45
57-606 ECLIPSE Model 706 Guided Wave Radar Transmitter
constant of the medium in which it is traveling, the dielectric
constant of the upper liquid must be known to accurately
determine the interface level.
The thickness of the upper layer can be determined by
knowing the time between the first and second reflections
as well as the upper layer dielectric constant.
In order to properly process the reflected signals, the
Model 706 is specified for those applications where the
thickness of the upper layer is greater than 2 inches (5 cm).
The maximum upper layer is typically limited to the length
of the probe.
Emulsion Layers
As emulsion (rag) layers can decrease the strength of the
reflected signal, GWR offers best performance in applica-
tions having clean, distinct layers. However, the ECLIPSE
Model 706 transmitter will operate in most emulsions and
tend to read the top of the emulsion layer. Contact the
factory for application assistance and questions regarding
emulsion layers.
3.2.5 Saturated Steam Applications
(Boilers, Feedwater Heaters, etc.)
As the temperature of a saturated steam application
increases, the dielectric constant of the steam vapor space
also increases. This increase in vapor space dielectric causes
a delay in the GWR signal propagation as it travels down
the probe, causing the liquid level to appear lower than
actual.
NOTE: The measurement error associated with this propagation delay
does depend on temperature and is a function of the square
root of the vapor space dielectric constant. For example, with
no compensation, a +450 °F (+230 °C) application would show
a level error of about 5.5%, while a +600 °F (+315 °C) applica-
tion would show an error approaching 20%!
The ECLIPSE Model 706 transmitter and Model 7yS
Coaxial Steam probe provide a unique solution to this
application. The effects of the changing steam conditions
can be compensated for by utilizing a mechanical steam
target placed inside and near the top of the Model 7yS
coaxial probe.
Knowing exactly where the target is located at room tem-
perature, and then continuously monitoring its apparent
location, the vapor space dielectric can be back-calculated.
Knowing the vapor space dielectric, accurate compensation
of the actual liquid level reading is accomplished.