May 2016
Reference Manual
00809-0100-4530, Rev DD
310
C.5
Probe End Projection
Probe End Projection is used for two purposes:
Use the probe end echo as reference, in case the surface echo is lost, to calculate
the surface echo position.
Use the probe end echo as reference when the surface echo is close to the probe
end to enhance accuracy of the surface echo position.
By using the Probe End Projection function, the device is capable of measuring the product
level even if the surface echo is lost. The Probe End Projection is suited for challenging
applications with very poor reflectivity (low dielectric constant). Due to the poor reflectivity
of the product, situations may occur where the surface pulse is invisible to the transmitter
at long measuring ranges.
If the surface becomes invisible, the device will revert to use the probe end, and the most
recently estimated value of the dielectric constant to calculate the surface. Once the
surface reappears, the device will immediately use direct measurement on the surface
again. The calculated surface value is less accurate than the value with direct measurement.
When the microwaves emitted by the Rosemount 5300 Transmitter propagate through the
product in the tank, the probe end echo appears to be located below the actual probe end.
The apparent displacement of the probe end echo peak 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
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 echo peak. 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
.
