Emerson Process Management ROSEMOUNT 5300 - Manual (Page 258)

Reference Manual
00809-0100-4530, Rev BA
July 2009
Rosemount 5300 Series
C-10
PROBE END
PROJECTION Probe End Projection allows you to measure product level when the surface
pulse is too weak to be detected. For example, long measuring range and
products with very poor reflectivity (low dielectric constant).
A product with very low reflectivity is characterized by its low dielectric
constant. Such a product reflects relatively small amounts of the microwave
energy emitted from the Rosemount 5300 transmitter, and most of it is
transmitted through the product. Consequently, situations may occur where
the surface pulse is invisible to the transmitter at long measuring ranges. The
Probe End Projection function in the Rosemount 5300 transmitter makes it
possible to carry out accurate measurements even under such
circumstances.
When the microwaves emitted by the Rosemount 5300 transmitter propagate
through the product in the tank, the Probe End pulse appears to be located
below the actual probe end. The apparent displacement of the Probe End
pulse is a consequence of the reduced propagation speed of the
measurement signal through the product compared to the speed through air.
The displacement of the Probe End pulse can be observed by using the Echo
Curve Analyzer in the Rosemount Radar Master (see “Using the Echo Curve
Analyzer” on page 7-10).
For products with very low dielectric constants the product surface level can
be determined by comparing the actual probe end position as given by the
Probe Length value, with the apparent position of the Probe End pulse. The
difference is related to the properties of the product, i.e. the Dielectric
Constant, and the distance D travelled by the measurement signal through
the product, see Figure C-8.
Figure C-8. The properties of the
product makes the probe end
pulse appear to be below the
actual probe end.
Apparent Probe
End position
Surface pulse is
missing due to low
product reflectivity
Actual Probe
End position
D
Probe End pulse

The product Level is
given by the relation
between Probe End
displacement

, the
Dielectric Constant of the
product, and distance D
Note! It is important that the
Probe Length and product
Dielectric Constant are given
with high accuracy.