Technical information

7500 RTG
2 Varec, Inc.
Function and System Design
Measuring Principle
The Radar Tank Gauge is a "downward-looking"
measuring system, operating based on the time-of-
flight method. It measures the distance from the
reference point (process connection) to the product
surface. Radar impulses are emitted by an antenna,
reflected off the product surface and received again by
the radar system.
Antenna Selection
It is essential for each and every application and
installation to evaluate the right antenna type. The
antenna selection depends on the following criteria:
• Type of application (i.e. free space vs. stilling well)
• Installation possibilities (size, location and height of
nozzle)
• Properties of the product stored in the tank (radar
reflectivity, vapor pressure, temperature, etc.)
• Accuracy requirements
The 7500 Series Radar Tank Gauge series radar comes
with 4 basic radar antenna forms.
Horn antenna
The 7530 RTG with horn antenna
is suitable for free space
applications that disallow the use
of a parabolic antenna due to
tank/nozzle geometry. It is
essential that the horn extends
below the nozzle. The general rule
for diameter selection is "the
larger, the better," as a larger aperture of the antenna
generates a narrower beam and has a better gain –
signal to noise (S/N) ratio.
Rod antenna
The 7531 RTG with rod antenna is
used for highly accurate
measurements where only small
diameter nozzles are available and
tanks containing condensing
products (or heavy water
condensation) or corrosive
products, such as sulphur, as the
rod is easy to clean and has good
"drip-off" properties. The
"inactive" length of the antenna should extend below
the nozzle.
Planar antenna (for stilling well)
The 7532 RTG with planar antenna
is specifically suited for stilling
well applications with ranges up to
38 m (124 ft). The emitted circular
mode radar pattern is a must for
high accuracy applications on stilling wells. This special
mode allows the software to compensate for variations
of the inside diameter of the stilling well and layering of
adhering product. The diameter of the antenna itself fits
in 6” (DN150) stilling wells directly. Cone adapters allow
installation on larger diameter stilling wells. A good
match between well and adapter is essential. The Varec
planar antenna with pulsed radar technology allows
direct installation even on tapered stilling wells – a
unique feature.
Parabolic antenna
The 7533 RTG with parabolic
antenna is excellently suited for
free space applications up to 40 m
(131 ft). The parabolic antenna is
the largest free space antenna with
the smallest beam angle. It is ideal
for applications close to tank
walls, where a manway cover is
available. The parabolic antenna is also an excellent
choice on products with a low reflectivity, such as
asphalts and bitumens.
Tank Gauging System
The Varec 4590 Tank Side Monitor
provides integrated
communications for sites with
multiple tanks, each with one or
more sensors on the tank, such as
radar, spot or average
temperature, capacitive probe for
water detection and/or pressure
sensors. Multiple protocols out of
the Tank Side Monitor guarantee connectivity to nearly
any of the existing industry standard tank gauging
protocols. Optional connectivity of analog 4...20 mA
sensors, digital I/O and analog output simplify full tank
sensor integration. Use of the proven concept of the
intrinsically safe HART bus (HART multidrop) for all on-
tank sensors yields extremely low wiring costs, while at
the same time providing maximum safety, reliability
and data availability.
High Accuracy
The mm-accuracy of the 7500 Series Radar Tank Gauge
is achieved using the patented algorithms of the
Microprocessor’s PhaseMaster® software.
Custody Transfer Applications
The 7500 Series Radar Tank Gauge is suitable for
custody transfer and inventory control applications. The
on-site testing has to be done in compliance with the
applicable regulatory standards. The 7500 Series Radar
Tank Gauge can be sealed after successful on-site
calibration to be protected against any access to the
electronics compartment and any changes of software
settings. If the 7500 Series Radar Tank Gauge is used
for custody transfer or inventory control, any
temperature influence
on the tank shell hight can be
compensated for using the Tank Side Monitor (TSM). In
addition, the vertical movement of the gauge reference