VEGA VEGAPULS 56 Profibus PA - Manual (Page 4)

4 VEGAPULS 56 Profibus PA
Product description
1 Product description
Level measurement of high temperature
processes or products with high tempera-
tures was previously very difficult or even
impossible. If such measurement also had to
be done under high pressure, there was
practically no measuring system available at
all, let alone a non-contact measurement
system with good measuring accuracy.
Up to now, levels in distillation and stripper
columns (e.g. of sump, plate or head prod-
ucts) could usually only be measured by
pressure transmitters or differential pressure
measurements. The installation required for
such pressure measuring systems (pressure
cables, pressure transmitters…) is consider-
able and expensive, often amounting to sev-
eral times the value of the sensor itself. Be-
cause of the lack of suitable alternatives,
instrumentation departments have not only
had to accept this fact, but also the high
maintenance costs (cleaning of measuring
pipes, errors by condensation, buildup on
the diaphragm…) and the often inadequate
accuracy (temperature errors, density fluc-
tuations, installation faults…).
In the petrochemical industry, the require-
ments for a non-contact level sensor are
therefore the following:
• independent of pressure and temperature
• process temperature up to 400°C
• process pressure up to 64 bar
• high resistance wetted parts for universal
use
• accuracy 0.1 %
• rugged metal housing
• Ex approved (available in EEx d and EEx
ia)
• loop-powered as well as usable in digital
networks
This initial set of requirements defined the
development goals for the VEGAPULS 56
series, a high-temperature radar level meas-
uring system. The series represents a com-
pletely new development of high-temperature
radar sensors for temperatures up to 400°C
and pressures up to 64 bar.
These sensors would not have been possible
without the recent new results of materials
research and production technology. A
specially developed ceramic (with high-
frequency properties similar to those of the
plastics normally used) is used as coupling
material. As opposed to plastic, this ceramic
has a very high chemical and thermal resist-
ance.
The sensor materials in contact with the proc-
ess are all highly resistant. This refers not so
much to the flange material of high-alloy
stainless steel (1.4571 or superior), as to the
specially developed ceramic (Al
2
O
3
) and the
components connecting it. The ceramic rod
receives the radar signals from the high-
frequency module and acts with its cone-
shaped end as emitter and receiver. The seal
between stainless steel flange and ceramic
rod is made with a Tantalum seal ring.
1.1 Function
Ra dio d etecting a nd r anging: Radar.
VEGAPULS radar sensors are used for non-
contact and continuous distance measure-
ment. The measured distance corresponds
to a filling height and is outputted as level.
Measuring principle:
emission – reflection – reception
Extremely small 5.8 GHz radar signals are
emitted from the antenna of the radar sensor
as short pulses. The radar impulses reflected
by the sensor environment and the product
are received by the antenna as radar ech-
oes. The running period of the radar im-
pulses from emission to reception is
proportional to the distance and hence to the
level.