VEGA VEGAPULS 56 Profibus PA - Manual (Page 5)

VEGAPULS 56 Profibus PA 5
Time transformation
Pulse sequence
Meas. distance
emission - reflection - reception
1 ns
278 ns
t t
Product description
The radar impulses are emitted by the an-
tenna system as impulse packets 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 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.
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 in a slow-
motion picture, then freezes and processes
them.
Through this, it is possible for VEGAPULS
series 56 radar sensors to process the slow-
motion pictures of the sensor environment
precisely and in detail in cycles of 0.5 to 1
second without using time-consuming fre-
quency 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
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 ensure a sufficient re-
flection for a reliable measurement.
All products with a dielectric constant
ε
r
of
more than 2.0 reflect radar impulses suffi-
ciently (note: air has a dielectric constant
ε
r
of
1).
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