VEGA VEGAPULS 45 4 … 20 mA; HART compact sensor - Manual (Page 5)

VEGAPULS 42, 44 and 45 – 4 … 20 mA 5
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
Product description
With standard flanges of DN 50 to DN 150,
ANSI 2“ to ANSI 6“ or G 1½ A and 1½“ NPT,
the sensor antenna systems can be adapted
to various products and measuring environ-
ments.
The high-quality materials can also withstand
extreme chemical and physical conditions.
The sensors deliver stable, reproducible
analogue or digital level signals with reliability
and precision and have a long useful life.
Continuous and accurate
Unaffected by temperature, pressure and
atmosphere content, VEGAPULS radar sen-
sors measure quickly and accurately the
levels of widely varying products.
VEGAPULS can achieve this through a spe-
cial time transformation procedure which
spreads out the more than 3.6 million echo
images per second in a slow-motion picture,
then freezes and processes 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).
Nearly 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
greater than 2.0 reflect radar pulses suffi-
ciently (note: air has a dielectric constant
ε
r
of
1). Signal reflectivity grows stronger with
increasing conductivity or increasing dielec-
tric constant of the product. Hence, nearly all
substances can be measured.
Temperature influence: Temperature error absolutely
zero (e.g. at 500°C 0.018 %)
100 500 1000 1300 ˚C 0
0
0,01
0,02
0,03
%
0,018 %
0,023 %
Pressure influence: Error with pressure increase very
low (e.g. at 50 bar 1.44 %)
10
0
0
5
%
1,44 %
2,8 %
10
50
20 30 40 60
100
70 80 90 110 120 130 140
bar
0,29 %
3,89 %