Manual Supplement
00809-0400-4811, Rev AA
May 2007
Vapor Influence
Rosemount 3300 Series
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 1-2
Influence of Water Vapor . . . . . . . . . . . . . . . . . . . . . . . . . . page 1-2
Configuration of the 3300 transmitter . . . . . . . . . . . . . . . . page 1-3
This instruction is a supplement to the Rosemount 3300 Series Reference
Manual, see manual manual 00809-0100-4811.
Explosions could result in death or serious injury:
Before connecting a HART-based communicator in an explosive atmosphere, make
sure the instruments in the loop are installed in accordance with intrinsically safe or
non-incendive field wiring practices.
Failure to follow safe installation and servicing guidelines could result in death or
serious injury:
Use the equipment only as specified in the Rosemount 3300 Series Reference Manual
(Reference number 00809-0100-4811) and in this manual supplement. Failure to do so
may impair the protection provided by the equipment.
www.rosemount.com
Manual Supplement
00809-0400-4811, Rev AA
Rosemount 3300 Series
INTRODUCTION The Rosemount 3300 Series Radar Transmitter is a smart, two-wire
continuous level transmitter that is based on Time Domain Reflectometry
(TDR) principles. Low power nano-second-pulses are guided along a probe
immersed in the process media. When a pulse reaches the surface of the
material it is measuring, part of the energy is reflected back to the transmitter
head, and the time difference between the generated and reflected pulse is
converted into a distance from which the total level or interface level is
calculated (see below).
For radar level gauging the actual measured quantity is the propagation time
through the empty space between the radar level transmitter and the liquid
surface. Important for the typical accuracy of a radar level transmitter is that
the propagation speed of the radar signal in most cases is very close to the
perfectly constant velocity of light in vacuum. However in some important
cases the deviation is not negligible and must be taken into account to get
high accuracy. High tank pressure in combination with certain gases are
examples.
May 2007
INFLUENCE OF WATER VAPOR
Figure 1-1. Dielectric constant
versus temperature for saturated
water vapor
Water vapour at high pressure can have a big influence on radar level
transmitter measurements. This is due to the high pressure as well as the
polar structure of water molecules. In such cases the 3300 transmitter can be
configured to compensate for this effect by entering the dielectric constant of
the vapor.
Water has an unusual high critical temperature and pressure (374 ºC and 221
bar respectively, above which level measurement may be impossible), and in
power plants the use of water in the vicinity of those limits may occur. In a
closed vessel containing water liquid and water vapour existing data bases
(traditionally referred to as a Mollier diagram) have been used to calculate
pressure and vapour density and from this deduce the dielectric constant of
the vapour. The dielectric constant will change as given in the diagram below
covering the temperature range 0-360 °C.
Pressure (Bar)
Dielectric constant
1-2
Tem peratue (°C)
Dielectric constant
Pressure
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