All radar gauges are not TankRadar

All radar gauges are not TankRadar
How to choose a truly reliable and
accurate radar tank gauging system for
custody transfer and inventory purposes.
Rosemount TankRadar Rex provides
In fact, it’s the only radar gauge that does.
Only Rosemount TankRadar Rex has all the features for giving you the
highest accuracy and reliability in field operation. Examples of such
features are digital reference, temperature controlled electronics, and
Low Loss Mode in still pipes. Compare for yourself:
Rosemout TankRadar Rex
Other radar tank gauges
(depending on manufacturer)
Instrument measuring accuracy better than 0.5 mm
(5/256 in.) over the entire temperature range.
Accuracy affected by changing ambient
temperature.
Accuracy specified in technical documentation is
based on maximum error.
Specified measuring accuracy is “typical error”,
which might be one third or less of maximum error.
To provide an ultra stable, self calibrating reference
for the radar signal, a digital oscillator is used.
Analog reference cable with individual temperature
characteristics, giving accuracy losses at varying
ambient temperatures.
Intrinsic accuracy.
Software compensated accuracy.
To keep highest measuring precision, and to increase Electronics is subject to changing ambient temperalifetime, the gauge electronics is kept at constant
tures affecting accuracy and lifetime.
temperature. Very high gauge MTBF, 112 years.
When measuring inside a still pipe, Low Loss Mode
(originally developed by Rosemount Tank Gauging)
is used to achieve required accuracy in existing still
pipes with rust and deposits.
No Low Loss Mode for still pipes. Might require stainless steel pipes or inside coating of pipes.
To ensure excellent accuracy, emitted microwaves
No polarization of the radar signal.
have circular polarization to take away disturbances
when mounting the gauge on existing manways near
the tank wall.
Transmitter electronics can easily be exchanged as
the electronics does not have to be matched with a
specific antenna.
Antenna and electronics have to be matched individually. Individual antenna data has to be set in the
gauge electronics.
Drip-off antenna with high tolerance against contamination and condensed water.
Flat antenna with horizontal surface allowing water
and product condensation that disturbs the radar
signal and gives measurement errors.
Electronic boards vertically mounted to ensure further protection from moisture.
Horizontal electronic boards.
Temperature measurement with high accuracy
standard RTDs.
Temperature measurement by less accurate Thermocouples.
highest custody transfer accuracy.
Exchange electronics easily
as no matching between
antenna and electronics is
necessary.
To ensure highest measuring accuracy , fully digital signal processing with
digital filtering is used.
Temperature controlled
electronics increases accuracy and lifetime.
Digital reference oscillator
gives an ultra stable reference for the measuring
signal.
External Metrological Seal
ensures no unauthorized
changes of zero settings. No
power down needed during
adjustments.
Superior lightning protection provided by full
galvanic separation, filters,
varistors, and fuses.
Antennas made for
heavy duty handling in tank
farm environments. Made
of stainless steel and PTFE
only. Carefully computer
calculated curvature.
Drip-off antenna to take
away disturbances from
water condensation.
Rosemount TankRadar Rex for
With superior reliability as well.
All radar gauges with highest accuracy use the FMCW (Frequency
Modulated Continuous Wave) method, also called synthesized pulse
radar (SPR). It was developed for tank gauging by us in the early
1970th’s. Since then, seven generations of radar gauges have been
launched.
The FMCW-technique (SPR)
Custody transfer requirements in
various countries
The FMCW-method is based on a radar sweep with varying
frequency.
This method means that the transmitted radar signal
has a linear frequency variation. The reflection from
the liquid surface has a slightly different frequency
compared with the signal transmitted from the antenna when the reflection is received. The difference
in frequency is measured and is directly proportional
to the distance to the liquid surface.
1. LNE (France) requirement. Field accuracy.
Max permissible error “moyenne”.
. PTB (Germany) requirement. Field accuracy.
Max permissible error.
. NMi (The Netherlands) requirement. Transfer accuracy.
Max permissible error.
. OIML (Organisation Internationale de Métrologie Legalé) requirement. Transfer accuracy. Max permissible
error.
5. Rosemount TankRadar Rex measurement log.
6. API (American Petroleum Institute), 3/16 inch (4 mm).
The digital reference gives higher accuracy
A radar gauge needs an internal reference to make
the radar sweep absolutely linear, thereby achieving
highest accuracy. Each deviation from the linearity
produces a corresponding inaccuracy. Two types of
internal references are used for tank gauging; analog
reference cable or digital oscillator.
To achieve the highest precision, Rosemount TankRadar Rex uses a digital crystal oscillator, that gives the
most stable reference that is available with today’s
technology. In this way the TankRadar Gauges are
leading the digitalization process by using both a
digital reference and digital filter technology. Not
because of the technology itself but because it is
required to achieve real custody transfer accuracy.
The measuring accuracy of one Rosemount TankRadar Rex
gauge taken from the production line. Accuracy within
±0.5 mm (5/256 in.) from 0-25 m (0-80 ft) in a calibrated
test range. Some important metrological authority
requirements are indicated in the diagram.
installed custody transfer accuracy.
Temperature control for precision and
long life
With more stable temperature conditions for the
electronics, the service life of the gauges will be
prolonged and the accuracy is further improved. The
Rosemount TankRadar Rex gauge is continuously
controlling the temperature for the electronics, a
feature which is one of the main reasons for the more
than 112 years of mean time between failure (MTBF)
of the gauges.
Lightning Protection
Lightning can be a source of disturbances and
breakdowns of field instruments. The Rosemount
TankRadar Rex gauges use elaborate design solutions
to reduce the risk of damages from lightning to a
minimum.
Rosemount TankRadar Rex means reliable and accurate
tank gauging in extreme climates from Siberia to the
Saudi Arabian deserts.
The Rosemount TankRadar Rex gauges are designed
to operate in all types of climates. In many areas the
typical surface temperature can vary from night to
day with as much as 30 °C (54 °F). If uncontrolled, this
type of temperature cycling is not good for the electronics. It resembles the “burn-in” conditions used to
quickly degrade electronics in laboratory testing.
­ Both power supply and measurement signals are
fully galvanically separated from the field cabling.
­ There are filters for peaks and disturbances as well
as fuses.
­ Multiple varistors inside the gauge protect the
electronics from over voltages.
The diagram shows the influence of temperature on
Rosemount TankRadar Rex and a radar gauge from
another supplier with an analog reference cable and no
temperature control. A change of temperature from 0 to
40 °C (32 to 104 °F) results in a drift of 4 mm (0.16 in.) for
the competitor, while the TankRadar Rex gauge is stable
within 0.5 mm (0.02 in.). The measurements are made in a
test range approved by a government body.
Measurement close to tank wall
A standard manway (or flange) is normally 0.3-1 m
(1-3 ft) from the tank wall. Both the RTG 3920 Horn
Antenna Gauge and the RTG 3930 Parabolic Antenna
are specially designed to be mounted close to the wall.
accuracy in ”normal” existing still pipes. This method
has been verified by independent certification bodies
like the Dutch NMI.
The use of the Low Loss Mode (H01 mode) for this
purpose is an innovation originally developed for
Rosemount Tank Gauging radar gauges.
Pioneer with long experience
Each tank is unique as far as the combination of product, pressure, temperature, installation requirements
and process conditions, are concerned.
For LPG tanks, the Rosemount Rex 3960 gauge effectively handles all cases of normal LPG storage. The
gauge calculates influence from gas mixes consisting
of 1, 2 or 3 gases.
W12
W11
FOR
INTRINSICALLY
SAFE CIRCUITS
ONLY
"i"
The Rosemount TankRadar Rex fixed roof gauges can be
installed on the existing manway or nozzle and measure
with full accuracy. There are no requirements to mount
the gauge at a certain, tank height related, distance from
The RTG 3920 Horn Antenna Gauge radar signal is
polarized so that the direct reflection from the liquid
surface is the only visible reflection and any wall disturbance will be blanked out. The RTG 3930 Parabolic
Antenna has a narrow radar beam due to the large
17" antenna diameter so that the wall echo will be
small and uncritical.
Innovative technology
To get highest accuracy on floating roof tanks using
still pipes with rust and deposits, Rosemount TankRadar Rex uses a special microwave mode ; the Low Loss
Mode. This is necessary to achieve custody transfer
Pipe seen from above
The Rosemount Rex 3960 gauge uses a verification pin
mounted in the still-pipe.
Verification is made inside the tank using a verification
pin, and the LPG radar level gauging can be verified
without interrupting normal operation. Emerson has
delivered more than 4 000 radar gauges for LPG
applications so far.
Approved by the authorities
More than 100 000 Rosemount TankRadar gauges
have been installed in tanks with all imaginable difficulties and requirements. Our experience gives you a
confidence in our products’ good functionality under
the most varying conditions.
Rosemount TankRadar Rex has a large number of
approvals for legal custody transfer from the whole
world, e.g. PTB, NMI, and GOS. Other important
approvals include the CE mark and TÜV overfilling
protection, pressure, and firesafe approvals.
H11 is the normal mode
of a circular waveguide.
Low Loss Mode.
Very low losses from
rust or deposits.
To be sure to get state-of-the-art field performance
in radar tank gauging, Rosemount Tank Gauging
products is the obvious choice.
Quick Microwave technology course
Condensation Proof design –
what to avoid.
Drip-off means no condensation
If the antenna has an inclined polished PTFE-surface
where the microwaves are emitted, it will be less
susceptible to condensed water or product. The
drops of condensation will drip-off the active part of
the antenna.
Antennas with large, flat, nearly horizontal, dielectric
(non metallic) surfaces are most likely to be affected
by condensation. Below are a few antenna designs
that have the potential of becoming condensation
sensitive.
Horn with lens or
compensated horn
Process
Seal
In this way the radar signal will be less weakened
which results in higher accuracy and better reliability.
Planar antenna
In a comparison condensation test of a planar
antenna and Rex 3950 in a tank atmosphere with
high degree of condensation, the excellent performance of the Rex 3950 drip-off design of the antenna
was proven. After full condensation was developed,
the planar antenna had lost the surface echo while
Rex 3950 still was measuring accurately and with an
antenna echo below the noise threshold.
No drip-off surface
Drip-off surfaces made of
polished PTFE.
Antenna design with no horizontal surfaces. All
regular Rosemount TankRadar gauges for high-end
applications have drip-off antennas.
A parabolic antenna withstands rough
environments
Asphalt, bitumen and liquid sulphur are tough applications where the parabolic antenna works better
than any other design. Antenna condensation is also
the reason for using a radar frequency in the 10 GHz
band because a higher frequency band such as 24
GHz would be more than 10 times more sensitive to
water and product condensation.
Condensation test of planar antenna. Picture shows tank
spectrum after full condensation developed.
Noise threshold
Condensation test of Rex 3950 antenna having a
drip‑off design. Picture shows tank spectrum after full
condensation developed.
Parabolic antenna still working after use in heavily
contaminating double blown bitumen with temperatures
over 220 °C (430 °F).
Quick Microwave technology course (continued)
Antenna size affects gain
Antenna
gain (dB)
A larger antenna diameter has a higher gain or
amplification, a more concentrated radar signal and
therefore receives a stronger echo. The received
power from the surface is proportional to the fourth
power of the antenna diameter given a fixed microwave frequency. There is no way around this law
of physics which is valid whether the antenna is a
parabolic, cone or array antenna. A larger antenna
provides a narrow focused beam for more reliable
measurement for liquids with low radar reflection,
on longer distances, in dirtier environments and with
higher accuracy.
Angle from
vertical
1. Ø450 mm (18 in.) antenna
. Ø200 mm (8 in.) antenna
The diagram shows the antenna gain for two antennas
with different size; 200 mm (8 in.) and 450 mm (18 in.)
diameter. TankRadar gauges uses the 450 mm (18 in.)
parabolic antenna with the highest gain.
Ø200 mm (8 in.) antenna.
Wide beam, low focus.
Ø450 mm (18 in.) antenna.
Narrow beam, high focus.
The illustration shows the distribution of the amplitude
from a 200 mm (8 in.) and a 450 mm (18 in.) diameter
antenna. The larger antenna has a radar signal with
about 100 times larger intensity. This means that it can
more effectively produce an echo when the oil surface is
turbulent or if the tank has a lot of disturbing echoes.
The Emerson logo is a trademark and servicemark of Emerson Electric Co.
The contents of this publication are presented for information purposes only, and while effort has been made to ensure their accuracy, they are not to be construed
as warranties or guarantees, expressed or implied, regarding the products or services described herein or their use or applicability. All sales are governed by our terms
and conditions, which are available on request. We reserve the right to modify or improve the designs or specifications of our products at any time without notice.
Rosemount Tank Radar AB accepts no responsibility for any errors that may appear in this description.
Emerson Process Management
Rosemount Tank Gauging
North America: Rosemount Tank Gauging North America Inc. Houston, Texas.
Tel: 1-800-SAAB TNK. E-mail: [email protected] Middle East:
Box 13045
SE-402 51 Göteborg
SWEDEN
Phone: +46 31 337 00 00
Fax: +46 31 25 30 22
E-mail: [email protected]
Rosemount Tank Gauging Middle East SPC, Bahrain. Tel: +973 17 22 66 10. Email: [email protected] INDIA: Rosemount Tank Gauging India Pvt.
Ltd., Pune. Tel: +91 20 5602 3747. E-mail: [email protected] UK:
Rosemount Tank Gauging UK Ltd., Wokingham. Tel: +44 (0) 118 973 6670. Email: [email protected] LATIN AMERICA & CARRIBEAN: Rosemount
Tank Gauging, Tel: +58 212 242 0237, E-mail: [email protected]
OTHER COUNTRIES: Find your local representative at www.rosemount-tg.com
www.rosemount-tg.com
Ref. no. 201021En. Second edition. Rev B, March 2007.