May 2016
Reference Manual
00809-0100-4530, Rev DD
315
Special adjustments can also be made by trimming the appropriate amplitude thresholds.
See section
“Interface peak not found” on page 160
for further information.
C.8
Dynamic Vapor Compensation
Rosemount 5300 Series is based on the Time Domain Reflectometry (TDR) technology
where low power nanosecond microwave pulses are guided down a probe submerged in
the process media. When a radar pulse reaches a media with a different dielectric constant,
part of the energy is reflected to the transmitter. The time difference between the
transmitted pulse and the reflected pulse is converted into a distance from which the total
level or interface level is calculated.
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. For typical radar
level transmitter accuracy, the propagation speed of the radar signal should be close to the
velocity of light in vacuum. However, in some important cases, the deviation is not
negligible and must be taken into account for accuracy. High tank pressure in combination
with certain gases is an example.
High pressure water steam can influence radar level transmitter measurements. This is due
to the high pressure as well as the polar structure of water molecules. In such cases, the
Rosemount 5300 Series Level Transmitter can be configured for compensation for this
effect.
Water has high critical temperature and pressure (705
o
F / 374
o
C and 3205 psi / 221 bar,
respectively). However, Dynamic Vapor Compensation has a maximum temperature and
pressure of 676
o
F / 358
o
C and 2610 psi / 180 bar. Above these limits, level measurement
may not be possible since the separation between gas and liquid becomes indistinct.
In a closed vessel containing water liquid and water vapor, existing databases (referred to as
a Mollier diagram) have been used to calculate pressure and vapor density, and deduce the
dielectric constant of the vapor from this. The dielectric constant changes as given in
.
Figure C-14. Dielectric Constant versus Temperature for Saturated Water Vapor
32 (0)
212 (100)
392 (200)
572 (300)
752 (400)
32 (0)
212 (100)
392 (200)
572 (300)
752 (400)
32 (0)
212 (100)
392 (200)
572 (300)
752 (400)
Press
u
re
(
B
ar
)
Di
e
le
ctr
ic
c
o
n
st
ant
32 (0)
212 (100)
392 (200)
572 (300)
752 (400)
Temperature (
o
F/
o
C)
Dielectric constant
Pressure
