal running periods of less than
one billionth of a second must be processed
and the echo image evaluated in a fraction of
a second.
Product description