VEGA PULS41 User Manual
Operating Instructions
VEGAPULS 41 (Profibus PA)
PROF I
PROCESS FIELD BUS
BUS
Contents
Safety information ........................................................................ 3
Note Ex area ................................................................................ 3
1 Product description .................................................................. 4
1.1 Function................................................................................. 4
1.2 Application features ............................................................. 6
1.3 Profibus output signal .......................................................... 7
1.4 Adjustment ............................................................................ 8
1.5 Type survey ........................................................................ 12
1.6 Antennas............................................................................. 12
2 Mounting and installation ..................................................... 13
2.1 General installation instructions ........................................ 13
2.2 Measurement of liquids ..................................................... 16
2.3 Measurement in standpipe (surge or bypass tube) ...... 17
2.4 False echoes ...................................................................... 22
2.5 Common installation mistakes ........................................... 24
Contents
3 Electrical connection .............................................................. 26
3.1 Connection – Connection cable – Screening ................... 26
3.2 Sensor address ................................................................. 29
3.3 Connecting the sensor ...................................................... 31
3.4 Connecting the external indicating instrument ................ 32
3.5 Bus configuration ............................................................... 33
2 VEGAPULS 41 – Profibus PA
27292-EN-041227
Contents
4 Set-up ........................................................................................ 38
4.1 Adjustment media .............................................................. 38
4.2 Adjusting the sensor with the adjustment module
MINICOM ............................................................................ 38
6 Diagnostics............................................................................... 44
6.1 Simulation ............................................................................ 44
6.2 Error codes ........................................................................ 44
7 Technical data .......................................................................... 45
7.1 Technical data ..................................................................... 45
7.2 Approvals ........................................................................... 49
7.3 Data format of the output signal ........................................ 50
7.4 Dimensions ......................................................................... 51
7.5 CE conformity declaration ................................................. 53
Safety information
Please read this manual carefully, and also take
note of country-specific installation standards
(e.g. the VDE regulations in Germany) as well
as all prevailing safety regulations and accident prevention rules.
For safety and warranty reasons, any internal
work on the instruments, apart from that involved in normal installation and electrical connection, must be carried out only by qualified
VEGA personnel.
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VEGAPULS 41 – Profibus PA 3
Note Ex area
Please note the attached safety instructions
containing important information on installation
and operation in Ex areas.
These safety instructions are part of the operating instructions manual and come with the Ex
approved instruments.
1 Product description
Product description
Radar sensors usually come with horn or rod
antennas. PTFE rod antennas are suitable for
many applications with chemically aggressive products, but are unsuitable for small
vessels due to their size. Also the reception
efficiency of the rod antenna is lower than that
of the (less resistant) horn antenna. The two
new radar sensors, VEGAPULS 43 with DN
50 and DN 80 process fittings and the described VEGAPULS 41 with 1½“ process
fitting, perfectly round out the instrument
series. Horn and rod antennas that protrude
into the vessel belong to the past. The antenna of VEGAPULS 41 consists of a small
40 mm TFM-PTFE cone that is suitable for
chemically aggressive environments.
Fluorothermoplasts and perfluoroelastomers
(PTFE) have been known as the „Mercedes“
of plastic materials for many years. They are
resistant to virtually all chemical media, such
as e.g. amines, ketones, esters, acids (sulphuric acid, phosphoric acid, hydrochloric
acid, nitric acid), alkalis (caustic soda), oxidants, fuels and oils. These plastics do not
become brittle or age and are suitable for
temperatures up to 150°C. The only limits to
these materials are applications with fluorine
under high pressure or with liquid alkali metals (sodium or potassium), where adverse
reactions may occur. The cone acts like a
lens that focuses short (0.15 mW) radar
pulses into a beam and sends them towards
the product. During the pulse breaks, the
cones operate like a unidirectional microphone with optimum reception efficiency. The
intelligent, extremely fast electronics converts
the radar echo into a precise image of the
environment and level, which is outputted as
a 4 … 20 mA or Profibus signal.
Due to their small housing dimensions and
process fittings, the compact sensors are
unobtrusive and, above all, cost-effective
monitors of your product levels. With their
integrated display, they enable highprecision level measurements and can be
used for applications in which the
advantages of non-contact measurement
could never before be realized.
VEGAPULS radar sensors are perfectly
adapted to two-wire technology. The supply
voltage and the output signal are transmitted
via one two-wire cable. The instruments
produce an analogue 4 … 20 mA signal as
output, i.e. measuring signal.
1.1 Function
Radio detecting and ranging: Radar.
VEGAPULS radar sensors are used for noncontact, continuous distance measurement.
The measured distance corresponds to a
filling height and is outputted as level.
Measuring principle:
emission – reflection – reception
Extremely small 26 GHz radar signals are
emitted from the antenna of the radar sensor
as short pulses. The radar pulses reflected
by the sensor environment and the product
are received by the antenna as radar echoes. The running period of the radar pulses
from emission to reception is proportional to
the distance and hence to the level.
4 VEGAPULS 41 – Profibus PA
27292-EN-041227
Product description
Meas.
distance
emission - reflection - reception
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 pulse intervals,
the antenna system operates as a receiver.
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.
1 ns
278 ns
Hence, it is possible for the 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 timeconsuming 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 dependent 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
greater than 2.0 reflect radar pulses sufficiently (note: air has a dielectric constant εr of
1). Signal reflectivity grows stronger with
increasing conductivity or increasing dielectric constant of the product. Hence, nearly all
substances can be measured.
r
Pulse sequence
VEGAPULS radar sensors can achieve this
through a special time transformation procedure which spreads out the more than 3.6
million echo images per second into a quasi
slow-motion picture, then freezes and processes them.
%
50
40
30
20
10
5 %
5
0
2
0
25 %
4 6 8 12 14 16 18
10
40 %
20
ε
Reflected radar power dependent on the dielectric
constant of the measured product
tt
Time transformation
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VEGAPULS 41 – Profibus PA 5
r
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 environments.
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.
Continuous and reliable
Unaffected by temperature, pressure and
individual atmosphere content, VEGAPULS
radar sensors are used for quick and reliable
continuous level measurement of widely varying products.
%
0,03
0,02
0,01
0
100 500 1000 1300 ˚C
0
0,018 %
Temperature influence: Temperature error absolutely
zero (e.g. at 500°C 0.018 %)
%
10
5
0,29 %
0
10
0
1,44 %
20 30 40 60
50
Pressure influence: Error with pressure increase very
low (e.g. at 50 bar 1.44 %)
0,023 %
2,8 %
70 80 90 110 120 130 140
100
3,89 %
bar
1.2 Application features
Applications
• level measurement of any liquid
• measurement also in vacuum
• all slightly conductive materials and all
substances with a dielectric constant > 2.0
can be measured
• measuring range 0 … 10 m.
Two-wire technology
• power supply and output signal on one
two-wire cable (loop powered)
• Profibus PA (Profile 3).
Rugged and abrasionproof
• non-contact
• high-resistance materials
Exact and reliable
• accuracy 0.05 %.
• resolution 1 mm
• unaffected by noise, vapours, dusts, gas
compositions and inert gas stratification
• unaffected by varying density and temperature of the medium
• measurement in pressures up to 3 bar and
product temperatures up to 150°C.
Communicative
• integrated measured value display
• optional display module separate from
sensor
• adjustment with detachable adjustment
module, pluggable in the sensor or in the
external display
• adjustment with HART
• adjustment with the PC.
®
handheld
Approvals
• CENELEC, ATEX, PTB, FM, CSA, ABS,
LRS, GL, LR, FCC.
6 VEGAPULS 41 – Profibus PA
27292-EN-041227
Product description
1.3 Profibus output signal
PROPRO
PROcess
PROPRO
sult of a joint project of thirteen companies
and five universities. The companies Bosch,
Klöckner-Möller and Siemens played a decisive role. The specifications of the bus are
described in the protocol layers 1, 2 and 7 of
the ISO/OSI reference model and are available from the PNO (Profibus user organisation). Since layers 3 … 5 have not yet been
developed as a standard, Profibus still has a
lot of far-reaching potential.
Today approx. 600 companies make use of
Profibus technology and belong to the PNO.
Profibus
Specification, Profibus
Periphery and Profibus
mation.
As a process automation bus, Profibus PA
also enables power supply over the bus. Up
to 32 sensors can be operated on a shielded
two-wire cable that carries both power supply and measurement signal. In Ex areas, up
to ten sensors can be connected from the PA
level to one two-wire cable (EEx ia).
Bus structure
The Profibus DP and PA network consists of
up to 126 master and slave participants.
Data are always exchanged from point to
point, with the data traffic being exclusively
controlled and checked by master devices.
Communication is carried out acc. to the
Token-Passing procedure. This means that
the master holding the Token can contact the
slaves, give instructions, enquire data and
cause the slaves to receive and transmit
data. After the work is done or after a predetermined time interval, the Token is passed
on by the master to the next master.
FIFI
BUSBUS
FIeld
BUS (PROFIBUS) is the re-
FIFI
BUSBUS
FMSFMS
FMS stands for Fieldbus Messaging
FMSFMS
DPDP
DP for Decentralised
DPDP
PP
AA
P
A for Process Auto-
PP
AA
Master-Class 1
is the actual automation system, i.e. the process control computer or the PLC that enquires and processes all measured values.
Master-Class 2
One or several Master-Class 2 can operate in
a Profibus network. As a rule, Master-Class 2
devices are engineering, adjustment or visualisation stations. The VEGA adjustment software VVO (VEGA Visual Operating) operates
as Master-Class 2 participant on the DP bus
and can work on an engineering PC, on an
adjustment PC or on the process control
computer and can access any VEGA sensor
on the PA level.
Instrument master file
A so-called GSD file is delivered with every
VEGAPULS Profibus sensor. This file is required to integrate the sensor into the bus
system. The GSD (instrument master file)
contains, beside the sensor name and the
manufacturer, the sensor-specific communication parameters which are necessary for a
stable integration of the sensor in the bus.
Load the GSD file belonging to the sensor
into your bus configuration program. If the
GSD file is not available, it can be
downloaded from the VEGA homepage: http:/
/www.vega.com.
Do not confuse the GSD file with the EDD
(Electronic Device Description), a file which is
necessary for the PDM environment (this can
be also found on the VEGA homepage).
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VEGAPULS 41 – Profibus PA 7
Product description
1.4 Adjustment
Every measurement set-up is unique. For
that reason, every radar sensor needs, beside the adjustment, some basic information
on the application and the environment, e.g.
which level means "empty“ and which level
"full“. Beside this "empty and full adjustment“,
many other settings and adjustments are
possible with VEGAPULS radar sensors. The
output of echo curves and the calculation of
vessel linearisation curves by means of vessel dimensions are only two examples.
Profibus adjustment structure
In the Profibus environment, there are different adjustment concepts and adjustment
tools which often differ considerably from
manufacturer to manufacturer. From the user’s point of view, the ideal solution would be
a manufacturer-independent adjustment
program which could be operated directly on
the Profibus DP/PA, on the sensor, as well as
at any system node (e.g. an engineering
station or the process control center).
In the past, only the program „SIMATIC
PDM“, based on the HART
structure, could fulfil this wish (though with
the limitations common to HART
®
HART
, the availability of an instrument-specific database for a comprehensive adjustment with PDM (Process Device Managing)
is a requirement. Otherwise, only the basic
instrument functions, such as adjustment, are
available. In the PDM environment, this instrument-specific database is called EDD (Electronic Device Description), in perfect analogy
to the HART
®
environment which also requires, except with VEGA HART
ments, a DD (Device Description) for each
sensor.
®
adjustment
®
). As with
®
instru-
The disadvantages of the HART
®
environment
are well known: for each sensor/participant,
an individual DD must be loaded, which in
addition, must always be the latest and most
up-to-date DD. Special adjustment options
such as e.g. the output of an echo curve, are
available neither with HART
®
nor with PDM.
User-friendly adjustment is out of the question. With VEGA’s adjustment software VVO,
those restrictions belong to the past.
The legitimate wish of many Profibus users
for a manufacturer-independent adjustment
tool without EDD has been realised in the
form of PACTware
number of process technology companies
developed PACTware
CC
tion
Configuration
CC
TM
. An association of a
TM
PP
: a
Process
TT
Tool that can run different
TT
PP
AA
Automa-
AA
manufacturer software tools under a standardized user interface and adjustment structure. Specialists call this technology Field
Device Transcription (FDT). Just as different
Windows printer drivers enable operation of
completely different printers under a single
user interface, PACTware
TM
enables operation
of all field instruments under a single user
interface. Instrument-specific databases
(EDD), like those for SIMATIC PDM, are not
required.
As a result of this development, four adjustment media are available for VEGA Profibus
sensors:
- adjustment with the PC and the adjustment
program VVO (VEGA Visual Operating) as
stand-alone tool, on the segment coupler
or directly on the sensor
- adjustment with the detachable adjustment
module MINICOM in the sensor
- adjustment with the SIMATIC PDM adjust-
ment program (requires EDD instrument
databases) from process control
- adjustment with the manufacturer-inde-
pendent user interface PACTware
TM
on the
sensor, from process control or on the
segment coupler.
8 VEGAPULS 41 – Profibus PA
27292-EN-041227
Product description
Adjustment with the PC
Generally, the set-up and adjustment of radar
sensors is most conveniently carried out on
the PC with the adjustment program
PAC Twa re
leads quickly through adjustment and parameter setting by means of pictures, graphics and process visualisations.
The adjustment software PACT
the FDT concept (Field Device Tool) operates
as an independent adjustment program on
any PC, engineering station or process control computer.
The adjustment program requires for communication with Profibus sensors either a
Profibus-Master-Class2 interface card or the
interface adapter VEGACONNECT 3. The PC
with the Profibus interface card can be connected directly to any point on the DP bus
with the standard RS 485 Profibus cable. In
conjunction with the adapter
VEGACONNECT, the PC can be connected
directly to the sensor. VEGACONNECT communicates via a small plug directly with the
individual sensor.
The adjustment and parameter data can be
saved at any time on the PC with the adjustment software and can be protected by
passwords. If necessary, the adjustments
can be transferred quickly to other sensors.
In practice, the adjustment software
PAC T
engineering station or an operating station.
As a Master-Class 2 operating via the
Profibus interface card (e.g. from Softing), it
accesses VEGA sensors directly over the
bus, from the DP level to the PA via the segment coupler.
TM
under Windows®. The program
TM
ware
is often installed as a tool on an
ware
TM
acc. to
Beside the instrument master file (GSD), with
which a sensor is logged into the Profibus
system, most Profibus sensors require, in
addition, a so-called EDD (Electronic Device
Description) for each individual sensor, to
enable access and adjustment from the bus
level.
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VEGAPULS 41 – Profibus PA 9
PACTware
SPS
Adr. 10
Master-Class 1
Adr. 1
Profibus DP interface card as
Master-Class 2 (e.g. Softing)
3
Product description
Adr. 60
Adr. 59
Adr. 21
Adr. 22
3
Adr. 23
DP-Bus
Adr. 24
Adr. 57
Adr. 58
Segment coupler
Adr. 25
Adr. 25 … 56
PA-
Bus
Adr. 26
2
Adr. 27
(max. 32 participants)
Adr. 28
Adr. 29
Adjustment of the VEGAPULS radar sensors from process control via a Profibus interface card in the process
control computer or in an additional PC. The adjustment software VEGA Visual Operating (VVO) accesses the
sensors bidirectionally via the interface (interface card).
27292-EN-041227
10 VEGAPULS 41 – Profibus PA
Product description
Adjustment with the adjustment module
MINICOM
The small (3.2 cm x 6.7 cm) 6-key adjustment
module with display allows the adjustment to
be carried out in clear text dialogue. The
adjustment module can be plugged into the
radar sensor or into the optional, external
indicating instrument.
Tank 1
m (d)
12.345
Detachable adjustment module MINICOM
Unauthorised sensor adjustments can be
prevented by removing the adjustment module.
ESC
+
-
OK
Adjustment with SIMA TIC PDM adjustment program
To adjust all essential functions of the VEGA
sensor with the adjustment station SIMATIC
PDM from Siemens, a so-called EDD is required. Without this EDD, only the basic functions such as min./max. wet adjustment or
integration time can be adjusted with the
PDM adjustment program. Further important
adjustment functions, such as the input of the
meas. environment or a false echo storage
are not available without EDD. After integration of the EDD files in the Simatic PDM adjustment software, all important adjustment
functions are accessible. If it is not at hand,
the obligatory GSD (instrument master file)
as well as the EDD (Electronic Device Description) necessary for PDM can be
downloaded from the VEGA homepage
(www.vega.com).
ESC
+
-
Tank 1
m (d)
OK
12.345
2
-
Tank 1
m (d)
12.345
PA- Bus
ESC
+
OK
4
max. 25 m
Adjustment with detachable adjustment module. The
adjustment module can be plugged into the radar
sensor or into the external indicating instrument
VEGADIS 50.
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VEGAPULS 41 – Profibus PA 11
Types and versions
1.5 T ype survey
VEGAPULS 41 sensors are manufactured
with process connection G 1½ A or 1½“ NPT.
Features
• Application preferably for liquids in storage
tanks and process vessels with increased
accuracy requirements and in corrosive
environments.
• Measuring range 0 … 10 m
• Ex approved in Zone 1 (IEC) or Zone 1
(ATEX) classification mark
EEx ia [ia] IIC T6.
• Integrated measured value display.
1.6 Antennas
The antenna is the eye of the radar sensor.
The shape of the antenna, however, doesn’t
give a casual observer the lightest clue on
how carefully the antenna geometry must be
adapted to the physical properties of electromagnetic waves. VEGAPULS 41 radar sensors are equipped with a completely
encapsulated antenna.
PTFE is commonly found in hygienic applications. The small plastic cone of the
VEGAPULS 41 radar sensor, operating as
antenna, consists of a TFM-PTFE material.
This is a fluorothermoplast, which has additional distinct advantages compared to PTFE,
such as, e.g., reduced load deformation,
denser polymer structure as well as a
smoother surface (Ra < 0.8 µm). The other
known advantages of PTFE, such as, e.g.,
high temperature resistance (up to 150°C),
high chemical resistance as well as resistance to brittleness and ageing are still
present or have even been enhanced.
Perfluorelastomers and fluorothermoplasts
are resistant to virtually all chemical media
such as, e.g., amines, ketones, esters, acids
(sulphuric acid, phosphoric acid, hydrochloric acid, nitric acid), alkalis (caustic soda),
oxidants, fuels and oils. Beside their use in
the chemical industry, these materials are
being applied more and more in sterilisation
and pharmaceutical technologies. The only
limits to these materials are in applications
with fluorine under high pressure or with
liquid alkali metals (sodium or potassium),
where explosive reactions may occur.
12 VEGAPULS 41 – Profibus PA
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Mounting and installation
2 Mounting and installation
2.1 General installation instructions
Measuring range
The reference plane for the
measuring range of the sensor
is the lower edge of the flange.
Keep in mind that in measuring
environments where the medium can reach the sensor
flange, buildup can form on the
antenna, possibly causing
measurement errors.
Note: Series 40 sensors are
suitable for measurement of
solids only under certain conditions.
empty
full
Measuring range (operating range) and max. measuring distance
Note: Use of the sensors for applications with solids is limited.
max.
Meas. range
Reference plan
max.
min.
False echoes
Flat obstructions and struts cause strong
false echoes. They reflect the radar signal
with high energy density.
Interfering surfaces with rounded profiles
scatter the radar signals into the surrounding
space more diffusely and thus generate false
If flat obstructions in the range of the radar
signals cannot be avoided, we recommend
diverting the interfering signals with a deflector. The deflector prevents the interfering
signals from being directly received by the
radar sensor. The signals are then so lowenergy and diffuse that they can be filtered
out by the sensor.
echoes with a lower energy density. Hence,
those reflections are less critical than those
from a flat surface.
Round profiles diffuse radar signals
Profile with smooth interfering surfaces cause large
false signals
Cover smooth, flat surface with deflectors
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VEGAPULS 41 – Profibus PA 13
Mounting and installation
Emission cone and false echoes
The radar signals are focused by the antenna system. The signals leave the antenna
in a conical path similar to the beam pattern
of a spotlight. This emission cone depends
on the antenna used. Any object in this beam
cone will reflect the radar signals. Within the
first few meters of the beam cone, tubes,
struts or other installations can interfere with
the measurement. At a distance of 6 m, the
false echo of a strut has an amplitude nine
times greater than at a distance of 18 m.
At greater distances, the energy of the radar
signal distributes itself over a larger area,
thus causing weaker echoes from obstructing surfaces. The interfering signals are
therefore less critical than those at close
range.
If possible, orient the sensor axis perpendicularly to the product surface and keep
vessel installations (e.g. pipes and struts) out
of the emission cone.
The illustrations of the emission cones are
simplified and represent only the main beam
- a number of weaker beams also exist. Un-
der difficult measuring conditions, the antenna location and alignment must be chosen
with the objective of reducing false echoes.
Only giving attention to the size of the useful
echo is not adequate when measuring conditions are unfavourable.
In a difficult measuring environment, searching for a mounting location with the lowest
possible false echo intensity will bring the
best results. In most cases, the useful echo
will then be present with sufficient strength.
With the adjustment software PACT
ware
TM
on
the PC, you can have a look at the echo image and optimise the mounting location.
If possible, provide a "clear view“ to the
product inside the emission cone and avoid
vessel installations in the first third of the
emission cone.
Optimum measuring conditions exist when
the emission cone reaches the measured
product perpendicularly and when the emission cone is free from obstructions.
Examples of vessel echoes
The following vessel images show a typical
echo pattern in a vessel. This is the example
of a process vessel with a slow doublebladed stirrer. In the lower par t, the vessel is
equipped with heating spirals. A thin, angled
inlet tube ends in the vessel centre between
the stirrer blades.
14 VEGAPULS 41 – Profibus PA
27292-EN-041227
Mounting and installation
Empty vessel ¼ filling
When the vessel is empty, you see the echoes of the vessel installations around the
emission cone. Beside the large bottom echo,
you see a number of additional false echoes.
The false echoes of the vessel installations
are saved during a false echo recording. For
this reason, the false echo recording must be
carried out when the vessel is empty.
False echoes from the top down:
- first inlet tube fastening
- upper stirrer blade
- second inlet tube fastening
- angled inlet tube
- upper heating tubes
- lower stirrer blade
- remaining heating tubes
- vessel bottom
After filling, the bottom echo is replaced by
the product echo.
½ filling
The product echo moves to the centre of the
meas. range. At the end of the meas. range,
you now see an echo at a position where the
bottom echo previously was in the empty
vessel. This echo is a multiple echo of the
product echo and is located at twice the
distance of the product echo.
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VEGAPULS 41 – Profibus PA 15
Mounting and installation
Filled vessel
In a completely filled vessel, you see additional multiple echoes at two, three or four
times the distance of the product surface
echo.
2.2 Measurement of liquids
Radar sensors are usually mounted on short
DIN socket pieces. The lower side of the
instrument flange is the reference plane for
the measuring range. - The socket piece
should be as short as possible, max. 70 mm.
When mounting on dished vessel tops, the
antenna length should correspond at least to
the length of the sockets.
In vessels with dished or rounded tops,
please do not mount the instrument in the
centre or close to the vessel wall.
Dished tank tops can act as paraboloidal
reflectors. If the radar sensor is placed in the
focal point of the parabolic tank, the radar
sensor receives amplified false echoes. The
radar sensor should be mounted outside the
focal point. Parabolically amplified echoes are
thereby avoided.
Antenna directly on the vessel top
If the stability of the vessel will allow it (sensor
weight), flat mounting directly on the vessel
top is a good and cost-effective solution. The
top side of the vessel is the reference plane.
Screwed antennas, especially when used on
small vessels, are mounted in sockets. The
antenna fits into even the smallest vessel
connection openings with 1½“ socket. The
socket must not be longer than 70 mm.
Reference plane
< 70 mm
Screwed antenna on 1½“ mounting boss
16 VEGAPULS 41 – Profibus PA
27292-EN-041227
Mounting and installation
2.3 Measurement in standpipe (surge or bypass tube)
General instructions
Pipe antennas are preferred in vessels which
contain many installations, e.g. heating tubes,
heat exchangers or fast-running stirrers.
Measurement is then possible where the
product surface is very turbulent, and vessel
installations can cause no false echoes.
Due to the concentration of the radar signals
within the measuring tube, even products
with small dielectric constants (ε
3) can be reliably measured in surge or by-
pass tubes.
Surge pipes which are open at the bottom
must extend over the full measuring range
(i.e. down to 0% level), as measurement is
only possible within the tube. The tube inner
diameter should be max. 100 mm or correspond to the size of the antenna horn.
Make sure the required upper vent hole in
the surge pipe is aligned with the sensor
type label.
As an alternative to a surge pipe in the vessel, a pipe antenna system outside the vessel in a bypass tube is also possible.
The surge and bypass tubes must generally
be made of metal. For plastic tubes, a
closed, conductive jacket is always required.
When using a metal tube with plastic inner
coating, make sure that the thickness of the
coating is minimal (approx. 2 … 4 mm).
Align the sensor so that the type label lies on
the same axis as the tube holes or the tube
connection openings. The polarisation of the
radar signals enables a considerably stabler
measurement with this alignment.
= 1.6 up to
r
When mounting a VEGAPULS 41 sensor on a
bypass tube (e.g. on a previous floating or
displacer unit), the radar sensor should be
placed approx. 300 mm or more from the
max. level.
For products with small dielectric constants
(< 4), a much longer bypass tube than would
otherwise be required by the lower tube
connection should be used. Products with
small dielectric constants are partly penetrated by the radar signals, allowing the
tube bottom to produce a stronger echo than
the product (when the bypass tube is nearly
empty). By extending the tube downward,
some liquid remains at the bottom even when
the vessel is completely empty.
Type label
> 300 mm
100 %
0 %
Tube flange system as bypass tube
300 ... 800 mm
If enough liquid (300 … 800 mm) remains in
the blind lower end of the tube, the portion of
the signal that penetrates the liquid and reflects from the tube bottom is sufficiently
damped - the sensor can then easily distinguish it from the echo of the liquid surface. A
deflection plate located at the bottom of a
vertical pipe has a similar function. It deflects
signals that reach the tube bottom into the
standard connection opening.
27292-EN-041227
VEGAPULS 41 – Profibus PA 17
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